These correlative relationships are potentially misleading; while the binding of PD-L1 with its cognate receptor is a well-characterized immune checkpoint that negatively regulates CD8+ T cell-mediated anti-tumour activity [101,102], one study on primary human MBL samples refuted any significance of the PD-1/PD-L1 pathway in MBL, citing an absence of PD-L1 expression by tumour cells and a corresponding minimal infiltration of PD-1+ T lymphocytes present within the TIME [99]. The gene discussed is CD8A; the disease is neoplasm.