High-dose methotrexate (HD-MTX) is a key drug in the treatment of various cancers. Massive fluid infusion is necessary during HD-MTX therapy to ensure proper methotrexate excretion. There are no reports on the safety of HD-MTX therapy in patients with congenital solitary kidney (CSK). A 5-year-old male child with CSK and B-cell precursor acute lymphoblastic leukemia was treated with four cycles of HD-MTX therapy. HD-MTX therapy was safely administered without delayed MTX excretion or renal dysfunction. This case showed that HD-MTX therapy was well tolerated by a pediatric patient with CSK.

Poor graft function (PGF) is a major obstacle to successful allogeneic stem cell transplantation after achieving normal bone marrow function. We report a successful treatment of domino DLI for poor graft function in younger brother with hyper IgM syndrome from HLA-identical elder brother with the same disorder with a history of HLA-mismatched unrelated bone marrow transplantation using same donor. Immunological profiling revealed that DLI-induced T-regulatory cells could correct skewed immune responses in the BM microenvironment due to secondary PGF pathogenesis. Immunological tolerized domino DLI can be a new therapeutic option for secondary PGF in HLA-identical sibling pairs with congenital immunodeficiency.