PDCD1 and HIV infectious disease: The dysregulation of the immune system observed during chronic HIV infection involves a progressive exhaustion of CD8+ T cells characterized by the overexpression of co-inhibitory receptors, such as PD-1 (programmed cell death-1), CTLA-4 (cytotoxic T lymphocyte-associated protein 4), LAG-3 (lymphocyte-activation gene 3), TIGIT (T cell immunoreceptor with immunoglobulin and ITIM domains), or Tim-3 (T cell immunoglobulin and mucin domain-containing protein 3).