Completed Preclinical Life-Supporting Orthotopic Pig-to-baboon Cardiac Xenotransplantation Study (oXHTx): First Successful and Reproducible Long-Term Survival Up to Half a Year Fulfilling the ISHLT Prerequisite for Clinical Cardiac Xenotransplantation

Objectives: The ISHLT advisory board guidelines for XT recommend a 90-day survival of minimal 60% (6 of 10 baboons) in a life-supporting orthotopic pig-to-baboon model (oXHTx) as a prerequisite to begin a clinical cardiac XT program. For that aim, we reproduced an excellent survival of transgenic pig hearts up to 945 days of a non–life-supporting heterotopic abdominal model (Mohiuddin et al, Nat Commun 2016;7:11138) in our life-supporting orthotopic model with the same CD40mAb costimulation blockade immunosuppression (IS). Other problems typically for oXHTx like the early perioperative xenograft dysfunction (PCXD) and cardiac xenograft overgrowth were solved with a new nonischemic cold organ preservation technique and a p.o. growth control by antihypertensive and antiproliferative drugs.

Methods: We performed eight orthotopic heart XT in baboons with GalKO/hCD46/hTM transgenic (tg) pig hearts using a basic IS consisting of ATG, rituximab, mycophenolate (MMF), cortisone, and 50 mg/kg CD40mAb (mouse/rhesus-Ab). To avoid PCXD as a kind of early cardiac low output, we replaced the crystalloid cardioplegia with a nonischemic 8-degree cold perfusion solution with oxygenated erythrocytes. To prevent pig xenograft overgrowth and hypertrophy, antihypertensive drugs (enalapril, metoprolol) and a mTOR inhibitor (temsirolimus) as antiproliferative drugs were applied.

Results: If compared to our previous group with crystalloid cardioplegia (Längin et al, Nature 2018;564:430–433), no PCXD was found in this group with nonischemic cold perfusion. One baboon died on day 14 of a pancreatitis, another on day 26 of kidney failure/sepsis. With successful therapy of xenograft (over)growth, hypertrophy, and diastolic LV failure, all other six recipient baboons were long-term surviving (four were actively terminated after 90 days according to the guidelines of our government). Two further experiments could be prolonged up to 182 and 195 days. All baboons lived under excellent physical conditions and no hyperacute rejection or DXR was observed.

Conclusion: In the last 2 years after 25 years of experimental research in oXHT of multi-tg pig hearts, we have achieved a major progress and the essential milestone and breakthrough with this group realizing a constant reproducible long-term survival of 3 to 6 months. Thus, currently the prerequisites according to the ISHLT for beginning a clinical phase I study are fulfilled and pave the way to clinical cardiac XT in the next 2 to 5 years.