No abstract

Hematopoietic reconstitution (HR) after peripheral blood stem cell transplantation is characterized by a delay of 8 and 12 days for recovery to safe levels of neutrophils and platelets even in patients with the most rapid engraftment. We postulate that a further enhancement in the rate of HR may be achieved by transplanting with an expanded postprogenitor cell population that can provide mature functional cells within days of infusion. In this study we investigated the ability of combinations of hematopoietic growth factors (HGF) to generate nascent granulocyte-macrophage colony-forming units (CFU-GM) in a 7-day suspension culture of peripheral blood CD34+ cells. A combination of 6 HGF, ie, interleukin-1 beta (IL-1), IL-3, IL-6, granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage- CSF (GM-CSF), and stem cell factor (SCF), was identified as the most potent combination of those tested. Subsequently, large volume suspension cultures of CD34+ cells from the same patients using the same 6-factor combination were established and monitored for 21 days. An exponential rate of nucleated cell production (mean 1,324-fold increase) occurred during culture. CFU-GM production paralleled nucleated cell production until day 10, peaked at day 14 (mean 66-fold increase), and was then maintained until day 21. Cells produced in culture were predominantly neutrophil precursors and developed normally as assessed by morphology, immunophenotype, and superoxide generation. This stroma-free, cytokine-driven culture system can achieve a degree of amplification, which suggests the feasibility of ex vivo culture of hematopoietic progenitor cells as an adjunct to hematopoietic stem cell transplantation.

Haemopoietic reconstitution (HR) using autologous peripheral blood stem cells (PBSC) was attempted after intensive chemotherapy or chemoradiotherapy in two patients with relapsed acute non-lymphoblastic leukaemia (ANLL). The PBSC were collected by leukapheresis very early in first remission and cryopreserved in liquid nitrogen. Both patients demonstrated early evidence of trilineage engraftment. The first patient received melphalan 200 mg/m2 followed by rescue with 1.3 X 10(8) mononuclear cells/kg body weight containing 29 X 10(4) granulocyte-macrophage progenitor cells (CFU-GM)/kg, and HR was evident by Day 14. The second patient was treated with supralethal chemoradiotherapy followed by rescue with 3.0 X 10(8) mononuclear cells/kg containing 23 X 10(4) CFU-GM/kg. He demonstrated early engraftment with near normal peripheral blood counts by Day 16. There was a subsequent fall in both bone marrow cellularity and peripheral blood counts to a level of low but persistent activity. There was a further phase of haematological recovery from 8 weeks following transplantation with an increase in peripheral blood counts and bone marrow cellularity until final relapse at 13 weeks. This study demonstrates that circulating stem cells have haemopoietic reconstitutive capacity, previously only shown with buffy coat cells from chronic granulocytic leukaemia. The minimum number of PBSC required for satisfactory engraftment remains unknown, although it seems probable that the ratio of pluripotent stem cells to committed progenitor cells is lower in very early remission peripheral blood than in either allogeneic normal bone marrow or autologous bone marrow collected later in stable remission. The question of leukaemic contamination of the PBSC remains to be answered.