Friday, April 26, 2013

SIV isn't HIV

SIV, the so-called simian immunodeficiency virus isn't the same virus as HIV, the human immunodeficiency virus, and rhesus macaques aren't human beings.

These two confounding facts were again responsible for yet another HIV vaccine clinical trial being shut down.
Federal researchers have faced a major setback in the pursuit of an HIV vaccine, shutting down a clinical trial on Thursday after determining that volunteers who received the vaccination shot were more likely to contract the virus than those who were given a placebo. The vaccine also failed to reduce virus levels in the blood of volunteers who contracted HIV, according to the National Institute of Allergy and Infectious Diseases (NIAID). ...

The study began in 2009, and researchers had immunized half of the 2,504 volunteers with a DNA-based vaccine called HVTN 505 that was intended to “prime the immune system to attack the AIDS virus. Then a different vaccine, encasing the same material inside a shell made of a disabled cold virus, acts as a booster shot to strengthen that response. Neither vaccine could cause HIV,” according to the Associated Press.
....
Results from a series of nonhuman primate studies influenced the decision to expand the HVTN 505 trial, says Dieffenbach. Animal data showed that about half of rhesus macaques given a simian immunodeficiency virus (SIV) vaccine regimen similar to the HIV vaccine regimen used in the HVTN 505 trial were protected against SIV following SIVsmE660 challenge, and that a low level of neutralizing antibodies to Env, and an Env-specific CD4+ T-cell response correlated with this protective effect.

Dieffenbach says the large number of animals (129 macaques) used in the study, and the fact that the protection occurred in the presence of robust cellular responses and low levels of SIV-neutralizing antibodies, suggested that the HVTN 505 regimen could have the capacity to prevent HIV acquisition in people. “You are only as good as the data you have in front of you,” says Dieffenbach, reflecting on the expansion of the HVTN 505 trial. “We [haven’t had] many efficacy trials and if we have the opportunity and there is plausibility, we need as a field to take a chance.”
....
The study, led by Louis Picker, a professor of pathology at the Oregon Health & Science University [Oregon National Primate Research Center], showed that 12 of 24 Indian rhesus macaques vaccinated with a replication-competent rhesus cytomegalovirus (rhCMV) viral vector vaccine candidate encoding the simian immunodeficiency virus (SIV)mac239 proteins Env, Pol, Gag, and Vpr/Vpx demonstrated early and complete control of viral replication for more than a year after repeat, homologous, low dose SIVmac239 challenge....
No surprises here.

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