CTLA4 and neoplasm: However, in the “immune-active” tumours, upregulation of pro-inflammatory signals is accompanied by the expression of interferon-gamma-inducible immune regulatory molecules like programmed death ligand-1 (PD-L1) and indoleamine 2,3-dioxygenase dioxygenase (IDO), whose levels correlate with response to anti-PD-1 and anti-cytotoxic T-lymphocyte-associated protein 4 (anti-CTLA4) treatment.