Erythropoietin responsiveness in vivo of Friend virus target cells for transformation and virus replication.

Techniques that allow the selective stimulation of the erythropoietin-responsive cell population in mice with suppressed multipotential hemopoietic stem cells were used to identify (1) the in vivo target cell transformed by Friend virus (FV) into a tumor colony-forming unit and (2) a target cell for FV replication in vivo. Plethoric mice with busulphan-induced reductions in stem cell populations (characterized as colony-forming units) and stimulated erythropoietin-responsive cell compartments were given FV; control groups, not receiving erythropoietin, also received FV. A comparison of the number of target cells transformed in each group provided evidence identifying the ERC as the in vivo compartment in which the target cell detected by tumor colony formation resides. Differences in plasma virus titers revealed that the erythropoietin-responsive cell is also predominantly responsible for the production of FV as measured by focus-forming activity.