Abstract 1780: TCR-T and CAR-T cells targeting HLA-A2/MAGEA4 demonstrate differential tumor control, reflecting co-stimulatory signaling requirements

The clinical success of cancer immunotherapy, including engineered T cell therapies, has revolutionized treatment paradigms and patient outcomes. While hematological tumors have benefited most from cell therapy approaches, the treatment of solid tumors remains a challenge in part due to the limited availability of abundant and tumor-specific cell-surface antigens. Peptides derived from intracellular tumor-specific proteins, such as cancer-testis antigens (CTAs), that are presented via HLA (pHLA) enable a therapeutic opportunity to target tumors while sparing normal tissue. Surface-accessible pHLA complexes may be targeted with engineered T cell receptors or TCR mimetic antibodies reformatted to chimeric antigen receptors (CARs). Using MAGE-A4 as a model CTA, we compared engineered human TCR- and CAR-T cells head-to-head to understand how to best deploy these modalities. To this end, we generated fully-human, HLA-A2/MAGE-A4(230-239)-specific TCR and CARs harboring CD28/CD3z or 41BB/CD3z signaling domains. TCR and CAR-T cells demonstrated similar robust on-target reactivity, cytokine release, and target cell lysis in vitro. In vivo, each of these modalities showed potent, dose-dependent anti-tumor efficacy against human xenograft tumors expressing low, endogenous levels (~500 cell-surface copies) of the MAGE-A4 peptide. However, differences emerged when we examined the in vivo kinetics and durability of tumor suppression. MAGE-A4 CD28/z CAR-T demonstrated the most rapid and potent tumor clearance, while the 41BB/z CAR-T showed delayed but ultimately complete efficacy. TCR-T cells induced tumor regressions during the first 2 weeks of treatment, but this response was transient and followed by tumor relapse. These differential responses correlated with early, modest accumulation of CD28/z CAR-T in line with fast tumor clearance. 41BB/z CAR-T showed a remarkable ~800-fold expansion in the tumor versus limited in vivo TCR-T proliferation. Mechanistically, the MAGE-A4 TCR induced strong CD3 proximal signaling associated with a greater induction of T cell dysfunction markers and limited cytotoxic potential in vitro. However, stimulating 41BB signaling pathways in the MAGE-A4 TCR T cells augmented long-term cytotoxicity. These data demonstrate that tumor-specific pHLA complexes can be potently targeted by both TCR and CAR-T cells, and that co-stimulatory signaling is necessary to mediate durable anti-tumor activity.

Citation Format: Corinne E. Decker, Jacqueline Idun, Katja Mohrs, Thomas Meagher, Kevin Bray, Iryna Petriv, Jonathon Golas, Timothy Helms, Dharani Ajithdoss, Gavin Thurston, John Lin, Jessica R. Kirshner, David J. DiLillo. TCR-T and CAR-T cells targeting HLA-A2/MAGEA4 demonstrate differential tumor control, reflecting co-stimulatory signaling requirements [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1780.

Blocking common γ chain cytokine signaling ameliorates T cell-mediated pathogenesis in disease models

The common γ chain (γc; IL-2RG) is a subunit of the interleukin (IL) receptors for the γc cytokines IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. The lack of appropriate neutralizing antibodies recognizing IL-2RG has made it difficult to thoroughly interrogate the role of γc cytokines in inflammatory and autoimmune disease settings. Here, we generated a γc cytokine receptor antibody, REGN7257, to determine whether γc cytokines might be targeted for T cell-mediated disease prevention and treatment. Biochemical, structural, and in vitro analysis showed that REGN7257 binds with high affinity to IL-2RG and potently blocks signaling of all γc cytokines. In nonhuman primates, REGN7257 efficiently suppressed T cells without affecting granulocytes, platelets, or red blood cells. Using REGN7257, we showed that γc cytokines drive T cell-mediated disease in mouse models of graft-versus-host disease (GVHD) and multiple sclerosis by affecting multiple aspects of the pathogenic response. We found that our xenogeneic GVHD mouse model recapitulates hallmarks of acute and chronic GVHD, with T cell expansion/infiltration into tissues and liver fibrosis, as well as hallmarks of immune aplastic anemia, with bone marrow aplasia and peripheral cytopenia. Our findings indicate that γc cytokines contribute to GVHD and aplastic anemia pathology by promoting these characteristic features. By demonstrating that broad inhibition of γc cytokine signaling with REGN7257 protects from immune-mediated disorders, our data provide evidence of γc cytokines as key drivers of pathogenic T cell responses, offering a potential strategy for the management of T cell-mediated diseases.

A class of costimulatory CD28-bispecific antibodies that enhance the antitumor activity of CD3-bispecific antibodies

T cell activation is initiated upon binding of the T cell receptor (TCR)/CD3 complex to peptide-major histocompatibility complexes ("signal 1"); activation is enhanced by engagement of a second "costimulatory" receptor, such as the CD28 receptor on T cells binding to its cognate ligand(s) on the target cell ("signal 2"). CD3-based bispecific antibodies act by replacing conventional signal 1, linking T cells to tumor cells by binding a tumor-specific antigen (TSA) with one arm of the bispecific and bridging to TCR/CD3 with the other. Although some of these so-called TSAxCD3 bispecifics have demonstrated promising antitumor efficacy in patients with cancer, their activity remains to be optimized. Here, we introduce a class of bispecific antibodies that mimic signal 2 by bridging TSA to the costimulatory CD28 receptor on T cells. We term these TSAxCD28 bispecifics and describe two such bispecific antibodies: one specific for ovarian and the other for prostate cancer antigens. Unlike CD28 superagonists, which broadly activate T cells and resulted in profound toxicity in early clinical trials, these TSAxCD28 bispecifics show limited activity and no toxicity when used alone in genetically humanized immunocompetent mouse models or in primates. However, when combined with TSAxCD3 bispecifics, they enhance the artificial synapse between a T cell and its target cell, potentiate T cell activation, and markedly improve antitumor activity of CD3 bispecifics in a variety of xenogeneic and syngeneic tumor models. Combining this class of CD28-costimulatory bispecific antibodies with the emerging class of TSAxCD3 bispecifics may provide well-tolerated, off-the-shelf antibody therapies with robust antitumor efficacy.

Enhanced IL-36R signaling promotes barrier impairment and inflammation in skin and intestine

Deficiency in interleukin-36R (IL-36R) antagonist caused by loss-of-function mutations in IL-36RN leads to DITRA (deficiency of IL-36 receptor antagonist), a rare inflammatory human disease that belongs to a subgroup of generalized pustular psoriasis (GPP). We report a functional genetic mouse model of DITRA with enhanced IL-36R signaling analogous to that observed in patients with DITRA, which provides new insight into our understanding of the IL-36 family of molecules in regulating barrier integrity across multiple tissues. Humanized DITRA-like mice displayed increased skin inflammation in a preclinical model of psoriasis, and in vivo blockade of IL-36R pathway using anti-human IL-36R antibody ameliorated imiquimod-induced skin pathology as both prophylactic and therapeutic treatments. Deeper characterization of the humanized DITRA-like mice revealed that deregulated IL-36R signaling promoted tissue pathology during intestinal injury and led to impairment in mucosal restoration in the repair phase of chronic dextran sulfate sodium (DSS)-induced colitis. Blockade of IL-36R pathway significantly ameliorated DSS-induced intestinal inflammation and rescued the inability of DITRA-like mice to recover from mucosal damage in vivo. Our results indicate a central role for IL-36 in regulating proinflammatory responses in the skin and epithelial barrier function in the intestine, suggesting a new therapeutic potential for targeting the IL-36R axis in psoriasis and at the later stages of intestinal pathology in inflammatory bowel disease.

REGN-COV2 antibodies prevent and treat SARS-CoV-2 infection in rhesus macaques and hamsters

An urgent global quest for effective therapies to prevent and treat coronavirus disease 2019 (COVID-19) is ongoing. We previously described REGN-COV2, a cocktail of two potent neutralizing antibodies (REGN10987 and REGN10933) that targets nonoverlapping epitopes on the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. In this report, we evaluate the in vivo efficacy of this antibody cocktail in both rhesus macaques, which may model mild disease, and golden hamsters, which may model more severe disease. We demonstrate that REGN-COV-2 can greatly reduce virus load in the lower and upper airways and decrease virus-induced pathological sequelae when administered prophylactically or therapeutically in rhesus macaques. Similarly, administration in hamsters limits weight loss and decreases lung titers and evidence of pneumonia in the lungs. Our results provide evidence of the therapeutic potential of this antibody cocktail.

Pigs that recover from porcine reproduction and respiratory syndrome virus infection develop cytotoxic CD4+CD8+ and CD4+CD8- T-cells that kill virus infected cells

Porcine reproductive and respiratory syndrome virus (PRRSV) infection is difficult to control because the virus undergoes antigenic variation during infection and also modulates the protective host immune response. Although current vaccines do not provide full protection, they have provided insight into the mechanisms of protection. Live PRRSV vaccines induce partial protection before the appearance of neutralizing antibody, suggesting cell-mediated immunity or other mechanisms may be involved. Herein, we demonstrate recovery from infection is associated with development of cytotoxic T-lymphocytes (CTL) that can kill PRRSV-infected target cells. Initial experiments showed survival of PRRSV-infected monocyte derived macrophage (MDM) targets is reduced when overlaid with peripheral blood mononuclear cells (PBMC) from gilts that had recovered from PRRSV infection. Further studies with PBMC depleted of either CD4⁺ or CD8⁺ T-cells and positively selected subpopulations of CD4⁺ and CD8⁺ T-cells showed that both CD4⁺ and CD8⁺ T-cells were involved in killing. Examination of killing at different time points revealed killing was biphasic and mediated by CTL of different phenotypes. CD4⁺CD8^+high were associated with killing target cells infected for 3–6 hours. CD4⁺CD8^- CTL were associated with killing at 16–24 hours. Thus, all the anti-PRRSV CTL activity in pigs was attributed to two phenotypes of CD4⁺ cells which is different from the anti-viral CD4^-CD8⁺ CTL phenotype found in most other animals. These findings will be useful for evaluating CTL responses induced by current and future vaccines, guiding to a novel direction for future vaccine development.