Umbilical Cord Blood Stem Cells As Third-Party Adjuvant Infusion in Human Leukocyte Antigen Antibody-Positive Patients Undergoing Allogeneic Hematopoietic Stem Cell Transplantation

Introduction: The presence of human leukocyte antigen (HLA) antibodies, even if not donor-specific antibodies (DSA), is an important risk factor for graft failure (GF) or poor graft function (PGF) in patients undergoing allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, there is no ideal strategy for eradicating or descending HLA antibodies in this population. In the present study, we investigated the efficacy and safety of unrelated umbilical cord blood stem cells (CBCs) as a third-party adjuvant infusion in patients with HLA antibodies undergoing allo-HSCT.

Methods:Patients undergoing allo-HSCT from July 2017 to June 2021 were enrolled in this study and HLA antibodies were routinely tested before transplantation. Patients were divided into three groups: Group A (patients with positive/weak positive HLA antibodies and with CBCs infusion), Group B (patients with HLA antibodies positive/weak positive without CBCs infusion), and Group C (patients without HLA antibody nor CBCs infusion). Single unrelated CBCs (HLA4/6 or more compatible ) were infused four hours before donor stem cells. The clinical characteristics of the patients and the paired donors were collected. The occurrence of granulocyte and platelet engraftment time, graft-versus-host disease (GVHD), cytomegalovirus (CMV), Epstein-Barr virus (EBV) reactivation, one-year and two-year relapse-free survival (RFS), transplantation-related mortality (TRM), and overall survival (OS) for all three groups of patients were also analyzed in this study.

Results:A total of 90 patients were included in this study (17 in group A, 36 in group B, and 37 in group C). The baseline clinical characteristics of the patients were presented in Table 1. No obvious adverse effects were observed in the process of CBCs infusion. All the patients achieved 100% donor chimerism without CBCs engraftment. There were no significant differences in granulocyte and platelet engraftment time between the three groups. Two patients in Group A and C, and 3 patients in Group B developed PGF, respectively. There were no significant differences in the incidence and grades of acute or chronic GVHD among the three groups ( Figure A, B). In the first 3 months after allo-HSCT, the incidence of EBV reactivation was higher in patients in Group B than that in Group A and C, respectively ( Figure C). There were no significant differences in the CMV reactivation between the three groups in the first 3 months after transplantation ( Figure D). Patients in Group A and B both had lower 1-year RFS and higher 1-year TRM, compared with Group C, respectively ( Figure E, F). However, there were no significant statistical differences in 2-year RFS and TRM between the three groups. Although patients in Group A had longer 2-year OS than that in Group B, there were no significant differences between the two groups: Group A vs Group B (76.5% vs 55.6%, P = 0.194), Group B vs Group C (55.6% vs 85.5%, P < 0.05)( Figure G). A multifactorial Cox regression risk model was established to explore the risk factors affecting OS and suggested that patients' pre-transplantation status (with active malignant disease or minimal residual disease positive) and HLA antibodies pre-transplant were the most independent risk factors for OS (HR = 4.380, 95% CI = 1.544-12.427, P<0.05; HR = 0.196, 95% CI = 0.065-0.587, P<0.05).

Conclusions: Patients with positive/weak positive HLA antibodies receiving CBCs as a third-party adjunctive infusion were safe, and there was a benefit in the incidence of EBV reactivation compared to such a population without CBCs infusion. The patients with negative HLA antibodies had higher 1-year RFS and lower 1-year TRM than those with positive/weakly positive HLA antibodies regardless CBCs infusion. Due to the small number of included cases, we will expand the sample number to further validate our results in the future.