Significance of a Single Human Leukocyte Antigen Mismatch on the Outcome of Nonmyeloablative Allogeneic Stem Cell Transplantation from Related Donors Using the Mexican Schedule.

The Mexican approach was used to conduct nonmyeloablative stem cell transplantation (SCT) in patients with various malignant and non-malignant hematologic diseases. Patients received a modified, low-intensity conditioning regimen, which included oral busulphan 4 mg/kg on Days −6 and −5, IV cyclophosphamide 350 mg/m² on Days −4, −3, and −2, IV fludarabine 30 mg/m² on Days −4, −3, and −2, oral cyclosporine A 5 mg/kg twice daily staring on Day −1 (continuing until Day 180), and IV methotrexate 5 mg/m² on Days +1, +3, +5, and +11. Allografts were prospectively performed in 58 patients using sibling donors that were either human leukocyte antigen (HLA) identical (6/6) or compatible with 1 mismatch (5/6). In allografts where the donor was an HLA identical sibling (n = 40), the median overall survival was 33 months compared to 8 months when the donor was an HLA compatible sibling (n = 18; P <.01). The 52-month survival was 47% versus 38% in patients receiving allografts from HLA-identical donors and HLA-compatible donors, respectively. The prevalence of acute graft-versus-host-disease (GVHD) was 57% versus 38%, the prevalence of chronic GVHD was 25% versus 11%, and the relapse rate was 45% versus 55% in patients receiving allografts from HLA-identical donors and HLA-compatible donors, respectively. Two patients failed to engraft; both were 5/6 matches. Despite a trend toward less favorable results in patients allografted from HLA compatible (5/6) siblings, most differences in outcome were not significant, likely due to the small number of patients in the study. These data suggest that nonmyeloablative SCT using the Mexican approach may be a valid option for individuals with either an HLA identical or HLA compatible sibling donor.