PDCD1 and cancer: Given the important role of PD-1 overexpression to tumor-specific T-cell immunity, it might be plausible to follow-up on patients exhibiting an increase in PD-1 in response to anti-CD3 treatment, paying specific attention to documented cancer-associated PD-1 polymorphisms: PD-1.1 (rs36084323), PD-1.3 (rs11568821), PD-1.5 (rs2227981), PD-1.9 (rs2227982), and PD-1 (rs7421861; Salmaninejad et al, 2018).