Chiron has announced that it is terminating the SILCAAT study of interleukin-2 treatment because the study design no longer meets the company's needs for licensing of the drug and is costing the company too much money.
The company hopes to submit licensing applications for IL-2 in the USA and European Union soon based on a analysis of existing data from the study, and to win marketing approval based on the effect of IL-2 on CD4 cell counts and viral load in patients who had a poor immunologic response to HAART. However, these data are not unblinded yet, and the company said there are no guarantees. Whilst previously reported studies suggest a benefit from IL-2 in this patient group, if SILCAAT data do not support licensing, a question mark will hang over the future use of IL-2 in HIV treatment.
"Continued improvements in HIV treatment (i.e., HAART) have led to reduced incidence of clinical events and a decrease in the overall rate of disease progression. Since the primary endpoint for the SILCAAT trial is time to first AIDS-defining event or death, decreases in clinical events and disease progression make the duration of time required to maintain a study of this magnitude infeasible for Chiron," said Craig Wheeler, President of Chiron, in a press release issued yesterday.
SILCAAT is an international randomised study of the use of IL-2 in people with CD4 counts between 50 and 300 cells/mm3 and undetectable viral load on a stable HAART regimen. The study was intended to follow patients for around four years in order to assess the effect of IL-2 treatment on the risk of opportunistic infections and death. Chiron has decided to terminate a study that is already estimated to have cost the company $20 million. Chiron has also terminated a study of a new hepatitis B treatment because it cannot find a development partner; HBV-MF59 is an immunotherapy for chronic HBV infection currently in Phase II trials
Patients already receiving IL-2 in SILCAAT will continue to receive IL-2 treatment if they want it, and data will continue to be collected on these individuals. The US National Institutes of Health-sponsored ESPRIT study of IL-2 treatment in people with CD4 cell counts above 300 will continue, and is still recruiting patients in the United Kingdom.
CORRECTION: the previous version of this story reported that Chiron needed to recruit 3,000 patients to the study. In fact, the recruitment target was 2,000, and 1957 participants had already joined the study by the time it was halted. We also reported that fewer clinical events had occurred than expected. We have been informed by Clifford Lane, a member of the Scientific Committee of the SILCAAT study, that this is not true, and that at the last DSMB review, the events rate was noted to be on target. Click here to read a statement from the study's Scientific Committee on why SILCAAT should not close.