Role of perioperative cardiac xenograft dysfunction (PCXD) in the (life-supporting) orthotopic (oXHTx) and heterotopic (htXHTx) cardiac xenotransplantation (XT) baboon model on the way to a clinical trial
Paolo Brenner1,2, Bruno Reichart2, Matthias Längin2,3, Martin Bender2,3, Tanja Mayr2, Sonja Güthoff2, Sebastian Michel1, Stefan Buchholz2, Julia Radan1, Maren Mokelke1, Ines Buttgereit1, Elisabeth Neumann1, Andreas Bauer2, Nikolai Klymiuk4, Eckhard Wolf4, Christoph Walz6, Keith Reimann5, David Ayares7, Christian Hagl1, Stig Steen8, Jan-Michael Abicht2,3.
1Dept. of Cardiac Surgery, Clinic of Grosshadern, University of Munich (LMU), Munich, Germany; 2Walter-Brendel-Center, University of Munich (LMU), Munich, Germany; 3Dept. of Anaesthesiology, Clinic of Grosshadern, University of Munich (LMU), Munich, Germany; 4Dept. of Molecular Animal Breeding and Biotechnology, University of Munich (LMU), Munich, Germany; 5MassBiologics, University of Massachusetts Medical School, Boston, MA, United States; 6Dept of Pathology, Clinic of Grosshadern, University of Munich (LMU), Munich, Germany; 7Revivicor Inc., ,, Blackburg, VA, United States; 8Dept. of Cardiothoracic Surgery, University of Lund, Lund, Sweden
Aim: In a life-supporting cardiac heterotopic thoracic (htXTx) and orthotopic baboon XT model (oXHTx) we tried to aim the ISHLT guidelines for clinical XT (90-days-survival of 60%). Specific problems for oXTx like the perioperative cardiac xenograft dysfunction (PCXD, caused by ischemic crystalloid cardioplegia) and cardiac xenograft overgrowth (caused by the quick pig heart growth and hypertrophy) were solved with a new non-ischemic cold preservation (CP) technique and a p.o. growth control. OXTx data were compared with previous htXTx.
Methods: The htXTx`s (Barnard and Losman`s piggyback technique) were done in 19 baboons (Group G1, 2 with CD40Ab), oXTx (Lower and Shumway technique) in 19 cases using GalKO/hCD46/hTMtg pig hearts. Basic IS consisting of ATG, rituximab, mycophenolate, cortisone and CD40mAb. To prevent PCXD as an early cardiac low output due to Bretschneider cardioplegia in Group G2 (n=5) we used a non-ischemic 8oC cold „Steen’s“ perfusion with oxygenated blood in a Group G3 (n=5). To inhibit pig xenograft overgrowth (XOG), antihypertensive drugs (enalapril, metoprolol) and a mTOR inhibitor (temsirolimus) were given in a final group G4 (n=9).
Results: Excluding 5 cases of technical failures in htXTx all recipients were weaned from ECC. Survival after htXTx was 13 and 35 days with CD40Ab and without 2, 4, 7, 9, 12, 14, 16, 17, 19, 19, 37 up to 50 days and after oXTx 1 (n=4), 2 (n=2), 18, 27, 30, 40 days and in G4 15, 27, 51, 90 (n=4),182 and 195 days. Causes of death were in htXTx without CD40Ab 4 cases of delayed xenograft rejection (DXR), myocardial hypertrophy, lung failure and sepsis due to “over”-IS. In G2 3 baboons died of PCXD. In G3 no PCXD occurred and they died of cardiac hypertrophy/liver congestion. Combining CP and (over)growth inhibition, now in G4 6 baboons achieved long-term survival, 4 were actively terminated after 90 days and 2 were extended to half a year (182 and 195 days). Two baboons with pCMV+ donor hearts died of infections (d15, d27). No hyperacute or DXR was observed. All long-term survivors were in excellent physical conditions. In G1 with htXTx PCXD was observed (n=3), but not relevant, since baboons heart supported during PCXD recovering after 48 hours. In G1 in the longer-term, the xenograft (over)growth impedes the lung function. The htXTx model was limited by a rapid growing pig heart in the small right thorax of an adult baboon.
Conclusion: While in previous htXTx PCXD was also found sometimes, it was not relevant and reversible after 48 hours, in oXTX it is a major hurdle. A breakthrough was the non-ischemic cold preservation and overgrowth inhibition to achieve reproducible long-term survival up to 3 (n=4) and 6 months (n=2) which meets the ISHLT guidelines for a clinical phase I study in next years (as bridge-to-allotransplantation or destination therapy). In future also other blood cardioplegia techniques from Buckberg, Calafiore or Del Nido should be tested for xenograft cold preservation.