Impact of ABO Incompatibility on Engraftment , Transfusion Requirement and Survival after Unrelated Cord Blood Transplantation：a Single Institute Experience in China
Authors: Yan Jiawei , Sun Guangyu , Yao Wen , Zhang Lei , Wan Xiang , Tang Baolin , Zhu Xiaoyu , Ding Kaiyang , Zheng Changcheng , Liu Huilan , Sun Zimin 
Published: November 2019

Abstract
Few reports have focused on the impact of ABO incompatibility on the clinical outcomes, after unrelated cord blood transplantation (UCBT). Therefore, we retrospectively analyzed the impact of ABO mismatching on the clinical outcomes of 177 patients with hematologic malignancies, which underwent single UCBT in Anhui Provincial Hospital from May 2008 to April 2014. The study patients included 86 ABO-identical, 52 minor, 32 major, and 11 bidirectional ABO-incompatible recipients. All of them received a homogeneous intensified myeloablative pre-transplantation conditioning regimen of total body irradiation (TBI)cyclophosphamide (CY) [TBI (total,12 Gy; four fractions) and CY (60 mg/kg daily for 2 days)] (age≥14 years) or BuCY2 [busulfan (0.8 mg/kg every 6 h for 4 days) and CY]. Medians of 3.85×107/kg (range, 1.03-10.43) total nucleated cell (TNC) and 2.0×105/kg (range, 0.45-6.88) CD34+cells were transfused.
Of the 177 patients who underwent UCBT, 169 achieved successful neutrophil engraftment. In patients receiving ABO-identical, minor, major, and bidirectional ABO-incompatible UCBT, the cumulative incidences of neutrophil engraftment were 92.7%, 100%, 96.9% and 90.9%, respectively (P=0.509). The median days to achieve neutrophil engraftment were 17, 18, 17, and 20, respectively (P=0.409). The cumulative incidences of platelet engraftment were 81.7%, 86.5% , 87.5% and 63.6%, respectively(P=0.436) .And the median days to achieve platelet engraftment for the 4 groups were 36, 40, 36, and 38, respectively; (P=0.545). All of the data did not show any significant difference among the 4 groups. Neutrophil engraftment(cumulative incidence, 95.5% versus 95.3% , P=0.861; median day, 17 versus 18, P=0.717) also did not differ significantly between the ABO-identical/minor ABO-incompatible and major/bidirectional ABO-incompatible recipients (HR1.08, P=0.680). And platelet engraftment (83.6% versus 81.4%, P=0.964; median day, 38 versus 37, P=0.699) reached the similar result (HR1.104, P=0.621).
We investigated the results from a 169-patient population with neutrophil engraftment, the average units of platelets (Plts) and red blood cells (RBCs) transfused during the hospitalization after the UCBT were 0.204 units/kg(range, 0.03-1.45)and 0.159 units/kg (range, 0-1.56).In patients with ABO-identical, minor, major, and bidirectional ABO-incompatible UCBT, the average units of Plts transfused after UCBT were 0.221, 0.202, 0.169, and 0.195 units/kg(P=0.53), respectively, and the average units of RBCs transfused were 0.151, 0.156, 0.163, and 0.221 units/kg (P=0.847), respectively. No signiﬁcant differences in the transfusion requirements among the 4 groups were noted, so did the comparison between the ABO-identical/minor ABO-incompatible and major/bidirectional ABO-incompatible recipients.
With a median follow-up of 12 months (range, 3-74 months), the disease-free survival (DFS) rates among the ABO-identical, minor, major, and bidirectional ABO-incompatible groups were 67.1%, 57.7%, 62.5 % and 54.5%, respectively (P=0.804), and the overall survival (OS) also did not differ significantly among the four groups (68.3%, 61.5%, 65.6%, and 63.6%, respectively; P=0.929). When it came to the comparison between the ABO identical/minor incompatible group and the ABO major/bidirectional incompatible group, the DFS (63.4% versus 60.5%; P=0.995) and OS estimates (65.7% versus 65.1%; P=0.820) were not significantly different, either. What’s more, none of the patients clinical developed severe immune hemolysis or pure red-cell aplasia after transplantation.
In summary, the results above indicated that :1) ABO incompatibility did not seem to have a significant impact on clinical outcomes after UCBT, such as engraftment, transfusion requirements and survival. 2) No patients developed pure red-cell aplasia after UCBT. 3) In addition, we also compared the outcomes between the ABO-identical and bidirectional ABO-incompatible groups, even it did not show any significant difference, the former did better on platelet engraftment (81.7% versus 63.6%) and DFS (67.1 versus 54.5%). The reason led to this result may be the lack of bidirectional ABO-incompatible recipients. Therefore, we’d better avoid selecting bidirectional ABO-incompatible in UCBT to improve the patients’ recovery and survival time.

Disclosures
No relevant conflicts of interest to declare.