Studies have shown that under the continuous stimulation of tumour-derived vascular endothelial growth factor (VEGF), CD8+ T cells show a state of ‘failure’ and express various inhibitory receptors, including PD-1, T cell immunoglobulin and mucin domain-containing 3 (TIM3), lymphocyte activation gene 3 (LAG3) and cytotoxic T lymphocyte-associated antigen 4 (CTLA4) [60, 61]. This evidence concerns the gene PDCD1 and neoplasm.