P006 Assessing the functional significance of HLA antibodies in renal allograft

Objective To assess potential function of the anti-HLA antibodies in terms of complement binding and non-complement binding in highly sensitized patients and to correlate the functional properties with in-vitro cytotoxicity assays and biopsy. Methods The Class I and II HLA antibody profiles of 78 patients were analyzed to determine antibody strength and specificity and to determine if any of the identified antibodies are complement binding. In vivo correlation was done in 37 patients who had a biopsy and donor-specific antibody (DSA) assessment. The HLA class I and II antibody specificities were determined by single antigen bead assay (SAB) and the C1q binding assay (C1q-B) using Luminex platform (One Lambda, Canoga Park CA). In vitro cytotoxicity assays were done by T-AHG and Amos CDC. Results Of the 2941 antibodies identified by SAB in 78 patients, 1940 (66%) were Class I and 1001 (34%) were Class II specific. In all, 758 (39%) of the Class I antibodies with ⩾ 5000 MFI and 484 (48%) of the Class II antibodies were with an MFI of ⩾ 5000. Of the total 2941 HLA antibodies, 238 (8%) were C1q-B. Of the C1q-B, 77 (32%) were directed against Class I HLA and 161 (68%) were directed against Class II. Importantly, 92% of all C1q Class I antibodies identified were defined as strong among the total 2941 HLA specific antibodies. Biopsy results were available from 37 patients and 15 of them had no C1q Class I or Class II DSAs and no AMR while 6 (16%) patients were C1q Class I and Class II positive DSA and AMR. Fourteen percent ( n  = 5) of the total patients were C1q Class I negative and C1q Class II positive and per biopsy were classified as C4d negative AMR. Of the 49 patients with CDC and C1q data available 19 (39%) nine were C1q Class I and Class II DSA negative and CDC B-cell and T-cell negative while 5 (10%) were C1q Class I and Class II DSA positive and CDC B-cell positive T-cell negative. In all, 4 were C1q Class I negative and Class II positive with CDC T-cell negative and CDC B-cell positive. Conclusions This limited retrospective analysis confers that assaying for C1q binding antibodies is very likely to have clinical relevance in terms of the functional effect of the multiple HLA antibodies on the allograft. The class II antibodies and antibodies with higher MFIs are are more likely to be C1q-B.