IN-VITRO SENSITIVITY OF HUMAN HEMATOPOIETIC PROGENITOR CELLS TO 4-HYDROPEROXYCYCLOPHOSPHAMIDE

Protracted engraftment and prolonged thrombocytopenia remain problems when marrow purged with 4-hydroperoxycyclophosphamide (4-HC) is employ ed for autotransplants. Toxic effects of 4-HC on early progenitor and stem cells might play an important causative role. Surprisingly, few i nvestigations have examined the effects of 4-HC on progenitor cells ot her than colony-forming units-granulecyte/macrophage (CFU-GM) and burs t-forming units-erythroid (BFU-E), and only one study could be found w here 4-HC exposure was carried out on cells purified beyond the buffy coat stage. Since the cellular milieu, and in particular the red blood cell count, can ameliorate 4-HC toxicity, the suppressive effect of t his agent on marrow stem cells might be underestimated. We therefore i nvestigated the relative 4-HC sensitivity of different human bone marr ow progenitor cells in vitro using partially purified adherent cell- a nd T lymphocyte-depleted bone marrow mononuclear cells (A(-)T(-)MNC). Cells were exposed to increasing doses (10 to 200 mu g/mL) of 4-HC usi ng a standard purging protocol established for bone marrow buffy coat cells. Effects on mixed (CFU-Mix), erythroid (CFU-E and BFU-E), granul ocyte-macrophage (CFU-GM), and stromal cell (CFU-F) progenitors were d etermined. In addition, we examined the 4-HC sensitivity of megakaryoc yte progenitors (CPU-Meg) since, to our knowledge, this has not been r eported before. As expected, increasing doses of 4-HC led to progressi ve inhibition of hematopoietic colony formation. CFU-F, CPU-Mix, and C FU-Meg appeared most resistant to 4-HC exposure, while CFU-E, BFU-E, a nd CFU-GM appeared most sensitive. At doses over 100 mu g/mL, the usua l concentration recommended. for purging of buffy coat cells, hematopo ietic colony formation was completely inhibited. These data suggest th at if more highly purified marrow cells are employed for purging, lowe r 4-HC doses may need to be used. They also suggest that the thrombocy topenia that frequently accompanies 4-HC purging is not likely due to loss of CPU-Meg.