cIAP1/2 Antagonism Induces Antigen-Specific T Cell-Dependent Immunity

Checkpoint blockade immunotherapy has failed in pancreatic cancer and other poorly responsive tumor types in part due to inadequate T cell priming. Naive T cells can receive costimulation not only via CD28 but also through TNF superfamily receptors that signal via NF-κB. Antagonists of the ubiquitin ligases cellular inhibitor of apoptosis protein (cIAP)1/2, also called second mitochondria-derived activator of caspases (SMAC) mimetics, induce degradation of cIAP1/2 proteins, allowing for the accumulation of NIK and constitutive, ligand-independent activation of alternate NF-κB signaling that mimics costimulation in T cells. In tumor cells, cIAP1/2 antagonists can increase TNF production and TNF-mediated apoptosis; however, pancreatic cancer cells are resistant to cytokine-mediated apoptosis, even in the presence of cIAP1/2 antagonism. Dendritic cell activation is enhanced by cIAP1/2 antagonism in vitro, and intratumoral dendritic cells show higher expression of MHC class II in tumors from cIAP1/2 antagonism-treated mice. In this study, we use in vivo mouse models of syngeneic pancreatic cancer that generate endogenous T cell responses ranging from moderate to poor. Across multiple models, cIAP1/2 antagonism has pleiotropic beneficial effects on antitumor immunity, including direct effects on tumor-specific T cells leading to overall increased activation, increased control of tumor growth in vivo, synergy with multiple immunotherapy modalities, and immunologic memory. In contrast to checkpoint blockade, cIAP1/2 antagonism does not increase intratumoral T cell frequencies. Furthermore, we confirm our previous findings that even poorly immunogenic tumors with a paucity of T cells can experience T cell-dependent antitumor immunity, and we provide transcriptional clues into how these rare T cells coordinate downstream immune responses.

NKG2A and HLA-E define an alternative immune checkpoint axis in bladder cancer

Programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1)-blockade immunotherapies have limited efficacy in the treatment of bladder cancer. Here, we show that NKG2A associates with improved survival and responsiveness to PD-L1 blockade immunotherapy in bladder tumors that have high abundance of CD8+ T cells. In bladder tumors, NKG2A is acquired on CD8+ T cells later than PD-1 as well as other well-established immune checkpoints. NKG2A+ PD-1+ CD8+ T cells diverge from classically defined exhausted T cells through their ability to react to human leukocyte antigen (HLA) class I-deficient tumors using T cell receptor (TCR)-independent innate-like mechanisms. HLA-ABC expression by bladder tumors is progressively diminished as disease progresses, framing the importance of targeting TCR-independent anti-tumor functions. Notably, NKG2A+ CD8+ T cells are inhibited when HLA-E is expressed by tumors and partly restored upon NKG2A blockade in an HLA-E-dependent manner. Overall, our study provides a framework for subsequent clinical trials combining NKG2A blockade with other T cell-targeted immunotherapies, where tumors express higher levels of HLA-E.

Inhibition of CDK4/6 Promotes CD8 T-cell Memory Formation

CDK4/6 inhibitors are approved to treat breast cancer and are in trials for other malignancies. We examined CDK4/6 inhibition in mouse and human CD8+ T cells during early stages of activation. Mice receiving tumor-specific CD8+ T cells treated with CDK4/6 inhibitors displayed increased T-cell persistence and immunologic memory. CDK4/6 inhibition upregulated MXD4, a negative regulator of MYC, in both mouse and human CD8+ T cells. Silencing of Mxd4 or Myc in mouse CD8+ T cells demonstrated the importance of this axis for memory formation. We used single-cell transcriptional profiling and T-cell receptor clonotype tracking to evaluate recently activated human CD8+ T cells in patients with breast cancer before and during treatment with either palbociclib or abemaciclib. CDK4/6 inhibitor therapy in humans increases the frequency of CD8+ memory precursors and downregulates their expression of MYC target genes, suggesting that CDK4/6 inhibitors in patients with cancer may augment long-term protective immunity. SIGNIFICANCE: CDK4/6 inhibition skews newly activated CD8+ T cells toward a memory phenotype in mice and humans with breast cancer. CDK4/6 inhibitors may have broad utility outside breast cancer, particularly in the neoadjuvant setting to augment CD8+ T-cell priming to tumor antigens prior to dosing with checkpoint blockade.This article is highlighted in the In This Issue feature, p. 2355.

Intratumoral IL12 mRNA Therapy Promotes TH1 Transformation of the Tumor Microenvironment

PURPOSE

While immune checkpoint inhibitors such as anti-PD-L1 are rapidly becoming the standard of care in the treatment of many cancers, only a subset of treated patients have long-term responses. IL12 promotes antitumor immunity in mouse models; however, systemic recombinant IL12 had significant toxicity and limited efficacy in early clinical trials.

EXPERIMENTAL DESIGN

We therefore designed a novel intratumoral IL12 mRNA therapy to promote local IL12 tumor production while mitigating systemic effects.

RESULTS

A single intratumoral dose of mouse (m)IL12 mRNA induced IFNγ and CD8⁺ T-cell-dependent tumor regression in multiple syngeneic mouse models, and animals with a complete response demonstrated immunity to rechallenge. Antitumor activity of mIL12 mRNA did not require NK and NKT cells. mIL12 mRNA antitumor activity correlated with TH1 tumor microenvironment (TME) transformation. In a PD-L1 blockade monotherapy-resistant model, antitumor immunity induced by mIL12 mRNA was enhanced by anti-PD-L1. mIL12 mRNA also drove regression of uninjected distal lesions, and anti-PD-L1 potentiated this response. Importantly, intratumoral delivery of mRNA encoding membrane-tethered mIL12 also drove rejection of uninjected lesions with very limited circulating IL12p70, supporting the hypothesis that local IL12 could induce a systemic antitumor immune response against distal lesions. Furthermore, in ex vivo patient tumor slice cultures, human IL12 mRNA (MEDI1191) induced dose-dependent IL12 production, downstream IFNγ expression and TH1 gene expression.

CONCLUSIONS

These data demonstrate the potential for intratumorally delivered IL12 mRNA to promote TH1 TME transformation and robust antitumor immunity.See related commentary by Cirella et al., p. 6080.

Altered Binding of Tumor Antigenic Peptides to MHC Class I Affects CD8+ T Cell-Effector Responses

T-cell priming occurs when a naïve T cell recognizes cognate peptide-MHC complexes on an activated antigen-presenting cell. The circumstances of this initial priming have ramifications on the fate of the newly primed T cell. Newly primed CD8⁺ T cells can embark onto different trajectories, with some becoming short-lived effector cells and others adopting a tissue resident or memory cell fate. To determine whether T-cell priming influences the quality of the effector T-cell response to tumors, we used transnuclear CD8⁺ T cells that recognize the melanoma antigen TRP1 using TRP1^high or TRP1^low TCRs that differ in both affinity and fine specificity. From a series of altered peptide ligands, we identified a point mutation (K8) in a nonanchor residue that, when analyzed crystallographically and biophysically, destabilized the peptide interaction with the MHC binding groove. In vitro, the K8 peptide induced robust proliferation of both TRP1^high and TRP1^low CD8⁺ T cells but did not induce expression of PD-1. Cytokine production from K8-stimulated TRP1 cells was minimal, whereas cytotoxicity was increased. Upon transfer into B16 tumor-bearing mice, the reference peptide (TRP1-M9)- and K8-stimulated TRP1 cells were equally effective at controlling tumor growth but accomplished this through different mechanisms. TRP1-M9-stimulated cells produced more IFNγ, whereas K8-stimulated cells accumulated to higher numbers and were more cytotoxic. We, therefore, conclude that TCR recognition of weakly binding peptides during priming can skew the effector function of tumor-specific CD8⁺ T cells.

IAP Antagonists Enhance Cytokine Production from Mouse and Human iNKT Cells

Inhibitor of apoptosis protein (IAP) antagonists are in clinical trials for a variety of cancers, and mouse models show synergism between IAP antagonists and anti-PD-1 immunotherapy. Although IAP antagonists affect the intrinsic signaling of tumor cells, their most pronounced effects are on immune cells and the generation of antitumor immunity. Here, we examined the effects of IAP antagonism on T-cell development using mouse fetal thymic organ culture and observed a selective loss of iNKT cells, an effector cell type of potential importance for cancer immunotherapy. Thymic iNKT-cell development probably failed due to increased strength of TCR signal leading to negative selection, given that mature iNKT cells treated with IAP antagonists were not depleted, but had enhanced cytokine production in both mouse and human ex vivo cultures. Consistent with this, mature mouse primary iNKT cells and iNKT hybridomas increased production of effector cytokines in the presence of IAP antagonists. In vivo administration of IAP antagonists and α-GalCer resulted in increased IFNγ and IL-2 production from iNKT cells and decreased tumor burden in a mouse model of melanoma lung metastasis. Human iNKT cells also proliferated and increased IFNγ production dramatically in the presence of IAP antagonists, demonstrating the utility of these compounds in adoptive therapy of iNKT cells. Cancer Immunol Res; 6(1); 25-35. ©2017 AACR.

Monoclonal Invariant NKT (iNKT) Cell Mice Reveal a Role for Both Tissue of Origin and the TCR in Development of iNKT Functional Subsets

Invariant NKT (iNKT) cell functional subsets are defined by key transcription factors and output of cytokines, such as IL-4, IFN-γ, IL-17, and IL-10. To examine how TCR specificity determines iNKT function, we used somatic cell nuclear transfer to generate three lines of mice cloned from iNKT nuclei. Each line uses the invariant Vα14Jα18 TCRα paired with unique Vβ7 or Vβ8.2 subunits. We examined tissue homing, expression of PLZF, T-bet, and RORγt, and cytokine profiles and found that, although monoclonal iNKT cells differentiated into all functional subsets, the NKT17 lineage was reduced or expanded depending on the TCR expressed. We examined iNKT thymic development in limited-dilution bone marrow chimeras and show that higher TCR avidity correlates with higher PLZF and reduced T-bet expression. iNKT functional subsets showed distinct tissue distribution patterns. Although each individual monoclonal TCR showed an inherent subset distribution preference that was evident across all tissues examined, the iNKT cytokine profile differed more by tissue of origin than by TCR specificity.

CXCR3+ monocytes/macrophages are required for establishment of pulmonary metastases

We present a new foundational role for CXCR3⁺ monocytes/macrophages in the process of tumor engraftment in the lung. CXCR3 is associated with monocytic and lymphocytic infiltration of inflamed or tumor-bearing lung. Although the requirement for tumor-expressed CXCR3 in metastatic engraftment has been demonstrated, the role of monocyte-expressed CXCR3 had not been appreciated. In a murine model of metastatic-like melanoma, engraftment was coordinate with CXCR3⁺ monocyte/macrophage accumulation in the lungs and was sensitive to pharmacologic inhibition of CXCR3 signaling. Tumor engraftment to lung was impaired in CXCR3^−/− mice, and transient reconstitution with circulating CXCR3-replete monocytes was sufficient to restore engraftment. These data illustrate the paradoxical pro-tumor role for CXCR3 in lung immunobiology wherein the CXCR3 axis drives both the anti-tumor effector cell chemoattraction and pro-tumor infiltration of the lungs and suggests a potential therapeutic target for lung-tropic metastasizing cancers.

Melanoma Induces, and Adenosine Suppresses, CXCR3-Cognate Chemokine Production and T-cell Infiltration of Lungs Bearing Metastatic-like Disease

Despite immunogenicity, melanoma-specific vaccines have demonstrated minimal clinical efficacy in patients with established disease but enhanced survival when administered in the adjuvant setting. Therefore, we hypothesized that organs bearing metastatic-like melanoma may differentially produce T-cell chemotactic proteins over the course of tumor development. Using an established model of metastatic-like melanoma in lungs, we assessed the production of specific cytokines and chemokines over a time course of tumor growth, and we correlated chemokine production with chemokine receptor-specific T-cell infiltration. We observed that the interferon (IFN)-inducible CXCR3-cognate chemokines (CXCL9 and CXCL10) were significantly increased in lungs bearing minimal metastatic lesions, but chemokine production was at or below basal levels in lungs with substantial disease. Chemokine production was correlated with infiltration of the organ compartment by adoptively transferred CD8(+) tumor antigen-specific T cells in a CXCR3- and host IFNγ-dependent manner. Adenosine signaling in the tumor microenvironment (TME) suppressed chemokine production and T-cell infiltration in the advanced metastatic lesions, and this suppression could be partially reversed by administration of the adenosine receptor antagonist aminophylline. Collectively, our data demonstrate that CXCR3-cognate ligand expression is required for efficient T-cell access of tumor-infiltrated lungs, and these ligands are expressed in a temporally restricted pattern that is governed, in part, by adenosine. Therefore, pharmacologic modulation of adenosine activity in the TME could impart therapeutic efficacy to immunogenic but clinically ineffective vaccine platforms.

Chronic cold-stress suppresses chemokine production and CD8+ T cell infiltration in the tumor microenvironment (TUM7P.1024)

Recently it was reported that maintenance of mice at thermoneutral temperatures (TT, the temperature at which basal metabolism is sufficient to maintain body temperature, 30oC) enhanced antitumor immune responses and reduced tumor growth, relative to standard vivarium temperatures (ST, 22oC). We hypothesized that mice maintained at ST may have impaired production of T cell chemoattractant cytokines and subsequent T cell infiltration. In mice bearing breast tumors or solid or metastatic-like melanomas, intratumoral expression of CXCL9 and CXCL10 (CXCR3-cognate chemokines) was enhanced by maintenance of hosts in TT conditions. Further, tumors of TT-housed mice contained increased numbers of CD8+ T cells. We further hypothesized that the effect of temperature on T cell chemokine pathways may be a result of chronic cold stress, which may induce norepinephrine (NE) production and subsequent activation of β-adrenergic signaling pathways. We observed that pharmacologic blockade of β-adrenergic receptors in mice bearing solid or metastatic-like melanomas recapitulated the increased intratumoral expression of CXCL9 and CXCL10 and increased CD8+ T cell numbers. Because melanoma cells express β-adrenergic receptors, we suggest that chronic cold stress may induce systemic NE production, leading to tumor local activation of receptors and inhibition of tumor-derived chemokine production. These studies suggest potential interventions to improve existing T cell-based immunotherapies.

Melanoma induces, and adenosine suppresses, CXCR3-cognate chemokine production and T cell infiltration of lungs bearing metastatic-like disease (TUM7P.1017)

Melanoma-specific vaccines have minimal efficacy in patients with established disease but enhance survival when administered in the adjuvant setting. Therefore, we hypothesized that organs bearing metastatic-like melanoma may differentially produce T cell chemotactic proteins over the course of tumor development. Using an established model of metastatic-like melanoma in lungs, we assessed the production of specific cytokines and chemokines over a time-course of tumor growth, and we correlated chemokine production with chemokine receptor-specific T cell infiltration. CXCR3-cognate chemokines (CXCL9 and CXCL10) were significantly increased in lungs bearing minimal metastatic lesions, but chemokine was at or below basal levels in lungs with substantial disease. Chemokine production correlated with infiltration of the organ compartment by transferred CD8+ tumor antigen-specific T cells in a CXCR3- and host IFN-γ-dependent manner. Adenosine signaling suppressed chemokine production and T cell infiltration in the advanced metastatic lesions, and suppression could be partially reversed by the adenosine receptor antagonist aminophylline. Our data demonstrate that CXCR3-cognate ligand expression is required for efficient T cell access of tumor-infiltrated lungs, and ligands are expressed in a temporally-restricted pattern that is governed, in part, by adenosine. Modulation of adenosine activity may impart therapeutic efficacy to immunogenic but clinically ineffective vaccines.

Peptide vaccination in Montanide adjuvant induces and GM-CSF increases CXCR3 and cutaneous lymphocyte antigen expression by tumor antigen-specific CD8 T cells

T cell infiltration of melanoma is associated with enhanced clinical efficacy and is a desirable endpoint of immunotherapeutic vaccination. Infiltration is regulated, in part, by chemokine receptors and selectin ligands on the surface of tumor-specific lymphocytes. Therefore, we investigated the expression of two homing molecules--CXCR3 and CLA - on vaccine-induced CD8 T cells, in the context of a clinical trial of a melanoma-specific peptide vaccine. Both CXCR3 and CLA have been associated with T cell infiltration of melanoma. We demonstrate that a single subcutaneous/intradermal administration of peptide vaccine in Montanide adjuvant induces tumor-specific CD8 T cells that are predominantly positive for CXCR3, with a subpopulation of CXCR3(+)CLA(+) cells. Addition of GM-CSF significantly enhances CXCR3 expression and increases the proportion of CLA-expressing cells. Concurrent with CXCR3 and CLA expression, vaccine-induced CD8 cells express high levels of Tbet, IFN-γ, and IL-12Rβ1. Collectively, these studies demonstrate that peptide vaccination in adjuvant induces CD8 T cells with a phenotype that may support infiltration of melanoma.

Hematopoietic expression of CXCR3 is required for melanoma engraftment of lung (TUM7P.936)

Chemokine receptors have an established role in immune cell trafficking, and a less well-defined role in metastasis. Recent literature has demonstrated a role for tumor-expressed CXC chemokine receptor 3 (CXCR3) in metastasis to lymph nodes, but no study has evaluated the role of host CXCR3 expression in melanoma metastasis. To assess this possibility, we injected B16 melanoma intravenously into CXCR3wt or CXCR3-/- mice and assayed for melanoma-specific gene expression (tyrosinase) 24 hours later. Gene expression was significantly (9.5-fold) higher in CXCR3wt mice. At 24h, this is likely due to differential engraftment of the melanoma in the lung, as opposed to different growth. To determine if the CXCR3-expressing host contribution is an immune component, we phenotyped cells in the lungs 24 hours after melanoma injection. Neutrophils, CD8+ T cells, and B cells were significantly increased in CXCR3-/- mice versus CXCR3wt mice after melanoma injection, whereas macrophages/DCs, CD4+ T cells, and NK cells were not significantly different. Using bone marrow chimeras, we have shown that melanoma engraftment in the lungs requires a host CXCR3-expressing cell of the hematopoietic cell lineage. A role for host CXCR3-expressing cells to mediate melanoma engraftment in the lungs has not been previously shown, and these studies may predict future targets for the reduction or prevention of melanoma metastases in patients.

Regulation of CXCR3 chemokine production and CD8+ T cell infiltration in the metastatic melanoma microenvironment (P5091)

Vaccine-based immune therapy has shown minimal efficacy against established tumors. However, vaccination in the adjuvant setting prolongs disease-free survival. We previously demonstrated that CXCR3 expression by tumor antigen-specific T cells correlates with this. We hypothesized that melanoma engraftment may induce spatially- and temporally-restricted expression of CXCR3 chemokines in the tumor microenvironment, leading to transient infiltration of CXCR3+ T cells into tumor. We used a model of murine metastatic-like melanoma to evaluate tyrosinase expression as a measure of tumor burden. We observed a positive correlation between tyrosinase and CXCL9 (r2 = 0.73) and CXCL10 (r2 = 0.86) expression over time, demonstrating that melanoma growth in the lung is sufficient to induce CXCR3-cognate chemokines. In a time-course study, we observed that CXCL9 and CXCL10 expression decrease after day 15; we hypothesize that diminished chemokine production is due to reduced interferon signaling. We are investigating this possibility. Our preliminary flow cytometry analyses suggest a positive correlation between CD8+ T cell infiltration and the expression of CXCL9/10, suggesting that metastatic melanomas are transiently receptive to T cell infiltration. Therefore, successful immunotherapy of metastatic melanoma may require adjuvant therapy to induce or extend the chemotactic window for T cell infiltration.

Abstract 3827: Interferons induce CXCR3-cognate chemokine production by melanoma

Immune-mediated cancer regression requires tumor infiltration by Ag-specific effector T cells, but lymphocytes are commonly sparse in melanoma metastases. Activated T cells express CXCR3, whose cognate chemokines are CXCL9/MIG, CXCL10/IP-10 and CXCL11/I-TAC. Little is known about expression of these chemokines in lymph node (LN) metastases of melanoma. We evaluated whether metastatic melanoma induces these CXCR3-cognate chemokines in human LN-derived tissues. Also, because these chemokines can be induced by interferon (IFN), we evaluated whether type I or II IFNs (IFN-α or IFN-γ, respectively) can modulate chemokine expression in an in vitro model of the human tumor microenvironment. Production of CXCL9-11 by melanoma-infiltrated nodes (MIN) was no different than tumor-free nodes (TFN); both produced less than activated LN (sentinel immunized nodes, SIN). These data suggest melanoma infiltration into LN neither induces nor reduces CXCL9-11. Stimulation with IFN-α or IFN-γ increased production of CXCL10-11 from MIN, but not TFN or SIN. IFN-γ also increased production of CXCL9 in MIN. In IFN-treated MIN, the primary source of CXCL9-11 was melanoma cells themselves, whereas CD14+ cells were the source of these molecules in SIN. Melanoma cell lines expressed IFN receptors and produced CXCL9-11 in response to IFN treatment. Treatment of melanoma cell lines or primary melanomas in vitro with IFN-γ induced the migration of CXCR3+ T cells in transwell assays, whereas T cell did not significantly migrate in response to resting melanoma cells. Thus, melanoma infiltration of LN is insufficient to induce the production of CXCL9-11, but melanoma may be a significant source of IFN-induced chemokines. Collectively, these data suggest that IFN-α or IFN-γ may act in the tumor microenvironment to increase the chemotactic gradient for CXCR3+ T cells, thus enhancing the capacity of therapeutic vaccines to mediate clinical efficacy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3827.