In vivo generation of CAR-T cells: Current obstacles, strategic solutions, and clinical translation.

Chimeric antigen receptor T (CAR-T) cell therapy has transformed the treatment of hematologic malignancies, but conventional ex vivo manufacturing remains costly, labor-intensive, and difficult to scale. In vivo CAR-T generation, which reprograms endogenous T cells directly within patients using engineered vectors, offers a simplified and potentially more accessible alternative. This review outlines the major barriers to in vivo CAR-T development-including inefficient systemic delivery, off-target transduction, the trade-off between transfection efficiency and biosafety, and limited persistence of CAR expression. We summarize emerging engineering strategies such as targeted vector systems, combinatorial T-cell recognition, tunable expression control, and approaches to enhance functional durability. Recent early-phase clinical trials demonstrate the feasibility of in vivo CAR-T induction. We also discuss future opportunities and challenges that will shape the translation of this rapidly evolving therapeutic paradigm.