Comparable Outcomes Between Unrelated and Haploidentical Stem Cell Transplantation in Adult Patients With Severe Aplastic Anemia

Background. Regarding patients with severe aplastic anemia (SAA) who fail immunosuppressive therapy and lack an HLA-matched sibling donor (MSD), the best alternative donor including unrelated (URD) and haploidentical (HAPLO) donors for allogeneic stem cell transplantation (SCT) remains to be established. Methods. We analyzed the comprehensive outcomes of 153 consecutive adult SAA patients treated with SCT from alternative donors: 73 HLA-well matched (8/8) URDs (WM-URDs), 34 mismatched (6-7/8) URDs (MM-URDs), and 46 HAPLOs. Results. Neutrophil/platelet engraftments were achieved at a median of 11/15 days for WM-URDs, 13/16.5 days for MM-URDs, and 12/14 days for HAPLOs, respectively. The 3-year overall survival (OS), failure-free survival, cumulative incidence of graft-failure, and transplant-related mortality were statistically not different among the 3 groups: 90.3%, 87.5%, 2.7%, and 9.8% for WM-URDs; 85.3%, 81.7%, 0%, and 14.7% for MM-URDs, and 84.4%, 82.3%, 6.5%, and 11.2% for HAPLOs, respectively. The rates of other complications, including graft-versus-host disease, cytomegalovirus DNAemia, hemorrhagic cystitis, invasive fungal disease, secondary malignancies, and sinusoidal obstruction syndrome, were also statistically not different. Subgroup analysis of the MM-URD group showed that the 3-year OS of patients receiving SCTs from 6/8-URDs were worse than those receiving SCTs from 7/8-URDs (75.0% versus 94.4%, P=0.26). Conclusions. There was no significant difference in the SCT outcomes with WM-URDs, MM-URDs, or HAPLO donors. The clinician can make the best choice among these alternative donor sources based on the host/donor features and the urgency of the need for SCT. However, the selection of 6/8-URDs should be avoided due to inferior survival outcomes.