Associations among white blood cells, CD34⁺ cells and GM-CFU in predicting the optimal timing of peripheral blood stem cell collections by apheresis

Aims: To analyze preapheresis blood CD34⁺ cells and corresponding apheresis products in order to investigate whether peripheral blood CD34⁺ cell counts correlate with peripheral blood progenitor cell (PBPC) yields and to determine the optimal timing for starting PBPC collections in our clinical setting. Material and Methods: Thirty-eight patients with hematological malignancies and undergoing varied mobilization regimens were enrolled. White blood cell counts (WBC), CD34⁺ cells and granulocyte-macrophage colony-forming units (GM-CFU) enumeration were performed on blood samples taken immediately prior to each apheresis procedure and in the corresponding PBPC collection. Results: A total of 61 apheresis procedures were performed, with a median of two collections per patient (range 1-3). The number of CD34⁺ cell/ml in the preapheresis blood correlated closely with CD34⁺ cells/kg and, to a lesser degree, with GM-CFU/kg in the apheresis products (r = 0.81 and r = 0.67, respectively, P <0.0001). WBC showed significant but poor correlation with CD34⁺ cells/kg and GM-CFU/kg (r = 0.43 and r = 0.45, respectively, P=0.004). A significant correlation was also found between CD34⁺ cells/kg and GM-CFU/kg in PBPC collections (r = 0.62, P <0.0001). Linear regression analysis indicated that the minimum threshold of 2 × 10⁶ CD34⁺ cells/kg might be attained with a single apheresis if the CD34⁺ cells/ml in the peripheral blood measured prior to apheresis on the day of collection is ≥ 26 × 10³ CD34⁺ cells/ml. Conclusion: Collectively, these data demonstrate that circulating CD34⁺ cells is more useful than GM-CFU or WBC for predicting the optimal timing of PBPC harvests.