PDCD1 and neoplasm: In first instance, type I and II interferon signalling activates negative feedbacks restraining T cell functions (such as PD-L1 expression on myeloid and tumour cells, PD-1, and CTLA-4 expression on T cells); moreover, TLRs can be expressed by tumour cells as well and those agonists can support their proliferation potential [213, 214].