For instance, CD4 T cell counts are used to start prophylaxis against cryptococcal infection in patients with ≤ 100 CD4 cells/μL and stop prophylaxis when patients have reached > 200 cells/μL, or to start co-trimoxazole prophylaxis to prevent HIV-related infections caused by a variety of bacterial, fungal and protozoan infections in case CD4 counts are ≤ 350 cells/μL [6,7]. This evidence concerns the gene CD4 and cryptococcosis.