Extended preservation of human livers: a nature inspired, high subzero controlled, limited freezing approach

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ABSTRACT 1 in 5 liver waitlist patients do not receive a new liver in time, while many more patients are never listed but could benefit from liver replacement. While “bridge-to-transplant” technologies (ventricular assist devices and dialysis) have transformed the outlook for heart failure and kidney failure, no such treatment exists for patients with liver failure. Current liver sharing limits (approx. 500 miles) are based on limited preservation durations (6-10 hours). By extending preservation to just a few days we can enable nationwide (theoretically global) donor-recipient matching, allowing many livers that go untransplanted today (e.g. subsets of extended criteria donor livers that have been shown to offer substantial survival benefits) to be offered to the patients who most need them. Transplant surgeons have expressed excitement about this possibility, and it is thought that this achievement would have a profound impact on liver waitlist mortality. Among other benefits, this can also increase graft lifespan and reduce immunological rejection, eliminate the need for costly jet and helicopter transport, transform the practice of liver transplantation from emergency surgery to a flexibly scheduled procedure, and mitigate the severe disparities in liver transplantation. It will also allow immune tolerance induction protocols that have now achieved success in living donation to be adapted to the deceased donor context. To meet these needs, we will develop a comprehensive system for banking human livers for transplantation for periods of 5-7 days with a stretch goal of 10+ days or longer. We have created an integrated two-pronged approach to develop new stasis cocktails optimized for the critical phases of liver preservation: preconditioning and protection (prior to storage), preservation (during storage) and revival- resuscitation-repair (after storage). In parallel, we are creating devices for advanced perfusion, storage, and organ assessment before transplant decision. Our approach adapts the best strategies of freeze-tolerant and hibernating species, augmenting them with recent scientific and bioengineering advances. Importantly, we do not seek to solve all the problems of classical cryopreservation, but rather to be the first to develop preservation in thermodynamic equilibrium at high subzero (HSZ) temperatures (-10°C to -30°C), combined with programmed metabolic depression and enhanced stress tolerance. Feasibility of this approach has already been demonstrated; we have banked rat livers for 5 days at HSZ temperatures, and successfully preserved the first whole human liver lobe at -15°C. For this fast-track proposal, the Phase 1 goal will be to further refine our protocols and validate our initial unprecedented storage duration by banking rat livers for 5-7 days and using comprehensive post-preservation normothermic machine perfusion with functional assessment. We will also scale to whole human liver lobes, with subsequent hepatocyte isolation. Phase 2 will focus on optimizing key parameters that affect preservation outcomes in rat and human livers. Our goal is 6-10+ days of storage via (i) optimal modulation of ice growth, (ii) nature-inspired de-toxify/reenergize perfusion phase and (iii) precise control of thermodynamics using a prototype Bio-Thermodulator device.