Scientists at the National Institutes of Health (NIH) and Emory University have achieved sustained control of SIV, the simian form of HIV, in infected monkeys with an experimental treatment regimen.

Sustained control means that once antiretroviral therapy (ART) was stopped, the virus did not return. The monkeys’ immune systems have been suppressing the virus to undetectable levels for almost two years since completing the treatment. Furthermore, the regimen appears to have replenished the key immune cells that the SIV had killed, something unachievable with ART alone.

“Our data suggest that the immune systems of these animals are controlling SIV replication in the absence of antiretroviral therapy,” Dr. Anthony S. Fauci, who co-led the study as chief of the Laboratory of Immunoregulation at the NIH’s National Institute of Allergy and Infectious Diseases (NIAID), said in a press release. “The experimental treatment regimen appears to have given the immune systems of the monkeys the necessary boost to put the virus into sustained remission.”

The regimen consisted of 90 days of ART combined with 23 weeks of treatment with a laboratory-derived monkey antibody, a4b7 integrin, which helps T cells find their way to the intestines, the first place HIV infection takes hold. This antibody is similar to the human drug vedolizumab, which was approved by the U.S. Food and Drug Administration for treating ulcerative colitis and Crohn’s disease in 2014.

NIAID is currently conducting a clinical trial testing the safety of vedolizumab and its effect on HIV in people infected with the virus.

In the newly published experiment, investigators infected 18 monkeys with a disease-causing clone of SIV. Five weeks after infection, all the animals began receiving a 90-day course of daily ART. Four weeks later, 11 monkeys began receiving infusions of the antibody every three weeks while the other seven began receiving infusions of a placebo antibody.

Three developed antibodies against the a4b7 antibody and were excluded from further study. Drugs were withdrawn at week 18 and antibodies at week 32.

Senior author Dr. Aftab Ansari, professor of pathology and laboratory medicine at Emory University School of Medicine (Photo courtesy of Emory)

When ART was stopped, SIV came back in the seven control animals. Six of the eight antibody-treated animals also showed some rebound of viral levels, but they controlled it within four weeks. The other two never even rebounded.

Commenting on the study in HealthDay News, Dr. Marcella Flores, amfAR’s associate director of research, said that people with HIV “can really find some hope in these findings,” especially since vedolizumab is already on the market.

But she said there are still plenty of unanswered questions, including whether an antibody can help if it’s given after the acute stage of infection—when few people know they have the virus.

Flores said it’s also unclear how treatment with the a4b7 antibody led to the regulation of SIV in the study monkeys.

Lastly, she noted in the HealthDay News article that with antibody therapy, people can develop their own antibodies against the treatment, such as the case with the three monkeys who were excluded from the study.

The study was published in the Oct. 14 issue of Science.

New Antibody Therapy Sends HIV-Like Infection Into Sustained Remission

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