In vivo chimeric antigen receptor T cell therapy: From mechanistic innovation to clinical translation

Conventional ex vivo chimeric antigen receptor (CAR) T cell therapy is limited by cumbersome manufacturing workflows, prohibitive costs and various treatment-related risks. In vivo CAR-T technology directly generates engineered cells within patients, conferring distinct advantages in operational simplicity, biosafety and clinical accessibility. This review systematically evaluates existing delivery platforms and classifies in vivo CAR-T into two core paradigms: persistent engineering and transient reprogramming, each featuring distinct properties tailored to different clinical indications. It further summarizes preclinical advances and clinical data covering hematological malignancies, solid tumors, autoimmune disorders and organ fibrosis, in which numerous investigational candidates have exhibited encouraging efficacy. Ultimately, five translational barriers summarized as the 5S challenges (specificity, stability, safety, suppression and scalability) and their matched optimization tactics are comprehensively discussed. This review provides a clinician-oriented decision matrix that links carriers selection to disease biology, and a 5S optimization framework to guide next-generation vector design. Collectively, these insights establish a translational roadmap for customizing in vivo CAR-T design to specific clinical indications and take a critical step toward realizing the full therapeutic potential of this disruptive modality.