Abstract PR08: Armored CAR T cells genetically modified to secrete IL-12 show enhanced efficacy and overcome a hostile tumor microenvironment in mouse ovarian peritoneal carcinomatosis

Chimeric antigen receptor T cell (CAR T) therapy for solid tumors has not replicated the success seen with hematologic malignancies such as CD19-expressing B cell acute lymphoblastic leukemia (B-ALL) and Myeloma. One hypothesis for this lack of efficacy is an immunosuppressive tumor microenvironment that renders adoptively transferred cells ineffective. Armored CAR T cells are CAR T cells that have been further engineered to express additional costimulatory ligands, soluble cytokines or secretable proteins in order to overcome a hostile tumor microenvironment. IL-12 is a proinflammatory cytokine that is only secreted by antigen presenting cells and has been shown to activate effector cells, suppress regulatory T cells and reprogram tumor associated macrophages. We hypothesize that CAR T cells that have been genetically engineered to secrete IL-12 will be more efficacious in the treatment of Muc16^ecto positive ovarian cancer by overcoming an otherwise immunosuppressive ascitic tumor microenvironment. Herein we report the mechanisms of enhanced efficacy of an IL-12-armored CAR T cell (4H1128ζ-IL12) directed towards the retained portion of Muc16 (Muc16^ecto). Using an immunocompetent syngeneic peritoneal carcinomatosis model of ovarian cancer (i.p ID8-muc16^ecto), we show superior therapeutic efficacy of armored CAR T cells compared to second generation CARs (4H1128ζ). Tumor-bearing mice treated after 35 days with 4H1128ζ-IL12 were tumor-free for over 100 days compared to 4H1128ζ-treated mice (o.s: not reached vs 46 days, p= 0.008). Even when the tumor was allowed to establish for 42 days, mice treated with 4H1128ζ-IL12 survived longer than 4H1128ζ- treated mice (o.s: 97 vs 54 days, p= 0.0123). Investigations into the mechanism of improved survival in armored CAR T cell-treated mice showed increased in vivo expansion and modulation of the immunosuppressive ascites cytokine milieu via increased secretion of IL-12, IFN-γ, and TNF-α. Furthermore, 4H1128ζ-IL12 CAR T cells demonstrated enhanced in vitro proliferation and cytotoxic activity when cultured in ascites compared to control CAR T cells. Taken together, these results show that armored CAR T cells can be successfully engineered to overcome an otherwise immunosuppressive solid tumor microenvironment. These results represent the mechanistic companion of an ongoing phase I clinical trial of IL-12 armored CAR T cells in patients with relapsed/refractory ovarian cancer (NCT02498912).

This abstract is also being presented as Poster A32.

Citation Format: Oladapo Yeku, Terence Purdon, David Spriggs, Renier Brentjens. Armored CAR T cells genetically modified to secrete IL-12 show enhanced efficacy and overcome a hostile tumor microenvironment in mouse ovarian peritoneal carcinomatosis. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2016 Oct 20-23; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2017;5(3 Suppl):Abstract nr PR08.