Deficiency of CD34+c-kit+ and CD34+38- hematopoietic precursors in aplastic anemia after immunosuppressive treatment

Abstract

To characterize the persistent abnormalities of hematopoiesis in aplastic anemia (AA) after immunosuppression with antilymphocyte globulin (ALG), we analyzed the quantity, phenotype, and growth properties of hematopoietic progenitor cells in 13 patients who received ALG treatment. Flow cytometry (FACS) 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+ cells were reduced 2-10-fold and showed no correlation with the ALG-induced 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 levels of c-kit mRNA by reverse transcription-polymerase chain reaction (RT-PCR). Furthermore, the CD34+ cell population was almost completely depleted of CD34+CD38-early hematopoietic progenitors in all AA patients. The proportion of CD34+ cells expressing lineage differentiation antigens CD33, CD71, and CD45RA in AA was increased, as compared to control BM. Formation of hematopoietic colonies by FACS-purified CD34+ cells was nearly absent in 4 relapsed patients, normal in 4 of 9, and decreased (up to 10-fold) in 5 of 9 patients in remission. The degree of impairment of colony-forming ability by AA progenitors correlated well with the reduction of CD34+c-kitC cells. The best proliferative 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-forming ability and long-term regenerative capacity of AA marrow after immunosuppression. Analysis of the immunophenotypes and the proliferative properties of purified progenitors may be useful for estimating degree of hematopoietic recovery in ALG-treated patients. 0 1996 Wiley-Liss, Inc.

Alterations in Hematopoietic Microenvironment in Patients with Aplastic Anemia

“…Aplastic anemia (AA) is an acquired disease characterized by low blood cell production due to chronic depression of hematopoiesis in the bone marrow (BM). AA has the following characteristics: decreased hematopoietic stem cell (HSC) number, 1–3 impaired HSC function, 4–7 and increased HSC apoptosis level 8–10 . The pathogenesis of AA remains unclear.…”

Estimation of CD34+ in Patients with Hypocellular Marrow and Treatment Response in Aplastic Anemia

“…This is supported by other studies which report that CD34 cells are significantly decreased in bone marrow of patients with AA. 17,18 Normal CD34 levels may be explained by a relatively low cellular area of bone marrow (being evaluated for CD 34) early in the disease among severe AA or a non-severe AA. As MDS cytogenetics were not done on all hypocellular bone marrows, the 2 patients with AA but high CD34 levels probably were hMDS.…”

Quantitative analysis of bone marrow CD34 cells in aplastic anemia and hypoplastic myelodysplastic syndromes

“…These patients may have moderate AA, a less severe form of AA that can persist for months or years, progress to more severe disease, or even resolve spontaneously. 5,30,31 As some cases of moderate AA 5,30,31 and lowgrade MDS (e.g., the 5qÀ syndrome 32,33 ) never progress to 34,35 whereas hypoplastic MDS patients generally have higher bone marrow CD34 þ cell counts. 9,10,36,37 However, significant overlap in the CD34 percentages between these two disorders has precluded using this assay diagnostically.…”