Treatment of Mixed Chimerism After Hematopoietic Stem Cell Transplantation in Patients with Thalassemia Major

Background: Incomplete donor cell chimerism often occurs in thalassemia transplant due to host cells remain or reappear overtime, which is termed as mixed chimerism (MC). Objective: To compare the immunosuppression withdrawal (ISW) and donor lymphocyte infusion (DLI) in the correction of mixed chimerism (MC) after thalassemia transplantation. Methods: Eighty-seven patients with post-transplant MC admitted in our center from January 2010 to December 2019 were analyzed. Among them donor cells of 90%-95% and 75%-89% were classified as MC1 and MC2 respectively. MC3 donor cells <75%. The incidence and correction rate of MC, the occurrence rate of graft versus host disease (GVHD), timing of DLI were studied. Results: DLI was associated with higher correction rates and higher GVHD than ISW. In MC1 group, higher GVHD occurred in early and intermediate stage (<I>P</I> = 0.024/0.023) than ISW. In MC2 group, DLI in late stages had higher correction rates than ISW (<I>P</I> = 0.001). Conclusion: ISW was the primary strategy for MC1 patients. DLI should be given to the late-stage MC2 patients quickly. The earlier the treatment is provided, regardless of ISW or DLI, the more likely that patients develop GVHD.