Potent, protective anti-HIV immune responses generated by bimodal HIV envelope DNA plus protein vaccination

Abstract

It is generally thought that an effective vaccine to prevent HIV-1 infection should elicit both strong neutralizing antibody and cytotoxic T lymphocyte responses. We recently demonstrated that potent, boostable, long-lived HIV-1 envelope (Env)-specific cytotoxic T lymphocyte responses can be elicited in rhesus monkeys using plasmid-encoded HIV-1 env DNA as the immunogen. In the present study, we show that the addition of HIV-1 Env protein to this regimen as a boosting immunogen generates a high titer neutralizing antibody response in this nonhuman primate species. Moreover, we demonstrate in a pilot study that immunization with HIV-1 env DNA (multiple doses) followed by a final immunization with HIV-1 env DNA plus HIV-1 Env protein (env gene from HXBc2 clone of HIV IIIB; Env protein from parental HIV IIIB) completely protects monkeys from infection after i.v. challenge with a chimeric virus expressing HIV-1 env (HXBc2) on a simian immmunodeficiency virusmac backbone (SHIV-HXBc2). The potent immunity and protection seen in these pilot experiments suggest that a DNA prime/DNA plus protein boost regimen warrants active investigation as a vaccine strategy to prevent HIV-1 infection.

Figure 1

Anti-HIV Env CTL responses in rhesus monkeys after HIV env DNA and o-gp160 vaccinations. Rhesus PBMCs were tested for cytotoxicity after restimulation in vitro for 7 days with autologous B cell lines infected with vaccinia-env and tested for lysis in a 4-h ⁵¹Cr release assay using similar antigen-sensitized cells for targets. Cytoxicity curves are shown for individual monkeys for each vaccination group: HIV env DNA plus o-gp160 vaccinees (solid lines), naive/o-gp160 vaccinees (broken lines), and naive/vector DNA plus ovalbumin-vaccinated monkeys (dotted lines). No specific killing was found using wild-type vaccinia-treated targets.

Figure 2

Anti-HIV Env antibody responses in rhesus monkeys after HIV env DNA and o-gp160 vaccinations. Sera from vaccinated monkeys were tested at the indicated timepoints relative to the final vaccination for anti-gp120 ELISA antibody responses (shown as end point titers in A) and for SHIV-HXBc2-neutralizing antibody titers (B). Data for individual monkeys are depicted in each figure.

Figure 5

Antibody responses of rhesus monkeys after HIV gp160t DNA (3X) and gp160t DNA/o-gp160 (1X) vaccinations. Serial dilutions of sera were tested for anti-gp120 ELISA antibody responses 2 weeks after the final vaccination (solid lines) compared with preimmune sera from the same monkeys (dotted lines). ELISA responses are also shown for a pool of sera obtained from HIV+ humans (dashed line). Anti-SHIV-HXBc2 neutralization titers for each serum sample are indicated in the legend.

Figure 3

Seroconversion to SIV Gag antigen reactivity was detected in plasma of control but not experimental vaccinated monkeys after SHIV-HXBc2 challenge. Plasma from the HIV env DNA plus o-gp160 (Group I), naive/o-gp160 (Group II), and naive/vector DNA plus ovalbumin (Group III) vaccinated monkeys were assessed for antibody reactivity to HIV-2 Western immunoblot strips at 3, 6, and 11 weeks after virus inoculation. The two panels at left show positive and negative plasma control sample Western reactivities.

Figure 4

PBMCs from HIV env DNA plus o-gp160-immunized rhesus monkeys were negative for SIV gag/pol DNA by PCR analysis. DNA was isolated from PBMCs of the experimental vaccinated monkeys (0092 and 0003) and two of the control naive/vector DNA plus ovalbumin-vaccinated monkeys (0059 and 0053) at the times noted and subjected to PCR amplification using oligomers specific for either SIV gag/pol or, as a control, the cellular CD4 gene.