Stable mixed chimerism without relapse after related allogeneic umbilical cord blood transplantation in a child with severe aplastic anemia.

Umbilical cord blood (UCB) cells from HLA-matched donors are used as an alternative to bone marrow for allogeneic transplantation and reports of successful UCB transplantation in patients with severe aplastic anemia (SAA) are scarce. SAA was discovered in a 4-year-old girl in February 1990. Transfusion support started in August 1990 and standard treatments were unsuccessful. The birth of an HLA-compatible brother in October 1993 permitted the cryopreservation of UCB. In December 1994 UCB transplantation was decided upon. No toxicity occurred. G-CSF was started at day 28. WBC and PMN reached 0.5 x 10(9)/l at days 33 and 37. RBC and platelet transfusion independence were reached at days 50 and 52. Mixed chimerism was demonstrated in blood cells at 1.5, 4 and 6 months after UCBT by molecular biology (VNTR). FISH studies yielded similar results at 15 and 18 months. Twenty months after UCBT, molecular biology showed full donor chimerism. Clinical follow-up (last follow-up: 32 months post transplant) is unremarkable. We suggest that CY and ATG may be a suitable regimen for related HLA-compatible UCBT in patients with SAA. Residual recipient cells can disappear even very late after UCBT, permitting the establishment of complete donor chimerism.