Temporal replacement of donor erythrocytes and leukocytes in nonanemic W44J/W44J and severely anemic W/Wv mice.

The dominant white spotting, W, locus in the mouse encodes Kit, a receptor molecule with cytosolic tyrosine kinase activity. Mutations in Kit deplete hematopoietic cells by an as yet unknown mechanism, but one that presumably affects the early progenitors of all cell lineages. To examine cell lineage-specific changes caused by different W mutations, we injected genetically marked normal marrow cells into mutant mice and monitored repopulation kinetics. In the present report, we compare repopulation of the various peripheral blood cells in nonanemic W44J/W44J and severely anemic W/Wv mice administered increasing increments of donor cells. At all doses of cells tested, donor erythrocyte repopulation precedes leukocyte repopulation regardless of the recipient phenotype. There is, in fact, little difference in the rate or extent of nonerythroid repopulation in W44J/W44J mice injected with between 6 x 10(6) and 2 x 10(7) donor cells. The fact that donor cells rapidly replace erythrocytes, even in the nonanemic W44J/W44J host, while other cell lineages become donor type more slowly provides further evidence that mutations at the W locus are especially damaging to erythrocyte progenitors. We suggest that host nonerythroid hematopoietic cells compete with normal cells, probably at the level of early progenitors rather than at the level of the totipotent hematopoietic stem cell. The fact that successively higher doses of donor cells do not markedly alter nonerythroid repopulation kinetics implies that it may be possible to maximize autologous therapeutic marrow transplantation.