HIV virus that causes AIDS was different from other viruses known since the very immune cells that these vaccines aim to increase may have already been affected by the virus, effectively making the entire process futile, says a new study.
This reason has been cited for the unique challenge that scientists faced in developing an HIV vaccine fore more than three decades all over the world. Since 1987, more than 30 HIV vaccines have been tested in approximately 60 Phase I/II trails, involving more than 10,000 healthy volunteers.
These trials have been conducted in the United States, Europe, Brazil, China, Cuba, Haiti, Kenya, Peru, Thailand, Trinidad, and Uganda. The World Health Organization estimates that more than $500 million per year has been spent on HIV vaccine research, including industry and research agencies in industrialized countries.
“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 Guido Silvestri from Emory University, Georgia, in the US.
The mechnamism of the HIV/AIDS vaccine development essentially focused on developing vaccines that stimulate anti-viral T cells, which are in two main categories, defined by the molecules found on their surfaces. The CD8 molecule is for “killer” cells, CD4 is a marker for “helper” cells.
CD4+ T cells are known to be primary targets for HIV and SIV (simian immunodeficiency virus) infection, prompting several studies to propose that CD8+ T cells could help in controlling the AIDS and researchers immunised monkeys with five different combinations of vaccines encoding SIV proteins.
SIV infected primates, experiencing AIDS-like illness in humans, received an initial immunisation followed by two booster shots after 16 and 32 weeks but it failed to prevent the SIV infection. In fact, these monkeys became infected with higher levels of activated CD4+T cells in rectal biopsies before challenge, Silvestri said.
“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,” he noted. The findings have been published in the journal Proceedings of the National Academy of Sciences.