Engineering the next generation of cellular therapies for solid tumors: multi-specific armored CARs and TME reprogramming strategies.

Chimeric antigen receptor (CAR) T-cell therapy has revolutionized hematologic oncology but remains largely ineffective against solid tumors, which evade immune attack through antigen heterogeneity, a suppressive tumor microenvironment (TME), and physical barriers. This review critically examines next-generation engineering strategies designed to overcome these formidable obstacles. We focus on the development of multi-specific and logic-gated CARs to prevent antigen escape and enhance precision, alongside "armored" constructs that secrete immunomodulatory payloads (e.g., cytokines, enzymes) or express dominant-negative receptors to reprogram the immunosuppressive stroma. Furthermore, we explore cooperative strategies that directly target and remodel the TME, including cancer-associated fibroblasts, the fibrotic extracellular matrix, abnormal vasculature, and suppressive myeloid cells. Early clinical signals are encouraging, but translation to solid tumors remains constrained by safety and manufacturing challenges and by limited predictive biomarkers. Here we synthesize advances in multispecific/logic-gated receptors, armored payloads, and TME-reprogramming strategies, highlighting translational priorities and pragmatic design principles for safer, manufacturable clinical candidates. Here, we argue that the most realistic path to meaningful clinical impact in solid tumors is a staged, biomarker-driven deployment of integrated platforms that (1) prioritize antigen breadth and safety in early clinical testing, (2) pair focused stromal remodeling with localized payload delivery, and (3) reserve the most complex synthetic circuits for settings where validated predictive biomarkers support risk-benefit tradeoffs.