Cytokine-mobilized peripheral blood progenitor cells for allogeneic reconstitution of miniature swine

Background. Because of the relative ease of acquisition, increased yield, a nd improved engraftment characteristics, mobilized peripheral blood progeni tor (stem) cells (PBSCs) have recently become the preferred source for hema topoietic stem cell transplantation. In our laboratory, procurement of a me gadose of PBSCs is necessary for on-going studies evaluating non-myelosuppr essive transplant regimens for the induction of mixed chimerism and allogra ft tolerance. To exploit hematopoietic growth factor synergy, we have sough t to combine growth factors with proven utility to improve PBSC mobilizatio n and maximize our PBSC procurement through an automated collection procedu re. Methods. Mobilization characteristics of PBSCs were determined in 2-5-month -old miniature swine. Animals received either swine recombinant stem cell f actor (pSCF, 100 mu g/kg) and swine recombinant interleukin 3 (pIL-3, 100 m u g/kg), administered intramuscularly for 8 days, or pSCF, pIL-3, and human recombinant granulocyte-colony stimulating factor (hG-CSF), at 10 mu g/kg. Leukapheresis was performed beginning on day 5 of cytokine treatment and c ontinued daily for 3 days. Results. Collection of PBSCs from cytokine-mobilized animals via an automat ed leukapheresis procedure demonstrated a 10-fold increase in the number of total nucleated cells (TNC) (20-30x10(10) TNC) compared to bone marrow har vesting (2-3x10(10) total TNC), A more rapid rise in white blood cells (WBC s) was seen after administration of all three cytokines compared to pSCF an d pIL-3 alone. An increase in colony-forming unit granulocyte-macrophage fr equency measured daily from peripheral blood during cytokine treatment, was seen with the addition of hG-CSF to pSCF/pIL-3 correlating well with the r ise in WBCs. Similarly, the addition of IG-CSF demonstrated a notable incre ase in the median progenitor cell yield from the 3-day leukapheresis proced ure. Cytokine-mobilized PBSCs were capable of hematopoietic reconstitution. PBSCs mobilized with pSCF/pIL-3 were infused into an SLA-matched recipient conditioned with cyclophosphamide (50 mg/kg) and total body irradiation 11 50 cGy, Neutrophil and platelet engraftment occurred on days 5 and 7, respe ctively, with minimal evidence of graft-versus-host disease. Complete donor chimerism has been demonstrated 331 days after transplant. Conclusions. Our preliminary results show that in this well-defined miniatu re swine model, recombinant swine cytokine combinations (pSCF, pIL-3 with o r without hG-CSF) successfully mobilize a high yield of progenitor cells fo r allogeneic transplantation. Furthermore these cytokine-mobilized PBSCs de monstrate the potential to reconstitute hematopoiesis and provide long-term engraftment in miniature swine.