Introduction: The trisaccharide epitope defines A&B blood group antigens where antibody binds to subtype chains (I-VI), but only subtype II is expressed on cardiac vascular endothelium. Following pediatric ABO-incompatible heart transplantation (ABOiHTx) there is evidence of humoral tolerance to this but not other allograft blood group antigen subtypes. This study reports subtype-specific antibody quantification in adult ABOi kidney transplant (ABOiKTx) recipients.

Methods: Plasma samples were obtained from 68 ABOiKTx recipients with blood group A donors. Antibody to ABH subtype antigens I-VI was quantified using a microarray platform in which the mean fluorescence intensity (MFI) of binding is proportionate to the concentration of antibody and a haemagglutination (HA) assay.

Results: Before and after a course of plasma exchange (PEx) or trisaccharide-based immuno-adsorption (IA), HA did not differ between treatment types. In the microarray assay, PEx reduced MFI of IgG and IgM binding to all blood group A subtypes and the Galili antigen. IA reduced the MFI of IgG binding to subtype II & VI equivalent to PEx, but the MFI of IgG binding to subtype III, IV & V remained significantly higher following IA (p<0.01) compared to PEx; the MFI of Galili antigen binding was unaltered. At 12 months post-ABOiKTx, the MFI of IgG binding to all subtypes had increased compared with pre-ABOiKTx (post-PEx /- IA), although IgG subtype binding remained below pre-treatment levels (p<0.01). Subtype II had the greatest relative reduction in IgG MFI at 12 months, as previously reported in paediatric ABOiHTx, but many adults nevertheless maintain moderate antibody levels even to this subtype.

Discussion: These data demonstrate that IA preferentially removes IgG to subtype II compared to IgG to subtypes III/IV (subtypes for which there is evidence that these tetrasaccharides contribute to epitope generation). In the long-term, most adult recipients achieve very low levels of antibody to donor A antigen subtype II (a 'tolerant' phenotype) but a small proportion maintain significant antibody levels (an 'accommodated' phenotype).

CITATION INFORMATION: Bentall A, Jeyakanthan M, Pearcey J, Motyka B, Cairo C, Lowary T, Buriak J, West L, Ball S. Differential Effect of Antibody Removal on ABO Blood Group Type Chain Specific Antibodies Over Time. Am J Transplant. 2017;17 (suppl 3).

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