Figure 2.

Mechanisms of tumor immune evasion and suppression of immune checkpoints following restoration of anti-tumor immunity Tumor cells evade immune surveillance by promoting immune checkpoint activation. Tumor cells express the immune checkpoint activator PD-L1 and produce antigens, which are captured by antigen presenting cells. These cells present antigens to cytotoxic CD8⁺ T cells through the interaction of major histocompatibility complex (MHC) molecules and T cell receptor (TCR). T cell activation requires costimulatory signaling mediated by B7 and CD28 interactions. Inhibitory signals from CTLA-4 and PD-1 checkpoints inhibit T cell responses and promote tumor proliferation. ICIs, such as anti-PD-L1, anti-PD-1, and anti-CTLA-4, block immunosuppressive checkpoints (CTLA-4, PD-1, and PD-L1, respectively), thereby restoring anti-tumor immune responses. By Figdraw.