Utility of the virtual crossmatch in solid organ transplantation

PURPOSE OF REVIEW: Solid-phase assays covered with single HLA molecules - such as single-antigen flow-beads (SAFBs) - allow determining the presence of donor-specific HLA antibodies (HLA-DSAs) 'virtually' by comparison of the HLA-antibody specificities of the recipient with the HLA typing of the donor. In this review, prospects and current limitation of the virtual crossmatch are discussed. RECENT FINDINGS: Several prospective and retrospective studies indicate that a negative virtual crossmatch is associated with a very low risk of early rejection and good long-term allograft survival. By contrast, a positive virtual crossmatch is associated with a significant risk for early rejection and decreased allograft survival. However, these studies revealed that not all HLA-DSAs detected by SAFB have a detrimental clinical impact. SUMMARY: The virtual crossmatch has emerged as a very useful tool for pretransplant risk assessment and organ allocation. Further advances of the virtual crossmatch approach will require improvements on the technical part of SAFB analysis and a better understanding and definition of pathogenic factors of HLA-DSA. Together with an extended HLA typing of the donor, this scenario will provide us the full benefits of applications based on virtual crossmatching.