In vivo CAR mRNA engineering of both adaptive and myeloid cells enables potent anti-tumor control of solid cancers

Background: In solid tumors, chimeric antigen receptor (CAR) T cell therapies are limited by their inability to overcome poor trafficking, antigen heterogeneity and the immunosuppressive myeloid cells in the tumor microenvironment (TME). Here, we introduce in vivo multi-immune cell programming designed to precisely and simultaneously program multiple immune cell types using a single engineered product. This approach builds on the clinical experience with in vivo CAR-mRNA engineered CAR myeloid cells that created a pro-inflammatory tumor environment. Combining non-targeted and targeted LNP delivery, optimized mRNA, and cell-specific CAR architecture, we endow myeloid cells, NK cells and T cells with tailored effector functions. Methods: Anti-HER2 CAR mRNAs optimised for myeloid, NK or T cell signalling were encapsulated in LNPs and delivered intravenously. Anti-tumor efficacy was evaluated in immunocompetent hHER2 transgenic mice bearing syngeneic hHER2-MC38 colon adenocarcinoma tumors. Results: In a colorectal tumor model, myeloid- and NK-cell reprogramming with CAR mRNA/LNPs drove tumor regression, prolonged survival, remodeling of the tumor microenvironment, greater antigen presentation, and enhanced T-cell infiltration and activation. Likewise, T cell engineered with CAR mRNA/tLNPs elicited robust anti-tumor activity. Notably, co-delivery of cell-specific CAR mRNA/LNPs to both myeloid and T-cell compartments produced even stronger tumor control, highlighting the power of coordinated multi-lineage immune engineering. Conclusions: This work demonstrates that simultaneous In vivo engineering of myeloid cells, T cells, and NK cells with CARs can orchestrate the coordinated actions of both innate and adaptive immunity for potent anti-tumor activity. This strategy offers a scalable and off-the-shelf approach for cell therapy and establishes a new therapeutic paradigm for overcoming the complexity of solid tumors.