Immune reactions and long-term therapy with human leukocyte interferon.

Twenty patients with osteosarcoma were treated with exogenous human leukocyte interferon for periods ranging from 6 to 18 months. Eleven of them remained free from detectable tumour growth during this treatment. Blood samples from all patients were tested for antibodies against interferon and against impurities in the interferon preparations. No patient developed detectable levels of neutralizing antibodies against interferon. All patients formed antibodies against contaminants in the concentrated crude interferon and the partially purified interferon preparation which had been used for treatment.