Antibodies to gp120 and PD-1 expression on virus-specific CD8+ T cells in protection from simian AIDS

Abstract

We compared the relative efficacies against simian immunodeficiency virus (SIV) challenge of three vaccine regimens that elicited similar frequencies of SIV-specific CD4(+) and CD8(+) T-cell responses but differed in the level of antibody responses to the gp120 envelope protein. All macaques were primed with DNA plasmids expressing SIV gag, pol, env, and Retanef genes and were boosted with recombinant modified vaccinia Ankara virus (MVA) expressing the same genes, either once (1 × MVA) or twice (2 × MVA), or were boosted once with MVA followed by a single boost with replication-competent adenovirus (Ad) type 5 host range mutant (Ad5 h) expressing SIV gag and nef genes but not Retanef or env (1 × MVA/Ad5). While two of the vaccine regimens (1 × MVA and 1 × MVA/Ad5) protected from high levels of SIV replication only during the acute phase of infection, the 2 × MVA regimen, with the highest anti-SIV gp120 titers, protected during the acute phase and transiently during the chronic phase of infection. Mamu-A*01 macaques of this third group exhibited persistent Gag CD8(+)CM9(+) effector memory T cells with low expression of surface Programmed death-1 (PD-1) receptor and high levels of expression of genes associated with major histocompatibility complex class I (MHC-I) and MHC-II antigen. The fact that control of SIV replication was associated with both high titers of antibodies to the SIV envelope protein and durable effector SIV-specific CD8(+) T cells suggests the hypothesis that the presence of antibodies at the time of challenge may increase innate immune recruiting activity by enhancing antigen uptake and may result in improvement of the quality and potency of secondary SIV-specific CD8(+) T-cell responses.

Fig 1

Clinical and virological outcome of vaccinations. (A) Schematic representation of the immunization regimens. The arrows indicate times of immunizations and of challenge exposure to SIV_mac251, performed by the intrarectal route at week 74 in all animals and at week 52 in the 1 × MVA group. (B, C, D, E) Plasma virus levels are presented for each animal. *, identified Mamu-A*01⁺ macaques. (F, G, H) Comparison of mean virus load in plasma in macaques from the different groups.

Fig 2

Antibody titers and kinetics of CD8⁺CM9⁺ T-cell response in the vaccinated macaques. Endpoint antibody titers to p27 Gag (A) and gp120 (B) in the sera of the immunized monkeys. (C) Correlative analysis between the titers of the gp120-binding antibodies in all the vaccinated animals and plasma viral loads at week 6 postinfection. (D to G) Frequency and kinetics of CM9⁺CD8⁺ T cells in blood of the macaques during immunization and following challenge exposure to SIV_mac251. (H to K) Relative frequency of CD95⁺CD28⁻ (effector memory [EM] in solid black bars) and CD95⁺CD28⁺ (central memory [CM] in white bars) CM9⁺CD8⁺ T cells in blood of vaccinated and control macaques following challenge exposure to SIV_mac251. The data are shown as means for each group, calculated using the individual frequency of EM or CM on the total Gag-CM9⁺ memory population.

Fig 3

PD-1 expression on CD8⁺CM9⁺ T-cell response in the vaccinated macaques. (A) CFSE gating strategy and mean fluorescence intensity (MFI) of PD-1 expression on nonproliferating CFSE^hi CM9⁺CD8⁺ T cells from representative macaques. (B to D) PD-1 level of expression on CFSE^lo or CFSE^hi CM9⁺ CD8⁺ T cells from animals from the 2 × MVA and 1 × MVA/Ad5 groups were analyzed at week 74 (before challenge) and at weeks 7 and 24 after challenge exposure to SIV_mac251. (E) PD-1 expression levels on low and high proliferating CD8⁺CM9⁺ T cells in the two groups of vaccinated animals at all time points. The plot includes all the data points, and each dot represents one macaque. (F and G) Frequency of Gag-specific T cells 5 days following stimulation with Gag peptides in the presence (or absence) of anti-PD-L1 blocking antibody; CD8⁺ T cells (F) and CD4⁺ T cells (G) are gated on CFSE^low cells. (H to J) PD-L1 expression on human mDCs (H) and on pDCs (J) and CD86 expression on human mDCs (I) following in vitro infection with Ad5 or MVA.

Fig 4

Heat map representation of gene expression within CM9⁺ CD8⁺ T cells at 24 weeks following challenge. (Upper panel) Genes from representative pathways analyzed with GSEA and displayed as a heat map to demonstrate differential expression between Adv CM9⁺ and MVA CM9⁺ cells. Each pathway comprising selected top upregulated genes is represented by a different color. The false color expression in log₂ scale is depicted on the right side of the figure. The heat map shows the expression level of each gene (red, upregulated; blue, downregulated). Eight significant pathways are shown (P values < 0.05) (6 upregulated in Ad5 CM9⁺ samples and 2 upregulated in MVA CM9⁺ cells), as is a subset of 30 most up- and downregulated genes (22 upregulated in Ad5 CM9⁺ samples and 8 upregulated in MVA CM9⁺ samples). (Lower panel) Genes upregulated and downregulated in antigen presentation pathways.