Abstract

In the first preventative human immunodeficiency virus (HIV) vaccine study to be carried out in Africa, 40 HIV-seronegative Ugandan volunteers were randomly assigned to receive a canarypox vector containing HIV-1 clade B (env and gag-pro) antigens (ALVAC-HIV; n=20), control vector containing the rabies virus glycoprotein G gene (n=10), or saline placebo (n=10). Cytotoxic T lymphocyte activity against target cells expressing clade A, B, and D antigens was assessed using standard chromium-release and confirmatory interferon-γ enzyme-linked immunospot (ELISPOT) assays. Neutralizing antibody responses to cell line–adapted strains and primary isolates in all 3 clades were also tested. Twenty percent of vaccine recipients generated detectable cytolytic responses to either Gag or Env, and 45% had vaccine-induced HIV-specific CD8+ T cell responses, as measured by the ELISPOT assay. In contrast, only 5% of the control group had vaccine-specific responses. Neutralizing antibodies against primary and laboratory-adapted HIV-1 clade B strains were seen in 10% and 15% of vaccine recipients, respectively, but responses against clades A and D were not detected. Although the immunogenicity of this clade B–based vaccine was low, ALVAC-HIV elicited CD8+ T cell responses with detectable cross-activity against clade A and D antigens in a significant proportion of vaccine recipients

Human immunodeficiency virus (HIV) infection and AIDS are currently the leading causes of death in sub-Saharan Africa [1]. There is a critical need for a safe, effective, and accessible preventative HIV vaccine in Africa [2]. The success of a vaccine likely will depend on the induction of responses active against all HIV-1 subtypes (clades) relevant to a particular geographic region [3]. Vaccine trials in the areas hardest hit by the epidemic have been constrained not only by a lack of clinical and laboratory infrastructure but also by the lack of vaccines that target the virus subtypes endemic to these regions [3, 4]. Indeed, concerns about the lack of sufficient immunologic cross-reactivity in Africa to the clade B viruses has largely precluded vaccine testing, because immunogens based on African clades remain in development

The HIV epidemic has spread rapidly in Uganda, but no vaccines are currently available that are based on locally endemic strains. The Joint United National Programme on HIV/AIDS and the World Health Organization have estimated that the HIV seroprevalence in the adult Ugandan population is 8.3% [1] and that 3 clades (clades A, D, and C) account for most new infections [5, 6]. Previous studies of HIV-1–specific cellular immune responses in infected Ugandans have shown cross-clade recognition by immune responses generated in natural infection [7]. Such observations raise the question of whether existing vaccines based on clade B viruses might generate cross-clade responses sufficient to induce effective immune responses in regions where non–clade B viruses are endemic

Decisions to move forward with particular HIV-1 vaccine candidates are based in part on the prevailing understanding of the correlates of protective immunity in this infection. Increasing evidence suggests that cytotoxic T lymphocyte (CTL) responses will be a critical component of an effective vaccine. Although vaccines that induce CTL responses are unlikely to prevent an initial round of cellular infection, CTL are able to lyse infected cells before progeny virions are produced [8] and therefore have the potential to limit virus load and slow disease progression. Studies that used animal models of HIV-1 infection have shown that CD8+ T cells are critical to initial and long-term control of infection, and successful vaccination has been associated with the induction of strong CTL responses [9–12 ]

In addition to identifying vaccine candidates that elicit protective immunity, it is important to conduct studies in the areas where the epidemic is spreading most rapidly. Despite significant public health gains in developing countries, the lack of clinical and laboratory infrastructure remains a critical issue in vaccine development in most of sub-Saharan Africa [2, 13]

On the basis of these considerations, we initiated a trial of a candidate recombinant HIV-canarypox vaccine in uninfected persons in Uganda. This phase 1 HIV vaccine study, the first in Africa, evaluated the safety and cross-clade immunogenicity of a clade B–based vaccine in an uninfected Ugandan population. The main goals of this trial were (1) to establish an effective clinical and laboratory infrastructure to conduct vaccine trials and (2) to determine whether this clade B–based vaccine would be able to induce immune responses to the vaccine subtype, as well as cross-reactive responses to the viruses endemic in this region of Africa

Subjects, Materials, and Methods

Study designThis study, HIV Network for Prevention Trials (HIVNET) 007, was a randomized, double-blind, placebo-controlled clinical trial conducted at the Joint Clinical Research Centre in Kampala, Uganda. HIV-seronegative Ugandan volunteers with a low risk of HIV infection were selected using the following criteria: age ⩾18 years; lifetime number of sex partners ⩽2; and no newly acquired sexually transmitted diseases in the preceding 6 months. Twenty individuals were randomly assigned to receive a recombinant HIV-1 clade B–canarypox vaccine (vCP205 [Aventis-Pasteur]; ALVAC-HIV), 10 received a recombinant canarypox vaccine containing the rabies virus gpG gene (vCP65 [Aventis-Pasteur]; ALVAC-RG), and 10 received saline placebo. Immunizations were performed at time point 0 and at 1, 3, and 6 months. All volunteers, coordinators, and laboratory personnel were blinded to the immunization received. Safety considerations included close monitoring for local toxicity and systemic symptoms after each immunization and throughout the trial. Self-reports of adverse events were collected for 3 days after immunization, and serious adverse events were recorded through follow-up visits during the 2-year course of study. Recruitment began on February 1999, full enrollment was completed by August 1999, and the study ended in September 2001

VaccinesALVAC-HIV expresses the HIV-1 envelope protein gp120 (strain MN), which is linked to the transmembrane domain of gp41 (strain LAI), and the HIV strain LAI genes that encode the entire Gag protein and the protease section of the pol gene [14]. ALVAC-HIV was grown on specific pathogen–free chick embryo fibroblasts to a final titer of 106.42 TCID50/mL. The control vaccine was ALVAC-RG, given at a titer of 106.2 TCID50/mL. All vaccines were stored at 4°C until administration, and all immunizations were given by intramuscular injection into the deltoid muscle

CTL activityNumbers of HIV-specific CTL were measured by the standard AIDS Vaccine Evaluation Group protocol [14, 15]. On days 0, 42, 98, 182, 287, and 546, peripheral blood mononuclear cells (PBMC) were freshly isolated and stimulated in vitro, as described elsewhere [14, 15]. Cytotoxic activity was evaluated in a standard chromium-release assay after 14 days of stimulation, using a ratio of effector to target cells of 50:1. Target cells consisted of autologous B lymphoblastoid cell lines infected with recombinant vaccinia viruses expressing clade A, B, or D proteins, with parental WR vaccinia as a control. Recombinant vaccinia viruses were provided by the National Institutes of Health AIDS Research and Reference Reagent Program (Rockville, MD) and included NYCBH and WR (control vaccinia), vP1291 (multigene WR vaccinia expressing gp120 from strain MN and Gag-Pro from strain LAI), vP1174 (clade B Env), vP1489 (clade A Env), vT173 (clade D Env), VDK1 (clade B Gag), vT135 (clade A Gag), and vT157 (clade D Gag). Positive cytolytic activity against HIV proteins was defined as at least 10% specific lysis and >50% reduction of lysis following depletion of CD8+ cells. Cumulative response rates were reported as the percentage of individuals who demonstrated responses to ⩾1 antigen at any time point

Interferon (IFN)–γ ELISPOTA modified ELISPOT was used to detect peptide-specific IFN-γ release by cryopreserved PBMC [7]. Samples were tested at baseline (time point 0), after the third and fourth immunizations, and 3 months after the last immunization (months 0, 3, 6, and 9). Cross-clade T cell recognition of Gag protein from clade A and clade D viruses also was evaluated at month 6. Synthetic peptides (clade A, B, and D Gag and clade B Env; 20 aa in length and overlapping adjacent peptides by 10 aa) were provided by the AIDS Research and Reference Reagent Program. PBMC were thawed and enriched for CD8+ cells using a bispecific CD3/CD4 monoclonal antibody [16] in the presence of interleukin-2 [17] and tested for activity by ELISPOT at 14 days. The number of spot-forming cells per 106 CD8+ cells was calculated as the average number of spots in replicate wells subtracted from the average number of spots in the control wells. Responses were considered to be positive if the number of spot-forming cells was at least twice that of the control, present at 2 different cell concentrations, and confirmed with a subsequent assay (ELISPOT or flow cytometry; see below). The background number of spot-forming cells was, on average, <15 sfc/well (range, 0–20 sfc/well) and included wells containing cells with medium alone or with irrelevant peptides

Intracellular cytokine flow cytometryCD8+ cells were incubated with peptides (10 μg/mL) at 37°C in 5% CO2 for 2 h in the presence of costimulatory anti-CD28 and anti-CD49d (1 μg/mL [Becton-Dickinson]). Brefeldin A (10 μg/mL) was subsequently added, and the cells were stained and analyzed as described elsewhere [18]. The negative control consisted of unstimulated cells (in the presence of anti-CD28 and anti-CD49d but without peptide). The positive control consisted of cells stimulated with the mitogen phematohemagglutinin (0.25 μg/mL [Murex Biotech]). Responses were considered to be positive if they were at least twice that of the control and were >0.1%

Virus neutralization assaySerum specimens were assayed for the ability to neutralize HIV cell line–adapted strains, as well as primary isolates. Nonrecombinant HIV-1 X4 strain MN and virus isolates UG92029 and UG92046, of subtypes B, A, and D, respectively, were used in the virus neutralization assays. Positive control serum samples were donated by the Medical Research Council AIDS reagent repository (Cambridge, UK). Neutralization of cell line–adapted viruses was performed as described elsewhere [19], with a few modifications. Primary HIV-1 isolates UG92029 and UG92046 were adapted to grow in H9 cell lines and then in MT-2 cell lines, as described elsewhere [20]. In brief, 5×105 H9 cells were infected with 1 mL of primary virus supernatant at 37°C for 2 h in 24-well plates; the cells were then diluted 1:4 in growth medium by splitting into 2 different wells and incubated further at 37°C for up to 3 weeks. Virus production in the culture supernatant was monitored using an in-house p24 antigen ELISA. The H9-adapted viruses, including strain MN, were then adapted to MT-2 cell lines, as described above. Virus production was monitored by checking for syncytium formation. After 2 weeks, the cultures were expanded in 50-mL flasks. Heat-inactivated serum was diluted 5-fold in growth medium (RPMI 1640 medium with 10% fetal calf serum, 2 mMl-glutamine, 100 IU/mL penicillin, and 100 μg/mL streptomycin) and incubated with an equal volume of 102 TCID50 of the viral isolate. After 1 h at 37°C, 100 μL of growth medium containing 5×102 MT-2 cells was added. Each serum dilution was tested in duplicate. The neutralization titer was determined at day 4 as the reciprocal of the highest dilution that prevented syncytium formation by 90%, compared with medium only and HIV-1–negative plasma control wells. Virus neutralization titers of ⩾20 were considered to be positive. Neutralization of primary isolates was carried out as described elsewhere [21]. Pooled donor cells were used and culture medium was changed on days 1, 2, and 3 for both virus titration and neutralization. Neutralization titers were calculated as the reciprocal plasma dilutions required to reduce p24 antigen production by 50%, compared with the HIV-1–negative plasma control

Statistical analysisData were collected onsite using optical character recognition software (TELEform; Cardiff) and analyzed using SAS for Windows, version 7.0 (SAS Institute). Statistical analysis included comparison of groups at baseline to ensure appropriateness of randomization. Given the size of this phase 1 trial (40 subjects), statistical analyses were limited. However, the protocol was statistically powered (80%) to detect a minimum 40% difference between the CTL response in the vaccine arm and either control arm with α=.05 (2-sided). In addition, the neutralizing antibody response had statistical power of 87% to detect a minimum 50% difference between the vaccine and placebo arms

Results

Vaccine safetyA total of 444 individuals were evaluated for participation in the study, and 174 volunteers met enrollment criteria (figure 1). Standard clinical criteria for enrollment were applied [14], and the lack of locally established normal ranges for laboratory values necessitated exemption status for several volunteers but did not significantly delay enrollment. Forty volunteers were enrolled, 8 women and 32 men, and >95% completed all of 4 of the follow-up visits (at 14 days after each vaccination). Adverse reactions to immunizations with ALVAC-HIV in the Ugandan cohort were similar to those in previous trials with these vaccines in HIV-seronegative volunteers in developed countries [14]. No severe (grade III or IV) adverse reactions attributable to receipt of this vaccine were observed. HIV seroconversion occurred in 2 subjects in the saline placebo arm during the trial. Seropositivity was confirmed by Western blot, and plasma viremia was detected in both of these subjects (virus loads were 18,000 and 110,000 HIV-1 RNA copies/mL). Heteroduplex mobility assay and viral sequencing of the envelope region [5] confirmed that the infecting viral strains were clade A and D viruses (data not shown)

Figure 1

Flow chart showing enrollment and subject distribution patterns for the HIV Network for Prevention Trials 007 vaccine study. The study examined the use of a canarypox vector containing human immunodeficiency virus type 1 (HIV-1) clade B antigens (ALVAC-HIV) as a vaccine. Controls were a canarypox vector containing the rabies virus gpG gene (ALVAC-RG) and saline placebo. AST, aspartate aminotransferase; B-LCL, B lymphoblastoid cell lines; HBsAg, hepatitis B virus surface antigen; RPR, rapid plasma reagent; TPHA, Treponema pallidum hemagglutination assay; UTI, urinary tract infection

Figure 1

Flow chart showing enrollment and subject distribution patterns for the HIV Network for Prevention Trials 007 vaccine study. The study examined the use of a canarypox vector containing human immunodeficiency virus type 1 (HIV-1) clade B antigens (ALVAC-HIV) as a vaccine. Controls were a canarypox vector containing the rabies virus gpG gene (ALVAC-RG) and saline placebo. AST, aspartate aminotransferase; B-LCL, B lymphoblastoid cell lines; HBsAg, hepatitis B virus surface antigen; RPR, rapid plasma reagent; TPHA, Treponema pallidum hemagglutination assay; UTI, urinary tract infection

Detection of immune responses by chromium-release assay using freshly isolated PBMCPBMC obtained from the study subjects were evaluated to determine the cumulative percentage of persons exhibiting vaccine-specific (clade B) CTL responses to HIV Gag or Env protein or both. Table 1 lists the positive responses to HIV proteins detected using the chromium-release assay in the 3 groups of subjects (ALVAC-HIV, ALVAC-RG, and saline placebo). Immunogenicity to the vaccine was seen in 4 of the 20 individuals who received ALVAC-HIV, and the earliest activity was detected after the second immunization, although activity did not persist after the final vaccine dose (figure 2). Of the 4 individuals who had vaccine-specific responses, none had responses to >1 HIV protein, and only 2 subjects had responses that were detected at >1 time point

Table 1

Cross-sectional and cumulative rates of response to human immunodeficiency virus (HIV) proteins, measured by chromium-release assay, among volunteers receiving a canarypox vector containing HIV-1 antigens (ALVAC-HIV; n=20), a control vector containing the rabies virus gpG gene (ALVAC-RG; n=10), or saline placebo (n=10)

Table 1

Cross-sectional and cumulative rates of response to human immunodeficiency virus (HIV) proteins, measured by chromium-release assay, among volunteers receiving a canarypox vector containing HIV-1 antigens (ALVAC-HIV; n=20), a control vector containing the rabies virus gpG gene (ALVAC-RG; n=10), or saline placebo (n=10)

Figure 2

Vaccine-specific responses over time, measured by chromium-release assay, in 4 subjects in the HIV Network for Prevention Trials 007 vaccine study. Cytotoxic T lymphocyte (CTL) activity against Gag or Env for the 4 volunteers with vaccine-specific responses are shown for each immunization time point and months 9 and 18. CTL activity was detected using a 4-h chromium-release assay with a ratio of effector to target cells of 50:1. Target cells were infected with vaccinia viruses expressing Gag and Env. Lysis values are shown after subtraction from control vaccinia vector lysis

Figure 2

Vaccine-specific responses over time, measured by chromium-release assay, in 4 subjects in the HIV Network for Prevention Trials 007 vaccine study. Cytotoxic T lymphocyte (CTL) activity against Gag or Env for the 4 volunteers with vaccine-specific responses are shown for each immunization time point and months 9 and 18. CTL activity was detected using a 4-h chromium-release assay with a ratio of effector to target cells of 50:1. Target cells were infected with vaccinia viruses expressing Gag and Env. Lysis values are shown after subtraction from control vaccinia vector lysis

We next evaluated cross-recognition of clade A and clade D virus in these 4 subjects with response to vaccine, using target cells expressing Gag and Env proteins derived from these endemic African clades. Of the 4 ALVAC-HIV recipients with detectable clade B–specific CTL responses, 2 demonstrated cross-recognition to another clade, 1 to clade A and 1 to clade D (figure 3). Responses to clade B and non–clade B vectors were also tested in the 2 control groups. Subject 070-38, in the saline placebo group, had detectable vaccine-specific (clade B) responses to Env after the second immunization. CTL activity for this individual did not persist but was subsequently confirmed by both ELISPOT and flow cytometric assays (data not shown). Subject 129-09, in the ALVAC-RG control group, had no detectable vaccine-specific CTL response, although a clade A Gag–specific CTL response was detected after the second immunization and clade D Gag–specific CTL activity was detected after the third immunization. Overall, the results of the chromium-release assay showed the ALVAC-HIV vaccine to be weakly immunogenic. However, the data demonstrate that it is possible to evaluate vaccine-induced responses with a radioactive readout in Uganda

Figure 3

Cross-clade cytotoxic T lymphocyte responses to proteins from human immunodeficiency virus of clades A and D in subjects 079-08 (A) and 095-40 (B). Freshly isolated peripheral blood mononuclear cells were stimulated in vitro with a recombinant vaccinia virus expressing multigene clade B antigen (vP1291) and tested for cytolytic activity after 14 days. Autologous B lymphoblastoid cell lines infected with recombinant vaccinia viruses expressing clades A, B, and D were used as target cells. The ratio of effector to target cells was 50:1. Lysis value are given after subtraction of control lysis. The CD8-mediated response was considered to be positive if the percentage of virus-specific lysis was ⩾10% and a reduction of >50% was observed after CD8+ cell depletion

Figure 3

Cross-clade cytotoxic T lymphocyte responses to proteins from human immunodeficiency virus of clades A and D in subjects 079-08 (A) and 095-40 (B). Freshly isolated peripheral blood mononuclear cells were stimulated in vitro with a recombinant vaccinia virus expressing multigene clade B antigen (vP1291) and tested for cytolytic activity after 14 days. Autologous B lymphoblastoid cell lines infected with recombinant vaccinia viruses expressing clades A, B, and D were used as target cells. The ratio of effector to target cells was 50:1. Lysis value are given after subtraction of control lysis. The CD8-mediated response was considered to be positive if the percentage of virus-specific lysis was ⩾10% and a reduction of >50% was observed after CD8+ cell depletion

Detection of immune responses by ELISPOT after in vitro expansion of previously cryopreserved PBMCTo further evaluate the immunogenicity of the ALVAC-HIV vaccine, cryopreserved PBMC were subjected to additional analysis. PBMC enriched for CD8+ cells by in vitro stimulation with a bispecific CD3/CD4 monoclonal antibody were tested in an IFN-γ ELISPOT, using overlapping synthetic HIV peptides. These assays were performed in blinded fashion at baseline, after the third and fourth immunizations, and at month 9; results are shown in figure 4. The cumulative rates of response to Gag and Env were 40% and 35%, respectively, for ALVAC-HIV recipients, whereas cumulative rates of 10% and 0%, respectively were observed in the control groups (saline placebo and ALVAC-RG). Vaccine-specific responses were detected up to 3 months after the last immunization, and consistently positive responses were detected in 4 of the 9 subjects who had vaccine-specific responses. The positive results of the chromium-release assay were confirmed in all 4 cases by ELISPOT. Likewise, the positive results of the CTL assay found for 1 subject were confirmed by ELISPOT. To confirm that the detected activity represented CD8+ T cell responses, HLA restriction was performed in the same IFN-γ ELISPOT. Recognized HLA-restricted peptides in subjects who had vaccine-specific responses corresponded to targeted regions described in virus isolated from individuals with natural HIV-1 infection (table 2) [22]. An example is shown for subject 072-01, who demonstrated an Env-specific response on the chromium-release assay. The epitope specificity was confirmed by intracellular cytokine flow cytometry and shown by ELISPOT to be HLA class I restricted (figure 5). Cross-clade CD8+ T cell activity to clade A and clade D Gag proteins was evaluated at the fourth immunization time point, using overlapping peptides corresponding to specific subtypes. All 4 subjects with vaccine-specific responses who demonstrated clade B Gag–specific activity recognized one or both endemic clade A and D viruses (table 2). A total of 5 subjects with vaccine-specific responses were found to have cross-clade reactivity against Gag or Env proteins, as measured by the chromium-release assay or IFN-γ ELISPOT (figure 2 and table 2). These results indicate that ALVAC-HIV induced CTL responses that are major histocompatibility class I epitope–restricted and that cross-clade recognition was detected, albeit in a minority of vaccine recipients

Figure 4

Immune responses to a canarypox vector containing human immunodeficiency virus type 1 (HIV-1) clade B Gag (A) Env (B) or both (C); control vector containing the rabies virus gpG gene (ALVAC-RG); and saline placebo were measured at time point 0 and months 3, 6, and 9. One subject in the placebo arm had an Env-specific response at month 6. No response was detected at time point 0. ELISPOT results are reported as the percentage of subjects with positive responses. The cumulative percentage of positive responses to Gag, Env, and Gag/Env were calculated for volunteers who had vaccine-specific responses for all the time points tested

Figure 4

Immune responses to a canarypox vector containing human immunodeficiency virus type 1 (HIV-1) clade B Gag (A) Env (B) or both (C); control vector containing the rabies virus gpG gene (ALVAC-RG); and saline placebo were measured at time point 0 and months 3, 6, and 9. One subject in the placebo arm had an Env-specific response at month 6. No response was detected at time point 0. ELISPOT results are reported as the percentage of subjects with positive responses. The cumulative percentage of positive responses to Gag, Env, and Gag/Env were calculated for volunteers who had vaccine-specific responses for all the time points tested

Table 2

Vaccine-induced epitope-specific responses among recipients of a canarypox vector containing human immunodeficiency virus type 1 antigens (ALVAC-HIV)

Table 2

Vaccine-induced epitope-specific responses among recipients of a canarypox vector containing human immunodeficiency virus type 1 antigens (ALVAC-HIV)

Figure 5

Characterization of CD8-mediated response to human immunodeficiency virus (HIV) antigens in subject 072-01. A After 4 doses of vaccine, a chromium-release assay demonstrated a clade B Env–specific response but no cross-reaction with clade A or D. B The epitope was mapped to HIV-1 strain MN Env peptide (aa 291–310) and confirmed by intracellular interferon (IFN)–γ flow cytometry (gated on CD8+CD3+ lymphocytes). Cells were stimulated with medium alone (control) or HIV peptide (Env). C HLA restriction of the Env peptide (HLA-A74) was performed using ELISPOT and target cells including autologous (A2,74;B8,35) and partially matched B lymphoblastoid cell lines pulsed with Env peptide. PE, phycoerythrin; PerCP, peridinin chlorophyll protein

Figure 5

Characterization of CD8-mediated response to human immunodeficiency virus (HIV) antigens in subject 072-01. A After 4 doses of vaccine, a chromium-release assay demonstrated a clade B Env–specific response but no cross-reaction with clade A or D. B The epitope was mapped to HIV-1 strain MN Env peptide (aa 291–310) and confirmed by intracellular interferon (IFN)–γ flow cytometry (gated on CD8+CD3+ lymphocytes). Cells were stimulated with medium alone (control) or HIV peptide (Env). C HLA restriction of the Env peptide (HLA-A74) was performed using ELISPOT and target cells including autologous (A2,74;B8,35) and partially matched B lymphoblastoid cell lines pulsed with Env peptide. PE, phycoerythrin; PerCP, peridinin chlorophyll protein

Neutralizing antibody responsesThree of the 20 ALVAC-HIV vaccine recipients (15%) had significant levels of neutralizing antibodies against the cell line–adapted HIV-1 strain MN, as defined by a reduction in virus production of at least 90%. Two of these subjects demonstrated activity against clade B primary virus as well (table 3). The neutralizing antibody responses persisted up to day 365 in 2 subjects. No neutralizing antibodies against clade A and clade D viruses, which are endemic in Uganda, were detected. None of the subjects in the control groups had detectable levels of neutralizing antibodies against either cell line–adapted or primary viruses. Of note, plasma from all subjects was HIV negative in binding assays (using V3 peptides, recombinant p24 HIV-1 strain LAI-BRU, and recombinant gp120 HIV-1 strain MN), except for 1 naturally infected subject whose plasma tested positive on the p24 antibody assay (data not shown)

Table 3

Titers of neutralizing antibody against the cell line–adapted virus (CLAV) and primary human immunodeficiency virus type 1 (HIV-1) clade B (strain MN) in recipients of a canarypox vector containing HIV-1 antigens (ALVAC-HIV)

Table 3

Titers of neutralizing antibody against the cell line–adapted virus (CLAV) and primary human immunodeficiency virus type 1 (HIV-1) clade B (strain MN) in recipients of a canarypox vector containing HIV-1 antigens (ALVAC-HIV)

Discussion

There is a critical need to establish the clinical and laboratory infrastructure for performing preventative HIV vaccine trials in developing countries. Africa faces an overwhelming burden of HIV-1 infection, and it is estimated that >70% of the world’s 30 million infected adults live in sub-Saharan Africa. A safe and effective vaccine for prevention of HIV infection and AIDS would be the best approach to controlling this pandemic. The study presented here, the first trial of a preventative HIV-1 vaccine in Africa, established the feasibility of conducting vaccine trials in areas with limited infrastructure and demonstrated the safety, as well as limited immunogenicity, of the recombinant HIV-canarypox vaccine vCP205 in the Ugandan population

The HIVNET 007 trial, which included low-risk HIV-1–seronegative adults in Uganda, provides new data on the vaccine-induced immune responses in a population affected by non–clade B HIV-1 strains. Previous vaccine studies in developed countries have demonstrated that ALVAC-HIV is immunogenic [15, 23–25 ]. The Ugandan trial demonstrated that the canarypox vaccine has limited immunogenicity in this region, and vCP205 (ALVAC-HIV) currently is not being manufactured by Aventis-Pasteur. The observed difference in vaccine-induced immunity, as measured by cytolytic activity or cytokine release, may be due to functional impairment of the CD8+ T cells [26] or to the different sensitivities of the 2 methods. Ongoing studies are currently under way to thoroughly validate the IFN-γ ELISPOT for clinical studies within the HIV Vaccine Trials Network and will likely lead to more-conclusive characterizations of the specificity of various immunological assays. The rate of response to the vaccine, as detected by chromium-release assay, was lower overall (20% to both Env and Gag) than has been reported in other ALVAC-HIV vaccine studies that were carried out in developed countries (33%–62%) [14, 15]. The decreased immunogenicity may be due to more complex factors, such as ethnic genetic variability. In this regard, it has recently been shown that individuals with specific HLA types are more likely to have responses specific to candidate HIV vaccines [27]. These findings emphasize the need for more local phase 1/2 testing of candidate vaccines

The present HIV vaccine study is important in several aspects. It establishes the feasibility of conducting HIV vaccine trials in developing nations. The clinical monitoring and immunogenicity studies (except for ELISPOT, which was performed in the United States) were all conducted locally. The success of this study reflected the committed and coordinated international effort to test the candidate vaccine. ALVAC-HIV was well tolerated and safe in our Ugandan cohort. The immune responses elicited overall were weak and inconsistent, and the CTL activity may be near the assay’s detection limit. The immunogenic regions identified in several of the subjects with vaccine-specific responses suggested that ALVAC-HIV elicited responses that have previously been shown to be targeted in natural HIV infection [22]. Perhaps the more important finding of this study is the demonstration of cross-reactive immune responses elicited from a single-clade vaccine in a region of multiple HIV clade prevalence. The small study size does not allow significant assessment of cross-clade activity in this vaccine trial, but our data suggest that cross-immunity can be elicited using a single clade–based vaccine—in this case, using a clade that is not endemic to the region. Further studies using multiple-clade or clade-matched immunogens in ethnically and geographically different populations will be needed to determine the best candidate vaccine and approach both globally and locally

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