Anti-Gal and Anti-non Gal Antibodies in Regeneration of Extracellular Matrix Bio-Implants

This chapter describes antibodies that are detrimental to porcine (and other mammals’) ECM bio-implants in humans, and discusses methods for overcoming the detrimental effects of these antibodies. Porcine extracellular matrix (ECM) is produced from tissues that undergo decellularization by incubation with various detergents. This treatment removes phospholipids, glycolipids and cholesterol but retains the ECM of the treated tissue. It is assumed that stem cells that migrate in vivo into the bio-implant receive “cues” from the ECM to differentiate into mature cells that repopulate the bio-implant and restore its structure and function. This regeneration process is hampered by two types of antibodies that are reactive against the ECM bio-implants: The natural anti-Gal antibody and anti-non gal antibodies. Anti-Gal is the most abundant natural antibody in humans and it binds to the α-gal epitope which is abundant in porcine tissues as well as in other nonprimate mammals. Binding of anti-Gal to α-gal epitopes on the bio-implant results in complement activation and chemotactic recruitment of macrophages which bind to the Fc portion of anti-Gal immunocomplexed with the ECM, causing degradation of the ECM. In addition, α-gal epitopes on the ECM elicit an increase of ~100 fold in the titer of anti-Gal within 2 weeks. This elicited anti-Gal antibody further exacerbates the destruction of the ECM bio-implant. Anti-Gal/α-gal epitope interactions may be avoided by enzymatic destruction of α-gal epitopes on the ECM with recombinant α-galactosidase or by using tissues from α1,3-galactosyltransfrase knockout pigs which are devoid of α-gal epitopes. Anti-non gal antibodies are produced in human recipients of ECM bio-implants against ECM peptide sequences differing from those in homologous proteins in humans. Such immunogenic peptides are present in most mammalian proteins, including components of various ECMs and they elicit anti-non gal antibody production when introduced into humans. Production of anti-non gal antibodies is slower than that of anti-Gal, however, they damage the regeneration process by inducing macrophage mediated degradation of the ECM bio-implant. In addition, these antibodies mask the ECM peptides, thereby preventing the interaction with stem cells for directing the differentiation of these cells. It is hypothetically suggested that accelerated recruitment of stem cells into ECM bio-implant, prior to the production of anti-non gal antibodies at detrimental titers, may enable progression of the regeneration process without the intervention of these antibodies. Such accelerated recruitment of stem cells may be induced by in vitro administration of α-gal nanoparticles into the implant. α-Gal nanoparticles present multiple α-gal epitopes, which bind anti-Gal and induce recruitment of macrophages by generating complement chemotactic factors. The recruited macrophages bind the anti-Gal coated nanoparticles via Fc/Fcγ receptor interaction and are polarized into M2 macrophages that secrete “pro-healing” cytokines/growth factors which recruit stem cells. The stem cells migrating into the ECM bio-implant are directed by the ECM to differentiate into cells that regenerate the bio-implant and restore its function without being negatively affected by the anti-non gal antibodies.