Avian myeloblastosis provirus cloned in a lambda bacteriophage is leukemogenic

The avian myeloblastosis virus provirus inserted in a lambda bacteriophage, recombinant clone 11A1-1 (Souza et al., Proc. Natl. Acad. Sci. U.S.A. 77:3004-3008, 1980), was transfected into chicken embryo fibroblasts which had been preinfected with either Rous-associated virus type 61 or the transformation-defective avian sarcoma virus tdB77. Within 4 to 5 h after transfection, the cells were injected into 16-day-old chicken embryos or 1-day-old chicks. Acute myeloblastic leukemia developed after a long latent period. Filtered (0.22-micrometer pores) supernatant of transformed buffy-coat cell cultures from one leukemic chicken of the lambda 11A1-1 (tdB77) group rapidly transformed yolk sac cells in vitro. Results from an infectivity interference assay and analysis of proviral DNA fragments generated with restriction endonucleases were consistent with the presence in leukemic cells of defective avian myeloblastosis virus and tdB77 as the helper virus.