Functional assessment of HLA antibodies (Abs) has historically been limited to complement-based assays, which have known limitations. Moreover, HLA Abs mediate injury by complement-independent mechanisms, including direct signaling via HLA antigens and via Fc receptor (FcR) engagement. We have hypothesized that comprehensive assessment of the pathogenicity of HLA Abs requires assessment of FcR binding capacity. Initial validation of an FcR binding assay is presented.

METHODS

Data from 48 patients (pts) with antibody mediated rejection (AMR) were analyzed. Pathologic data included Banff component scoring and C4d staining. Serum samples obtained prior to transplantation, at the time of AMR diagnosis and following AMR treatment were analyzed by HLA single antigen bead (SAB) microarrays, C1q assay, IgG isotype-specific SAB assays (IgG1, IgG2, IgG3 and IgG4), and FcR binding assays (performed according to standard SOPs for the laboratory-developed test).

RESULTS

FcR assay inter-and intra-run CVs were <10%. Correlation between SAB assay Ab strength and FcR assay was high (r=0.70, p = 0.0075); correlation between FcR assay and C1q assay was lower (0.57) due to negative C1q assay results when HLA Ab strength was moderate or low. In 14 pts with AMR and low strength DSA (<2000 MFI) C1q assays were negative (14/14 pts), whereas 10/14 (70%) pts were positive by FcR assay (p=0.0004). 10 pts with AMR and moderate strength DSA (4000-8000 MFI), 1 of 10 (10%) had positive C1q assay, whereas 8/10 (80%) patients had a positive FcR assay (p=0.007). FcR assay results positively correlated with IgG1 and IgG3 isotype-specific SAB assay.

Banff component acute glomerulitis (g) scores correlated with FcR binding (p = 0.01) but not C1q (p=0.92) assays, with similar results for chronic glomerulopathy (cg) scoring (p=0.033) C1q (p =0.49). Death censored graft survival after AMR in patients with weak FcR binding DSA was higher than in pts with moderate or strong FcR binding DSA. Similarly, reduced allograft survival was observed in pts with strong FcR binding DSA as compared to all pts with lower FCR blnding DSA.

Conclusions: FcR binding capacity of HLA antibodies provides information unique to that derived from SAB and C1q assays, and correlates with 1) SAB testing, 2) IgG1 and IgG3 isotype specific SAB testing, 3) g and cg Banff component scoring, and 4) death censored renal allograft survival following AMR. This initial validation analysis indicates that assessment of FcR binding capacity of HLA antibodies provides useful clinical information.

CITATION INFORMATION: Woodle E, Girnita A. Fc Receptor Binding Assay for Functional Assessment of HLA Antibodies: Initial Clinical Validation. Am J Transplant. 2016;16 (suppl 3).

« Back to 2016 American Transplant Congress