Impact of HIV-1 infection and highly active antiretroviral therapy on the kinetics of CD4 ⁺ and CD8 ⁺ T cell turnover in HIV-infected patients

Abstract

To evaluate the effects of HIV infection on T cell turnover, we examined levels of DNA synthesis in lymph node and peripheral blood mononuclear cell subsets by using ex vivo labeling with BrdUrd. Compared with healthy controls (n ‫؍‬ 67), HIV-infected patients (n ‫؍‬ 57) had significant increases in the number and fraction of dividing CD4 ؉ and CD8 ؉ T cells. Higher percentages of dividing CD4 ؉ and CD8 ؉ T cells were noted in patients with the higher viral burdens. No direct correlation was noted between rates of T cell turnover and CD4 ؉ T cell counts. Marked reductions in CD4 ؉ and CD8 ؉ T cell proliferation were seen in 11͞11 patients 1-12 weeks after initiation of highly active antiretroviral therapy (HAART). These reductions persisted for the length of the study (16 -72 weeks). Decreases in naïve T cell proliferation correlated with increases in the levels of T cell receptor rearrangement excision circles. Division of CD4 ؉ and CD8 ؉ T cells increased dramatically in association with rapid increases in HIV-1 viral loads in 9͞9 patients 5 weeks after termination of HAART and declined to pre-HAART-termination levels 8 weeks after reinitiation of therapy. These data are consistent with the hypothesis that HIV-1 infection induces a viral burden-related, global activation of the immune system, leading to increases in lymphocyte proliferation.AIDS ͉ proliferation ͉ immune activation ͉ T cell receptor rearrangement excision circles H IV-1 infection is associated with a failure in T cell homeostasis, resulting in a gradual decline in CD4 ϩ T cell numbers. Studies examining lymphocyte turnover rates during infection with HIV or simian immunodeficiency virus have generated mixed results. Most of these discrepancies are likely the result of differences in the methods used to measure turnover rates, the use of longitudinal as opposed to cross-sectional cohorts, or the sensitivity and specificity of the assays used.An initial study of lymphocyte turnover rates using 3 Hthymidine to label CD4 ϩ and CD8 ϩ T cells found increased turnover rates in patients with HIV-1 infection (1). Studies of lymphocyte turnover derived through analysis of immediate changes in CD4 ϩ T cell counts in the blood after highly active antiretroviral therapy (HAART) also led to estimates of high rates of CD4 turnover (2-4), although others have suggested that lymphocyte redistribution may be the major cause for CD4 increases immediately after HAART (5-8). Measurements of lymphocyte proliferation using Ki-67, BrdUrd, and 2 H-glucose have yielded varying results (9-19); however, the general consensus is that T cell proliferation is increased in HIV͞simian immunodeficiency virus-infected subjects. Variations in these studies may be caused by the difference in sample numbers, cross-sectional versus longitudinal studies, patient cohort composition, and whether one is measuring the absolute or fractional level of cell division.To gain better insight into the immunopathogenic effects of HIV-1 infection, and to attempt to resolve some of the controversy...

Differential requirements for antigen or homeostatic cytokines for proliferation and differentiation of human Vγ9Vδ2 naive, memory and effector T cell subsets

“…Although the relative contributions of different cytokines to homeostatic proliferation in humans are difficult to address directly, recent reports are consistent with the view that human and murine T cells have similar requirements [13,14,21,[28][29][30][31][32]. Thus, antigen-independent naive T cell proliferation in the mouse requires TCR tickling, IL-7, and lymphopenia, whereas CD8 memory T cells turn over constitutively, express high levels of the IL-2/ 15Rb chain and require IL-15 or IL-7.…”

“…5C) and were also able to consistently reduce the viability of intracellular Mtb (Fig. 5D) [21][22][23]. Cells that pass the G1 cell cycle checkpoint are committed to replicate DNA and complete the cell cycle [22].…”

“…Cells that pass the G1 cell cycle checkpoint are committed to replicate DNA and complete the cell cycle [22]. The in vivo turnover of T cells can therefore be assessed by ex vivo bromodeoxyuridine (BrdU) incorporation [21]. Freshly purified PBMC from five healthy donors were cultured in the presence of BrdU, and Vc9Vd2 T cells were purified and analyzed for BrdU incorporation in relation to CD27 and CD45RA expression.…”

“…This assay was carried out by using the procedure reported by Lempicki et al [21]. Vc9Vd2 T cells were isolated by positive selection as described above and incubated with 10 lM BrdU (Sigma) for 4 h at 37 C, 5% CO 2 .…”

Increased peripheral expansion of naive CD4+ T cellsin vivoafter IL-2 treatment of patients with HIV infection

“…Ex vivo labeling of proliferating naive CD4ϩ T cells was carried out by incubating freshly isolated PBMCs with BrdUrd for 4 h at 37°C as described (11). Labeled cells were analyzed by FACS.…”