In Vivo mRNA-Lipid Nanoparticle CAR-T Cell Engineering: Advances, Challenges, and Clinical Translation.

Chimeric antigen receptor T (CAR-T) cell therapy has transformed the treatment of hematologic malignancies, yet its broader application, particularly in solid tumors, remains constrained by high cost, labor-intensive manufacturing, limited production capacity, and variable clinical performance, as well as barriers such as poor trafficking, antigen heterogeneity, and an immunosuppressive tumor microenvironment. In vivo CAR-T cell engineering, in which CAR-T cells are generated directly within the patient, offers a paradigm shift by eliminating the need for ex vivo cell processing and complex logistical infrastructure. Among emerging approaches, messenger RNA (mRNA)-loaded lipid nanoparticles (LNPs) have emerged as a promising and clinically tractable platform for in vivo CAR-T cell generation, enabling direct reprogramming of T lymphocytes within the patient and thereby circumventing the need for leukapheresis, viral vector production, and prolonged ex vivo culture, effectively transforming the patient into their own cell therapy factory. This review synthesizes advances in mRNA-LNP-mediated in vivo CAR-T cell generation, encompassing ionizable lipid chemistry and emerging T cell-targeted delivery strategies, including surface functionalization approaches. We discuss the implications of transient CAR expression for immune activation, safety, and therapeutic durability, alongside CAR design optimization through co-stimulatory domains and safety switches. Preclinical evidence from murine tumor models and non-human primates is integrated with current regulatory considerations, and key barriers to clinical translation are highlighted. Collectively, progress in nucleic acid delivery, synthetic immunology, and precision medicine positions in vivo mRNA-CAR-T therapy as a promising modality for oncology and beyond.