PDCD1 and HIV-1 infection: Several studies have identified numerous inhibitory receptors that are elevated on T cell in several tumors and HIV-1 infection; such as programmed cell death-1 (PD-1), cytotoxic T-lymphocyte associated protein 4 (CTLA-4 and CD152), CD244 (2B4), CD160, lymphocyte activation gene 3 (LAG-3), T cell immunoglobulin and mucin 3 (Tim-3), and T-cell immunoglobulin and ITIM domain (TIGIT), among others (8–15).