Targeting Pathogenic Post-Ischemic Self-Recognition by Natural IgM to Protect Against Post-Transplant Cardiac Reperfusion Injury
Background—Natural IgM antibodies represent a class of innate pattern recognition receptors that recognize danger associated molecular patterns expressed on stressed or dying cells. They play important roles in tissue homeostasis by disposing of pre-necrotic cells and suppressing inflammation. However, ischemic insult leads to a pathogenic level of IgM binding and complement activation, resulting in inflammation and injury. We investigate the role of self-reactive IgM in the unique setting of transplantation, where the donor organ undergoes both cold and warm ischemia, and global ischemic insult.
Methods and Results—By transplanting hearts from wild-type donor mice into antibody-deficient mice reconstituted with specific self-reactive IgM mAbs, we identified neoepitopes expressed post-transplant, and demonstrated a key role for IgM recognition of these epitopes in graft injury. With this information, we developed and characterized a therapeutic strategy that exploited the post-ischemia recognition system of natural antibodies. Based on neoepitope identification, we constructed an anti-annexin-IV single chain antibody (scFv) and an scFv linked to Crry, an inhibitor of C3 activation (scFv-Crry). In an allograft transplant model, in which recipients contain a full natural antibody repertoire, both constructs blocked graft IgM binding and complement activation, and significantly reduced graft inflammation and injury. Furthermore, scFv-Crry specifically targeted to the transplanted heart and, unlike complement deficiency, did not affect immunity to infection, an important consideration for immunosuppressed transplant recipients.
Conclusions—We identified pathophysiologically important epitopes expressed within the heart post-transplant, and describe a novel translatable strategy for targeted complement inhibition that has several advantages over currently available approaches.
- Received September 24, 2014.
- Revision received December 23, 2014.
- Accepted January 16, 2015.