ABH-Glycan Microarray Characterizes ABO Subtype Antibodies: Fine Specificity of Immune Tolerance After ABO-Incompatible Transplantation.

Organ transplantation from ABO blood group-incompatible (ABOi) donors requires accurate detection, effective removal and subsequent surveillance of antidonor antibodies. Because ABH antigen subtypes are expressed differently in various cells and organs, measurement of antibodies specific for the antigen subtypes in the graft is essential. Erythrocyte agglutination, the century-old assay used clinically, does not discriminate subtype-specific ABO antibodies and provides limited information on antibody isotypes. We designed and created an ABO-glycan microarray and demonstrated the precise assessment of both the presence and, importantly, the absence of donor-specific antibodies in an international study of pediatric heart transplant patients. Specific IgM, IgG, and IgA isotype antibodies to nonself ABH subtypes were detected in control participants and recipients of ABO-compatible transplants. Conversely, in children who received ABOi transplants, antibodies specific for A subtype II and/or B subtype II antigens-the only ABH antigen subtypes expressed in heart tissue-were absent, demonstrating the fine specificity of B cell tolerance to donor/graft blood group antigens. In contrast to the hemagglutination assay, the ABO-glycan microarray allows detailed characterization of donor-specific antibodies necessary for effective transplant management, representing a major step forward in precise ABO antibody detection.

Chemical Basis for Qualitative and Quantitative Differences Between ABO Blood Groups and Subgroups: Implications for Organ Transplantation.

Blood group ABH(O) carbohydrate antigens are carried by precursor structures denoted type I-IV chains, creating unique antigen epitopes that may differ in expression between circulating erythrocytes and vascular endothelial cells. Characterization of such differences is invaluable in many clinical settings including transplantation. Monoclonal antibodies were generated and epitope specificities were characterized against chemically synthesized type I-IV ABH and related glycans. Antigen expression was detected on endomyocardial biopsies (n = 50) and spleen (n = 11) by immunohistochemical staining and on erythrocytes by flow cytometry. On vascular endothelial cells of heart and spleen, only type II-based ABH antigens were expressed; type III/IV structures were not detected. Type II-based ABH were expressed on erythrocytes of all blood groups. Group A1 and A2 erythrocytes additionally expressed type III/IV precursors, whereas group B and O erythrocytes did not. Intensity of A/B antigen expression differed among group A1 , A2 , A1 B, A2 B and B erythrocytes. On group A2 erythrocytes, type III H structures were largely un-glycosylated with the terminal "A" sugar α-GalNAc. Together, these studies define qualitative and quantitative differences in ABH antigen expression between erythrocytes and vascular tissues. These expression profiles have important implications that must be considered in clinical settings of ABO-incompatible transplantation when interpreting anti-ABO antibodies measured by hemagglutination assays with reagent erythrocytes.

Pediatric cardiac transplantation using hearts previously refused for quality: a single center experience.

Pediatric donor hearts are regularly refused for donor quality with limited evidence as to which donor parameters are predictive of poor outcomes. We compare outcomes of recipients receiving hearts previously refused by other institutions for quality with the outcomes of recipients of primarily offered hearts. Data for recipients aged ≤18 and their donors were obtained. Specific UNOS refusal codes were used to place recipients into refusal and nonrefusal groups; demographics, morbidity and mortality were compared. Kaplan-Meier analysis with log-rank test was used to determine differences in graft survival. A multivariable Cox proportional hazards model was constructed to determine independent risk factors for postoperative mortality. From July 1, 2000 to April 30, 2011, 182 recipients were transplanted and included for analysis. One hundred thirty received a primarily offered heart; 52 received a refused heart. No difference in postoperative complications or graft survival between the two groups (p = 0.190) was found. Prior refusal was not an independent risk factor for recipient mortality. Analysis of this large pediatric cohort examining outcomes with quality-refused hearts shows that in-hospital morbidity and long-term mortality for recipients of quality-refused hearts are no different than recipients of primarily offered hearts, suggesting that donor hearts previously refused for quality are not necessarily unsuitable for transplant and often show excellent outcomes.