Mesenchymal Progenitors of Intragraft Fibroblast

Children'S Hospital Los Angeles, Los Angeles CA

Investigators

Abstract

Recent observations indicate that fibroblasts of recipient origin may actively participate in the development of chronic allograft rejection. Recipient-derived fibroblasts have been showed to contribute to fibrosis in human renal transplants as well as rodent heart allografts. These exciting findings could impact human health care in a positive way: if the progenitors of graft-proliferating fibroblasts are identified, new strategies aiming at inhibition of these cells will become possible for the treatment of chronic rejection. In order to appreciate this potential, the scientific community must determine the phenotype(s) of the mesenchymal stem cells (MSC) that give rise to intragraft fibroblasts, and must understand the mechanisms that control their homing to allografts. The central hypothesis for the research proposal is that proliferating intragrafl fibroblasts are derived from mesenchymal progenitors of host origin, which are committed de novo in the bone marrow, released into blood circulation, attracted by local factors to home to allograft during chronic rejection. Three Specific Aims will be pursued: (1) Identify the progenitor cells of intragrafl fibroblasts. The proliferative hierarchy of the fibroblastic lineage of MSC will be determined using MSC differentiation cultures, immunophenotyping and fibroblast functional assays. Vector-marked syngeneic MSCs of defined phenotype will then be engrafted into rat recipients of cardiac allograft for assessment of their capacity to home to allografts. Clonal integration analysis will determine if the progeny of vector-marked MSC is originated from the same precursor, or discrete stem cell. (2) Determine the mechanism that is responsible for the recruitment and proliferation of fibroblast progenitors in allografts. Studies are designed to test a hypothesis that homing of MSC to allograft is mediated by binding of CD44 expressed by the progenitors to extracellular matrix hyaluronan (HA); MCP-1 promotes MSC migration by up-regulating expression of selected CD44v isoforms and supports fibroblast proliferation by stimulating macrophage production of fibrogenic factors. (3) Determine the feasibility of using fibroblast progenitors as a vehicle for gene delivery to allografls. Mesenchymal progenitors will be transduced with retroviral vectors containing a hepatocyte growth factor (HGF) gene and then engrafted into allograft recipients. Studies are designed to examine the distribution of the engrafted MSC in allograft and bone marrow, kinetics of HGF production, its impact on bone marrow cell biology and the development of graft fibrosis. Our studies will provide definitive proof that mesenchymal progenitors of recipient origin play a pathogenic role in the development of graft fibrosis, and will determine the phenotype of fibroblast progenitors, the recruitment mechanism, and the feasibility of using MSC for gene therapy of chronic rejection.