Hematopoietic Progenitor Cell Counts of the Leukapheresis Product Determined Using Sysmex XN Analyzers Predict a Sufficient Number of CD34+Stem Cells in a Peripheral Blood Stem Cell Harvest for Autologous Transplantation

Objective Several institutions outsource CD34+ cell counting of leukapheresis products, limiting rapid measurements, as results are obtained the next day. This problem is compounded with plerixafor use, a stem cell-mobilizing drug that increases leukapheresis efficiency but requires administration the day before leu-kapheresis. Use of this drug for a second leukapheresis procedure before the first-day leukapheresis CD34+ count results are confirmed causes unnecessary leukapheresis and expensive plerixafor administration. We in-vestigated whether or not measuring hematopoietic progenitor cells in leukapheresis products (AP-HPCs) us-ing a Sysmex XN-series analyzer could resolve this problem. Methods We retrospectively compared the absolute AP-HPC value per body weight with the CD34+ (AP-CD34+) count in 96 first-day leukapheresis product samples obtained between September 2013 and January 2021. Comparisons were also conducted according to regimen: granulocyte colony-stimulating factor (G-CSF) monotherapy, chemotherapy plus G-CSF, or plerixafor mobilization. Results AP-CD34+ and AP-HPC counts correlated strongly (rs=0.846) overall and, in particular, under che-motherapy plus G-CSF (rs=0.92) but correlated mildly under G-CSF monotherapy (rs=0.655). AP-HPCs could not completely be dichotomized based on an AP-CD34+ threshold of 2x106/kg for any stimulation procedure. In most cases with AP-HPCs >6x106/kg, the AP-CD34+ count exceeded 2.0x106/kg, but in 5.7% of these cases, the AP-CD34+ count was <2.0x106/kg. A cut-off of AP-HPCs >4.843x106/kg yielded a sensitivity of 71% and specificity of 96% for predicting AP-CD34+ >= 2x106/kg. Conclusion AP-HPCs can identify cases in which sufficient stem cells have been collected.