Development and Serial Cell-Free Passage of a Highly Potent Strain of Mouse Leukemia Virus. ∗

Summary

1. A strain of a filterable mouse leukemia agent has been developed from a spontaneous Ak leukemia through several successive cell-free inoculations of newborn C3H mice. 2. This agent induced acute, generalized leukemia within 2 1/2 to 3 1/2 months in 40 to 100% of the inoculated newborn C3H mice (Bittner substrain). 3. Newborn mice had to be inoculated; adult C3H mice were with few exceptions resistant to inoculation of the cell-free agent. 4. The leukemic agent could be preserved at −70°C from 46 days to 5 1/2 months, with no apparent loss of infectivity.