BACKGROUND : Recently, allogeneic peripheral blood stem cell transplantation (Allo-PBSCT) instead of bone marrow transplantation (BMT) has been widely used with the benefits of an earlier recovery of blood cells and a lower incidence of graft failure because of higher CD34+ cell dose. However, recent studies suggested that the higher dose of CD34+ cells might be related to the lower survival and the higher morbidity due to chronic graft versus host disease (cGVHD). We have analyzed the impact of
transplanted CD34+ cell dose on clinical outcomes in unmanipulated allo-PBSCT from HLA identical siblings.
METHODS : Thirty-one consecutive adult patients with hematological diseases, who survived until at least day 90 after allo-PBSCT and were evaluable for cGVHD, were included. Peripheral blood stem cells were collected from HLA-matched sibling donors mobilized with G-CSF and/or GM-CSF. The patients were classified into a 'low' or 'high' CD34+ cell dose group based on whether they received less or
more than a median CD34+ cell dose of 11.17 x 106/kg, respectively.
RESULTS : The median CD34+ cell dose was 11.17 x 10 6 /kg (range, 4.12-58.80 x 10 6/kg). Acute GVHD (grade II-IV) appeared in 24 patients (77.4%) and extensive cGVHD in 14 patients (45.2%). During the follow-up (median: 340 days, range: 111-1263 days), relapses were observed in 12 patients (38.7%) and 19 patients are still alive. There was a significant difference in the incidence of extensive cGVHD (20.0% vs 68.8%, P=0.011) and relapse (60.0% vs 18.8%, P=0.029) between low and high CD34+ cell dose groups, but no difference of the incidence of acute GVHD or the days of engraftments between the two groups. The estimated survival rate was significantly different between the two groups (3 year survival rate, 31.5% vs 79.8%, P=0.022) and the patients with extensive cGVHD showed a higher survival rate than those without extensive cGVHD (55.6% vs 12.5%, P=0.013).
CONCLUSION : Better survival rate was observed in high CD34+ cell dose group for alloPBSCT, while a higher incidence of extensive cGVHD was noted. The optimal dose of CD34+ cells need to be determined to minimize the morbidity related to cGVHD and to improve survival.

Keywords: Allogeneic peripheral blood stem cell transplantation, Graft versus host disease, CD34+ cell dose,