Chimeric antigen receptor (CAR) T cell therapy redirects T cells to activate and subsequently kill antigen- expressing cancer cells. This is achieved by coupling a cancer antigen-specific extracellular single-chain variable IgG fragment (scFv) to intracytoplasmic, endogenous T cell activation signaling domains. CAR T cell therapy has shown promise for treating hematopoietic malignancies; however, relapse of antigen-negative tumors remains a significant source of failure for these patients. Further, little success has been seen in treating solid tumors with immunosuppressive microenvironments. Combination therapy with CAR T cells and checkpoint blockade is a possible approach to overcome these obstacles. Checkpoint blockade therapy antagonizes the signaling pathways that suppress the immune system. Current checkpoint blockade strategies have focused on altering T cell-tumor interactions, but recent studies also show promise in abrogating innate immune checkpoints, specifically the CD47-SIRP? signaling axis. This pathway, known as the ?do not eat me? signal, prevents both antibody mediated macrophage phagocytosis and active cross priming of T cells by dendritic cells, and is thus involved in suppressing both innate and adaptive immune processes. Cancer cells have co-opted this pathway to evade immune attack. However, early stage clinical trials of anti-CD47 agents show systemic toxicities of anemia and thrombocytopenia. Our long-term goal is to engineer a more potent CAR T cell that can overcome antigen loss relapse and the immunosuppressive tumor microenvironment. To accomplish this, we propose to investigate the combination of CAR T cell therapy with intrinsic SIRP? protein secretion to activate antibody therapy and antigen presentation, as this combination should potently engage both innate and adaptive immunity to lead to a more complete antitumor response. We have already engineered human CD19 CAR T cells to secrete a small molecule, high affinity, SIRP? mimic, CV1. These CV1-secreting CAR T cells, named OrexiCAR T cells, retain their cytotoxic function and the cell-secreted CV1 can potentiate mAb therapy. In addition, we have shown that cancer antigen stimulation of the OrexiCAR T cells in vitro leads to a large increase in secreted CV1. Here, we propose to study OrexiCAR T cells in a fully immunocompetent, syngeneic setting to determine which mechanisms contribute to their potency. We believe the proposed research will allow a better understanding of OrexiCAR T cell efficacy and its applicability to the clinic.
The Aims are: 1) To construct mouse CD19 OrexiCAR vectors, transduce into primary mouse cells, and validate functions of CAR and CV1 in vitro and 2) To evaluate the anti-tumor effect of mOrexiCAR T cells in an immunocompetent, syngeneic mouse model and to discover and describe the immunologic mechanism
CAR T cell therapy has proven an innovative and effective treatment option for some B cell malignancies and this proposal aims to broaden the potency of this strategy to better overcome antigen loss variant and immunosuppressive solid tumor microenvironments that allow escape of cancers. We have already generated and validated a human targeted OrexiCAR T cell that we believe can potentiate both the innate and adaptive immune system, but to understand this therapy in a more clinically relevant setting, this proposal aims to construct and test a fully syngeneic murine OrexiCAR T cell to dissect the mechanisms of action and resistance of this therapy and determine its applicability to the clinic. The proposed research will not only aid in the clinical translation of a new class of CAR T cell therapy, but may also provide insights into new logical combinations for CAR T cell therapy.
