Researchers have found an explanation for why some vaccines designed to fight HIV can lead to an increase in infection.
The research team determined the "backfire effect" is most likely caused by an increase in the number of immune cells that are viral targets, Emory Health Sciences reported. In a nonhuman primate model of HIV transmission the researchers observed an increased risk of infection associated with higher levels of viral target cells in gateway mucosal tissue.
"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," said senior author Guido Silvestri, chief of microbiology and immunology at Yerkes National Primate Research Center.
Most efforts to create and AIDS vaccine have looked at ways to stimulate antiviral T cells. T cells come in two major categories: CD8 which is a marker for "killer cells" and CD4 which is a marker for "helper cells."
In the recent study researchers immunized rhesus macaques with five different combinations of vaccines that encoded SIV (Simian immunodeficiency virus) proteins found on the inside of the virus. The immunization generally did not prevent the transmission of SIV, but the monkeys did show higher levels of CD4+T cells in rectal biopsies.
"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 said.
The findings highlight the need for researchers to focus on methods that elicit antiviral immune responses without increasing the level of CD4+ T cells in the portals of entry for the virus.
The findings were published in a recent edition of the Proceedings of the National Academy of Sciences.
