Coinfusion of mobilized hematopoietic stem cells from an HLA-mismatched third-party donor with umbilical cord blood graft to support engraftment.

We evaluated the role of mismatched third-party hematopoietic stem cells (TPC) in shortening the neutropenia after umbilical cord blood transplantation (UCBT). A TPC graft was given to 7/37 children with UCBT to support engraftment due to anticipated increased risk of nonengraftment (N=6) or active infection (N=1). TPC grafts were collected with apheresis from haploidentical family members. The median UCB and CD34 cell counts were 5.10 (range, 4.13 to 9.98)×10/kg and 5.98 (range, 4.40 to 14.00)×10/kg, respectively. The median time to neutrophil engraftment was shorter in the patients with TPC (12 d; range, 9 to 24 d) than those without (23 d; range, 12 to 44 d) (P=0.010). TPC chimerism was lost in median at 28 (range, 24 to 103) days posttransplant. TPC grafts from mothers engrafted similarly as the grafts from other family members. UCB graft cell count and the use of methotrexate posttransplant strongly contributed to engraftment. TPC may form a valuable transient bridging graft over the neutropenia after UCBT in patients with anticipated high-risk of nonengraftment or toxicity due to pretransplant infections.