Preserved long-term repopulation and differentiation properties of hematopoietic grafts subjected to ex vivo expansion with stem cell factor and interleukin 11

Background The ex vivo expansion of hematopoietic grafts has been proposed as an efficient procedure for improving the hematological recovery of recip ients. The fate of the long-term repopulating cells during the ex vivo mani pulation of the graft is, however, a critical issue in ex vivo expansion pr otocols and ultimately will define the applicability of this new technology in hematopoietic transplants, Methods. The repopulating ability of mouse hematopoietic samples was determ ined by means of bone marrow (BM*) competition assays, using congenic strai ns that express the pan-leukocyte Ly-5.1 and Ly-5.2 antigens, The generatio n of potential changes in the repopulating properties of human hematopoieti c samples subjected to ex vivo expansion was determined by comparing the en graftment of fresh and ex vivo-manipulated CD34(+) cord blood cells in irra diated nonobese diabetic/severe-combined immunodeficient (NOD/SCID) mice. Results. Under our optimized conditions of mouse BN incubation (stem cell f actor plus interleukin-ll, either with Or without macrophage inflammatory p rotein-1 alpha or Flt3 Ligand), both the short-term and the mid-term repopu lating ability of the ex vivo-expanded samples mere significantly improved when compared with fresh samples. in the long-term, no changes in the repop ulation and differentiation properties of the graft were observed as a resu lt of the ex vivo expansion process. As deduced from the analysis of NOD/SC ID mice transplanted with fresh and ex vivo expanded human CD34(+) cord blo od cells, the in vitro stimulation mediated by SCF/IL-11/FLT3L was capable of preserving the ability of the grafts to repopulate the lympho-hematopoie sis of recipents for at least 3 months. Conclusion. These results indicate that under our optimized conditions of e x vivo expansion, the amplification of the hematopoietic progenitors respon sible for the short- and mid-term repopulating properties of the graft can take place without compromising the long-term lympho-hematopoietic repopula ting properties.