Bovine leukaemia virus packaging cell line for retrovirus-mediated gene transfer.

Retroviral packaging cell lines were constructed by using the gag-pol gene of spleen necrosis virus, the gag-pol gene of Moloney murine leukaemia virus and the env gene of bovine leukaemia virus. The plasmids containing the gag-pol genes and the plasmid containing the env gene were cotransfected into NIH/3T3 and D17 cells. The cells containing the helper virus constructs were tested for their ability to package replication-defective murine leukaemia and avian reticuloendotheliosis retrovirus vectors. The titre of vector virus produced by each of the retroviral packaging cell lines was about 10(2) colony-forming units per ml of medium. Tests for events that might result in intact replication-competent retroviruses showed no evidence for the generation of such viruses. The vector viruses were able to infect dog and rat cells. Bovine cells were infected only after their cocultivation with the retroviral packaging cell lines producing murine leukaemia virus vectors, perhaps as a result of a low concentration of receptors.