Murine Myeloproliferative Virus in Cell Culture

Summary

A stable cell line, MCF-6, isolated from a leukemic mouse was maintained in culture for more than 28 months with 99 passages and frozen and reactivated 3 times at the most recent completed bioassay without need for animal or embryo passage rejuvenation. Cells or supernatant from MCF-6 produced myeloproliferative disorders when injected into neonatal BALB/c mice, with mortalities of 70–90% and mean latencies of onset of between 100–150 days. Older animals were not susceptible to virus or MCF-6 cells. The culture produced abundant virulent virus with the supernatant, at a dilution of 10^−3.1, infecting 50% of the hosts. Electron micrographs of MCF-6 supernatant showed particles similar to published descriptions of murine leukemia-inducing viruses. Cells from the culture did not transplant and, thus, were probably nonmalignant. Spleen cells from infected mice, however, were transplantable and produced malignancy in 92% of young adult animals inoculated, with a mean latency of 31 days.