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 following 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 HLA antigen 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. We report results of prospectively monitoring for alloimmunization in our recent CBT experience. Among 46 consecutive patients, four patients (9%) (5 out of 88 units (6%)) had evidence of at least moderate antibodies to HLA antigens on cord units originally selected for transplantation. Virtual crossmatch can be used to screen for donor-directed antibodies in CBT. As possible, units should be changed to avoid sensitized mismatches.