Cyclophosphamide induced sensitivity against avian RNA myeloblastosis virus in age-resistant hosts

The effect of cyclophosphamide administration on survival of 4- to 7-week-old chickens as well as on induction of leukemia after avian myeloblastosis virus (AMV) injection was studied. The drug treatment alone did not cause any neoplastic effect in the birds during 4 months of observation. Immediate application of AMV to cyclophosphamide-pretreated age-resistant chickens induced acute myeloblastic leukemia in about 80 per cent of test animals. The sensitivity of chickens against AMV, induced by cyclophosphamide, had transient character only. When AMV was injected delayed, 3 or 10 days later, after the administration of the drug was completed, a rapid and pronounced increase of resistance was observed again.