Changes in protective antibody titers over time after ASCT. Protective serum antibody titers for (A) measles, (B) mumps, (C) tetanus, and (D) diphtheria declined significantly within 1 to 2 years after transplantation in all 6 patients with a follow-up of at least 6 months after transplantation. A paired t test was used to compare pretransplantation and posttransplantation data.