The goals of this research program are to understand the molecular and cellular basis of graft-versus-host disease (GVHD), and to use this understanding to prevent the toxicity and mortality caused by GVHD. This application takes advantage of mouse models of human stem cell transplantion, in which we have shown that host antigen presenting cells (APCs) rapidly prime antigen-specific donor T cells that will later go on to cause phenotypic GVHD. Moreover, we have new evidence that APC-T cell activation is a multi-step process, which may allow decisive intervention by targeting each of these activation steps. To most directly explore and exploit these findings, we propose to investigate: 1) The relative contributions of distinct APC subsets (dendritic cells, macrophages, B cells, and activated endothelial cells), and of host- versus donor-derived APCs, to initiating GVHD; 2) The immunoregulatory signals by which APCs stimuate allogeneic T cell survival essential for subsequent T cell activation, proliferation and differentiation in vivo; and 3) Whether ex vivo selection of host miHA-acivated donor CD44hiCD8+ T cells, or in vivo blockade of APC-donor T cell linteractions, can effectively prevent GVHD. These studies will establish the preclinical basis for therapeutic approaches targeting APCs for the prevention of GVHD. Based upon the results of these studies, our long-term goal is to develop the appropriate reagents to target human APCs, including DCs and macrophages, at the cellular and/or molecular levels, to prevent GVHD in clinical trials.
