Introduction: The first genetically engineered (GE) pig-to-human cardiac xenotransplantation (xTX) was performed after expanded access authorization from FDA at our institution. We report the immune monitoring status in the recipient after cardiac xTX.

Methods: Peripheral blood mononuclear cells (PBMCs) of the recipient were immunostained for T and B cells and analyzed with flow cytometry. Intracellular cytokine-secreting cells and serum cytokine were analyzed. Anti-pig non-gal antibodies (IgG and IgM) were tested using donor-specific porcine aortic endothelial cells (PAECs) from the 10 GE pigs.

Results: The 10 GE pig heart recipients received modified immunosuppression (IS) which was significantly less than previously reported successful IS for cardiac xTX in non-human primates due to pancytopenia. Induction included ATG (after xTX), Rituxan (one dose only), C1 esterase, and costimulation blockade with humanized anti-CD40 (KPL404) antibody. KPL404, MMF, and an anti-viral drug were used for maintenance. The recipient survived for 60 days. Initially, peripheral T and B cells were depleted. T cells repopulated 10 days after Tx, but  B cells remained low throughout and re-emerged after POD 47. The ratio of CD4/CD8 began increasing around day 19, peaked at day 21, and then started to decline before increasing again around POD 50. There was no significant difference in peripheral intracellular cytokine-secreting cells (IFN-g, TNFa, and IL-17) after xTX compared to pre-xTX levels. Anti-pig antibody levels in the patient's serum dropped with induction therapy and remained low until POD 47. However, a sharp increase of IgG and IgM was observed to a lesser extent, coinciding with the increase in serum troponin and xenograft failure.

Conclusion: Our study demonstrates that immune monitoring accurately reflects the immune response status of the recipient after cardiac xTX and continuous monitoring will aid in the early detection of rejection even and allow effective intervention.