Research

Microsurgery Studies Focus on Induction of Transplant Tolerance and Return of Function

The Microsurgery Laboratory of the Department of Plastic and Reconstructive Surgery has a broad research focus and includes studies related to the following categories:

Transplantation

The major focus of our Microsurgery Laboratory has been on induction of tolerance in composite tissue allografts. CTAs comprise a combination of skin, subcutaneous tissue, neurovascular tissue, and mesenchymal tissue such as bone,muscle, fascia and cartilage (e.g., the hand, knee joint or larynx). Although “nonvital to life,” these tissues are structurally, functionally and aesthetically important to those who specialize in functional restoration of musculoskeletal defects.Most attempts at composite tissue transplantation have been unsuccessful, which illustrates the difficult barrier associated with vascularized allografts composed of a variety of tissues. Several experimental designs of tolerance induction have been reported. Side effects related to these protocols limit their use to only carefully selected applications.

Our recent approach to induce tolerance is based on the pivotal role of T cells in allograft rejection. To create a window of immunological incompetence, we are investigating the possibility of specifically eliminating alphabeta- T-cell receptor-positive cells, which confer the ability to reject allograft tissues.We achieved significant depletion of this T-cell population at the end of immunodepleting therapy and observed the potential for repopulation of the recipient T cells’ repertoire once the treatment protocol was stopped. This allowed for over 700 days of allograft survival without chronic immunosuppression.

The functional outcome of CTAs is assessed by our standardized technique, including clinical tests and electrophysiological methods.We evaluate the hemodynamics of the rejecting and surviving allografts at the microcirculatory level using our intravital microscopy system.Microvascular permeability is monitored following FITC albumin injection under fluorescence microscopy.

Our newest approach is directed toward evaluating the role of bone-marrow-derived stem and proprietor cells in tolerance induction following vascularized bone-marrow transplantation. These findings will increase our understanding of mechanisms involved in CTA rejection, tolerance induction, development of GVHD and optimization of clinically applicable treatment protocols.

Microcirculation

Our work focuses on ischemia-reperfusion injury and the hemodynamic effects of TNFalpha, VEGF 165 and angiopoietin 1 on the cremaster muscle’s microcirculation. Our intravital microscopy system measures RBC velocity, vessel diameters, capillary density and leukocyte endothelial interactions (rolling, sticking, transmigrating leukocytes), and endothelial edema index as we evaluate vascular permeability. The new cremaster muscle transplantation model was established and is tested in TNF-alpha Receptor I, II and I + II knock-out mouse models.

Nerve Regeneration

We are evaluating different surgical techniques used for enhancing nerve regeneration.We are studying the effect of Cyclosporine A on nerve degeneration, as well as the effect of different enhancing factors (such as DHEA and VEGF 165) on nerve regeneration in normal and diabetic rats, using the standard clinical and functional tests, such as somatosensory evoked potentials, motor evoked potentials, walking track analysis, pin-prick test, and toe spread test. Nerve morphometry of EM sections is assessed by our computerized system, which measures total number of myelinated axons, axon diameters, cross sectional area and myelin thickness.

Wound Healing

This category involves the induction of angiogenesis in abdominal skin flaps and a limb ischemia model by the recombinant adenovirus VEGF 165. The effect of pre-operative vs. post-operative radiation on wound healing is studied on the rat TRAM flap model.

Biomechanical Engineering

We are participating in the development and evaluation of the tissue oxygen sensor for monitoring of free flaps and compartment syndromes in cooperation with Norfolk Engineering Company in an NIH-funded study.

Microsurgery Courses

All residents of CCF surgical specialties are trained in basic microsurgical techniques during 1 week (40 hours) of CME-approved courses. In addition, physicians from other U.S. residency programs (Ohio, New Jersey, Alaska, and Tennessee) and from Europe and Asia are being trained.