Correlation Between Actual Stem Cells Collected By Apheresis and Predicted Stem Cells Based on Pre-Apheresis Peripheral Blood CD34+ Cell Counts

Introduction. Stem cell (SC) mobilization and collection from peripheral blood (PB) is a broadly used strategy in the setting of autologous stem cell transplantation (ASCT). An adequate correlation between CD34⁺ cell count in PB and CD34⁺ cell count in apheresis product is essential for the planning of the mobilization-apheresis process. Prediction of SC yield in the basis of peripheral blood stem cell (PBSC) number and blood volume processed (BVP) was proposed by Pierelli et al (Vox Sanguinis (2006)91:126-34).

Objective. Evaluation of correlation between pre-apheresis PBSC count and CD34⁺ cell dose collected in the first apheresis procedure. Evaluation of correlation between predicted CD34⁺ yield by Pierelli's method and actual CD34⁺ yield collected in the first apheresis procedure.

Patients and Methods. Eighty-four apheresis procedures performed to 79 patients in a single institution between 2008 and 2015 were retrospectively evaluated. Data analyzed included age, gender, body weight, diagnosis, date of first apheresis, pre-apheresis PB CD34⁺ counts, CD34⁺ cell dose collected in the first apheresis product and total BVP. Only patients in whom pre-apheresis PBSC count was available were included in this analysis. Median age was 52 years (16-66), 30 (38%) were females. Median body weight was 71 kg (47 - 120). Diagnosis was non-Hodgkin lymphoma (48%), multiple myeloma (24%), Hodgkin lymphoma (22%), acute myeloblastic leukemia (4%), amyloidosis (1%) and solid tumor (1%). Using the method described by Pierelli et al, predicted CD34⁺ yields were calculated (predicted CD34⁺ cells/kg= PB CD34⁺ cells/mL x 0.4 x BVP per kg (mL/kg). Correlation between variables was analyzed by Pearson's coefficient (r). An r value close to 1 indicates significant correlation between variables. An r value close to 0 indicates no statistical correlation. Predicted yields were classified in low (lower than 2 x 10⁶ CD34⁺ cells / kg) (n=34), intermediate (2 to 5) (n=28) or high (higher than 5) (n=22), according with the conventional limits for SC dose in the setting of ASCT. Positive predictive value (PPV) of predicted yields was calculated as the proportion of actual yields falling into each category of predicted yields.

Results. Median pre-apheresis PBSC count was 25 CD34⁺ cells / uL (5-310). Median BVP was 240 mL/kg (143-360). Median predicted CD34⁺ yield was 2.1x10⁶ CD34⁺ cells/kg (0.5-29.41) and median actual CD34⁺ yield was 2.84 x10⁶ CD34+ cells/kg (0.26-38.21). Pearson's correlation coefficient (r) between pre-apheresis PBSC and collected CD34⁺ cells was 0.842 (p=0.000). Pearson's correlation coefficient (r) between predicted and actual CD34⁺ was 0.836 (p=0.000). Median ratio actual CD34⁺ cells / predicted CD34⁺ cells was 1.10 (0.31-4.55). PPV of predicted yields higher than 5 x 10⁶ CD34⁺ cells /kg was high (95%). Only 18% of cases with a predicted yield between 2 and 5 x 10⁶ CD34⁺/kg had an actual CD34⁺ yield lower than 2 x 10⁶ CD34⁺/kg.

Conclusion. The results show a significant correlation between PBSC count and collected SC during the first apheresis procedure. A significant correlation between predicted and actual CD34⁺ yields reproduce what has been shown by others regarding the predictive power of this formula. The PPV of this method is higher for predicted CD34⁺ yields higher than 5 x 10⁶ CD34⁺ cells/kg.