Tumor Immune Evasion Mechanisms and Immunotherapy Strategies

The immune system patrols the body to detect and eliminate nascent tumor cells, known as cancer immunosurveillance. However, tumors can develop various evasion strategies to avoid immune destruction and continue growing unchecked. Key mechanisms include loss of antigen presentation (e.g., downregulation of MHC class I molecules), secretion of immunosuppressive cytokines (such as TGF- and IL-10), expression of inhibitory checkpoint ligands (like PD-L1), and recruitment of regulatory immune cells (Tregs, MDSCs). These evasion tactics undermine anti-tumor T-cell responses and pose significant obstacles to effective therapy. In recent years, immunotherapy has revolutionized cancer treatment by harnessing the immune system most notably via immune checkpoint blockade (targeting CTLA-4, PD-1/PD-L1) and engineered cell therapies (CAR-T and TCR-T cells) yielding durable remissions in multiple cancers. However, resistance remains common, often driven by the exact evasion mechanisms. This review summarizes the current understanding of tumor immune evasion and the corresponding immunotherapeutic approaches. This review discusses major evasion pathways, recent advances in checkpoint inhibitors, cancer vaccines, and adoptive cell therapies, as well as the rationale for combination regimens. Finally, it analyzes the limitations and future directions in overcoming resistance and optimizing immunotherapy. Understanding and targeting immune escape is crucial to improving patient outcomes in oncology.