CD4 and infection: However, also like the passaged virus swarm from which it was derived, in immunocompetent PTMs (i.e., those not CD8α-depleted at the time of infection), stHIV-A19 viral loads progressively declined during the chronic phase of infection with no progressive CD4+ T-cell loss or disease progression (Table 1), indicating a requirement for CD8α+ cell-depletion for disease development in this model [54].