To date, more than 20 immunosuppressive factors produced by tumor and/or stromal cells have been discovered, including transforming growth factor-β1 (TGFβ1) (Wang et al., 2015), prostaglandin E2 (Kalinski, 2012), vascular endothelial growth factor (VEGF) (Shibuya, 2013), interleukin-10 (Geginat et al., 2016), interleukin-4 (Egawa et al., 2013), cyclooxygenase-2 (Li et al., 2013), programmed cell death 1 (Gatalica et al., 2014), and cytotoxic T-lymphocyte associated antigen 4 (Lan et al., 2013). The gene discussed is PDCD1; the disease is neoplasm.