MURINE MODEL FOR HUMAN CORD-BLOOD TRANSPLANTATION - NEAR-TERM FETAL AND NEONATAL PERIPHERAL-BLOOD CELLS CAN ACHIEVE LONG-TERM BONE-MARROW ENGRAFTMENT IN SUBLETHALLY IRRADIATED ADULT RECIPIENTS

The purposes of the research reported here were first to explore a mur ine model for human placental and umbilical cord blood transplantation and second to evaluate the engraftment ability of ex vivo cultured he matopoietic cells. Murine near-term fetal and neonatal peripheral broo d (FNPB) cells, genetically marked with the human multiple drug resist ance transgene (MDR1) were used for syngeneic transplants into subleth ally irradiated adult mice. Donor cells were transplanted either fresh and untreated, or after ex vivo culture in the presence of the hemato poietic growth factors recombinant murine stem cell factor, recombinan t human interleukin-3 (rHu IL-3), and rHu IL-6, in a liquid culture sy stem. To evaluate, count, and characterize FNPB progenitor cell-derive d colonies, neonatal mouse mononuclear cells were cultured directly in methylcellulose with growth factors. To assess their ex vivo expansio n ability, FNPB mononuclear cells were first cultured in liquid medium for 3 to 8 days and then transferred to semisolid assay prates. Evalu ation of the cell counts after liquid culture showed a 1.4- to 11.6-fo ld increase, and the numbers of colonies observed in methylcellulose w ere similar to those produced by fresh FNPB cells. Donor-type engraftm ent was demonstrated by polymerase chain reaction (PCR) amplification of the human MDR1 transgene in the peripheral blood of all surviving a nimals (5 of 7 recipients of the fresh, and 3 of 8 recipients of the e x vivo-cultured cells) 2 to 4 months after transplantation. The propor tion of donor leukocytes in the peripheral blood of the recipients (ch imerism) was evaluated using fluorescence in situ hybridization (FISH) analysis 4 to 6 months after transplantation and ranged from 2% to 26 %. In addition, bone marrow cultures were obtained from two recipient animals: one had received fresh-untreated cells and was evaluated 8 mo nths after transplant, the other had received ex vivo cultured cells a nd was tested 14 months after grafting. The derived hematopoietic colo nies were tested by PCR and the transgene was detected, conclusively p roving long-term engraftment of donor cells. These results indicate th at FNPB transplants can be successfully performed in sublethally irrad iated mice with and without ex vive culture. Long-term donor-type engr aftment with sustained chimerism has been demonstrated. Thus, murine n eonatal blood grafts can be used as an animal model for cord blood tra nsplantation for gene therapy studies where complete myeloablation is not desirable and partial replacement of defective marrow may be suffi cient. Furthermore, the possibility of numerically expanding hematopoi etic progenitor cells contained in neonatal blood without affecting th eir engraftment ability could facilitate use of cord brood grafts in a dult recipients. (C) 1997 by The American Society of Hematology.