Multiclade human immunodeficiency virus type 1 envelope immunogens elicit broad cellular and humoral immunity in rhesus monkeys

Abstract

The development of a human immunodeficiency virus type 1 (HIV-1) vaccine that elicits potent cellular and humoral immune responses recognizing divergent strains of HIV-1 will be critical for combating the global AIDS epidemic. The present studies were initiated to examine the magnitude and breadth of envelope (Env)-specific T-lymphocyte and antibody responses generated by vaccines containing either a single or multiple genetically distant HIV-1 Env immunogens. Rhesus monkeys were immunized with DNA prime-recombinant adenovirus boost vaccines encoding a Gag-Pol-Nef polyprotein in combination with either a single Env or a mixture of clade-A, clade-B, and clade-C Envs. Monkeys receiving the multiclade Env immunization developed robust immune responses to all vaccine antigens and, importantly, a greater breadth of Env recognition than monkeys immunized with vaccines including a single Env immunogen. All groups of vaccinated monkeys demonstrated equivalent immune protection following challenge with the pathogenic simian-human immunodeficiency virus 89.6P. These data suggest that a multicomponent vaccine encoding Env proteins from multiple clades of HIV-1 can generate broad Env-specific T-lymphocyte and antibody responses without antigenic interference. This study demonstrates that it is possible to generate protective immune responses by vaccination with genetically diverse isolates of HIV-1.

FIG. 1.

Vaccine-elicited cellular immune responses to HIV-1 clade-A, clade-B, clade-C, and 89.6P Env antigens by PBL of rhesus monkeys following DNA prime and rAd boost immunizations. PBL were freshly isolated at weeks 12 (post-DNA prime), 27 (post-rAd boost), and 42 (day of challenge) postimmunization and were assessed for IFN-γ ELISPOT responses following stimulation with peptide pools spanning the indicated HIV-1 Env proteins. Data are presented as the mean number of antigen-specific SFC per 10⁶ PBL ± SEM from six monkeys per group.

FIG. 2.

Vaccine-elicited cellular immune responses to SIV Gag and Pol by PBL of rhesus monkeys following DNA prime-rAd boost immunizations. PBL were freshly isolated at week 27 postimmunization (1 week following rAd boost) and assessed for IFN-γ ELISPOT responses following stimulation with peptide pools spanning the SIV Gag and Pol proteins. Data are presented as the mean number of antigen-specific SFC per 10⁶ PBL ± SEM from six monkeys per group.

FIG. 3.

Titers of antibodies to HIV-1 clade-A, clade-B, or clade-C Env proteins in plasma from rhesus monkeys following DNA prime-rAd boost immunizations. Plasma samples were obtained at week 28 postimmunization (2 weeks following rAd boost), and titers of anti-gp145 antibody to the indicated HIV-1 Env proteins were determined by ELISA. Data are presented as the mean geometric titer from six monkeys per group.

FIG. 4.

Antibody neutralizing activity in plasma of rhesus monkeys following DNA prime-rAd boost immunizations. Plasma samples were obtained from vaccinated and control monkeys at week 28 postimmunization (2 weeks following rAd boost) and were tested at a 1:5 dilution for neutralizing activity against panels of clade-A, clade-B, and clade-C HIV-1 isolates. The dashed line represents a reference point of 20% neutralization, as noted in Results. Data are presented as the mean percent neutralizing activity ± SEM from six monkeys per group. Note that the top panel of clade-A viruses also includes a control MuLV Env pseudovirus.

FIG. 5.

Cellular immune responses to HIV-1 Env and SIV Gag and Pol by PBL of vaccinated and control rhesus monkeys following SHIV-89.6P challenge. PBL were freshly isolated 2 weeks following challenge and assessed for IFN-γ ELISPOT responses following stimulation with peptide pools spanning the indicated HIV-1 Env proteins or the SIV Gag and Pol proteins. Data are presented as the mean number of antigen-specific SFC per 10⁶ PBL ± SEM from six monkeys per group.

FIG. 6.

Plasma viral RNA levels following SHIV-89.6P challenge. The peak plasma viral RNA level for each monkey was measured on day 16 postchallenge. The set point plasma viral RNA level for each monkey was calculated as the median of values detected between days 85 and 169 postchallenge. Log viral copies per milliliter from individual monkeys are shown, with horizontal bars indicating the median value of the six monkeys per experimental group. The detection limit of the assay, 125 copies/ml, is shown by a dashed line.

FIG. 7.

Peripheral blood CD4⁺ T lymphocytes post-SHIV-89.6P challenge. The percentage of CD3⁺ CD4⁺ T lymphocytes in the peripheral blood of the rhesus monkeys was assessed by flow cytometry through day 169 following SHIV-89.6P infection. Data are presented as the mean percentage of peripheral blood CD4⁺ T lymphocytes from six monkeys per group ± SEM.