EARLY HEMATOPOIETIC PROGENITORS IN THE PERIPHERAL-BLOOD OF PATIENTS WITH SEVERE APLASTIC-ANEMIA (SAA) AFTER TREATMENT WITH ANTILYMPHOCYTE GLOBULIN (ALG), CYCLOSPORINE-A AND G-CSF

Background and Objective. We previously reported that patients with ac quired severe aplastic anemia (SAA) treated with antilymphocyte globul in (ALG), 6-methylprednisolone, cyclosporin A (CyA) and granulocyte co lony-stimulating factor (C-CSF) can mobilize peripheral blood hemopoie tic progenitors (PBHP). The aim of the present study was to assess phe notypic and functional properties of these PBHP. Methods. We studied s even patients who underwent 43 leukophereses (median 5) between day +3 0 and +80 following ALC, while in treatment with CyA and G-CSF. Mobili zed peripheral blood hemopoietic progenitors were analyzed using surfa ce markers, conventional assays for clonogenic cells (CFU-GM, BFU-E, C FU-GEMM) as well as the recently developed assay for long-term culture initiating cells (LTC-ICs). Results. The proportion of CD34(+) cells ranged between 0% and 5.4% (median 0.3%), CD34(+)DR(-) between 0% and 3.5% (median 0.1%) and CD8(+) cells between 3.3% and 56% (median 31%). When light density mononuclear cells (MNC) were plated in vitro, we c ould grow colony-forming units-granulo-macrophage (CFU-CM) (range 0-45 /10(5) MNC; normal controls 21-200/10(5) MNC), burst-forming units-ery throid (BFU-E)(range 0-5/10(5) MNC; normal controls 0-6/10(5) MNC), mu ltipotent colonies (CFU-GEMM)(range 0-3/10(5) MNC; normal controls 0-6 /10(5) MNC) and high proliferative potential colony-forming cells (HPP -CFC) (range 0-3.4/10(5) MNC). We studied long-term culture-initiating cells (LTC-ICs) in 18 leukophereses from 4 patients; in 7/18 samples LTC-ICs were grown at low frequency (range 0.4-2/10(6) MNC) (normal co ntrols 5-130/10(6) MNC), and in one patient in the absence of CFU-CM g rowth. The total yield of LTC-ICs in two patients was 7.64 and 10.5x10 (2)/kg of body weight. Interpretation and Conclusions. This study sugg ests that cells with the phenotype and in vitro function of early hemo poietic progenitors are found, though in small numbers, in the periphe ral blood of patients with SAA after treatment with immunosuppressants and prolonged C-CSF administration. Whether G-CSF-mobilized progenito rs contribute to hemopoietic recovery in these patients remains to be determined. (C) 1997, Ferrata Storti Foundation.