Does a Useful Test Exist to Properly Evaluate the Pathogenicity of Donor-specific Antibodies? Lessons From a Comprehensive Analysis in a Well-studied Single-center Kidney Transplant Cohort

Abstract

Background. Donor-specific antibodies (DSA) play a major role in antibody-mediated rejection (AMR) and graft dysfunction. However, the clinical relevance of complement-binding anti-HLA antibodies remains unclear. Methods. Here, we analyzed DSA detected in the serum (sDSA) using single antigen bead, C1q, and C3d assays combined with the study of intragraft DSA (gDSA) in 86 patients who had DSA and underwent a kidney biopsy for cause (n = 58) or without evidence of kidney dysfunction (n = 28). DSA characteristics were collected and related to the presence of AMR, graft histological features, and allograft survival. Results. Forty-five patients (52%) had C1q+ DSA, and 42 (51%) had C3d+ DSA. Allograft biopsies revealed AMR in 63 cases (73%), regardless of kidney function. gDSA were identified in 74% of biopsies. We observed a strong correlation among single antigen bead mean fluorescence intensity and complement assays positivity, presence of gDSA, and AMR occurrence. Conclusions. Complement-binding DSA per se were not significantly associated with allograft survival in the entire study sample. Finally, gDSA predicted subsequent graft loss in patients who showed a stable renal function at the day of biopsy. Our data suggest that DSA mean fluorescence intensity and presence of gDSA might provide prognostic information during posttransplant monitoring.

Approaches for the characterization of clinically relevant pre‐transplant human leucocyte antigen (HLA) antibodies in solid organ transplant patients

“…An increased level of denatured antigen has been reported in the LABScreen assay compared to the LIFECODES (Ravindranath et al, 2018) assay, although conversely LIFECODES has been reported to demonstrate lower sensitivity than LABScreen (Gautier Vargas et al, 2019;Ravindranath et al, 2018).…”

“…The association between a high MFI value and complementfixing has been reported as a confounding factor for both the C1q and C3d assays (Cioni et al, 2017;Claisse et al, 2017;Courant et al, 2018;Gautier Vargas et al, 2019;Kamburova et al, 2018;Karahan et al, 2017;Ko et al, 2018;Moreno Gonzales et al, 2017;Schaub et al, 2014;Tait et al, 2013;Yell et al, 2015), although antibodies with high MFI value are not always reported to be complement fixing (Chen et al, 2011;Navas et al, 2019;Zeevi et al, 2012). As the density and avidity of bound antibody affects the efficiency of C1qbinding, it would suggest that lower titre antibodies (reported as 1:34 to 1:64 titre) (Tambur & Wiebe, 2018) may give a false negative result for assessment of complement-fixing ability (Filippone & Farber, 2016;Schaub et al, 2014;Tambur et al, 2015;Thurman et al, 2019).…”

Clinical relevance of donor‐specific antibodies directed at HLA‐C: A long road to acceptance

“…Intragraft DSA eluted from transplant biopsies and then identified by SAFB demonstrated the ability of DSA to bind to donor cells in vivo. Intragraft DSA were also detected during ABMR, underlining direct involvement of DSA in graft injuries leading to graft loss 2,59‐64 . Interestingly, two studies showed that 20% to 50% of circulating anti‐HLA‐C DSA were also detected within the graft, that is, at the same rate as for other class I DSA 60,61 …”

“…Intragraft DSA were also detected during ABMR, underlining direct involvement of DSA in graft injuries leading to graft loss. 2,[59][60][61][62][63][64] Interestingly, two studies showed that 20% to 50% of circulating anti-HLA-C DSA were also detected within the graft, that is, at the same rate as for other class I DSA. 60,61 After binding to the graft, DSA are deleterious via several pathways.…”

Challenges of Diagnosing Antibody-Mediated Rejection: The Role of Invasive and Non-Invasive Biomarkers

“…However, they also show that high MFI value non-complement-fixing DSAs correlate with risk of ABMR and graft loss just as well [ 38 ]. Other investigators have not demonstrated the independent association of C3d and C1q fixation with rejection and graft loss [ 39 , 40 , 41 ]. The intra-graft homing ability of a DSA has also been suggested as a potential marker of its pathogenicity [ 42 , 43 ].…”