Introduction: With 50% perioperative cardiac xenograft dysfunction (PCXD) frequently occurred after ischemic crystalloid cardioplegia (Bretschneider) in oXHTx. This is a major hurdle for long-term survival in a life-supporting orthotopic cardiac pig-to-baboon xenotransplantation (XT) model (oXHTx). A great breakthrough was to prevented this by using a new non-ischemic cold preservation technique from Stig Steen. The oXHTx data of PCXD were compared with our previous heterotopic thoracic (htXTx) model. The common problem of the xenograft „over“growth (XOG) had to be solved with antiproliferative drugs.

Methods: In a group G1 (n=19) „piggyback heart“ technique of htXTx from Barnard and Losman was used in baboons (2 with CD40Ab). OXTx using GalKO/hCD46/hTMtg pig hearts was performed in another 19 cases. Immunosuppression (IS) consisted of rituximab, ATG, mycophenolate, cortisone and a CD40mAb for costimulation blockade. As an early cardiac low output the PCXD in the oXTx group G2 (n=5) was prevented in a group G3 (n=5) by using a new, non-ischemic 8^oC „Steen’s“ cold perfusion (CP) technique with oxygenated blood. For xenograft overgrowth inhibition (XOGI) in a final preclinical group G4 (n=9) the mTOR inhibitor temsirolimus and antihypertensive drugs were applied.

Results: All baboons were weaned from ECC. Technical failures (n=5) in htXTx were excluded. In the htXTx model survival was 13 and 35 days with CD40Ab and without 2, 4, 7, 9, 12, 14, 16, 17, 19, 19, 37 up to 50 days. Survival after oXTx was 1 (n=4), 2 (n=2), 18, 27, 30, 40 days and G4 15, 27, 51, 90 (n=4),182 and 195 days. Four baboons in htXTx group G1 died of delayed xenograft rejection (DXR) and sepsis due to an “over”-IS, 3 baboons in G2 died of PCXD with Bretschneider cardioplegia. After CP in G3 no PCXD was found and they died mostly of liver failure and cardiac overgrowth. In the preclinical group G4 combining CP and XOGI four baboons were terminated at day 90 and two survived 182 and 195 days, 2 died (d15, d27) of sepsis with pCMV-positive donor hearts. All baboons were in excellent general conditions. No hyperacute and DXR was found. PCXD was also registered in G1 (htXTx) in a low pressure curve inside the xenograft (n=3), but was in hemodynamics not relevant, because the baboons own heart supported during PCXD, which disappeared after 48 hours. In total the htXTx model was limited by a rapid growing pig heart in the small right thorax of the recipient compressing the right lung.

Conclusion: In the htXTx group G1 we could also find signs of PCXD indirectly, but it was not relevant and reversible after 2 days, but in oXTx it was a major problem. The essential progress is the CP and XOGI in terms of long-term survival, which now fulfills the ISHLT guidelines (90-days-survival of 60%) for a clinical phase I trial. CP was also used in the compassionate use patient in Baltimore 1/2022. Also other blood cardioplegic solutions like Buckberg, Calafiore or Del Nido must be tested for future XT.