CIRCULATION OF CD34+ HEMATOPOIETIC STEM-CELLS IN THE PERIPHERAL-BLOOD OF HIGH-DOSE CYCLOPHOSPHAMIDE-TREATED PATIENTS - ENHANCEMENT BY INTRAVENOUS RECOMBINANT HUMAN GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR

  • 1 November 1989
    • journal article
    • research article
    • Vol. 74  (6) , 1905-1914
Abstract
We report that hematopoietic progenitor cells expressing the CD34 antigen (CD34+ cells) transiently circulate in the peripheral blood (PB) of cancer patients treated with 7 g/m2 cyclophosphamide (HD-CTX) with or without recombinant human granulocyte macrophage-colony stimulating factor (rHuGM-CSF). In adult humans, CD34+ cells represent a minor fraction (1% to 4%) of bone marrow (BM) cells, comparing virtually all hematopoietic colony-forming progenitors in vitro and probably also stem cells capable of restoring hematopoiesis of lethally irradiated hosts. We show that CD34+ cells circulation is fivefold enhanced by rHuGM-CSF 5.5 protein .mu.g/kg/day by continuous intravenous infusion for 14 days after HD-CTX. During the third week after HD-CTX (ie, when CD34+ cells peak in the circulation), large-scale collection of PB leukocytes by three to four continuous-flow leukaphereses allows the yield of 2.19 to 2.73 .times. 108 or 0.45 to 0.56 .times. 109 CD34+ cells depending on whether or not patients receive rHuGM-CSF. The number of kCD34+ cells retrieved from the circulation by leukaphereses exceeds the number that can be harvested by multiple BM aspiration under general anesthesia. Thus, after therapy, with HD-CTX and rHuGM-CSF, PB represents a rich source of hematopoietic progenitors possibly usable for restoring hematopoiesis after myeloablative chemoradiotherapy. To determine whether CD34+ cells found in the PB are equivalent to their marrow counterpart, we evaluated their in vitro growth characteristics and immunological phenotype by colony assays and dual-color immunofluorescence, respectively. We show that PB CD34+ cells possess qualitatively normal hematopoietic colony growth and high cloning efficiency comparable to that observed with BM CD34+ cells. In addition, PB CD34+ cells display heterogeneous surface membrane differentiation antigens analogous to BM CD34+ cells. The availability of large quantities of CD34+ cells by leukapheresis is relevant to the field of stem cell transplantation and possibly to genetic manipulations of the hematopoietic system in humans.

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