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

INTRODUCTION: 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. AREAS COVERED: 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. EXPERT OPINION: 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.