CAR immunotherapy for cancer: from ex vivo manufacturing to in vivo immune cell engineering

Over the past decade, chimeric antigen receptor (CAR) T-cell therapy has achieved durable remissions in patients with relapsed or refractory haematological malignancies. However, its broader clinical adoption remains constrained by patient-specific ex vivo manufacturing, substantial treatment-related toxicities and limited efficacy in solid tumours. In vivo CAR immunotherapy enables endogenous immune cells to be genetically reprogrammed directly within the body, bypassing leukapheresis, ex vivo expansion and individualized cell manufacturing. This Review focuses specifically on in vivo CAR immune cell engineering for cancer therapy, encompassing haematological malignancies and solid tumours; applications in non-malignant diseases, including autoimmune disorders, are outside its scope. We examine emerging technologies for generating CAR immune cells in vivo and discuss how viral vectors, non-viral nanocarriers and biomimetic delivery systems could improve the precision, scalability and controllability of cancer immunotherapy. We further highlight immune effectors beyond CAR T cells, including CAR macrophages and CAR natural killer cells, whose distinct cytotoxic, phagocytic and immunomodulatory functions may offer complementary approaches to treating solid tumours. We discuss strategies involving tumour-microenvironment remodelling, metabolic adaptation and precision genome engineering to improve immune-cell persistence, mitigate functional exhaustion, enhance tumour infiltration and limit antigen escape. Emerging clinical studies in haematological malignancies provide initial proof of concept that functional CAR cells can be generated in patients, although long-term safety, durability and reproducibility remain to be established. A central challenge is to generate these cells with sufficient cellular and spatial precision while maintaining control over their activity over time. We discuss how cell-subset-specific delivery, programmable CAR circuits, multicellular engineering, intelligent biomaterials and artificial intelligence could support the development of in vivo CAR immunotherapy as a scalable, controllable and potentially repeatable cancer treatment.