Development of neutralizing interferon antibodies after treatment with recombinant interferon-alpha 2b in patients with malignant carcinoid tumors.

Human leukocyte interferon (IFN) as well as recombinant (r)IFN-alpha 2b have demonstrated significant antitumor effects in patients with malignant carcinoid tumors, with objective response rates of about 50%. The development of anti-IFN-alpha 2b antibodies has been investigated in 20 patients treated with rIFN-alpha 2b. Three different assays have been used, one neutralization assay and two immunoassays. Increased titers of anti-IFN antibodies were obtained with all three assays in 3 patients (15%). Concomitantly with the development of neutralizing IFN antibodies, a loss of antitumor activity was observed in 2 patients. Neutralizing IFN antibodies may occur as soon as within 3 months of treatment with recombinant IFN-alpha 2b. The frequency of neutralizing IFN antibodies and their clinical significance need to be explored further. Standardized and relevant methods for antibody determinations also must be established.