Low incidence of serum neutralizing factors in patients receiving recombinant alfa-2b interferon (Intron A).

The development of serum neutralizing factors against recombinant alfa-2b interferon (Intron A) was reviewed in a large clinical experience. In 537 patients receiving systemic therapy, neutralizing factors developed in only 13 (2.4 percent). In 1,326 patients who received intranasal administration and 154 with intralesional administration, the incidence was less than 1 percent. Patients in whom antibody developed had no predisposing characteristics that could be identified, no particular types of patients with cancer had a high rate of neutralizing factors, and two of 10 patients with cancer in whom neutralizing factor developed were still able to show clinical responses. In patients in whom neutralizing factor was present, there was no discernible difference in the incidence or severity of interferon side effects as compared with patients who had no demonstrable neutralizing factor levels. This form of recombinant alpha-2 interferon appears to have a very low antigenic potential.