Lifesparing Ability (In Lethally Irradiated Mice) of <tex-math>$W/W^{{\rm v}}$</tex-math> Mouse Marrow with No Macroscopic Colonies

Marrow suspensions from W/W^v genetically anemic mice had 13% the 30-day lifesparing ability of +/+ marrow cells in lethally irradiated recipients, but formed less than 0.01% as many macroscopic spleen colonies. Although <tex-math>$75\times 10^{6}\ W/W^{v}$</tex-math> cells produced no colonies after 9 or 10 days, they increased spleen weights significantly in irradiated recipients, but with less than 1% of +/+ cell efficiency. Nonerythroid cell proliferation (DNA synthesis) measured by¹²⁵ IUdR uptake in recipients of W/W^v cells was 44% that in recipients of +/+ cells. Erythroid proliferation was insignificant in recipients of W/W^v cells, and substantial (150% of nonerythroid proliferation) in recipients of +/+ cells. Recipients of large doses of W/W^v cells survived as well as +/+ cell recipients for 190 days, but more died between 190 and 372 days. The macrocytic anemia of the W/W^v cell donors was permanently acquired in 2-3 months by 60-80% of W/W^v cell recipients, and recipients saved by W/W^v marrow cells produced erythrocytes with donor-type hemoglobin. These results indicate that marrow cells can be effective at saving and repopulating lethally irradiated mice even though they form no macroscopic spleen colonies.