Comparable Outcomes between Unrelated Donor (8/8 or 7/8 matched) and Haploidentical Donor for Allogeneic Stem Cell Transplantation in Adult Patients with Severe Aplastic Anemia

Background

Either allogeneic hematopoietic stem cell transplantation (SCT) from HLA-matched sibling donor or immunosuppressive therapy (IST) has been recommended as one of the standard treatments for severe aplastic anemia (SAA). Regarding only 30% of chance finding HLA‐matched sibling donor, SCT from an alternative donor including unrelated (URD) or haplo-identical related donor (HAPLO) is considered to be a treatment option after failure to IST in patients who lack of a HLA-matched sibling donor. The aim of this study was to compare the outcomes of URD SCT and HAPLO SCT for SAA patients.

Method

Consecutive 152 adult patients with SAA who received first SCT between March 2002 and May 2018 were included: 73 of HLA-well-matched (8/8) URD (WM-URD), 34 of HLA-mismatched URD (MM-URD), and 45 of HAPLO. With the intention to have a follow-up period at least 1 year, data were analyzed at May 2019. A conditioning regimen with total body irradiation (TBI) and cyclophosphamide was used for URD-SCT, whereas that with TBI and fludarabine was administered for HAPLO-SCT (Lee et al, BBMT 2011;17:101, Park et al, BBMT 2017;23:1498, Lee et al, Am J Hematol 2018;93:1368). The combination of tacrolimus and methotrexate were used as graft-versus-host disease (GVHD) prophylaxis.

Results

The median follow-up was 53.4 (range, 0.2-174.1) months. The median age of URD and HAPLO cohort was 30 (range 18-59) and 34 (range 18-59) years, respectively. Except for one and three patients who failed respective a neutrophil and platelet engraftment, other patients achieved neutrophil and platelet engraftments with median 11 and 15 days for WM-URD, 13 and 16.5 days for MM-URD, and 12 and 14 days for HAPLO, respectively. The five-years overall survival (OS), failure-free survival (FFS), and cumulative incidences (CIs) of graft-failure and transplant-related mortality were similar among three groups: 88.3%, 85.5%, 2.7%, and 11.7% for WM-URD; 81.7%, 81.7%, 0%, and 18.3% for MM-URD, and 86.3%, 84.1%, 6.7%, and 9.2% for HAPLO. The 180-days CI of grade II-IV acute GVHD in WM-URD, MM-URD and HAPLO were 35.6%, 52.9%, and 28.9%, respectively; and moderate to severe chronic GVHD were 28.7%, 38.7% and 11.8% in respective cohort. The CI of grade II-IV acute GVHD and moderate to severe chronic GVHD were significantly higher in MM-URD than those in HAPLO (both, p=0.026). ATG is the only factor affecting both grade II-IV acute GVHD (Hazard ratio 0.511, p=0.01) and moderate to severe chronic GVHD (Hazard ratio 0.378, p=0.003) in multivariate analysis. Other complications including CMV DNAemia, hemorrhagic cystitis, invasive fungal disease, secondary malignancy, and sinusoidal obstruction syndrome were similar among three groups. Survival outcomes of a subgroup of ≥ 2 allele MM-URD (n=16) extracted form MM-URD were inferior that of other donor types (n=136): 75.0% vs. 86.9% (p=0.163) for 5-year OS and 75.0% vs. 84.7% (p=0.272) for 5-year FFS.

Conclusion

This study shows that there were no significant differences between alternative donor sources in the absence of suitable matched sibling donor. Host/donor features and urgency of transplant should drive physician towards the best choice among alternative donor sources for SAA patients treated with SCT. However, selection of ≥ 2 allele MM-URD should not be recommended due to high incidence of GVHD and inferior outcomes.

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