EDUCATION SESSION 12: CELLULAR THERAPY New Strategies for Blood Progenitor Cell Mobilization

After 20 years of painstaking clinical trials in peripheral blood stem cell mobilization and transplantation, a large database has accumulated on how to mobilize and to collect factors affecting mobilization, the progenitor cell dose effect on haemopoietic recovery, and even ambulatory transplant (To et al, 1997). Currently an increasing number of allogeneic transplants and most autologous transplants are performed using mobilized blood cells. Moreover analysis of the types of cells mobilized and mechanistic studies based on in vitro and animal models are contributing to developing new strategies of mobilization. Current protocols of mobilization include G-CSF alone (autologous/allogeneic) or a combination of chemotherapy and haemopoietic growth factors such as G-CSF and GMCSF (autologous). Adequate progenitor cell yields for single rescue (2 x 10 CD34+ cells/kg BW) can be achieved in most patients except those who have been heavily pretreated. The yield per apheresis can be increased by performing 3 to 4 blood volume aphereses without exhaustion of the circulating pool of progenitors or dangerous thrombocytopenia. However, up to 10% of allogeneic donors and 30% of autologous donors failed to mobilize sufficient progenitors and apheresis and cryopreservation put a demand on health care resources and may be uncomfortable for patients. The heterogeneity of mobilization response may well be due to polygenetic influences as seen in studies of different mouse strains (Roberts et al, 1997). Three questions will be addressed: can we avoid apheresis altogether, how can we increase yield of mobilization and how can we develop better mobilization strategies.