Dosing of Post-Thaw Colony Forming Units (CFU) and CD34 Cells Predict Engraftment and Survival in Recipients of Banked Unrelated Donor Umbilical Cord Blood (UCB) for Allogeneic Transplantation.
Authors: Kurtzberg Joanne , Mendizabal Adam , Carter Shelly , Allison June , Avrutsky Sophie , Stephens Connie , Waters-Pick Barbara 
Published: October 2019

Abstract
A single umbilical cord blood unit (CBU) often doses patients at the threshhold for successful hematopoietic cell transplantation. While both cryopreserved and infused total nucleated cell (TNC) content is somewhat predictive of outcomes, there has been no reliable "potency" assay developed for UCB. Frequently, pre-cryopreserved and post-thaw recoveries are inconsistent and unpredictable. The lack of standardization from cord blood bank to bank and transplant center laboratory to laboratory further complicates interpretation of the data that is currently available. Our program is in the unique position to operate both a public cord blood bank, "The Carolinas Cord Blood Bank" (CCBB) and adult and pediatric blood and marrow transplant programs performing >100 unrelated donor cord blood transplants (UCBT) per year, placing us in the unique position of evaluating cord blood pre-cryopreservation and post-thaw TNC, viability, CD34 and colony forming assays (CFU-GM, CFU-GEMM, BFU-E) in the same laboratory, eliminating the potential for differences in laboratory practices. We have evaluated the results of 218 transplants performed from CBUs obtained from the CCBB and transplanted at our center. These units did not require transfer from the bank to the transplant center (TC) eliminating the possibility that warming of CBUs during shipping could compromise cell potency. In this dataset, the cummulative incidence (CINC) of neutrophil engraftment (ANC 500/uL by day +42) was 79.4% (95% CI 74–84.8) and platelet engraftment (PLT 50K by day 180) was 61.3% (95% CI 54.8–67.8). The CINC of event-free survival (EFS) at day 180 and 1 year was 68.7% (95% CI 62.5–75) and 62.5% (95% CI 56–69.1), respectively. The CI of acute grades II–IV graft-versus-host disease at days 100 and 150 was 10.6% (95% CI 6.5–14.7%). The CI of relapse at 1 year was 8.1% (95% CI 4.4–11.8%). Thus, most deaths occurred from graft failure, infection or regimen related toxicity all of which could be influenced by graft potency. We also expanded our dataset to include an additional 405 transplants where the CBU was shipped from other cord blood banks and transplanted at Duke. In this group, the CINC of neutrophil engraftment was 78.2% (95% CI 75–81.2) and the CI of EFS at day 180 and 1 year was 60–2 (95% CI 56.3–64) and 51% (95% CI 47–55), respectively. We hypothesized that post-thaw CFU and or CD34 would be better predictors of engraftment and survival than TNC. We examined the impact of post-thaw total CFU and CD34 recoveries and dosing on neutrophil engraftment and overall survival in these patients. Dosing of post-thaw CFU/kg infused (median 3.5x10e4/kg) correlated with neutrophil engraftment (p=<0.01). Dosing of post-thaw CD34/kg (median 1.8x10e5/kg) correlated with both neutrophil engraftment (p=<0.01) and event-free survival (p=<0.01). These data suggest that it would be possible to create a potency assay that could be tested prior to final CBU selection allowing for transplantation of the highest quality unit to the patient. This would require correlation of post-thaw recovery from the CBU with either a segment or cryovial from the same unit. These studies will allow for comparison of results from shipped versus local CBU transplants to ask whether shipping of CBUs affects potency at transplant. These studies should be planned for the National Cord Blood Inventory program.