Washing after thawing of frozen UCB used for hematopoietic stem cell transplantation (HSCT) is widely practiced for the purpose of removal of the cryoprotectant DMSO and free hemoglobin from lysed red cells. An updated retrospective audited analysis was performed on the outcomes of 208 PD UCB used in 186 patients with known thaw conditions that have engraftment and/or survival data −106 washed (W) and 80 non-washed (NW). When the DMSO dose was kept under the recommended 1 g per kg of recipient weight, the only severe adverse reaction was a seizure and encephalopathy following infusion of a NW PD UCB that resolved without any sequelae. Total nucleated cell recovery after thawing as reported by transplant centers was higher for NW (median 89% vs. 75%). The Kaplan-Meier estimate of 3-month neutrophil (ANC500) engraftment were 91±4% for NW versus 88±4% for W with median time to neutrophil of 21 versus 24 days (p = 0.02). The K-M estimate for 6-month platelet 20K engraftment were 86±6% for NW and 78±5% for W with median time to engraftment at 46 days for NW and 55 days for W (p = 0.002). Acute grade III–IV GvHD were similar at 12% (NW) and 13% (W), but extensive chronic GvHD were 4% (NW) and 19% (W). 1-year TRM were 25±5% for NW and 34±5% for W (p=0.75), with relapse rate at 16±5% for NW and 28±5% for W (p=0.09). K-M estimates of 1-year OS were 63±6% versus 53±5% (p = 0.54), and for 1-year DFS were 62±6% versus 48±5% (p = 0.23) for NW and W respectively. To our knowledge, this was the largest transplant outcome study comparing no post-thaw wash versus wash for UCB, though the conclusions are confined to PD CBU. No clear benefits of post-thaw washing were seen for PD UCB. HSCT with NW PD UCB was at least as efficacious as that using W PD UCB with respect to GvHD, TRM, relapse rate, 1-year OS and DFS. Moreover, washing may have a negative impact on neutrophil and platelet engraftment of PD UCB.

Disclosures: Lawrence Petz, Brian Wang, Tina Wu, and Robert Chow are employees of StemCyte.; Lawrence Petz, Brian Wang, Tina Wu, and Robert Chow have stock options of StemCyte.; Robert Chow is a Board Director of StemCyte.

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