Orthotopic Hindlimb Transplantation in the Mouse

ABSTRACT

There are many potential advantages to using a mouse as a model for composite tissue transplantation, particularly to examine the mechanisms behind various tolerance induction protocols. The purpose of this study was to evaluate the reliability of a new hindlimb transplant model in the mouse. Fifteen Swiss-Webster mice, 14 to 16 weeks old (35 to 50 g), had syngeneic hindlimb transplants performed. The donor limb was attached to the recipient limb stump first by bony fixation using an intramedullary rod (22-gauge needle, 2.5 mm in length). The venous anastomosis was performed across a stent fashioned from a 27-gauge nylon I.V. catheter tip cover and secured with two simple ties using 10-0 nylon. The arterial anastomosis was performed with interrupted 11-0 nylon stitches. Eleven of the fifteen transplanted limbs survived for the duration of the study (30 days). All four failures occurred within 4 hr postoperatively, (venous thrombosis, n = 2; arterial thrombosis, n = 2). Clamp time decreased throughout the study, averaging 56 min for the final four transplants and 88 min total operative time. Orthotopic hindlimb transplantation can be reliably achieved in a mouse. The mouse model should be useful to the future study of composite tissue allotransplantation.

KEYWORD

Composite tissue transplantation - murine hindlimb transplant

REFERENCES

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Drs. Foster and Liu have reported their model of orthotopic hindlimb transplantation in mice. They successfully transplanted 11 of 15 mice for a survival of 30 days. The average vessel diameter was just less than 0.5 mm. In order to perform the technically challenging venous anastomosis, the authors utilized a ``cuff'' technique, by suturing the ends of the veins across a stent of intravenous catheter. Despite an improved learning curve, the ischemia time was still close to an hour, underscoring the technical difficulty of this model. Nonetheless, operative and ischemic times were improved, compared to traditional anastomotic techniques in the vein.[1]

The use of the operating microscope and development of microsurgical techniques have been ongoing since the 1950s and 1960s. The first successful human upper-extremity replantations were performed in the 1960s.[2] The use of free-tissue transfer was pioneered in the 1970s and 1980s, and is now part of the plastic surgeon's armamentarium. Therefore, the technical challenge of clinical tissue replantation or transplantation has been met. The next challenge is overcoming the immunologic barrier.

The first successful human organ transplantation was performed by Dr. Joseph E. Murray in 1954[3]; since that first step, solid organ transplantation has become a reality in modern medicine. The next frontier is composite tissue allotransplantation (CTA), such as hand transplantation. As stated by Drs. Foster and Liu, the clinical application of CTA would include using muscle, skin, nerve, and other tissues for the treatment of difficult wounds, in which donor-site morbidity can be avoided. However, while solid organ transplantation is a life-saving procedure, the benefits of CTA will be improvement in the quality of life and limb salvage. The ethical debate is whether the benefit of CTA will justify the potential risks of immunosuppression.[4] In a perfect world, the recipient would be induced to develop selective tolerance to transplanted tissue without the need for immunosuppression.

For decades, rats have been used as surgical models for transplantation. But most immunologic assays, antibodies, and proteins, as well as knockout animals, have been developed in mouse models. A challenge in the laboratory has been the development of appropriate surgical models in mice, although their small size poses significant technical difficulties. The authors are to be congratulated on the development of their mouse model, using the cuff technique with decreased ischemic and operative times. The effects of pharmacologic and immunologic manipulations on the survival of the allograft can be studied in this model. Perhaps the authors would consider performing nerve anastomoses: long-term results in the transplanted limb should include function (or lack thereof) of the allograft.

Last but not least, a mouse model of limb transplantation illustrates the importance of collaboration between basic scientists and surgeon-scientists. The surgeon has the technical know-how to perform the operation, and the basic scientist can manipulate the immune system in the model. This cooperative effort can serve only to improve our understanding of the science and physiology of transplantation biology.

REFERENCES

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