ABO Tolerance Following Treatment of Infant Mice with A-Expressing MHC-Identical Erythrocytes

Purpose ABO-incompatible heart transplantation (ABOi HTx) is safe in young children and increases donor access. Post-ABOi HTx, B cell tolerance develops to donor ABO blood group antigen(s) by mechanisms not fully defined. To study ABO tolerance, we developed A-transgenic mice (A-Tg) that express A-antigen on vascular endothelium, erythrocytes (RBCs) and lymphocytes; we demonstrated A-antigen-specific tolerance induced by HTx into 4 wk-old, MHC-identical, wild-type (WT) mice. Intentional induction of tolerance may allow subsequent ABOi HTx. Recently, we showed ABO tolerance could be intentionally induced in WT mice after ip injection of infant mice with intact A-Tg blood cells (BCs). Herein, we sought to determine specific A-Tg cell type(s) capable of inducing tolerance. Methods WT BALB/c (BALB) mice at 7 days of age were left untreated or injected ip (weekly × 3) with either unfractionated BCs, erythrocytes (RBCs), peripheral blood mononuclear cells (PBMCs), or splenocytes from A-Tg BALB mice (see Table). Two weeks later, all mice were injected ip (weekly × 5) with human A-RBC (A-antigen challenge) in an attempt to elicit anti-A antibody (Ab) production. Serum anti-A and third-party (non-A anti-human) Ab were assessed by hemagglutination or ABH glycan microarray. Results In response to challenge with A-antigen, high levels of anti-A Ab were produced both in untreated mice and in mice previously treated with A-Tg PBMCs or splenocytes (Table). In contrast, anti-A Ab remained undetectable/very low in mice treated as infants with A-Tg BCs or RBCs. Third-party Ab responses were high for all groups. Conclusion A-Tg RBCs induced robust A-antigen-specific tolerance in infant mice, whereas A-Tg lymphocytes (PBMCs, splenocytes) did not. Future studies will explore mechanisms of A-Tg RBC tolerance induction with the goal to design synthetic ABH-multivalent polyethylene glycol (PEG) glycoconjugates for intentional ABO tolerance to allow subsequent ABOi HTx safely.