Assessing the correlation between C3d-binding de novo donor specific HLA antibodies and rejection in kidney transplant recipients

Aim Solid phase assays have the ability to detect even low levels of HLA antibodies, but potentially lack the ability to distinguish between clinically relevant or irrelevant DSA. Here we test the clinical significance of a novel C3d binding assay. Methods Serum samples from 85 kidney transplant recipients were retrospectively analyzed using the Immucor© Single Antigen immunoassays, to detect either IgG or C3d binding HLA antibodies. Inclusion criteria included patients that developed de novo DSA by Luminex One Lambda (OL) single antigen assay and had a biopsy obtained at the same time point as the serum sample. Median fluorescence intensity (MFI) value of 1000 was arbitrarily used to assign positive responses. Results Of the 85 patients: 21 had AMR, 12 cell-mediated rejection (CMR), 11 mixed rejection (AMR + CMR), 4 with pathologic finding other than rejection, such as BK virus, and 41 had normal biopsies. C3d DSA were detected in 16/85 patients with the majority having AMR in 11/16 patients (69%) compared to 1/16 patients (6%) with CMR, 2/16 patients (12.5%) with a mixed rejection, and 2/16 patients (12.5%) with negative biopsies. These 2 negative biopsy patients had strong MFI values for Immucor IgG DSA and strong titers on the OL platform; moreover, both of these patients went on to have AMR later on. Immucor IgG assay detected 29/85 patients with DSA, in which, the majority of C3d positive DSA (16/16) being Immucor IgG class II DSA-positive. Immucor IgG positive DSA with negative C3d results had lower MFI (Fig. 1). All the C3d positive assays corresponded to moderate to high titer OL results (titers ⩾ 1 : 64 ), although three samples had class II specificities with titers ⩾ 1 : 128 were not C3d positive. Conclusion C3d-binding antibodies seem to be associated with stronger antibodies with at least moderate level titer and rejection. Further studies are required to substantiate our results. Download full-size image