PDCD1 and neoplasm: In prostate cancer, the loss of ß2-microglobulin decreases the expression of MHC-I molecules on the cells’ surface, thus hindering cytotoxic T-cells from recognising tumour cells and facilitating resistance to immune checkpoint inhibitors as well as T-cell based immunotherapy [137], resistance to PD-1 inhibitors and increased levels of cancer-associated fibroblasts [138].