Post-Thaw Colony Forming Unit (CFU) Counts and Yield Are the Most Important Predictors of Engraftment and Survival Following Unrelated Donor Cord Blood Transplantation (CBT): A COBLT Study Report.

Total nucleated cell count (TNC), CD34 and CFU content of cryopreserved cord blood units (CBUs) are measurements of hematopoietic potential previously demonstrated to be predictive of engraftment and/or survival post-transplant. Pre-cryopreservation measurements do not capture downstream events in cord blood banking that could impact CBT outcome: freezing, long-term storage, shipment to the transplant center and thawing. We hypothesized post-thaw enumeration of these measures would be more predictive of outcome. These tests were routinely performed at two of the COBLT transplant centers, at the time of CBU thaw. We examined the correlation of these laboratory measures pre-cryopreservation and post-thaw with engraftment and survival of 153 patients with leukemia and metabolic disorders undergoing myeloablative transplantation. The median age of recipients was 4.4 years (range 0.1 – 17.9) and weight 19.1 kg (range 3.9 – 118.4).Pre-cryopreservation Thaw Yield Median (range) Median (range) Median (range) TNC/kg x 107/kg 6.9 (1.5 – 50.4) 5.7 (1.1 – 31.6) 80.9% (43.0 – 98.9) CD34/kg x 105/kg 2.3 (0.1 – 20.1) 2.0 (0.2 – 15.5) 72.6% (16.1 – 99.6) CFU/kg x 104/kg 20.2 (1.7 – 169.7) 3.0 (0.0 – 31.1) 17.7% (0.0 – 82.7) Trypan blue viability 99 (91 – 100) 98 (83 – 100) —Overall 114/153 engrafted by day +42 with a median day to engraftment of 29 days. In multivariate analysis, post-thaw CFU count and yield were the highest correlates with engraftment (p<0.0001 and p<0.02, respectively) and survival (p=0.05 and p=0.02, respectively). If the CFU yield was 50–100% of pre-cryopreservation CFU then the probability of engraftment by day +42 was 93%. However, engraftment by day +42 fell to 63% when the yield was <5% (16% of CBUs). Survival at 2 years was poorer if CFU yield was less than 5% compared to >5% (38% vs. 65%, p =0.05). Importantly, post-thaw yield of TNC and trypan blue viability did not correlate with engraftment. Total hematopoietic content of units (TNC, CD34, and CFU) was strongly predictive of engraftment. However, independently, low CFU counts and poor yield of CFU at time of CBU thaw is a harbinger of poor/nonengraftment and is evidence of deterioration of the product between time of processing and infusion. Low CFU count or poor yield of CFU post-thaw may be used clinically to predict engraftment in patients undergoing CBT. These findings illustrate the need for the development of product release testing criteria for CBUs and should be a priority for the cord blood community.

Duke Scholars

Author Joanne Kurtzberg Pediatrics, Transplant and Cellular Therapy