60-OR

Abstract

Aim The C1qScreen™ assay detects complement binding HLA antibodies. Recent studies suggest that the presence of C1q positive donor specific antibodies (DSA) is associated with poor post-transplant outcomes. However, in some patients with documented episodes of antibody mediated rejection or graft failure, C1q binding DSA are not detected by the C1qScreen™ suggesting poor assay sensitivity. The goal of this study was to develop an enhanced C1q assay to improve the detection of complement binding HLA DSA. Methods Nine patient sera with well characterized (using IgG single antigen bead (SAB) assay) post-transplant DSA were tested for C1q binding using the standard C1qScreen™ and three modified protocols: 1) extended incubation (EI), 2) wash modified (WM) and 3) anti-human globulin (AHG) C1q enhanced (ACE) protocol. The number of class I/II DSA detected and DSA MFI values obtained with each protocol were compared. Results The C1qScreen™ was positive for only 30% of Class I (9/30) and 52% of Class II (15/29) IgG DSA specificities. The average MFI DSA values were markedly reduced compared with the IgG-SAB assay. The EI and WM protocols exhibited higher average DSA MFI values (2.25 and 3.4 fold higher respectively) compared to the standard protocol but only 2 additional DSA specificities were detected. In contrast, the ACE protocol identified 10 additional Class I (19/30; 63%) and 4 additional Class II (19/29; 66%) DSA specificities with an average increase in DSA MFI of 4.7 fold when compared with the standard C1qScreen™. Conclusions The C1qScreen™ exhibits poor assay sensitivity and fails to adequately identify many post-transplant complement fixing HLA DSA. The sensitivity of the C1qScreen™ to detect DSA can be improved with various protocol modifications. The ACE protocol was the most sensitive of the assays tested and detected the majority of post transplant HLA DSA. Future studies will investigate the clinical significance of HLA DSA detected by the ACE protocol.