A study on the correlation of clinical factors with actual CD 34+ stem cell yield using COM.TEC cell separator

Marjorie Rose Bravo, Honorata Baylon. MD

Objectives: Peripheral blood stem cell collection is emerging as the preferred method of harvesting stem cells for hematopoietic stem cell transplantation. There are conflicting data with regards to the clinical parameters that can be used to determine the optimal timing of harvest and the optimal cut off for peripheral blood CD34 + cell count to ensure an adequate leukopheresis CD34+ cell count of >2 x 106 cells/kf body weight. The aims of this study are to establish correlation of peripheral blood CD34+ cell counts, white blood cell count, hematocrit, and machine estimated / predicted CD34+ cell count with the actual leukopheresis CD34+ cell count yield and to establish our institution’s cut off level for peripheral CD34+ cell count that would five an adequate yield.

Methodology: A retrospective review was done of all peripheral blood stem cell transplants done by the Blood and Marrow Transplant service from January 2013 to April 2015. A total of 13 patients were included in this study and majority were allogeneic transplants and all donors were adults. Mobilization was with G-CSF or G-CSF plus chemotherapy. On the day prior to the intended harvest all donors had CBC and peripheral blood CD34+ stem cell count (in cells/mL) determination. Leukopheresis was done the next day if peripheral blood CD34+ cell count was ³ 20 cells/mL and a second collection was done if there was inadequate number of actual CD34+ cell  in the leukopheresis product. The same COM.TEC Cell Separator (Fresenius HemoCare, Bad Homburg, Germany) was the only machine used for all procedures utilizing the Auto MNC program, which also gave predicted CD34+ cell count. Linear regression models and Pearson’s correlation coefficient were used to determine correlation. Receiver operative characteristics (ROC) curve was used to determine an optimal PB CD34+ count.

Results: A total of 18 leukopheresis procedures were done from January 2013 to April 2015. Five donors (38%) had a second harvest due to inadequacy of CD 34+ cell yield; 80% of which were patients for autologous transplant. Healthy donors for allogeneic transplants had higher SBC counts (median 43,225 vs 42,000), hematocrit (median 44% vs  42%), pre-leukopheresis CD34+ cell count (median 44 cells/mL vs 38 cells/mL) and actual CD34+ cell yield (1.98 vs 6.19 x 106 cells/kg) compared to the autologous patients. No correlation was found between pre-leukopheresis WBC count and actual CD34+ cell yield (r=0.004, p=0.98). A weak correlation was seen with pre-leukopheresis hematocrit level (r=0.3, p value = 0.2) but it was not statistically significant. A significant moderate degree of correlation was seen between peripheral blood CD34+ count with actual CD34+ cell count (r=0.76, p value 0.004) and machine predicted CD34+ cell count (r=0.73, p value 0.0005).

Conclusion: The evaluation of our transplant data showed that in the past 3 years, all the transplants done in our center were through peripheral blood stem cell harvest. Autologous patients were more prone to having poor mobilization compared to healthy donors which maybe due to being heavily treated prior to the stem cell collection. In the future, we would need to consider the possibility of collecting stem cells earlier in the treatment process to avoid the problem of poor mobilization and the need for more leukopheresis procedures in patients for autologous transplantation. The most ideal test to predict the actual stem cell yield and the optimal timing for leukopheresis is the peripheral blood CD34+ cell count done the day prior to the procedure as this has a moderate correlation with actual yield. WBC and hematocrit are not good predictors. The center data show that we should use a higher peripheral blood CD34+ level cut off of 40 cells/mL. using this new threshold level may in effect lessen the need for more leukopheresis procedures. This study may be further improved by increasing the included population and including an analysis of patients separated into disease categories and determining the effect of CD34+ cell levels with transplant outcomes.