Granulocyte colony-stimulating factor (G-CSF) is the standard growth factor for mobilizing hematopoietic progenitor cells in healthy peripheral blood progenitor cell (PBPC) donors. G-CSF is given daily for 5 days to PBPC donors prior collecting PBPC concentrates by apheresis. PBPC donors given G-CSF experience splenic enlargement and, rarely, spontaneous rupture of the spleen. We evaluated the incidence and time course of splenic enlargement in PBPC concentrate donors and accessed factors effecting size changes. Healthy adults were given G-CSF (10 micrograms/kg/day) for 5 days and a PBPC concentrate was collected by apheresis. Ultrasound was used to assess craniocaudal spleen length prior to giving G-CSF, the day of apheresis, and 4 or 10 days after apheresis. Among 38 healthy subjects a 5-day course of G-CSF causes spleen length to increase in 95% of the donors. The mean spleen length increased from a baseline length of 10.8 ? 1.7 cm to 12.2 ? 1.7 cm and the mean increase in length was 13%. However, spleen enlargement was transient. Four days after apheresis the spleen length fell to 11.3 ? 1.8 cm, but it remained greater than baseline levels. Ten days after apheresis, spleen length fell to 10.5 ? 1.2 cm and did not differ from baseline length. The magnitude of spleen length increase was not affected by donor gender, race, or age. We are currently investigating the mechanisms of G-CSF mobilization of stem cells into the peripheral blood. Plasma protein profiles are being compared before and after G-CSF administration. Associations between the expression of cell adhesion molecules on mature neutrophils and neutrophil precursors and spleen size change will also be investigated.
