Characterization of L5178Y leukemic cells which rapidly develop and lose implantation ability.

Two populations of L5178Y murine leukemic cells, maintained by different methods, were studied for their implantation ability in BDF₁ mice. Implantation ability was measured by number of tumor nodules formed, liver weight, and day of death of the animal. 1) Cells from a population grown for 10 years $\text{in vitro}$ had no implantation ability; i.e., no tumor nodules were formed when injected into the tail vein. After 30 days of growth in the peritoneal cavity of BDF₁ mice, these same cells were injected into the tail vein and 10 days later had produced over 200 liver tumor nodules. When cells taken from these tumors were recultured for 60 days $\text{in vitro}$, they lost the acquired implantation ability, but regained it after another single peritoneal passage. 2) L5178Y murine leukemic cells grown for six years in ascites tumor cells were extremely tumorigenic; over 200 tumor nodules appeared in the liver after tail vein injection. These cells were not rendered less tumorigenic and did not lose their implantation ability by $\text{in vitro}$ culturing for 60 days. The results suggest that implantation ability is a property of the cell's growth environment; furthermore, they have strong implications for the $\text{in vivo}$ and $\text{in vitro}$ manipulation of this property.