HLA-mismatched haploidentical transplantation using low-dose anti-thymocyte globulin (ATG: thymoglobulin)

Objectives: To clarify optimal strategies for human leukocyte antigen (HLA)-mismatched haploidentical hematopoietic stem cell transplantation (HSCT). Methods: Twelve patients who underwent HSCT from a haploidentical related donor using low-dose thymoglobulin were analyzed retrospectively. Thymoglobulin was added to conditioning regimens at 2.5 mg/kg/day for 2 days (days −4 and −3). Prophylaxis against graft-versus-host disease (GVHD) was performed with cyclosporine and methotrexate. Results: The median age of the patients was 33 years. Six patients had previous allogeneic HSCT, and HSCT was performed in non-remission for nine patients. All patients but one, who died due to early infection, achieved neutrophil engraftment at a median of 17 days with complete donor-type chimerism. Acute and chronic GVHD were observed in six and five patients, respectively, but no patients died of GVHD-associated complication. No one developed cytomegalovirus disease, but Epstein–Barr virus-related lymphoproliferative disorder was observed in one patient. Long-term survival in remission without immunosuppressive agents are observed in two patients who underwent HSCT in remission, but the majority of patients who underwent HSCT in non-remission experienced disease progression. Conclusion: Haploidentical HSCT could be performed with thymoglobulin at 5 mg/kg, with the balance between GVHD and relapse rate. The dose reduction of thymoglobulin may be considered for advanced hematological malignancy.