Antigen Loss or Alteration: Tumors may downregulate or mutate antigens recognized by TCRs, leading to reduced visibility to T cells; Immunosuppressive Tumor Microenvironment: The presence of regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs), and immunosuppressive cytokines can inhibit T cell activation and function; Checkpoint Molecule Upregulation: Tumor cells may express immune checkpoint molecules like PD-L1, which can inhibit T cell activity; and HLA Loss: Downregulation of major histocompatibility complex (MHC) molecules can prevent T cell recognition of tumor cells. Here, HLA-C is linked to neoplasm.