Storage of peripheral blood stem cell samples alters flow cytometric CD34+ results

With the use of monoclonal antibodies against the CD34 antigen, flow cytometry (FC) permits rapid assessment of the quality of hematopoietic grafts. We examined PBSC samples (n = 40) to investigate possible influences of storage time and temperature on FC results. After cytapheresis, a sample of the PBSC product was collected and divided into 4 aliquots. Immediate analysis was performed on one aliquot. The other 3 specimen were stored for a) 24 h at room temperature (RT, 20 +/- 2 degrees C), at room temperature with agitation and c) at +4 degrees C. For flow cytometric analyses, samples were labeled with two CD34 markers (HPCA-2, Becton Dickinson Corp. [BD], USA; QBend-10, Immunotech Corp. [IT], Germany). After 24 h CD34+ signals had decreased by 25.4% (BD) and 27.0% (IT) in average, when samples were stored at room temperature in comparison to the results obtained directly after cytapheresis (p < 0.05). At RT in combination with agitation, there was an increase in signal rates compared to baseline values, probably due to binding of CD34 antibodies to myeloid or non-viable cells (+ 9.2% [BD] and 11.2% [IT]). At a storage temperature of +4 degrees C, CD34+ events did not decrease significantly (-0.7% [BD] and -0.2% [IT]). Our data demonstrate that FC results may be influenced by temperature, agitation and storage time.