CD8 apoptosis may be a predictor of T cell number normalization after immune reconstitution in HIV

Abstract

Background: As part of the Houston Vanguard study, a subset of 10 patients randomized to receive IL-2 therapy were compared to 4 patients randomized to not receive IL-2, for markers of T cell activation and death during the first three cycles of IL-2. All patients were treated with combination antiretroviral therapy (ART) and were virally suppressed. The purpose of the study was to examine the role of CD8(+) T cell death in responses to ART and IL-2 therapy.

Methods: Lymphocytes were examined at Day 0, 5 and 30 days during three cycles of IL-2 therapy. CD25, CD38, HLA-DR expression and annexin (cell death) were examined on CD4 and CD8 subpopulations. Follow up studies examined CD4 levels and CD4:CD8 reconstitution after 6 years using both univariant and multivariate analyses.

Results: Human lymphocytes responded to IL-2 therapy by upregulation of CD25 on CD4(+) T cells, leading to an increase in CD4 cell counts. CD8(+) T cells did not increase CD25 expression, but upregulated activation antigens (CD38 and DR) and had increased death. At baseline, 7 of the 14 patients had high CD8+ T cell apoptosis (mean 17.0% +/- 6.0). We did an exploratory analysis of immune status after six years, and found that baseline CD8+ T cell apoptosis was correlated with CD4 cell count gain beginning two years post enrollment. Patients with low levels of CD8(+) T cell apoptosis at baseline (mean 2.2% +/- 2.1) had significantly higher CD4 cell counts and more normalized CD4:CD8 ratios than patients with high CD8(+) T cell apoptosis (mean CD4 cell counts 1,209 +/- 164 vs 754 +/- 320 cells/mm(3); CD4:CD8 ratios 1.55 vs. 0.70, respectively).

Conclusion: We postulate that CD8(+) T cell apoptosis may reflect inherent activation status, which continues in some patients even though viral replication is suppressed which influences the ability of CD4(+) T cells to rebound. Levels of CD8(+) T cell apoptosis may therefore be an independent predictor of immune status, which should be shown in a prospective study.

Figures

Figure 1

Increase in CD25 Expression on CD4+ T Cells 5 Days after IL-2 Therapy Initiation. Histogram of a representative response of CD4+ and CD8+ T cells to scIL-2. Shown are staining of CD4+ and CD8+ T cells with CD25 at Day 0 and after 5 days of self administered scIL-2. Only the CD4+T cells show an increase of CD25 after 5 days.

Figure 2

CD4+ T Cells Respond to IL-2 by Up-regulating CD25 Expression 5 Days after Every Cycle. a and b. IL-2 induces more CD25 expression on CD4+ T cells. Values are percentage of (a) CD4+ or (b) CD8+ T cells which express CD25. Representative low-dose recipient shown. Patient received scIL-2 on days 1–5, 65–69 and 121–125

Figure 3

Increase in CD38+DR+ CD8+ T Cells 5 Days after scIL-2 Therapy Initiation. Cytograms of CD38 and DR expression on CD8+ T cells during a single cycle of scIL-2. Both the percentage of CD38DRbright cells increases as well as the MFI of CD38 on the whole population. (CD38 MFI DAY 0 = 7.41, DAY 5 = 20.9, DAY 30 = 7.46)

Figure 4

Activation and death of CD8 T cells in a patient receiving three cycles of high dose scIL-2. Dying CD8+ T cells are activated. Values are percentage of CD8+ T cells that are CD38+ DRHi (diamonds) or that bind Annexin V (circles). Patient received 7.5 MIU scIL-2 on days 1–5, 57–61 and 114–118.

Figure 5

CD4:CD8 Ratios over Time in Low versus High CD8 Apoptosis Groups. The low baseline CD8+ T cell annexin group has a higher mean CD4:CD8 ratio after six years than high baseline CD8+ T cell annexin group. The results are the mean values of CD4:CD8 ratio ± SD. A repeated measures ANOVA indicated a statistically significant difference (p = 0.041).