Accrual and Demographic Data
Three hundred 30 participants were enrolled at 10 sites in the United States between December 2000 and August 2001 and were randomized to 1 of 4 groups (see ). Overall, 305 (92%) participants completed all 4 vaccinations, with 279 (85%) completing follow-up. A total of 25 participants discontinued vaccinations for diverse reasons, including 1 pregnancy and 1 HIV infection. No participants discontinued because of concerns regarding vaccine toxicity.
shows the group stratification by gender, sexual preference, race, HIV risk group, and age. The median age of enrolled participants was 35.0 years; 82% of enrollees were non-Hispanic whites, and 12% were non-Hispanic African Americans. For all demographic variables, no statistically significant differences were observed across groups (P > 0.05, Fisher exact test).
Demographics and Vaccination Frequencies
Safety and Tolerability
Overall, the vCP1452 and rgp120 injections were well tolerated. Two vaccinees (1 in group A and 1 in group B) experienced severe pain or tenderness that completely resolved within 24 to 72 hours of onset. When compared with placebo, rates for maximum pain or tenderness and for maximum erythema or induration were significantly higher in all vaccine groups for the ALVAC injection (left arm, P > 0.01) but not for the rgp120 injection (right arm, P ≥ 0.13).
Systemic reactogenicity, including malaise, myalgia, headache, nausea, or fever, was generally mild, although 6 vaccinees (1 in group A, 1 in group B, and 4 in group C) experienced severe systemic side effects that resolved within 1 to 5 days after vaccination. Of the participants experiencing a temperature ≥38.3°C, 6 of 120, 2 of 60, 0 of 60, and 1 of 90 were observed in groups A, B, C, and D, respectively. There were no significant trends or abnormalities in hematologic, renal, or hepatic profiles or in CD4+ T-cell counts seen in any of the 4 groups. Comparing rates of participants experiencing 1 or more AEs, there were no significant differences between treatment groups overall (P = 0.82, Fisher exact test).
Three grade 3 AEs for which relatedness to the study product was definite (n = 1), probable (n = 1), or “cannot rule out” (n = 1) were reported: 2 from group A and 1 from group B. These included 2 severe reactogenicity experiences (“probably related” chills in group A and “definitely related” bilateral arm pain or tenderness in group B). The third grade 3 AE (group A) was a T-cell lymphoma diagnosed 4 months after the final vaccination; the participant was treated with chemotherapy, and disease was still present at the end of the study. In addition, there were 2 participants with miscarriages (groups A and C) determined to be unrelated to the study product (1 group C participant had 2 miscarriages). There were 6 participants (5 vaccinees and 1 placebo recipient) who became HIV infected, 2 before completion of the immunization schedule and 4 between 1 and 7 months after vaccination.
Anti-Gag p24 binding antibodies were detected by ELISA (data not shown) at day 182, 2 weeks after the final vaccination, in all vaccine groups with response rates ranging from 23% (95% CI: 8% to 38%) to 36% (95% CI: 21% to 51%). Responses peaked at day 182 and were detectable by day 364 in only 2 group A participants. There was no significant difference between vaccine groups in the number of recipients mounting p24 antibodies at day 182, suggesting that rgp120 coadministration in groups B and C did not significantly enhance Gag-specific antibody responses.
As depicted in , HIV-1MN neutralizing antibody (nAb) titers were significantly higher (P < 0.01) in all vaccine groups for days 98, 182, and 364 when compared with placebo but only in group C for day 42. At day 98, net response rates ranged from 70% (95% CI: 57% to 81%) to 83% (95% CI: 69% to 93%). Notably, nAb titers were low when detectable (geometric mean titer [GMT] range: 18.1−44.9) in those receiving ALVAC alone (group A). Their responses peaked after the third vaccination, decreasing in magnitude by days 182 and 364.
FIGURE 1 nAbs against HIV-1MN in peripheral blood measured by vital dye neutralization assay. Antibody levels are expressed as log titers by day within group. Each box plot displays the 25th percentile, the median, and the 75th percentile. The whiskers on each (more ...)
The magnitude and frequency of nAb titers to HIV-1MN
were consistently higher (average GMT >3-fold) in groups receiving rgp120 compared with vCP1452 alone (P < 0.01 at day 182). Interestingly, a single boost with vCP1452 plus rgp120 after 2 doses of vCP1452 alone (group B, day 98) was superior to 2 doses of vCP1452 plus rgp120 boosted with vCP1452 alone (group C; P < 0.01). By month 6, however, group C responses were clearly boosted with 1 additional dose of vCP1452 plus rgp120, whereas group B responses were not (see ). The explanation for this is unclear but suggests that 3 injections of subunit protein are better than 2 and/or that the rgp120 schedule with the 5-month boost interval (0, 1, and 6 months) is superior to the 3-month interval (3 and 6 months). By day 364, without any additional boosts, the antibody responses in all groups receiving vaccine were detected at low titers and were not significantly different irrespective of schedule. This suggests that Env-specific memory B cells persist and is consistent with previous observations regarding the longevity of these responses.22
Induction of nAbs to HIV-IIIIB was examined in a subset (n = 62) of samples from day 182 (data not shown). These sera were less able to neutralize HIV-1IIIB than HIV-1MN, and greater response frequencies were observed in the groups receiving rgp120 (14 of 20 subjects [70%] in groups B and C) versus vCP1452 only (0 of 25 subjects [0%] in group A) or placebo (0 of 17 subjects [0%] in group D) (P < 0.01). Similarly, day 182 anti-HIV-1IIIB antibody titers were significantly higher in the rgp120-treated groups (P < 0.01). There was no evidence of nAb activity against primary clade B isolates.
Vaccine-induced HIV-1–specific T-cell responses were measured at 2 weeks after the third and fourth vaccinations (days 98 and 182) in fresh PBMCs using a chromium release CTL assay. Significant net cumulative CD8+ CTLs to any antigen (gag, env, nef,or pol) were detected at day 98 or day 182 in 16% (95% CI: 2% to 35%) to 24% (95% CI: 5% to 43% of vaccinees with no significant differences between those who received ALVAC alone versus ALVAC plus rgp120 (). There were no significant CD8+ CTL net point prevalence rates at day 98 or day 182 (see ). No significant CD4+ T-cell responses were measured via chromium release assay (data not shown).
CD8+ CTL Responses to Any HIV Antigen Detected via Chromium Release Assay at Day 98 or Day 182*
IFNγ ELISpot assays were conducted in 2 HVTN CILs that divided cryopreserved PBMCs based on study site. Significant net cumulative IFNγ-secreting CD8+ T-cell responses were detected to env, gag, pol,or nef at days 98 or 182 in 23% (95% CI: 6% to 40%) of group B participants (). For group A participants, net cumulative CD8+ ELISpot responses were only 13% (95% CI: 21% to 26%). Gag-specific responses contributed most significantly to the overall CD8+ T-cell response rates, and net point prevalence response rates to any of the antigens only reached statistical significance for group B at day 98 (28% response, 95% CI: 8% to 47%; see ). The day 98 net point prevalence response rates in the other 2 active groups did not reach statistical significance, nor did the CD8+ T-cell responses at day 182 in any of the vaccine groups, suggesting that the higher day 98 group B response rate might be a function of the multiplicity of comparisons rather than a true higher response rate.
CD8+ and CD4+ IFNγ ELISpot Assay T-Cell Responses to Any HIV Antigen at Day 98 or Day 182*
CD4+ T-cell responses were also examined by IFNγ ELISpot assay. A significant net cumulative CD4+ T-cell response rate of 15% was detected to env, gag, pol,or nef at days 98 or 182 (95% CI: 3% to 28%) for participants in group B only (see ). No significant net point prevalence CD4+ T-cell response rates were observed. ELISpot assays were also performed on unfractionated PBMCs at the day 364 time point from a subset of 191 subjects, and no appreciable responses were detected (data not shown).