Hematopoietic Precursors Resistant to Treatment With 4-Hydroperoxycyclophosphamide: Requirement for an Interaction With Marrow Stroma in Addition to Hematopoietic Growth Factors for Maximal Generation of Colony-Forming Activity

Abstract

AbstractWe tested the ability of CD34+lin– precursor cells isolated from marrow after treatment with 4-hydroperoxycyclophosphamide (4HC) to generate colony-forming cells (CFC). In liquid cultures, recombinant human stem cell factor (SCF), in combination with interleukin-1 (IL-1), IL-3, IL-6, granulocyte-macrophage colony-stimulating factor, or granulocyte colony-stimulating factor caused untreated, but not 4HC-treated, CD34+lin– cells to form CFC. However, generationof CFCfromCD34+lin– cells treated with 60 µg/mL of 4HC was possible in the presence of an irradiated allogeneic stromal cell layer. This generation was increased when combinations of hematopoietic growth factors including SCF and IL-3 were added. Maximal generation of CFC was seen after 11 to 21 days of culture. At that time, generation of CFC from CD34+lin– 4HC-treated cells equalled that from untreated cells. The phenotype of these 4HC-resistant CD34+lin– precursors was also further defined as CD38–. These studies show that the generation of CFC from the 4HC-resistant, highly immature population of CD34+lin– cells requires an as yet undefined interaction with marrow stroma in addition to known hematopoietic growth factors.