Editorial on “PD-1 is a haploinsufficient suppressor of T cell lymphomagenesis”

Many things have occurred in Oncology since the discovery of programmed death-1 (PD-1) and PD-1 ligand 1 (PD-L1) (1,2). PD-1/PD-L1 interaction appeared to be another one of many regulatory ligand-receptor interactions between antigen presenting cells (APCs) and T cells (3). But it turned out that this interaction was not like any other, at least from a clinical point of view with possibly the exception of CTLA-4/CD28. PD-L1 is a B7-related type I transmembrane protein belonging to the immunoglobulin superfamily constitutively expressed by the myeloid lineage and other cell types.