Subnormothermic Ex Situ Limb Perfusion Using Red Blood Cells and Plasma: Critical Component Analysis
Abstract
The long-term objective of this application is to keep vascularized composite tissues viable at or beyond 48 hours using ex-vivo perfusion systems. This goal is directly in line with the FY19 RTRP focus area of developing or advancing an existing innovative ex vivo tissue perfusion strategy to extend the timeline between procurement and transplantation. Vascularized composite tissues consist of skin, muscle, bone, tendon, vessels, and nerves. These are used to reconstruct hand, face, abdominal wall, uterus, and penial defects. At room temperature, these tissues can only survive 4 hours without blood flow. It can be extended up to 6 hours if the part is preserved at 4 °C. This time limit imposes significant logistic challenges in VCA transplantation. Once a potential donor is identified, all standard tests and preparations need to be performed in a few hours. If a decision is made to move forward, procured hand or face needs to be transplanted to the recipient, ideally within 4 hours. Beyond that time without blood flow, tissue loses its viability and no longer functions. To minimize this damage, surgeons use static cold preservation methods to reduce tissue metabolism, which fails beyond 6 hours. This time constraint imposes a single-center approach, narrowing down the choice and limiting the search for suitable recipients. Moreover, cold preservation of tissues, although it may reduce the metabolic rate initially, may result in other immunologic disturbances including chronic rejection of those grafts in the long term. In this application, we propose to use various components of the human blood under sub-normothermic (21-24°C) temperatures using established methods of pulsatile ex-vivo perfusion systems. There is no doubt that full blood is the best perfusate perfected after billions of years of evolution. Human blood consists of red blood cells (RBCs), white blood cells (WBCs), platelets, and plasma. The use of full blood as a perfusate is not practical, and WBCs may trigger an immune response. Successful removal of WBCs and platelets from whole blood leaves the other two components (RBCs and plasma) behind. This solution makes the perfect perfusate for tissue survival since red blood cells are essential to carry the oxygen, and the plasma contains many proteins and growth hormones essential for endothelial stability. Both red blood cells and plasma are vital for oxygenation, energy production, and survival of tissues. The critical components of the plasma needed for survival of the tissue are not identified previously. Identification of these critical components will have the potential for indefinite survival of tissues, not only for VCAs, but also for other solid organs. Proposed research has a strong potential to be quickly translated into clinical practice as the machine perfusion systems and plasma separation technologies are already in place. Two scientific discoveries are unique to this application. First, we propose to use sub-normothermic temperatures around 21° to 24°C. At this temperature, overall energy expenditure is low, but aerobic metabolism and ATP production are still active. We determined this to be the critical temperature after years of experimentation on metabolic analysis of muscle cells. This temperature is also ideal for plasma performance. Second, we propose to use a paracorporeal (live) animal as the plasma donor to determine the effects of fresh plasma infusion in real time. This system, unique to our laboratory, is modeled after parabiosis research and is the only method to define the role of short acting hormones in maintaining endothelial integrity. Over the course of the last 15 years, more than 100 hand and face transplantations have been performed around the world with an over 90% success rate. Although a third of those transplantations were performed in the U.S., this is far less than the demand on VCA transplantation. For example, there are over 2 mi
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 10, 2021
- Source ID
- W81XWH2010832
Entities
People
- Kagan Ozer
Organizations
- United States Army
- University of Michigan