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HIV-1 Vaccine Shows Strong T-Cell Response in Phase 1 Study
The experimental HIV vaccine regimen exhibited an acceptable safety profile and elicited robust immune responses in 99% of trial participants from sub-Saharan Africa. Its ability to induce broad T-cell responses makes it a promising tool for HIV-1 prevention and cure strategies.
METHODOLOGY:
HIVconsvX is an experimental vaccine comprising six cross-clade conserved HIV immunogens, delivered in two stages using nonreplicating vectors — initially a chimpanzee adenovirus (ChAdOx1), followed by a modified vaccinia virus Ankara (MVA).
Researchers conducted a phase 1 randomized clinical trial across clinical research centers in Uganda, Kenya, and Zambia to evaluate the safety and immunogenicity of the HIVconsvX T-cell vaccine, delivered in a regimen that included (C1), (M3), and (M4).
Overall, 88 healthy adults without HIV-1 (median age, 30 years; 65% men) were randomly assigned to receive either the vaccine (n = 72) or placebo (n = 16) from July 2021 to November 2022 and were followed up for 40 weeks.
Participants in the vaccine group received a C1 prime dose on day 0, followed by M3 and M4 boosters on day 28; participants in the placebo group received placebo doses on days 0 and 28.
The primary endpoint was vaccine safety, with solicited and unsolicited adverse events, including serious events, assessed until the end of the study period and measurement of HIVconsvX-specific T-cell responses.
TAKEAWAY:
Overall, the vaccine regimen was well tolerated with no grade 3 solicited reactions after the C1 administration; 18% were grade 2, and only 2% were grade 3 after M3/M4.
The vaccine regimen was highly immunogenic, inducing HIVconsvX-specific responses in 99% of participants who completed all vaccine doses ( P < .0001).
< .0001). HIVconsvX-specific T cells peaked at a median of 2310 spots per million peripheral blood mononuclear cells. Men had significantly higher responses than women ( P = .0451).
= .0451). Upon reexposure to the virus, the T cells proliferated and neutralized HIV-1 isolates from clades A, B, C, and D.
IN PRACTICE:
'We foresee the future development and use of the HIVconsvX vaccines as a potentially key component of a combined package of tools for cure and prevention,' the authors wrote.
SOURCE:
This study was led by Chama Chanda, MB ChB, Center for Family Health Research Zambia, Lusaka, Zambia. It was published online on May 16, 2025, in The Lancet Microbe .
LIMITATIONS:
This study looked at responses in peripheral blood mononuclear cells, whereas control of HIV-1 is primarily mediated in lymphoid organs and tissues, such as the gut.
DISCLOSURES:
This study was funded by the European and Developing Countries Clinical Trials Partnership. One author was a co-inventor of the HIVconsvX immunogens. Other authors declared having no competing interests.
