OR21 Clinical significance of C3D binding donor specific anti-HLA antibodies detected by single antigen beads after kidney transplantation

Abstract

Aim Recent interest in characterizing the complement-fixing ability of post-transplant donor specific alloantibodies (DSA) resulted in the enhancement of Luminex solid phase alloantibody assays (SAB) to determine DSA complement-fixing capacity. Previous studies have reported a significantly worse clinical outcome after kidney transplantation for SAB C1q-binding versus non-C1q-binding DSA. A newly available SAB method detects C3d-binding rather than C1q. The purpose of this study was to compare the clinical outcomes in kidney transplant recipients that developed de novo DSA post-transplant stratified by C3d binding by SAB assay (Lifecodes, Immucor). Methods A cohort of 222 recipients transplanted between 2002 and 2013, with previously identified post-transplant de novo DSA, were retested by Luminex SAB IgG and C3d assay using the Immucor LSA Single Antigen Class I and Class II beads. This 222 patient cohort was 45.2 ± 12.1 (19–74) years old, 63% male ( n = 139), 35% African-American ( n = 77), 33% sensitized pre-transplant ( n = 73), and 11% retransplant recipients ( n = 25). The median time to first rejection episode experienced by 112/222 (50.4%) recipients was 18.8 months (range 8 days to 6.6 years). The median time of sera testing was 35.8 months post-transplant (range 8 days to 10 years). Results In 149/222 (67%) recipients, the SAB C3d assay was positive. Analysis of anti-HLA class specificity revealed 72 (32.4%) of recipients were SAB C3d negative, 16 (7%) were anti-HLA Class I only positive, 111 (50%) were anti-HLA Class II only positive, and 23 (10%) were positive for anti-HLA Class I and Class II. Death censored graft survival after sera acquisition for testing was significantly worse for all SAB C3d positive versus C3d negative recipients. The difference in graft survival was most pronounced when anti-HLA Class I SAB C3d binding was detected. Conclusion We conclude that C3d binding in this SAB assay identifies de novo DSA kidney recipients at highest risk for graft loss. I. Balazs: Employee; Company/Organization; Immucor, Inc.