Blood Group A Transgenic Mice: A Model for ABO-Incompatible (ABOi) Heart Transplantation (HTx)

Purpose Our group demonstrated that infant ABOi HTx results in development of immune tolerance to donor ABO antigen(s). We recently developed mice transgenic for expression of A- and H-glycosyltransferases (AH-Tg, C57BL/6 (B6) background). By lectin staining, AH-Tg mice express blood group A-antigen on vascular endothelium of solid organs including heart. Human ‘A into O’ HTx can be approximated using AH-Tg mice as donors and B6 wild-type (WT) mice as recipients. Herein we sought to characterize ‘natural’ and induced anti-A antibodies (Abs) in WT mice and binding to A-expressing AH-Tg hearts, and to investigate AMR following transplantation of AH-Tg heart grafts into WT mice with high anti-A titre. We hypothesize that serum from WT mice with high anti-A titre will bind to AH-Tg cardiac tissue, and that AH-Tg heart grafts will undergo AMR following transplantation into WT recipients with high anti-A Abs. Methods and Materials Juvenile WT B6 mice were induced to produce anti-A Abs by i.p. injection of blood group A red blood cells. Sera from WT and AH-Tg mice of different ages were assessed for anti-A Ab by hemagglutination assay. Binding of serum anti-A Abs to AH-Tg hearts was determined by immunohistochemistry (IHC). WT mice with high anti-A titres received AH-Tg heart transplants; AMR was assessed by IHC. Results Increasing anti-A Abs were detected with age in WT mice (n=108). No AH-Tg mice had detectable anti-A Abs (n=19). Using a commercial anti-A Ab, we detected A-antigen on vascular endothelium of hearts, kidneys, livers, and lungs from AH-Tg mice. Serum from older WT mice with natural anti-A Abs or from younger A-antigen-sensitized WT mice bound to AH-Tg but not WT cardiac tissue. Conclusions This study provides insight into the development of anti-A Abs in WT mice and confirms A-antigen expression on AH-Tg cardiac endothelium by serum anti-A Abs. Studies are ongoing to examine AMR following transplantation of AH-Tg heart grafts into WT mice with high anti-A titres.