Exploratory analysis describing ultrasonic (US) evaluation of spleen size during peripheral blood progenitor cell (PBPC) mobilization by filgrastim in normal donors

Abstract

7102 Background: Filgrastim is used to mobilize CD34+ cells into the peripheral blood that are collected by apheresis for allogeneic transplantation. We prospectively evaluated spleen size during PBPC mobilization Methods: Donors ≥18 yrs eligible to be PBPC donors per institutional guidelines enrolled. Splenic assessments were done before, during, and after PBPC mobilization. Filgrastim dose and schedule and leukapheresis (LK) procedures were per local practice. Spleen size by US was measured in 3 dimensions: longitudinal (craniocaudal), transverse, and diagonal (perpendicular to transverse). Splenic volume was estimated by taking the cross-product of 3 dimensions and multiplying by 0.52, approximating an ellipse volume. Stiff (ASH 2007) reported the primary endpoint, fold change from baseline in splenic volume during mobilization. Exploratory analyses, including a linear regression evaluating the effect of age and baseline spleen size on fold-change, were performed. Results: 309 enrolled, median age 44yrs, 56% male. Median fold volume change from baseline to first LK was 1.47, resolving to near baseline 1 week after last LK. No significant clinical sequelae, including splenic rupture, were reported. Older donors appeared to have the smallest baseline spleen volume and the largest fold change (table). Linear regression analyses indicated age was a significant predictor for both baseline spleen volume (p=0.0031) and spleen volume fold change from baseline at first LK (p=0.0499). Conclusions: During mobilization, spleen volume transiently increased from baseline to day of 1st LK and returned to near baseline 1 week after last LK. Older donors tended to have smaller baseline splenic volume and greater fold changes in spleen size. Preclinical models suggest decreasing hematopoietic stem cell homing after mobilization with aging (Morrison 1996; Wagers 2002), which could result in splenic accumulation of progenitor and stem cells. [Table: see text] [Table: see text]