Reduced protection from simian immunodeficiency virus SIVmac251 infection afforded by memory CD8+ T cells induced by vaccination during CD4+ T-cell deficiency

Abstract

Adaptive CD4(+) and CD8(+) T-cell responses have been associated with control of human immunodeficiency virus/simian immunodeficiency virus (HIV/SIV) replication. Here, we have designed a study with Indian rhesus macaques to more directly assess the role of CD8 SIV-specific responses in control of viral replication. Macaques were immunized with a DNA prime-modified vaccinia virus Ankara (MVA)-SIV boost regimen under normal conditions or under conditions of antibody-induced CD4(+) T-cell deficiency. Depletion of CD4(+) cells was performed in the immunized macaques at the peak of SIV-specific CD4(+) T-cell responses following the DNA prime dose. A group of naïve macaques was also treated with the anti-CD4 depleting antibody as a control, and an additional group of macaques immunized under normal conditions was depleted of CD8(+) T cells prior to challenge exposure to SIV(mac251). Analysis of the quality and quantity of vaccine-induced CD8(+) T cells demonstrated that SIV-specific CD8(+) T cells generated under conditions of CD4(+) T-cell deficiency expressed low levels of Bcl-2 and interleukin-2 (IL-2), and plasma virus levels increased over time. Depletion of CD8(+) T cells prior to challenge exposure abrogated vaccine-induced protection as previously shown. These data support the notion that adaptive CD4(+) T cells are critical for the generation of effective CD8(+) T-cell responses to SIV that, in turn, contribute to protection from AIDS. Importantly, they also suggest that long-term protection from disease will be afforded only by T-cell vaccines for HIV that provide a balanced induction of CD4(+) and CD8(+) T-cell responses and protect against early depletion of CD4(+) T cells postinfection.

Figures

FIG. 1.

Study design. Immunization regimens. The total numbers of animals per group and of MamuA*-01+ macaques included in each group are indicated in parentheses. A single inoculation of the anti-CD4 antibody was given 45 weeks before challenge exposure to macaques in groups 2 and 4. Four inoculations of the anti-CD8 antibody were given before challenge exposure to animals in group 5. α, anti.

FIG. 2.

In vivo depletion of T-cell subsets. Absolute CD3+ CD4+, CD3+ CD8+, and CD20+ T-cell counts per mm3 of blood in macaques treated with the anti-CD4 antibody (OKT4A-IgG1) (A and B), left untreated (C), and treated with the anti-CD8 antibody (cM-T807) (D) are shown. Arrows represent times of inoculation of CM-T807 and challenge exposure to SIV. Results for MamuA*-01+ macaques in group 5 are shown in bold.

FIG. 3.

Frequency of Ki67+ and CCR5+ CD4+ T cells in blood of macaques either untreated or treated with the OKT4A-IgG1 depleting antibody. (A) Percentage of Ki67+ CD4+ T cells at weeks 6, 19 to 23, and 47 to 52 in blood of macaques from groups 3 (untreated) and 4 (treated). (B) Percentage of CCR5+ CD4+ T cells at weeks 6, 19 to 23, and 47 to 52 in blood of macaques from groups 3 (untreated) and 4 (treated).

FIG. 4.

Levels of viral RNA in plasma following challenge exposure to SIVmac251. Plasma virus levels in each macaque from groups 1 (mock infected) and 2 (mock infected and T-cell depleted) (A), group 3 (vaccinated) (B), group 4 (vaccinated and CD4+ T-cell depleted) (C), group 5 (vaccinated and CD8+ T-cell depleted) (D) are shown. The asterisk refers to the MamuA*-01+ macaques. (E) Comparative analysis of the geometrical mean plasma virus levels in macaques from groups 1 and 2 versus groups 3, 4, and 5. Comparative analysis of the geometrical mean plasma virus levels in Mamu-A*01+ (F) and Mamu-A*01− (G) macaques within groups 3 and group 4. Depl, depleted; vacc, vaccinated.

FIG. 5.

Virus level in tissues of macaques mock vaccinated, vaccinated, and vaccinated under conditions of CD4 deficiency. Mean SIV Gag copies in total CD4+ T cells (A) or CD4+ T-cell subsets (B) from lymph nodes (LN) at week 6 are shown. The standard deviation is derived from a total of five animals in group 3, four animals in group 4, and two animals in group 1. SIV Gag copies in total CD4+ T cells (C) or CD4+ T-cell subsets (D) in lymph nodes or blood at week 24 are shown. The standard deviation is derived from a total of three animals in group 3, and three animals in group 4. One animal in group 1 was analyzed at this time point. CM, central memory; TM, total memory CD4 T cells.

FIG. 6.

Immune responses to SIV following vaccination. Proliferative responses induced by the MVA boost to p24 Gag (A) and the gp120 Env (B). (C) ELISPOT assay of Gag in blood of the immunized macaques (D) Titers of serum antibodies to gp120 following vaccination with MVA-SIV. (E) Frequency of Gag181-189 (Gag181) tetramer-positive CD8+ T cells in blood of macaques from groups 1, 3, and 4 before and after booster immunization with MVA-SIV. (F) Percentage of Gag181-189 tetramer-positive T cells expressing Bcl-2 at 1 or 2 weeks (weeks 27 and 28) following booster immunization with MVA-SIV. ELISA, enzyme-linked immunosorbent assay.

FIG. 7.

Immune responses to SIV following challenge exposure. (A) Expansion of Gag181-189 (Gag181) tetramer-positive CD8+ T cells in blood of macaques from groups 1, 3, and 4 following challenge exposure to SIVmac251. (B) SIV Gag-specific IFN-γ, TNF-α, and IL-2 production in CD8+ and CD4+ T-cell responses in blood and lymph nodes from macaques 898L, 899L, 905L, 215M, 881L, 317M, 319M, 222M, 550M, 556M, 564M, 217M, 220M, 901L, 223M, 225M, 298M, and 299M, obtained at week 6 following SIVmac251 challenge exposure. (C) Quantification of immune responses in purified mononuclear cells collected from blood and lymph nodes of macaques 889L, 898L, 215M, 217M, 220M, 223M, and 22H obtained at week 24 (left). SIV Gag-specific IFN-γ, TNF-α, and IL-2 production in CD8+ and CD4+ T-cell responses at week 24 in blood of the same macaques.