CD4 and HIV infectious disease: On the other hand, lower HIV infection susceptibility, potentially (but controversially) associated with factors such as HLA alleles, partner-specific alloimmunity, reduced CD4+ T cell susceptibility, variability of cellular proteins involved in HIV-1 replication, host antiviral cellular proteins, or some related host genetic factor [15]–[23], may explain why some of the women have remained negative despite high-risk exposures and therefore remain uninfected although significantly older.