Haploidentical peripheral blood stem cell transplantation without irradiation or busulfan after reduced-intensity conditioning for KMT2A(MLL)-rearranged infant B-cell precursor acute lymphoblastic leukemia: Report of two cases.

We present two infants with KMT2A(MLL)-gene-R-associated BCP-ALL, who received HLA haploidentical PBSCT after RIC. The patients developed ALL at age 6 months and 3 months, respectively. Case 1 underwent PBSCT at the second CR with detectable KMT2A-AFF1(MLL-AF4) fusion gene transcript at 11 months of age, and Case 2 at the first CR without KMT2A-MLLT1(MLL-ENL) fusion gene transcript at 8 months of age. Both patients received G-CSF-mobilized unmanipulated peripheral blood mononuclear cells from their HLA haploidentical mothers after administration of FLU, MEL, and ATG. Tacrolimus, methotrexate, and mPSL were administered as prophylaxis against GVHD. Engraftment was rapidly obtained with complete chimerism in both patients. Acute adverse events included acute GVHD in Case 1 and bacterial sepsis in Case 2. At last clinical check at age 5 years and 4 years, respectively, both patients were recurrence-free and attained normal growth and development. We conclude that PBSCT from an HLA haploidentical mother with non-TBI and non-BU regimen seems feasible and efficacious, offering favorable life quality for infants.