CD4 and infection: However, in BLT mice, the growth of HIV-1 fsΔ-1 and HIV-1 fsΔ-13 was ~3-fold lower than WT HIV-1, and the level of systemic CD4+ T cell decrease and thymopathy by HIV-1 fsΔ-1 and HIV-1 fsΔ-13 infections (~50% reduction) were milder than WT HIV-1 (~90% reduction) [45].