Can We Use CAR-T Cells to Overcome Immunosuppression in Solid Tumours?

Chimeric antigen receptor (CAR)-T-cell therapy has revolutionised haematological cancer treatment. However, its application in solid tumours remains significantly limited by the immunosuppressive tumour microenvironment (TME), poor antigen specificity, and physical barriers to infiltration. This review explores a compelling question: can CAR-T cells be adapted to overcome immunosuppression in solid tumours effectively? We provide an in-depth analysis of the immunological, metabolic, and structural challenges posed by the TME and critically evaluate emerging engineering strategies designed to enhance CAR-T cells' persistence, targeting, and function. These include metabolic reprogramming, hypoxia-responsive constructs, checkpoint-resistant designs, and innovative delivery techniques such as locoregional administration and nanotechnology-assisted targeting. We highlight promising preclinical and early clinical studies demonstrating that armoured CAR-T cells secreting cytokines like interleukin (IL)-12 and IL-18 can reprogram the TME, restoring antitumour immunity. Moreover, we examine synergistic combination therapies that integrate CAR-T cells with immune checkpoint inhibitors, radiotherapy, oncolytic viruses, and epigenetic modulators. Special attention is given to personalised strategies, such as bispecific targeting and precision delivery to tumour-associated vasculature or stromal elements, which are showing encouraging results in overcoming resistance mechanisms. This review aims not only to synthesise current advancements but also to ignite optimism in the potential of CAR-T-cell therapy to breach the immunological fortress of solid tumours. As we enter a new era of synthetic immunology, this evolving landscape offers hope for durable remissions and novel treatment paradigms. For clinicians, researchers, and biotech innovators, this paper provides a roadmap toward transforming a therapeutic dream into clinical reality.