Humoral Reactivity of Renal Transplant-Waitlisted Patients to Cells from GGTA1/CMAH/B4GalNT2, and SLA Class I Knockout Pigs.

Background: Anti-pig antibodies are a barrier to clinical xenotransplantation. We evaluated antibody binding of waitlisted renal transplant patients to 3 glycan KO pig cells and Class I swine leukocyte antigens (SLA). Methods: Peripheral blood mononuclear cells (PBMCs) from SLA identical wild type, GGTA1 KO, GGTA1/CMAH KO, and GGTA1/CMAH/B4GalNT2 KO pigs were screened for human antibody binding using flow cytometric crossmatch (FCXM). Sera from 820 patients were screened on B4GalNT2/CMAH/GGTA1 KO cells and a subset with elevated binding was evaluated further. FCXM was performed on SLA intact cells and GGTA1/SLA Class I KO cells after depletion with wild type (WT) pig RBCs to remove cell surface reactive antibodies, but leave SLA antibodies. Lastly, human and pig reactive antibodies were eluted and tested for cross species binding and reactivity to single antigen HLA beads. Results: Sequential glycan KO modifications significantly reduce antibody binding of waitlisted patients. Sera exhibiting elevated binding without reduction after depletion with WT RBCs demonstrate reduced binding to SLA class I KO cells. Human IgG, eluted from human and pig PBMC, interacted across species and bound single antigen HLA beads in common epitope-restricted patterns. Conclusions: Many waitlisted patients have minimal xenoreactive antibody binding to the triple KO pig, but some HLA antibodies in sensitized patients cross react with class I SLA. SLA class I is a target for genome editing in xenotransplantation. Copyright (C) 2017 Wolters Kluwer Health, Inc. All rights reserved.

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