Peripheral immune tolerance as a driver of tumor immune escape and therapy resistance.

Peripheral immune tolerance, essential for preventing autoimmunity, is increasingly co-opted by tumors to drive progression, metastatic dissemination, and immunotherapy resistance. Whereas central tolerance eliminates autoreactive clones, peripheral tolerance remains dynamically regulated by antigen persistence, cytokine gradients, metabolic cues, and stromal architecture, a plasticity that tumors exploit to build a multilayered immunosuppressive ecosystem. This narrative review synthesizes multi-omic, spatial, cellular, and molecular evidence, emphasizing 2021 to 2025 publications alongside foundational studies, to propose tumor-induced peripheral tolerance (TIPT) as a unifying framework for immune escape and treatment failure. TIPT emerges from coordinated suppression by tumor-resident regulatory T cells, myeloid-derived suppressor cells, regulatory B cells, M2-like macrophages, tolerogenic dendritic cells, and exhausted CD8? T cells, sustained by suppressive cytokine networks, metabolic deprivation, epigenetic fixation of dysfunctional states, and stromal-vascular exclusion barriers. Spatially organized tolerance niches are associated with immune evasion, metastatic seeding, and resistance to checkpoint blockade. Strategies targeting suppressive cell populations, metabolic pathways, chromatin regulators, and stromal barriers are in clinical development, but clinical benefit has been established for only a limited subset, and anti-TIGIT antibodies failed to meet primary endpoints in phase 3 lung cancer trials. Machine-learning models show promise for predicting tolerance states and guiding combination design, but prospective clinical validation is still needed. TIPT may represent an important, potentially actionable determinant of tumor evolution and immunotherapy response, and durable cancer control is likely to require combined strategies that dismantle this tolerance ecosystem.