Factorindependent erythropoietic progenitor cells in leukemia induced by the myeloproliferative leukemia virus. Blood 73:1161–1167

The myeloproliferative leukemia virus (MPLV). a novel murine retroviral complex that does not transform fibro-blasts, has been shown to cause an acute leukemia in adult mice accompanied by a progressive polycythemia. The present study demonstrates that. on in vivo inoculation. MPLV induces a rapid suppression of growth factor requirement for in vitro colony formation by both the late and the primitive erythroid progenitor cells. CFU-e-derived erythrocytic colonies developed and differentiated in semi-solid medium without the addition of erythropoietin (Epo). In addition, the formation of CFU-e colonies was not altered by the presence of specific neutralizing Epo anti-bodies. In the spleen. the CFU-e pool size increased rapidly up to 30-fold. By day 6 postinfection. 100 % of these progenitor cells were Epo-independent. The in vivo effect