Monkey-infecting virus may provide part of future HIV vaccine

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A PROTEIN from Simian Immunodeficiency Virus (SIV), which can infect monkeys and apes, has shown promise as a potential component of a vaccine against Human Immunodeficiency Virus (HIV), in a new study from scientists at Scripps Research in La Jolla, California.

Chimpanzee SIV, which can cause an AIDS-like disease in the natural host, is the virus that “jumped” to humans and evolved into HIV roughly a century ago in Africa. SIV’s outer-envelope protein, Env, shares a key structure with HIV’s Env; that and other properties make SIV Env attractive as a potential component of a future vaccine against HIV infection.

In the study, published in the May 21 issue of Cell Reports, the Scripps Research scientists found that inoculating mice with SIV Env proteins elicited antibodies that neutralise infection against multiple HIV strains.

“We’ve shown here that one can use shapes from chimpanzee-infecting SIV to stimulate the production of antibodies against the human-infecting HIV,” says co-senior author Dr Dennis Burton, the James and Jessie Minor Chair in Immunology in the Department of Immunology and Microbiology at Scripps Research. “It’s a simple but inspired strategy, reminiscent of the use of cowpox virus to immunise against small- pox virus over 200 years ago, and should help us in making an HIV vaccine.”

Despite medications that can control HIV and reduce transmission, the disease  remains a leading cause of death and a health threat to millions world-wide. Approximately 37 million people worldwide were living with HIV at the end of 2017, according to the Centers for Disease Control and Prevention. A vaccine for HIV would help prevent infection and control the spread of disease.

The traditional approach to designing a viral vaccine is to use a weakened or engineered version of the virus as the “immunogen” that stimulates the immune system to produce protective antibodies. But that doesn’t work against HIV. The AIDS-causing virus rapidly mutates its outermost structures during infection, constantly creating new strains or variants that can evade antibodies produced against prior variants. A vaccine based on one HIV strain encountered in the past would be ineffective against virtually all versions of HIV a person would be likely to encounter in the future.

As an alternative approach, Burton’s group and others want to design HIV vaccines that focus the antibody response on the few truly vulnerable parts of the virus. These vulnerable viral structures, or “broadly neutralising epitopes,” are so important to HIV’s ability to infect cells and replicate that they vary by a limited amount from one strain to the next.