Machine Learning Links T-cell Function and Spatial Localization to Neoadjuvant Immunotherapy and Clinical Outcome in Pancreatic Cancer

Tumor molecular data sets are becoming increasingly complex, making it nearly impossible for humans alone to effectively analyze them. Here, we demonstrate the power of using machine learning (ML) to analyze a single-cell, spatial, and highly multiplexed proteomic data set from human pancreatic cancer and reveal underlying biological mechanisms that may contribute to clinical outcomes. We designed a multiplex immunohistochemistry antibody panel to compare T-cell functionality and spatial localization in resected tumors from treatment-naïve patients with localized pancreatic ductal adenocarcinoma (PDAC) with resected tumors from a second cohort of patients treated with neoadjuvant agonistic CD40 (anti-CD40) monoclonal antibody therapy. In total, nearly 2.5 million cells from 306 tissue regions collected from 29 patients across both cohorts were assayed, and over 1,000 tumor microenvironment (TME) features were quantified. We then trained ML models to accurately predict anti-CD40 treatment status and disease-free survival (DFS) following anti-CD40 therapy based on TME features. Through downstream interpretation of the ML models' predictions, we found anti-CD40 therapy reduced canonical aspects of T-cell exhaustion within the TME, as compared with treatment-naïve TMEs. Using automated clustering approaches, we found improved DFS following anti-CD40 therapy correlated with an increased presence of CD44+CD4+ Th1 cells located specifically within cellular neighborhoods characterized by increased T-cell proliferation, antigen experience, and cytotoxicity in immune aggregates. Overall, our results demonstrate the utility of ML in molecular cancer immunology applications, highlight the impact of anti-CD40 therapy on T cells within the TME, and identify potential candidate biomarkers of DFS for anti-CD40-treated patients with PDAC.

Machine learning links T cell function and spatial localization to neoadjuvant immunotherapy and clinical outcome in pancreatic cancer

Tumor molecular datasets are becoming increasingly complex, making it nearly impossible for humans alone to effectively analyze them. Here, we demonstrate the power of using machine learning to analyze a single-cell, spatial, and highly multiplexed proteomic dataset from human pancreatic cancer and reveal underlying biological mechanisms that may contribute to clinical outcome. A novel multiplex immunohistochemistry antibody panel was used to audit T cell functionality and spatial localization in resected tumors from treatment-naive patients with localized pancreatic ductal adenocarcinoma (PDAC) compared to a second cohort of patients treated with neoadjuvant agonistic CD40 (αCD40) monoclonal antibody therapy. In total, nearly 2.5 million cells from 306 tissue regions collected from 29 patients across both treatment cohorts were assayed, and more than 1,000 tumor microenvironment (TME) features were quantified. We then trained machine learning models to accurately predict αCD40 treatment status and disease-free survival (DFS) following αCD40 therapy based upon TME features. Through downstream interpretation of the machine learning models' predictions, we found αCD40 therapy to reduce canonical aspects of T cell exhaustion within the TME, as compared to treatment-naive TMEs. Using automated clustering approaches, we found improved DFS following αCD40 therapy to correlate with the increased presence of CD44+ CD4+ Th1 cells located specifically within cellular spatial neighborhoods characterized by increased T cell proliferation, antigen-experience, and cytotoxicity in immune aggregates. Overall, our results demonstrate the utility of machine learning in molecular cancer immunology applications, highlight the impact of αCD40 therapy on T cells within the TME, and identify potential candidate biomarkers of DFS for αCD40-treated patients with PDAC.

An open protocol for modeling T Cell Clonotype repertoires using TCRβ CDR3 sequences

T cell receptor repertoires can be profiled using next generation sequencing (NGS) to measure and monitor adaptive dynamical changes in response to disease and other perturbations. Genomic DNA-based bulk sequencing is cost-effective but necessitates multiplex target amplification using multiple primer pairs with highly variable amplification efficiencies. Here, we utilize an equimolar primer mixture and propose a single statistical normalization step that efficiently corrects for amplification bias post sequencing. Using samples analyzed by both our open protocol and a commercial solution, we show high concordance between bulk clonality metrics. This approach is an inexpensive and open-source alternative to commercial solutions.

Abstract NG04: Agonistic anti-CD40 converts regulatory T cells in to Type 1 effector cells within the tumor microenvironment

Regulatory T cells (Tregs) are a pillar of the tumor microenvironment (TME), contributing to the restraint and dysfunction of adaptive immune responses against the tumor. Even small proportions of Tregs in the TME can subvert effector T cell responses, revealing the potent suppressive role of Tregs in both primary and acquired resistance to immune interventions. Therapeutically targeting Tregs to render the TME sensitive to immune destruction has been most successful using anti-CTLA-4, which is reported to bind intratumoral Tregs and mediate antibody dependent cellular cytotoxicity (ADCC). However, this therapy results in clinical responses in only a subset of patients and many tumor types are resistant to anti-CTLA-4, highlighting the need for improved options in targeting Tregs in the TME.As with most immune cells, Tregs exist on a spectrum, ranging from highly immunosuppressive to those with T helper (Th) effector functions, including production of interferon (IFN)-gamma. In studies of intestinal Treg subsets, conversion from a FoxP3+ suppressor conventional (cTreg) phenotype to a Th1-like ‘ExTreg’ phenotype has been reported. Given our recent findings that immunotherapy-induced CD4 T cells contribute to tumor rejection1,2, the impact of this switch from cTreg to ExTreg could be substantial in the context of the developing anti-tumor immune response. Here, we report for the first time the conversion of cTregs to ExTregs in the TME as a result of treatment with agonistic anti-CD40 monoclonal antibody. We employed anti-CD40 in the genetically engineered LSL-KrasG12D/+; LSL-Trp53R172H/+; Pdx-1-Cre (KPC) mouse model of pancreatic ductal adenocarcinoma (PDAC) as a means of priming an adaptive T cell response against established, highly immunosuppressive tumors3. We have previously reported the positive impact of anti-CD40 combined with dual immune checkpoint blockade (anti-PD-1 and anti-CTLA-4; ICB) on the generation of protective CD4 and CD8 T cell responses in the context of PDAC, concurrent with a decline of Tregs in the PDAC TME1. Leveraging a PDAC tumor clone with a relatively high T cell infiltrate to assess the impact of ‘successful’ immunotherapy on the TME4, we observed significant alterations in the Treg compartment after combination anti-CD40 and ICB administration, including a global reduction in Tregs and a pattern of Treg localization at the tumor edge. Interrogation of the mechanisms underlying Treg loss after therapy revealed the effect was entirely dependent on CD40 stimulation, as anti-CD40 alone mediated this effect and mice lackingCD40 expression were resistant to Treg reduction. Given that Tregs do not express CD40, excluding the role of ADCC in mediating Treg loss in the TME, we hypothesized that CD40-expressing antigen presenting cells may mediate intratumoral Treg reduction. We found that dendritic cells (DCs) and the IL-12/IFN-gamma cytokine signaling pathway regulated Treg loss, but that Tregs were not dying at increased rates, as FoxP3+ cells did not express increased levels of cleaved caspase 3 after treatment with anti-CD40. Using FoxP3eGFP-Cre-ERT2 xGt(ROSA)26Sortm(CAGtdTomato)/Hze (R26tdTomato) mice to conduct lineage tracing experiments, we determined that Tregs in the PDAC TME downregulated FoxP3 expression, converting from a cTreg to ExTreg phenotype. Concurrently, all Treg subsets upregulated expression of the Th1transcription factor Tbet, and ExTregs increased production of IFN-gamma. This effect was completely lost in mice treated with antibodies blocking either IL-12p40 or IFN-gamma, highlighting the role of this cytokine axis in regulating ExTreg generation and acquisition of Th1effector functions. Furthermore, nuclear translocation of the nuclear factor of activated T cells (NFAT1), a reliable marker of extremely recent cognate antigen stimulation of T cells (<45minutes), was observed at increased levels within the ExTreg compartment, an effect that was lost in mice treated with MHC II blocking antibody. Coupled with increased expression of phosphorylated STAT1 expression within the ExTreg compartment, these findings suggest a role for DCs in presenting antigen directly to ExTregs in the context of IL-12/IFN-gamma stimulation to promote Th1 effector functions in the PDAC TME. Importantly, the generation of Th1-likeExTregs was not observed in mice treated with anti-CTLA-4, emphasizing the unique contribution of CD40 in driving this conversion and acquisition of anti-tumor functions within the ExTreg compartment. The use of agonistic CD40 antibody to reprogram Tregs in the suppressive PDAC TME reveals a previously underappreciated potential of this immunotherapeutic approach. Here our findings suggest that Tregs in the TME may not be a harbinger of poor prognostic outcomes and instead find that Treg plasticity may be leveraged for improved patient outcomes. Simultaneously alleviating T cell suppression while promoting effector functions may provide early modifications in the TME during a crucial time point of the nascent anti-tumor immune response that could ultimately dictate therapeutic responsiveness. This work was supported in part by the Intramural Research Program of NIAID, the Postdoctoral Research Associate Training (PRAT) Program, and NCI at the NIH, in addition to the Parker Institute for Cancer Immunotherapy.1. Morrison, A. H., Diamond, M. S., Hay, C. A., Byrne, K. T. & Vonderheide, R. H. Sufficiency ofCD40 activation and immune checkpoint blockade for T cell priming and tumor immunity. Proc National Acad Sci 201918971 (2020). doi:10.1073/pnas.19189711172. Huffman, A. P., Lin, J. H., Kim, S. I., Byrne, K. T. & Vonderheide, R. H. CCL5 mediatesCD40-driven CD4+ T-cell tumor infiltration and immunity. Jci Insight (2020).doi:10.1172/jci.insight.1372633. Byrne, K. T. & Vonderheide, R. H. CD40 Stimulation Obviates Innate Sensors and Drives T Cell Immunity in Cancer. Cell Reports 15, 2719-2732 (2016).4. Li, J., Byrne, K. T., Yan, F., Yamazoe, T., Chen, Z., Baslan, T., Richman, L. P., Lin, J. H., Sun, Y. H., Rech, A. J., Balli, D., Hay, C. A., Sela, Y., Merrell, A. J., Liudahl, S. M., Gordon, N., Norgard, R. J., Yuan, S., Yu, S., Chao, T., Ye, S., Eisinger-Mathason, T. S. K., Faryabi, R. B., Tobias, J. W., Lowe, S. W., Coussens, L. M., Wherry, E. J., Vonderheide, R. H. & Stanger, B. Z. Tumor Cell-Intrinsic Factors Underlie Heterogeneity of Immune Cell Infiltration and Response to Immunotherapy. Immunity 49, 178-193.e7 (2018).

Citation Format: Vivien Maltez, Charu Arora, Rina Sor, Ronald N. Germain, Robert H. Vonderheide, Katelyn T. Byrne. Agonistic anti-CD40 converts regulatory T cells in to Type 1 effector cells within the tumor microenvironment. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr NG04.

An open protocol for modeling T Cell Clonotype repertoires using TCRβ CDR3 sequences

T cell receptor repertoires can be profiled using next generation sequencing (NGS) to measure and monitor adaptive dynamical changes in response to disease and other perturbations. Genomic DNA-based bulk sequencing is cost-effective but necessitates multiplex target amplification using multiple primer pairs with highly variable amplification efficiencies. Here, we utilize an equimolar primer mixture and propose a single statistical normalization step that efficiently corrects for amplification bias post sequencing. Using samples analyzed by both our open protocol and a commercial solution, we show high concordance between bulk clonality metrics. This approach is an inexpensive and open-source alternative to commercial solutions.

Abstract IA005: Generating T cell responses against pancreatic cancer

The ultimate promise of tumor immunotherapy is dependent on the generation of an effective immune response against cancer, including CD4 and CD8 T cells. However, driving T cell responses in tumors such as pancreatic ductal adenocarcinoma (PDAC) requires overcoming significant hurdles in the tumor microenvironment (TME). Local and systemic suppression of dendritic cell function depresses endogenous T cell immunity against PDAC, which is further exacerbated by tumor cell intrinsic recruitment of suppressive myeloid cells and macrophages to the tumor site. To bypass these barriers, we’ve utilized agonistic anti-CD40 antibody, which mimics the endogenous CD40 ligand, to license and mature dendritic cells and re-educate tumor-associated myeloid cells towards a Th1/M1 phenotype in the PDAC TME. Using the KrasLSL-G12D/+,Trp53LSL-R172H/+,Pdx1-Cre (KPC) genetically engineered mouse model of pancreatic cancer, we show that combining standard-of-care chemotherapy with CD40 agonism promotes clonal T cell activation and expansion locally in the tumor site, resulting in regressions and cures of established tumors. This CD40-induced T cell response was further enhanced by the addition of dual immune checkpoint blockade (anti-PD-1 and anti-CTLA-4), but was independent of classical innate immune sensors such as Type I interferon receptor (IFNAR) and toll-like receptors (TLRs) previously thought to be critical for the generation of T cell immunity against tumors. These studies formed the preclinical rationale for trials investigating the use of agonistic CD40 therapy for patients with resectable or metastatic PDAC, and provided insight for immunological correlates of response in the clinical setting. More recently, we have reported on the negative impact of chemotherapy on the developing anti-tumor T cell response, emphasizing the need for additional investigations into the combination and sequencing of treatment modalities for enhanced outcomes in patients with PDAC. These studies reveal the potency of using an immunologically relevant mouse model to interrogate immune interventions in PDAC for patients with the greatest unmet clinical need.

Citation Format: Katelyn T. Byrne. Generating T cell responses against pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr IA005.

Sotigalimab and/or nivolumab with chemotherapy in first-line metastatic pancreatic cancer: clinical and immunologic analyses from the randomized phase 2 PRINCE trial

Chemotherapy combined with immunotherapy has improved the treatment of certain solid tumors, but effective regimens remain elusive for pancreatic ductal adenocarcinoma (PDAC). We conducted a randomized phase 2 trial evaluating the efficacy of nivolumab (nivo; anti-PD-1) and/or sotigalimab (sotiga; CD40 agonistic antibody) with gemcitabine/nab-paclitaxel (chemotherapy) in patients with first-line metastatic PDAC ( NCT03214250 ). In 105 patients analyzed for efficacy, the primary endpoint of 1-year overall survival (OS) was met for nivo/chemo (57.7%, P = 0.006 compared to historical 1-year OS of 35%, n = 34) but was not met for sotiga/chemo (48.1%, P = 0.062, n = 36) or sotiga/nivo/chemo (41.3%, P = 0.223, n = 35). Secondary endpoints were progression-free survival, objective response rate, disease control rate, duration of response and safety. Treatment-related adverse event rates were similar across arms. Multi-omic circulating and tumor biomarker analyses identified distinct immune signatures associated with survival for nivo/chemo and sotiga/chemo. Survival after nivo/chemo correlated with a less suppressive tumor microenvironment and higher numbers of activated, antigen-experienced circulating T cells at baseline. Survival after sotiga/chemo correlated with greater intratumoral CD4 T cell infiltration and circulating differentiated CD4 T cells and antigen-presenting cells. A patient subset benefitting from sotiga/nivo/chemo was not identified. Collectively, these analyses suggest potential treatment-specific correlates of efficacy and may enable biomarker-selected patient populations in subsequent PDAC chemoimmunotherapy trials.

Multiplex microscopy reveals unique spatiotemporal effects of cancer immunotherapies

Pancreatic ductal adenocarcinoma (PDA) is an aggressive and heterogeneous cancer that is often refractory to current treatments. To address this issue, we employ a mouse PDA-derived tumor clone library where individual clones elicit a spectrum of unique immune cell infiltration profiles in the tumor microenvironment (TME). We found that a combination of anti-PD1, anti-CTLA-4, and anti-CD40 results in tumor regression only in tumor clones with a high number of infiltrating T cells. The aim of our study is to gain mechanistic understanding into this therapeutic combination. To that end, we leverage quantitative high multiplex microscopy, enabling us to decipher the complexities of cellular behaviors, interactions, and phenotypes in an intact TME. We found that our therapy distinctively alters the TME of both responsive and non-responsive tumors. Unique to non-responsive tumors, we found discrete myeloid clusters scattered through the TME that increase in frequency and size post therapy. Additionally, we witnessed prominent cellular movement within myeloid clusters using 2-photon intravital imaging. In contrast, in the TME of responsive tumors our therapy severely depleted, reprogrammed, and restricted regulatory T cells to the tumor periphery within 48 hours post anti-CD40 administration. We found this to be ADCC–independent, but anti-CD40–dependent, with the mechanistic factors driving the fate of these cells under detailed investigation. Combined, these data reveal mechanistic insight into anti-CD40 combination therapies and provide a platform for investigating the factors driving the formation and maintenance of an immunosuppressive TME.

This work was supported by (1) Intramural Research Program of NIAID, NIH, (2) Postdoctoral Research Associate Training (PRAT) Fellowship of NIGMS, NIH, (3) Parker Institute for Cancer Immunotherapy, and (4) Bench to Bedside Award.

CD4+ T cells mediate non-canonical rejection of major histocompatibility class-I deficient pancreatic tumors independently of CD8+ T cells

Cytolytic CD8+ T cells are a major mediator of immune-induced tumor rejection, but many patients have primary or acquired resistance to CD8+ T cell immunity. Reduced major histocompatibility complex I (MHC I) expression contributes to resistance, including treatment-refractory pancreatic ductal adenocarcinoma (PDAC). Interrogating interventions in PDAC will reveal novel mechanisms regulating sensitivity to immunotherapy. Using a genetically engineered mouse model of PDAC, we previously reported that agonistic anti-CD40 and dual immune checkpoint blockade (ICB) induces CD8+ and a CD4+ T cell responses mediating tumor rejection. Here, we utilized CRISPR− Cas9 to disrupt the dominant MHC I (H-2Kb) allele expression in PDAC cell lines, precluding direct antigen presentation to CD8+ T cells. Injection of MHC I-deficient tumor clones revealed normal tumor growth at baseline, and significantly delayed tumor growth in response to CD40/ICB in a CD4+ T cell-dependent manner (p < 0.0001 vs. vehicle-treated mice). There was no direct contribution of tumor rejection by CD8+ T cells, despite the generation of a tumor-specific response (24.5% vs. 1.98% in vehicle-treated mice, p<0.003). CD4+ T cells upregulated IFN-γ production (52.3% vs. 11.9% in vehicle-treated mice, p<0.0001), and host IFN-γ expression was required. No changes were observed in the expression of cytotoxic molecules by CD4+ T cells after CD40/ICB, and depletion of myeloid cells did not dampen treatment efficacy. Thus, CD4+ T cells mediated PDAC rejection via non-canonical mechanisms after treatment with CD40/ICB. This study provides critical insight into novel mediators of tumor clearance, and opportunities to exploit CD4 T+ cells as regulators of tumor immunity.

Funded by the Parker Institute for Cancer Immunotherapy.

Neoadjuvant Selicrelumab, an Agonist CD40 Antibody, Induces Changes in the Tumor Microenvironment in Patients with Resectable Pancreatic Cancer

PURPOSE

CD40 activation is a novel clinical opportunity for cancer immunotherapy. Despite numerous active clinical trials with agonistic CD40 monoclonal antibodies (mAb), biological effects and treatment-related modulation of the tumor microenvironment (TME) remain poorly understood.

PATIENTS AND METHODS

Here, we performed a neoadjuvant clinical trial of agonistic CD40 mAb (selicrelumab) administered intravenously with or without chemotherapy to 16 patients with resectable pancreatic ductal adenocarcinoma (PDAC) before surgery followed by adjuvant chemotherapy and CD40 mAb.

RESULTS

The toxicity profile was acceptable, and overall survival was 23.4 months (95% confidence interval, 18.0-28.8 months). Based on a novel multiplexed immunohistochemistry platform, we report evidence that neoadjuvant selicrelumab leads to major differences in the TME compared with resection specimens from treatment-naïve PDAC patients or patients given neoadjuvant chemotherapy/chemoradiotherapy only. For selicrelumab-treated tumors, 82% were T-cell enriched, compared with 37% of untreated tumors (P = 0.004) and 23% of chemotherapy/chemoradiation-treated tumors (P = 0.012). T cells in both the TME and circulation were more active and proliferative after selicrelumab. Tumor fibrosis was reduced, M2-like tumor-associated macrophages were fewer, and intratumoral dendritic cells were more mature. Inflammatory cytokines/sec CXCL10 and CCL22 increased systemically after selicrelumab.

CONCLUSIONS

This unparalleled examination of CD40 mAb therapeutic mechanisms in patients provides insights for design of subsequent clinical trials targeting CD40 in cancer.

Abstract CT005: T cell inflammation in the tumor microenvironment after agonist CD40 antibody: Clinical and translational results of a neoadjuvant clinical trial

Deploying CD40 activation to stimulate T cell responses upstream of immune checkpoint molecules is a novel clinical opportunity for cancer immunotherapy. Despite numerous active clinical trials with agonistic CD40 monoclonal antibodies (mAb), biological treatment effects especially treatment-related modulation of the tumor microenvironment (TME), remain poorly understood. Here, we performed a neoadjuvant clinical trial of agonistic CD40 mAb (selicrelumab) administered intravenously with or without chemotherapy (gemcitabine and nab-paclitaxel) to 16 resectable patients with pancreatic ductal adenocarcinoma (PDAC) prior to surgery followed by adjuvant chemotherapy and CD40 mAb. The toxicity profile was acceptable, including only grade 1 or 2 cytokine release syndrome and expected toxicities from chemotherapy. Disease-free survival was 13.8 months (95% CI 2.9 - 24.8 months) and median overall survival was 23.4 months (95% CI 18.0 - 28.8), with 8 patients alive at a median of 20.0 months after surgery (follow-up range 12.2 to 34.8 months). Neoadjuvant selicrelumab induced major pharmacodynamic differences in the TME, as revealed by a multiplex imaging platform auditing the immune ecosystem, compared to resection specimens from PDAC patient previously untreated or given neoadjuvant chemotherapy/chemoradiotherapy only. For tumors resected after selicrelumab, 82% (9/11) were T-cell enriched, compared to 37% (38/104) (p=0.004) of untreated tumors and 23% (93/13) of chemotherapy/chemoradiation-treated tumors (p=0.012). Moreover, for selicrelumab tumors, tumor-associated fibrosis was less, “M2” macrophages were fewer, dendritic cells were more mature, and T cells were activated and proliferative, compared to the non-selicrelumab groups. In the periphery, CD8+ and CD4+ T cells were more activated and proliferative, and serum inflammatory cytokines CXCL10 and CCL22 increased after treatment. This study provides proof-of-concept in patients that agonistic CD40 mAb alters the TME, enhances T-cell infiltration, and modulates systemic inflammatory responses. These findings inform design of next-generation CD40 clinical trials.

Citation Format: Katelyn T. Byrne, Courtney B. Betts, Rosemarie Mick, Shamilene Sivagnanam, David L. Bajor, Daniel A. Laheru, E. Gabriela Chiorean, Mark H. O'Hara, Shannon M. Liudahl, Craig Newcomb, Cécile Alanio, Ana P. Ferreira, Byung S. Park, Takuya Ohtani, Austin P. Huffman, Sara A. Väyrynen, Andressa Dias Costa, Judith C. Kaiser, Andreanne M. Lacroix, Colleen Redlinger, Martin Stern, Jonathan A. Nowak, E. John Wherry, Martin A. Cheever, Brian M. Wolpin, Emma E. Furth, Elizabeth M. Jaffee, Lisa M. Coussens, Robert H. Vonderheide. T cell inflammation in the tumor microenvironment after agonist CD40 antibody: Clinical and translational results of a neoadjuvant clinical trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT005.

Synergistic immunotherapy of glioblastoma by dual targeting of IL-6 and CD40

Immunologically-cold tumors including glioblastoma (GBM) are refractory to checkpoint blockade therapy, largely due to extensive infiltration of immunosuppressive macrophages (Mϕs). Consistent with a pro-tumor role of IL-6 in alternative Mϕs polarization, we here show that targeting IL-6 by genetic ablation or pharmacological inhibition moderately improves T-cell infiltration into GBM and enhances mouse survival; however, IL-6 inhibition does not synergize PD-1 and CTLA-4 checkpoint blockade. Interestingly, anti-IL-6 therapy reduces CD40 expression in GBM-associated Mϕs. We identify a Stat3/HIF-1α-mediated axis, through which IL-6 executes an anti-tumor role to induce CD40 expression in Mϕs. Combination of IL-6 inhibition with CD40 stimulation reverses Mϕ-mediated tumor immunosuppression, sensitizes tumors to checkpoint blockade, and extends animal survival in two syngeneic GBM models, particularly inducing complete regression of GL261 tumors after checkpoint blockade. Thus, antibody cocktail-based immunotherapy that combines checkpoint blockade with dual-targeting of IL-6 and CD40 may offer exciting opportunities for GBM and other solid tumors.

cIAP1/2 antagonism eliminates MHC class I-negative tumors through T cell-dependent reprogramming of mononuclear phagocytes

Loss of major histocompatibility complex (MHC) class I and interferon-γ (IFN-γ) sensing are major causes of primary and acquired resistance to checkpoint blockade immunotherapy. Thus, additional treatment options are needed for tumors that lose expression of MHC class I. The cellular inhibitor of apoptosis proteins 1 and 2 (cIAP1/2) regulate classical and alternative nuclear factor κB (NF-κB) signaling. Induction of noncanonical NF-κB signaling with cIAP1/2 antagonists mimics costimulatory signaling, augmenting antitumor immunity. We show that induction of noncanonical NF-κB signaling induces T cell-dependent immune responses, even in β2-microglobulin (β2M)-deficient tumors, demonstrating that direct CD8 T cell recognition of tumor cell-expressed MHC class I is not required. Instead, T cell-produced lymphotoxin reprograms both mouse and human macrophages to be tumoricidal. In wild-type mice, but not mice incapable of antigen-specific T cell responses, cIAP1/2 antagonism reduces tumor burden by increasing phagocytosis of live tumor cells. Efficacy is augmented by combination with CD47 blockade. Thus, activation of noncanonical NF-κB stimulates a T cell-macrophage axis that curtails growth of tumors that are resistant to checkpoint blockade because of loss of MHC class I or IFN-γ sensing. These findings provide a potential mechanism for controlling checkpoint blockade refractory tumors.

Tumor Burden and Immunotherapy: Impact on Immune Infiltration and Therapeutic Outcomes

Cancer immunotherapy has revolutionized the treatment landscape in medical oncology, but its efficacy has been variable across patients. Biomarkers to predict such differential response to immunotherapy include cytotoxic T lymphocyte infiltration, tumor mutational burden, and microsatellite instability. A growing number of studies also suggest that baseline tumor burden, or tumor size, predicts response to immunotherapy. In this review, we discuss the changes in immune profile and therapeutic responses that occur with increasing tumor size. We also overview therapeutic approaches to reduce tumor burden and favorably modulate the immune microenvironment of larger tumors.

CD40 agonistic monoclonal antibody APX005M (sotigalimab) and chemotherapy, with or without nivolumab, for the treatment of metastatic pancreatic adenocarcinoma: an open-label, multicentre, phase 1b study

BACKGROUND

Standard chemotherapy remains inadequate in metastatic pancreatic adenocarcinoma. Combining an agonistic CD40 monoclonal antibody with chemotherapy induces T-cell-dependent tumour regression in mice and improves survival. In this study, we aimed to evaluate the safety of combining APX005M (sotigalimab) with gemcitabine plus nab-paclitaxel, with and without nivolumab, in patients with pancreatic adenocarcinoma to establish the recommended phase 2 dose.

METHODS

This non-randomised, open-label, multicentre, four-cohort, phase 1b study was done at seven academic hospitals in the USA. Eligible patients were adults aged 18 years and older with untreated metastatic pancreatic adenocarcinoma, Eastern Cooperative Oncology Group performance status score of 0-1, and measurable disease by Response Evaluation Criteria in Solid Tumors version 1.1. All patients were treated with 1000 mg/m² intravenous gemcitabine and 125 mg/m² intravenous nab-paclitaxel. Patients received 0·1 mg/kg intravenous APX005M in cohorts B1 and C1 and 0·3 mg/kg in cohorts B2 and C2. In cohorts C1 and C2, patients also received 240 mg intravenous nivolumab. Primary endpoints comprised incidence of adverse events in all patients who received at least one dose of any study drug, incidence of dose-limiting toxicities (DLTs) in all patients who had a DLT or received at least two doses of gemcitabine plus nab-paclitaxel and one dose of APX005M during cycle 1, and establishing the recommended phase 2 dose of intravenous APX005M. Objective response rate in the DLT-evaluable population was a key secondary endpoint. This trial (PRINCE, PICI0002) is registered with ClinicalTrials.gov, NCT03214250 and is ongoing.

FINDINGS

Between Aug 22, 2017, and July 10, 2018, of 42 patients screened, 30 patients were enrolled and received at least one dose of any study drug; 24 were DLT-evaluable with median follow-up 17·8 months (IQR 16·0-19·4; cohort B1 22·0 months [21·4-22·7], cohort B2 18·2 months [17·0-18·9], cohort C1 17·9 months [14·3-19·7], cohort C2 15·9 months [12·7-16·1]). Two DLTs, both febrile neutropenia, were observed, occurring in one patient each for cohorts B2 (grade 3) and C1 (grade 4). The most common grade 3-4 treatment-related adverse events were lymphocyte count decreased (20 [67%]; five in B1, seven in B2, four in C1, four in C2), anaemia (11 [37%]; two in B1, four in B2, four in C1, one in C2), and neutrophil count decreased (nine [30%]; three in B1, three in B2, one in C1, two in C2). 14 (47%) of 30 patients (four each in B1, B2, C1; two in C2) had a treatment-related serious adverse event. The most common serious adverse event was pyrexia (six [20%] of 30; one in B2, three in C1, two in C2). There were two chemotherapy-related deaths due to adverse events: one sepsis in B1 and one septic shock in C1. The recommended phase 2 dose of APX005M was 0·3 mg/kg. Responses were observed in 14 (58%) of 24 DLT-evaluable patients (four each in B1, C1, C2; two in B2).

INTERPRETATION

APX005M and gemcitabine plus nab-paclitaxel, with or without nivolumab, is tolerable in metastatic pancreatic adenocarcinoma and shows clinical activity. If confirmed in later phase trials, this treatment regimen could replace chemotherapy-only standard of care in this population.

FUNDING

Parker Institute for Cancer Immunotherapy, Cancer Research Institute, and Bristol Myers Squibb.

CCL5 mediates CD40-driven CD4+ T cell tumor infiltration and immunity

The role CD4+ T cells play in tumor immunity is less well appreciated than the cytotoxic role of CD8+ T cells. Despite clear evidence for CD4+ T cell dependency across multiple immunotherapies, the mechanisms by which CD4+ T cells infiltrate tumors remain poorly understood. Prior studies by our group have shown in a mouse model of pancreatic cancer that systemic activation of the cell surface TNF superfamily member CD40 drives T cell infiltration into tumors and, in combination with immune checkpoint blockade, leads to durable tumor regressions and cures that depend on both CD8+ and CD4+ T cells. Here, we used single-cell transcriptomics to examine the tumor microenvironment following treatment with agonist CD40 antibody with or without immune checkpoint blockade. We show that intratumor myeloid cells produce the chemokine CCL5 in response to CD40 agonist and that CCL5 mediates an influx of CD4+ T cells into the tumor microenvironment. Disruption of CCL5 genetically or pharmacologically mitigates the influx of CD4+ but not CD8+ T cells into tumors and blunts the therapeutic efficacy of immunotherapy. These findings highlight a previously unappreciated role for CCL5 in selectively mediating CD4+ T cell tumor infiltration in response to effective immunotherapy.

Abstract PR11: Tumor cell-intrinsic factors underlie the heterogeneity of immune infiltration and response to immunotherapy in pancreatic cancer

Intertumoral heterogeneity—the biologic and functional differences among different individual tumors—poses a challenge for immunotherapy. To understand the tumor cell-intrinsic factors underlying the heterogeneity of tumor immunity and sensitivity to immunotherapy, we established a new experimental system by generating a library of congenic pancreatic tumor cell clones from a genetic mouse model driven by mutant Kras and p53. These tumor cell clones robustly formed implanted tumors that recapitulated the T cell-inflamed and non-T cell-inflamed tumor microenvironments in human patients, associated with distinct patterns of infiltration by T cells and myeloid cells. We found that the non-T cell-inflamed phenotype was dominant over the T cell-inflamed phenotype in the local tumor microenvironment. Both quantitative and qualitative features, specifically expression of markers of prior TCR activation, of intratumoral CD8+ T cells predicted the response to immunotherapies. An integrated transcriptomic and epigenetic analysis revealed that tumor cell-intrinsic expression of the chemokine CXCL1 as a major determinant of the non-T cell-inflamed microenvironment, and ablation of tumor cell-intrinsic CXCL1, promoted T-cell infiltration and sensitivity to a combination of chemotherapies, CD40 agonist, and checkpoint blockades. These results demonstrated that heterogeneity of tumor immune phenotypes is driven by tumor cell-intrinsic factors that can be manipulated to influence the outcome of immunotherapies. The observation that non-T cell-inflamed phenotype is dominant emphasized the importance of targeting mechanisms driving T-cell low phenotype for improving immunotherapy response. This experimental system will provide opportunities for understanding other aspects of tumor heterogeneity as well.

This abstract is also being presented as Poster A45.

Citation Format: Jinyang Li, Katelyn T. Byrne, Fangxue Yan, Taiji Yamazoe, Zeyu Chen, Timour Baslan, Lee P. Richman, Jeffrey Lin, Yu H. Sun, Shannon M. Liudahl, John W. Tobias, Scott Lowe, Lisa M. Coussens, John E Wherry, Robert H. Vonderheide, Ben Z. Stanger. Tumor cell-intrinsic factors underlie the heterogeneity of immune infiltration and response to immunotherapy in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2018 Nov 27-30; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(4 Suppl):Abstract nr PR11.

Abstract PR04: STING and TLR-independent activation of T-cell responses against pancreatic cancer using agonistic CD40 antibody

Immunotherapy is increasingly used in combination with current standard-of-care treatments such as chemotherapy that likely provides danger signals via immunogenic tumor cell death and activation of STING or TLR pathways. However, both the toxicity and immunosuppressive effects of chemotherapy risks hindering clinical benefit. Agonistic CD40 antibody is a potent activator of immune responses, acting upstream of immune checkpoint blockade (ICB) by driving T-cell priming. Here, we show that anti-CD40 is sufficient to drive potent T-cell responses against murine KPC (KrasG12D;Trp53R172H;Pdx-Cre) pancreatic tumors if combined with ICB. CD40/ICB was more effective than CD40/ICB/chemotherapy (median overall survival 76 days vs. 44 days in CD40/ICB vs. CD40/ICB/chemotherapy-treated mice, p<0.01). Therapeutic efficacy of CD40/ICB was fully independent of the STING, MyD88, and IFNAR pathways, requiring instead host expression of CD40, cross-presenting dendritic cells, and an intact T-cell compartment. Therapy-induced CD4 and CD8 T cell responses displayed enhanced polyfunctional cytokine secretion (48.9% vs. 29.5% of CD8+ T cells in vehicle control treated mice), cleared established primary tumors (43% vs. 0% in vehicle control or single-treatment cohorts p<0.0001), and formed protective memory responses in 57% of CD40/ICB cured mice. Immunosuppressive regulatory T cells were noticeably absent from the tumor site after CD40 treatment (7% of CD4+ T cells vs. 33% in mice treated with ICB alone, p<0.01), concomitant with improved T-cell activation and proliferation, whereas ICB was needed to potentiate the full activation and reinvigoration of the T-cell response both locally and systemically. The efficacy of CD40/ICB in in this ICB-resistant KPC model opens the possibility of optimized immunotherapy regimens free of the toxicity and immunosuppressive effects of cytotoxic therapy.

This abstract is also being presented as Poster B08.

Citation Format: Katelyn T. Byrne, Alexander H. Morrison, Robert H. Vonderheide. STING and TLR-independent activation of T-cell responses against pancreatic cancer using agonistic CD40 antibody [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr PR04.

Abstract A28: Investigation of tumor-cell-intrinsic factors regulating immune infiltration and response to immunotherapy in pancreatic cancer

Resistance to immunotherapy is one major problem of current clinical care for cancer patients. While T-cell abundance is essential for tumor responsiveness to immunotherapy, factors that dictate T-cell infiltration in tumor microenvironments are not fully understood. To understand the tumor cell-intrinsic factors underlying the heterogeneity of tumor immunity and sensitivity to immunotherapy, we established a new experimental system by generating a library of congenic pancreatic tumor cell clones from a genetic mouse model driven by mutant Kras and p53. These tumor cell clones robustly formed implanted tumors that recapitulated the T cell-inflamed and non-T cell-inflamed tumor microenvironments in human patients, associated with distinct patterns of infiltration by T cells and myeloid cells. We found that the non-T cell-inflamed phenotype was dominant over the T cell-inflamed phenotype in the local tumor microenvironment. Both quantitative and qualitative features, specifically expression of markers of prior TCR activation, of intratumoral CD8+ T cells predicted the response to immunotherapies. An integrated transcriptomic and epigenetic analysis revealed that tumor cell-intrinsic expression of the chemokine CXCL1 as a major determinant of the non-T cell-inflamed microenvironment, and ablation of tumor cell-intrinsic CXCL1 promoted T-cell infiltration and sensitivity to a combination of chemotherapies, CD40 agonist, and checkpoint blockades. Similarly, we identified tumor cell-intrinsic EPHA2 and PTGS2 as key regulators of immune infiltration and immunotherapy response in our experimental system. Ablation of tumor cell-intrinsic EPHA2 or PTGS2 enhanced T-cell infiltration and suppressed myeloid cell infiltration in implanted pancreatic tumors, and increased sensitivities of tumors to the combined immunotherapy. These results demonstrated that heterogeneity of tumor immune phenotypes is driven by tumor cell-intrinsic factors that can be manipulated to influence the outcome of immunotherapies. The observation that non-T cell-inflamed phenotype is dominant emphasized the importance of targeting mechanisms driving T-cell low phenotype for improving immunotherapy response.

Citation Format: Jinyang Li, Katelyn T Byrne, Nune Markosyan, Taiji Yamazoe, Fangxue Yan, Zeyu Chen, Yu H. Sun, Jeffrey Lin, Yogev Sela, Robert J. Norgard, Salina Yuan, Allyson J. Merrell, John W. Tobias, Robert H. Vonderheide, Ben Z. Stanger. Investigation of tumor-cell-intrinsic factors regulating immune infiltration and response to immunotherapy in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr A28.

Ultrasound-Guided Orthotopic Implantation of Murine Pancreatic Ductal Adenocarcinoma

The recent success of immune checkpoint blockade in melanoma and lung adenocarcinoma has galvanized the field of immuno-oncology as well as revealed the limitations of current treatments, as the majority of patients do not respond to immunotherapy. Development of accurate preclinical models to quickly identify novel and effective therapeutic combinations are critical to address this unmet clinical need. Pancreatic ductal adenocarcinoma (PDA) is a canonical example of an immune checkpoint blockade resistant tumor with only 2% of patients responding to immunotherapy. The genetically engineered KrasG12D+/-;Trp53R172H+/-;Pdx-1 Cre (KPC) mouse model of PDA recapitulates human disease and is a valuable tool for assessing therapies for immunotherapy resistant in the preclinical setting, but time to tumor onset is highly variable. Surgical orthotopic tumor implantation models of PDA maintain the immunobiological hallmarks of the KPC tissue-specific tumor microenvironment (TME) but require a time-intensive procedure and introduce aberrant inflammation. Here, we use an ultrasound-guided orthotopic tumor implantation model (UG-OTIM) to non-invasively inject KPC-derived PDA cell lines directly into the mouse pancreas. UG-OTIM tumors grow in the endogenous tissue site, faithfully recapitulate histological features of the PDA TME, and reach enrollment-sized tumors for preclinical studies by four weeks after injection with minimal seeding on the peritoneal wall. The UG-OTIM system described here is a rapid and reproducible tumor model that may allow for high throughput analysis of novel therapeutic combinations in the murine PDA TME.

Tumor cell-intrinsic EPHA2 suppresses anti-tumor immunity by regulating PTGS2 (COX-2)

Resistance to immunotherapy is one of the biggest problems of current oncotherapeutics. WhileT cell abundance is essential for tumor responsiveness to immunotherapy, factors that define the T cell inflamed tumor microenvironment are not fully understood. We conducted an unbiased approach to identify tumor-intrinsic mechanisms shaping the immune tumor microenvironment(TME), focusing on pancreatic adenocarcinoma because it is refractory to immunotherapy and excludes T cells from the TME. From human tumors, we identified EPHA2 as a candidate tumor intrinsic driver of immunosuppression. Epha2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy. We found that PTGS2, the gene encoding cyclooxygenase-2, lies downstream of EPHA2 signaling through TGFβ and is associated with poor patient survival. Ptgs2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy; pharmacological inhibition of PTGS2 was similarly effective. Thus, EPHA2-PTGS2 signaling in tumor cells regulates tumor immune phenotypes; blockade may represent a novel therapeutic avenue for immunotherapy-refractory cancers. Our findings warrant clinical trials testing the effectiveness of therapies combining EPHA2-TGFβ-PTGS2 pathway inhibitors with anti-tumor immunotherapy, and may change the treatment of notoriously therapy-resistant pancreatic adenocarcinoma.

Abstract A054: Tumor cell intrinsic factors dictate immune cell infiltration and response to immunotherapy

The establishment of immune heterogeneity in the tumor microenvironment (TME) is poorly understood, despite recent data that the success of immunotherapies is dictated by the immune environment of the tumor site. Pancreatic ductal adenocarcinoma (PDA) is characteristically devoid of CD8 T-cells and resistant to therapeutic intervention. However, a small subset of patients (15%) have tumors highly infiltrated by CD8 T-cells, correlating with improved overall survival. To better elucidate the determinants of immune heterogeneity in the PDA TME, we generated clones from spontaneous tumors harvested from KrasG12D+/-;Trp53R172H+/-;Pdx-1 Cre (KPC) mice, a genetically engineered mouse model of PDA. Using a panel of 17 tumor clones, we found the clones segregated in to two groups with differential immune cell infiltration upon implantation in congenic C57BL/6 mice. 7/17 tumor clones were categorized as “T-cell high,” with an immune infiltrate comprising CD8 T-cells and CD103+ dendritic cells (DCs). In contrast, the remaining 10 tumor clones were categorized as “T-cell low” lines, with the TME dominated by myeloid cells and macrophages, especially granulocytic myeloid-derived suppressor cells. Hypothesizing that increased T-cell infiltrate would render PDA sensitive to therapy, we treated two T-cell high and two T-cell low tumor clones with combination immunotherapy. Mice bearing T-cell high clones responded to therapy (7/7 and 4/7 mice cured) and formed protective memory responses against secondary tumor challenge, while none of the mice bearing T-cell low tumors responded to treatment (0/7 and 0/7 mice cured). At baseline, T-cell high tumors had similar proportions of functional CD8 T-cells as in T-cell low tumors. However, the proportion of activated CD44hiPD-1+ CD8 T-cells was significantly increased in T-cell high tumors (62.2% vs. 35.1% in T-cell low clones, p<0.0001), and predicted response to therapy across the panel of tumor clones. CD44hiPD-1+ CD8 T-cells trafficked in to the tumor site independently of CXCR3 (53.8% in control vs. 50.0% in anti-CXCR3 treated tumors, p=0.8), in contrast to the bulk CD8 T-cell population which required CXCR3 to enter the TME (7.5% in control vs 0.53% in anti-CXCR3 treated tumors, p<0.01). Furthermore, in Batf3 KO mice, the T-cell high TME lacked CD8 T-cells and resembled the T-cell low phenotype, including resistance to combined immunotherapy with 0/7 mice responding to treatment, indicating the requirement for CD103+ DCs in the TME for T-cell infiltration and tumor regression. Co-mixing experiments revealed that the T-cell low phenotype was dominant in the local – but not systemic – setting, suggesting a secreted protein was involved in establishing the T-cell low TME, and CXCL1 was identified as a top candidate after transcriptomic and epigenetic profiling (padj = 0.088, basemean = 772.79). Overexpression of CXCL1 in T-cell high tumors converted the TME to a T-cell low phenotype, while ablation of CXCL1 in T-cell low tumors converted the TME to a T-cell high phenotype and rendered T-cell low sensitive to combined immunotherapy (16/16 responders or 7/16 responders in two independent CXCL1 KO T-cell low clones). These data reveal tumor cell intrinsic factors as major determinants of immune heterogeneity in the TME and highlight the use of this panel of clonal tumor lines as a tool to probe TME heterogeneity to develop optimized, patient-specific therapies.

Citation Format: Katelyn T. Byrne, Jinyang Li, Robert H. Vonderheide, Ben Stanger. Tumor cell intrinsic factors dictate immune cell infiltration and response to immunotherapy [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A054.

Tumor Cell-Intrinsic Factors Underlie Heterogeneity of Immune Cell Infiltration and Response to Immunotherapy

The biological and functional heterogeneity between tumors-both across and within cancer types-poses a challenge for immunotherapy. To understand the factors underlying tumor immune heterogeneity and immunotherapy sensitivity, we established a library of congenic tumor cell clones from an autochthonous mouse model of pancreatic adenocarcinoma. These clones generated tumors that recapitulated T cell-inflamed and non-T-cell-inflamed tumor microenvironments upon implantation in immunocompetent mice, with distinct patterns of infiltration by immune cell subsets. Co-injecting tumor cell clones revealed the non-T-cell-inflamed phenotype is dominant and that both quantitative and qualitative features of intratumoral CD8+ T cells determine response to therapy. Transcriptomic and epigenetic analyses revealed tumor-cell-intrinsic production of the chemokine CXCL1 as a determinant of the non-T-cell-inflamed microenvironment, and ablation of CXCL1 promoted T cell infiltration and sensitivity to a combination immunotherapy regimen. Thus, tumor cell-intrinsic factors shape the tumor immune microenvironment and influence the outcome of immunotherapy.

Abstract 1011: Tumor cell intrinsic factors dictate T cell infiltration and therapeutic response in pancreatic ductal adenocarcinoma

The establishment of immune heterogeneity in the tumor microenvironment (TME) is poorly understood, despite recent data that the success of immunotherapies is dictated by the immune environment of the tumor site. Pancreatic ductal adenocarcinoma (PDA) is characteristically devoid of CD8 T cells and resistant to therapeutic intervention. However, a small subset of patients (15%) have tumors highly infiltrated by CD8 T cells, correlating with improved overall survival. To better elucidate the determinants of immune heterogeneity in the PDA TME, we generated clones from spontaneous tumors harvested from KrasG12D+/-;Trp53R172H+/-;Pdx-1 Cre (KPC) mice, a genetically engineered mouse model of PDA. Using a panel of 17 tumor clones, we found the clones segregated in to two groups with differential immune cell infiltration upon implantation in congenic C57BL/6 mice. 7/17 tumor clones were categorized as ‘T cell high,' with an immune infiltrate comprising CD8 T cells, CD103+ dendritic cells (DCs), and a dearth of myeloid derived suppressor cells (MDSCs). In contrast, the remaining 10/17 tumor clones were categorized as ‘T cell low' lines, with TME dominated by myeloid cells and macrophages, especially granulocytic MDSCs. Hypothesizing that increased T cell infiltrate would render PDA sensitive to therapy, we treated two T cell high and two T cell low tumor clones with combination immunotherapy and chemotherapy. Mice bearing T cell high clones responded to therapy (7/7 and 4/7 mice cured) and formed protective memory responses against secondary tumor challenge, while none of the mice bearing T cell low tumors responded to treatment (0/7 and 0/7 mice cured). At baseline, T cell high tumors had similar proportions of functional CD8 T cells as in T cell low tumors (62.9% vs. 50.2% IFN-g+ in T cell high vs low, p=0.06). However, the proportion of activated CD44hiPD-1+ CD8 T cells was significantly increased in T cell high tumors (62.2% vs. 35.1% in T cell low clones, p<0.0001), and predicted response to therapy across the panel of tumor clones. CD44hiPD-1+ CD8 T cells trafficked in to the tumor site independently of CXCR3 (53.8% in control vs. 50.0% in anti-CXCR3 treated tumors, p=0.8), in contrast to the bulk CD8 T cell population which required CXCR3 to enter the TME (7.5% in control vs 0.53% in anti-CXCR3 treated tumors, p<0.01). Furthermore, in Batf3 KO mice, T cell high tumors lacked CD8 T cells and resembled T cell low tumors, indicating the requirement for CD103+ DCs in the TME for T cell infiltration. These data reveal tumor cell intrinsic factors as major determinants of immune heterogeneity in the TME, and highlight the use of this panel of clonal tumor lines as a tool to probe the immune heterogeneity of the TME. Future studies will identify the specific factors regulating T cell infiltration and mechanisms to convert T cell low tumors to T cell high tumors, thereby improving responses to immunotherapy.

Citation Format: Katelyn T. Byrne, Jinyang Li, Robert H. Vonderheide, Ben Z. Stanger. Tumor cell intrinsic factors dictate T cell infiltration and therapeutic response in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1011.

Abstract 4940: Nonredundant roles for immune checkpoint blockade and agonistic CD40 in mediating T-cell responses in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is a highly aggressive cancer that is resistant to most treatments, with a five-year survival rate of ~10%. Immune checkpoint blockade (ICB) has had dramatic effects in many tumor histologies, but is ineffective in PDA. CD40 lies upstream of the immune checkpoints in the T-cell activation pathway, presenting a unique opportunity to intercede with T-cell activation independently of ICB. We hypothesized that administering agonistic CD40 antibody would prime effector T-cell populations, synergizing with ICB to provide therapeutic benefit in PDA. We administered agonistic CD40 monoclonal antibody (clone FGK45, anti-CD40) combined with anti-PD1 and anti-CTLA4 monoclonal antibodies (ICB) to mice bearing subcutaneous PDA tumors established using syngeneic tumor cell lines derived from the KrasG12D+/-;Trp53R172H+/-;Pdx-1 Cre (KPC) genetically engineered mouse model of PDA. While tumor regressions were rare in mice treated with ICB or anti-CD40 alone (1/7 mice in each group), 100% of mice treated with ICB + anti-CD40 experienced tumor regressions (7/7 mice). Cell depletion experiments showed early tumor regressions depended primarily on CD4 T cells, although both CD4 and CD8 T cells were required for long-term remission. 50% of mice (4/8) treated with ICB + anti-CD40 remained tumor-free (median survival 112 days) and 3/4 mice resisted tumor rechallenge, indicative of a long-lived memory T-cell response against PDA. Treatment with ICB + anti-CD40, but neither alone, increased the total intratumoral CD3+ T-cell population 3.8-fold (p<0.01), with increases in both the CD4+ and CD8+ T-cell compartments (6.7-fold and 3.3-fold, respectively, p <0.016). CD40 stimulation, but not ICB, modulated the CD4 compartment in the TME, increasing the proportion of CD43+CD11a+ antigen-specific CD4 T helpers (41 - 43% v. 10%, +/-ICB v. control, p <0.03) and reducing FoxP3+ CD4+ T regulatory cells (Tregs) 2.7 to 3.7-fold (+/- ICB, p < 0.0001). This resulted in an increased ratio of CD8 T effector cells to Tregs (7.5 to 10.7 CD8/Treg, anti-CD40 +/-ICB, p<0.01) specifically after treatment with anti-CD40, regardless of ICB addition. ICB alone increased the proportion of proliferating CD8 T cells in the tumor draining lymph node that were ‘"reinvigorated" Eomes+Tbet-Ki67+ (17-19% +/- CD40 v. 8% control, p <0.01), but was unable to increase the same CD8 T-cell population in the tumor. However, the addition of CD40 to ICB reduced the frequency of PD1+ CD8 T effectors in the tumor (25% v. 52% control, p < 0.05), suggesting a tumor-specific benefit of ICB on the exhausted T-cell compartment. These studies reveal the nonredundant roles that agonistic CD40 and ICB play in generating a robust T-cell response against PDA, and highlight the clinical potential of combining CD40 activation with ICB as a novel therapeutic approach in ICB-resistant tumors.

Citation Format: Alexander H. Morrison, Katelyn T. Byrne, Robert H. Vonderheide. Nonredundant roles for immune checkpoint blockade and agonistic CD40 in mediating T-cell responses in pancreatic ductal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4940.

Immunotherapy and Prevention of Pancreatic Cancer

Pancreatic cancer is the third-leading cause of cancer mortality in the USA, recently surpassing breast cancer. A key component of pancreatic cancer's lethality is its acquired immune privilege, which is driven by an immunosuppressive microenvironment, poor T cell infiltration, and a low mutational burden. Although immunotherapies such as checkpoint blockade or engineered T cells have yet to demonstrate efficacy, a growing body of evidence suggests that orthogonal combinations of these and other strategies could unlock immunotherapy in pancreatic cancer. In this Review article, we discuss promising immunotherapies currently under investigation in pancreatic cancer and provide a roadmap for the development of prevention vaccines for this and other cancers.

Resident memory T cells in the skin mediate durable immunity to melanoma

Tissue-resident memory T (T_RM) cells have been widely characterized in infectious disease settings; however, their role in mediating immunity to cancer remains unknown. We report that skin-resident memory T cell responses to melanoma are generated naturally as a result of autoimmune vitiligo. Melanoma antigen-specific T_RM cells resided predominantly in melanocyte-depleted hair follicles and were maintained without recirculation or replenishment from the lymphoid compartment. These cells expressed CD103, CD69, and CLA (cutaneous lymphocyte antigen), but lacked PD-1 (programmed cell death protein-1) or LAG-3 (lymphocyte activation gene-3), and were capable of making IFN-γ (interferon-γ). CD103 expression on CD8 T cells was required for the establishment of T_RM cells in the skin but was dispensable for vitiligo development. CD103⁺ CD8 T_RM cells were critical for protection against melanoma rechallenge. This work establishes that CD103-dependent T_RM cells play a key role in perpetuating antitumor immunity.

Lack of immunoediting in murine pancreatic cancer reversed with neoantigen

In carcinogen-driven cancers, a high mutational burden results in neoepitopes that can be recognized immunologically. Such carcinogen-induced tumors may evade this immune response through "immunoediting," whereby tumors adapt to immune pressure and escape T cell-mediated killing. Many tumors lack a high neoepitope burden, and it remains unclear whether immunoediting occurs in such cases. Here, we evaluated T cell immunity in an autochthonous mouse model of pancreatic cancer and found a low mutational burden, absence of predicted neoepitopes derived from tumor mutations, and resistance to checkpoint immunotherapy. Spontaneous tumor progression was identical in the presence or absence of T cells. Moreover, tumors arising in T cell-depleted mice grew unchecked in immune-competent hosts. However, introduction of the neoantigen ovalbumin (OVA) led to tumor rejection and T cell memory, but this did not occur in OVA immune-tolerant mice. Thus, immunoediting does not occur in this mouse model - a likely consequence, not a cause, of absent neoepitopes. Because many human tumors also have a low missense mutational load and minimal neoepitope burden, our findings have clinical implications for the design of immunotherapy for patients with such tumors.

CD40 Stimulation Obviates Innate Sensors and Drives T Cell Immunity in Cancer

Cancer immunotherapies are more effective in tumors with robust T cell infiltrates, but mechanisms to convert T cell-devoid tumors with active immunosuppression to those capable of recruiting T cells remain incompletely understood. Here, using genetically engineered mouse models of pancreatic ductal adenocarcinoma (PDA), we demonstrate that a single dose of agonistic CD40 antibody with chemotherapy rendered PDA susceptible to T cell-dependent destruction and potentiated durable remissions. CD40 stimulation caused a clonal expansion of T cells in the tumor, but the addition of chemotherapy optimized myeloid activation and T cell function. Although recent data highlight the requirement for innate sensors in cancer immunity, these canonical pathways-including TLRs, inflammasome, and type I interferon/STING-played no role in mediating the efficacy of CD40 and chemotherapy. Thus, CD40 functions as a non-redundant mechanism to convert the tumor microenvironment immunologically. Our data provide a rationale for a newly initiated clinical trial of CD40 and chemotherapy in PDA.

CSF-1R-Dependent Lethal Hepatotoxicity When Agonistic CD40 Antibody Is Given before but Not after Chemotherapy

Cancer immunotherapies are increasingly effective in the clinic, especially immune checkpoint blockade delivered to patients who have T cell-infiltrated tumors. Agonistic CD40 mAb promotes stromal degradation and, in combination with chemotherapy, drives T cell infiltration and de novo responses against tumors, rendering resistant tumors susceptible to current immunotherapies. Partnering anti-CD40 with different treatments is an attractive approach for the next phase of cancer immunotherapies, with a number of clinical trials using anti-CD40 combinations ongoing, but the optimal therapeutic regimens with anti-CD40 are not well understood. Pancreatic ductal adenocarcinoma (PDA) is classically resistant to immunotherapy and lacks baseline T cell infiltration. In this study, we used a tumor cell line derived from a genetically engineered mouse model of PDA to investigate alterations in the sequence of anti-CD40 and chemotherapy as an approach to enhance pharmacological delivery of chemotherapy. Unexpectedly, despite our previous studies showing anti-CD40 treatment after chemotherapy is safe in both mice and patients with PDA, we report in this article that anti-CD40 administration <3 d in advance of chemotherapy is lethal in more than half of treated C57BL/6 mice. Anti-CD40 treatment 2 or 3 d before chemotherapy resulted in significantly increased populations of both activated myeloid cells and macrophages and lethal hepatotoxicity. Liver damage was fully abrogated when macrophage activation was blocked using anti-CSF-1R mAb. These studies highlight the dual nature of CD40 in activating both macrophages and T cell responses, and the need for preclinical investigation of optimal anti-CD40 treatment regimens for safe design of clinical trials.

Abstract A40: Agonistic CD40 antibody combined with chemotherapy drives TLR4/MyD88 independent regression of pancreatic tumors in a T cell dependent manner

This abstract is being presented as a short talk in the scientific program. A full abstract is printed in the Proffered Abstracts section (PR07) of the Conference Proceedings.

Citation Format: Katelyn T. Byrne, Robert H. Vonderheide. Agonistic CD40 antibody combined with chemotherapy drives TLR4/MyD88 independent regression of pancreatic tumors in a T cell dependent manner. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr A40.

Abstract PR07: Agonistic CD40 antibody combined with chemotherapy drives TLR4/MyD88 independent regression of pancreatic tumors in a T cell dependent manner

Pancreatic ductal adenocarcinoma (PDA) is a highly aggressive cancer that is resistant to most treatments, and more than 90% of patients with metastatic PDA die within five years of diagnosis. Recent clinical studies show that combining gemcitabine (Gem) with nanoparticle albumin-bound paclitaxel, Abraxane (Abrx), prolongs progression-free and overall survival as compared to Gem alone, but the objective response rate of the combination was only 23%, and nearly every patient eventually progressed. Given that CD40 activation can reverse tumor-induced immune suppression and promote anti-tumor T cell responses, we administered agonistic CD40 monoclonal antibody (FGK45) with combined Gem/Abrx chemotherapy to mice bearing subcutaneous PDA tumors established using syngeneic tumor cell lines derived from the KrasG12D+/-;Trp53R172H+/-;Pdx-1 Cre (KPC) genetically engineered mouse model of PDA. We found only rare tumor regressions in mice treated with chemotherapy alone (Gem, Abrx, or Gem/Abrx) or FGK45 alone, whereas more than 50% of mice treated with Gem/Abrx/FGK45 experienced tumor regressions (p&lt;0.0001). Mechanistic studies revealed that this effect was T cell dependent, and in some mice treated with Gem/Abrx/FGK45, tumors were completely rejected within 3 weeks and the mice remained tumor free for over 100 days, suggesting long-lived T cell memory directed against PDA. Although the overall CD3+ T cell population in the tumor after therapy did not vary across treatment cohorts, the proportion of FoxP3+CD4+ T regulatory cells (Tregs) was reduced 6.9-fold after treatment with Gem/Abrx/FGK45 (p&lt;0.05, Gem/Abrx/FGK45 treatment versus chemotherapy or FGK45 alone), with a concurrent 1.75-fold increase in activated CD44hiCD4+ T helper cells (p&lt;0.01). As a result, the ratio of CD4 Thelper or CD8 T effector cells to Tregs was increased intratumorally. The reduction of Tregs was observed early after therapy, and in the absence of Treg to Thelper conversion, suggesting a change in the priming of the CD4 compartment. Indeed, within 24 hours after Gem/Abrx/FGK45 treatment, antigen-presenting cells (APCs) in the tumor and draining lymph node had increased expression of both CD86 and MHCII (37% versus 10% in control group, p&lt;0.0001 by ANOVA), as well as increased production of TNF-alpha (39% versus 24% in control group, p&lt;0.0001 by ANOVA). These changes in the activation status of APCs in the Gem/Abrx/FGK45 treated-tumor microenvironment may help promote Thelper differentiation. Furthermore, responses to Gem/Abrx/FGK45 are independent of the TLR4 and MyD88 pathways, which have previously been reported as critical mediators of the anti-tumor immune response generated with chemotherapy. Spontaneous PDA tumors arising in KPC mice were also susceptible to Gem/Abrx/FGK45 therapy, exhibiting slowed growth rates and even tumor regression after treatment (37.5% stable disease or tumor regression, versus 0% in Gem/Abrx combined group), in a CD8 dependent manner. These studies not only highlight the clinical potential of adding CD40 activation to standard-of-care chemotherapy as a novel strategy for PDA, but also underscore an emerging hypothesis that T cell immune surveillance can be effective against this otherwise highly immunosuppressive tumor if triggered by robust vaccination.

This abstract is also presented as Poster A40.

Citation Format: Katelyn T. Byrne, Robert H. Vonderheide. Agonistic CD40 antibody combined with chemotherapy drives TLR4/MyD88 independent regression of pancreatic tumors in a T cell dependent manner. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr PR07.

Abstract 1356: Chemotherapy and agonistic CD40 cooperate to regress pancreatic adenocarcinoma independently of TLR4 and MyD88

Pancreatic ductal adenocarcinoma (PDA) is an aggressive and lethal disease, with current standards of care extending overall survival by only a few months, as observed with the combination of nab-paclitaxel (nP) and gemcitabine (Gem). As such, efforts have begun to focus on the prospect of immune therapy has a new paradigm for patients in PDA. Given the potential synergy between chemotherapy and immune stimulation to create an anti-tumor vaccine, we hypothesized that agonistic CD40 monoclonal antibody with combined Gem/nP chemotherapy can activate the immune response and reverse immunosuppression in the PDA microenvironment. Using the KrasG12D+/-;Trp53R172H+/-;Pdx-1 Cre (KPC) genetically engineered mouse model of PDA, we found that 37.5% of mice treated with Gem/nP/CD40 therapy had tumor regressions or stable disease, compared to only 9% of mice receiving Gem/nP without CD40 (p&lt;0.03). Furthermore, when mice were depleted of CD8 T cells, the tumor regressions were completely ablated. To understand the mechanism by which chemotherapy potentiated CD40 agonist treatment, we injected PDA cell lines generated from KPC tumors subcutaneously into C57Bl/6 mice, and found that more than 50% of mice treated with Gem/nP/CD40 experienced T cell dependent tumor regressions compared to only rare regressions in Gem/nP or CD40 treated mice (p&lt;0.0001). Tumor regressions were dependent on T cells and IFN-gamma, and accordingly, we found the proportions of both CD4 and CD8 T cells producing IFN-gamma to be increased 2- to 4-fold in mice treated with Gem/nP/CD40 as compared to other cohorts. Concurrent with increased effector T cells, the proportion of T regulatory cells in the tumor was reduced 6.9-fold after Gem/nP/CD40 (p&lt;0.05, versus Gem/nP or CD40 alone). The loss of the immunosuppressive tumor microenvironment was detectable 24 hours after Gem/nP/CD40 treatment, when CD11b+ and CD11c+ cells in the tumor reduced production of IL-10 and TGF-beta by 1.3 to 5-fold (compared to Gem/nP treatment), and increased production of IL-12 (35% versus 23% in CD40 treated mice), concurrent with increased expression of both CD86 and MHCII (37% versus 10% in control group). Despite prior results linking MyD88 signaling with immune potentiating effects of chemotherapy, we observed that responses to Gem/nP/CD40 were independent of MyD88, and TLR4 pathways. Tumor regressions with Gem/nP/CD40 were also independent of TRIF, IFNAR, Caspase 1 and 4, TLR3, muMT, TNF-alpha, and Perforin. These studies reveal a novel MyD88- and TLR4-independent mechanism of chemotherapeutic activation of the immune system, and highlight the significant clinical potential of combining Gem/nP with agonistic CD40 stimulation.

Citation Format: Katelyn T. Byrne, Robert H. Vonderheide. Chemotherapy and agonistic CD40 cooperate to regress pancreatic adenocarcinoma independently of TLR4 and MyD88. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1356. doi:10.1158/1538-7445.AM2015-1356

Special Conference on Tumor Immunology and Immunotherapy: A New Chapter

The overall objective of the fifth American Association for Cancer Research Special Conference, "Tumor Immunology and Immunotherapy: A New Chapter," organized by the Cancer Immunology Working Group, was to highlight multidisciplinary approaches of immunotherapy and mechanisms related to the ability of immunotherapy to fight established tumors. With the FDA approval of sipuleucel-T, ipilimumab (anti-CTLA-4; Bristol-Myers Squibb), and the two anti-PD-1 antibodies, pembrolizumab (formerly MK-3475 or lambrolizumab; Merck) and nivolumab (Bristol-Myers Squibb), immunotherapy has become a mainstream treatment option for some cancers. Many of the data presented at the conference and reviewed in this article showcase the progress made in determining the mechanistic reasons for the success of some treatments and the mechanisms associated with tolerance within the tumor microenvironment, both of which are potential targets for immunotherapy. In addition to combination and multimodal therapies, improvements in existing therapies will be needed to overcome the numerous ways that tumor-specific tolerance thwarts the immune system. This conference built upon the success of the 2012 conference and focused on seven progressing and/or emerging areas-new combination therapies, combination therapies and vaccine improvement, mechanisms of antibody therapy, factors in the tumor microenvironment affecting the immune response, the microbiomes effect on cancer and immunotherapy, metabolism in immunotherapy, and adoptive T-cell therapy. Cancer Immunol Res; 3(6); 1-8. ©2015 AACR.

Induction of T-cell Immunity Overcomes Complete Resistance to PD-1 and CTLA-4 Blockade and Improves Survival in Pancreatic Carcinoma

Disabling the function of immune checkpoint molecules can unlock T-cell immunity against cancer, yet despite remarkable clinical success with monoclonal antibodies (mAb) that block PD-1 or CTLA-4, resistance remains common and essentially unexplained. To date, pancreatic carcinoma is fully refractory to these antibodies. Here, using a genetically engineered mouse model of pancreatic ductal adenocarcinoma in which spontaneous immunity is minimal, we found that PD-L1 is prominent in the tumor microenvironment, a phenotype confirmed in patients; however, tumor PD-L1 was found to be independent of IFNγ in this model. Tumor T cells expressed PD-1 as prominently as T cells from chronically infected mice, but treatment with αPD-1 mAbs, with or without αCTLA-4 mAbs, failed in well-established tumors, recapitulating clinical results. Agonist αCD40 mAbs with chemotherapy induced T-cell immunity and reversed the complete resistance of pancreatic tumors to αPD-1 and αCTLA-4. The combination of αCD40/chemotherapy plus αPD-1 and/or αCTLA-4 induced regression of subcutaneous tumors, improved overall survival, and conferred curative protection from multiple tumor rechallenges, consistent with immune memory not otherwise achievable. Combinatorial treatment nearly doubled survival of mice with spontaneous pancreatic cancers, although no cures were observed. Our findings suggest that in pancreatic carcinoma, a nonimmunogenic tumor, baseline refractoriness to checkpoint inhibitors can be rescued by the priming of a T-cell response with αCD40/chemotherapy.

BRAF inhibition alleviates immune suppression in murine autochthonous melanoma

A growing body of evidence suggests that BRAF inhibitors, in addition to their acute tumor growth-inhibitory effects, can also promote immune responses to melanoma. The present study aimed to define the immunologic basis of BRAF-inhibitor therapy using the Braf/Pten model of inducible, autochthonous melanoma on a pure C57BL/6 background. In the tumor microenvironment, BRAF inhibitor PLX4720 functioned by on-target mechanisms to selectively decrease both the proportions and absolute numbers of CD4(+)Foxp3(+) regulatory T cells (Treg) and CD11b(+)Gr1(+) myeloid-derived suppressor cells (MDSC), while preserving numbers of CD8(+) effector T cells. In PLX4720-treated mice, the intratumoral Treg populations decreased significantly, demonstrating enhanced apopotosis. CD11b(+) myeloid cells from PLX4720-treated tumors also exhibited decreased immunosuppressive function on a per-cell basis. In accordance with a reversion of tumor immune suppression, tumors that had been treated with PLX4720 grew with reduced kinetics after treatment was discontinued, and this growth delay was dependent on CD8 T cells. These findings demonstrate that BRAF inhibition selectively reverses two major mechanisms of immunosuppression in melanoma and liberates host-adaptive antitumor immunity.

Autoimmune vitiligo does not require the ongoing priming of naive CD8 T cells for disease progression or associated protection against melanoma

Vitiligo is a CD8 T cell-mediated autoimmune disease that has been shown to promote the longevity of memory T cell responses to melanoma. However, mechanisms whereby melanocyte/melanoma Ag-specific T cell responses are perpetuated in the context of vitiligo are not well understood. These studies investigate the possible phenomenon of naive T cell priming in hosts with melanoma-initiated, self-perpetuating, autoimmune vitiligo. Using naive pmel (gp10025-33-specific) transgenic CD8 T cells, we demonstrate that autoimmune melanocyte destruction induces naive T cell proliferation in skin-draining lymph nodes, in an Ag-dependent fashion. These pmel T cells upregulate expression of CD44, P-selectin ligand, and granzyme B. However, they do not downregulate CD62L, nor do they acquire the ability to produce IFN-γ, indicating a lack of functional priming. Accordingly, adult thymectomized mice exhibit no reduction in the severity or kinetics of depigmentation or long-lived protection against melanoma, indicating that the continual priming of naive T cells is not required for vitiligo or its associated antitumor immunity. Despite this, depletion of CD4 T cells during the course of vitiligo rescues the priming of naive pmel T cells that are capable of producing IFN-γ and persisting as memory, suggesting an ongoing and dominant mechanism of suppression by regulatory T cells. This work reveals the complex regulation of self-reactive CD8 T cells in vitiligo and demonstrates the overall poorly immunogenic nature of this autoimmune disease setting.

Immune-mediated regression of established B16F10 melanoma by intratumoral injection of attenuated Toxoplasma gondii protects against rechallenge

Immune recognition of tumors can limit cancer development, but antitumor immune responses are often blocked by tumor-mediated immunosuppression. Because microbes or microbial constituents are powerful adjuvants to stimulate immune responses, we evaluated whether intratumoral administration of a highly immunogenic but attenuated parasite could induce rejection of an established poorly immunogenic tumor. We treated intradermal B16F10 murine melanoma by intratumoral injection of an attenuated strain of Toxoplasma gondii (cps) that cannot replicate in vivo and therefore is not infective. The cps treatment stimulated a strong CD8(+) T cell-mediated antitumor immune response in vivo that regressed established primary melanoma. The cps monotherapy rapidly modified the tumor microenvironment, halting tumor growth, and subsequently, as tumor-reactive T cells expanded, the tumors disappeared and rarely returned. The treatment required live cps that could invade cells and also required CD8(+) T cells and NK cells, but did not require CD4(+) T cells. Furthermore, we demonstrate that IL-12, IFN-γ, and the CXCR3-stimulating cytokines are required for full treatment efficacy. The treatment developed systemic antitumor immune activity as well as antitumor immune memory and therefore might have an impact against human metastatic disease. The approach is not specific for either B16F10 or melanoma. Direct intratumoral injection of cps has efficacy against an inducible genetic melanoma model and transplantable lung and ovarian tumors, demonstrating potential for broad clinical use. The combination of efficacy, systemic antitumor immune response, and complete attenuation with no observed host toxicity demonstrates the potential value of this novel cancer therapy.

Protective CD8 memory T cell responses to mouse melanoma are generated in the absence of CD4 T cell help

BACKGROUND

We have previously demonstrated that temporary depletion of CD4 T cells in mice with progressive B16 melanoma, followed by surgical tumor excision, induces protective memory CD8 T cell responses to melanoma/melanocyte antigens. We also showed that persistence of these CD8 T cells is supported, in an antigen-dependent fashion, by concurrent autoimmune melanocyte destruction. Herein we explore the requirement of CD4 T cell help in priming and maintaining this protective CD8 T cell response to melanoma.

METHODOLOGY AND PRINCIPAL FINDINGS

To induce melanoma/melanocyte antigen-specific CD8 T cells, B16 tumor bearing mice were depleted of regulatory T cells (T(reg)) by either temporary, or long-term continuous treatment with anti-CD4 (mAb clone GK1.5). Total depletion of CD4 T cells led to significant priming of IFN-γ-producing CD8 T cell responses to TRP-2 and gp100. Surprisingly, treatment with anti-CD25 (mAb clone PC61), to specifically deplete T(reg) cells while leaving help intact, was ineffective at priming CD8 T cells. Thirty to sixty days after primary tumors were surgically excised, mice completely lacking CD4 T cell help developed autoimmune vitiligo, and maintained antigen-specific memory CD8 T cell responses that were highly effective at producing cytokines (IFN-γ, TNF-α, and IL-2). Mice lacking total CD4 T cell help also mounted protection against re-challenge with B16 melanoma sixty days after primary tumor excision.

CONCLUSIONS AND SIGNIFICANCE

This work establishes that CD4 T cell help is dispensable for the generation of protective memory T cell responses to melanoma. Our findings support further use of CD4 T cell depletion therapy for inducing long-lived immunity to cancer.

New perspectives on the role of vitiligo in immune responses to melanoma

Melanoma-associated vitiligo is the best-studied example of the linkage between tumor immunity and autoimmunity. Although vitiligo is an independent positive prognostic factor for melanoma patients, the autoimmune destruction of melanocytes was long thought to be merely a side effect of robust anti-tumor immunity. However, new data reveal a key role for vitiligo in supporting T cell responses to melanoma. This research perspective reviews the history of melanoma-associated vitiligo in patients, the experimental studies that form the basis for understanding this relationship, and the unique characteristics of melanoma-specific CD8 T cells found in hosts with vitiligo. We also discuss the implications of our recent findings for the interpretation of patient responses, and the design of next-generation cancer immunotherapies.

IL-10 immunomodulation of myeloid cells regulates a murine model of ovarian cancer

Elevated levels of IL-10 in the microenvironment of human ovarian cancer and murine models of ovarian cancer are well established and correlate with poor clinical prognosis. However, amongst a myriad of immunosuppressive factors, the actual contribution of IL-10 to the ovarian tumor microenvironment, the mechanisms by which it acts, and its possible functional redundancy are unknown. We previously demonstrated that elimination of the myeloid-derived suppressor cell (MDSC) compartment within the ovarian tumor ascites inhibited tumor progression and, intriguingly, significantly decreased local IL-10 levels. Here we identify a novel pathway in which the tumor-infiltrating MDSC are the predominant producers of IL-10 and, importantly, require it to develop their immunosuppressive function in vivo. Importantly, we demonstrate that the role of IL-10 is critical, and not redundant with other immunosuppressive molecules, to in vivo tumor progression: blockade of the IL-10 signaling network results in alleviation of MDSC-mediated immunosuppression, altered T cell phenotype and activity, and improved survival. These studies define IL-10 as a fundamental modulator of both MDSC and T cells within the ovarian tumor microenvironment. Importantly, IL-10 signaling is shown to be necessary to the development and maintenance of a permissive tumor microenvironment and represents a viable target for anti-tumor strategies.

Autoimmune melanocyte destruction is required for robust CD8+ memory T cell responses to mouse melanoma

A link between autoimmunity and improved antitumor immunity has long been recognized, although the exact mechanistic relationship between these two phenomena remains unclear. In the present study we have found that vitiligo, the autoimmune destruction of melanocytes, generates self antigen required for mounting persistent and protective memory CD8+ T cell responses to melanoma. Vitiligo developed in approximately 60% of mice that were depleted of regulatory CD4+ T cells and then subjected to surgical excision of large established B16 melanomas. Mice with vitiligo generated 10-fold larger populations of CD8+ memory T cells specific for shared melanoma/melanocyte antigens. CD8+ T cells in mice with vitiligo acquired phenotypic and functional characteristics of effector memory, suggesting that they were supported by ongoing antigen stimulation. Such responses were not generated in melanocyte-deficient mice, indicating a requirement for melanocyte destruction in maintaining CD8+ T cell immunity to melanoma. Vitiligo-associated memory CD8+ T cells provided durable tumor protection, were capable of mounting a rapid recall response to melanoma, and did not demonstrate phenotypic or functional signs of exhaustion even after many months of exposure to antigen. This work establishes melanocyte destruction as a key determinant of lasting melanoma-reactive immune responses, thus illustrating that immune-mediated destruction of normal tissues can perpetuate adaptive immune responses to cancer.

Targeting transcription factor Stat4 uncovers a role for interleukin-18 in the pathogenesis of severe lupus nephritis in mice

Polymorphisms in the transcription factor Stat4 gene have been implicated as risk factors for systemic lupus erythematosus. Although some polymorphisms have a strong association with autoantibodies and nephritis, their impact on pathophysiology is still unknown. To explore this further we used signal transducers and activators of transcription 4 (Stat4) knockout MRL/MpJ-Fas(lpr)/Fas(lpr) (MRL-Fas(lpr)) mice and found that they did not differ in survival or renal function from Stat4-intact MRL-Fas(lpr) mice. Circulating interleukin (IL)-18 levels, however, were elevated in Stat4-deficient compared to Stat4-intact mice, suggesting that this interleukin might contribute to the progression of lupus nephritis independent of Stat4. In a second approach, Stat4 antisense or missense oligonucleotides or vehicle were given to MRL-Fas(lpr) mice with advanced nephritis. Each of these treatments temporarily ameliorated disease, although IL-18 was increased in each setting. Based on these findings, studies using gene transfer to overexpress IL-18 in MRL-Fas(lpr) and IL-12p40/IL-23 knockout MRL-Fas(lpr) mice reveal a critical role for IL-18 in mediating disease. Thus, the Stat4 and IL-12 (an activator of Stat4)-independent factor, IL-18, can drive autoimmune lupus nephritis in MRL-Fas(lpr) mice. Temporarily blocking Stat4 during advanced nephritis ameliorates disease, suggesting a time-dependent compensatory proinflammatory mechanism.

Circulating CSF-1 promotes monocyte and macrophage phenotypes that enhance lupus nephritis

Macrophages mediate kidney disease and are prominent in a mouse model (MRL-Fas(lpr)) of lupus nephritis. Colony stimulating factor-1 (CSF-1) is the primary growth factor for macrophages, and CSF-1 deficiency protects MRL-Fas(lpr) mice from kidney disease and systemic illness. Whether this renoprotection derives from a reduction of macrophages and whether systemic CSF-1, as opposed to intrarenal CSF-1, promotes macrophage-dependent lupus nephritis remain unclear. Here, we found that increasing systemic CSF-1 hastened the onset of lupus nephritis in MRL-Fas(lpr) mice. Using mutant MRL-Fas(lpr) strains that express high, moderate, or no systemic CSF-1, we detected a much higher tempo of kidney disease in mice with the highest level of CSF-1. Furthermore, we uncovered a multistep CSF-1-dependent systemic mechanism central to lupus nephritis. CSF-1 heightened monocyte proliferation in the bone marrow (SSC(low)CD11b(+)), and these monocytes subsequently seeded the circulation. Systemic CSF-1 skewed the frequency of monocytes toward "inflammatory" (SSC(low)CD11b(+)Ly6C(high)) and activated populations that homed to sites of inflammation, resulting in a more rapid accumulation of intrarenal macrophages (CD11b(+)CSF-1R(+) or CD68(+)) that induced apoptosis of tubular epithelial cells, damaging the kidney. In humans, we found increased levels of CSF-1 in the serum, urine, and kidneys of patients with lupus compared with healthy controls. Furthermore, serum and urine CSF-1 levels correlated with lupus activity, and intrarenal CSF-1 expression correlated with the histopathology activity index of lupus nephritis. Taken together, circulating CSF-1 is a potential therapeutic target for lupus nephritis.

Sunlight triggers cutaneous lupus through a CSF-1-dependent mechanism in MRL-Fas(lpr) mice

Sunlight (UVB) triggers cutaneous lupus erythematosus (CLE) and systemic lupus through an unknown mechanism. We tested the hypothesis that UVB triggers CLE through a CSF-1-dependent, macrophage (Mø)-mediated mechanism in MRL-Fas(lpr) mice. By constructing mutant MRL-Fas(lpr) strains expressing varying levels of CSF-1 (high, intermediate, none), and use of an ex vivo gene transfer to deliver CSF-1 intradermally, we determined that CSF-1 induces CLE in lupus-susceptible MRL-Fas(lpr) mice, but not in lupus-resistant BALB/c mice. UVB incites an increase in Møs, apoptosis in the skin, and CLE in MRL-Fas(lpr), but not in CSF-1-deficient MRL-Fas(lpr) mice. Furthermore, UVB did not induce CLE in BALB/c mice. Probing further, UVB stimulates CSF-1 expression by keratinocytes leading to recruitment and activation of Møs that, in turn, release mediators, which induce apoptosis in keratinocytes. Thus, sunlight triggers a CSF-1-dependent, Mø-mediated destructive inflammation in the skin leading to CLE in lupus-susceptible MRL-Fas(lpr) but not lupus-resistant BALB/c mice. Taken together, CSF-1 is envisioned as the match and lupus susceptibility as the tinder leading to CLE.