LONDON - Cantab Pharmaceuticals plc released positive data from the final stage of a Phase I trial of its DISC disabled virus vaccine for genital herpes.

In the trial, designed to demonstrate safety and immunogenicity of DISC HSV (herpes simplex virus) at three doses, both seropositive (previously infected, but with no clinical disease symptoms) and seronegative (not previously infected) subjects demonstrated an immune response.

The vaccine is being developed in collaboration with Glaxo Wellcome plc, which has already begun a Phase II trial to find the right dose to suppress recurrent genital herpes. The primary endpoint of this U.S./UK trial in 400 patients will be time to first recurrence. A decision on whether to do a Phase III trial will be made in the first half of 2001.

Cantab said the Phase I results indicated there also is potential to develop DISC HSV as a prophylactic vaccine. Melissa Hellberg, the company's corporate communications director, told BioWorld International, "These results obviously endorse both approaches. The current Phase II will explore therapy but prophylaxis is clearly on the radar screen."

Although it might be difficult to gain acceptance for a general vaccination program against a sexually transmitted disease, Hellberg said Glaxo Wellcome had done some market research that indicated a prophylactic vaccine would be deemed appropriate in some at-risk groups.

The Phase I involved 110 healthy adults who received two or three vaccinations at one of three doses. Immunogenicity was assessed by a number of cell-mediated immune responses, regarded as being important in controlling HSV infection. T-cell proliferation, production of interferon gamma (produced by lymphocytes in response to a viral infection), and production of cytotoxic T lymphocytes, all were induced by the vaccine. There were no serious side affects at any dose.

John Roberts, medical director of Cambridge-based Cantab, said it was significant that the vaccine elicited an immune response in previously uninfected subjects. "Importantly the magnitude of the response is similar to that seen in naturally infected subjects who are able to control their disease," he said.