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-12's 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.