Current evidence suggests that allosensitized T cells are potent accelerators of the chronic rejection histopathology (CRHP), especially transplant vascular sclerosis and interstitial fibrosis. However, the exact mechanisms by which T cells promote CHRP remain ill-defined. In addition, better in vivo experimental models need to be developed for the study of these disease processes. These are the broad goals of the proposed studies. The specific goals of the studies are: 1) To evaluate the contributions to CRHP development of graft-reactive T cells from the spleens of allograft-tolerant mice. These splenocytes have lost the ability to promote acute rejection but actively promote CRHP. Isolated splenocyte subsets will be transferred into SCID mice bearing cardiac allografts to determine how T cells and B cells contribute to CHRP development. CRHP will be measured by immunohistology and computerized morphometry. These studies are designed to test the hypothesis that both CD4+ and CD8+ T cells can promote CRHP development via mechanisms that are independent of B cells and alloantibody production. 2) To identify the splenic T cell subsets in naive mice that contribute to CHRP development. Isolated splenic T cells subsets from normal, IFNg- knockout, or IL4-knockout mice will be transferred into immunosuppressed SCID mice or B cell-reconstituted SCID mice prior to cardiac transplantation, and CRHP development will be monitored as before. These studies are designed to test the hypothesis that self MHC-restricted CD4+ T cells promote CHRP directly by producing IFNg, and possibly IL4. 3) To use gene transfer techniques to confirm the contributions of IFNg, IL4 and PDGF to TVS development in murine cardiac isograft recipients. Plasmid expression vectors containing a reporter gene, b-galactosidase, plus the gene for PDGF, IFNg or IL4 under the control of constitutive viral promoters have been produced. Cardiac vasculature will be transfected with these plasmids in association with immunoliposomes prior to transplantation into syngeneic recipients. Post-transplant changes in graft histology and composition will be measured by computerized morphometry, and the expression of relevant growth factors and cytokines will be measured by RT-PCR. These studies are designed to develop and field test new experimental approaches for the study of chronic rejection. They will also test the hypotheses that a gamma PDGF promotes the terminal stage of chronic rejection, b) that IFNg promotes chronic rejection by its influence on PDGF production, and 3) that IL4 promotes chronic rejection by its influence on alloantibody and collagen production. 4) To use these cell and gene transfer models as a panel of related test systems with which to systematically dissect the in vivo effects of rapamycin and angiopeptin on CHRP development in murine cardiac allografts. These studies will field test this analytic system for future use in evaluating the effects of new agents on key elements in the CRHP development cascade.