Anti-pig antibodies monitoring in the first cardiac xenotransplantation from genetically engineered pig to a human

Introduction: Humans have natural antibodies against some of the pig antigens (e.g., 1,3 Galactosyltranserase (GT), beta-1,4-N-Acetyl-Galactosaminyltransferase 2 (b-Gal), and N-Glycolylneuraminic acid (Neu5Gc)) which may trigger hyperacute rejection. A heart from a genetically engineered (GE) pig that lacks GTKO, b-GalKO, and cytidine monophosphate-N-acetylneuraminic acid hydroxylase (CMAHKO) along with overexpression of human gene (CD46, DAF, TBM, EPCR, CD47, and HO-1) was transplanted in a human patient with heart failure after expanded access authorization from FDA. We report the recipient’s anti-pig antibody levels at various time points after cardiac xenotransplantation (xTX). Methods: Serum from the recipient was collected before and after cardiac xTX at multiple time points and tested for anti-pig non-gal antibodies (IgG and IgM) using donor-specific porcine aortic endothelial cells (PAECs) from 10 GE pigs, TKO and GTKO by flow cytometry. Antibodies binding with PAECs for IgG and IgM were determined by calculating normalized mean fluorescence intensity (MFI, i.e., Geometric mean) with reference to positive control. Results: The first GE pig heart-to-human transplant recipient survived for 60 days. Anti-pig non-gal antibodies were dropped after xTX and remained low until 47 days, but IgG antibodies sharply increased. The rise in anti-non-gal antibodies coincided with the increase in troponin release. This increase in IgG antibodies also occurred after intravenous IgG (IVIG) administration. Later, IVIG was also tested for binding with PAECs which was also found to have high binding to donor PAECs. Conclusion: Our study demonstrates that human recipients had a very low titer of non-gal or anti-pig IgG and IgM antibodies during the first 47 days when the graft function was excellent. The antibody levels increased after 47 days coinciding with xenograft dysfunction. Early detection of these antibodies is a powerful tool and may allow a window for proper interventions to prevent antibody-mediated rejection.