ASSESSING PERMANENT DAMAGE TO PRIMITIVE HEMATOPOIETIC STEM-CELLS AFTER CHEMOTHERAPY USING THE COMPETITIVE REPOPULATION ASSAY

The competitive repopulation assay was used to document the effects of six chemotherapeutic agents on primitive hematopoietic stem cells. Th e assay measures the relative abilities of donor cells to produce circ ulating erythrocytes and lymphocytes in lethally irradiated congeneic mice over a period of 6 months. Long-lasting marrow reconstitutive def icits in cells of donor origin occurred after exposure to 5-fluorourac il (5FU), bis-chloronitrosourea (BCNU), cyclophosphamide (CTX), vincri stine (VCR), and actinomycin D (ACT) but not after exposure to cytosin e arabinoside (ARA). Repopulating abilities were reduced after as litt le as a single dose of CTX or BCNU. A second dose of BCNU caused even more severe effects. A single dose of 5FU had no effect on repopulatin g abilities despite a temporary 10-fold reduction in marrow cell numbe r, but multiple doses reduced the marrow stem-cell replicative ability to less than half of the normal control levels. These effects were no t reliably predicted or detected by colony-forming assays or by reduct ions in marrow cell number. Thus, long-lasting proliferative defects i n the primitive hematopoietic stem-cell (PHSC) population can result f rom the use of chemotherapeutic agents. Such findings may have clinica l implications, especially in individuals receiving repeated or prolon ged administration of these agents or in instances of marrow transplan tation.