20. Molecular approaches to improving hypothermic biopreservation of cells and tissues

The utilization of biopreservation strategies continues to grow at a rapid pace as advances in fields such as cell therapy, stem-cell research, personalized medicine, organ transplantation, etc. drive the need for improved storage and shipment of living products. Given the complexity of biologics, hypothermic preservation (4–10 °C) remains the preferred approach for short term (hours to days) maintenance enabling holding and transport under controlled conditions. Numerous reports have detailed the benefits of hypothermia to suppress physiological activity at the cellular level thereby extending the window of viability. Pivotal to the success of hypothermic preservation has been an understanding of the metabolic, biochemical and physical characteristics of cells both in their normothermic environment and how these factors change during hypothermia. The translation of this understanding is best exemplified by the advancements in preservation solution design. Through the application of knowledge pertaining to cell system response to cold stresses, the first intracellular-like cold-perfusion solution, University of Wisconsin solution (UW or Viaspan), was developed and has become the gold standard hypothermic storage medium. The success of this approach evolved, leading to the development of improved solutions such as Celsior, HTS, and Unisol among others; however, there remains a significant void that solution design alone cannot bridge. The recent discovery of molecular components to preservation failure has served to complicate our understanding and slow technological progress due to the complex nature of the responses involved. To this end, several fundamental discoveries related to the molecular response of cells to cold stress have recently been reported, including the co-initiation of apoptotic cell death and cell survival responses, the characterization of specific genes and pathways involved and the identification of specific stress related trigger events resulting in cellular demise. As studies have begun to uncover the specific molecular responses involved, they have identified a wide array of targets whose modulation can improve preservation outcome. Numerous reports have described the benefit of the incorporation of protective agents, such as specific inhibitors, into the preservation medium to achieve targeted molecular control thereby improving outcome. This presentation will provide an overview of the molecular-based discoveries in the area of hypothermic preservation with focused discussion on the recent discovery of the differential activation of the UPR (unfolded protein response) pathway and its impact on the response of cells and tissues to cold storage. Given what is now known about the complexity of the preservation process and the multitude of stresses induced, it is clear that future advances will only be accomplished through multifaceted approaches. This is evident when examining the current literature, as reports on cell preservation have moved from classical cell biology to include aspects of other disciplines including molecular biology, biochemistry, genomics, proteomics, etc. With continued advancements in our understanding of the molecular response of cells to cold, a more individualized and targeted approach may be achieved moving us further along the path toward improving the quality, usability and extend the storage interval of highly complex and specialized biologics.