Prospective monitoring for alloimmunization in cord blood transplantation: "virtual crossmatch" can be used to demonstrate donor-directed antibodies.

Preformed host antibodies may contribute to graft rejection after hematopoietic stem-cell transplantation. In cord blood transplantation (CBT), donor-directed host antibodies may be particularly relevant because patients are often markedly mismatched to donors, and limited donor cells preclude cross-matching. The recent development of single human leukocyte antigen (HLA) microbead array assays allows characterization of host alloreactivity to individual HLA antigens with sufficient sensitivity and specificity to allow consideration of "virtual crossmatch" testing as a surrogate for conventional crossmatch testing in the CBT setting.