Overcoming adaptive resistance to cancer immunotherapy: molecular targeting strategies for the tumor microenvironment

Immunotherapy resistance is mediated by mechanisms distinct from those underlying conventional chemotherapy, including tumor-intrinsic alterations, an immunosuppressive tumor microenvironment, and other host factors, that collectively constrain durable responses.

This review provides a systematic evaluation of molecular targeting strategies aimed at overcoming immunotherapy resistance. We examine the principal resistance mechanisms including antigen loss, upregulation of alternative checkpoints (LAG-3, TIM-3, TIGIT), metabolic T-cell impairment, myeloid-derived suppressor cell and regulatory T-cell infiltration, cancer stem cell-driven evasion, epigenetic silencing, and T-cell exhaustion. Novel pharmacological approaches for resistance circumvention, including next-generation checkpoint blockers, bispecific T-cell engagers, antibody-drug conjugates, epigenetic and metabolic modulators, microenvironment-remodeling agents, and PROTAC-based checkpoint degraders, are critically assessed with an aim to link preclinical mechanistic evidence to clinical outcomes.

Despite the increasing number of combination immunotherapy strategies, durable clinical benefit remains limited for many patients. We attribute this to tumor heterogeneity, adaptive feedback, and inadequate biomarker-guided patient selection. Future progress will require systems-level approaches integrating single-cell and spatial multi-omics with adaptive, pharmacodynamically informed clinical trial designs. Ultimately, improving long-term outcomes will depend on the ability to predict and intercept tumor-immune co-evolution before resistance becomes established.