Included studies have different definitions for immune status; some use low and high CD4 counts based on WHO criteria for AIDS [26,27], while others designate cut-off values such as CD4 > 300 cells/μL for a high CD4 count [30] or a CD4 count < 250 cells/μL for a low CD4 count, CD4 count = 250 to 500 cells/μL for a medium CD4 count, and CD4 count > 500 cells/μL for a high CD4 count [33]. This evidence concerns the gene CD4 and AIDS.