High subzero preservation of liver for transplantation

ABSTRACT With more than five times the number of patients on the wait list than will receive a donor organ in the USA, the field of transplantation is facing a serious donor shortage crisis. Despite decades of research, a major critical bottleneck is the current preservation times for whole organs are limited to few hours of storage. Longer preservation times are required to enable global matching programs, eliminate unnecessary waste of organs, and reduce costs associated with unplanned surgeries, and are enabling for mixed-chimerism based tolerance induction protocols which require the donor organ to be kept viable for days so that recipient preconditioning can be done safely. Consequently, the focus of this application is to address a major unmet need in transplantation by prolonging the length of time organs can be kept in “suspended animation” ex vivo. Our approach is inspired by the hibernating and freeze-tolerant animals in nature. We aim to embrace and control the ice formation to achieve high subzero storage temperatures in the presence of extracellular ice, and storage durations of weeks to ultimately months. It is our hypothesis that the presence of ice in a non-injurious frozen state enables storage at lower temperatures (down to -30°C) and consequently a deeper metabolic stasis for weeks, while also enabling scale-up to human organs. In the previous funding period, we developed a new method to use ice nucleating bacteria to tightly control ice formation temperature and developed a partial freezing protocol down to -15°C that can store rat livers up to 5 days with ex vivo function, and also established a proof-of-concept in human livers. In this competing renewal application, we propose to build on our success and reach preservation temperatures down to -30°C, thus achieving suspended animation for weeks. We propose (i) to control ice formation in liver, which our prior studies demonstrated to be a key barrier; (ii) to develop targeted approaches to improve preservation of endothelium, which are at the interface of tissue and ice and are the first point of injury, and (iii) to develop a choreographed metabolic protocol to maximize ATP recovery and improve viability of the grafts for transplant.