DESCRIPTION: This is a competitive renewal application to further characterize the molecular and cellular facets of host immunity in high-risk corneal transplantation. High-risk corneal grafts are characterized by their rapid and very high frequency of rejection. However, the precise molecular mechanisms that dictate their poor prognosis remain incompletely understood. The goal of the proposed studies is to gain new insights into the mechanisms that distinguish high-risk vs. low-risk transplant immunity. We hypothesize that the induction of immunity in high-risk corneal transplantation is fundamentally distinct from that in low-risk grafts by virtue of (i) enhanced trafficking of antigen-presenting cells into and out of grafts;(ii) altered functional phenotype of these cells rendering them more capable of stimulating T cells;and (iii) unique graft bed characteristics, in particular endowment of lymph and blood vessels, that amplify both the induction and expression of alloimmunity. We propose to pursue four specific aims: 1. Determine the contribution of APC trafficking to indirect sensitization in HR corneal transplants;2. Determine the cellular and molecular factors that regulate egress of APC from HR and LR corneal grafts;3. Characterize contribution of donor epithelium to modulating immuno-inflammatory responses in HR and LR grafts;and 4. Determine the contribution of host bed hemangiogenic and lymphangiogenic responses to HR vs. LR transplant immunity. Our study design relies on using the mouse model of orthotopic corneal transplantation in conjunction with a variety of inbred strains with defined immunogenetics, gene 'knockouts', and transgenics. Interventions, including cytokine, chemokine, integrin, costimulatory, and endothelial growth factor ligand and receptor blockade will be used to gain mechanistic insights. The long-term objective is to use the information derived from these projects to develop new prophylactic and treatment strategies to promote high-risk graft acceptance. The overall health relevance of this research is that corneal grafting represents by far the number one form of tissue transplantation performed in the United States. However, most high-risk patients reject their grafts and the immunosuppressive strategies currently in use are associated with significant toxicity and side-effects.