CD8+ lymphocytes control viral replication in SIVmac239-infected rhesus macaques without decreasing the lifespan of productively infected cells

Abstract

While CD8+ T cells are clearly important in controlling virus replication during HIV and SIV infections, the mechanisms underlying this antiviral effect remain poorly understood. In this study, we assessed the in vivo effect of CD8+ lymphocyte depletion on the lifespan of productively infected cells during chronic SIVmac239 infection of rhesus macaques. We treated two groups of animals that were either CD8+ lymphocyte-depleted or controls with antiretroviral therapy, and used mathematical modeling to assess the lifespan of infected cells either in the presence or absence of CD8+ lymphocytes. We found that, in both early (day 57 post-SIV) and late (day 177 post-SIV) chronic SIV infection, depletion of CD8+ lymphocytes did not result in a measurable increase in the lifespan of either short- or long-lived productively infected cells in vivo. This result indicates that the presence of CD8+ lymphocytes does not result in a noticeably shorter lifespan of productively SIV-infected cells, and thus that direct cell killing is unlikely to be the main mechanism underlying the antiviral effect of CD8+ T cells in SIV-infected macaques with high virus replication.

Figure 1. Experimental model to assess the lifespan of productively infected cells in the presence or absence of CD8+ T cells.

Top panel, group A; CD8+ lymphocyte depletion and ART during early chronic phase, ART alone during late chronic phase. Bottom panel, group B; ART alone during early chronic phase, CD8+ lymphocyte depletion and ART during late chronic phase. Animals were given OKT8F (CD8-depleting mAb) for 3 consecutive days (Group A, days 58–60; Group B, days 177–179). Antiretretroviral therapy (PMPA and FTC) was given for 28 consecutive days.

Figure 2. Administration of OKT8F results in near complete depletion of CD8+ lymphocytes.

(A) Representative flow cytometry plots (x-axis, CD8; y-axis, CD3) demonstrating CD8+ lymphocyte levels in blood (left, 7 days before depletion; right, 6 days after depletion). (B) Longitudinal assessment of the absolute number of CD8+ T cells in peripheral blood for each animal during early chronic phase (left) or late chronic phase (right). Each colored line indicates an individual animal (CD8+ lymphocyte-depleted). Gray lines indicate the average CD8+ T cell number in non-depleted (ART alone) RMs. Dotted vertical line indicates the first day of depleting Ab treatment, solid vertical line indicates the first day of ART. (C) Representative flow cytometry plots (x-axis, CD8; y-axis, CD3) demonstrating CD8+ lymphocyte depletion in rectal biopsies (left, 10 days before depletion; right, 6 days after depletion). (D) Longitudinal assessment of the percent of CD8+ T cells (compared to baseline) in rectal biopsies during early chronic phase (left) or late chronic phase (right). Bars represent average of treated animals. CD8+ T cells previously gated on live lymphocytes.

Figure 3. CD8+ lymphocyte depletion results in a 0.7–2.2 log₁₀ rise in viral load.

Change of viral load from baseline for each individual animal after CD8 depletion, during early chronic phase (white bars, left) or late chronic phase (black bars, right).

Figure 4. Treatment with PMPA and FTC effectively suppresses virus replication in SIVmac239-infected RMs.

(A, B) Plasma viral load (log₁₀) measured longitudinally for each individual animal (black lines, CD8+ lymphocyte-depleted, red lines, control) during (A) early chronic phase or (B) late chronic phase. (C,D) Average plasma viral load (log₁₀) for each group (black, CD8+ lymphocyte-depleted; red, control) during (C) early chronic phase or (D) late chronic phase. Error bars represent standard deviation. Dotted vertical line indicates the first day of depleting Ab treatment, solid vertical line indicates the first day of ART.

Figure 5. CD8+ lymphocyte depletion does not affect the lifespan of infected cells during SIV infection.

The estimated lifespan of productively infected cells, 1/δ, for each animal; CD8+ lymphocyte-depleted (black) and control (red) during (A) early chronic phase or (B) late chronic phase. P = n.s.

Figure 6. Changes in chemokines and cytokines after CD8+ lymphocyte depletion.

Levels of plasma MIP1α (top left), IFNγ (top right), IL-7 (bottom left) and TNFα (bottom right) were measured in all animals after CD8+ lymphocyte depletion, early phase shown here. Dotted line indicates first day of depleting treatment.

Figure 7. CD8+ lymphocyte depletion results in a rise in activated CD4+ T cells.

(A) Longitudinal assessment (individual animals from CD8-depleted group and mean and s.d. from control group) of the percent of CD4+CCR5+ (top left), CD4+Ki67+ (top right), CD4+HLA-DR+ (bottom left), and CD4+CD69+ (bottom right) T cells during early chronic infection. (B) Longitudinal assessment of the mean (and s.d.) percent of CD4+Ki67+ T cells in rectal biopsies (left) and bronchoalveolar lavage (right).