By Lisa Seachrist

Washington Editor

Chiron Corp. began patient enrollment in a Phase III study testing whether Proleukin (recombinant interleukin-2, IL-2) can forestall the progression of AIDS in HIV-infected patients with low CD4 T-cell counts.

The multicenter, international study will assess whether intermittent rounds of therapy with Proleukin in addition to other anti-HIV therapies can delay the progression of the disease compared to using the anti-HIV therapies alone.

"Using Proleukin to augment the immune system is a novel approach in the treatment of HIV," Lewis T. Williams, Emeryville, Calif.-based Chiron's chief scientific officer said in a prepared statement. "Current anti-HIV therapies target the virus specifically, while Proleukin is designed to bolster and help rebuild the compromised immune system."

Company officials could not be reached for direct comment.

A decline in CD4 cells and the functional impairment of those cells are the hallmarks of HIV infection. As a result of the decline the body becomes more susceptible to opportunistic infections and malignancies associated with AIDS. IL-2 is a naturally occurring protein produced by the human body that helps regulate the immune system. Phase II studies of Proleukin showed the drug in addition to standard HIV therapies increased the CD4 T-cell count and improved other measures of the immune system over the course of one year.

Based on the Phase II studies, Chiron is launching its international Phase III clinical trial, SILCAAT (Phase III Multicenter Randomized Study of Subcutaneous Recombinant, Human Interleukin-2 in HIV-Infected People with Low CD4 Counts Under Recombinant, Human Interleukin-2 Therapy). The trial will enroll an estimated 1,400 people at more than 100 sites worldwide.

Patients will be randomized to receive either Proleukin plus anti-HIV therapy or anti-HIV therapy alone. In order to be eligible for the study HIV-infected patients must have a CD4 T-cell count between 50 and 300, a viral load of less than 10,000 copies of viral RNA per milliliter of blood, and must have been on a stable regimen of at least two anti-HIV therapies for at least four months.

The researchers will assess the time to the first AIDS-defining event (illness associated with AIDS) as the primary endpoint of the study. Secondary endpoints will include CD4 T cell counts, changes in viral load and occurrence of adverse events. Side effects associated with Proleukin therapy include capillary leak syndrome and flu-like symptoms.

Proleukin was approved in 1992 as a therapy for metastatic renal cell carcinoma. In 1998, the label was expanded to include metastatic melanoma. The company just released 10-year data for the drug's use in these indications.

The data indicated Proleukin can extend cancer-free survival more than 10 years - without further treatment - in some patients with metastatic melanoma or metastatic kidney cancer.

For the 17 kidney cancer patients who had a complete response to Proleukin in one of seven Phase II studies of the drug, 65 percent were still cancer-free as of the update, for as long as 10 years following Proleukin therapy.

Of the 17 metastatic melanoma patients who achieved a complete response to Proleukin therapy, 59 percent were free of cancer up to 10 years after treatment. No patient who remained in remission beyond 30 months showed disease progression.

Chiron's stock (NASDAQ:CHIR) closed unchanged Wednesday at $28.375.