Each year in the United States more than 450,000 patients are treated for burn injuries with close to 30,000 hospitalizations in specialized burn centers. Human skin allografts are commonly used for temporary wound closure in severely burned victims to promote rapid healing. However, the intense antigenicity of skin allografts drives powerful anti-graft immune responses. Cell-to-cell interactions between donor and recipient leukocytes in skin-draining lymph nodes dictate the magnitude of rejection. Survival of skin allografts can be prolonged by giving transplant recipients immunosuppressants. But patients exposed to these drugs are at high risk for opportunistic infections. An unmet need is an effective strategy to suppress rejection of skin allografts without the need for high doses of immunosuppressants. In this project we propose to engineer selective immuosuppression by exploiting the different class II major histocompatibility complex (MHC) molecules between donor and recipient cells. To accomplish this, we will use a novel biomaterial system by which donor leukocytes are detained at the host-graft interface. Because only donor cells are targeted, the intervention is a form of targeted immunotherapy. The central hypothesis is that the anti-donor MHC injectable system we developed will attenuate rejection of skin allografts by impeding donor leukocytes trafficking to recipient lymph nodes. The system entails a low viscosity mixture of amphiphilic peptides ("EAK16-II" and its histidinylated analogue "EAKIIH6") and linker proteins (anti-H6 antibody and protein A/G). By tethering the components onto the His-tagged (EAK16-II/EAKIIH6) membrane antibodies are localized and oriented (Biomaterials, 2011, 32:249). Leukocytes emigrating from donor skins are detained on the membrane through interactions with anti-donor MHC-II antibodies. The reduced trafficking is expected to prolong survival of the skin graft sufficiently meaningful in burn treatment. We have evidence to show that the system is stable in vivo. Membrane-localized antibodies remain at injection site for at least 6 days, at concentrations significantly superior to antibodies injected in saline (Molecular Pharmaceutics, 2013, 10:1035). In addition, preliminary studies show that placing anti-donor MHC-II membranes at the graft-host interface significantly reduced donor leukocytes accumulation in recipient lymph nodes. This intervention resulted in attenuated T cell activation in the same mice. These published and preliminary data support the central hypothesis.
Three aims will be carried out to advance the strategy in a well-characterized mouse skin transplant model.
Aim 1 will serve to optimize anti-MHC-II antibody density and spacing on membrane with respect to cell capture in vitro.
In aim 2 we will validate the mechanism of impeding donor cell trafficking in vivo.
In aim 3 we will test the system for immunological endpoints by which comparison against a mainstay immunosuppressant will be made. The investigators have a track record of collaborative activities with combined expertise in macromolecule drug delivery (Meng), surface chemistry (Gawalt), immune analytics (Giannoukakis), and cell tracking (Waggoner). The public heath impact lies in leveraging an enabling technology by which acute rejection and serious infections in skin transplant patients can be mitigated. The research will be an important influence in the field of immune modulation because a pertinent animal model is used to test an original concept to overcome a major obstacle in burn wound care. The innovation lies in the ability to display antibodies through environmentally-responsive peptide co-assemblies. The platform is versatile;antibodies targeting other surface immune molecules can be displayed, thereby increasing the scope of the modulation.
This R21 project leverages a novel enabling technology that has the potential to advance substantially research in managing skin allograft rejection. The long-term goal is to improve health outcomes of skin transplant patients by decreasing the need for high-doses of non-specific immunosuppressants. Because the research team has hands-on experience with all techniques proposed, the studies can be completed within the two-year timeline. Successful completion of the study will render mechanistic understanding of the materials system, resulting in formulations optimized for performance.