SILCAAT IL-2 study saved as investigators take over responsibility and Chiron agrees to continue funding

The Chiron Corporation has apparently reversed its decision to stop funding the SILCAAT phase III study of recombinant interleukin-2 (IL-2), and has agreed to hand over responsibility for the trial to the investigators.

The agreement comes three months after an announcement of “a business decision” by the company that it would halt the study because it would take longer and be more expensive than expected.

SILCAAT (Study of IL-2 in people with low CD4+ T cell counts on Active Anti-HIV Therapy) is a randomised, controlled, open label trial of subcutaneous IL-2 that has been following nearly 2,000 people with advanced HIV infection at 137 clinical sites in 11 countries. The trial study is designed to compare outcomes of HIV-positive persons with CD4 cell counts between 50-299/mm3 randomised to receive IL-2 in addition to antiretroviral therapy with a control group of individuals treated with antiretroviral therapy alone.

Chiron completed two scheduled interim analyses of data from the trial, including data from 1,000 patients followed for a year. Participation is expected to last four to six years. The trial continued while Chiron negotiated with the Scientific Committee for SILCAAT.

Chiron said they had expected the study to cost $75 million, but that had now been revised up to $160 million. The announcement that Chiron would halt the trial provoked much criticism of the company.

Announcing the change of heart, Chiron president Craig Wheeler, said: “We did not anticipate the amount of support this trial had in the HIV scientific community.”

Chiron has not said how much funding it will make available to the study but a report in the San Francisco Chronicle said it would give $5 million annually for three to four years, rather than the original promise of $20 million a year for four to five years. A researcher was quoted in the Chronicle saying he feared the study could “fall apart” if colleagues dropped out because they could not cover their costs.

Interleukins signal the immune system to act when it is under attack. Interleukin-2 in particular causes more CD4+ T cells to be produced. During HIV infection, natural IL-2 production gradually declines. Treatment with supplemental IL-2 therapy is being studied as a way to increase CD4+ T cell counts and possibly improve immune function.