Reconstitution of Endothelial Progenitor Cells after Allogeneic Bone Marrow Transplantation in Children with Malignancies

Evidences have been reported that bone marrow (BM)-derived endothelial progenitor cells (EPCs) circulate in peripheral blood (PB) of healthy subjects. These EPCs seem to play an important role in maintaining homeostasis of vessel walls, participating in both neo-angiogenetic processes and re-endothelization of the wall of injured vessels. The aim of this study was to assess the number and origin of circulating EPCs in PB and BM of children who underwent allogeneic BMT for malignancies. Thirty-five patients with acute lymphoid leukemia (n=18), acute myeloid leukemia (n=13), non Hodgkin lymphoma (n=1), myelodysplastic syndrome (n=1), chronic myeloid leukemia (n=1), and rabdomyosarcoma (n=1) were enrolled in this study. We evaluated PB samples at 21 days, and either PB or BM samples at 45, 60, 90, 120, 180, and 365 days after transplantation. The number of EPCs was evaluated as CD34+VEGFR-2+ or CD34+CD133+VEGFR-2+ cells by cytofluorimetric analysis, and by in vitro culture. PB (n=10) and BM (n=10) samples from age-matched BM donors were analyzed as controls. Donor or recipient origin of EPCs was assessed, by micro-satellite analysis, on at least 10 individually-picked endothelial colonies. The percentage of circulating CD34+VEGFR-2+ cells was significantly lower (p=0.02) in patients tested 21 days after transplant (median 0.01%, 0–1.0) than in PB from controls (median 0.06%, 0–1.3). At the same time point, the percentage of CD34+ co-expressing the CD133 and VEGFR-2 antigens, representing a restricted subset of immature EPCs, was lower, although still not-statistically significant, in patients (median 0.0%, 0.0–4.6) than in controls (median 0.6%, 0.0–15.1); the number of EPC-derived colonies was also significantly lower (p