Background
Chimeric antigen receptor (CAR) T cells have shown remarkable clinical efficacy in hematological cancers but still face significant obstacles in the treatment of solid tumors, such as pancreatic ductal adenocarcinoma (PDAC). Two major hurdles in developing effective CAR T therapies for PDAC are the identification of tumor-associated antigens (TAA) and overcoming a complex immunosuppressive tumor microenvironment (TME). We hypothesize that the optimal CAR T cell to treat PDAC recognizes an ideal TAA and protects itself from TME immunosuppression. We propose a novel CAR T cell to target the Muc16-ectodomain (Muc16CD) combined with antagonism of the vasoactive intestinal peptide (VIP) checkpoint pathway in the PDAC TME as a viable therapy to treat pancreatic tumors. 

Methods
Patient data was assessed based upon data generated by the TCGA Research Network. Primary human T cells were retrovirally transduced to express Muc16CD-directed CARs with or without secretion of VIPR antagonists. PDAC PDX tumors and CAR T cells assayed by flow cytometry for phenotype and functional profile. In vivo, Panc1-Muc16CD-GFPffLuc tumors were engrafted into SCID/Beige mice and treated with CAR T cells.

Results
Muc16 expression is significantly increased in PDAC patient tissues compared to normal pancreas and associated with decreased overall survival. Congruently, we found that PDAC PDX tumors demonstrate robust expression of both Muc16CD and VIP and are vulnerable to Muc16CD-directed CAR T cell cytotoxicity. Additionally, VIP limits the proliferative capacity of CAR T cells, which is reversed by VIPR antagonist peptides (antVIPR). Therefore, we engineered anti-Muc16CD CARs to secrete antVIPR peptides to provide continuous and localized delivery within the TME. We find that antVIPR expression by CAR T cells enhances viability, activation profile, and demonstrate less-differentiated and less exhaustive phenotypes. Functionally, antVIPR CAR T cells have enhanced activation and proliferative advantage after chronic antigen-stimulation. In a xenograft model of PDAC, antVIPR CAR T cells reduce tumor burden and improve overall survival in mice bearing human VIP-expressing PDAC tumors. At 118 days, antVIPR CAR T-treated mice have more circulating CAR T cells than parental CAR T-treated mice. 

Conclusion
Muc16CD is a clinically relevant target for CAR T therapy in PDAC. Furthermore, antagonizing the VIP checkpoint pathway in CAR T cells produces enhanced phenotypic and functional profiles. Collectively, this data demonstrates that the combination of targeting Muc16CD and VIP with a novel CAR T cell can improve anti-tumor efficacy against PDAC. The long-term goal of this work is translating antVIPR-secreting CAR T cells for the treatment of PDAC.


Using CAR T Cell-Secreted Antagonistic Peptides to Target Distinct Immune Checkpoint Pathway in Pancreatic Tumors

 Hematology / Oncology / Pathology

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Using CAR T Cell-Secreted Antagonistic Peptides to Target Distinct Immune Checkpoint Pathway in Pancreatic Tumors

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