CTLA4 and neoplasm: Moreover, secreted factors from tumor cells also increase the expression of programmed cell death 1 ligand (PD-L1) and cytotoxic T lymphocyte antigen 4 (CTLA-4) ligands in monocytes and macrophages (Anderson et al., 2006; Matsunaga et al., 2011; Bloch et al., 2013).