OBJECTIVES OF PRESERVATION
Effective preservation is a requirement of techniques which involve transfer of viable organs and tissues. Graft damage must be minimized while the organ is still within the donor in preparation for graft procurement, during graft removal, during storage and transport of the graft, during the transplantation operation, and after reimplantation or revascularization. Some tissues, such as blood and skin, can be stored for several days or weeks. Vascularized autografts are usually reimplanted immediately, or within a few hours.
Allografts pose another problem. Not only must viability be maintained, but rejection of the grafts must be prevented by optimizing the match between donor and recipient tissue and by immunotherapy. These two objectives—preserving viability and preventing rejection—are closely linked. Optimal matching of antigens of graft and recipient requires a storage period of 24 h or more. Until recently storage for this length of time was only practicable for kidneys, but as prolonged storage becomes available for liver, pancreas, and heart, these grafts may also be allocated on the basis of improved tissue matching. Retrospective analysis has indicated that matching would improve the efficacy of cardiac transplants but this would require prolongation of the storage period beyond the current safe period of 6 h.
The process of clinical preservation usually begins with identification of the brain-dead, heart-beating cadaver donor. Effective preservation allows time for confirmatory tests of brain death, organization of operating teams for organ removal, typing and cross-matching of donor tissues against a pool of waiting recipients, excluding associated transplantable diseases such as infection or neoplasm in the donor, selecting and locating recipients and arranging their admission and preparation for surgery, arranging recipient operating teams, and time to transport organs over long distances, even between continents.
Good preservation also provides a window of diagnostic and therapeutic opportunity during the safe period of extracorporal storage. The time gained should be available for functional assessment of the graft to confirm its viability, and to predict early function after reimplantation. Good early function is obligatory in the case of heart and liver grafts. Immediate function of kidney and pancreas grafts, although not obligatory, is highly desirable and facilitates recipient management.
Effective immune manipulation of the recipient or of the graft itself during the period of storage is another (as yet largely unrealized) objective. Treatment of the stored organ to deplete it of antigen presenting cells, or other treatments to modify parenchymal and endothelial cell immunogenicity, could dramatically improve transplantation results.
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