Long-term marrow cultures from mice with busulfan-induced chronic latent aplasia.

Mice treated with busulfan develop chronic latent marrow aplasia characterized by near-normal peripheral leukocyte counts, hematocrits, and marrow cellularity but very reduced stem cell (CFU-S) and progenitor cell (CFU-GM) populations. To determine whether the lesion is primarily in the stem cells or whether there is also a microenvironmental component we have used the Dexter-type long-term marrow cultures. Normal marrow maintains hemopoiesis for several weeks to months in such cultures, whereas "busulfan-marrow" will not support long-term growth. When normal marrow cells were transplanted onto an established adherent layer, whether derived from normal or busulfan marrow, normal hemopoiesis was established. However, busulfan-treated marrow cells would not establish hemopoiesis even when transplanted onto a normal stem cell-depleted adherent layer. It appears, therefore, that the primary lesion induced by busulfan is in the stem cells rather than in the microenvironment.