Resistance to recombinant alpha interferon therapy in idiopathic mixed cryoglobulinemia: Reinduction of remission by natural alpha interferon both in antibody-positive and -negative patients

A subset of patients treated with recombinant interferon α-2a (rIFN-α2a) for idiopathic mixed cryoglobulinemia (IMC) developed clinical resistance to therapy after a sustained response. Neutralizing antibodies to rIFN-α2a were found in the sera of three out of four such patients, and in none of the patients who remained responsive to treatment. rIFN-α2a neutralizing antibodies appeared in serum samples of the former three patients 1, 5 and 6 months before evidence for clinical resistance, respectively. Antibody titres to rIFN-α2a were consistently higher than those to natural interferon (nIFN). In the fourth patient with clinical resistance, neutralizing antibodies could not be detected by a very sensitive bioassay in any of several serum samples taken before and after relapse. All the four patients could be reinduced into remission by the administration of nIFN-α. These data indicate that mechanisms other than the production of neutralizing antibodies can mediate acquired resistance to IFN therapy. Furthermore, both antibody-related and -unrelated resistance can be overcome by switching to different species of IFN-α.