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IMMUNIZATION PRODUCTS' "SALK" AIDS VACCINE SHOWS EFFECT ON VIRAL BURDEN, RESEARCHER TELLS AIDS CONFERENCE; JOINT VENTURE EXPLORING ACCELERATED APPROVAL

Executive Summary

Immune Response/Rhone-Poulenc Rorer's "Salk" HIV-1 immunotherapy vaccine "appears to induce a treatment effect on HIV viral burden as measured by HIV DNA" polymerase chain reaction, Alexandra Levine, University of Southern California School of Medicine, stated at a June 9 session of the Ninth International Conference on AIDS in Berlin. The Phase II/III randomized, double-blind, adjuvant-controlled trial tested a whole inactivated HIV-1 vaccine candidate depleted of envelope in 103 asymptomatic HIV-infected volunteers with a mean CD4 cell count of 656; three 100 mcg doses of vaccine were administered at zero, one and six months. The one-year trial was sponsored by Immunization Products Limited (IPL), a joint venture of Immune Response and Rhone-Poulenc Rorer. Compared to baseline, the viral burden of untreated subjects increased 48% during the study, while treated subjects showed a 10% rise, a statistically significant difference, Levine reported. Levine characterized the difference as showing that treatment produced a "relatively stable" viral burden. The difference in viral burden change was more pronounced in the second six months of the study and was continuing to grow at the end of the one-year follow-up. Treated subjects showed a statistically significant improvement in humoral immunity as measured by p24 antibody response and in cell- mediated immunity as measured by "lymphocyte stimulation indices," Levine reported. Delayed cutaneous hypersensitivity tests with HIV showed that immunized individuals developed a positive response after two to three doses, Levine said. Earlier trials of the vaccine have shown "a correlation between response to the...skin test and cytologic, virologic and clinical endpoints in time," Levine noted. Treated patients showed a statistically significant advantage in weight change, Levine reported. Immunized patients gained 2.3 kilograms during the study, compared to a half kilo for the controls. No significant differences between treated and control subjects were found in assays of p24 antigen positivity, viral co- culture or CD4 cell counts, Levine said. Analysis of changes in cytotoxic T lymphocyte levels occurring after immunization is not yet complete. Side effects were limited to injection site reactions, Levine said. Five-year follow-up data from Phase I studies continue to show safety, she added. At a press briefing following the conference, Nobel laureate Jonas Salk, who first proposed the idea of an HIV therapeutic vaccine in the British journal Nature in 1987, suggested that the trial provides more evidence validating his approach to treating HIV. He acknowledged that "these are simply trends. Time will tell how more marked [any clinical benefit] will be." The "next step," Levine added, "is a clinical endpoint trial." In a June 9 press release, Immunization Products said it "is continuing to work with the FDA to review the results of this and prior studies to determine the appropriate next steps in this program in accordance with the recently finalized regulations on accelerated approvals for potential HIV therapies." "Under these regulations...the agency, with the concurrence of the advisory committees, could consider the appropriateness of these data to support a product license application," IPL said. Both the Antiviral Drugs and the Vaccines & Related Biological Products Advisory Committees have stated that they would not rely solely on lab measures (specifically CD4 counts) as a basis for recommending approval without some sign of clinical effect. Weight changes have been used to supplement CD4 counts as a basis for approval of the nucleoside analogs ddI and ddC.
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