A new therapy that has been described as “probably the most exciting of the anti-HIV strategies around at the moment” (Alan Kingsman, Oxford Biomedica; BBC News) is producing encouraging results in Phase I safety trials, according to a report in New Scientist (15 May 2004).

VRX496 uses anti-sense technology to prevent HIV replication. T cells are isolated from patients and infected with a modified form of HIV containing an anti-sense gene. T cells containing the integrated viral genome are re-infused into patients so that when HIV tries to infect the modified T cells in vivo, the anti-sense mRNA is produced and binds to the sense viral mRNA, thereby preventing translation of viral proteins.

So far, three patients who had failed two regimens of anti-retroviral drug therapy have been treated with VRX496. Boro Dropulic, Founder and Chief Scientific Officer of VIRxSYS Corporation, which is developing VRX496, says that no adverse events have been observed in these patients and they are encouraged by the finding that “viral load results are not above pre-dose levels and CD4 counts have remained stable” (VIRxSYS). On the basis of these results, the Data Safety Monitoring Board, USA, recommended in April that a further two patients should be enrolled in the trial without delay.

Assuming that no safety concerns arise, the therapy could soon enter Phase II trials to determine efficacy. However, not everyone is convinced. This is the first time that a lentiviral vector has been used in a clinical trial in humans, and concerns about recombination and other safety issues have led many researchers to abandon research into gene therapy, according to Richard Sutton of Baylor College of Medicine (New Scientist).