Enrichment of CD34+ Hematopoietic Progenitor STEM CELLS and Depletion of CD3 CELLS Utilizing the Clinimacs®: Comparison of Immediate Versus Next Day Processing

There is an increase in utilizing matched unrelated donors (MUD) & haploidentical donors over the past 20 years (Cairo et al, Biol Blood and Marrow Transplant, 2008). However both of these allogeneic donor sources are associated with severe acute graft -versus -host diseases. We have previously reported the success of CD34 enrichment utilizing the Isolex® device (Geyer/Cairo et al, British Journal of Hematology, 2012). Positive selection of CD34+ cells with the CliniMACS® system has been shown as a highly effective technique for obtaining a T-lymphocyte-depleted product. We report our results with 55 procedures performed in the last two years at our Cell and Tissue Engineering Laboratory. To evaluate the impact of overnight storage on cell recovery, viability and sterility before processing, as well as to evaluate the CD34 +cells recovery in the final product. From October 2017 to August 2019, after consent, 37 donors were mobilized with G-CSF. Fifty-five leukapheresis harvests were performed using the Spectra Optia® Apheresis System. Twenty-six were stored overnight at 4°C before processing using the CliniMACS® device. WBC counts were performed using the Sysmex XE hematology analyzer. Phenotypic analysis was performed with a FACSCalibur BD flow cytometer on samples from leukapheresis products at the day of collection (Day 0), before processing (Day 1) and after the selection. The WMC Microbiology Laboratory performed the sterility testing using BACTEC FX System. Twenty-six products were stored overnight before processing with a mean ±sem nucleated cells (NC) of 19 × 108/kg (± 2.66) and CD34+ cells of 13.8 x106/kg (± 2.93) at Day 0 and NC of 16.2 × 108/kg (± 2.62) and CD34+ cells of 13.9 x106/kg (± 3.03) at Day 1. NC and CD34+ cells content were not significantly different at Day 0 and Day 1 (respectively p=0.95 and p=0.98). The median CD34 viability at Day 1 was 99% (range 93-99%). The sterility testing were all negative. Fifty-five products showed a median starting cellularity of 8.45 × 106 CD34+ cells (range 1.4-60.3 × 106). The median post selection CD34+ cells was 6.62 × 106 (range 1.2-46.2 × 106). The mean ±sem CD34 recovery was 9.64 × 106/kg (± 1.2) (Figure 1A) with a purity of 98.5%. The final T cell reduction was a mean ±sem of 0.38 × 105/kg (± 0.08) (Figure 1B). A mean ±sem of 9.75 × 106/kg (± 0.84) of CD34+ cells was infused. To enhance engraftment, 2 × 105/kg CD3+cells were added back to the selected product. All patients engrafted at a median time of 11 days. No patient developed an infusion reaction. Overnight storage of peripheral blood stem cells does not affect CD34+ cells enrichment, viability nor safety of the leukapheresis product. Our median of 80% of CD34 recovery is higher than the recovery of previous studies (Cairo et al, JAMA Pediatrics, 2019). These data demonstrate that CD34 enrichment on the following day using CliniMACS® device is reproducible and safe in pediatric and adult allogeneic recipients.