A very promising vaccine candidate for HIV/AIDS has shown the ability to completely clear the simian immunodeficiency virus (SIV), a very aggressive form of HIV that leads to AIDS in monkeys. Developed at the Vaccine and Gene Therapy Institute at the Oregon Health and Science University (OHSU), the vaccine proved successful in about fifty percent of the subjects tested and could lead to a human vaccine preventing the onset of HIV/AIDS and even cure patients currently on anti-retroviral drugs.

Antiretroviral drugs and HIV vaccine candidates typically aim at improving the immune response in the long term, but they can never completely clear the virus from the body. In fact, aside from a very few exceptional cases, researchers have long believed that HIV/AIDS could only be contained, but not completely cured.

The OHSU team led by Dr. Louis Picker has been working on its own vaccine for the past 10 years, showing that an immune response can in fact systematically wipe the virus out of the body.

As with most early vaccine candidates, the study revolves around SIV. SIV is much more aggressive than HIV: it replicates up to 100 times faster and when unchecked it can cause AIDS in only two years. When treated with the team's vaccine, half of the monkeys initially showed signs of infection, but those signs gradually receded before disappearing completely.

Louis Picker, M.D. (Photo: OHSU)

"The virus got in, it infected some cells, moved about in various parts of the body, but it was subsequently cleared, so that by two or three years later the monkeys looked like normal monkeys," says Dr. Picker. "There's no evidence, even with the most sensitive tests, of the SIV virus still being there."

Scientists at OHSU created the vaccine candidate by working with cytomegalovirus (CMV), another virus which is itself persistent, but doesn't cause disease. In fact, about half the people in the US and 99 percent of the population in the developing world already harbor this virus.

The vaccine was found to generate an immunoresponse very similar to the normal immunoresponse generated by CMV, which is highly persistent. The so-called "effector memory" T-cells that can search and destroy target cells were created and remained in the system, consistently targeting SIV-infected cells until the virus was cleared from the body.

Other vaccines generate an immunoresponse, but that response fades over time. According to Dr. Picker, it is the permanency of the T-cells that allows the immunoresponse to be consistent and chip away at the virus, eventually eliminating it completely from the system. No other vaccine concept has shown this kind of efficacy before.

"We might be able to use this vaccine either to prevent infection or, potentially, even to apply it to individuals who are already infected and on antri-retroviral therapy," says Dr. Picker. "It may help to clear their infections so ultimately they can go off the drugs."

The team is now trying to understand why some of the vaccinated animals did not respond positively, in the hopes of further increasing the efficacy of the vaccine.

The research appeared earlier today in the journal Nature.

Dr. Picker answers several key questions on the vaccine in the video interview below.

Source: OHSU

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