Allogeneic Bone Marrow Transplantation From HLA Mismatched Family Donors in Children with Aplastic Anemia
Authors: Muramatsu Hideki , Yabe Hiromasa , Kobayashi Ryoji , Kikuchi Akira , Kudo Kazuko , Kawa Keisei , Kato Koji , Suzuki Ritsuro , Takahashi Yoshiyuki , Inagaki Jiro , Inoue Masami , Kojima Seiji 
Published: October 2019

Abstract
Abstract 831
The first-line therapy for children with severe aplastic anemia (AA) is allogeneic hematopoietic stem cell transplantation (HSCT) from an human leukocyte antigen (HLA)-matched family donor, and immunosuppressive therapy (IST) is indicated for patients without HLA-matched family donors. While the standard therapy for children who fail to respond to IST is allogeneic HSCT from an HLA-matched unrelated donor, HSCT from an HLA-mismatched family donor has also been indicated. Compared with unrelated donors, an HLA-mismatched family donor has some advantages especially for children who need urgent transplantation.
We analyzed the clinical outcome of 578 children (325 boys and 253 girls) with AA (age, <20 years) who received allogeneic BMT between 1990 and 2009 in Japan, and registered to the Transplant Registry Unified Management Program (TRUMP). The median age at transplantation was 11 years (0–19), and the donors were serological 6/6 HLA-matched related donors (MRD) (n = 312), 1 locus-mismatched related donor (1MMRD) (n = 44), 2–3 loci-mismatched related (haploidentical) donors (n = 9), and HLA-matched unrelated donors (MUD) (n = 213). Causes of deaths were as follows: acute graft-versus-host disease (GVHD) (n = 4), chronic GVHD (n = 4), acute respiratory distress syndrome (n = 2), severe hemorrhage (n = 7), engraftment failure (n = 5), infection (n = 18), idiopathic pneumonia (n = 8), organ failure (n = 19), secondary malignancy (n = 4), and others (n = 4).
The probability of severe acute GVHD (grade III–IV) in patients transplanted from 1MMRD (26.9% ± 7.4%) was significantly higher than that in patients transplanted from MRD (4.9% ± 1.3%) (p < 0.001). The probability of 5-year overall survival (5y OS) of patients transplanted from 1MMRD (93.1% ± 3.9%) was comparable to that of patients transplanted from MRD (93.1% ± 1.5%) (p = not significant, NS), but it was significantly better than that of patients transplanted from haploidentical donors (66.7% ± 15.7%, p =.016) and MUD (79.0% ± 2.9%, p =.014). In the subgroup analysis of 1MMRD, no significant difference was observed between HLA class I-mismatched (n = 32) and class II-mismatched patients (n = 12) (5y OS; 93.8% ± 4.3% vs. 91.7% ± 8.0%, p = NS). Comparison of the survival outcome based on the transplant period (1990–1999 vs. 2000–2009) revealed that the probability of 5y OS of patients transplanted from 1MMRD was not significantly different (92.3% ± 5.2% (n = 26) vs. 94.4% ± 5.4% (n = 18), p = NS), while that of patients transplanted from MUD significantly improved in the same period as we reported previously (67.1% ± 5.5% (n = 73) vs. 86.1% ± 3.1% (n = 140), p =.001)(Yagasaki et al., Blood 2011). In multivariate analysis, haploidentical donors (p <.001), MUD (p <.001), age ≥ 10 years (p <.001), and transplant period (1990–1999 vs. 2000–2009, p =.006) were identified as independent covariates associated with unfavorable OS.
In summary, our analysis revealed that an HLA-mismatched related donor, especially 1MMRD, could be selected as a donor candidate for children with AA who need urgent transplantation.

Disclosures:
No relevant conflicts of interest to declare.