Various intrinsic and extrinsic tumour factors favour the development of immunosuppressive myeloid-derived suppressor cells (MDSCs) and regulatory T cells, increasing the expression of inhibitory checkpoint receptors, such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein-1 (PD-1) and lymphocyte-activation gene 3 (LAG-3), while reducing the expression and presentation of tumour-specific antigens18–20. This evidence concerns the gene PDCD1 and neoplasm.