HLA-matched sibling stem cell transplantation in children with ß-thalassemia with anti-thymocyte globulin as part of the preparative regimen: the Greek experience.

BU combined with CY, the preferred preparatory regimen for thalassemic patients, is associated with a substantial incidence of graft rejection especially in patients with advanced disease stage. This study retrospectively analyzes the outcome of 75 consecutive pediatric patients with ß-thalassemia who underwent HLA-matched sibling transplantation after anti-thymocyte globulin (ATG)-containing myeloablative conditioning regimens. With a median follow-up of 9 years (range 1-15 years), the overall survival (OS) and thalassemia free survival (TFS) rates were 96% and 92%, respectively. Both the estimated TRM and the cumulative incidence of rejection/failure were 4%. The cumulative incidences of acute GVHD grade II-III and grade III were 20% and 5.3%, respectively. No patient developed acute GVHD grade IV. Only two patients developed extensive chronic GVHD. The estimated OS and TFS for patients with Class 1 and 2 disease according to Pesaro criteria were 96.3% and 94.4%, whereas for patients with Class 3 disease they were 94.1% and 88.2%, respectively. In our series, the use of myeloablative conditioning regimens, which include ATG for the transplantation of thalassemic children from matched sibling donors, resulted in excellent outcomes with very low incidences of TRM and rejection.

Kinetics of quiescent cord blood stem/progenitor cells with high proliferative potential in stem-cell expansion culture.

BACKGROUND: The most primitive engrafting hematopoietic stem cell (HSC) resides mainly in a tumor growth factor-beta (TGF-beta)-dependent quiescent phase of the cell cycle. In this study, ex vivo expansion of UC blood (UCB) HSCs has been investigated, with the aim of showing whether quiescent HSCs can be recovered from expansion culture. METHODS: AC133(+) stem/progenitor cells from six full term-pregnancies UCB-samples were immunomagnetically selected, followed by ex vivo expansion culture in the presence of thrombopoietin (TPO), c-kit ligand (KL), flt-3 ligand (FL) and IL-6. Quiescent HSCs were detected by a clonogenic assay that allows the detection of multipotent and committed single- lineage quiescent stem/progenitor cells, named mHPP-Q and cHPP-Q, respectively, by means of a TGF-beta blocking Ab. RESULTS: Expansion culture of fresh selected AC133(+) cells for 1 week caused maintenance rather than expansion of mHPP-Q cells and a 1-fold increase in cHPP-Q cells. A further week culture initiated with 7-day expanded AC133(+) cells resulted in an additional 1.5-fold expansion of cHPP-Q while no mHPP-Q cells could be detected. Amplification of cHPP-Q cells in long-term expansion cultures initiated with 14-day expanded AC133(+) cells was observed for at least a further 4 weeks. DISCUSSION: A small proportion of HPP-Q cells recovered from 7-day expansion cultures retain their multilineage potential: longer culturing of these cells results in the loss of multilineage potential while they maintain quiescent behavior and high proliferative potential.

A functional hierarchy among the CD34+ hematopoietic cells based on in vitro proliferative and differentiative potential of AC133+CD34(bright) and AC133(dim/)-CD34+ human cord blood cells.

The 5-transmembrane receptor AC133 is expressed on a subpopulation of human hematopoietic cells that includes the CD34(bright) cells. We evaluated the developmental potential of AC133+CD34(bright) and AC133(dim/-)CD34+ cells isolated from 5 cord blood (CB) samples by studying the in vitro proliferative and differentiative potential of each population in both progenitor and mature cell expansion cultures. Seven-day culture of AC133+CD34(bright) cells with a cytokine combination favoring primitive progenitor cells causes a significant increase in CD34+, CFU-C and noncycling stem/progenitor cells HPP-Q (High Proliferative Potential-Quiescent), whereas culture of AC133(dim/-)CD34+ cells shows a limited increase in committed progenitor cells only. HPP-Q cells were not found in freshly isolated AC133(dim/-)CD34+ nor in expanded CD34+ cells derived from AC133(dim/-)CD34+ cells. No statistically significant difference was observed between the 1-week expanded AC133+ and the initial AC133+CD34(bright) cells regarding their clonogenic efficiency (CE), while expanded CD34+ cells derived from AC133(dim/-)CD34+ cells exhibited a decreased CE. Subexpansion of the reselected AC133+ derived from AC133+CD34(bright) cells reveals a further increase of stem/progenitor cells and the 14-day expanded AC133+ cells reveal an unchanged CE. Subexpansion of reselected 7-day CD34+ cells derived from AC133(dim/-)CD34+ cells was not possible. Culture of AC133+CD34(bright) cells in cytokines that favor megakaryopoiesis or erythropoiesis resulted in a significant expansion of CD41+ and CD71+ cells, respectively; AC133(dim/-)CD34+, in comparison, showed a limited potential to megakaryocytic differentiation and a decreased production of erythroid cells. Our data indicate that early high proliferating stem/progenitor cells and early committed progenitors are present in AC133+CD34(bright) cells, but not in AC133(dim/-)CD34+ cells; the latter represent late committed progenitors with limited proliferative potential.