该文报道了2例应用脐带间充质干细胞（umbilical cord mesenchymal stem cells UC-MSCs）治疗儿童异基因造血干细胞移植（hematopoietic stem cell transplantation, HSCT）后重型免疫介导性血小板减少症（immune-mediated thrombocytopenia, ITP）的患儿。例1为极重型再生障碍性贫血患儿，行单倍体骨髓+外周血HSCT，+25 d嵌合率达99.8%，+60 d出现重型ITP，给予静脉注射免疫球蛋白冲击治疗后血小板短暂上升后下降，给予环孢素、甲泼尼龙、利妥昔单抗治疗效果差。例2为戈谢病患儿，行非血缘脐血HSCT，+41 d查嵌合率为96.35%，+120 d出现重型ITP，先后给予3次静脉注射免疫球蛋白冲击治疗后血小板上升后又下降，给予地塞米松、泼尼松、环孢素及重组人血小板生成素治疗效果差。2例患儿均输注3次UC-MSCs，血小板上升并维持在正常水平。例1已随访10年，无病生存。UC-MSCs治疗对HSCT后一、二线治疗无效的重型ITP有一定疗效，可提高HSCT后重型ITP患儿的生活质量及无病生存率。

This report describes two cases of severe immune-mediated thrombocytopenia after allogeneic hematopoietic stem cell transplantation (HSCT) who were treated with umbilical cord mesenchymal stem cells (UC-MSCs). Case 1 was a child with severe aplastic anemia who underwent haploidentical bone marrow and peripheral blood HSCT, with a chimerism rate of 99.8% on day +25 and severe immune-mediated thrombocytopenia on day +60. After intravenous immunoglobulin (IVIG) pulse therapy, platelet count increased temporarily but then decreased, while cyclosporine, methylprednisolone, and rituximab had a poor therapeutic effect. Case 2 was a child with Gaucher's disease who underwent unrelated umbilical cord blood HSCT, with a chimerism rate of 96.35% on day +41 and severe immune-mediated thrombocytopenia on day +120. After three sessions of IVIG pulse therapy, the platelet count increased initially but subsequently decreased. Therapies with dexamethasone, prednisone, cyclosporine, and recombinant human thrombopoietin also yielded a poor response. Both children received three sessions of UC-MSCs infusion, and platelet counts increased and were subsequently maintained within the normal range. Case 1 has been followed up for 10 years and remains in disease-free survival. UC-MSCs infusion may be effective for severe immune-mediated thrombocytopenia that is unresponsive to first- and second-line therapies after HSCT and could potentially improve the quality of life and disease-free survival rate.