Long-term platelet production assessed in NOD/SCID mice injected with cord blood CD34+ cells, thrombopoietin-amplified in clinical grade serum-free culture

Objective. Delayed platelet recovery post-cord blood (CB) transplantation might be due to CB characteristics: low maturity of stem cell compartment, poor production of CD34(+)/CD41(+) cells when induced to differentiate along the megakaryocytic (MK) lineage, retention of a low ploidy in the expanded MKs. Ex vivo expansion of CB hematopoietic progenitor cells for reconstitution of different human hematopoietic lineages has already been developed in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. However, optimal conditions for MK-progenitor engraftment to reduce hemorrhaging risk still to be developed. This study assesses the hypothesis that CB-CD34(+) amplification with thrombopoietin (TPO) can be applied to a portion of a CB transplant unit to stimulate recovery along MK differentiation program. Materials and Methods. Human CB-CD34(+) cells were amplified in a serum-free, clinical grade medium with 100 ng/mL TPO alone and in addition to other cytokines (Kit ligand, interleukin-6, and Flt-3 ligand). Seven-day cultured cells were transplanted into irradiated NOD/SCID mice and engraftment, megakaryocytopoiesis, and platelet production were assessed. Results. Platelet release was successful and continuously present for at least 8 weeks in NOD/SCID mice transplanted with CB cells stimulated by TPO. Thrombocytopoiesis was more effective with transplanted TPO-amplified cells than with the cytokine cocktails. Conclusion. Platelet number obtained is within the minimum level considered sufficient for hemostasis. Furthermore, amplified cells maintain their self-renewal capacity and multilineage potential differentiation. Thus, transplantation of TPO-expanded CB cells has the potential favoring both platelet recovery and human engraftment. (C) 2008 ISEH - Society for Hematology and Stem Cells. Published by Elsevier Inc.