Successful haploidentical hematopoietic stem cell transplantation (HSCT) and durable engraftment by repeated donor lymphocyte infusions for a Chinese patient with transfusion‐dependent hemoglobin (Hb) Hammersmith and massive splenomegaly

Background Hemoglobin (Hb) Hammersmith is a rare form of unstable β‐chain hemoglobinopathy causing hemolytic anemia. This rare event led to a more serious transfusion‐dependent phenotype in a patient. It was successfully cured by haploidentical hematopoietic stem cell transplantation (HSCT). Methods and Results A 9‐year‐old mainland Chinese male with a history of neonatal unconjugated hyperbilirubinemia was diagnosed to have hemoglobin (Hb) Hammersmith. He required regular blood transfusion but was unable to be transfused to desired parameters for 8 years prior to transplant due to social and geographical reasons. He subsequently developed marrow hyperplasia and progressive splenomegaly (down to umbilicus level), suggestive of extramedullary hematopoiesis. Eventually, the family came to Hong Kong and complied to a more intensive transfusion regimen and preconditioning chemotherapy 3 months prior to transplant. He underwent haploidentical HSCT using paternal TCRαβ/CD45RA‐depleted graft but suffered from graft rejection, despite splenic irradiation for massive splenomegaly. It was successfully salvaged with second HSCT with unmanipulated graft from the same donor with additional serotherapy and donor lymphocyte infusions. Conclusion Allogenic haploidentical HSCT for hemoglobin Hammersmith is feasible but adequate immunosuppression during conditioning is crucial. Precise adoptive cell therapy can promote durable engraftment.