In Vivo Expansion Coincident with Excessive in Vitro Cell Death within the Memory Subset of CD8+ T Cells in HIV Type 1 Infection

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Abstract
In HIV-1-infected individuals the CD8+ T cell subset is considerably expanded. This has been shown to be caused predominantly by an increase in the number of CD8+CD28- T cells. To characterize further the subsets of CD8+ T cells, we have performed analyses of cell surface phenotype, T cell receptor V beta usage, and ability to survive in unstimulated cultures. CD8+CD28- T cells frequently expressed CD45RA. Nonetheless, coincident expression of CD95 (Fas) and high levels of integrins suggested that these cells were immunologically experienced. Contrary to what has been observed in CD8+CD28- T cells from uninfected individuals, a common hierarchy of V beta usage was found in CD8+CD28- T cells from HIV-1-infected individuals, which was adhered to by all the study participants, and which was shown to be similar to that observed within CD8+CD28+ T cells. Cells from the memory subsets of CD8+ T cells showed a high incidence of spontaneous death in unstimulated cultures, indicating that these cells have received signals for death by apoptosis in vivo . In contrast, most naive CD8+CD28+CD45RA+ cells survived. The CD8+CD28- memory subset is expanded in vivo despite evidence for coincident excessive cell death in vitro . Our results are consistent with the notion that frequent transitions occur from the memory CD8+CD28+CD45RA- T cell subset to the end-stage CD8+CD28- subset during HIV-1 infection.