HIV infection of CD4 + T cells in vitro induces changes in DNA methylation of genes that regulate immune responses (interferon gamma (IFNG), interleukin-2 (IL2), forkhead box P3 (FOXP3) and programmed cell death 1 (PDCD1, the gene encoding PD-1)) [13–16]. Here, PDCD1 is linked to HIV infectious disease.