Several studies have discovered that HIV vaccines can backfire and lead to increased rates of the infection, as opposed to reducing or eliminating the viral pathogen. Now, a new study published in the Proceedings of the National Academy of Sciences might have an explanation as to why this occurs.
"One of the reasons why it has been so difficult to make an AIDS vaccine is that the virus infects the very cells of the immune system that any vaccine is supposed to induce" senior author of the new study and chief of microbiology & immunology at Yerkes National Primate Research Center at Emory University in Atlanta, GA, Guido Silvestri says.
Vaccines that have been developed have largely focused on stimulating antiviral T cells. Of the two main groups of T cells, CD4+ T cells are the "helper" cells that are known to be the targets of the virus in both human and its non-human primate equivalent, simian immunodeficiency virus (SIV), while the CD8+ T cells are the "killer" cells that some studies believe may be the key to controlling the infection.
The new study proposes that vaccine researchers may need to avoid vaccines that activate too many of the viral target cells-which may in fact be having a detrimental affect on weakened patients suffering with HIV.
Silvestri and his fellow researchers immunized rhesus macaques with five different combinations of SIV vaccines and gave the monkeys boosters at 16 and 32 weeks. Following immunization, the rectums of the monkeys were exposed to SIV once per week, up to fifteen times in total. And the researchers found that the immunizations generally did not prevent infection.
Although the CD8+ T cells were detected in all the immunized monkeys, researchers found no correlation between the levels and a reduced likelihood of infection. The researchers did find, however, that the monkeys that did become infected had higher levels of the CD4+ T cells in rectal biopsies prior to infection.
"This study shows that if a vaccine induces high levels of activated CD4+ T cells in mucosal tissues, any potential protective effect of the vaccine may be hampered," Silvestri says.
This study sends a clear message to vaccine researchers that they should focus on products that create a strong antiviral immune response, without increasing the number of "helper" T cells to prevent the vaccine from backfiring-leading to an increased infection rate.
Currently, 1.1 million people are living with HIV in the United States, and nearly one in six are unaware that they are infected. Despite advances in treatments more than 15,000 people with AIDS still die each year.
