Granulopoiesis in long-term culture by marrow from mice with busulfan-induced chronic latent aplasia.

Mice given high-dose busulfan therapy develop a chronic latent marrow aplasia characterized by normal peripheral blood neutrophil numbers, hematocrits and marrow cellularity but reduced numbers of pluripotent hemopoietic stem cells (CFU-s) and granulocyte-monocyte progenitor cells (CFU-gm). To study the pathogenesis of this lesion, bone marrow was propagated in long-term marrow cultures (LTMC). Small amounts of normal marrow readily established and sustained long-term granulopoiesis in vitro. In contrast, inocula of marrow from busulfan-treated animals containing three to five times as many stem and progenitor cells failed to establish long-term granulopoiesis in vitro. These results suggest that high-dose busulfan therapy produces a qualitative defect in either the hemopoietic stem cells, the stromal-forming elements, or both, rendering them incapable of establishing long-term granulopoiesis in vitro. Furthermore, mixing experiments employing normal and busulfan-damaged marrow demonstrate that this qualitative defect is not due to the emergence of a suppressor cell population. LTMC can show types of marrow damage not detectable by other techniques currently available and represent a powerful tool for studying latent bone marrow failure.