VIR201 safe but no immune response as yet

Final results from the initial stage of Virax's Phase I/II study of its lead HIV immune based therapy, VIR201, have shown the drug to be safe but whether it will elicit an immune response is still open to question.

Preliminary results released at the end of November had indicated that VIR201 was well tolerated -- the primary outcome of the trial -- but at that time no immunogenicity data were available. The latest results show that VIR201, as administered and analysed in the study, did not elicit immune responses in the trial participants, said Virax CEO David Beames.

The company had hoped to see an increase in HIV specific T-cells in early-stage HIV patients treated with VIR201 for six-months, in line with pre-clinical findings, as a secondary goal of the study. At this stage, Virax does not know why the results were not as they had hoped but a company spokeswoman suggested that one possible explanation could be that the patient group tested was not suitable. The patients were primarily selected for the safety aspect of the trial and had undetectable viral levels, she said. Because these patients' HIV was under control it may have prevented an immune response from showing up.

The second part of the trial, the extension study, is still ongoing, with results due at the end of the year. Virax believes data from the extension study may give a better idea of VIR201's efficacy but said that because it was in the same patient population it remained to be seen whether any effect would show up as an immune response. Beames also pointed out that immunogenicity results from the initial phase of the trial, as well as those from the extension study, would provide information that would help to design future trials of VIR201 and other potential products.

The extension study differs to the initial phase of the trial, which involved 34 patients who received a series of injections of VIR201 over six months and remained on standard anti-retroviral therapies, in that it is a structured treatment interruption study and patients discontinue their standard treatment. The University of NSW-based National Centre for HIV Epidemiology and Clinical Research is conducting the trials.

VIR201 was created using Virax's Co-X-Gene platform technology. The drug uses a modified fowlpox virus to co-deliver both HIV antigen genes and a gene for gamma-interferon.