BCNU treatment of marrow stromal monolayers reversibly alters haematopoiesis

Summary. The marrow stromal microenvironment is essential for maintaining normal haematopoiesis. Chemotherapy drugs, such as the nitrosoureas, may impair the ability of the stroma to support haematopoiesis. To assess the effects of 1,3‐bis‐(2‐chloroethyl)‐1‐nitrosourea (BCNU) on in vitro haematopoiesis, stromal monolayers were treated with BCNU, 5 μg/ml weekly for 3 weeks, then seeded 24 h after the third treatment with haematopoietic progenitors. Three weeks after seeding, total adherent and non‐adherent cell numbers were similar in treated and control flasks as were adherent granulocyte/macrophage colony forming cell (GM‐CFC) numbers. In contrast, non‐adherent GM‐CFC were significantly reduced in treated flasks, to 40–60% of controls. However, no reduction in non‐adherent GM‐CFC number was seen if seeding was delayed for 7 d following BCNU treatment, suggesting the effects are reversible. Conditioned media from treated and control monolayers, harvested at a time corresponding to the time of seeding, showed no difference in colony stimulating activity. In addition, extracts of bound growth factors from treated and control monolayers also showed no differences in colony stimulating activity. Thus, BCNU can alter haematopoiesis through a reversible effect on the marrow stroma and this effect does not appear to be mediated by a change in stromal growth factor production.