MAINTENANCE OF TRANSPLANTATION POTENTIAL IN EX-VIVO EXPANDED CD34(-SELECTED HUMAN PERIPHERAL-BLOOD PROGENITOR CELLS())

CD34(+)-selected hematopoietic progenitor cells are being increasingly used for autotransplantation, and indicates that these cells can be e xpanded ex vivo. Of 15 patients with solid tumors undergoing a phase I /II clinical trial using CD34(+)-selected peripheral blood progenitor cells (PBPCs) after high-dose chemotherapy, we analyzed the frequency of long-term culture-initiating cells (LTCIC) as a measure of transpla ntation potential before and after ex vivo expansion of CD34(+) cells. PBPCs were mobilized by combination chemotherapy and granulocyte colo ny-stimulating factor (G-CSF). The original unseparated leukapheresis preparations, the CD34(+)-enriched transplants, as well as nonabsorbed fractions eluting from the CD34 immunoaffinity columns (Ceprate; Cell Pro, Bothell, WA) were monitored for their capacity to repopulate irra diated allogeneic stroma in human long-term bone marrow cultures. We f ound preservation of more than three quarters of fully functional LTCI C in the CD34(+)-selected fractions. Quantitation of LTCIC by limiting dilution analysis showed a 53-fold enrichment of LTCIC from 1/9,075 i n the unseparated cells to an incidence of 1/169 in the CD34(+) fracti ons. Thus, in a single apheresis, it was possible to harvest a median of 1.65 x 10(4) LTCIC per kg body weight (range, 0.71 to 3.72). In add ition, in six patients, large-scale ex vivo expansions were performed using a five-factor cytokine combination consisting of stem cell facto r (SCF), interleukin-1 (IL-1), IL-3, IL-6, and erythropoietin (EPO), p reviously shown to expand committed progenitor cells. LTCIC were prese rved, but not expanded during the culture period. Optimization of ex v ivo expansion growth factor requirements using limiting dilution assay s for LTCIC estimation indicated that the five-factor combination usin g SCF, IL-1, IL-3, IL-6, and EPO together with autologous plasma was t he most reliable combination securing both high progenitor yield and, at the same time, optimal preservation of LTCIC. Our data suggest that ex vivo-expanded CD34(+) PBPCs might be able to allow long-term recon stitution of hematopoiesis. (C) 1994 by The American Society of Hemato logy.