Recent data from our group and others have illustrated that clinically relevant mRNA LNPs (LNP, Onpattro®, Comirnaty®) massively target myeloid cells upon intravenous infusion. This project aims to further explore these interesting findings in the context of cancer immunotherapy. More specifically we aim to further explore mRNA LNP design for the in situ generation of Chimeric Antigen Receptor (CAR)-Ms as an alternative for autologous transfusion of virally transduced CAR-Ms thereby offering a more cost effective approach than cell-based approaches. CAR-Ms were recently identified as a highly interesting alternative for CAR-T cells as they can more effectively penetrate solid tumors thereby reducing tumor burden and creating a pro-inflammatory tumor microenvironment further boosting T-cell mediated immunity. As such, we aim to optimize mRNA LNP design to maximize myeloid cell uptake and mRNA expression levels on relevant murine and human cell lines as well as primary cells. Secondly we will further investigate our research hypothesis in relevant ‘cold’ and myeloid tumor models with the most promising mRNA LNP designs. This by further elucidating and quantifying the role of myeloid cell transport in the intratumoral accumulation of mRNA LNPs. Finally, we will further translate our findings by exploring the possibility to generate B7H3 directed CAR-Ms in situ as well as on human primary cells based on highly effective CAR constructs developed in the group of my co-promotor.