Investigational treatment combination improves virologic control in SIV-infected monkeys

Researchers have found that an investigational treatment combination of a therapeutic vaccine and an immune-stimulator improves virologic control and delays viral rebound following the discontinuation of antiretroviral therapy (ART) in non-human primates infected with SIV, the simian form of HIV.

The proof-of-concept study examined the combined effects of therapeutic vaccination with an adenovirus serotype 26 vector vaccine and an MVA vector vaccine (Ad26/MVA) and TLR-7 agonist stimulation in ART-suppressed, SIV-infected monkeys. Findings were published online today in Nature.

The study was a collaboration led by the Beth Israel Deaconess Medical Center (BIDMC) and the U.S. Military HIV Research Program (MHRP) of the Walter Reed Army Institute of Research (WRAIR), and includes scientists from Janssen Vaccines & Prevention B.V., one of the Janssen Pharmaceutical Companies of Johnson & Johnson, and Gilead Sciences, Inc.

Rhesus monkeys were started on suppressive ART seven days after infection with SIV. After 24 weeks, groups of animals then either received a placebo treatment, Ad26/MVA, TLR7 or a combination intervention of Ad26/MVA and TLR-7. At 72 weeks, ART was discontinued to test the ability of the investigational therapies to affect continued virological control.

"We found the combination of Ad26/MVA vaccination and TLR7 stimulation proved more effective than either component alone," said Col. Nelson Michael, director of MHRP, who helped design the preclinical study. "This was especially striking in viral load set-point, which impacts the future course of the disease."

In the combination group, the mean viral load set-point was reduced by 100 fold in all animals and researchers saw a 2.5-fold delay of viral rebound as compared with the other groups. TLR-7 alone did not impact viral load or rebound. The vaccine alone reduced viral load set-point by 10 fold and only marginally delayed rebound. Though all monkeys eventually experienced viral rebound following ART interruption, 33% of the monkeys in the combination intervention group showed effective virologic control to undetectable viral loads following ART discontinuation.

"A critical barrier to HIV cure is the viral reservoir that remains hidden and infects cells throughout the body, leading to viral rebound in the vast majority of HIV-infected individuals after they discontinue ART," said Dr. Merlin Robb, Deputy Director for Clinical Research at MHRP. "The combination of Ad26/MVA vaccination and TLR7 stimulation resulted in decreased levels of viral DNA in both lymph nodes and peripheral blood. With further optimization this combination strategy shows promise to acheive an HIV functional cure."

Additionally, cellular immune breadth correlated inversely with set-point viral loads and correlated directly with time to viral rebound. According to Michael, "this gives us an immunologic correlate which can potentially be used to predict responses in humans, but this needs to be confirmed in human clinical studies."

Ad26/MVA is a prime boost vaccine regimen. MHRP, in collaboration with Janssen, recently began evaluating this regimen as a therapeutic vaccine in HIV infected adults who initiated ART during acute HIV infection. That study is being conducted at the Thai Red Cross in Bangkok, and the protocol chair is Dr. Jintanat Ananworanich, MHRP's Associate Director for Therapeutics.