A new vaccine developed by Pfizer helps protect macaque monkeys against HIV infection, according to findings that may provide a way to combat the deadliest AIDS virus.
Initial tests on monkeys showed that the vaccine reduced the virus’s ability to cause sickness by 50% in at least two strains. Scientists say further work is needed to study whether this approach can work in people.
Current drugs can slow the progression of HIV infection but their effect is limited. Only a handful of people in the US who take one of the drugs seem to actually be improving, which puzzled scientists.
According to Viren L. Khamalekwada, lead author of the study and a professor of biomedical engineering at the University of Virginia in Charlottesville, the task ahead lies in expanding and refining the ways in which the gene therapy is delivered.
“We’re testing whether to use adeno-associated viruses (AAVs) and new types of vaccines designed to get two different proteins into cells,” he told the Guardian.
An AAV is a deadly, malicious virus that enters cells by hijacking and hijacking the host immune system. Once in a cell, the virus installs itself and tricks the body into thinking it’s a foreign invader. When the virus hijacks the immune system, the body soon becomes infected and begins producing proteins that help the virus enter and remain in the cell. A partial immune response to the virus brings it under control but can be overcome with repeated infections, says Khamalekwada. This leads to the development of HIV.
“The virus can form a bad state in the cell, make an aberrant protein, insert a gene in the cell, and it can begin to make more HIV even if the virus was already in the cell,” he explained. “With a protein injection we can get rid of the virus in the cell and raise the infection rate.”
“The benefit of these sequences is that they can target both AAVs and HIV,” he said.
Khamalekwada’s team used two different AAV gene replacement vaccines to see whether the proteins would target the two major HIV strains in the monkeys: Omicron 1 and Omicron 2.
They inoculated monkeys with the Omicron 1 AAV and the HIV-2 ENAV vaccine, then observed the two- or four-week epidemiological data for the different strains of the virus.
The results, presented at the International Conference on Microbicides in Brazil, showed that the strain of Omicron 1 had the strongest effect on the immune system. Injecting Omicron 1 boosted the immune system in seven of seven monkeys, who were infected with Omicron 1 and Omicron 2, compared with just three monkeys who were infected with HIV but not Omicron 1.
The more effective the vaccine, the longer it remained in the monkeys. For instance, injecting Omicron 1 into five of seven monkeys – including two monkeys who were infected but not Omicron 1 – worked for five months but the six monkeys who were infected but not Omicron 1 waited only two months.
The vaccine was also able to boost the viral load in all nine monkeys initially infected but not initially Omicron 1 and Omicron 2, but this finding was not repeated in the two monkeys who were infected with Omicron 1 but not Omicron 2.
“Our study showed this was a very strong effect,” said Khamalekwada.
But not all monkeys were treated with the vaccine, noted Kenneth G. Francis, professor of microbiology at the University of Texas in Dallas and a member of the medical advisory board at Pfizer.
“The vaccine did not cross-react to the virus in all strains, and so the vaccine is not 100% effective against all the strains,” he told the Guardian. “That’s why we’re still in the testing phase and why we think the vaccine could someday be used in humans.”