Modulation by a human interferon of antitumor effects of cyclophosphamide against a lymphosarcoma in hamsters

Administration to hamsters of a highly purified human leukocyte interferon subtype, IFN-alpha A, obtained by recombinant DNA methods, abolished the efficacy of high doses of cyclophosphamide (2.5 mg/hamster) against the TBD 932 lymphosarcoma. The effect was more pronounced with concomitant than with sequential treatments and did not occur with melphalan. Antagonistic effects occurred at high interferon doses (10(5) I.U./treatment), but an additive or synergistic positive effect occurred at lower interferon doses (10(3) I.U./treatment) and at lower, non-protective, doses of cyclophosphamide. These effects may be due to immunomodulatory responses induced by the drugs involved.