Trends in HLA antibody screening and identification and their role in transplantation.

HLA testing has been a staple in transplantation since the recognition that antibodies, directed against lymphocytes, were associated with allograft failure. This seminal finding led to the discovery of the MHC and the appreciation of the importance of HLA testing in transplantation. Early approaches focused on the importance of HLA matching, and were an important aspect of deceased organ donor allocation. More recently, and as a direct result of improvements in immunosuppression, there has been a movement away from 'matching' as the driving force in organ allocation. By contrast, we are now challenged with selecting donor-recipient pairs based on acceptable mismatches. For patients devoid of HLA antibodies, this is not an issue. However, for patients with HLA alloantibodies, that is, the sensitized patient, we face significant challenges in assessing the repertoire of the HLA antibody reactivity they possess. Over the past several years, significant advances in HLA antibody detection have occurred. Solid-phase, multiplex testing platforms have replaced traditional cell-based assays, and have provided better sensitivity and specificity in antibody detection. As a direct result of improved antibody identification, many programs are moving into the realm of the 'virtual crossmatch'. The virtual crossmatch has proven to be successful in renal, cardiac and lung transplantation, and has resulted in a greater percentage of sensitized patients gaining access to transplantation. This review will be devoted to highlighting the latest developments in antibody assessments and discussing their utilization in transplant testing.