Stable mixed donor–donor chimerism after double cord blood transplantation

Double cord blood transplantation (DCBT) has been used increasingly and has proven to be both safe and efficacious. In chimerism analysis, previous studies have indicated single unit predominance early after DCBT. In the present study, we evaluated the chimeric pattern in T-, B- and myeloid cells using PCR-based chimerism analysis in seven patients after DCBT: five patients had acute leukemia and two had lymphoma. Five patients received myeloablative conditioning and two patients were given reduced intensity conditioning. All patients received anti-thymocyte globulin (ATG) before DCBT. Three of the six evaluable patients showed donor–donor mixed chimerism in all cell lineages at 90 days after DCBT. Interestingly, two patients in long-term follow-up showed mixed donor chimerism in all cell lineages at 25 and 35 months after DCBT, respectively. Both patients are doing clinically well. Neither of the two developed GVHD after DCBT. In conclusion, in this study donor–donor mixed chimerism was common after high dose ATG and DCBT. Further studies are warranted concerning the immunological consequences of the phenomenon of donor–donor mixed chimerism after DCBT.