CTLA4 and neoplasm: As well as binding to CD28, as outlined above, B7 proteins on the surface of tumour cells constitute ligands for immune-checkpoint molecules: the PD-1 receptor ligands programmed death ligand 1 (PD-L1, also known as B7–H1/CD274) and programmed death ligand 2 (PD-L2, also known as B7-DC/CD273), and CTLA-4 ligands CD80 (B7.1) and CD86 (B7.2) activate immune checkpoints in T cells.