CD4 and HIV infectious disease: HIV co-infection was the most dominant factor changing the distribution of CD4+ and CD8+ immune subsets as individuals with TBI and HIV had significantly more EM and EMRA CD8+ T cells and fewer naïve CD4+ T cells compared to individuals with TBI (Figure 3D, Supplementary Figure 4B), possibly due to HIV infection of CD4+ T cells, although individuals from these cohorts had different demographics.