Resistance to recombinant interferon alfa-2a in hairy-cell leukemia associated with neutralizing anti-interferon antibodies.

To explain the hematologic deterioration occasionally observed during interferon therapy, we assayed serum specimens from 51 patients with hairy-cell leukemia receiving treatment with recombinant interferon alfa-2a for the presence of anti-interferon antibodies. After a median of seven months of therapy, anti-interferon antibodies were found in 31 patients. Fifteen of these patients had only non-neutralizing antibodies, but antibody from the other 16 neutralized the antiviral effects of recombinant interferon alfa-2a in vitro. In no case, however, did neutralizing antibody inhibit the antiviral effects of purified natural interferon alfa. Clinical resistance to interferon of various degrees was present in 6 of 16 patients with neutralizing antibodies; the remaining 10 patients and all 20 patients without antibody continue to respond after a minimum of two years of therapy. In all the patients with interferon resistance, antibody was present when it developed. These data suggest that the development of clinical resistance to interferon alfa-2a in hairy-cell leukemia is not necessarily related to an altered cellular response to interferon. Treatment with other interferons, such as purified natural interferon alfa, may be useful in patients with clinically important neutralizing antibodies against interferon alfa-2a.