Control of viremia and maintenance of intestinal CD4(+) memory T cells in SHIV(162P3) infected macaques after pathogenic SIV(MAC251) challenge

Abstract

Recent HIV vaccine failures have prompted calls for more preclinical vaccine testing in non-human primates. However, similar to HIV infection of humans, developing a vaccine that protects macaques from infection following pathogenic SIV(MAC251) challenge has proven difficult, and current vaccine candidates at best, only reduce viral loads after infection. Here we demonstrate that prior infection with a chimeric simian-human immunodeficiency virus (SHIV) containing an HIV envelope gene confers protection against intravenous infection with the heterologous, highly pathogenic SIV(MAC251) in rhesus macaques. Although definitive immune correlates of protection were not identified, preservation and/or restoration of intestinal CD4(+) memory T cells were associated with protection from challenge and control of viremia. These results suggest that protection against pathogenic lentiviral infection or disease progression is indeed possible, and may correlate with preservation of mucosal CD4(+) T cells.

Figure 1

Experimental design of the SHIV_162P3 inoculation and SIV_MAC251 challenge. SHIV infected macaques were subsequently intravenously challenged with different dosages of pathogenic SIV_MAC251 on the days post inoculation indicated in three separate experiments. For controls, four naïve Chinese origin macaques were concurrently inoculated with SIV_MAC251 (highlighted in red).

Figure 2

Plasma viral RNA levels in macaques after primary SHIV_162P3 infection, prior to pathogenic SIV_MAC251 challenge. All animals had high primary viremia 14–21 days after vaginal inoculation, which declined to low or undetectable levels by 70 days of infection. Viral loads were undetectable in 6 out of the 14 animals by 70 days post inoculation.

Figure 3

Plasma viral RNA levels in macaques following SIV_MAC251 challenge. Plasma viremia is reported as log₁₀ vRNA copies per ml of plasma (detection limit 30 vRNA copies/ml). Plasma viral loads from individual experiments (A) and mean +/− SE of the mean viral loads for each of the different groups (B) are shown. Note there was significantly higher viremia in non-immunized, control macaques (red lines) compared to immunized macaques during early (day 14), steady state (day 42) and late (day 282) stages of infection following SIV_MAC251 challenge. Plasma viral load from the 3 InRh in Group A is presented as a dashed line. (B) Mean plasma viral loads from 4 historical naive ChRh intravenously infected with 100TCID₅₀ SIV_MAC251 are shown as dashed purple line.

Figure 4

(A) Cell-associated viral RNA levels in jejunum LPL in macaques following SIV_MAC251 challenge (detection limit 30 vRNA copies). There was low to undetectable viremia in intestinal tissues at the day of SIV_MAC251 challenge in SHIV immunized macaques. By 21, 56 and 104 days post SIV_MAC251 challenge increased viral replication was noticed in naïve challenged macaques, whereas SHIV_162P3 immunized macaques had low to undetectable tissue viral load. Mean tissue VLs are shown with a line in each plot. (B) Kaplan-Meier survival curves for the immunized and non-immunized macaques in all three groups after SIV_MAC251 challenge demonstrating significantly increased survival of immunized macaques compared to controls. Survival comparisons were performed using a log-rank test.

Figure 5

Dynamics of CD4⁺ T cell percentages in peripheral blood (A) and axillary lymph node (B) of immunized and non-immunized macaques following SIV_MAC251 challenge. Note all non-immunized (naïve) challenged macaques had a rapid decrease in CD4⁺ T cells by day 14 after challenge in both peripheral blood and LN (red lines) whereas CD4⁺ T cells were preserved in immunized macaques. InRh macaques are delineated by dashed lines.

Figure 6

(A) A representative dot plots showing CD4⁺ T cells as a percentage of total T cells (gated through CD3⁺ lymphocytes) in macaques (Group B) after SIV_MAC251 challenge. Note that restoration and/or preservation of intestinal CD4⁺ T cells was observed in a SHIV immunized macaque (FA08) compared to the non-immunized macaque (V302), in which there was rapid and sustained loss of intestinal CD4⁺ T cells within 14 days of challenge. (B) Changes in intestinal CD4⁺ T cells of immunized and non-immunized macaques following challenge with SIV_MAC251. Note that in all groups, there was a rapid decrease in intestinal CD4⁺ T cells in all non-immunized (highlighted in red) compared to immunized macaques by day 14-post challenge. Intestinal CD4⁺ T cells of InRh are shown as dashed lines.

Figure 7

(A) Percentages of memory (CCR5⁺CD45RA^neg) CD4⁺ T cells in the intestine of a representative SHIV immunized (FA08) and non-immunized, naive (V302) macaque before (day 0) and 14 days after SIV_MAC251 challenge. Note the marked and rapid decrease in intestinal target cells (CD3⁺CD4⁺CCR5⁺CD45RA^neg) typical of naïve macaques challenged with SIV_MAC251, whereas these cells are maintained in the immunized macaque. (B) Percentages of intestinal CD4⁺CCR5⁺ cells (gated through CD3⁺ lymphocytes) are shown for groups A–C. Note a rapid decrease in CD4⁺CCR5⁺ T cells occurs in all non-immunized challenged macaques (highlighted in red) within 14 days of SIV_MAC251 challenge, whereas target cells are preserved in immunized macaques.