Shannon Argueta ¹ Yuxiao Wang ^1* Hongyun Zhao ¹ Neha Diwanji ^1* Michael Gorgievski ¹ Edward Cochran ¹ Ewa Grudzien-Nogalska ^1* Josephine D'Alessandro ^1* Bruce McCreedy ^2* Thomas Prod'homme ^1* Robert Hofmeister ^1* Jian Ding ¹ Daniel Getts ^1*

• ¹ Myeloid Therapeutics, Cambridge, United States
• ² ONK Therapeutics, Galway, Ireland

The approval of chimeric antigen receptor (CAR) T cell therapies for the treatment of B cell malignancies has fueled the development of numerous ex vivo cell therapies. However, these cell therapies are complex and costly, and unlike in hematological malignancies, outcomes with most T cell therapies in solid tumors have been disappointing. Here, we present a novel approach to directly program myeloid cells in vivo by administering novel TROP2 CAR mRNA encapsulated in lipid nanoparticles (LNPs). The CAR comprises a TROP2 specific single-chain variable fragment (scFv) fused to a truncated CD89 which requires association with the FcRγ signal adapter to trigger myeloid-specific cell activation. In vitro, transient expression of the TROP2 CAR on monocytes triggers antigen-dependent cytotoxicity and cytokine release.In tumor bearing mice and cynomolgus monkeys, the TROP2 CAR mRNA/LNP are primarily taken up by myeloid cells. In a mouse lung xenograft model, intravenous administration of TROP2 CAR mRNA/LNP results in tumor growth inhibition and in a B16-OVA immunocompetent melanoma mouse model, anti-tumor efficacy of a gp75-specific CAR correlates with increased number of activated T cells, activation of dendritic cells and a humoral response against B16-OVA melanoma tumors. These findings demonstrate that myeloid cells can be directly engineered in vivo to kill tumor cells and orchestrate an adaptive immune response.