Breaking the Barriers in CAR-T Cell Therapy: Addressing Toxicity, Tumor Microenvironment Suppression, Persistence Challenges, and Trafficking Deficits

Chimeric antigen receptor (CAR)-T cell therapy has transformed the management of hematologic malignancies but faces obstacles, including severe treatment-related toxicities, highly suppressive tumor microenvironment (TME), inadequate long-term persistence, and poor trafficking/infiltration into solid tumor. This review summarizes recent genetic engineering strategies designed to overcome these barriers and to improve the safety, durability, and spatial effectiveness of CAR-T cell therapy. To mitigate cytokine release syndrome and neurotoxicity, approaches such as affinity-tuned and humanized scFvs, hinge/TM optimization, ITAM calibration have been developed alongside programmable “switch-off” and “switch-on” systems incorporating suicide genes, antibody-bridging switches, and optogenetic or hypoxia-gated circuits. TME remodelling strategies leverage nanomaterials for localized cytokine delivery, cell-surface “backpack” systems, and oncolytic viruses engineered to release cytokines or checkpoint-blocking biologics. Enhancing durability and resistance to exhaustion increasingly relies on precision genome engineering, including CRISPR-based editing and multiplexed shRNA platforms targeting inhibitory receptors and exhaustion-driving transcriptional programs. Finally, chemokine-receptor engineering and local biomaterial-based delivery systems are discussed as routes to improve CAR-T trafficking and intratumoral persistence. We also highlight the remaining translational challenges including checkpoint redundancy, in vivo payload dilution, vector capacity limits, and the safety of multiplex genome editing. Collectively, these interdisciplinary innovations point towards integrated, patient-tailored CAR-T platforms that combine safety control, metabolic and transcriptional resilience, and improved TME navigation to enable broader clinical application.