DEFICIENCY OF CD34(-KIT(+) AND CD34(+)38(-) HEMATOPOIETIC PRECURSORS IN APLASTIC-ANEMIA AFTER IMMUNOSUPPRESSIVE TREATMENT()C)

To characterize the persistent abnormalities of hematopoiesis in aplas tic anemia (AA) after immunosuppression with antilymphocyte globulin ( ALG), we analyzed the quantity, phenotype, and growth properties of he matopoietic progenitor cells in 13 patients who received ALG treatment . Flow cytometry (FAGS) revealed a deficiency of CD34(+) cells in bone marrow (BM) of all patients. This deficiency was most severe (40-fold ) in 4 patients in AA relapse. In 9 patients in remission, CD34(+) cel ls were reduced 2-10-fold and showed no correlation with the ALG-induc ed improvement of peripheral blood cell counts. The proportion of CD34 (+) cells carrying c-kit receptors was abnormally low (2-10-fold below normal) in 5 of 13 AA patients. These patients also displayed low lev els of c-kit mRNA by reverse transcription-polymerase chain reaction ( RT-PCR). Furthermore, the CD34(+) cell population was almost completel y depleted of CD34(+)CD38(-) early hematopoietic progenitors in all AA patients. The proportion of CD34(+) cells expressing lineage differen tiation antigens CD33, CD71, and CD45RA in AA was increased, as compar ed to control BM. Formation of hematopoietic colonies by FAGS-purified CD34(+) cells was nearly absent in 4 relapsed patients, normal in 4 o f 9, and decreased (up to 10-fold) in 5 of 9 patients in remission. Th e degree of impairment of colony-forming ability by AA progenitors cor related well with the reduction of CD34(+)-c-kit(+) cells. The best pr oliferative response of CD34(+) cells was observed in the presence of stem cell factor and, in some cases, flt3 ligand. Our results indicate that the disease process in AA depletes immature BM progenitors, thus providing a plausible explanation for persistent defects in colony-fo rming ability and long-term regenerative capacity of AA marrow after i mmunosuppression. Analysis of the immunophenotypes and the proliferati ve properties of purified progenitors may be useful for estimating deg ree of hematopoietic recovery in ALG-treated patients. (C) 1996 Wiley- Liss, Inc.