Optimizing <i>In Vivo</i> CAR T-cell Engineering for Cancer Immunotherapy

Chimeric antigen receptor (CAR) T-cell therapy enables potent, antigen-specific immune responses and has demonstrated success in treating hematologic malignancies. However, conventional ex vivo CAR T manufacturing remains costly, individualized, and logistically complex, posing significant barriers to accessibility and scalability. In vivo CAR T-cell engineering offers a transformative alternative by reprogramming endogenous T cells within the patient, bypassing the need for cell harvesting and expansion. This review focuses on current in vivo CAR T delivery strategies, including viral vectors (such as lentiviruses, γ-retroviruses, adeno-associated viruses, and viral-like particles) and nonviral systems (such as lipid nanoparticles and polymer-based carriers), with a focus on how these platforms are engineered to achieve efficient, specific, and safe CAR transgene transfer. We also discuss the design principles of vector tropism, membrane modifications, and targeting ligands, as well as translational studies in both preclinical and clinical settings. Finally, the review explores delivery-related challenges and future perspectives for optimizing vector stability, enhancing T-cell targeting, and reducing immunogenicity to advance in vivo CAR T therapy toward broader clinical applications.