Antibody-mediated protection against mucosal simian-human immunodeficiency virus challenge of macaques immunized with alphavirus replicon particles and boosted with trimeric envelope glycoprotein in MF59 adjuvant

Abstract

We have previously shown that rhesus macaques were partially protected against high-dose intravenous challenge with simian-human immunodeficiency virus SHIV(SF162P4) following sequential immunization with alphavirus replicon particles (VRP) of a chimeric recombinant VEE/SIN alphavirus (derived from Venezuelan equine encephalitis virus [VEE] and the Sindbis virus [SIN]) encoding human immunodeficiency virus type 1 HIV-1(SF162) gp140DeltaV2 envelope (Env) and trimeric Env protein in MF59 adjuvant (R. Xu, I. K. Srivastava, C. E. Greer, I. Zarkikh, Z. Kraft, L. Kuller, J. M. Polo, S. W. Barnett, and L. Stamatatos, AIDS Res. Hum. Retroviruses 22:1022-1030, 2006). The protection did not require T-cell immune responses directed toward simian immunodeficiency virus (SIV) Gag. We extend those findings here to demonstrate antibody-mediated protection against mucosal challenge in macaques using prime-boost regimens incorporating both intramuscular and mucosal routes of delivery. The macaques in the vaccination groups were primed with VRP and then boosted with Env protein in MF59 adjuvant, or they were given VRP intramuscular immunizations alone and then challenged with SHIV(SF162P4) (intrarectal challenge). The results demonstrated that these vaccines were able to effectively protect the macaques to different degrees against subsequent mucosal SHIV challenge, but most noteworthy, all macaques that received the intramuscular VRP prime plus Env protein boost were completely protected. A statistically significant association was observed between the titer of virus neutralizing and binding antibodies as well as the avidity of anti-Env antibodies measured prechallenge and protection from infection. These results highlight the merit of the alphavirus replicon vector prime plus Env protein boost vaccine approach for the induction of protective antibody responses and are of particular relevance to advancing our understanding of the potential correlates of immune protection against HIV infection at a relevant mucosal portal of entry.

FIG. 1.

Experimental design. Four groups (six rhesus macaques in each group) were immunized following a prime-boost regimen (groups A to D), and one group received no immunizations (group E). Vaccinated animals received 3 priming immunizations with 2 different VRP preparations (GagPol and Env) at weeks 0, 4, and 8 by either the intranasal (IN), intrarectal (IR), or intramuscular (IM) route. At weeks 24, 36, and 58, animals were immunized i.m. with either Env protein in MF59 adjuvant (groups A to C) or VRP (group D). All groups were challenged i.r. at week 63 with SHIV_SF162P4.

FIG. 2.

Antibody responses following immunization and challenge. (A) Group geometric mean (Geomean) SF162 envelope-specific ELISA titers. (B) Avidity of HIV-1 strain SF162 envelope-specific antibodies. The molar concentration of NH₄SCN required for displacement of 50% Ab is shown. (C and D) Linear V1 (C) and V3 (D) antibody responses as measured by peptide ELISA. The animals were immunized as described in the legend to Fig. 1. Black arrows indicate when the animals were immunized, and red arrows indicate when the animals were challenged with SHIV. The values are means ± standard deviations (error bars).

FIG. 3.

Neutralizing antibody responses. (A) Neutralization of HIV-1 strain SF162 by sera from immunized rhesus macaques and macaques postchallenge. Sera taken following the third VRP prime, the second and third booster immunizations, and the SHIV challenge were assayed in TZM-bl cells for neutralizing activity against SF162. Individual serum samples were assayed, and the geometric mean (Geomean) 80% (ID₈₀) neutralization titer is shown. The values are means ± standard errors of means (error bars). The lowest dilution tested was 1:15. The black and red arrows indicate when the animals were immunized and challenged, respectively. (B) Peptide mapping of serum neutralizing epitopes. The percent inhibition of SF162 neutralization in the presence of 10 μg/ml of the indicated peptide is shown. Inhibition in the presence of V1 (filled) or V3 (open) peptides is shown. Each symbol shows the value for an individual animal in a group. Neutralization was carried out at a serum dilution corresponding to the ID₇₀ value.

FIG. 4.

VRP prime-protein boost vaccine regimen provided protection from SHIV infection. (A) The rhesus macaques were immunized with VRP encoding both SIV_mac239 GagPol and HIV-1_SF162 Env via the intranasal (IN), intrarectal (IR), or intramuscular (IM) route and boosted with Env or VRP encoding Env by the intramuscular route. The plasma viral load of individual animals was measured via a branched-DNA assay. The limit of detection for this assay was 100 copies/ml. (B) The peak viral load values (either 2 or 4 weeks following challenge) are indicated for individual animals, with the group means represented by horizontal lines. Significant reductions in group peak viral load compared to the control group were observed for the groups receiving VRP i.n. or i.m. P values for the means of the groups were determined by two-sided Wilcoxon rank sum analysis.

FIG. 5.

Antibodies with high neutralizing capacity, binding titers, and avidity prechallenge are associated with protection from SHIV infection. The animals were divided into protected and infected groups on the basis of the peak viral load (<2.7 and ≥4.0, respectively). Significant differences between groups were observed with respect to NAb titer, total Ab titer, and avidity. Avidity, total Abs, and Ab ratio are as described in footnotes to Table 1 (footnote c, a, and b, respectively). V1 and V3 NAbs are as described in the legend to Fig. 3. P values were obtained by the Mann-Whitney test.