CTLA4 and neoplasm: Not surprisingly, mice presenting gene deletion of either CTLA-4 or PD-1 develop severe systemic autoimmune diseases.9 There is much evidence of the interaction between tumor cells and these regulatory systems; interestingly, a correlation between prognosis and the expression levels of PD-L1 and PD-L2 in several tumor tissues has been found.12 Moreover, the interaction between PD-1 expressed by T lymphocytes and PD-L1 expressed by tumor cells is associated with faster tumor growth.12