Chiron Corporation announced that the company and the Scientific Committee for SILCAAT, a Phase III study for recombinant human interleukin-2 (IL-2, aldesleukin) in patients with HIV, have reached an agreement in principle to transfer the responsibility for the trial to the investigators. Chiron had announced last October that it was discontinuing the trial. At the time, the company said that it would work with the Scientific Committee to maximize the scientific value of the study and that it would explore a regulatory strategy in the U.S. and Europe. The SILCAAT trial has continued while Chiron and the Scientific Committee worked on a transition plan.

"This partnership fulfills our commitment to maximize the scientific value of SILCAAT by enabling the trial to continue under the auspices of the Scientific Committee," said Craig Wheeler, President, Chiron BioPharmaceuticals. "Chiron is committed to leveraging public-private partnerships to derive clinical benefits from products in our portfolio so that we can optimally invest our resources to address unmet medical needs."

The Scientific Committee, which is composed of researchers affiliated with the Hospital Henri Mondor in Paris, the National Institutes of Health, the University of Minnesota, and other research institutions, is expected to assume responsibility for the trial early in 2003. The Committee will provide for the collection and reporting of data and other information related to SILCAAT, as well as ensuring that SILCAAT will continue to be conducted in accordance with all applicable regulatory requirements.

Chiron will continue to have access to all data and other information developed in the conduct of SILCAAT for use in regulatory filings. Administrative oversight of the trial and sponsorship of the IND is expected to come from the University of Minnesota and the National Institutes of Health, respectively. Chiron will provide certain financial and operational support for the study, along with IL-2. In the event of a positive outcome for the trial, Chiron will continue to have the right to pursue regulatory submissions for IL-2 in the treatment of HIV.

SILCAAT is the acronym for Chiron's international Phase III Multicenter Randomized Study of the Biological and Clinical Efficacy of Subcutaneous Recombinant, Human Interleukin-2 in HIV-infected Patients with Low CD4 Counts Under Active Antiretroviral Therapy. The trial is an open-label study designed to compare outcomes of HIV-positive persons with CD4 cell counts between 50-299/mm3 randomized to receive IL-2 in addition to antiretroviral therapy with a control group of individuals treated with antiretroviral therapy alone.

Chiron had expected to complete the SILCAAT trial, including final patient follow-up, in 2007. Currently 1,975 patients of a target 2,000 subjects are enrolled in SILCAAT worldwide, with 137 clinical sites in 11 countries. The primary endpoint is time to first AIDS-defining event or death. Secondary endpoints include changes (from baseline) in CD4+ cell counts and in plasma viral load.

To date, Chiron has completed two scheduled interim analyses of data from the SILCAAT trial, including data from 1,000 patients followed for one year. Data from the second interim analysis of SILCAAT are consistent with results previously obtained in Phase II studies, which had shown substantial CD4 count increases and no negative effect of IL-2 on viral load. The safety of IL-2 is not a factor in Chiron's decision to discontinue SILCAAT. Data from two interim analyses of SILCAAT demonstrated that the safety of IL-2 was consistent with that seen in previous studies. Chiron has determined that data available from these interim analyses of secondary endpoints do not support an early approval in the U.S. Chiron remains blinded to primary endpoint data, which are not expected to be available until the conclusion of the trial.