The vaccine was shown to be safe when given to macaques, and the risk of infection from exposure was reduced by 79%. Improvements must now be made before it can be tested on humans.
Despite nearly four decades of efforts by the global scientific community, an effective vaccine to prevent HIV remains an elusive goalImmunologist Anthony Fauci, co-author of the study and also White House adviser on the health crisis, said in a statement.
This investigational messenger RNA vaccine combines several features that could overcome the shortcomings of other investigational HIV vaccines, and thus represents a promising approach, added the director of the American National Institute of Allergies and Infectious Diseases (NIAD).
Scientists from this institute have carried out this work in collaboration with researchers from Moderna, the American company behind one of the most widely used vaccines against COVID-19.
The study was published Thursday in the prestigious journal Nature.
The vaccine was first tested on mice and then on rhesus macaques. These received multiple booster doses over a period of one year. Despite high doses of messenger RNA, the product was well tolerated causing moderate side effects, such as temporary loss of appetite.
By week 58, all macaques had developed detectable antibody levels.
From week 60, the animals were exposed to the virus weekly, via the rectal mucosa. Since primates are not vulnerable to HIV-1, which infects humans, the researchers used a different, but similar virus, simian HIV (SHIV).
After 13 weeks, only two of the seven immunized macaques were uninfected. But while other unvaccinated macaques developed the disease after about three weeks, those who were immune took an average of eight weeks.
This level of risk reduction could have a significant impact on viral transmission, emphasizes the study.
The vaccine works by delivering genetic instructions to the body, causing the creation of two proteins characteristic of the virus. These are then assembled to form pseudoviral particles (VLPs), mimicking an infection in order to elicit an immune system response.
Scientists note, however, that the levels of antibodies elicited were relatively low, and that a vaccine requiring multiple injections would be difficult to implement in humans.
They thus wish to improve the quality and quantity of VLPs generated, before testing the vaccine on humans.