Detection and incidence of neutralizing antibodies to interferon-alpha-n1

Sera obtained from 612 patients enrolled in 40 different clinical trials with an interferon-alpha-n1 (IFN-alpha-n1) preparation have been tested for neutralizing activity against this IFN in a cytopathic effect inhibition assay. Positive samples were assayed in triplicate. Of 391 patients treated for human papillomavirus infections, 13 developed neutralizing antibodies (3.3%); two suffering from condylomata acuminata and 11 from juvenile laryngeal papillomatosis (JLP). None has positive titers prior to receiving IFN-alpha-n1 and none appeared to lose the benefits of IFN treatment. Serial specimens from four JLP patients demonstrated that titers rose during IFN treatment and declined postherapy. None of the 221 cancer patients from whom serum samples were available had positive titers. The overall incidence of IFN neutralizing sera from these IFN-alpha-n1 recipients was 2.1%.