TGF-β broadly modifies rather than specifically suppresses reactivated memory CD8 T cells in a dose-dependent manner

Transforming growth factor β (TGF-β) directly acts on naive, effector, and memory T cells to control cell fate decisions, which was shown using genetic abrogation of TGF-β signaling. TGF-β availability is altered by infections and cancer; however, the dose-dependent effects of TGF-β on memory CD8 T cell (Tmem) reactivation are still poorly defined. We examined how activation and TGF-β signals interact to shape the functional outcome of Tmem reactivation. We found that TGF-β could suppress cytotoxicity in a manner that was inversely proportional to the strength of the activating TCR or proinflammatory signals. In contrast, even high doses of TGF-β had a comparatively modest effect on IFN-γ expression in the context of weak and strong reactivation signals. Since CD8 Tmem may not always receive TGF-β signals concurrently with reactivation, we also explored whether the temporal order of reactivation versus TGF-β signals is of importance. We found that exposure to TGF-β before or after an activation event were both sufficient to reduce cytotoxic effector function. Concurrent ATAC-seq and RNA-seq analysis revealed that TGF-β altered ~10% of the regulatory elements induced by reactivation and also elicited transcriptional changes indicative of broadly modulated functional properties. We confirmed some changes on the protein level and found that TGF-β-induced expression of CCR8 was inversely proportional to the strength of the reactivating TCR signal. Together, our data suggest that TGF-β is not simply suppressing CD8 Tmem but modifies functional and chemotactic properties in context of their reactivation signals and in a dose-dependent manner.

Overcoming AML T cell therapy barriers with engineered proteins

Leukemia is the most common pediatric cancer and the second leading cause of cancer deaths in children. Adoptive cell therapy (ACT) has been validated in pediatric B cell acute lymphoblastic leukemia, where engineered cancer-targeting T cells can effectively eradicate tumor and tumor recurrence, generally more safely than drug and radiation therapy. However, ACT is not approved for patients with pediatric AML, other leukemias or solid tumors. Of note, pediatric AML patients have a worse 5-year survival rate than ALL.

AML cells can severely diminish ACT efficacy by expressing ligands that activate T cell inhibitory receptors and by downregulating costimulatory ligand expression. To address these issues, we developed fusion proteins that combine the ectodomain of an inhibitory T cell receptor with an intracellular costimulatory signaling domain. We have shown that this effectively “replaces a brake with an accelerator” in CD8 T cells, and have now developed FPs with different costimulatory domains to confer different attributes to T cells. Despite improved outcomes with single FP T cell therapy, we hypothesized that combining differently costimulated T cells would provide a synergistically diverse T cell response and improve outcomes. We tested 1:1 pairwise combinations of differently costimulated T cells that are also transduced with a tumor-specific TCR in serial killing over-time (SKO) assays and in vivo persistence studies. In survival studies, dual T cell therapy resulted in enhanced survival. We propose that a synergistically diverse T cell therapy provides enhanced antitumor efficacy over a monogenic cell product.

Engineering adoptive T cell therapy to co-opt Fas ligand-mediated death signaling in ovarian cancer enhances therapeutic efficacy

Background

In the USA, more than 50% of patients with ovarian cancer die within 5 years of diagnosis, highlighting the need for therapeutic innovations. Mesothelin (MSLN) is a candidate immunotherapy target; it is overexpressed by ovarian tumors and contributes to malignant/invasive phenotypes, making tumor antigen loss disadvantageous. We previously showed that MSLN-specific T cell receptor (TCR)-engineered T cells preferentially accumulate within established tumors, delay tumor growth, and significantly prolong survival in the ID8_VEGF mouse model that replicates many aspects of human disease. However, T cell persistence and antitumor activity were not sustained. We therefore focused on Fas/FasL signaling that can induce activation-induced cell death, an apoptotic mechanism that regulates T cell expansion. Upregulation of FasL by tumor cells and tumor vasculature has been detected in the tumor microenvironment (TME) of human and murine ovarian cancers, can induce apoptosis in infiltrating, Fas (CD95) receptor-expressing lymphocytes, and can protect ovarian cancers from tumor-infiltrating lymphocytes.

Methods

To overcome potential FasL-mediated immune evasion and enhance T cell responses, we generated an immunomodulatory fusion protein (IFP) containing the Fas extracellular binding domain fused to a 4-1BB co-stimulatory domain, rather than the natural death domain. Murine T cells were engineered to express an MSLN-specific TCR (TCR₁₀₄₅), alone or with the IFP, transferred into ID8_VEGF tumor-bearing mice and evaluated for persistence, proliferation, cytokine production and efficacy. Human T cells were similarly engineered to express an MSLN-specific TCR (TCR₅₃₀) alone or with a truncated Fas receptor or a Fas-4-1BB IFP and evaluated for cytokine production and tumor lysis.

Results

Relative to murine T cells expressing only TCR₁₀₄₅, T cells expressing both TCR₁₀₄₅ and a Fas-4-1BB IFP preferentially persisted in the TME of tumor-bearing mice, with improved T cell proliferation and survival. Moreover, TCR₁₀₄₅/IFP⁺ T cells significantly prolonged survival in tumor-bearing mice, compared with TCR₁₀₄₅-only T cells. Human T cells expressing TCR₅₃₀ and a Fas-4-1BB IFP exhibit enhanced functional activity and viability compared with cells with only TCR₅₃₀.

Conclusions

As many ovarian tumors overexpress FasL, an IFP that converts the Fas-mediated death signal into pro-survival and proliferative signals may be used to enhance engineered adoptive T cell therapy for patients.

A Fas-4-1BB fusion protein converts a death to a pro-survival signal and enhances T cell therapy

Adoptive T cell therapy (ACT) with genetically modified T cells has shown impressive results against some hematologic cancers, but efficacy in solid tumors can be limited by restrictive tumor microenvironments (TMEs). For example, Fas ligand is commonly overexpressed in TMEs and induces apoptosis in tumor-infiltrating, Fas receptor–positive lymphocytes. We engineered immunomodulatory fusion proteins (IFPs) to enhance ACT efficacy, combining an inhibitory receptor ectodomain with a costimulatory endodomain to convert negative into positive signals. We developed a Fas-4-1BB IFP that replaces the Fas intracellular tail with costimulatory 4-1BB. Fas-4-1BB IFP-engineered murine T cells exhibited increased pro-survival signaling, proliferation, antitumor function, and altered metabolism in vitro. In vivo, Fas-4-1BB ACT eradicated leukemia and significantly improved survival in the aggressive KPC pancreatic cancer model. Fas-4-1BB IFP expression also enhanced primary human T cell function in vitro. Thus, Fas-4-1BB IFP expression is a novel strategy to improve multiple T cell functions and enhance ACT against solid tumors and hematologic malignancies.

Engineering adoptive T cell therapy to co-opt Fas ligand-mediated death signaling in solid tumors

Over half of patients diagnosed with high grade serous ovarian cancer will die within five years, highlighting the need for therapy innovation. Engineering T cells to target proteins uniquely overexpressed in tumors has the potential to limit tumor growth without toxicity—mesothelin (Msln) is a rational immunotherapy target as it contributes to the malignant/invasive phenotype and has limited expression in healthy cells. T cells were engineered to express a high-affinity Msln-specific T cell receptor (TCRMsln) and adoptively transferred into a disseminated ID8VEGF murine model, which recapitulates many features of human ovarian cancer. TCRMsln+ T cells preferentially accumulated within established tumors, delayed tumor growth, and significantly prolonged survival. However, T cell persistence and anti-cancer activity were limited by elements in the tumor microenvironment (TME), including Fas Ligand (FasL) that can induce apoptosis in infiltrating lymphocytes expressing Fas receptor (Fas).

To overcome this potential T cell evasion mechanism, we generated a panel of immunomodulatory fusion proteins (IFPs) containing the Fas extracellular binding domain fused to a co-stimulatory domain, replacing the natural death domain. Relative to T cells modified with only TCRMsln, T cells that expressed both TCRMsln and a Fas IFP preferentially infiltrated tumors and expanded/persisted in the TME of tumor-bearing mice. Moreover, adoptive immunotherapy with TCRMsln+IFP+ T cells significantly prolonged survival in tumor-bearing mice, relative to TCRMsln+ only T cells. As many solid tumors overexpress FasL, IFPs may provide an opportunity to enhance engineered adoptive T cell therapy against many malignancies.

Abstract I11: Targeting pancreatic cancer with TCR-engineered T cells

We have been exploring in preclinical models and clinical trials methods to reproducibly provide therapeutic T-cell responses by transfer of genetically engineered T cells. Our largest clinical experience has been in treating human acute myelogenous leukemia (AML), in which we have utilized a high-affinity TCR specific for WT1, a protein associated with promoting leukemic transformation that is overexpressed in human leukemic stem cells, to genetically engineer CD8 T cells. We recently reported a study (Chapuis et al., Nat Med 2019) in which we treated leukemia patients at high risk of relapse (after hematopoietic cell transplant) that demonstrated all treated patients remain alive and relapse free at a median of 48 months, compared to a relapse rate of ~35% in the concurrent matched cohort (p<0.01). We have also been developing strategies to translate insights and technologies from this study to treatment of solid tumors. In a preclinical genetically engineered mouse model (KPC mice) of pancreatic cancer that faithfully replicates most aspects of human disease, we demonstrated (Stromnes et al., Cancer Cell 2015) that CD8 T cells engineered with a high-affinity TCR specific for mesothelin (Msln) can infiltrate pancreatic tumors, mediate antitumor activity, and provide therapeutic benefit. However, since the T cells are ultimately rendered dysfunctional in the tumor microenvironment (TME), prolonging survival has required repeated infusions of T cells to sustain antitumor activity. We have now isolated and validated a human high-affinity TCR specific for Msln for use in a planned clinical trial modeled after the approach successful in KPC mice. However, we would like to both enhance and sustain antitumor activity without requiring repeated infusions. In-depth analyses of the T cells, tumors, and the TME in treated KPC mice have illuminated strategies to potentially overcome the obstacles to tumor eradication, and we have been exploring molecular engineering approaches to achieve this. One approach has been to create synthetic immunomodulatory fusion proteins (IFPs) that have an ectodomain composed of the receptor for an inhibitory ligand encountered in the TME but, rather than the natural cytoplasmic tail that would deliver an inhibitory signal, the receptor has the tail of a costimulatory receptor and delivers an activation signal. Expression of such IFPs takes advantage of the inhibitory ligands commonly encountered in the TME by T cells by co-opting potential inhibitory signals and has resulted in enhanced T cell function, persistence/survival, and antitumor activity. Another major obstacle to sustained therapeutic activity appears to be the limited access in the TME to nutrients that effector T cells can utilize as an energy source. Analysis of the metabolites present in the TME and the transcriptional program in T cells has provided insights into genetic modifications that can be made to allow T cells to survive and function in the metabolically hostile TME. These and related studies will be discussed.

Citation Format: Philip D. Greenberg, Kristin G. Anderson, Dan Egan, Sunil R. Hingorani, Luigi Nezi, Teresa Manzo, Shannon K. Oda, Kelly G. Paulson, Rachel Perret, Leah Schmidt, Tom M. Schmitt, Ingunn M. Stromnes, Aude G. Chapuis. Targeting pancreatic cancer with TCR-engineered T cells [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr I11.

Engineered Adoptive T-cell Therapy Prolongs Survival in a Preclinical Model of Advanced-Stage Ovarian Cancer

Adoptive T-cell therapy using high-affinity T-cell receptors (TCR) to target tumor antigens has potential for improving outcomes in high-grade serous ovarian cancer (HGSOC) patients. Ovarian tumors develop a hostile, multicomponent tumor microenvironment containing suppressive cells, inhibitory ligands, and soluble factors that facilitate evasion of antitumor immune responses. Developing and validating an immunocompetent mouse model of metastatic ovarian cancer that shares antigenic and immunosuppressive qualities of human disease would facilitate establishing effective T-cell therapies. We used deep transcriptome profiling and IHC analysis of human HGSOC tumors and disseminated mouse ID8_VEGF tumors to compare immunologic features. We then evaluated the ability of CD8 T cells engineered to express a high-affinity TCR specific for mesothelin, an ovarian cancer antigen, to infiltrate advanced ID8_VEGF murine ovarian tumors and control tumor growth. Human CD8 T cells engineered to target mesothelin were also evaluated for ability to kill HLA-A2⁺ HGSOC lines. IHC and gene-expression profiling revealed striking similarities between tumors of both species, including processing/presentation of a leading candidate target antigen, suppressive immune cell infiltration, and expression of molecules that inhibit T-cell function. Engineered T cells targeting mesothelin infiltrated mouse tumors but became progressively dysfunctional and failed to persist. Treatment with repeated doses of T cells maintained functional activity, significantly prolonging survival of mice harboring late-stage disease at treatment onset. Human CD8 T cells engineered to target mesothelin were tumoricidal for three HGSOC lines. Treatment with engineered T cells may have clinical applicability in patients with advanced-stage HGSOC.

Abstract IA17: Utilizing synthetic biology and high-dimensional probing to address therapeutic obstacles and empower engineered T cells with the capacity to eradicate tumors

We have been exploring in preclinical models and clinical trials methods to reproducibly provide therapeutic T cell responses by transfer of genetically engineered T cells. Our largest clinical experience is in treating human Acute Myelogenous Leukemia (AML). After identifying that WT1, a gene associated with promoting leukemic transformation, is over-expressed in human leukemic stem cells, and demonstrating in a clinical trial that in vitro expanded WT1-specific CD8 T cell clones can be safely transferred, exhibit anti-leukemic activity, and provide therapeutic benefit to AML patients, we extensively screened normal human repertoires and isolated a high affinity TCR specific for WT1 for genetically engineering CD8 T cells to reproducibly create cells with high avidity for leukemic cells. We have initially pursued this strategy in a 2 Arm trial for leukemia patients either at high risk of relapse (Arm 1) after hematopoietic cell transplant (HCT) or who have already relapsed after HCT (Arm 2). The prophylactic arm is now completed, with very encouraging results- all patients treated with engineered T cells remain alive and relapse free at a median of 38 months, compared to a relapse rate of ~50% in a concurrent matched cohort. Results in relapsed patients (Arm 2) have been less effective, and we have used high-dimensional analyses including single cell RNAseq both to elucidate the reasons for failure to eradicate the leukemia and to design strategies to overcome these obstacles. Our results have identified several mechanisms by which the leukemia escapes, and we have been testing approaches that employ further genetic modification of the T cells to enhance efficacy. The predominant reason for leukemia progression despite targeted therapy with T cells is the inability of the T cells to persist and maintain function in the context of encountering a rapidly proliferating myeloid leukemia. This reflects both engagement of pathways inhibitory to T cells by the leukemic cells, and apoptosis of the T cells from repetitive stimulation. We are addressing this issue by creating immuno-modulatory fusion proteins (IFPs) that have the ectodomain of an inhibitory or death receptor fused to a survival costimulatory domain. Results with two such IFPs will be discussed, a CD200R/CD28 fusion that binds the inhibitory ligand CD200 commonly expressed on leukemic cells but provides a CD28 costimulatory signal and a Fas/4-1BB fusion that binds FasL but rather than induce death promotes proliferation and survival. A more uncommon reason explaining progression is loss of expression of the WT1 epitope being targeted. This has occurred in 2 patients, but for distinct reasons. In one patient this reflected loss of a component of the immunoproteasome, and we have now isolated a TCR that recognizes an epitope not dependent on the immunoproteasome. In a second patient the level of WT1 expression declined- interestingly, this patient was treated with Vidaza, which can increase expression of WT1, and post-Vidaza the transferred T cells persisting in the patient’s bone marrow recognized and responded in vivo to the relapsing leukemia. The approaches and technologies we are developing and testing in leukemia are also applicable to solid tumors, and preclinical studies in pancreatic and ovarian cancers will be discussed.

Citation Format: Kristin G. Anderson, Dan Egan, Sunil R. Hingorani, Shannon K. Oda, Kelly Paulson, Rachel Perret, Leah Schmidt, Thomas Schmitt, Ingunn Stromnes, Aude Chapuis, Philip D. Greenberg. Utilizing synthetic biology and high-dimensional probing to address therapeutic obstacles and empower engineered T cells with the capacity to eradicate 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 IA17.

Abstract IA02: Engineering T cells to eradicate tumors in the age of synthetic biology

Unlike cancer vaccines and immune modulators such as checkpoint inhibitors that seek to harness patient immune responses, adoptive therapy with genetically engineered T cells seeks to create responses that don’t exist in the patient’s immune system. Molecular technologies now make it feasible to not only create T cells with specificity for the tumor by introduction of a selected antigen-specific receptor, but also with qualities not naturally found, including improved function and resistance to immunosuppression. We have been exploring in preclinical models and clinical trials methods to reproducibly provide therapeutic T cell responses by transfer of genetically engineered T cells. For human acute myelogenous leukemia (AML), we have pursued targeting WT1, a gene overexpressed in human leukemic stem cells that is associated with promoting leukemic transformation. Preclinical studies performed in a mouse model demonstrated that CD8 T cells expressing a high affinity TCR specific for this oncogene can be safely administered, with no evidence of toxicity to the normal tissues known to express low but detectable levels of WT1. We have advanced this approach to a clinical trial in leukemia patients with poor prognostic factors that place them at high risk of relapse after hematopoietic cell transplant (HCT), using a high-affinity human TCR specific for WT1 to transduce CD8 cells and reproducibly create high-avidity T cells that recognize leukemic cells. Our clinical results demonstrate that such T cells can prevent leukemic relapse and sustain long-term remissions, and can mediate antileukemic activity in patients who have relapsed. This therapy is now being tested in AML patients who have minimal residual disease after induction therapy and are not candidates for HCT, as well as in solid tumors that similarly overexpress WT1.

Unfortunately, there are substantive obstacles in targeting established tumors that can preclude even a T cell expressing a high-affinity TCR from being effective. These impediments include the development of T cell dysfunction, particularly within the microenvironment of solid tumors, and we are using genetically engineered mouse models to elucidate the cellular and molecular pathways that need to be modulated to achieve meaningful therapeutic benefit in a variety of hematologic and solid tumor settings, including pancreatic and ovarian cancer. Our preclinical therapy studies reveal promising antitumor activity, but demonstrate that repeated infusions of functional T cells are required to sustain a therapeutic response in the context of the immunosuppressive tumor microenvironment, and we are engineering T cells to overcome these inhibitory signals and enhance efficacy. In place of current strategies that disrupt inhibitory pathways by systemic administration of blocking mAbs, which globally disrupt immune regulation and thus can have significant toxicity to the host, we are creating synthetic immunomodulatory fusion proteins that take advantage of the expression of inhibitory ligands by tumors by still binding the inhibitory ligand but alternatively delivering a costimulatory rather than inhibitory signal. Additionally, as the antitumor activity of CD8 T cells is enhanced by a concurrent CD4 T cell response, we are engineering CD4 T cells as well as CD8 T cells to create an orchestrated antitumor response. The results suggest that cancer therapy with engineered T cells can provide effective antitumor responses and will likely find an increasing role in the treatment of human cancers.

Citation Format: Philip D. Greenberg, Kristin G. Anderson, Dan Egan, Sunil R. Hingorani, Shannon K. Oda, Rachel Perret, Tom M. Schmitt, Ingunn M. Stromnes, Leah Schmidt, Aude G. Chapuis. Engineering T cells to eradicate tumors in the age of synthetic biology [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr IA02.

Cheating death: a Fas-41BB immunomodulatory fusion protein obviates a death signal to enhance T cell function and adoptive therapy targeting leukemia and solid tumors

Fas/FasL signaling plays a significant role in the generation and persistence of tumors. We and others have detected FasL expression in the tumor microenvironment (TME) of human ovarian, pancreatic, and other cancers, where it can function to protect tumor cells from tumor-infiltrating lymphocytes. Adoptive immunotherapy, a promising treatment option, uses genetically modified T cells to eliminate tumors. However, efficacy of T cell immunotherapy is dampened by limited costimulation as well as increased inhibitory and death signals in the TME. We previously showed enhanced therapeutic efficacy by engineering T cells to express an immunomodulatory fusion protein (IFP) to convert the inhibitory CD200R signal to a costimulatory CD28 signal and questioned if IFPs could use a 4-1BB signal to enhance in vivo persistence and memory formation. 4-1BB forms a trimer when binding its ligand, that is requisite for an effective costimulatory signal. We and others engineered T cells to express 4-1BB with an ectodomain that dimerizes, however this IFP did not improve T cell function. We hypothesized a Fas IFP with a 4-1BB signal would effectively replace Fas signaling and provide costimulation, as Fas also trimerizes when engaged by ligand. T cells transduced with the Fas-4-1BB IFP exhibited enhanced accumulation and function in vitro. In a model of leukemia, Fas-4-1BB-transduced T cells eradicated otherwise lethal disease and exhibited increased persistence. Preliminary data in the autochthonous KPC pancreatic and ID8 ovarian cancer models support increased efficacy. We describe for the first time that an IFP can generate an effective 4-1BB signal to overcome obstacles in the TME and enhance T cell immunotherapy of solid and liquid malignancies.

Abstract IA01: Engineering T cell responses to tumors: Taking the immune system where no responses have gone before

We have entered a new and exciting era in cancer therapy, in which immunotherapeutic strategies are achieving unprecedented successes and are increasingly becoming incorporated into standard of care regimens. Checkpoint blockade is dependent on inducing and/or reactivating or sustaining responses to the tumor by T cells already in the patient. Similarly, vaccines attempt to generate and/or expand responses of T cells naturally present in the normal repertoire. However, these strategies require that functional tumor-reactive T cells exist in the patient's repertoire and that the method pursued can harness those T cells to create a potent response that will function in the tumor microenvironment, which limits the settings in which these approaches will prove effective. Adoptive T cell therapy, in which patient T cells can be expanded to large numbers ex vivo before infusion, provides a means to bypass or overcome these obstacles, particularly with the advent of genetic engineering that now makes it possible to create T cells not only with specificity for the tumor but also with qualities not naturally found, including improved function and resistance to immunosuppression. We have been exploring in preclinical models and clinical trials methods to reproducibly provide therapeutic T cell responses by transfer of genetically engineered T cells. The first issue is to identify tumor antigens that can be safely, effectively, and reproducibly targeted. We have used analyses of differential gene expression to search for antigenic targets that are either uniquely expressed in a tumor or are differentially expressed at high levels in the tumor with much lower and limited expression in normal tissues, and that preferentially are associated with the malignant phenotype to reduce the risk of antigen loss by the tumor. In our search for targets in acute myelogenous leukemia (AML), we found that WT1, a gene known to be associated with promoting leukemic transformation, is expressed in comparative abundance in human leukemic stem cells. The next step is to generate T cells specific for the target antigen that can recognize and eliminate malignant cells expressing the antigen. Extensive screening of normal human repertoires revealed a high affinity TCR specific for WT1 that can recognize leukemic cells, and that could be inserted into CD8 T cells to reproducibly produce high avidity T cells for use in therapy. Preclinical studies performed in a mouse model demonstrated that CD8 T cells specific for this oncogene expressing a high affinity TCR can be safely administered, with no evidence of toxicity to the normal tissues known to express low but detectable levels of WT1. We have advanced this approach targeting WT1 to an initial clinical trial in leukemia patients with poor prognostic factors that make them at high risk of relapse after hematopoietic cell transplant (HCT). The Vα and Vβ genes of the human WT-1 specific TCR were codon optimized to enhance expression, modified by a point mutation in each chain to create an interchain disulfide bond that minimizes the potential problem of mispairing of the introduced TCR chains with the endogenous TCR chains, and inserted these TCR genes into a lentiviral vector. Preliminary results of this trial, which has provided evidence that such T cells can prevent leukemic relapse and sustain long-term remissions, will be discussed. This therapy is now being advanced for use in AML patients who are not HCT candidates. We have also now initiated additional trials with this TCR for treatment of patients with non-small cell lung cancer (NSCLC) or mesothelioma, as WT1 is commonly overexpressed in NSCLC as well as many other malignancies. For many candidate target antigens that are also normal self-antigens, isolation of high affinity TCRs may not be readily achieved from normal repertoires. However, it is now feasible to engineer TCRs that have higher affinities than normally exist for their antigen target. We have developed strategies to enhance the affinity of isolated TCRs with retention of specificity, including saturation mutagenesis of CDR3 regions and an in vitro thymic selection system that allows for capture of a more diverse set of high affinity specific TCRs during TCR gene rearrangement. These approaches induce modifications to the TCR region that predominantly makes contacts with the peptide epitope rather than MHC, which is necessary to minimize the risk of off-target toxicity from promiscuous peptide/MHC recognition. However, it remains essential that such modified TCRs do not induce unanticipated tissue damage, and we are using bioinformatics, functional screening, and modeling in the mouse to uncover any potential for off-target toxicity. Unfortunately, providing a high avidity T cell response does not necessarily result in tumor eradication, as there are other substantive obstacles that can preclude even a T cell expressing a high affinity TCR from being effective. These impediments include the development of T cell dysfunction, particularly within the microenvironment of solid tumors, and we are using genetically engineered mouse models to elucidate the cellular and molecular pathways that need to be modulated to achieve meaningful therapeutic benefit in a variety of solid tumor settings, including pancreatic and ovarian cancer. Our preclinical therapy studies, particularly in a pancreatic ductal adenocarcinoma (PDA) model, already appear very promising, as we have demonstrated that T cells expressing a high affinity TCR targeting a tumor antigen expressed by PDA cells can infiltrate the tumor, mediate tumor lysis, modify the tumor stroma, and provide therapeutic benefit. We have now identified high affinity human TCRs specific for this tumor antigen, and plan to use the insights derived from these studies to initiate within the next year clinical trials in human pancreatic and ovarian cancers. The genetically-engineered mouse models of spontaneously developing tumors we are using, which recapitulate many aspects of the analogous human cancer, are also making it possible to assess strategies to improve the efficacy of T cell therapy. These models have helped elucidate the importance of not only cell extrinsic mechanisms of regulation and dysfunction that render T cells unresponsive, particularly via inhibitory cells commonly present in the tumor microenvironment that interfere with an effector response, such as the accumulation of regulatory CD4 T cells (Treg), myeloid derived suppressor cells (MDSC), and tumor-associated macrophages (TAM), but also the cell intrinsic mechanisms that derive in large part from persistent stimulation by the tumor antigen and ultimately can render T cells progressively dysfunctional, leading to epigenetic modifications that eventuallly result in non-responsive cells that cannot be readily rescued. These cumulative mechanisms highlight the difficulties eliciting and/or sustaining responses to tumor antigens. Strategies to disrupt inhibitory pathways by systemic administration of mAbs or cytokines are currently being pursued clinically, but such reagents globally disrupt inhibitory pathways and thus can have significant toxicity to the host. Therefore, we are evaluating strategies to sustain function and anti-tumor activity by genetically modifying T cells to enhance function and to be resistant to obstacles that prevent tumor eradication. As different tumor types exhibit unique characteristics and are capable of engaging distinct inhibitory pathways, improved understanding of the immunobiology of the tumor type to be treated will likely prove essential for designing effective therapies. However, the relatively straightforward means to use synthetic biology to genetically engineer T cells to acquire novel capacities to overcome inhibitory signals and function in the tumor microenvironment suggests that cancer therapy with engineered T cells will likely find an increasing role in the treatment of human cancers.

Citation Format: Philip D. Greenberg, Kristin G. Anderson, Dan Egan, Sunil R. Hingorani, Shannon K. Oda, Rachel Perret, Andrea Schietinger, Tom M. Schmitt, Ingunn M. Stromnes, Alec Wilkens, Aude G. Chapuis. Engineering T cell responses to tumors: Taking the immune system where no responses have gone before [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr IA01.

Expression of a CD200-targeted chimeric costimulatory receptor enhances T cell effector function and adoptive immunotherapy of disseminated leukemia

CD200 (OX2) is an immunosuppressive surface protein upregulated in leukemia and other malignancies, with expression associated with inhibition of antitumor T cell responses and decreased overall survival of patients. Our lab has developed several T cell receptors (TCR) to target intracellular antigens upregulated in malignancies and we questioned if the efficacy of TCR gene therapy could be improved by co-opting CD200 inhibition with a CD200R-CD28 immunomodulatory fusion protein (IFP) that could potentially convert CD200/CD200R signaling into a costimulatory signal. T cells transduced with CD200R-CD28 exhibited enhanced proliferation, accumulation, and effector function in response to CD200+ target cells in vitro. Repeated restimulation with irradiated CD200+ tumor cells enriched the cells transduced with the IFP compared to wild type T cells. The CD200R-CD28 transduced T cells also exhibited enhanced killing of CD200+ compared to CD200− tumor cells. In adoptive therapy of disseminated leukemia, CD200R-CD28-transduced tumor-specific T cells eradicated otherwise lethal disease without a requirement for IL-2 administration to sustain in vivo persistence. Comparison of IFPs with CD28, 4-1BB, and CD28/4-1BB dual costimulatory domains suggested the CD28 signaling domain provides the most significant enhancement of anti-tumor activity. Additionally, modification of the IFP ectodomain length revealed the importance of optimizing the tumor-T cell distance for costimulatory signaling. Transduction of human primary T cells with the equivalent human IFP also resulted in increased proliferation and cytokine production in response to CD200+ leukemia cells, supporting clinical translation of this strategy.

Lysophosphatidic acid inhibits CD8 T cell activation and control of tumor progression

CD8 T lymphocytes are able to eliminate nascent tumor cells through a process referred to as immune surveillance. However, multiple inhibitory mechanisms within the tumor microenvironment have been described that impede tumor rejection by CD8 T cells, including increased signaling by inhibitory receptors. Lysophosphatidic acid (LPA) is a bioactive lysophospholipid that has been shown repeatedly to promote diverse cellular processes benefiting tumorigenesis. Accordingly, the increased expression of LPA and LPA receptors is a common feature of diverse tumor cell lineages and can result in elevated systemic LPA levels. LPA is recognized by at least 6 distinct G-protein-coupled receptors and several of which are expressed by T cells, although the precise role of LPA signaling in CD8 T cell activation and function has not been defined. Here, we demonstrate that LPA signaling via the LPA5 receptor expressed by CD8 T cells suppresses antigen receptor signaling, cell activation and proliferation in vitro and in vivo. Importantly, in a mouse melanoma model tumor-specific CD8 T cells that are LPA5-deficient are able to control tumor growth significantly better than wild-type tumor-specific CD8 T cells. Together, these data suggest that the production of LPA by tumors serves not only in an autocrine manner to promote tumorigenesis but also as a mechanism to suppress adaptive immunity and highlights a potential novel target for cancer treatment.

Abstract SY31-03: Employing TCRs in engineered T cells to develop therapeutic reagents for effectively targeting malignancies

Effective cellular therapy for human malignancies requires first identifying and validating an appropriate antigenic target, and then establishing in each patient a tumor-reactive T cell response of high avidity and high magnitude that is safe and can infiltrate and retain function in the tumor microenvironment. We have been exploring in preclinical models and clinical trials methods to reproducibly provide such responses by transfer of genetically engineered T cells that acquire target specificity by virtue of an introduced high affinity TCR. To identify candidate antigens in leukema, we examined purified human leukemic stem cells for over-expression of genes based on comparisons to purified human hematopoietic stem cells as well as normal somatic tissues. Our analysis revealed that WT1, a gene known to be associated with promoting leukemic transformation, is expressed in comparative abundance in human leukemic stem cells. Preclinical studies were then performed in a mouse model, and revealed that CD8 T cells specific for this oncogene with even higher avidity than can be detected in normal repertoires could be safely administered, with no evidence of toxicity to the normal tissues known to express low but detectable levels of WT1. For our initial clinical trial, poor prognosis leukemia patients who relapsed after hematopoietic cell transplant (HCT) were treated with transfer of WT1-specific CD8 T cells clones isolated and expanded in vitro from the HCT donor. This study demonstrated that such T cells were safe, mediated in vivo anti-leukemic activity, and were associated with maintenance of long-term remissions in some patients, but generating sufficient numbers of WT1-specific CD8 T cells with high avidity for the target in each patient represented a substantive problem. Therefore, to create a more predictably effective standardized reagent for treatment of patients with a tumor that expresses the target antigen and shares the associated MHC restricting allele, we pursued methods to genetically engineer patient T cells to acquire high avidity for the tumor target. This requires identifying a high affinity TCR and producing a vector that can achieve high-level expression of the genes encoding the Vα and Vβ genes of a TCR demonstrated to have high affinity for the target epitope. Therefore, we screened a large number of normal repertoires for the presence of high avidity WT1-specific CD8 T cells, and selected the T cell clone expressing the highest affinity TCR. We then incorporated changes in the TCR genes such as codon optimization to enhance expression, and introduced a point mutation in each chain to create a disulfide bond that minimizes the potential problem of mispairing of the introduced TCR chains with the endogenous TCR chains. We have now have now initiated a trial in which this high affinity, WT1-specific, HLA-A2-restricted TCR is being introduced into patient CD8 T cells with a lentiviral vector and the transduced cells are being infused into the patient. The early results from this trial appear promising in terms of both evidence of antileukemic activity and the capacity for the transferred cells to persist in patients, and we plan to begin very shortly another trial in patients with non-small cell lung cancer (NSCLC) utilizing this same TCR, as WT1 is also commonly overexpressed in NSCLC as well as many other malignancies.

For many candidate target antigens that are also normal self-antigens, isolating high affinity TCRs may not be readily achieved from normal repertoires. Therefore, we have developed strategies to enhance the affinity of isolated TCRs with retention of specificity, including saturation mutagenesis of CDR3 regions and an in vitro thymic selection system that allows for capture of a more diverse set of high affinity specific TCR genes during TCR gene rearrangement. These approaches induce modifications to the TCR region that predominantly makes contacts with the peptide epitope rather than MHC, which is necessary to minimize the risk of off-target toxicity from promiscuous peptide/MHC recognition. However, it remains essential that such modified TCRs do not induce unanticipated tissue damage, and we are using bioinformatics as well as modeling in the mouse to uncover any potential for off-target toxicity.

Unfortunately, providing a high avidity T cell response does not necessarily result in tumor eradication, as there are other substantive obstacles that can preclude even a T cell expressing a high affinity TCR from being effective. These impediments include the development of T cell dysfunction, particularly within the microenvironment of solid tumors, and we are using genetically engineered mouse models to elucidate the cellular and molecular pathways that need to be modulated to achieve meaningful therapeutic benefit in a variety of solid tumor settings, including pancreatic and ovarian cancer. Our preclinical therapy studies, particularly in a pancreatic ductal adenocarcinoma (PDA) model, already appear very promising, as we have demonstrated that T cells expressing a high affinity TCR targeting a tumor antigen expressed by PDA cells can infiltrate the tumor, mediate tumor lysis, modify the tumor stroma, and provide therapeutic benefit. We have already identified high affinity human TCRs specific for this tumor antigen, and plan to use the insights derived from these studies to initiate within the next 1-2 years clinical trials in human pancreatic and ovarian cancers.

The genetically-engineered mouse models of spontaneously developing tumors we are using, which recapitulate many aspects of the analogous human cancer, are also making it possible to assess strategies to improve the efficacy of T cell therapy. These models have helped elucidate the importance of not only cell extrinsic mechanisms of regulation and dysfunction that render T cells unresponsive, particularly via inhibitory cells commonly present in the tumor microenvironment that interfere with an effector response such as the accumulation of regulatory CD4 T cells (Treg), myeloid derived suppressor cells (MDSC), and tumor-associated macrophages (TAM), but also the cell intrinsic mechanisms that derive in large part from persistent stimulation by the tumor antigen and ultimately can render T cells progressively dysfunctional, leading to epigenetic modifications that eventually result in non-responsive cells that cannot be readily rescued. These cumulative mechanisms highlight the difficulties eliciting and/or sustaining responses to tumor antigens. Strategies to disrupt inhibitory pathways by systemic administration of mAbs or cytokines are currently being pursued clinically, but such reagents globally disrupt inhibitory pathways which can have significant toxicity to the host. Therefore, we are evaluating strategies to sustain function and anti-tumor activity by genetically modifying T cells to enhance function and to be resistant to obstacles that prevent tumor eradication. As different tumor types exhibit unique characteristics and are capable of engaging distinct inhibitory pathways, improved understanding of the immunobiology of the tumor type to be treated will likely prove essential for designing effective therapies. However, the relatively straightforward means to use synthetic biology to genetically engineer T cells to acquire novel capacities to overcome inhibitory signals and function in the tumor microenvironment suggests that cancer therapy with engineered T cells will likely find an increasing role in the treatment of human cancers.

Citation Format: Philip D. Greenberg, Tom M. Schmitt, Andrea Schietinger, Ingunn M. Stromnes, Sunil R. Hingorani, Shannon K. Oda, Rachel Perret, Kristin G. Anderson, Merav Bar, Aude G. Chapuis. Employing TCRs in engineered T cells to develop therapeutic reagents for effectively targeting malignancies. [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 SY31-03. doi:10.1158/1538-7445.AM2015-SY31-03

Lysophosphatidic acid receptor 5 inhibits B cell antigen receptor signaling and antibody response

Lysophospholipids have emerged as biologically important chemoattractants capable of directing lymphocyte development, trafficking, and localization. Lysophosphatidic acid (LPA) is a major lysophospholipid found systemically, and its levels are elevated in certain pathological settings, such as cancer and infections. In this study, we demonstrate that BCR signal transduction by mature murine B cells is inhibited upon LPA engagement of the LPA5 (GPR92) receptor via a Gα12/13-Arhgef1 pathway. The inhibition of BCR signaling by LPA5 manifests by impaired intracellular calcium store release and most likely by interfering with inositol 1,4,5-triphosphate receptor activity. We further show that LPA5 also limits Ag-specific induction of CD69 and CD86 expression and that LPA5-deficient B cells display enhanced Ab responses. Thus, these data show that LPA5 negatively regulates BCR signaling, B cell activation, and immune response. Our findings extend the influence of lysophospholipids on immune function and suggest that alterations in LPA levels likely influence adaptive humoral immunity.

Alternative splice forms of CTLA-4 induced by antisense mediated splice-switching influences autoimmune diabetes susceptibility in NOD mice

Activated and regulatory T cells express the negative co-stimulatory molecule cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) that binds B7 on antigen-presenting cells to mediate cellular responses. Single nucleotide polymorphisms in the CTLA-4 gene have been found to affect alternative splicing and are linked to autoimmune disease susceptibility or resistance. Increased expression of a soluble splice form (sCTLA-4), lacking the transmembrane domain encoded by exon 3, has been shown to accelerate autoimmune pathology. In contrast, an exon 2-deficient form lacking the B7 ligand binding domain (liCTLA-4), expressed by diabetes resistant mouse strains has been shown to be protective when expressed as a transgene in diabetes susceptible non-obese diabetic (NOD) mice. We sought to employ an antisense-targeted splice-switching approach to independently produce these CTLA-4 splice forms in NOD mouse T cells and observe their relative impact on spontaneous autoimmune diabetes susceptibility. In vitro antisense targeting of the splice acceptor site for exon 2 produced liCTLA-4 while targeting exon 3 produced the sCTLA-4 form in NOD T cells. The liCTLA-4 expressing T cells exhibited reduced activation, proliferation and increased adhesion to intercellular adhesion molecule-1 (ICAM-1) similar to treatment with agonist α-CTLA-4. Mice treated to produce liCTLA-4 at the time of elevated blood glucose levels exhibited a significant reduction in the incidence of insulitis and diabetes, whereas a marked increase in the incidence of both was observed in animals treated to produce sCTLA-4. These findings provide further support that alternative splice forms of CTLA-4 affects diabetes susceptibility in NOD mice and demonstrates the therapeutic utility of antisense mediated splice-switching for modulating immune responses.

Arginine-rich cell-penetrating peptides facilitate delivery of antisense oligomers into murine leukocytes and alter pre-mRNA splicing

Phosphorodiamidate morpholino oligomers (PMO) are synthetic antisense molecules that interfere with translation, pre-mRNA splicing and RNA synthesis. Like other gene-silencing technologies, PMO are poorly taken up by primary leukocytes without the use of physical or chemical delivery techniques. We sought an alternative delivery mechanism of PMO into immune cells that eliminates the need for such manipulations. Here we demonstrate the first use of arginine-rich cell-penetrating peptides (CPPs) to deliver PMO (P-PMO) directly into primary murine leukocytes for inhibition of gene expression and promotion of altered pre-mRNA splicing. We compared the P-PMO delivery efficacy of four arginine-rich CPPs including HIV Tat and penetratin, and one histidine rich CPP, and found that the (RXR)(4) peptide was the most efficacious for PMO delivery and targeted antisense effect. The delivery and antisense effects of P-PMO are time- and dose-dependent and influenced by the activation and maturation states of T cells and dendritic cells, respectively. Targeted expression of several genes using P-PMO is shown including surface signaling proteins (CD45 and OX-40), a cytokine (interleukin-2), and a nuclear transcription factor (Foxp3). Considering the abundance of naturally occurring alternatively spliced gene products involved in immune regulation, P-PMO offer an effective method for modulating gene activity for immunological research and applications beyond traditional antisense approaches.