40 Days Survival after Orthotopic Cardiac Xenotransplantation of Multi-Transgenic Pig Hearts in a Pig-to-Baboon Model with CD40mAb or CD40L Costimulation Blockade and Xenograft Preservation using “Steens” Cold Blood Cardioplegia Perfusion

Abstract

Introduction: We used a non-toxic immunosuppression based on CD40/CD40L co-stimulation blockade in group G1 and additionally to improve primary xenograft function in a group G2 a new non-ischemic myocardial preservation technique to achieve a constant preclinical long-term survival in a life-supporting cardiac xenotransplantation model (pig-to-baboon). Methods: According to the technique of Lower and Shumway 9 orthotopic (OHXTx) heart transplantations were performed in baboons with genetically-modified GalKO/hCD46/hTM transgenic pig hearts. The immunosuppression (IS) consisted of ATG, rituximab, MMF, tapered down cortisone and CD40 antibody or PASylated Fab-CD40L. Because a “perioperative cardiac xenograft dysfunction” (PCXD) played a critical role, cardioplegia with crystalloid solution (Bretschneider solution, 50 ml/kg; G1: n = 5) was replaced in the last 4 cases of G2 by Steen´s “non-ischemic preservation technique”: This 8°C cold myocardial perfusion solution consists of a modified Krebs-Henseleit solution with albumin and 10% erythrocytes, hormones and vasoactive agents (Steen et al, 2016*). Under pressure, flow and temperature control heart is constantly perfused during explantation and storage time, intermittently during implantation, using an independent portable heart-lung-machine. Results: Ischemic time ranged from 112–128 min. Survival in G1 with Bretschneider solution were 3, 1, 30, 1 and 1 day(s). Using non-ischemic preservation technique in G2 PCXD was not observed and the recipients survived 18, 1**, 27 and 40 days. Baboons mostly died of respiratory problems, renal and hepatic failure, one was sacrificed due to a major p.o. neurological deficit**, another died after hematothorax, but no hyperacute or delayed xenograft rejection was found. A problem after 3 weeks was a donor organ (over)growth. All long-term surviving baboons (especially in G2) were in good general conditions. Conclusion: With conventional hypothermic, ischemic heart preservation techniques, perioperative cardiac xenograft dysfunction plays a detrimental role after orthotopic xHTx. This was prevented with the Steen’s “non-ischemic preservation technique, an important step on the way to a long-term survival of 2–3 months as an important prerequisite for cardiac xenotransplantation in a clinical use.