Background: A large Phase 2b proof-of-concept study called “Imbokodo” was initiated in 2017 to assess the preventive vaccine efficacy of a prime/boost regimen using mosaic antigens encoded by Ad26 and gp140 Env protein in HIV-uninfected women in sub-Saharan Africa. The vaccine schedule in Imbokodo involves 4 vaccination visits over 48 weeks, a long regimen that may be a factor in limiting adherence. We explored in HPX1002/IPCAVD010 whether shorter, simpler regimens might be equally immunogenic to an Imbokodo-like regimen.
Methods: HPX1002/IPCAVD010 was a randomized, placebo-controlled, double-blind Phase 1 study in 36 HIV-uninfected adults (12 per arm) to evaluate the safety and immunogenicity of 3 different vaccine regimens with Ad26 vectors expressing mosaic Env and Gag/Pol antigens (Ad26.Mos.HIV) and aluminium-phosphate adjuvanted Clade C gp140 trimeric envelope protein (gp140 Env). Group 1 received Ad26 double prime at Weeks 0 and 12 and a double boost with Ad26+gp140 at Weeks 24 and 48. Group 2 received Ad26+gp140 at weeks 0, 12 and 24. Group 3 received Ad26 at Wk 0, and Ad26+gp140 at weeks 8 and 24. The study was conducted at Beth Israel Deaconess Medical Center in Boston, MA, USA. Data from Baseline, 28 and 52 were analyzed.
Results: All vaccine regimens appeared to be well tolerated. Pain and fatigue were the most frequently reported solicited events. The shortened regimens (Groups 2 and 3) elicited equivalent antibody titers against autologous Clade C Env at peak immunity to the Imbokodo-like regimen (41,007 and 49,243 GMT vs. 44,590 GMT, respectively), with this peak occurring earlier in the shortened regimens. Antibody responses remained elevated (>5,000 GMT) in Groups 2 and 3 at week 52. ADCP, Env-specific IgG3, tier 1A neutralizing activity and broad cellular immune responses were detected in all groups.
Conclusions: In this Phase 1 study, we demonstrate that Ad26.Mos.HIV combined with gp140 Env protein can elicit HIV-specific immune responses in shortened, 24 week vaccine schedules that appeared to be similar to responses elicited in a longer, 48 week vaccine schedule that is currently being evaluated in a clinical efficacy study. Further studies are required to test the protective efficacy of these shortened vaccine regimens.

Antibody Titers Against Autologous Clade C Env in IPCAVD010
[Antibody Titers Against Autologous Clade C Env in IPCAVD010]