Introduction: Current generation of adoptive cell therapy relies on ex vivo engineering of immune cells with tumor-targeting chimeric antigen receptors. In addition to manufacturing challenges, ex vivo engineered cells such as CAR-NK and CAR-T show limited tumor infiltration and persistency within tumor microenvironment. A method leveraging mRNA-based delivery for in-vivo engineering of these cells could address these issues but has not been established. Conventional mRNA/LNP when infused systemically result in significant accumulation in liver tissue and the CAR has no immune cell specificity in their expression or function.

Method: Many immune receptors are heterodimeric complexes composed of a ligand binding subunit (e.g. CD16 and TCR) and a signaling adaptor containing Immunoreceptor Tyrosine-based Activation Motif (ITAM) (e.g. FcRγ and CD3ζ). Notably, the cell surface expression of the ligand binding subunit often depends on the expression of the ITAM adaptor. Based on this we fused HER2-targeting scFv to multiple activating receptors whose expression is restricted to NK cells and T cells, and evaluated their expression and anti-tumor function.

Results: We developed a series of Natural Cytotoxic Receptor (NCR)-based in vivo CAR constructs by fusing HER2-targeting scFv to the native extracellular and transmembrane sequences of the receptor NKp30, NKp44 and NKp46, These CARs engage signaling adaptor FcRγ or DAP12 expressed in NK cells, and exhibit potent tumoricidal activity against HER2+ ovarian cancer cells as well as mediate tumor-induced cytokine and chemokine response. Using Huh7 liver cell as a model for off-target expression in hepatocytes, we found that NKp44 and NKp46-based CAR requires their cognate signaling adaptors for stable cell surface expression. We also showed that similar strategy can be used to design receptors for selective expression on the surface of T cells utilizing CD3ε chain fused with tumor targeting scFv.

Conclusion: These results demonstrated the feasibility of engineering primary NK cells with CARs based on the NCR family of receptors NKp44 and NKp46, whose expression requires the immune-restricted signaling adaptors. These CAR-NK receptors do not contain intracellular signaling motifs but can engage and activate their signaling natural adaptors to initiate tumor killing and cytokine response. An mRNA/LNP based delivery of NKp44-based CAR for cancer treatment is currently under clinical development.

Citation Format: Neha Diwanji, Daniel Getts, Yuxiao Wang. In vivo programming of natural killer cells and T cells using mRNA delivered cytotoxic chimeric antigen receptors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1319.