An experimental HIV vaccine produced promising results in a small Phase 1 clinical trial, according to a study published Thursday — World AIDS Day — in the academic journal Science. 

The two-dose vaccine, called eOD-GT8 60mer, induced broadly neutralizing antibody precursors in 97% of trial participants — or all but one — at “substantial frequencies in each individual,” the paper said.

Broadly neutralizing antibodies are rare, highly potent antibodies that can neutralize a wide variety of virus strains, including of HIV, which causes AIDS. 

The clinical trial enrolled 48 healthy adults ages 18 to 50. Eighteen received 20-microgram vaccine doses eight weeks apart, as well as an adjuvant with their second shot. Eighteen others were administered 100-microgram doses eight weeks apart as well as the adjuvant. And 12 were given placebos.

All vaccine recipients were found to have produced antibodies after one dose, but none among the placebo group had, the researchers found. The vaccine-induced responses increased after the second shot. No participants were infected with HIV during the study.

The data “demonstrates for the first time that one can design a vaccine that elicits made-to-order antibodies in humans,” co-senior author William Schief, a professor and immunologist at Scripps Research and executive director of vaccine design at the International AIDS Vaccine Initiative Neutralizing Antibody Center, said in a news release.

"We believe this vaccine design strategy will be essential to make an HIV vaccine and may help the field create vaccines for other difficult pathogens,” Schief added.

To date, attempts to develop an HIV vaccine that generates broadly neutralizing antibodies have been unsuccessful. 

The researchers used a strategy known as “germline targeting” in hopes of eventually producing broadly neutralizing antibodies that can protect against HIV. The process begins with stimulating rare broadly neutralizing antibody precursor B cells that can eventually evolve into the cells that can produce the antibodies to block various strains of the virus.

The scientists designed a customized molecule — known as an immunogen — to prime the immune system and generate responses from the precursor cells. 

The researchers collected and analyzed immune cells from the blood and lymph nodes of participants. The results established “clinical proof of concept” in support of developing such a vaccine, but further research is needed before one could be available to the public. 

One major unanswered question is how long the triggered antibodies might last.

The clinical trial found no serious side effects. Those reported were generally mild or moderate and were resolved within a day or two. They included injection-site pain, malaise and headache.

More than 38 million people worldwide are living with HIV, according to the United Nations. An estimated 1.5 million people were infected with HIV and about 650,000 people died of AIDS-related illnesses in 2021.

“HIV represents an area of dire unmet need across the world, which is what makes the findings from our Phase I clinical trial so encouraging,” Dr. Mark Feinberg, president and CEO of the International AIDS Vaccine Initiative, said in a news release. “Through the close-knit collaboration of many different scientists, disciplines, and institutions, we are that much closer to designing an effective vaccine that could help end the HIV pandemic.”

More than 20 HIV-related vaccine clinical trials are currently underway, according to the IAVI.

In the meantime, other options to reduce the risk of HIV infection include daily pills and frequent infections of pre-exposure prophylaxis, or PrEP.

The study was conducted by researchers at the National Institutes of Health, the Fred Hutchinson Cancer Center, Scripps Research, the IAVI, Duke University, George Washington University and Karolinska Institutet in Sweden.