The preservation of tissues for transplantation.

This paper is a written version of a lecture given during the celebration of Professor Rudolf Klen's 90th birthday. Dr. Klen played by far the major part in the introduction and the development of Tissue Banking in Europe. His concept of a tissue bank envisaged the storage of all types of cell, tissue and organ that physicians and surgeons might need for the treatment of their patients. There has been much progress towards this goal, but still the final objective remains elusive. This review of the current position starts with the recognition that some tissues are required to comprise or include cells that exhibit all the formal characteristics of life if they are to function as grafts, whereas other tissues do not. For some tissues, the preservation of mechanical properties is crucial: for others it is not. These considerations are crucial for the design of preservation methods for specific tissues: bone tendon and skin can provide useful grafts in the absence of living cells and this may even be true of cardiac valves: the crucial requirement here is that the mechanical properties remain intact. Simply freezing at around -80 degrees C may be sufficient. In contrast, many cell systems, and all metabolizing organs do require healthy cells to function. Cryopreservation is often an effective remedy for isolated cells, for example haemopoietic stem cells, but the damaging effects of the formation of ice are sufficient to rule out this approach for whole vascularised organs and for some tissues too. The damaging mechanisms are discussed, and it is concluded that the site of ice crystallization is crucial. Cartilage has hitherto been recalcitrant, but we have recently developed a method that permits this tissue to be stored at liquid nitrogen temperatures without any ice and with the recovery of living cells and intact mechanical properties after storage. Thus, many methods are available to help develop tissue banking originally envisioned by Dr. Klen.