Abstract 6597: Highly localized, inducible interleukin 12 release augments ICAM 1 CAR T cell activity against solid tumors
Background: Chimeric antigen receptor (CAR) T cells have demonstrated continued success in the treatment of hematological malignancies. By contrast, limited efficacy of CAR T cells has been seen in solid tumors due to multiple obstacles including impaired T cell infiltration and immune suppressive tumor environment, resulting in lack of proliferation and function. Previously, we have developed a micromolar affinity tuned CAR T cells targeting overexpressed ICAM 1 against a variety of tumors. To combat the immunosuppressive microenvironment in solid tumors, we developed a novel lentivirus vector that incorporates expression cassettes for CAR, somatostatin receptor 2 (SSTR2) for PET/CT imaging of T cells, and CAR activation dependent release of IL 12. Inducible IL 12 (iIL 12) expression was enabled by a synthetic promoter containing both NFkB and NFAT promoter elements by T cells to leverage IL 129s ability to promote Th1 response and at the same time to minimize systemic toxicity of IL 12. The iIL 12 CAR T exhibited much more robust killing of subcutaneous and peritoneal tumors, which showed partial to limited response to conventional CAR T cells without inducible cytokines. Methods: CAR T cells were generated by double lentiviral transduction of primary human T cells at 24 and 48 hours after activation with anti CD3/CD28 Dynabeads. NSG mice inoculated with subcutaneous anaplastic thyroid cancer cells (8505c) and triple negative breast cancer cells (MDA MB 468) and intraperitoneal gastric cancer cells (MKN28) were treated with with or without iIL 12 CAR T cells. Tumor growth was monitored regularly by bioluminescence imaging. PET/CT imaging was implemented to monitor T cell localization and biodistribution using 18F NOTA octreotide, a radiotracer targeting SSTR2. Results: Jurkat cells expressing iIL 12 ICAM 1 CAR produced IL 12 in an antigen density dependent manner when co incubated with ICAM 1 positive tumor cells or HEK 293T cells transduced to express human ICAM 1. In in vitro cytotoxicity assay, iIL 12 CAR T cells exhibited significantly augmented tumor lytic activity than conventional ICAM 1 CAR T cells. In striking contrast to conventional ICAM 1 CAR T cells which did not control tumor growth, iIL 12 CAR T cells mediated complete regression of various solid tumors and prolonged mouse survival significantly. Based on PET/CT imaging, both conventional and iIL 12 CAR T cells showed high levels of T cell infiltration and localization in tumor lesions. These results suggest that conventional CAR T cells quickly exhausted and lost function after penetration, while locally released IL 12 played an important role in improving anti tumor responses. Furthermore, serum levels of IL 12 in mice treated with iIL 12 CAR T cells were not detectable, indicating that IL 12 secretion was tightly controlled and limited to tumor sites. Conclusions: These findings demonstrate that local release of inducible IL 12 can help overcome hostile tumor microenvironment and augment anti tumor immune responses. Studies are underway to evaluate the feasibility of inducible IL 12 armored ICAM 1 CAR T cells as a potential therapy with favorable safety and efficacy profiles. Citation Format: Yanping Yang, Jaclyn E. McCloskey, Yogindra Vedvyas, Irene M. Min, Eric von Hofe, Moonsoo M. Jin. Highly localized, inducible interleukin 12 release augments ICAM 1 CAR T cell activity against solid tumors [abstract] In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27 28 and Jun 22 24. Philadelphia (PA) AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6597.