Long-term lymphocyte subset number reconstitution is unique but comparable between umbilical cord blood and unrelated bone marrow transplantation.

The number of umbilical cord blood transplantation (U-CBT) procedures has been growing annually, but little research has been done on long-term immune recovery after U-CBT. Infection risk is high in U-CBT recipients, and this can be partially attributed to immature immunocompetent cells in umbilical cord blood. In this study, we analyzed lymphocyte subset (LST) number to determine the long-term recovery timeline. We included 36 U-CBT and 10 unrelated bone marrow transplantation (U-BMT) recipients who survived more than 2 years after transplantation, and followed them for up to 10 years post-transplant. Recovery kinetics in the early phase post-transplant was different for each LST. Recovery of CD19 B cells was faster after U-CBT than after U-BMT in the first 5 years after transplantation. Although CD4 T cells increased in the first several months after U-CBT, long-term cell count recovery was impaired in approximately 20% of patients. Thus, although the LST recovery pattern after U-CBT was unique, LST number recovery was statistically comparable between U-CBT and U-BMT past 5 years post-transplantation.