811 Histological evidence of acute rejection after terminating anti CD40 antibody (2C10R4) treatment in GTKO.hCD46.hTBM pig to baboon cardiac xenografts surviving for over one year
Wednesday November 18, 2015 from 15:30 to 17:00
Room 109

Muhammad M Mohiuddin, United States

Chief, Transplantation Section

Cardiothoracic Surgery Research Program



Histological evidence of acute rejection after terminating anti CD40 antibody (2C10R4) treatment in GTKO.hCD46.hTBM pig to baboon cardiac xenografts surviving for over one year

Justin Miller1, Avneesh Singh1, Michael Eckhaus2, Philip Corcoran1, Marvin Thomas2, Billeta Lewis2, Keith Reimann3, David Ayares4, Keith Horvath1, Muhammad Mohiuddin1.

1Cardiothoracic Surgery Research Program, NHLBI /NIH, Bethesda, MD, United States; 2Division of Veterinary Resources / ORS, NIH, Bethesda, MD, United States; 3University of Massachusetts, Boston, MD, United States; 4Revivicor, Inc, Blacksburg, VA, United States

Introduction: The development of genetically modified pigs and targeted immunomodulation with antibody therapy has helped significantly in advancing the field of xenotransplantation. We report the histological results from a series of five heterotopic pig cardiac xenografts in baboons with short-term (ST) and long-term (LT) graft survivals with modified anti CD40 antibody (2C10R4) therapy.
Methods: Five baboons, weighing between 14 and 18 kg received a heterotopic heart transplant from genetically modified pigs with alpha 1-3 galactosyltransferase knockout (GTKO) and expressed human CD46 (hCD46) and Thrombomodulin (hTBM) molecules (Revivicor, Inc., Blacksburg, VA). The immunosuppressive regimen consisted of cobra venom factor, anti CD20 antibody, thymoglobulin, MMF), Methylprednisolone (2mg/kg tapered off in 4-6 weeks), and 2C10R4 (50mg/kg on d -1, 0, 5, 9, 14 then once weekly). The three ST animals had their 2C10R4 dose reduced from 50mg/kg to 25mg/kg at 100 days post-transplant. The two LT animals had their dosages reduced at one year and later weaned off completely. Open cardiac biopsies were performed in the longest survivor of the ST animals, and open cardiac biopsies were taken periodically throughout the LT animal’s survival to assess for any changes that might suggest rejection. Histology of the rejecting grafts was compared with the previous biopsy samples.
Results: The grafts in ST animals survived for 146, 159, and 298 days and in LT animals for 616 and 945 days. The ST group grafts rejected 46, 59, and 198 days after decreasing dose of 2C10R4. The LT group grafts survived for 251 and 580 days after decreasing the dose and rejected 56 and 93 days after stopping the antibody treatment. Histology was remarkable for no evidence of thrombotic microangiopathy (TM) myocyte loss, fibrosis or cellular infiltration in the ST or LT animals prior to reducing 2C10R4. There was also no evidence of these findings in the LT animals until the discontinuation of the 2C10R4. In samples taken from the ST necropsy, there was histological evidence of TM, myocardial coagulative necrosis, myocyte loss, hemorrhage and fibrosis. In LT grafts there was acute TM and vasculitis with diffuse myocardial necrosis and epicardial hemorrhage, with minimal to mild or no interstitial lymphocytic infiltrates.
Conclusions: Histological examination was able to confirm the role of anti CD40 (2C10R4) antibody in the survival of xenografts. Only when the 2C10R4 dose was decreased in ST animals or discontinued in LT animals, the grafts were acutely rejected with histological evidence of TM and diffuse myocardial necrosis. Despite of presence of cellular infiltrates in some areas, no evidence of chronic cellular rejection was found.

Division of Veterinary Resources / ORS, NIH. NHLBI Animal Surgery and Resources.

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