Steven Little1
University of Pittsburgh1
Steven Little1
University of Pittsburgh1
<b>Introduction</b><br/>Vascular composite Allograft (VCA) transplantation (Tx) involves the Tx of a functional unit of multiple tissues, such as skin, muscle, tendon, nerve, and bone. VCA, such as hand transplants, have tremendous potential to restore normal form and function (body integrity and sensory-motor ability) for amputees (such as wounded warriors) lacking conventional reconstructive or prosthetic options. Despite encouraging patient and graft survival, the widespread application of the life-enhancing benefits of VCA has been hampered by the toxicity and complications associated with high-dose, multi-drug immunosuppression, which are highly toxic and cause kidney and heart failure. We have recently developed a platform called <b>S</b>ustained-release, <b>M</b>icroparticle-based, <b>A</b>nti-<b>R</b>ejection <b>T</b>herapy through <b>E</b>nhancement of <b>R</b>egulatory T-cells (<b>S.M.A.R.T.E.R.</b>) Platform for VCA Immunomodulation that takes advantage of the body’s own regulatory functions instead of suppressing the entire immune system. Indeed, these formulations mimic a strategy used by tumors to avoid immune rejection. We have shown that these systems can effectively recruit Tregs toward the site of injection in vivo, with these recruited Tregs demonstrating significant promise for promoting local immunological homeostasis. Here, we propose this S.M.A.R.T.E.R. platform in the context of VCA for the establishment of tolerance of transplants.<br/> <br/><b>Methods</b><br/>The S.M.A.R.T.E.R. platform consists of safe, biodegradable polymer (poly(lactic-co-gylcolic)acid) microspheres that are engineered to either sustain a gradient of a Treg-recruiting chemokine (CCL22) or release a combination of three Treg inducing factors (TGF-beta, IL2, rapamycin) at the local site of injection. Formulations were fabricated using a double emulsion method and characterized for size, morphology, drug loading, release, and bioactivity. Blank formulations (unloaded polymer microspheres) were prepared as a control. Formulations were applied subcutaneously to rat full hind limb allografts (Brown Norway to White Lewis) at both the time of transplant and 3 weeks post-transplant. ALS and FK-506 were applied at the time of transplantation, with FK-506 being removed at day 21. Rats were monitored for signs of rejection out to 300 days post-transplant. In addition, both brown Norway (donor antigen) and Wistar Furth (3<sup>rd</sup> party) skin transplantation was performed on long term survivors to probe for systemic dominant tolerance.<br/> <br/><b>Results</b><br/>ALS and FK-506 immunosuppression removal resulted in 100% graft rejection in all untreated and blank carrier groups. Rats treated with the S.M.A.R.T.E.R. platform showed over 90% long term survival (post 300 days). White Lewis survivors treated with the S.M.A.R.T.E.R. platform accepted Brown Norway skin transplants with no systemic immunosuppression, but robustly rejected skin transplants from Wistar Furth rats.<br/> <br/><b>Conclusion/Impact</b><br/>The proposed S.M.A.R.T.E.R. platform is a powerful strategy in inducing survival and systemic dominant tolerance in the most difficult and immunogenic transplantation model (VCA) and would represent a way to avoid the life-long systemic immunosuppression that currently follows VCA procedures.