211: False Negative Virtual Crossmatch in Lung Transplantation

Abstract

Purpose: At our institution, virtual crossmatch for thoracic organ transplantation utilizes a flow cytometry based PRA screening assay to determine the presence of anti HLA antibodies (Ab). In 15/16 cases, a negative virtual crossmatch (XM) successfully predicted a negative retrospective complement dependent cytotoxicity (CDC) XM. We determined the molecular basis of a discrepancy between the virtual cross-match and post-transplant positive CDC XM in a patient who underwent bilateral lung transplantation. Methods and Materials: Pre-transplant serum was analyzed using flow cytometry, ELISA, and single antigen bead assays. High resolution HLA typing was performed on donor tissue to assess donor HLA antigens. The presence of Ab was followed overtime utilizing flow cytometric analysis of donor cells with recipient serum. Results: Both the ELISA and flow cytometry PRA screens were negative for preformed antibody against HLA molecules. Following a positive CDC XM, single antigen Luminex based assay was performed and revealed anti-donor DR13 Ab. This Ab was eliminated using a protocol of apheresis, IVIG and anti CD20 therapy. Clinical improvement of the patient correlated with decreasing antibody titers following therapy. Conclusions: The current practice of utilizing a single method (ie flow cytometry PRA screen) to assess patients for the presence of anti HLA antibodies can result in the failure to identify clinically relevant Ab. The predictive value of the virtual crossmatch can be improved through the addition of a Luminex based assay system. A combination of plasma phoresis, IVIG and anti CD20 antibody can be used to successfully treat acute graft dysfunction associated with preformed donor specific anti HLA antibodies.