Ex vivo expanded mobilized peripheral blood CD34(+) cells accelerate haematological recovery in a baboon model of autologous transplantation

To address the value of ex vivo expanded haematopoietic cells for shortenin g cytopenia in autologous haematopoietic transplantation, we designed an ex vivo expansion protocol based on a cocktail of early acting cytokines and short-term culture and tested it in a baboon model. Expansion involved enri ched CD34(+) peripheral blood haematopoietic cells cultured for 6 d with a combination of FLT3-L, stem cell factor (SCF), thrombopoietin (TPO) and int erleukin (IL)-3 (50 ng/ml each); CD34(+) cells, granulocyte-macrophage colo ny-forming units (GM-CFU) and megakaryocytic colony-forming units (MK-CFU) were amplified, respectively, 10.5-, 20.5- and 17.9-fold. Baboons were subm itted to a myeloablative regimen consisting of cyclophosphamide plus total body irradiation (TBI; 6 Gy) and were then grafted with either 2 x 10(6)/kg unmanipulated CD34(+) cells (control group, n = 4) or cells cultured from 2 x 10(6)/kg CD34(+) cells (expansion group, n = 4). No cytokines were admi nistered after transplantation. All the animals engrafted. The mean times t o white blood cell (WBC), granulocyte and platelet recovery were significan tly shorter in the expansion group than in the control group: WBC (> 1 x 10 (9)/l) and neutrophil (> 0.5 x 10(9)/l) recovery occurred on days 8 (range 6-9) and 9 (range 6-11), respectively, compared with days 12 (range 10-15) and 14 (range 11-16); platelets recovered (> 20 x 10(9)/l) on day 9 (range 7-12) compared with day 13 (range 11-15) in the control group (P < 0.05). N o toxicity was observed after reinfusion. No secondary hypoplasia was obser ved during more than 12 months of follow-up. Functions of both neutrophils and platelets produced from expanded cells were normal in terms of oxidativ e metabolism, chemotaxis and the bleeding time. This study shows that in co mparison with unmanipulated cells peripheral bleed haematopoietic cells exp anded from similar doses of CD34(+) cells, under the conditions defined her e, accelerated both neutrophil and platelet recovery without impairing long -term haematopoiesis.