A gene therapy approach to treating HIV infection has shown activity in reducing viral load and improving CD4 cell counts in a Phase I trial published in the Proceedings of the National Academy of Sciences.

The immunotherapy, developed by US company VIRxSYS, is now in Phase II testing with results from these studies due next year.

The trial evaluated the safety and tolerability of the intravenous therapy - known as VRX496 - in five subjects with chronic HIV infection who had failed to respond to at least two antiretroviral (ARV) drug regimens.

All patients had stable or decreased viral load, with three of the five patients exhibiting clinically significant reductions in viral load without changes in their ARV treatment at six months post infusion. Four of the five patients had stable or increased CD4 T cell counts. In addition, all five patients had stable or increased immune response to HIV antigens and other pathogens.

"Gene therapy has long been discussed as an alternative treatment to HIV," said senior author Carl June of the University of Pennsylvania School of Medicine. "The results from this Phase I trial are encouraging, particularly since these are late-stage patients.”

VRX496 is a lentiviral vector used to deliver a long antisense sequence designed to inhibit the formation of HIV’s viral envelope and block replication. Because it modifies host cells, the hope is that a single dose will provide long-lasting protection: some patients who have reached the three year post-infusion safety visit continue to exhibit persistence of modified cells, decreased viral load and increased CD4 counts over baseline, according to VIRxSYS.