Different patterns of immune responses but similar control of a simian-human immunodeficiency virus 89.6P mucosal challenge by modified vaccinia virus Ankara (MVA) and DNA/MVA vaccines

Abstract

Recently we demonstrated the control of a mucosal challenge with a pathogenic chimera of simian and human immunodeficiency virus (SHIV-89.6P) by priming with a Gag-Pol-Env-expressing DNA and boosting with a Gag-Pol-Env-expressing recombinant modified vaccinia virus Ankara (DNA/MVA) vaccine. Here we evaluate the ability of the MVA component of this vaccine to serve as both a prime and a boost for an AIDS vaccine. The same immunization schedule, MVA dose, and challenge conditions were used as in the prior DNA/MVA vaccine trial. Compared to the DNA/MVA vaccine, the MVA-only vaccine raised less than 1/10 the number of vaccine-specific T cells but 10-fold-higher titers of binding antibody for Env. Postchallenge, the animals vaccinated with MVA alone increased their CD8 cell numbers to levels that were similar to those seen in DNA/MVA-vaccinated animals. However, they underwent a slower emergence and contraction of antiviral CD8 T cells and were slower to generate neutralizing antibodies than the DNA/MVA-vaccinated animals. Despite this, by 5 weeks postchallenge, the MVA-only-vaccinated animals had achieved as good control of the viral infection as the DNA/MVA group, a situation that has held up to the present time in the trial (48 weeks postchallenge). Thus, MVA vaccines, as well as DNA/MVA vaccines, merit further evaluation for their ability to control the current AIDS pandemic.

FIG. 1.

Temporal levels of Gag-specific T cells. (A) Gag-specific CD8 T-cell responses in MVA-only and DNA/MVA-vaccinated animals. Symbols for individual animals are given in Fig. 3. (B) Gag-specific IFN-γ ELISPOTs for DNA/MVA-vaccinated (open bars) and MVA-only (hatched bars) macaques at various times before and after challenge. Three pools of 10 to 13 Gag peptides (22-mers overlapping by 12) were used for the analyses. The numbers above data bars represent the geometric means for the ELISPOTs within each group. The numbers at the bottom of the graph designate individual animals. #, data not available; ∗, less than 20 spot-forming units (SFU); NA, data not available for group. Data for the Gag-Pol-Env groups are for the group that received 2.5 mg of DNA as an intradermal prime (see reference 2).

FIG. 2.

Temporal antibody responses. (A) Temporal assays of anti-Env binding, anti-Env neutralizing, and anti-Gag binding antibodies. Micrograms of total antibody against SIV239 Gag or 89.6 Env were determined using ELISAs. The titers of neutralizing antibody for SHIV-89.6 and SHIV-89.6P were determined using MT-2 cell killing and neutral red staining (16). Neutralization titers are the reciprocal of the serum dilution giving 50% neutralization of the indicated viruses grown in human PBMC. Symbols for animals are the same as those in Fig. 3. Data for the Gag-Pol-Env groups are in part reproduced from reference . (B) Avidity of anti-Env binding antibody at 2 weeks postchallenge. GM, geometric mean titer.

FIG. 3.

Temporal viral loads and CD4 counts after challenge of vaccinated and control animals. (A) Geometric mean viral loads. (B) Geometric mean CD4 counts. (C) Viral loads. (D) CD4 counts for individual animals in the vaccine and control groups. The key to the animal numbering system is presented in panel D. Assays for the Gag-Pol-Env groups for the first 12 weeks had a background of 1,000 copies of RNA per milliliter of plasma. Animals with loads below 1,000 were scored with a load of 500. For all other assays, the background for detection was 300 copies of RNA/ml, and animals with levels of virus below 300 were scored at 300. † represents the death of an animal. Data for the DNA/MVA group are in part reproduced from reference 2. GM, geometric mean titers of each group.

FIG. 4.

Postchallenge anti-Gag CD8 T cells and anti-Env binding antibody. Data are the same as those in Fig. 1 and 2 but are plotted on a linear scale to better show the differences in postchallenge patterns of anamnestic immune responses in the DNA/MVA and MVA-only groups.

FIG. 5.

Viral loads and infected cells in the peripheral blood at 2 weeks postchallenge. (A) Intracellular p27 staining. PBMC were fixed and stained for intracellular Gag, CD3, and CD8. Cells were gated on lymphocytes, followed by gating for CD3⁺ and CD8⁻, and were then analyzed for Gag. The frequencies in the graph represent Gag-positive cells as the percentage of total CD4 cell levels. Representative data are shown for each group: animal 3 (prechallenge) and animals 3, 45, and 26 (postchallenge). (B) Comparison of viral loads and numbers of infected cells at 2 weeks postchallenge. Geometric means for viral RNA copies and percent infected CD4 cells are represented as horizontal bars on the respective graphs. Filled symbols represent the DNA/MVA-vaccinated animals, and open symbols represent the MVA-only-vaccinated animals. The diagonal lines represent the trend lines for the DNA/MVA-vaccinated animals (solid) and the MVA-only-vaccinated animals (dashed).