It had not been well investigated how unrelated bone marrow transplantation affected pediatric patients with hematological malignancies when there is human leukocyte antigen (HLA) mismatching at the HLA-A, -B, -C, and -DRB1 loci. 

For a study, researchers examined 1,330 hematological malignancy patients who received their first unrelated bone marrow transplant in Japan between 1993 and 2017 and were all ≤15 and had undergone a previous transplant. 

The findings demonstrated that whereas an HLA mismatch was strongly related to a low relapse rate, it was also related to higher non-relapse mortality. In addition, HLA mismatch and poor overall survival had a statistically significant correlation. An HLA-C mismatch, as in adults, had a substantially detrimental effect on survival, according to locus mismatch analysis. However, in pediatric patients, an HLA-DRB1 mismatch exhibited no detrimental effect, despite the fact that these HLA mismatch effects have been lessened in recent cases. 

Together, the data indicated that an HLA-matched donor for pediatric patients should be the primary choice; however, kids without a matching sibling or matched unrelated donor can choose an unrelated donor with an HLA-DRB1 mismatch if they are available.