HLA-specific memory B cells may contribute to the serum HLA antibody pool upon antigen re-exposure. The aim of this pilot study was to investigate the presence of concurrent donor-specific memory B cell-derived HLA antibodies (DSA-M) in renal allograft recipients with pretransplant donor-specific HLA antibodies (DSA) and its association with occurrence of antibody-mediated rejection (AMR) using a recently developed method.
Twenty patients with Luminex single antigen bead (SAB) assay-defined DSA but negative complement-dependent cytotoxicity crossmatches were enrolled. Plasma samples and peripheral blood mononuclear cells (PBMC) were collected at 3 timepoints (pretransplant, month 6, month 12). We analyzed IgG-purified and concentrated culture supernatants from polyclonally activated PBMC using SAB assays and compared HLA antibody profiles with same day plasma results.
Plasma SAB analysis revealed 35 DSA in 20 patients pretransplant. DSA-M were detected in 9/20 (45%) patients and for 10/35 specificities (29%). While median mean fluorescence intensity (MFI) values of DSA with concurrent DSA-M (5877) were higher than those of DSA without DSA-M (1476), 3/6 patients with AMR and low MFI DSA (<3000) had DSA-M. Overall, pretransplant DSA/DSA-Mpos
allograft recipients showed a higher incidence of biopsy-proven (sub)clinical AMR (p=0.032) and a higher extent (g≥1+ptc≥1) of microvascular inflammation (67% versus 9%, p=0.02). In 17 patients (28 DSA) with posttransplant analyses, persisting DSA posttransplant had more often DSA-M (6/12; 50%) than nonpersisting DSA (2/16; 13%).
Assessment of DSA-M might be a novel tool to supplement serum HLA antibody analysis for pretransplant risk stratification in patients with DSA.