FOXO1 enhances CAR T cell stemness, metabolic fitness and efficacy

Chimeric antigen receptor (CAR) T cell therapy has transformed the treatment of haematological malignancies such as acute lymphoblastic leukaemia, B cell lymphoma and multiple myeloma1-4, but the efficacy of CAR T cell therapy in solid tumours has been limited5. This is owing to a number of factors, including the immunosuppressive tumour microenvironment that gives rise to poorly persisting and metabolically dysfunctional T cells. Analysis of anti-CD19 CAR T cells used clinically has shown that positive treatment outcomes are associated with a more 'stem-like' phenotype and increased mitochondrial mass6-8. We therefore sought to identify transcription factors that could enhance CAR T cell fitness and efficacy against solid tumours. Here we show that overexpression of FOXO1 promotes a stem-like phenotype in CAR T cells derived from either healthy human donors or patients, which correlates with improved mitochondrial fitness, persistence and therapeutic efficacy in vivo. This work thus reveals an engineering approach to genetically enforce a favourable metabolic phenotype that has high translational potential to improve the efficacy of CAR T cells against solid tumours.

Insights into Cancer Immunotherapies: Recent Breakthroughs, Opportunities, and Challenges

This Special Issue reminds us that, although incredible developments have occurred in the field of cancer immunotherapy, there is still plenty of room for improvement [...].

Enhancing Adoptive Cell Transfer with Combination BRAF-MEK and CDK4/6 Inhibitors in Melanoma

Despite the success of immune checkpoint inhibitors that target cytotoxic lymphocyte antigen-4 (CTLA-4) and programmed-cell-death-1 (PD-1) in the treatment of metastatic melanoma, there is still great need to develop robust options for patients who are refractory to first line immunotherapy. As such there has been a resurgence in interest of adoptive cell transfer (ACT) particularly derived from tumor infiltrating lymphocytes. Moreover, the addition of cyclin dependent kinase 4/6 inhibitors (CDK4/6i) have been shown to greatly extend duration of response in combination with BRAF-MEK inhibitors (BRAF-MEKi) in pre-clinical models of melanoma. We therefore investigated whether combinations of BRAF-MEK-CDK4/6i and ACT were efficacious in murine models of melanoma. Triplet targeted therapy of BRAF-MEK-CDK4/6i with OT-1 ACT led to sustained and robust anti-tumor responses in BRAFi sensitive YOVAL1.1. We also show that BRAF-MEKi but not CDK4/6i enhanced MHC Class I expression in melanoma cell lines in vitro. Paradoxically CDK4/6i in low concentrations of IFN-γ reduced expression of MHC Class I and PD-L1 in YOVAL1.1. Overall, this work provides additional pre-clinical evidence to pursue combination of BRAF-MEK-CDK4/6i and to combine this combination with ACT in the clinic.

A Histone Deacetylase Inhibitor, Panobinostat, Enhances Chimeric Antigen Receptor T-cell Antitumor Effect Against Pancreatic Cancer

PURPOSE

In this article, we describe a combination chimeric antigen receptor (CAR) T-cell therapy that eradicated the majority of tumors in two immunocompetent murine pancreatic cancer models and a human pancreatic cancer xenograft model.

EXPERIMENTAL DESIGN

We used a dual-specific murine CAR T cell that expresses a CAR against the Her2 tumor antigen, and a T-cell receptor (TCR) specific for gp100. As gp100 is also known as pMEL, the dual-specific CAR T cells are thus denoted as CARaMEL cells. A vaccine containing live vaccinia virus coding a gp100 minigene (VV-gp100) was administered to the recipient mice to stimulate CARaMEL cells. The treatment also included the histone deacetylase inhibitor panobinostat (Pano).

RESULTS

The combination treatment enabled significant suppression of Her2⁺ pancreatic cancers leading to the eradication of the majority of the tumors. Besides inducing cancer cell apoptosis, Pano enhanced CAR T-cell gene accessibility and promoted CAR T-cell differentiation into central memory cells. To test the translational potential of this approach, we established a method to transduce human T cells with an anti-Her2 CAR and a gp100-TCR. The exposure of the human T cells to Pano promoted a T-cell central memory phenotype and the combination treatment of human CARaMEL cells and Pano eradicated human pancreatic cancer xenografts in mice.

CONCLUSIONS

We propose that patients with pancreatic cancer could be treated using a scheme that contains dual-specific CAR T cells, a vaccine that activates the dual-specific CAR T cells through their TCR, and the administration of Pano.

Enhancing co-stimulation of CAR T cells to improve treatment outcomes in solid cancers

Co-stimulation is a fundamental component of T cell biology and plays a key role in determining the quality of T cell proliferation, differentiation, and memory formation. T cell-based immunotherapies, such as chimeric antigen receptor (CAR) T cell immunotherapy, are no exception. Solid tumours have largely been refractory to CAR T cell therapy owing to an immunosuppressive microenvironment which limits CAR T cell persistence and effector function. In order to eradicate solid cancers, increasingly sophisticated strategies are being developed to deliver these vital co-stimulatory signals to CAR T cells, often specifically within the tumour microenvironment. These include designing novel co-stimulatory domains within the CAR or other synthetic receptors, arming CAR T cells with cytokines or using CAR T cells in combination with agonist antibodies. This review discusses the evolving role of co-stimulation in CAR T cell therapies and the strategies employed to target co-stimulatory pathways in CAR T cells, with a view to improve responses in solid tumours.

Understanding T cell phenotype for the design of effective chimeric antigen receptor T cell therapies

Rapid advances in immunotherapy have identified adoptive cell transfer as one of the most promising approaches for the treatment of cancers. Large numbers of cancer reactive T lymphocytes can be generated ex vivo from patient blood by genetic modification to express chimeric antigen receptors (CAR) specific for tumor-associated antigens. CAR T cells can respond strongly against cancer cells, and adoptive transferred CAR T cells can induce dramatic responses against certain types of cancers. The ability of T cells to respond against disease depends on their ability to localize to sites, persist and exert functions, often in an immunosuppressive microenvironment, and these abilities are reflected in their phenotypes. There is currently intense interest in generating CAR T cells possessing the ideal phenotypes to confer optimal antitumor activity. In this article, we review T cell phenotypes for trafficking, persistence and function, and discuss how culture conditions and genetic makeups can be manipulated to achieve the ideal phenotypes for antitumor activities.

Challenges and Opportunities for Effective Cancer Immunotherapies

Using immunotherapy to treat cancers can be traced back to the 1890s, where a New York physician William Coley used heat-killed bacteria to treat cancer patients, which became known as "Coley's toxin" [...].

Primary and metastatic breast tumors cross-talk to influence immunotherapy responses

The presence of a tumor can alter host immunity systematically. The immune-tumor interaction in one site may impact the local immune microenvironment in distal tissues through the circulation, and therefore influence the efficacy of immunotherapies to distant metastases. Improved understanding of the immune-tumor interactions during immunotherapy treatment in a metastatic setting may enhance the efficacy of current immunotherapies. Here we investigate the response to αPD-1/αCTLA4 and trimAb (αDR5, α4-1BB, αCD40) of 67NR murine breast tumors grown simultaneously in the mammary fat pad (MFP) and lung, a common site of breast cancer metastasis, and compared to tumors grown in isolation. Lung tumors present in isolation were resistant to both therapies. However, in MFP and lung tumor-bearing mice, the presence of a MFP tumor could increase lung tumor response to immunotherapy and decrease the number of lung metastases, leading to complete eradication of lung tumors in a proportion of mice. The MFP tumor influence on lung metastases was mediated by CD8⁺ T cells, as CD8⁺ T cell depletion abolished the difference in lung metastases. Furthermore, mice with concomitant MFP and lung tumors had increased tumor specific, effector CD8⁺ T cells infiltration in the lungs. Thus, we propose a model where tumors in an immunogenic location can give rise to systemic anti-tumor CD8⁺ T cell responses that could be utilized to target metastatic tumors. These results highlight the requirement for clinical consideration of cross-talk between primary and metastatic tumors for effective immunotherapy for cancers otherwise resistant to immunotherapy.

Novel combination immunotherapy for pancreatic cancer: potent anti-tumor effects with CD40 agonist and interleukin-15 treatment

Objectives

With the poorest 5‐year survival of all cancers, improving treatment for pancreatic cancer is one of the biggest challenges in cancer research. We sought to explore the potential of combining both priming and activation of the immune system. To achieve this, we combined a CD40 agonist with interleukin‐15 and tested its potential in pancreatic cancer.

Methods

Response to this combination regimen was assessed in pancreatic ductal adenocarcinoma mouse models, and a thorough analysis of the tumor microenvironment was performed.

Results

We demonstrated profound reduction in tumor growth and increased survival of mice with the majority of mice being cured when both agents were combined, including an unprecedented 8‐fold dose reduction of CD40 agonist without losing any efficacy. RNAseq analysis showed involvement of natural killer (NK) cell‐ and T‐cell‐mediated anti‐tumor responses and the importance of antigen‐presenting cell pathways. This combination resulted in enhanced infiltration of tumors by both T cells and NK cells, as well as a striking increase in the ratio of CD8⁺ T cells over Tregs. We also observed a significant increase in numbers of dendritic cells (DCs) in tumor‐draining lymph nodes, particularly CD103⁺ DCs with cross‐presentation potential. A critical role for CD8⁺ T cells and involvement of NK cells in the anti‐tumor effect was highlighted. Importantly, strong immune memory was established, with an increase in memory CD8⁺ T cells only when both interleukin‐15 and the CD40 agonist were combined.

Conclusion

These novel preclinical data support initiation of a first‐in‐human clinical trial with this combination immunotherapy strategy in pancreatic cancer.

Enhancing chimeric antigen receptor T-cell immunotherapy against cancer using a nanoemulsion-based vaccine targeting cross-presenting dendritic cells

Objectives

Adoptive transfer of chimeric antigen receptor (CAR)-modified T cells is a form of cancer immunotherapy that has achieved remarkable efficacy in patients with some haematological cancers. However, challenges remain in CAR T-cell treatment of solid tumours because of tumour-mediated immunosuppression.

Methods

We have demonstrated that CAR T-cell stimulation through T-cell receptors (TCRs) in vivo can generate durable responses against solid tumours in a variety of murine models. Since Clec9A-targeting tailored nanoemulsion (Clec9A-TNE) vaccine enhances antitumour immune responses through selective activation of Clec9A⁺ cross-presenting dendritic cells (DCs), we hypothesised that Clec9A-TNE could prime DCs for antigen presentation to CAR T cells through TCRs and thus improve CAR T-cell responses against solid tumours. To test this hypothesis, we used CAR T cells expressing transgenic TCRs specific for ovalbumin (OVA) peptides SIINFEKL (CAROTI) or OVA_323-339 (CAROTII).

Results

We demonstrated that the Clec9A-TNEs encapsulating full-length recombinant OVA protein (OVA-Clec9A-TNE) improved CAROT T-cell proliferation and inflammatory cytokine secretion in vitro. Combined treatment using the OVA-Clec9A-TNE and CAROT cells resulted in durable responses and some rejections of tumours in immunocompetent mice. Tumour regression was accompanied by enhanced CAROT cell proliferation and infiltration into the tumours.

Conclusion

Our study presents Clec9A-TNE as a prospective avenue to enhance CAR T-cell efficacy for solid cancers.

Cross-talk between tumors at anatomically distinct sites

Cancer tissue is not homogenous, and individual metastases at different anatomical locations can differ from the primary tumor and from one another in both their morphology and cellular composition, even within an individual patient. Tumors are composed of cancer cells and a range of other cell types, which, together with a variety of secreted molecules, collectively comprise the tumor microenvironment (TME). Cells of the TME can communicate with each other and with distant tissues in a form of molecular cross-talk to influence their growth and function. Cross-talk between cancer cells and local immune cells is well described and can lead to the induction of local immunosuppression. Recently, it has become apparent that tumors located remotely from each other, can engage in cross-talk that can influence their responsiveness to various therapies, including immunotherapy. In this article, we review studies that describe how tumors systemically communicate with distant tissues through motile cells, extracellular vesicles, and secreted molecules that can affect their function. In addition, we summarize evidence from mouse studies and the clinic that indicate an ability of some tumors to influence the progression and therapeutic responses of other tumors in different anatomical locations.

Tissue-specific tumor microenvironments influence responses to immunotherapies

Objectives

Investigation of variable response rates to cancer immunotherapies has exposed the immunosuppressive tumor microenvironment (TME) as a limiting factor of therapeutic efficacy. A determinant of TME composition is the tumor location, and clinical data have revealed associations between certain metastatic sites and reduced responses. Preclinical models to study tissue‐specific TMEs have eliminated genetic heterogeneity, but have investigated models with limited clinical relevance.

Methods

We investigated the TMEs of tumors at clinically relevant sites of metastasis (liver and lungs) and their impact on αPD‐1/αCTLA4 and trimAb (αDR5, α4‐1BB, αCD40) therapy responses in the 67NR mouse breast cancer and Renca mouse kidney cancer models.

Results

Tumors grown in the lungs were resistant to both therapies whereas the same tumor lines growing in the mammary fat pad (MFP), liver or subcutaneously could be completely eradicated, despite greater tumor burden. Assessment of tumor cells and drug delivery in 67NR lung or MFP tumors revealed no differences and prompted investigation into the immune TME. Lung tumors had a more immunosuppressive TME with increased myeloid‐derived suppressor cell infiltration, decreased T cell infiltration and activation, and decreased NK cell activation. Depletion of various immune cell subsets indicated an equivalent role for NK cells and CD8⁺ T cells in lung tumour control. Thus, targeting T cells with αPD‐1/αCTLA4 or trimAb was not sufficient to elicit a robust antitumor response in lung tumors.

Conclusion

Taken together, these data demonstrate that tissue‐specific TMEs influence immunotherapy responses and highlight the importance in defining tissue‐specific response patterns in patients.

Genetic Redirection of T Cells for the Treatment of Pancreatic Cancer

Conventional treatments for pancreatic cancer are largely ineffective, and the prognosis for the vast majority of patients is poor. Clearly, new treatment options are desperately needed. Immunotherapy offers hope for the development of treatments for pancreatic cancer. A central requirement for the efficacy of this approach is the existence of cancer antigen-specific T cells, but these are often not present or difficult to isolate for most pancreatic tumors. Nevertheless, specific T cells can be generated using genetic modification to express chimeric antigen receptors (CAR), which can enable T cell responses against pancreatic tumor cells. CAR T cells can be produced ex vivo and expanded in vitro for infusion into patients. Remarkable responses have been documented using CAR T cells against several malignancies, including leukemias and lymphomas. Based on these successes, the extension of CAR T cell therapy for pancreatic cancer holds great promise. However, there are a number of challenges that limit the full potential of CAR T cell therapies for pancreatic cancer, including the highly immunosuppressive tumor microenvironment (TME). In this article, we will review the recent progress in using CAR T cells in pancreatic cancer preclinical and clinical settings, discuss hurdles for utilizing the full potential of CAR T cell therapy and propose research strategies and future perspectives. Research into the use of CAR T cell therapy in pancreatic cancer setting is rapidly gaining momentum and understanding strategies to overcome the current challenges in the pancreatic cancer setting will allow the development of effective CAR T cell therapies, either alone or in combination with other treatments to benefit pancreatic cancer patients.

Abstract PR06: Dual-specific T-cells and an indirect vaccine eradicate large solid tumors

While immunotherapy can eliminate substantial burdens of some leukemias, the ultimate challenge remains the eradication of large solid tumors and metastases for most cancers. Here we generate dual-specific T-cells expressing a chimeric antigen receptor (CAR) specific for Her2 and a TCR specific for the melanocyte protein (gp100). Injection of T-cells, together with a vaccine that contains a recombinant vaccinia virus expressing gp100, induced durable complete remission of a variety of Her2+ tumors and established metastases, some in excess of 150 mm2, in immunocompetent mice expressing Her2 in normal tissues. Tumor destruction occurred rapidly over seven days and was associated with an extensive infiltrate of T-cells. Mice that had rejected tumors were resistant to rechallenge with the same Her2+ tumor cells, indicating the formation of immune memory. Furthermore, we have established methods to transduce dual-specific T-cells from human peripheral blood with both a TCR specific for gp100 and a CAR for Her2. From as little as 1 ml of human buffy coat, we could generate sufficient numbers of cells for a course of treatment for a patient. The stimulation of gp100 through TCR enhanced the human dual-specific CAR T-cell proliferation, secretion of IFN-γ and killing of Her2+ human cancer cells in vitro. These characteristics were identified to be important for eradicating tumors in the mouse models. Taken together, our data provide valuable information for the development of CAR T-cell therapies for patients with solid cancers and evidence for pursuing a phase I clinical trial.

Citation Format: Clare Y. Slaney, Bianca von Scheidt, Phillip K. Darcy, Michael H. Kershaw. Dual-specific T-cells and an indirect vaccine eradicate large solid tumors [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr PR06.

Abstract A048: Targeting the tumor microenvironment to enhance immunotherapy against cancer

Immunotherapies that harness the immune system against cancer are an attractive proposition for cancer treatment. While there have been some promising successes, only a small fraction of patients obtain clinical benefit. It has become clear that the immunosuppressive tumor microenvironment (TME) is a major obstacle for immunotherapies, because the TME suppresses immune responses, leading to reduced efficacy. We previously demonstrated that the site of tumor growth is a major determinant in sculpting the organ-specific TME, and thus predisposes treatment efficacy (1). In this project, we hypothesize that the TME of visceral tumors is more immunosuppressive than those of the tumors growing elsewhere. We investigated in murine models the difference in the TME in breast cancer growing orthotopically and the same breast cancer growing in the common metastatic sites, such as the lungs. Our findings showed that the breast cancer growing in the lungs was resistant to immunotherapies such as anti-PD1 and anti-CTLA-4, whereas the breast cancer growing orthotopically could be completely eradicated even when the cancer burden was greater. Through an institutional prospective community-based rapid autopsy program (CASCADE), we obtained genetically matched metastases and surrounding tissues from several sites in the same breast cancer patients and investigated the TME from these tumors using novel technologies such as RNAseq and multiplex immunohistochemistry. Strikingly, the TMEs from the same organs in different patients have similar immune gene expression profiles and in contrast, TMEs from the same patient differ greatly in different organs. Together, our research demonstrates an organ-specific difference between TMEs that leads to different responses to therapies. We anticipate that further study of how cancer cells sculpt the TME at different sites will greatly enhance our understanding of the TME and provide promising targets to enhance current immunotherapies, especially for patients who do not respond to existing therapies. Reference: 1. Devaud C., et al. Molecular Therapy 2014;22:18-27.

Citation Format: Clare Y. Slaney, Amanda J. Oliver, Michael H. Kershaw. Targeting the tumor microenvironment to enhance immunotherapy against cancer [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A048.

Dual PD-1 and CTLA-4 Checkpoint Blockade Promotes Antitumor Immune Responses through CD4+Foxp3- Cell-Mediated Modulation of CD103+ Dendritic Cells

Immunotherapy is widely accepted as a powerful new treatment modality for the treatment of cancer. The most successful form of immunotherapy to date has been the blockade of the immune checkpoints PD-1 and CTLA-4. Combining inhibitors of both PD-1 and CTLA-4 increases the proportion of patients who respond to immunotherapy. However, most patients still do not respond to checkpoint inhibitors, and prognostic biomarkers are currently lacking. Therefore, a better understanding of the mechanism by which these checkpoint inhibitors enhance antitumor immune responses is required to more accurately predict which patients are likely to respond and further enhance this treatment modality. Our current study of two mouse tumor models revealed that CD4⁺Foxp3^- cells activated by dual PD-1/CTLA-4 blockade modulated the myeloid compartment, including activation of conventional CD103⁺ dendritic cells (DC) and expansion of a myeloid subset that produces TNFα and iNOS (TIP-DCs). CD4⁺Foxp3^- T cell-mediated activation of CD103⁺ DCs resulted in enhanced IL12 production by these cells and IL12 enhanced the therapeutic effect of dual PD-1/CTLA-4 blockade. Given the importance of these myeloid subsets in the antitumor immune response, our data point to a previously underappreciated role of CD4⁺Foxp3^- cells in modulating this arm of the antitumor immune response. Cancer Immunol Res; 6(9); 1069-81. ©2018 AACR.

Tissue-Dependent Tumor Microenvironments and Their Impact on Immunotherapy Responses

Recent advances in cancer immunology have led to a better understanding of the role of the tumor microenvironment (TME) in tumor initiation, progression, and metastasis. Tumors can occur at many locations within the body and coevolution between malignant tumor cells and non-malignant cells sculpts the TME at these sites. It has become increasingly clear that there are specific differences of the TMEs at different anatomical locations, and these tissue-specific TMEs regulate tumor growth, determine metastatic progression, and impact on the outcome of therapy responses. Herein, we review the scientific advances in understanding tissue-specific TMEs, discuss their impact on immunotherapeutic response, and assess the current clinical knowledge in this emerging field. A deeper understanding of the tissue-specific TME will help to develop effective immunotherapies against tumors and their metastases and assist in predicting clinical outcomes.

An ultrastructural investigation of tumors undergoing regression mediated by immunotherapy

While immunotherapy employing chimeric antigen receptor (CAR) T cells can be effective against a variety of tumor types, little is known about what happens within the tumor at an ultrastructural level during tumor regression. Here, we used transmission electron microscopy to investigate morphologic and cellular features of tumors responding to immunotherapy composed of adoptive transfer of dual-specific CAR T cells and a vaccine, supported by preconditioning irradiation and interleukin-2. Tumors responded rapidly, and large areas of cell death were apparent by 4 days after treatment. The pleomorphic and metabolically active nature of tumor cells and phagocytic activity of macrophages were apparent in electron microscopic images of tumors prior to treatment. Following treatment, morphologic features of various types of tumor cell death were observed, including apoptosis, paraptosis and necrosis. Large numbers of lipid droplets were evident in tumor cells undergoing apoptosis. Macrophages were the predominant leukocyte type infiltrating tumors before treatment. Macrophages decreased in frequency and number after treatment, whereas an increasing accumulation of neutrophils and T lymphocytes was observed following treatment. Phagocytic activity of macrophages and neutrophils was apparent, while T cells could be observed in close association with tumor cells with potential immunological synapses present. These observations highlight the cellular composition and ultrastructural appearance of tumors undergoing regression mediated by immunotherapy.

Abstract 631: Dual-specific T cells are highly effective in eradicating solid tumors

Chimeric antigen receptor (CAR) T cell therapy is a novel form of adoptive cellular therapy and has recently generated remarkable effects in patients with hematological cancers. However, the success against solid cancers has been modest. The major challenges are the hostile tumor microenvironment and the low efficiency of CAR T cells infiltrating the tumor. Here, we present a major advancement in CAR T therapy that eradicated large established solid cancers, some in excess of 150 mm2, in immunocompetent mice.

We hypothesized that a vaccine composed of a recombinant poxvirus could be used as an antigen delivery vehicle to specifically activate CAR T cells through their T cell receptor (TCR) and simultaneously change the tumor microenvironment, allowing the recruitment and activation of CAR T cells. The approach involves adoptive cell transfer incorporating vaccination (ACTIV) therapy. We generated dual-specific T cells expressing a CAR specific for the tumor antigen Her2 and a TCR specific for the melanocyte protein (gp100). Injection of T cells, together with recombinant vaccinia virus expressing gp100, induced durable complete remission of a variety of Her2+ tumors and established metastases, some in excess of 150 mm2, in immunocompetent mice expressing Her2 in normal tissues, including the breast and brain. Tumor destruction mediated by dual-specific T cells occurred rapidly over a period of seven days and was associated with an extensive proliferation and infiltration of the dual-specific CAR T cells. Mice that had rejected tumors were resistant to rechallenge with the same Her2+ tumor cells and partially resistant to rechallenge with Her2- tumor cells, indicating the formation of immune memory and epitope spreading. This mouse model study supports the view that it is possible to design a highly effective CAR T cell therapy for solid cancers and metastases, even when the target antigen is also expressed in vital tissues.

To explore the translational potential for using the dual specific CAR T cell strategy, we established methods to transduce the T cells from human peripheral blood with both a TCR specific for gp100 and a CAR for Her2. From as little as 1 ml of human buffy coat, we could generate more than 109 dual-specific CAR T cells, which is sufficient for a course of treatment. The human dual-specific CAR T cells were functional in secreting IFN-γ and killing human cancer cells when co-cultured with the gp100 or Her2 expressing human cancer cells. The stimulation of gp100 through TCR enhanced the dual-specific CAR T cell proliferation, secretion of IFN-γ and killing of Her2+ human cancer cells in vitro. These characteristics were identified to be important for eradicating tumors in the mouse models. Taken together, our data provide valuable information for the development of CAR T cell therapies for patients with solid cancers.

Citation Format: Clare Y. Slaney, Bianca von Scheidt, Phillip K. Darcy, Michael H. Kershaw. Dual-specific T cells are highly effective in eradicating solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 631. doi:10.1158/1538-7445.AM2017-631

Targeting the adenosine 2A receptor enhances chimeric antigen receptor T cell efficacy

Chimeric antigen receptor (CAR) T cells have been highly successful in treating hematological malignancies, including acute and chronic lymphoblastic leukemia. However, treatment of solid tumors using CAR T cells has been largely unsuccessful to date, partly because of tumor-induced immunosuppressive mechanisms, including adenosine production. Previous studies have shown that adenosine generated by tumor cells potently inhibits endogenous antitumor T cell responses through activation of adenosine 2A receptors (A2ARs). Herein, we have observed that CAR activation resulted in increased A2AR expression and suppression of both murine and human CAR T cells. This was reversible using either A2AR antagonists or genetic targeting of A2AR using shRNA. In 2 syngeneic HER2+ self-antigen tumor models, we found that either genetic or pharmacological targeting of the A2AR profoundly increased CAR T cell efficacy, particularly when combined with PD-1 blockade. Mechanistically, this was associated with increased cytokine production of CD8+ CAR T cells and increased activation of both CD8+ and CD4+ CAR T cells. Given the known clinical relevance of the CD73/adenosine pathway in several solid tumor types, and the initiation of phase I trials for A2AR antagonists in oncology, this approach has high translational potential to enhance CAR T cell efficacy in several cancer types.

A Multifunctional Role for Adjuvant Anti-4-1BB Therapy in Augmenting Antitumor Response by Chimeric Antigen Receptor T Cells

Adoptive immunotherapy utilizing chimeric antigen receptor (CAR) T cells has demonstrated high success rates in hematologic cancers, but results against solid malignancies have been limited to date, due in part to the immunosuppressive tumor microenvironment. Activation of the 4-1BB (CD137) pathway using an agonistic α-4-1BB antibody is known to provide strong costimulatory signals for augmenting and diversifying T-cell responses. We therefore hypothesized that a combination of α-4-1BB and CAR T-cell therapy would result in improved antitumor responses. Using a human-Her2 self-antigen mouse model, we report here that α-4-1BB significantly enhanced CAR T-cell efficacy directed against the Her2 antigen in two different established solid tumor settings. Treatment also increased the expression of IFNγ and the proliferation marker Ki67 in tumor-infiltrating CAR T cells when combined with α-4-1BB. Strikingly, α-4-1BB significantly reduced host immunosuppressive cells at the tumor site, including regulatory T cells and myeloid-derived suppressor cells, correlating with an increased therapeutic response. We conclude that α-4-1BB has a multifunctional role for enhancing CAR T-cell responses and that this combination therapy has high translational potential, given current phase I/II clinical trials with α-4-1BB against various types of cancer. Cancer Res; 77(6); 1296-309. ©2017 AACR.

Dual-specific Chimeric Antigen Receptor T Cells and an Indirect Vaccine Eradicate a Variety of Large Solid Tumors in an Immunocompetent, Self-antigen Setting

Purpose: While adoptive transfer of T cells bearing a chimeric antigen receptor (CAR) can eliminate substantial burdens of some leukemias, the ultimate challenge remains the eradication of large solid tumors for most cancers. We aimed to develop an immunotherapy approach effective against large tumors in an immunocompetent, self-antigen preclinical mouse model.Experimental Design: In this study, we generated dual-specific T cells expressing both a CAR specific for Her2 and a TCR specific for the melanocyte protein (gp100). We used a regimen of adoptive cell transfer incorporating vaccination (ACTIV), with recombinant vaccinia virus expressing gp100, to treat a range of tumors including orthotopic breast tumors and large liver tumors.Results: ACTIV therapy induced durable complete remission of a variety of Her2⁺ tumors, some in excess of 150 mm², in immunocompetent mice expressing Her2 in normal tissues, including the breast and brain. Vaccinia virus induced extensive proliferation of T cells, leading to massive infiltration of T cells into tumors. Durable tumor responses required the chemokine receptor CXCR3 and exogenous IL2, but were independent of IFNγ. Mice were resistant to tumor rechallenge, indicating immune memory involving epitope spreading. Evidence of limited neurologic toxicity was observed, associated with infiltration of cerebellum by T cells, but was only transient.Conclusions: This study supports a view that it is possible to design a highly effective combination immunotherapy for solid cancers, with acceptable transient toxicity, even when the target antigen is also expressed in vital tissues. Clin Cancer Res; 23(10); 2478-90. ©2016 AACR.

Abstract A104: Eradication of large solid tumors in immunocompetent mice using dual specific CAR T cells and vaccination

While adoptive cell transfer (ACT) using chimeric antigen receptor-expressing (CAR) T cells has led to remarkable complete responses in leukemia, complete responses of solid tumors in patients are few. Similarly, previous investigations in mice have demonstrated clearance of large burdens of disseminated cancer using CAR T cells, but large solid tumors (>1 cm2) have not responded fully. Here we report the generation of transgenic mice containing dual specific CAR T cells with specificity for Her2 and the melanoma-associated antigen pMEL (gp100), designated CARaMEL mice. In response to Her2-positive cancer cells, T cells from CARaMEL mice could secrete cytokines and engage in cytolysis mediated by an anti-Her2 CAR. Through their endogenous TCR, CARaMEL T cells could proliferate extensively in response to gp100. We demonstrate the ability of CARaMEL T cells in ACT incorporating vaccination (ACTIV) therapy to induce eradication of large tumors of various histologies, including orthotopic breast tumors, subcutaneous sarcoma and colon carcinoma liver tumors. Tumor models were performed in immunocompetent mice expressing human Her2 in normal brain and breast tissue. Effective ACTIV therapy included a lymphodepleting preparative regimen, ACT, high-dose IL-2 and recombinant vaccinia virus expressing gp100. ACTIV therapy was associated with expansion of dual-specific T cells and extensive tumor infiltration by CARaMEL T cells. Infiltration of CARaMEL T cells was also observed in normal tissues including brain. Long term surviving mice were totally resistant to rechallenge with Her2-expressing tumor cells, and partially resistant to Her2-negative tumor cells. We anticipate studies currently underway to provide mechanistic insight into the antitumor activity of ACTIV therapy.

Citation Format: Clare Y. Slaney, Jennifer A. Westwood, Paul A. Beavis, Phillip K. Darcy, Michael H. Kershaw. Eradication of large solid tumors in immunocompetent mice using dual specific CAR T cells and vaccination. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr A104.

Releasing the Brake on Oncolytic Viral Therapy

Oncolytic virus that selectively targets and eradicates tumor cells and immune checkpoint blockade that unleashes host antitumor immune responses show synergistic effects against cancer. This combination holds great promise for future treatment of a broad range of cancers in patients. Clin Cancer Res; 21(24); 5417-9. ©2015 AACR.See related article by Rojas et al., p. 5543.

Loss of Host Type-I IFN Signaling Accelerates Metastasis and Impairs NK-cell Antitumor Function in Multiple Models of Breast Cancer

Metastatic progression is the major cause of breast cancer-related mortality. By examining multiple syngeneic preclinical breast cancer models in mice lacking a functional type-I interferon receptor (Ifnar1(-/-) mice), we show that host-derived type-I interferon (IFN) signaling is a critical determinant of metastatic spread that is independent of primary tumor growth. In particular, we show that bone metastasis can be accelerated in Balb/c Ifnar1(-/-) mice bearing either 4T1 or 66cl4 orthotopic tumors and, for the first time, present data showing the development of bone metastasis in the C57Bl/6 spontaneous MMTV-PyMT-driven model of tumorigenesis. Further exploration of these results revealed that endogenous type-I IFN signaling to the host hematopoietic system is a key determinant of metastasis-free survival and critical to the responsiveness of the circulating natural killer (NK)-cell population. We find that in vivo-stimulated NK cells derived from wild-type, but not Ifnar1(-/-), mice can eliminate the 4T1 and 66cl4 breast tumor lines with varying kinetics in vitro. Together, this study indicates that the dysregulated immunity resulting from a loss of host type-I IFN signaling is sufficient to drive metastasis, and provides a rationale for targeting the endogenous type-I IFN pathway as an antimetastatic strategy.

Enhancing the efficacy of adoptive cellular therapy by targeting tumor-induced immunosuppression

Strategies aimed at stimulating the immune system against cancer have signaled a new era for designing new effective therapies for patients. Recent breakthroughs in adoptive cellular therapy and in using checkpoint inhibitors for some patients have renewed much enthusiasm in this field. However, it has become apparent that tumors can use a multitude of inhibitory networks to effectively reduce antitumor immunity. This review discusses our current knowledge of these immune suppressive mechanisms used by tumors and describes potential new strategies that may counteract this problem resulting in significantly increasing therapeutic outcomes of adoptive immunotherapy in a higher proportion of patients.

CD73: A potential biomarker for anti-PD-1 therapy

In our recent study, we show that tumoral CD73 expression limits the efficacy of anti-PD-1 therapy, and this is rescued by concomitant A_2A blockade. Since CD73 is known to be overexpressed in several human cancers and A_2A antagonists have undergone clinical trials for Parkinson's Disease, this combination warrants further investigation.

BMP4 inhibits breast cancer metastasis by blocking myeloid-derived suppressor cell activity

The TGFβ growth factor family member BMP4 is a potent suppressor of breast cancer metastasis. In the mouse, the development of highly metastatic mammary tumors is associated with an accumulation of myeloid-derived suppressor cells (MDSC), the numbers of which are reduced by exogenous BMP4 expression. MDSCs are undetectable in naïve mice but can be induced by treatment with granulocyte colony-stimulating factor (G-CSF/Csf3) or by secretion of G-CSF from the tumor. Both tumor-induced and G-CSF-induced MDSCs effectively suppress T-cell activation and proliferation, leading to metastatic enhancement. BMP4 reduces the expression and secretion of G-CSF by inhibiting NF-κB (Nfkb1) activity in human and mouse tumor lines. Because MDSCs correlate with poor prognosis in patients with breast cancer, therapies based on activation of BMP4 signaling may offer a novel treatment strategy for breast cancer. Cancer Res; 74(18); 5091-102. ©2014 AACR.

Trafficking of T cells into tumors

T cells are a crucial component of the immune response to infection and cancer. In addition to coordinating immunity in lymphoid tissue, T cells play a vital role at the disease site, which relies on their efficient and specific trafficking capabilities. The process of T-cell trafficking is highly dynamic, involving a series of distinct processes, which include rolling, adhesion, extravasation, and chemotaxis. Trafficking of T cells to the tumor microenvironment is critical for the success of cancer immunotherapies such as adoptive cellular transfer. Although this approach has achieved some remarkable responses in patients with advanced melanoma and hematologic malignancy, the success against solid cancers has been more moderate. One of the major challenges for adoptive immunotherapy is to be able to effectively target a higher frequency of T cells to the tumor microenvironment, overcoming hurdles associated with immunosuppression and aberrant vasculature. This review summarizes recent advances in our understanding of T-cell migration in solid cancer and immunotherapy based on the adoptive transfer of natural or genetically engineered tumor-specific T cells and discusses new strategies that may enhance the trafficking of these cells, leading to effective eradication of solid cancer and metastases.

The role of Type I interferons in immunoregulation of breast cancer metastasis to the bone

Breast cancer spread to distant sites is often incurable. Our recent findings demonstrate that Type I interferons secreted by tumor cells induce anti-metastatic immune responses that prevent breast cancer metastasis to the bone. This provides novel insights into the importance of the crosstalk between neoplastic and immune cells in the metastatic process.

Clinical application of genetically modified T cells in cancer therapy

Immunotherapies are emerging as highly promising approaches for the treatment of cancer. In these approaches, a variety of materials are used to boost immunity against malignant cells. A key component of many of these approaches is functional tumor-specific T cells, but the existence and activity of sufficient T cells in the immune repertoire is not always the case. Recent methods of generating tumor-specific T cells include the genetic modification of patient lymphocytes with receptors to endow them with tumor specificity. These T cells are then expanded in vitro followed by infusion of the patient in adoptive cell transfer protocols. Genes used to modify T cells include those encoding T-cell receptors and chimeric antigen receptors. In this review, we provide an introduction to the field of genetic engineering of T cells followed by details of their use against cancer in the clinic.

A modified superantigen rescues Ly6G- CD11b+ blood monocyte suppressor function and suppresses antigen-specific inflammation in EAE

In a previous study, we showed that the Ly6G(-)CD11b(+) blood monocytes residing in naïve mice are intrinsically immunosuppressive and that loss of this suppressive function may contribute to the development of autoimmunity in experimental autoimmune encephalomyelitis (EAE), a murine model of human multiple sclerosis. Here we report that mice treated with a modified superantigen coupled to myelin oligodendrocyte glycoprotein 35-55 (MOG(35-55)) peptide (DM-MOG(35-55)) suppressed the development of EAE. The treatment was associated with impaired MOG(35-55)-specific T cell proliferation and a decrease in IL-17 and IFNγ production in the draining lymph nodes. Analysis of circulating blood immune cells showed that the suppressor function of Ly6G(-)CD11b(+) blood monocytes was reduced in EAE mice, but was restored in mice treated with DM-MOG(35-55). Importantly, adoptive transfer of blood CD11b(+)Ly6G(-) cells isolated from DM-MOG(35-55)-treated mice protected recipient mice from developing EAE. Together, these results show that DM coupled to the auto-antigen MOG(35-55): 1) suppresses EAE via antigen-specific suppression of T cell responses, and 2) re-establishes suppressor function of Ly6G(-)CD11b(+) blood monocytes. Auto-antigens coupled to DM could therefore represent a new therapeutic approach for controlling inappropriate inflammation in autoimmune diseases such as multiple sclerosis by inducing antigen-specific T cell suppression.

The emerging role of immunosurveillance in dictating metastatic spread in breast cancer

It is now well known that the immune system can recognize transformed cells and control the initiation and growth of some cancers, a process termed tumor immunosurveillance. Key regulators of this process have been described in the primary tumor setting, where the balance of protumor and antitumor responses dictates tumor initiation and progression. Accumulating evidence suggests that immunosurveillance may also be critical for regulating metastatic spread, the most fatal aspect of cancer, and that mechanisms of overcoming immune control may be quite different from those at the primary site. Our recent findings support loss of type I interferon (IFN) signaling as a tumor-cell intrinsic mechanism of evading metastasis-specific immune responses in breast cancer. We revealed that type I IFN-induced innate (natural killer) and adaptive (CD8(+) T cell) responses suppressed bone metastatic growth and this was associated with decreased accumulation of immune suppressor cells (myeloid-derived suppressor cells). This review summarizes recent findings that are in support of tumor-induced immunosurveillance in regulating metastatic spread, including evidence that immune regulation of primary tumors may be distinct from those dictating metastasis.

Silencing of Irf7 pathways in breast cancer cells promotes bone metastasis through immune escape

Breast cancer metastasis is a key determinant of long-term patient survival. By comparing the transcriptomes of primary and metastatic tumor cells in a mouse model of spontaneous bone metastasis, we found that a substantial number of genes suppressed in bone metastases are targets of the interferon regulatory factor Irf7. Restoration of Irf7 in tumor cells or administration of interferon led to reduced bone metastases and prolonged survival time. In mice deficient in the interferon (IFN) receptor or in natural killer (NK) and CD8(+) T cell responses, metastasis was accelerated, indicating that Irf7-driven suppression of metastasis was reliant on IFN signaling to host immune cells. We confirmed the clinical relevance of these findings in over 800 patients in which high expression of Irf7-regulated genes in primary tumors was associated with prolonged bone metastasis-free survival. This gene signature may identify patients that could benefit from IFN-based therapies. Thus, we have identified an innate immune pathway intrinsic to breast cancer cells, the suppression of which restricts immunosurveillance to enable metastasis.

Naïve blood monocytes suppress T-cell function. A possible mechanism for protection from autoimmunity

In certain disease context, cells of the monocyte/macrophage lineage are known to exhibit T-cell suppressor function. However, whether naïve monocytes are also able to suppress T-cell responses has not been previously investigated. In this study, we have discovered that CD11b(+)Ly6G(-) mononuclear cells in the blood of naïve mice are potent suppressors of T-cell proliferation in vitro. The suppression of T-cell proliferation requires cell-cell contact and is partially dependent on nitric oxide production. Following the induction of experimental autoimmune encephalomyelitis in mice, the suppressor function of this blood CD11b(+)Ly6G(-) cell population is impaired. Therefore, blood CD11b(+)Ly6G(-) cells appear to be intrinsically suppressive and may have a key role in maintaining immune homoeostasis. Loss of this suppressive function may contribute to development of autoimmunity.