Trans-Species Rescue of Defective Genomes of Murine Sarcoma Virus from Hamster Tumor Cells with Helper Feline Leukemia Virus

This report describes a trans-species rescue of defective MSV genome with helper leukemia virus derived from cats. This rescue was achieved by in vitro co-cultivation of hamster tumor cells with feline embryo cells in the presence of helper feline leukemia virus (FeLV), or by inoculation of tumor cells into FeLV-infected newborn cats. The rescued focus-forming viruses produced foci in feline embryo cultures but not in cultures of mouse, rat, and hamster species. One isolate was tested and found to induce sarcoma in a kitten. Antigenic and viral interference studies indicated that the focus-forming virus has the viral envelope of FeLV. Virus stocks consisted of a mixture of focus-forming particles and a 1000-fold excess of helper FeLV. Virus assay pattern in feline embryo cultures with or without added helper FeLV indicated that this helper virus is required for the transformation of feline cells.