(Reuters Health)—Gene therapy with an HIV-based lentiviral vector can decrease viral loads and increase CD4 T cell counts in chronically infected patients who have failed to respond to at least two antiretroviral regimens, results from a phase I study suggest.

“Gene therapy has long been discussed as an alternative treatment to HIV,” senior author Dr. Carl H. June, from the University of Pennsylvania School of Medicine, said in a statement. “The results from this phase I trial are encouraging -- particularly since these are late-stage patients -- and demonstrate that gene therapy has the potential to treat HIV and other serious human diseases.”

The open-label, non-randomized trial evaluated the safety and efficacy of VRX496, an HIV-1-derived vector that expresses an antisense sequence against an HIV envelope protein, which prevents viral replication.

Treatment involves transducing a patient’s CD4+ T cells with VRX496 and then infusing the cells back into the patient. According to the report in the November 6th early edition of the Proceedings of the National Academy of Sciences, this therapeutic approach was well tolerated and appeared to be safe.

None of the five study patients experienced an increase in viral load and three patients showed a clinical significant reduction in loads at 6 months with no change in their antiretroviral regimen. One subject’s viral load decrease was sustained to 36 months. CD4+ T cell counts remained stable or increased in four patients.

“This is an important milestone in the development of what we believe will be the next generation of HIV therapy,” Dr. Riku Rautsola, President and CEO of VIRxSYS Corp, the company responsible for VRX496, said in a statement. “VRX496 is engineered in a way that debilitates HIV’s ability to replicate and mutate around the therapy, overcoming a common problem with current drug treatments.”

To verify the safety of this approach, the researchers will continue to follow the current study group annually for 15 years in accordance with US Food and Drug Administration guidelines. The authors note that two studies are currently underway testing VRX496 at multiple doses.

Proc Natl Acad Sci USA 2006.

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