Rescue of avian leukosis subgroup-J-associated acutely transforming viruses carrying different lengths of the v-fps oncogene and analysis of their tumorigenicity

In our previous study, six subgroup J strains of avian leukosis virus (ALV-J)-associated acutely transforming viruses carrying different lengths of the v-fps oncogene, designated as Fu-J and Fu-J1–5, were isolated and characterized from fibrosarcomas in ALV-J-infected chickens. In the present study, the oncogenic potential of Fu-J and Fu-J1–5 was investigated using a reverse genetics technique. Six replication-defective viruses, named rFu-J and rFu-J1–5, were rescued with the replication-competent rescued ALV-J strain rSDAU1005 as a helper virus by co-transfection of chicken embryo fibroblast monolayers with infectious clone plasmids. Experimental bird studies were performed, demonstrating that only the rescued rFu-J virus carrying the complete v-fps oncogene with rSDAU1005 as the helper virus could induce acute fibrosarcoma after inoculation in specific-pathogen-free (SPF) chickens. These results provide direct evidence that the replication-defective acutely transforming Fu-J virus, with the complete v-fps oncogene, was associated with acute fibrosarcoma in chickens infected with ALV-J in the field, as reported previously.