If confirmed, the biomarker may be able to predict which patients will benefit most from the therapeutic HIV vaccine candidate Vacc-4x, which is being developed by the Norwegian vaccine company Bionor Pharma.
St George's, University of London has had a long-standing collaboration with Bionor Pharma in a project to study HIV-associated immune activation that drives disease progression. Based on St George's work within this field, Bionor Pharma has developed a peptide (C5/gp41732-744 ) that can be used to detect antibodies against a part of the HIV envelope glycoprotein. The presence of antibodies to this part of HIV has been associated with slowed disease progression in the absence of combination antiretroviral therapy (ART).
Analysis of antibody responses to C5/gp41732-744 among patients who participated in a large Phase II clinical study has revealed that participants with baseline anti-C5/gp41732-744 antibody levels above 4μg/ml who received Vacc-4x had a statistically significant reduction in median viral load setpoint of log 0.94 (88%) compared to their median pre-ART viral load setpoint (p=0.005, n=12). Participants with anti-C5/gp41732-744 antibody levels below 4μg/ml who received Vacc-4x had a median viral load reduction of log 0.20 or 37% (p=0.019, n=27) compared to their median pre-ART viral load setpoint. The earlier Phase II study on which this subset analysis was based found a statistically significant 60% reduction in median viral load setpoint compared to historic viral load levels among participants who received Vacc-4x, interrupted ART for six months, and had pre-ART viral load data available. In contrast, those who received placebo did not experience a statistically significant change in viral load compared to pre-ART viral load setpoint.
Therapeutic HIV vaccines are designed to train the immune system to seek out and kill virus-producing cells in order to control the patient's HIV for prolonged periods of time. A successful therapeutic vaccine may negate the need for daily antiretroviral therapy (ART) for some people with HIV or provide an option for those who do not respond to ART.
Professor Angus Dalgleish, of St George's, University of London, said: "In spite of very effective drugs against HIV these need to be taken daily and have significant side-effects.
"The ability to replace this daily medication with a vaccine that allows several months of being off medication, not to mention the enormous financial gains that would be delivered to health services, is a step closer with these preliminary results."
Further study will be needed to confirm anti-C5/gp41732-744 antibody levels as a biomarker for improved response to Vacc-4x. Approximately 21% of participants in the Phase II study had antibody levels above 4ĩg/ml prior to Vacc-4x vaccination.
Vacc-4x is also being studied in a clinical trial to assess whether a 'kick-kill' strategy, which is designed to reverse HIV latency using HDAC inhibitor romidepsin and to train the immune system to kill virus-producing cells using Vacc-4x, may be effective in reducing the HIV reservoir.