Beyond αβ T cells: NK, iNKT, and γδT cell biology in leukemic patients and potential for off-the-shelf adoptive cell therapies for AML

Acute myeloid leukemia (AML) remains an elusive disease to treat, let alone cure, even after highly intensive therapies such as stem cell transplants. Adoptive cell therapeutic strategies based on conventional alpha beta (αβ)T cells are an active area of research in myeloid neoplasms given their remarkable success in other hematologic malignancies, particularly B-cell-derived acute lymphoid leukemia, myeloma, and lymphomas. Several limitations have hindered clinical application of adoptive cell therapies in AML including lack of leukemia-specific antigens, on-target-off-leukemic toxicity, immunosuppressive microenvironments, and leukemic stem cell populations elusive to immune recognition and destruction. While there are promising T cell-based therapies including chimeric antigen receptor (CAR)-T designs under development, other cytotoxic lymphocyte cell subsets have unique phenotypes and capabilities that might be of additional benefit in AML treatment. Of particular interest are the natural killer (NK) and unconventional T cells known as invariant natural killer T (iNKT) and gamma delta (γδ) T cells. NK, iNKT, and γδT cells exhibit intrinsic anti-malignant properties, potential for alloreactivity, and human leukocyte-antigen (HLA)-independent function. Here we review the biology of each of these unconventional cytotoxic lymphocyte cell types and compare and contrast their strengths and limitations as the basis for adoptive cell therapies for AML.

Targeting MDSC Differentiation Using ATRA: A Phase I/II Clinical Trial Combining Pembrolizumab and All-Trans Retinoic Acid for Metastatic Melanoma

PURPOSE

A phase Ib/II clinical trial was conducted to evaluate the safety and efficacy of the combination of all-trans retinoic acid (ATRA) with pembrolizumab in patients with stage IV melanoma.

PATIENTS AND METHODS

Anti-PD-1 naïve patients with stage IV melanoma were treated with pembrolizumab plus supplemental ATRA for three days surrounding each of the first four pembrolizumab infusions. The primary objective was to establish the MTD and recommended phase II dose (RP2D) of the combination. The secondary objectives were to describe the safety and toxicity of the combined treatment and to assess antitumor activity in terms of (i) the reduction in circulating myeloid-derived suppressor cell (MDSC) frequency and (ii) progression-free survival (PFS).

RESULTS

Twenty-four patients were enrolled, 46% diagnosed with M1a and 29% with M1c stage disease at enrollment. All patients had an ECOG status ≤1, and 75% had received no prior therapies. The combination was well tolerated, with the most common ATRA-related adverse events being headache, fatigue, and nausea. The RP2D was established at 150 mg/m2 ATRA + 200 mg Q3W pembrolizumab. Median PFS was 20.3 months, and the overall response rate was 71%, with 50% of patients experiencing a complete response, and the 1-year overall survival was 80%. The combination effectively lowered the frequency of circulating MDSCs.

CONCLUSIONS

With a favorable tolerability and high response rate, this combination is a promising frontline treatment strategy for advanced melanoma. Targeting MDSCs remains an attractive mechanism to enhance the efficacy of immunotherapies, and this combination merits further investigation. See related commentary by Olson and Luke, p. 1167.

Precision of CT-derived alveolar recruitment assessed by human observers and a machine learning algorithm in moderate and severe ARDS

BACKGROUND

Assessing measurement error in alveolar recruitment on computed tomography (CT) is of paramount importance to select a reliable threshold identifying patients with high potential for alveolar recruitment and to rationalize positive end-expiratory pressure (PEEP) setting in acute respiratory distress syndrome (ARDS). The aim of this study was to assess both intra- and inter-observer smallest real difference (SRD) exceeding measurement error of recruitment using both human and machine learning-made lung segmentation (i.e., delineation) on CT. This single-center observational study was performed on adult ARDS patients. CT were acquired at end-expiration and end-inspiration at the PEEP level selected by clinicians, and at end-expiration at PEEP 5 and 15 cmH₂O. Two human observers and a machine learning algorithm performed lung segmentation. Recruitment was computed as the weight change of the non-aerated compartment on CT between PEEP 5 and 15 cmH₂O.

RESULTS

Thirteen patients were included, of whom 11 (85%) presented a severe ARDS. Intra- and inter-observer measurements of recruitment were virtually unbiased, with 95% confidence intervals (CI_95%) encompassing zero. The intra-observer SRD of recruitment amounted to 3.5 [CI_95% 2.4-5.2]% of lung weight. The human-human inter-observer SRD of recruitment was slightly higher amounting to 5.7 [CI_95% 4.0-8.0]% of lung weight, as was the human-machine SRD (5.9 [CI_95% 4.3-7.8]% of lung weight). Regarding other CT measurements, both intra-observer and inter-observer SRD were close to zero for the CT-measurements focusing on aerated lung (end-expiratory lung volume, hyperinflation), and higher for the CT-measurements relying on accurate segmentation of the non-aerated lung (lung weight, tidal recruitment…). The average symmetric surface distance between lung segmentation masks was significatively lower in intra-observer comparisons (0.8 mm [interquartile range (IQR) 0.6-0.9]) as compared to human-human (1.0 mm [IQR 0.8-1.3] and human-machine inter-observer comparisons (1.1 mm [IQR 0.9-1.3]).

CONCLUSIONS

The SRD exceeding intra-observer experimental error in the measurement of alveolar recruitment may be conservatively set to 5% (i.e., the upper value of the CI_95%). Human-machine and human-human inter-observer measurement errors with CT are of similar magnitude, suggesting that machine learning segmentation algorithms are credible alternative to humans for quantifying alveolar recruitment on CT.

Response to PEEP in COVID-19 ARDS patients with and without extracorporeal membrane oxygenation. A multicenter case–control computed tomography study

Background

PEEP selection in severe COVID-19 patients under extracorporeal membrane oxygenation (ECMO) is challenging as no study has assessed the alveolar recruitability in this setting. The aim of the study was to compare lung recruitability and the impact of PEEP on lung aeration in moderate and severe ARDS patients with or without ECMO, using computed tomography (CT).

Methods

We conducted a two-center prospective observational case–control study in adult COVID-19-related patients who had an indication for CT within 72 h of ARDS onset in non-ECMO patients or within 72  h after ECMO onset. Ninety-nine patients were included, of whom 24 had severe ARDS under ECMO, 59 severe ARDS without ECMO and 16 moderate ARDS.

Results

Non-inflated lung at PEEP 5 cmH₂O was significantly greater in ECMO than in non-ECMO patients. Recruitment induced by increasing PEEP from 5 to 15 cmH₂O was not significantly different between ECMO and non-ECMO patients, while PEEP-induced hyperinflation was significantly lower in the ECMO group and virtually nonexistent. The median [IQR] fraction of recruitable lung mass between PEEP 5 and 15 cmH₂O was 6 [4–10]%. Total superimposed pressure at PEEP 5 cmH₂O was significantly higher in ECMO patients and amounted to 12 [11–13] cmH₂O. The hyperinflation-to-recruitment ratio (i.e., a trade-off index of the adverse effects and benefits of PEEP) was significantly lower in ECMO patients and was lower than one in 23 (96%) ECMO patients, 41 (69%) severe non-ECMO patients and 8 (50%) moderate ARDS patients. Compliance of the aerated lung at PEEP 5 cmH₂O corrected for PEEP-induced recruitment (C_{BABY LUNG}) was significantly lower in ECMO patients than in non-ECMO patients and was linearly related to the logarithm of the hyperinflation-to-recruitment ratio.

Conclusions

Lung recruitability of COVID-19 pneumonia is not significantly different between ECMO and non-ECMO patients, with substantial interindividual variations. The balance between hyperinflation and recruitment induced by PEEP increase from 5 to 15 cmH₂O appears favorable in virtually all ECMO patients, while this PEEP level is required to counteract compressive forces leading to lung collapse. C_{BABY LUNG} is significantly lower in ECMO patients, independently of lung recruitability.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-04076-z.

The novel coreceptor CD8α:MyD88 enhances T-cell proliferation, activation, and antitumor response at low-dose IL-2 in B16 melanoma

The gamma common chain (γc) cytokine receptor plays a central role in Type I cytokine signaling, and in the generation and expansion of antitumor T-cells. Adoptive T-cell therapies (ACT) benefit from IL-2 treatment but is limited by a short half-life and high toxicities. Reducing IL-2 mediated toxicities while retaining antitumor T-cell efficacy is needed to improve clinical outcomes in ACT-treated patients. Other γc cytokines such as IL-7 and 15 have shown benefits for ACT by increasing generation and expansion of long-lived antitumor T-cells with reduced cytokine toxicity. Our lab previously demonstrated that MyD88 (critical adaptor protein in toll-like receptor signaling) is necessary for CD8 T-cell expansion. Induced MyD88 signaling in T-cells via expression of novel coreceptor CD8a:MyD88 (CM T-cells) resulted in enhanced proliferation, activation, and durably reduced tumor size in mouse melanoma models upon ACT treatment. CM T-cells expressed higher γc receptor levels which is required for IL-2, IL-7 and IL-15. Therefore, we hypothesized that CM T-cells have increased sensitivity to γc cytokine signaling resulting in enhanced proliferation, activation, and antitumor activity. CM T cells cultured at 10–25 times lower concentrations of IL-2, -15, -7 demonstrated enhanced cell proliferation and activation and was associated with increased JAK-STAT signaling intensity and persistence. CM T-cell ACT treatment of mice with B16-F10 tumors reduced tumor growth even at the lowest IL-2 concentration (5000 IU IL-2). In conclusion, CM T-cells require lower concentrations of type I cytokines for enhanced antitumor immunity and highlights the potential of CM T-cells to improve clinical outcomes with reduced toxicities.

Supported by grants from NSF GRFP, NCI (R01CA207913, P30CA046934), Dept of VA Merit Award (BX004935-01), University of Colorado Comprehensive Cancer Center (UCCCC), Leukemia and Lymphoma Society Translational Research Program

DNA-PK inhibition plus immune adjuvants promotes CD8 TIL infiltration, neoantigen presentation, and diversifies the tumor-reactive TCRβ repertoire in B16 melanoma

Despite significant improvements in cancer immunotherapies, enhancing immunogenicity of non-responsive tumors warrants further investigation. A prior drug screen of ~3,000 compounds identified NU7441, a DNA PK inhibitor, as an effective compound that promotes immunogenicity of various melanoma lines in vitro. In this study, we hypothesized that in vivo combination therapy NU7441, STING-L, and CD40 agonist will enhance tumor immunogenicity resulting in both expansion and increased cytotoxic activity of CD8+TCRβ tumor-reactive TILs in B16 melanoma models. Results obtained by flow cytometry demonstrated that combination treatment 1) significantly increased the ratio of CD8/CD4 TILs, 2) expanded several tumor-reactive TCRβ clones, 3) increased granzyme B production and expression of 4-1BB and PD-1, 4) increased ratio of DC/MDSC infiltration, and 5) potentially identified a novel cytotoxic CD8+CD11c+GR-1+ population. Additionally, the expansion of tumor-reactive TCRs was attributed to DNA-PKi’s ability to both expand and diversify the number of neoantigen transcripts resulting in a broader neoantigen expression profile. RNA-seq identified 27 unique neoantigens as potential novel targets in melanoma immunotherapy. TILs isolated from B16 tumors were co-cultured with dendritic cells transfected with tandem-mini genes, each encoding ~10 neoantigens, and T cells were analyzed by flow cytometry to quantify the TCRβ repertoire and functional response to neoantigens. We demonstrate combination treatment with NU7441, STING-L and CD40 agonist enhance antitumor responses through increased myeloid cell infiltration and sensitization of tumor cells to T cell-mediated killing from an expanded CD8+TCRβ repertoire.

Supported by R01CA207913 NCI BX004935-01, VA, Merit Award P30CA046934, NCI Leukemia and Lymphoma Society Department of Defense Gates Grubstake University of Colorado Anschutz Medical Campus Cancer League of Colorado

Identifying novel epigenetic modifiers that sensitize T cell malignancies to CD8+ T cell mediated cytotoxicity by high throughput drug screen

T Cell Lymphomas are a rare subtype of Lymphoma, occurring in ~1% of all cancers and response rates to current therapies reach only ~23%. The lack of unique targetable T cell antigens as well as their tendency to overcome chemotherapies results in a high incidence of relapse in most patients leading to remission rates of approximately two years. Immunotherapies, especially immune-checkpoint blockade, have slightly improved outcomes in refractory disease, but there remains a need for stronger and more durable responses. The chemotherapeutic potential of epigenetic modifiers is just beginning to be explored. HDAC inhibitors, DNA demethylating agents, and histone methyltransferase inhibitors reshape the transcriptome, potentially altering the expression of immune modulatory pathways. We hypothesized that pretreating T cell malignancies with epigenetic modifiers will alter key genetic signatures that sensitize them to CD8+ T cell-mediated cytotoxicity. We pretreated five T cell lymphoma cell lines, representative of different T cell malignant diseases with compounds from an FDA-approved 700+ epigenetic modifying drug library at four different concentrations and then co-cultured them with a tumor-reactive HLA-A2-matched primary (derived from PBMCs) cytotoxic CD8+ T cell line. Changes in T cell mediated cytotoxicity and alterations in immune modulating surface markers and potential CAR-T cell targets (CD30, CCR4, and CD47) were assessed by flow cytometry. Several promising compounds were identified by their ability to improve T cell mediated cytotoxicity, increase expression of immune stimulatory markers, decrease expression of immune inhibitory markers, and augment expression of existing CAR-T target antigens.

Supported by NIH and the Colorado Clinical and Translational Sciences Institute (CCTSI)

A novel linked TCR: MyD88 receptor improves anti-tumor responses while maintaining antigen specificity

The treatment of malignant tumors utilizing engineered T cell receptor (TCR) therapies in the clinic have demonstrated encouraging therapeutic potential in a subset of patients. Limitations to T cell-based therapies include down-regulation of tumor-antigen presentation by the tumor cells, poor TCR activation, and the immunosuppressive effects of the tumor microenvironment (TME). Attempts to ameliorate these issues by utilizing T cells engineered with tumor-reactive TCRs with increased affinity showed enhanced responses. However, affinity-modified TCRs are more promiscuous and can lead to off-target toxicity. We and others have demonstrated that activating MyD88 signaling (a key adapter protein in toll-like receptor signaling) in T cells enhances effector function and expansion while simultaneously reducing their propensity to enter an exhausted state. In these studies, we designed novel receptors in which the death and intermediate domains of MyD88 are fused to the TCR. T cells engineered to express this novel TCR:MyD88 receptor showed improved responses in a tumor-antigen dependent manner, as demonstrated by increased proliferation and expression of effector molecules, without reducing the specificity of the TCR. In mouse models, TCR:MyD88 T cells conferred improved anti-tumor responses against tumors expressing suboptimal levels of target antigen which was associated with increased T cell infiltration, reduced T cell exhaustion, and an altered TME. These results demonstrate the ability of TCR:MyD88 to improve current therapies without sacrificing the specificity of the TCR which we believe can be utilized to improve the outcome of patients suffering from advanced cancer while reducing toxicities.

Supported by -US Department of Veteran Affairs -Leukemia Lymphoma Society -University of Colorado -Shoots Medical Center -NCI (R01CA207913)

Controllable regulation of CD3ζ and MyD88 signaling in T cells expands and enhances the neoantigen-reactive repertoire resulting in effective antitumor activity

Background

Adoptive cell therapy (ACT) of tumor-reactive T cells including tumor infiltrating lymphocytes (TIL) represents one of the most promising forms of therapies for treating patients with solid tumors. However, durable responses are observed in a small subset of patients and in certain cancer types. Major hurdles to achieving durable responses include: 1) suboptimal TCR responses due to sparse and/or weakly immunogenic tumor antigen presentation, 2) development of dysfunctional or exhausted T cells, 3) low TIL persistence, and 4) tumor infiltration. We and others have demonstrated that activating MyD88 signaling in T cells strongly amplifies weak TCR responses and imparts T cells novel anti-tumor properties.

Hypothesis

TILs engineered with a novel fusion protein consisting of CD3ζ:MyD88 will activate MyD88 signals in a TCR-dependent manner resulting in enhanced activity and against a broader panel of neoantigens.

Method & Results

CD4 and CD8 TILs from a variety of human tumors engineered CD3ζ:MyD88 demonstrated: a) dramatically improved ability to expand in vitro resulting (generating 10–100X TILs than conventional TILs within a few weeks), b) persist for months in tissue culture, c) more polyfunctional cells, d) destruction of established melanoma tumors in vivo, e) enhanced responses against a panel of antigens with no overt autoimmunity.

Conclusions

CD3ζ:MyD88 represents a unique and universal approach to safely enhance T cell response to tumor antigens.

Chimeric non-antigen receptors in T cell-based cancer therapy

Adoptively transferred T cell-based cancer therapies have shown incredible promise in treatment of various cancers. So far therapeutic strategies using T cells have focused on manipulation of the antigen-recognition machinery itself, such as through selective expression of tumor-antigen specific T cell receptors or engineered antigen-recognition chimeric antigen receptors (CARs). While several CARs have been approved for treatment of hematopoietic malignancies, this kind of therapy has been less successful in the treatment of solid tumors, in part due to lack of suitable tumor-specific targets, the immunosuppressive tumor microenvironment, and the inability of adoptively transferred cells to maintain their therapeutic potentials. It is critical for therapeutic T cells to overcome immunosuppressive environmental triggers, mediating balanced antitumor immunity without causing unwanted inflammation or autoimmunity. To address these hurdles, chimeric receptors with distinct signaling properties are being engineered to function as allies of tumor antigen-specific receptors, modulating unique aspects of T cell function without directly binding to antigen themselves. In this review, we focus on the design and function of these chimeric non-antigen receptors, which fall into three broad categories: ‘inhibitory-to-stimulatory’ switch receptors that bind natural ligands, enhanced stimulatory receptors that interact with natural ligands, and synthetic receptor-ligand pairs. Our intent is to offer detailed descriptions that will help readers to understand the structure and function of these receptors, as well as inspire development of additional novel synthetic receptors to improve T cell-based cancer therapy.

Naturally Occurring Genetic Alterations in Proximal TCR Signaling and Implications for Cancer Immunotherapy

T cell-based immunotherapies including genetically engineered T cells, adoptive transfer of tumor-infiltrating lymphocytes, and immune checkpoint blockade highlight the impressive anti-tumor effects of T cells. These successes have provided new hope to many cancer patients with otherwise poor prognoses. However, only a fraction of patients demonstrates durable responses to these forms of therapies and many develop significant immune-mediated toxicity. These heterogeneous clinical responses suggest that underlying nuances in T cell genetics, phenotypes, and activation states likely modulate the therapeutic impact of these approaches. To better characterize known genetic variations that may impact T cell function, we 1) review the function of early T cell receptor-specific signaling mediators, 2) offer a synopsis of known mutations and genetic alterations within the associated molecules, 3) discuss the link between these mutations and human disease and 4) review therapeutic strategies under development or in clinical testing that target each of these molecules for enhancing anti-tumor T cell activity. Finally, we discuss novel engineering approaches that could be designed based on our understanding of the function of these molecules in health and disease.

Testing Cancer Immunotherapy in a Human Immune System Mouse Model: Correlating Treatment Responses to Human Chimerism, Therapeutic Variables and Immune Cell Phenotypes

Over the past decade, immunotherapies have revolutionized the treatment of cancer. Although the success of immunotherapy is remarkable, it is still limited to a subset of patients. More than 1500 clinical trials are currently ongoing with a goal of improving the efficacy of immunotherapy through co-administration of other agents. Preclinical, small-animal models are strongly desired to increase the pace of scientific discovery, while reducing the cost of combination drug testing in humans. Human immune system (HIS) mice are highly immune-deficient mouse recipients rtpeconstituted with human hematopoietic stem cells. These HIS-mice are capable of growing human tumor cell lines and patient-derived tumor xenografts. This model allows rapid testing of multiple, immune-related therapeutics for tumors originating from unique clinical samples. Using a cord blood-derived HIS-BALB/c-Rag2nullIl2rγnullSIRPαNOD (BRGS) mouse model, we summarize our experiments testing immune checkpoint blockade combinations in these mice bearing a variety of human tumors, including breast, colorectal, pancreatic, lung, adrenocortical, melanoma and hematological malignancies. We present in-depth characterization of the kinetics and subsets of the HIS in lymph and non-lymph organs and relate these to protocol development and immune-related treatment responses. Furthermore, we compare the phenotype of the HIS in lymph tissues and tumors. We show that the immunotype and amount of tumor infiltrating leukocytes are widely-variable and that this phenotype is tumor-dependent in the HIS-BRGS model. We further present flow cytometric analyses of immune cell subsets, activation state, cytokine production and inhibitory receptor expression in peripheral lymph organs and tumors. We show that responding tumors bear human infiltrating T cells with a more inflammatory signature compared to non-responding tumors, similar to reports of "responding" patients in human immunotherapy clinical trials. Collectively these data support the use of HIS mice as a preclinical model to test combination immunotherapies for human cancers, if careful attention is taken to both protocol details and data analysis.

Soluble Sema4D in Plasma of Head and Neck Squamous Cell Carcinoma Patients Is Associated With Underlying Non-Inflamed Tumor Profile

Semaphorin 4D (Sema4D) is a glycoprotein that is expressed by several tumors and immune cells. It can function as a membrane bound protein or as a cleaved soluble protein (sSema4D). We sought to investigate the translational potential of plasma sSema4D as an immune marker in plasma of patients with head and neck squamous cell carcinoma (HNSCC). Paired peripheral blood and tumor tissue samples of 104 patients with HNSCC were collected at the same time point to allow for real time analysis. Scoring of the histological inflammatory subtype (HIS) was carried out using Sema4D immunohistochemistry on the tumor tissue. sSema4D was detected in plasma using direct ELISA assay. Defining elevated sSema4D as values above the 95^th percentile in healthy controls, our data showed that sSema4D levels in plasma were elevated in 25.0% (95% CI, 16.7–34.9%) of the patients with HNSCC and showed significant association with HIS immune excluded (HIS-IE) (p = 0.007), Sema4D^+ve tumor cells (TCs) (p = 0.018) and PD-L1^+ve immune cells (ICs) (p = 0.038). A multi-variable logistic regression analysis showed that HIS was significantly (P = 0.004) associated with elevated sSema4D, an association not explained by available patient-level factors. Using the IO-360 nanoString platform, differential gene expression (DGE) analysis of 10 HNSCC tumor tissues showed that patients with high sSema4D in plasma (HsS4D) clustered as IFN-γ negative tumor immune signature and were mostly HIS-IE. The IC type in the HsS4D paired tumor tissue was predominantly myeloid, while the lymphoid compartment was higher in the low sSema4D (LsS4D). The Wnt signaling pathway was upregulated in the HsS4D group. Further analysis using the IO-360, 770 gene set, showed significant non-inflamed profile of the HsS4D tumors compared to the LsS4D. In conclusion, our data reveals an association between sSema4D and the histological inflammatory subtype.

MyD88 Costimulation in Donor CD8+ T Cells Enhances the Graft-versus-Tumor Effect in Murine Hematopoietic Cell Transplantation

Donor-derived lymphocytes from allogeneic hematopoietic cell transplantation (allo-HCT) or donor lymphocyte infusion can mediate eradication of host tumor cells in a process labeled the graft-versus-tumor (GVT) effect. Unfortunately, these treatments have produced limited results in various types of leukemia because of an insufficient GVT effect. In this context, molecular engineering of donor lymphocytes to increase the GVT effect may benefit cancer patients. Activating MyD88 signaling in CD8+ T cells via TLR enhances T cell activation and cytotoxicity. However, systemic administration of TLR ligands to stimulate MyD88 could induce hyperinflammation or elicit protumor effects. To circumvent this problem, we devised a synthetic molecule consisting of MyD88 linked to the ectopic domain of CD8a (CD8α:MyD88). We used this construct to test the hypothesis that MyD88 costimulation in donor CD8+ T cells increases tumor control following allo-HCT in mice by increasing T cell activation, function, and direct tumor cytotoxicity. Indeed, an increase in both in vitro and in vivo tumor control was observed with CD8α:MyD88 T cells. This increase in the GVT response was associated with increased T cell expansion, increased functional capacity, and an increase in direct cytotoxic killing of the tumor cells. However, MyD88 costimulation in donor CD8+ T cells was linked to increased yet nonlethal graft-versus-host disease in mice treated with these engineered CD8+ T cells. Given these observations, synthetic CD8α:MyD88 donor T cells may represent a unique and versatile approach to enhance the GVT response that merits further refinement to improve the effectiveness of allo-HCT.

Induction of IRAK-M in melanoma induces caspase-3 dependent apoptosis by reducing TRAF6 and calpastatin levels

Melanoma represents the most serious type of skin cancer. Although recent years have seen advances using targeted and immunotherapies, most patients remain at high risk for tumor recurrence. Here we show that IRAK-M, a negative regulator of MyD88 signaling, is deficient or low in melanoma and expression levels correlate with patient survival. Inducing IRAK-M expression using genetic approaches or epigenetic modifiers initiates apoptosis by prompting its interaction with TRAF6 via IRAK-M's C-terminal domain. This complex recruits and degrades calpastatin which stimulates calpain activity and triggers caspase-3-dependent but caspase-8,-9-independent apoptosis. Using a drug screen, we identified compounds that induced IRAK-M expression. Administration of IRAK-M-inducing drugs reduced tumor growth in mice but was ineffective against IRAK-M knock-down tumors. These results uncover a previously uncharacterized apoptosis pathway, emphasize IRAK-M as a potential therapeutic target and suggest that the anticancer activity of certain drugs could do so through their ability to induce IRAK-M expression.

Synthetic MyD88 co-stimulation in donor CD8+ T cells enhances T cell activation, function, and tumor control in experimental hematopoietic cell transplant

Allogeneic hematopoietic cell transplantation is a potentially curative treatment for blood cancers. Nevertheless, some patients will relapse and succumb to their cancer. Donor lymphocyte infusion of CD8+ T cells with transplant evidently provides further protection from recurrent malignancies. Further engineering the donor CD8+ T cells to respond to the tumor may provide even further protection in patients. Novel co-stimulation through Toll-like Receptors in CD8+ T cells enhances T cell activation and function through the MyD88 adaptor protein. Previously, we developed a synthetic MyD88 linked to CD8 which drives MyD88 signaling with T cell activation. This tool enables assessment of the role of MyD88 in CD8+ T cell function and helps determine the benefit of this pathway in T cell immunotherapies. Our studies show that donor CD8+ T cells transduced with this construct (CD8-MyD88 T cells) increase the graft-versus-tumor response in experimental mouse transplants with A20 lymphoma. Further studies show engineered CD8-MyD88 T cells proliferate better in the host and elicit greater production of functional cytokines and Granzyme B compared to controls. Increased granzyme B production from CD8-MyD88 T cells did not hinder their activation and these cells displayed enhanced survival. Using in vitro cytotoxicity assays we determined that the tumor control is a direct result of T cell cytotoxicity and that this effect is enhanced with host-Antigen Presenting Cells. Increases in GvHD were indicated in host mice, specifically relating to weight loss, however the symptoms occurred with no mortality. Future experiments will explore the specific mechanism of tumor killing and delineate the cause of GvHD symptoms from donor CD8-MyD88 T cells.

Myeloid-derived suppressor cells are bound and inhibited by anti-thymocyte globulin

Myeloid-derived suppressor cells (MDSCs) inhibit T cell responses and are relevant to cancer, autoimmunity and transplant biology. Anti-thymocyte globulin (ATG) is a commonly used T cell depletion agent, yet the effect of ATG on MDSCs has not been investigated. MDSCs were generated in Lewis Lung Carcinoma 1 tumor-bearing mice. MDSC development and function were assessed in vivo and in vitro with and without ATG administration. T cell suppression assays, RT-PCR, flow cytometry and arginase activity assays were used to assess MDSC phenotype and function. MDSCs increased dramatically in tumor-bearing mice and the majority of splenic MDSCs were of the polymorphonuclear subset. MDSCs potently suppressed T cell proliferation. ATG-treated mice developed 50% fewer MDSCs and these MDSCs were significantly less suppressive of T cell proliferation. In vitro, ATG directly bound 99.6% of MDSCs. CCR7, L-selectin and LFA-1 were expressed by both T cells and MDSCs, and binding of LFA-1 was inhibited by ATG pre-treatment. Arg-1 and PD-L1 transcript expression were reduced 30–40% and arginase activity decreased in ATG-pretreated MDSCs. MDSCs were bound and functionally inhibited by ATG. T cells and MDSCs expressed common Ags which were also targets of ATG. ATG may be helpful in tumor models seeking to suppress MDSCs. Alternatively, ATG may inadvertently inhibit important T cell regulatory events in autoimmunity and transplantation.

An Anticancer Drug Cocktail of Three Kinase Inhibitors Improved Response to a Dendritic Cell-Based Cancer Vaccine

Monocyte-derived dendritic cell (moDC)-based cancer therapies intended to elicit antitumor T-cell responses have limited efficacy in most clinical trials. However, potent and sustained antitumor activity in a limited number of patients highlights the therapeutic potential of moDCs. In vitro culture conditions used to generate moDCs can be inconsistent, and moDCs generated in vitro are less effective than natural DCs. On the basis of our study highlighting the ability for certain kinase inhibitors to enhance tumor antigenicity, we therefore screened kinase inhibitors for their ability to improve DC immunogenicity. We identified AKT inhibitor MK2206, DNA-PK inhibitor NU7441, and MEK inhibitor trametinib as the compounds most effective at modulating moDC immunogenicity. The combination of these drugs, referred to as MKNUTRA, enhanced moDC activity over treatment with individual drugs while exhibiting minimal toxicity. An evaluation of 335 activation and T-cell-suppressive surface proteins on moDCs revealed that MKNUTRA treatment more effectively matured cells and reduced the expression of tolerogenic proteins as compared with control moDCs. MKNUTRA treatment imparted to ICT107, a glioblastoma (GBM) DC-based vaccine that has completed phase II trials, an increased ability to stimulate patient-derived autologous CD8+ T cells against the brain tumor antigens IL13Rα2(345-354) and TRP2(180-188) In vivo, treating ICT107 with MKNUTRA, prior to injection into mice with an established GBM tumor, reduced tumor growth kinetics. This response was associated with an increased frequency of tumor-reactive lymphocytes within tumors and in peripheral tissues. These studies broaden the application of targeted anticancer drugs and highlight their ability to increase moDC immunogenicity.

Abstract 2103: Acoustic activation of the glioma-brain microenvironment

Introduction

Glioblastoma (GBM) is a malignant brain tumor characterized by diffuse brain invasion, molecular and cellular heterogeneity, and immune evasion, making current chemo-radiation treatments and emerging immunotherapies minimally effective. Transcranial MRI-guided focused ultrasound (MRgFUS) is a novel therapeutic modality, enabling the safe and targeted application of ultrasound energy in the brain. Recently, we demonstrated how MRgFUS can be used to transiently disrupt the blood-brain barrier (BBB) for enhanced delivery of stem cells and locally administered nanoparticles. In addition to creating structural effects, MRgFUS exposures are also capable of generating effects at the molecular level by modulating the levels of cytokines, chemokines and trophic factors in a tempo-spatially controlled manner. In the current study, we investigated the effects of MRgFUS on the GBM immune microenvironment.

Materials and Methods

C57BL/6 mice were implanted with luciferase expressing mouse GL261 glioma cells in the right striatum. MRgFUS exposures were applied using an MRI-guided system. Tumor, spleen, and superficial lymph nodes were collected seven days after MRgFUS treatment. Flow cytometry and immunohistochemistry were performed for the following antibodies: CD45-PE, CD3-FITC, CD8-PErCp/Cy5.5, TIM3-BV605, PD-1-PacBlue, CD4-APC, Nk1.1-FITC, Cd11b-Percp/Cy5.5, CD11c-B650, CD86-APC, GR1-PacBlue, FoxP3-PE, and CD25-APC. Statistical analysis of the data was performed using unpaired T-tests.

Results

MRgFUS treatment of tumors resulted in a statistically significant increase in the percentage of Foxp3+ CD25+ T-regulatory cells (Tregs) in the spleen compared to untreated controls. Analysis of superficial cervical lymph nodes following MRgFUS treatment revealed that myeloid-derived suppressor cells (MDSCs) were significantly increased while CD8+ T cells were significantly decreased in MRgFUS-treated tumors compared to untreated controls.

Conclusions

These findings suggest that MRgFUS treatment of intracranial GBM tumors results in the redistribution of key immune cell types within the tumor microenvironment as well as the body lymphoid tissues. Specifically, we found that Tregs and MDSCs moved away from the tumor, and CD8+ T cells moved into the tumor at 1 week post-treatment. This suggests that MRgFUS has the potential to awaken the suppressed GBM microenvironment and augment immunotherapy in brain cancer. Additional studies to help elucidate the underlying mechanisms and further evaluate the potential of this approach are ongoing.

Citation Format: Pavlos Anastasiadis, Kenisha Younger, Nathan B. Roberts, Joseph A. Frank, Victor Frenkel, Eduardo Davila, Graeme Woodworth. Acoustic activation of the glioma-brain microenvironment [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 2103.

MyD88-stimulated T cells acquire resistance to MDSC-mediated suppression

The immunosuppressive tumor microenvironment presents a significant challenge to developing effective T cell-based cancer immunotherapies. The heterogeneous population of myeloid-derived suppressor cells (MDSCs) is a major contributor to the suppressive tumor microenvironment in many cancers. Generating tumor-reactive T cells with the capacity to resist MDSC-mediated suppression would help facilitate the production of potent anti-tumor T cell therapies. The activation of the Toll-like receptor-Myeloid differentiation primary response 88 (TLR-MyD88) signaling pathway in CD8+ T cells enhances cell proliferation, cytotoxic function, and survival. Our studies show that TLR-stimulated T cells are resistant to MDSC-mediated suppression from multiple cancer cell lines. MyD88-activated CD8+ T cells co-cultured with tumor-derived MDSCs displayed enhanced proliferation and cytokine production over control T cells. This is recapitulated using synthetic co-receptor CD8a-MyD88 engineered T cells which exhibit greater potential for proliferation, even in the presence of MDSCs. Our future objectives are to understand the mechanisms by which MyD88 stimulated T cells gain resistance properties and observe this phenomenon in vivo. We look to utilize these observations to augment antitumor immune responses.

Cross-species transcriptional analysis reveals conserved and host-specific neoplastic processes in mammalian glioma

Glioma is a unique neoplastic disease that develops exclusively in the central nervous system (CNS) and rarely metastasizes to other tissues. This feature strongly implicates the tumor-host CNS microenvironment in gliomagenesis and tumor progression. We investigated the differences and similarities in glioma biology as conveyed by transcriptomic patterns across four mammalian hosts: rats, mice, dogs, and humans. Given the inherent intra-tumoral molecular heterogeneity of human glioma, we focused this study on tumors with upregulation of the platelet-derived growth factor signaling axis, a common and early alteration in human gliomagenesis. The results reveal core neoplastic alterations in mammalian glioma, as well as unique contributions of the tumor host to neoplastic processes. Notable differences were observed in gene expression patterns as well as related biological pathways and cell populations known to mediate key elements of glioma biology, including angiogenesis, immune evasion, and brain invasion. These data provide new insights regarding mammalian models of human glioma, and how these insights and models relate to our current understanding of the human disease.

Concurrent Inhibition of Pim and FLT3 Kinases Enhances Apoptosis of FLT3-ITD Acute Myeloid Leukemia Cells through Increased Mcl-1 Proteasomal Degradation

Purpose:fms-like tyrosine kinase 3 internal tandem duplication (FLT3-ITD) is present in 30% of acute myeloid leukemia (AML), and these patients have short disease-free survival. FLT3 inhibitors have limited and transient clinical activity, and concurrent treatment with inhibitors of parallel or downstream signaling may improve responses. The oncogenic serine/threonine kinase Pim-1 is upregulated downstream of FLT3-ITD and also promotes its signaling in a positive feedback loop, suggesting benefit of combined Pim and FLT3 inhibition.Experimental Design: Combinations of clinically active Pim and FLT3 inhibitors were studied in vitro and in vivoResults: Concurrent treatment with the pan-Pim inhibitor AZD1208 and FLT3 inhibitors at clinically applicable concentrations abrogated in vitro growth of FLT3-ITD, but not wild-type FLT3 (FLT3-WT), cell lines. AZD1208 cotreatment increased FLT3 inhibitor-induced apoptosis of FLT3-ITD, but not FLT3-WT, cells measured by sub-G₁ fraction, annexin V labeling, mitochondrial membrane potential, and PARP and caspase-3 cleavage. Concurrent treatment with AZD1208 and the FLT3 inhibitor quizartinib decreased growth of MV4-11 cells, with FLT3-ITD, in mouse xenografts, and prolonged survival, enhanced apoptosis of FLT3-ITD primary AML blasts, but not FLT3-WT blasts or remission marrow cells, and decreased FLT3-ITD AML blast colony formation. Mechanistically, AZD1208 and quizartinib cotreatment decreased expression of the antiapoptotic protein Mcl-1. Decrease in Mcl-1 protein expression was abrogated by treatment with the proteasome inhibitor MG132, and was preceded by downregulation of the Mcl-1 deubiquitinase USP9X, a novel mechanism of Mcl-1 regulation in AML.Conclusions: The data support clinical testing of Pim and FLT3 inhibitor combination therapy for FLT3-ITD AML. Clin Cancer Res; 24(1); 234-47. ©2017 AACR.

A Synthetic CD8α:MyD88 Coreceptor Enhances CD8+ T-cell Responses to Weakly Immunogenic and Lowly Expressed Tumor Antigens

T cell-based immunotherapies are a promising approach for patients with advanced cancers. However, various obstacles limit T-cell efficacy, including suboptimal T-cell receptor (TCR) activation and an immunosuppressive tumor environment. Here, we developed a fusion protein by linking CD8α and MyD88 (CD8α:MyD88) to enhance CD8⁺ T-cell responses to weakly immunogenic and poorly expressed tumor antigens. CD8α:MyD88-engineered T cells exhibited increased proliferation and expression of effector and costimulatory molecules in a tumor antigen-dependent manner. These effects were accompanied by elevated activation of TCR and Toll-like receptor signaling-related proteins. CD8α:MyD88-expressing T cells improved antitumor responses in mice. Enhanced antitumor activity was associated with a unique tumor cytokine/chemokine signature, improved T-cell infiltration, reduced markers of T-cell exhaustion, elevated levels of proteins associated with antigen presentation, and fewer macrophages with an immunosuppressive phenotype in tumors. Given these observations, CD8α:MyD88 represents a unique and versatile approach to help overcome immunosuppression and enhance T-cell responses to tumor antigens. Cancer Res; 77(24); 7049-58. ©2017 AACR.

Exploring the Concept of Radiation "Booster Shot" in Combination with an Anti-PD-L1 mAb to Enhance Anti-Tumor Immune Effects in Mouse Pancreas Tumors

Radiotherapy (RT) has long been known to be immunogenic. Mounting preclinical data demonstrate a synergistic anti-tumor effect when RT is used in combination with immune check point inhibitors (ICI). However, it is unclear how to best integrate RT with an ICI (i.e. dose fractionation, sequence, etc.). Here we explored the concept that RT delivered as an in situ tumor vaccine sequentially to separate tumors over time might stimulate more potent and rapid antitumor immune response than RT delivered to only one tumor. In essence, radiation to a second tumor could be likened to giving a vaccine "booster shot". Mice bearing pancreatic tumors in three different sites were injected with anti-PD-L1 antibody and exposed to three daily consecutive fractions of 4 Gy each at one or two sites with a one week interval. Our data indicate that delivering an RT to one tumor followed by an RT "booster shot" to a second tumor, compared to treating only one tumor with RT, significantly reduced tumor growth at a third non-irradiated site. This abscopal effect to the non-irradiated site was observed earlier (day 9) in mice that received RT to two tumors versusa single tumor (day 17). Decreased growth of the non-irradiated tumor correlated with a transient increase of the CD4/CD8 ratio in the tumor, increase myeloid-derived suppressor cells and tumor associated macrophages in the draining lymph nodes. These data warrant further exploration of sequentially treating multiple lesions with RT and ICI with the intent of generating a robust anti-tumor immune response.

A Multikinase and DNA-PK Inhibitor Combination Immunomodulates Melanomas, Suppresses Tumor Progression, and Enhances Immunotherapies

Combination therapies have the potential to improve outcomes in melanoma patients but have not yet been clinically efficacious. Here, we used high-throughput flow cytometry-based screening to identify and characterize candidate therapies that might synergize with and augment T-cell immunotherapy efficacy. Two lead therapies, regorafenib (Reg) and NU7441, were selected based on their ability to alter a variety of immunomodulatory proteins, including CD55, CD73, CD155, programmed death-ligand 1 (PD-L1), nerve growth factor receptor (NGFR), and HLA class I in a heterogeneous panel of melanomas. The therapies also upregulated several melanoma antigens, inhibited proliferation, and perturbed activation of oncogenic signaling pathways in melanomas. T cells treated with the therapies proliferated normally and exhibited a favorably altered phenotype, including increased CD25, CD28, inducible T-cell costimulator (ICOS), and reduced expression of coinhibitory receptors. Cytokine production was also increased in treated T cells. When administered in mice, REg suppressed melanoma progression in a CD8⁺ T cell-dependent manner when used alone and with various immunotherapies. Additionally, Reg altered the number, phenotype, and function of various T-cell subsets in the tumor microenvironment. These studies reveal that Reg and NU7441 influence the immunobiology of both tumor cells and T cells and enhance the efficacy of various immunotherapies. Cancer Immunol Res; 5(9); 790-803. ©2017 AACR.

TLR-stimulated T cells acquire resistance to MDSC mediated suppression

The immunosuppressive tumor microenvironment presents a significant challenge to developing effective T cell-based cancer immunotherapies. Myeloid-derived suppressor cells (MDSCs), a heterogeneous group of cells, are a major contributor to the suppressive tumor microenvironment. MDSCs are immature myeloid cells that develop in response to chronic inflammation generated by an infection or a tumor. Currently, strategies to block MDSC-mediated suppression generate modest anti-tumor responses. This is in part due to lack of specific markers to target MDSCs and inability to simultaneously inhibit the multitude of suppressive mechanisms employed by MDSCs. Generating tumor-reactive T cells with the capacity to resist MDSC-mediated suppression would help facilitate the production of potent anti-tumor T cell therapies. The activation of the Toll-like receptor-Myeloid differentiation factor 88 (TLR-MyD88) signaling pathway in CD8+ T cells enhances cell proliferation, cytotoxic function, and survival. Our studies show that TLR-stimulated T cells are resistant to MDSC-mediated suppression. MyD88-activated CD8+ T cells co-cultured with tumor-derived MDSCs displayed enhanced proliferation and cytokine production over control T cells. Our future objectives are to understand the molecular mechanisms by which TLR-activated T cells acquire resistance properties and to exploit this knowledge to improve antitumor immune responses by overcoming MDSC-mediated suppression.

Translational effects and coding potential of an upstream open reading frame associated with DOPA Responsive Dystonia

Upstream open reading frames (uORFs) have emerged as major post-transcriptional regulatory elements in eukaryotic species. In general, uORFs are initiated by a translation start codon within the 5' untranslated region of a gene (upstream ATG; uATG), and they are negatively correlated with translational efficiency. In addition to their translational regulatory role, some uORFs can code for biologically active short peptides. The importance of uATGs/uORFs is further underscored by human diseases associated with single nucleotide polymorphisms (SNPs), which disrupt existing uORFs or introduce novel uORFs. Although several functional proteins translated from naturally occurring uORFs have been described, the coding potential of uORFs created by SNPs has been ignored because of the a priori assumption that these proteins are short-lived with no likely impact on protein homeostasis. Thus, studies on SNP-created uORFs are limited to their translational effects, leaving unexplored the potential cellular consequences of a SNP/uORF-encoded protein. Here, we investigate functionality of a uATG/uORF introduced by a +142C>T SNP within the GCH1 gene and associated with a familial form of DOPA Responsive Dystonia. We report that the +142C>T SNP represses GCH1 translation, and introduces a short, frame shifted uORF that encodes a 73-amino acid peptide. This peptide is localized within the nucleus and compromises cell viability upon proteasome inhibition. Our work extends the list of uATG/uORF associated diseases and advances research on peptides translated from SNP-introduced uORFs, a neglected component of the proteome.

Abstract B31: IRAK-4 signaling in melanoma contributes to reduced expression of inflammatory factors in vitro while contributing to tumor growth in vivo

An underlying and universal hindrance to T-cell-based cancer therapies is the development of immunosuppressive mechanisms that in large part originate from the persistent expression of inflammatory factors. Understanding the fundamental mechanisms that regulate chronic inflammation and targeting of this pathway(s) is critical for developing effective strategies to restore anti-tumor T-cell activity. We recently reported that the IL-1 receptor associated kinase-4 (IRAK-4) is over-expressed and activated in most melanoma cases. IRAK-4 is a central kinase in the inflammatory process that regulates the expression of various inflammatory and immunosuppressive molecules. Inhibiting IRAK-4 activity in melanoma drastically reduced the expression of various inflammatory factors in vitro. Furthermore, IRAK-4 signaling in melanoma contributed to tumor growth in vivo and was associated with an increased frequency of phenotypically exhausted (PD1+Lag3+) tumor infiltrating T-cells, myeloid derived suppressor cells, and a trend toward higher numbers of CD4+ T regs. Ongoing studies are focused on testing the hypothesis that targeting IRAK-4 signaling in tumor cells will alter the expression of inflammatory factors in the tumor environment which will reduce immunosuppression and sensitize melanoma to T-cell-mediated killing.

Citation Format: Jackline Joy Martin Lasola, Degui Geng, Rojesh Shrestha, Eduardo Davila. IRAK-4 signaling in melanoma contributes to reduced expression of inflammatory factors in vitro while contributing to tumor growth in vivo. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr B31.

Repurposing platinum-based chemotherapies for multi-modal treatment of glioblastoma

Glioblastoma (GBM) is a fatal brain cancer for which new treatment options are sorely needed. Platinum-based drugs have been investigated extensively for GBM treatment but few have shown significant efficacy without major central nervous system (CNS) and systemic toxicities. The relative success of platinum drugs for treatment of non-CNS cancers indicates great therapeutic potential when effectively delivered to the tumor region(s). New insights into the broad anticancer effects of platinum drugs, particularly immunomodulatory effects, and innovative delivery strategies that can maximize these multi-modal effects and minimize toxicities may promote the re-purposing of this chemotherapeutic drug class for GBM treatment.

Cross-talk between 4-1BB and TLR1-TLR2 Signaling in CD8+ T Cells Regulates TLR2's Costimulatory Effects

The activation of TLR-MyD88 (Toll-like receptor-myeloid differentiation factor 88) signaling within T cells functions as a potent costimulatory signal that boosts antitumor and antiviral responses. However, the molecular mechanisms underlying the costimulatory processes are poorly understood. We compared microarray gene analysis data between TLR1-TLR2-stimulated and unstimulated T-cell receptor transgenic "pmel" and MyD88(-/-) pmel CD8(+) T cells and identified changes in the expression of several TNF family members. In particular, TLR stimulation increased 4-1BB levels in pmel but not in MyD88(-/-)pmel T cells. A link between 4-1BB and TLR1-TLR2 signaling in CD8(+) T cells was highlighted by the suboptimal responses of 4-1BB(-/-) T cells to TLR1-TLR2 agonist, but their normal response to CD28 or OX40 costimulation. Blocking 4-1BB signaling with antibodies also hindered the costimulatory effects of the TLR1-TLR2 agonist. The elevated levels of 4-1BB transcripts in TLR1-TLR2-stimulated cells were not due to increased mRNA stability nor increased histone activation, but instead were associated with increased binding of p65 and c-Jun to two distinct 4-1BB promoter sites. Combining TLR1-TLR2 ligand with an agonistic antibody to 4-1BB enhanced the antitumor activity in mice with established melanoma tumors. These studies reveal that the costimulatory effects of TLR1-TLR2 signaling in CD8(+) T cells are in part mediated by 4-1BB and are important for mounting an effective antitumor immune response. Cancer Immunol Res; 4(8); 708-16. ©2016 AACR.

Amplifying T cell responses to tumor antigens using a synthetic CD8-MyD88 co-receptor

T cell–based immunotherapies are among the most promising approaches for patients with advanced melanoma and other cancers. The goal of this study is to boost T cell anti-tumor responses by harnessing the costimulatory effects of MyD88 signaling in T cells. We previously demonstrated that Toll-like receptor (TLR) engagement on T cells increases their proliferation, effector function, and survival in a MyD88-dependent manner. However, a challenge to stimulating TLRs on T cells in vivo is inefficiencies in delivering TLR ligands to the tumor site or adverse effects of TLR signaling in cancer cells. We hypothesized that coupling TLR and T cell receptor (TCR) signaling would provide antigen-dependent co-stimulation resulting in enhanced anti-tumor function. We developed a novel synthetic co-receptor consisting of a CD8a and MyD88 fusion protein to induce MyD88 signaling in a TCR–dependent but TLR ligand–independent mechanism. We have compelling data indicating that CD8-MyD88 stimulation improves T cell expansion and function in a tumor antigen–dependent manner. Furthermore, CD8-MyD88 T cells exhibit promising anti-tumor responses in mice with established melanoma tumors. Our strategy represents a universal approach since the CD8-MyD88 is not limited to a specific tumor antigen nor MHC haplotype. CD8-MyD88 also improves T cell responses to low concentrations of antigen, providing the opportunity to expand a large repertoire of tumor-reactive T cells. Furthermore, CD8-MyD88 activates MyD88 signaling in the engineered T cells exclusively, thus eliminating undesirable responses of TLR signaling in tumor cells. These studies represent a novel and versatile therapeutic approach for boosting T cell responses to a variety of cancers.

A multikinase inhibitor and DNA-PK inhibitor combination reduces tumor growth and alters the tumor microenvironment of B16 melanoma

Recent breakthroughs in targeted therapies and immunotherapies for melanoma have prolonged survival in certain patients. Yet, many patients are not candidates for targeted therapies and response rates to immunotherapies remain low. Thus, there is an unmet need to develop novel melanoma therapies that generate: the high response rates that are characteristic of targeted therapies, the durable responses often observed with immunotherapies, and can be used in a majority of melanoma patients. Therefore, a high-throughput approach evaluating nearly 2,000 compounds was taken to identify FDA-approved therapies that alter the expression of immunologically relevant molecules commonly found on human melanomas. Eight compounds were identified based on their ability to reduce melanoma proliferation without negatively impacting T cell proliferation and function. Studies examining the expression of immunosuppressive molecules on melanoma, melanoma proliferation, and T cell-melanoma co-cultures were used to select a multikinase inhibitor and DNA-PK inhibitor for further investigation. The compounds sensitized melanoma to T cell cytotoxicity which was associated with increased MHC class I and antigen expression. In mice with established B16 tumors, the therapeutic combination significantly reduced tumor growth while prolonging survival. Preliminary data suggests that the drug combination impacts the tumor microenvironment and alters various immune cells present in the tumor. Studies using alternative models of melanomas and additional therapeutic combinations are ongoing. These studies represent a proof of concept demonstrating the ability to repurpose drugs to immunosensitize tumors to T cell-based therapies.

Producer T cells: Using genetically engineered T cells as vehicles to generate and deliver therapeutics to tumors

Adoptive cell transfer (ACT) is an emerging anticancer therapy that has shown promise in various malignancies. Redirecting antigen specificity by genetically engineering T cells to stably express receptors has become an effective variant of ACT. A novel extension of this approach is to utilize engineered T cells to produce and deliver anticancer therapeutics that enhance cytotoxic T cell function and simultaneously inhibit immunosuppressive processes. Here, we review the potential of using T cells as therapeutic-secreting vehicles for immunotherapies and present theoretical and established arguments in support of further development of this unique cell-based immunotherapy.

Ameliorating the tumor microenvironment for antitumor responses through TLR5 ligand-secreting T cells

Toll-like receptor (TLR) agonists are potent immunostimulatory agents that have demonstrated great potential for cancer immunotherapy. We have genetically-engineered tumor-specific T cells to deliver and secrete the TLR5 ligand (TLR5L) flagellin to the tumor site to provide costimulation for antitumor immune activity. We found that TLR5L-secreting T cells offered a therapeutic benefit by altering several aspects including augmenting T cell effector function and expansion as well as reshaping the tumor microenvironment toward one that enhances antitumor T cell responses.

Abstract 4974: IL-1 receptor-associated kinase-1 and -4 expression in Hodgkin lymphoma

BACKGROUND: The Toll-like receptor (TLR) mediates nuclear factor kappa B (NFkB) activation in lymphocytes using a family of intermediary proteins called IL-1 receptor associated kinase (IRAK). Mutations within and upregulation of this pathway have been described in the carcinogenesis of non-Hodgkin lymphoma (NHL), but it is not known whether IRAK proteins are present in Hodgkin lymphoma (HL). Furthermore, Epstein-Barr virus (EBV) has been shown to activate NFkB in HL but its association with proteins upstream of NFkB is not described.

METHODS: 1. We performed Western blots on two Hodgkin Reed-Sternberg (HRS) cell lines to detect total IRAK-1 and -4, and phospho-IRAK-1 and -4 (the activated forms). 2. Archived lymph node biopsy samples from Hodgkin lymphoma patients diagnosed at the University of Maryland were stained for IRAK-4.

RESULTS: 1. IRAK-1, IRAK-4, p-IRAK-1 and p-IRAK-4 were present in the malignant HRS cells in two HRS cell lines (HDLM-2 and KM-H2). 2. Seventeen lymph node biopsy samples showed marked positivity for IRAK-4 (mean of 2.3 on a 0-4 scale), as well as lesser positivity in surrounding reactive lymphocytes and histiocytes (mean of 1.6). The only sample to achieve a staining level of 4 was of mixed cellularity subtype, and was EBER-positive and HIV-negative.

CONCLUSIONS: The IRAK proteins are present in the malignant HRS cells of Hodgkin lymphoma. Further work will examine IRAK-1, and phospho-IRAK-1 and -4 in the lymph node samples. Future studies should also examine whether IRAK causes downstream NFkB activation in HL as it does in NHL, and whether HRS cells depend on IRAK's presence for survival. A possible association with EBV infection will also be investigated. IRAK is a targetable protein with inhibitors available, so this and future studies may reveal new therapeutic strategies in relapsed Hodgkin lymphoma.

Citation Format: Victoria S. Giffi, Kenisha M. Younger, Zeba Singh, Qing Chen, Eduardo Davila, Amy S. Kimball. IL-1 receptor-associated kinase-1 and -4 expression in Hodgkin lymphoma. [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 4974. doi:10.1158/1538-7445.AM2015-4974

Abstract 4701: NY-ESO T cells administered post ASCT for MM exhibit extended functionality without exhaustion in a natural pattern of effector and memory programming

Adoptive immunotherapy for cancer has been limited by a lack of antigen specificity, low levels of target expression, and failure to break self-tolerance. We hypothesized that infusion of genetically modified tumor-specific T cells following autologous stem cell transplant (ASCT) may overcome these barriers for multiple myeloma (MM). To test this, we conducted a phase I/II clinical trial (NCT01352286) in which T cells engineered with an HLA-A*0201 restricted, affinity-enhanced TCR recognizing NY-ESO-1 / LAGE-1 peptides (NY-ESOc259-T), were infused in the setting of profound lymphodepletion that accompanies high-dose chemotherapy given with ASCT.

HLA-A*0201 MM patients eligible for ASCT, with antigen positive tumor were enrolled. NY-ESOc259-T was manufactured in a 10 day process using anti-CD3/CD28 microbeads and lentiviral vector, and was administered two days following ASCT. IMWG criteria were used to assess response at day 100 with the addition of a near complete response category (nCR) due to the common occurrence of oligoclonal banding observed following rapid post-ASCT immune reconstitution. Blood and marrow samples were taken at multiple timepoints for serum cytokine analysis, NY-ESOc259-T persistence and trafficking, multiparameter flow analysis to examine the phenotype and function of NY-ESOc259-T, and tumor biomarker analysis. 25 of 29 enrolled patients were infused. A mean of 2.8 × 109 engineered cells were administered (range 8.3 × 108-4.2 × 109), and the average transduction efficiency was 33% (range 30%-45%). Patients tended to have advanced disease (64% chromosomal abnormalities, and 24% prior ASCT). At 3 months, 67% (16/24) and 58% (14/24) of patients were in VGPR and nCR or better, respectively. Infusions were well-tolerated and no cytokine release syndrome was reported. NY-ESOc259-T persisted at 6 months in all but one patient, and in a subset of patients at 2 years; marrow infiltration was consistently observed from day 7 through day 180. NY-ESOc259-T initially displayed a dominant activated effector phenotype which converted towards a dominant effector memory phenotype by 1 year post infusion, in a pattern that mirrored clinical responses. Persisting cells demonstrated a polyfunctional response (IFN-γ and TNF-α) with a cytotoxic (CD107a and granzyme B) signature without overexpression of exhaustion markers (PD-1, LAG-3, and TIM-3). Tumor biomarker analysis is ongoing. MM relapse occurred in 13/25 patients.

This data show that NY-ESOc259-T cells exhibit robust trafficking and expansion, durable persistence without exhaustion, and follow a natural immune expansion and contraction pattern consistent with an antigen-driven mechanism of action. Relapse correlated with a loss of persistence or tumor antigen escape, suggesting that targeting multiple antigens and maintenance infusions may increase durable remissions.

Citation Format: Aaron Rapoport, Edward Stadtmauer, Luca Melchiori, Ryan Wong, Eduardo Davila, Gwendolyn Binder-Scholl, Tom Holdich, Dan Vogl, Brendan Weiss, Jeffrey Finkelstein, Simon Lacey, Sarah Bond, Marylene Fortin, Yoav Peretz, Joanna Brewer, Alan Bennett, Andrew Gerry, Nick Pumphrey, Helen Tayton-Martin, Lilliam Ribeiro, Ashraf Badros, Saul Yanovich, Nancy Hardy, Jean Yared, Naseem Kerr, Sunita Philip, Sandra Wesphal, Bruce L. Levine, Carl June, Michael Kalos, Bent Jakobsen. NY-ESO T cells administered post ASCT for MM exhibit extended functionality without exhaustion in a natural pattern of effector and memory programming. [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 4701. doi:10.1158/1538-7445.AM2015-4701

Identification and characterization of novel immunosensitizing therapeutics for melanoma (VAC3P.1060)

Recent breakthroughs in the field of immunotherapy have revolutionized the treatment of melanoma patients. Specifically, immune checkpoint blockade of CTLA-4 and PD-1 have prolonged overall survival in a subset of melanoma patients. Despite dramatic and durable results in some cases, low overall response rates to these therapies leave the majority of melanoma patients without effective immunotherapeutic treatment options. In order to identify immunotherapies which might offer improved response rates with the potential to be rapidly translated to the clinic, we developed a high-throughput screen and tested over 2000 compounds, many of which are FDA-approved for various malignancies or other diseases. The screen revealed distinct families of multikinase inhibitors and DNA-damage repair inhibitors as novel melanoma immunosensitizing agents. We show that these two classes of drugs can reduce the expression of various immunosuppressive molecules (e.g. PD-L1, CD155) on the cell surface of a wide variety of genetically distinct human melanoma cell lines. Notably, the drugs also increased the expression of HLA and melanoma antigens in most cases. Importantly, preliminary data suggests that drug treatment sensitizes melanoma cells to T cell mediated cytotoxicity. Further preclinical studies are underway to verify drug targets, identify mechanisms of action, and establish in vivo anti-tumor activity.

TLR5 Ligand-Secreting T Cells Reshape the Tumor Microenvironment and Enhance Antitumor Activity

The tumor microenvironment counters antitumor T-cell responses, in part, by blunting their activation and infiltration. Ligands that engage Toll-like receptors (TLR) on T cells and antigen-presenting cells can act as potent immune adjuvants. In this study, we show how tumor-reactive T cells engineered to secrete bacterial flagellin, a TLR5 ligand (TLR5L), can engender a costimulatory signal that augments antitumor activity. Human T cells engineered to express TLR5L along with DMF5, a T-cell receptor that recognizes the melanoma antigen MART-127-35 (DMF5(TLR5L) T cells), displayed increased proliferation, cytokine production, and cytolytic activity against melanoma cells. In a xenogenetic model, adoptive transfer of DMF5(TLR5L) T cells reduced tumor growth kinetics and prolonged mouse survival. In a syngeneic model, similarly engineered melanoma-reactive T cells (pmel(TLR5L)) displayed a relative increase in antitumor activity against established tumors, compared with unmodified T cells. In this model, we documented increased T-cell infiltration associated with increased levels of CCR1 and CXCR3 levels on T cells, a reduction in PD-1(+)Lag3(+) T cells and CD11(+)Gr1(+) myeloid-derived suppressor cells, and changes in the chemokine/cytokine profile of tumors. Our findings show how T cell-mediated delivery of a TLR agonist to the tumor site can contribute to antitumor efficacy, in the context of adoptive T-cell immunotherapy.

Inhibition of IRAK1/4 sensitizes T cell acute lymphoblastic leukemia to chemotherapies

Signaling via the MyD88/IRAK pathway in T cells is indispensable for cell survival; however, it is not known whether this pathway functions in the progression of T acute lymphoblastic leukemia (T-ALL). Here, we determined that compared with thymic and peripheral T cells, T-ALL cells from patients have elevated levels of IRAK1 and IRAK4 mRNA as well as increased total and phosphorylated protein. Targeted inhibition of IRAK1 and IRAK4, either with shRNA or with a pharmacological IRAK1/4 inhibitor, dramatically impeded proliferation of T-ALL cells isolated from patients and T-ALL cells in a murine leukemia model; however, IRAK1/4 inhibition had little effect on cell death. We screened several hundred FDA-approved compounds and identified a set of drugs that had enhanced cytotoxic activity when combined with IRAK inhibition. Administration of an IRAK1/4 inhibitor or IRAK knockdown in combination with either ABT-737 or vincristine markedly reduced leukemia burden in mice and prolonged survival. IRAK1/4 signaling activated the E3 ubiquitin ligase TRAF6, increasing K63-linked ubiquitination and enhancing stability of the antiapoptotic protein MCL1; therefore, IRAK inhibition reduced MCL1 stability and sensitized T-ALL to combination therapy. These studies demonstrate that IRAK1/4 signaling promotes T-ALL progression through stabilization of MCL1 and suggest that impeding this pathway has potential as a therapeutic strategy to enhance chemotherapeutic efficacy.

IL-1 Receptor-Associated Kinase Signaling and Its Role in Inflammation, Cancer Progression, and Therapy Resistance

Chronic inflammation has long been associated with the development of cancer. Among the various signaling pathways within cancer cells that can incite the expression of inflammatory molecules are those that activate IL-1 receptor-associated kinases (IRAK). The IRAK family is comprised of four family members, IRAK-1, IRAK-2, IRAK-3 (also known as IRAK-M), and IRAK-4, which play important roles in both positively and negatively regulating the expression of inflammatory molecules. The wide array of inflammatory molecules that are expressed in response to IRAK signaling within the tumor microenvironment regulate the production of factors which promote tumor growth, metastasis, immune suppression, and chemotherapy resistance. Based on published reports we propose that dysregulated activation of the IRAK signaling pathway in cancer cells contributes to disease progression by creating a highly inflammatory tumor environment. In this article, we present both theoretical arguments and reference experimental data in support of this hypothesis.

Trojan T cell horse: TLR5 ligand-secreting T cells reshape the tumor microenvironment and exhibit enhanced antitumor activity (TUM2P.909)

T cell responses are downregulated by the immunosuppressive tumor microenvironment. On the basis of previous studies demonstrating that Toll-like receptor (TLR) engagement on T cells augments their responses, we hypothesized that T cells engineered to secrete the TLR5 ligand flagellin would enhance T cell costimulation in the tumor environment and augment antitumor activity. Human T cells engineered to express the MART-1 TCR and secrete TLR5-ligand (TLR5-L) responded to lower tumor antigen levels resulting in increased proliferation, cytolytic activity and reversed tumor growth associated with prolonged mouse survival in a xenogeneic model. Treatment with TLR5-L-secreting T cells eradicated tumor in 40% of mice in a syngeneic model. Intratumoral secretion of TLR5-L by T cells reshaped the tumor microenvironment in part by inducing of a distinct chemokine/cytokine profile rendering it more immunogenic and permissive to T cell infiltration. Furthermore, tumor lysis by TLR5-L-producing T cells triggered the priming of endogenous tumor-reactive CD8 and CD4 T cells. Characterization of the cellular composition of the tumor and spleen revealed a reduction in MDSCs in the spleen and increased expression of MHC I in the tumor. This study demonstrates for the first time the ability to use T cells to deliver a TLR agonist to the tumor site and that intratumoral TLR5-L contributes to various processes involved in tumor regression.

Costimulatory effects of TLR1-TLR2 stimulation on CD8+ T cells is dependent on 4-1BB signaling (TUM7P.941)

Toll-like receptors (TLRs) play a significant role in amplifying immune responses against tumors. Our studies demonstrate that activated CD8+ T cells express TLRs and upon stimulation with TLR1-TLR2 agonists, exhibit enhanced T cell survival and proliferation. To define how TLR signaling promotes these processes, we compared gene expression analysis between TLR1-TLR2-stimulated and unstimulated CD8+ and MyD88-/- CD8+ T cells and identified significant increases in the expression levels of five TNF family members. We sought to test the hypothesis that the costimulatory effects of TLR1-TLR2 stimulation on CD8+ T cells were dependent on the function of one of these costimulatory molecules. Blocking CD137 (4-1BB) using blocking antibodies, but not the other TNF family members, dramatically reduced the costimulatory effects of TLR-mediated T cell proliferation. Likewise, 4-1BB -deficient CD8+ T cells did not respond to TLR stimulation. While TLR signals are capable of upregulating antiapoptotic proteins such as BCL2 and BCL-xL, mechanistically, we postulate that 4-1BB activation stabilizes these proteins, hence promoting survival. Adoptive transfer of pmel T cells along with the 4-1BB agonistic antibody, 3H3 and the TLR ligand, Pam3CSK4 was able to reduce tumor growth in a B16 melanoma model. These studies indicate that the costimulatory effects of TLR1-TLR2 signaling in CD8+ T cells mediated by 4-1BB signals are vital for mounting an effective antitumor response.

Eomesodermin is required for antitumor immunity mediated by 4-1BB-agonist immunotherapy

CD8⁺ T cells in progressing tumors frequently fail to mount an effective antitumor response often in association with the expression of inhibitory receptors, including programmed cell death-1 (PD-1) and lymphocyte-activation gene 3 (Lag3). Using a lymphoma tumor model, we demonstrate that tumor-infiltrating CD8⁺ T cells from growing tumors co-express inhibitory receptors and co-stimulatory receptors, including 4-1BB (TNFRSF9) as well as high levels of 2 transcription factors, Eomesodermin (Eomes) and T-bet (Tbx21), critical determinants of CD8⁺ T cell fate. Immunotherapy with an agonistic anti-4–1-BB antibody altered the ratio of Eomes to T-bet expression in tumor-infiltrating CD8⁺ T cells by increasing Eomes and decreasing T-bet expression. 4-1BB-agonist immunotherapy was also associated with downregulated expression of the inhibitory receptors PD-1 and Lag3 on tumor-infiltrating CD8⁺ T cells, a molecular phenotype associated with subsequent attenuation of tumor growth. Furthermore, 4-1BB-agonist immunotherapy failed to effect tumor progression in mice with Eomes deficient T cells. However, upon resumption of tumor growth, tumor-infiltrating CD8⁺ T cells from treated animals continued to express high levels of Eomes as well as elevated levels of the inhibitory receptors PD-1 and Lag3. Our data suggest that tumor-infiltrating CD8⁺ T cells are poised between activation and inhibition as dictated by expression of both co-stimulatory receptors and inhibitory receptors and demonstrate that T cell expression of Eomes is necessary, but not sufficient, for efficacious 4-1BB-agonist-mediated immunotherapy.

Neuroimmune semaphorin 4A as a drug and drug target for asthma

Neuroimmune semaphorin 4A (Sema4A) has been shown to play an important costimulatory role in T cell activation and regulation of Th1-mediated diseases such as multiple sclerosis (MS), experimental autoimmune encephalomyelitis (EAE), and experimental autoimmune myocarditis (EAM). Sema4A has three functional receptors, Tim-2 expressed on CD4+ T cells, Th2 cells in particular, and Plexin B1 and D1 predominantly expressed on epithelial and endothelial cells, correspondingly. We recently showed that Sema4A has a complex expression pattern in lung tissue in a mouse model of asthma. We and others have shown that corresponding Plexin expression can be found on immune cells as well. Moreover, we demonstrated that Sema4A-deficient mice displayed significantly higher lung local and systemic allergic responses pointing to its critical regulatory role in the disease. To determine the utility of Sema4A as a novel immunotherapeutic, we introduced recombinant Sema4A protein to the allergen-sensitized WT and Sema4A(-/-) mice before allergen challenge. We observed significant reductions in the allergic inflammatory lung response in Sema4A-treated mice as judged by tissue inflammation including eosinophilia and mucus production. Furthermore, we demonstrated that in vivo administration of anti-Tim2 Ab led to a substantial upregulation of allergic inflammation in WT mouse lungs. These data highlight the potential to develop Sema4A as a new therapeutic for allergic airway disease.

A high throughput method for enrichment of natural killer cells and lymphocytes and assessment of in vitro cytotoxicity

In vitro assessment of lymphocyte and natural killer (NK) cell cytotoxicity typically employs density gradient centrifugation and magnetic cell separation to isolate effector cells, and chromium release to assess cytotoxicity. In order to improve the rapidity and scalability of in vitro cytotoxicity assessment, we evaluated the efficacy of a protocol utilizing tetrameric antibody complexes and SepMate™ isolation tubes to negatively select NK cells (TACs/Sep), and calcein-AM release to measure cytotoxicity. We compared the efficiency and accuracy of this protocol to a conventional approach employing density gradient centrifugation and magnetically labeled antibodies (DG/MACS) to isolate NK cells and chromium release to measure cytotoxicity. The TACs/Sep method significantly decreased the time required for NK cell isolation (1h vs. 4h), but resulted in higher red blood cell contamination. NK cell activation marker expression (including CD94, NKG2D, NKp30, NKp46, DNAM-1, 2B4, KIR2DL1/S1, KIR2DL2/L3, intracellular granzyme B, and perforin) was similar when comparing NK cells isolated by the TACs/Sep or DG/MACS methods, but the TACs/Sep method induced higher expression of CD16. In vitro cytotoxicity against HT29 colon cancer and K562 leukemia cells was not affected by the isolation method. Lastly, by combining the TACs/Sep NK cell isolation method with calcein-acetoxymethyl diacetylester (calcein-AM) release, the time required to assess in vitro cytotoxicity was reduced by 33% (4h) compared to protocols employing DG/MACS and chromium release. Altogether, these results provide the foundation for the development of a rapid, high throughput functional assay, and make it practical for the multiplexing of downstream applications, such as flow cytometric analysis and enzyme-linked immunosorbent assays (ELISAs).

TLR agonists: our best frenemy in cancer immunotherapy

Various TLR agonists are currently under investigation in clinical trials for their ability to orchestrate antitumor immunity. The antitumor responses are largely attributed to their aptitude to stimulate APCs such as DCs which in turn, activate tumor-specific T cell responses. However, there is a potential for TLR signaling to occur on cells other than professional APCs that could negate antitumor responses or even worse, promote tumor growth. The impetus for this review is twofold. First, there is accumulating data demonstrating that the engagement of TLRs on different T cell subsets and different cancer types could promote tumor growth or conversely, contribute to antitumor responses. Second, the efficacy of TLR agonists as monotherapies to treat cancer patients has been limited. In this review, we discuss how TLR signaling within different T cell subsets and cancer cells can potentially impact the generation of antitumor responses. Based on evidence from preclinical models and clinical trials, we draw attention to several criteria that we believe must be considered when selecting TLR agonists for developing effective immunotherapeutic strategies against cancer.