Recent studies have also shown that targeting the surface receptors cytotoxic T-lymphocyte antigen 4 (CTLA-4) and programmed death-1 (PD-1) on both effector and regulatory T cells, a process known as checkpoint blockade, can dramatically improve anti-tumor immunity [40–44], especially in advanced stage melanoma [45–47]. The gene discussed is PDCD1; the disease is melanoma.