Daniel Joyce, MD
Cleveland Clinic Foundation
Organ transplantation has been applied for many decades, however the outcome of cellular transplants (e.g. islet cells, hepatocytes) remains disappointing. It is thought that non-parenchymal cells may protect parenchymal cells from rejection. We have identified that hepatic stellate cells (HSCs) have potent immunosuppressive activity. HSCs effectively protect islet allografts in a mouse model. This is mediated by the induction of apoptosis in effector T cells and by the generation of Treg cells and myeloid derived suppressor cells (MDSCs). The use of HSCs to protect cell transplants from rejection is very attractive but not practical since the HSCs must be of recipient origin and the harvest of HSCs would involve a partial hepatectomy. A solution has emerged based on our recent findings: HSCs are potent inducers of MDSCs. MDSCs can be produced in vitro in large quantities by the addition of HSCs into bone marrow derived dendritic cell culture; this is mediated by soluble factors, most notably iC3b.
This project intends to determine the optimal culture conditions to generate human MDSCs in vitro and to identify the molecules that act synergistically with iC3b to promote MDSC production. We will then characterize the immunomodulatory activity of human MDSCs in vivo and explore their utilization for protecting cell transplants in a humanized mouse model. We will first study the immunomodulatory effect of MDSCs by footpad injection of allogeneic dendritic cells in Hu-NOD/SCID/IL-2Ɣc mice that have been adoptively transferred with human primary bone marrow culture. The impact of MDSCs on the T cell response will be assessed by analysis of the popliteal lymph nodes. The ultimate goal of the study is to assess if systemic administration of MDSCs can protect islet cell allografts, this will be studied in the Hu-NOD/SCID/IL-2Ɣc mouse model, we will induce diabetes mellitus and then transplant human islet cell allografts under the renal capsule, glycemic control will then be monitored. In the event of sustained euglycemia we will confirm that same is maintained by the transplanted islets by removing the graft bearing kidney which is expected to lead to rapid elevation in blood glucose levels. The mice will be sacrificed and we will analyse the islet grafts, draining lymph nodes, irrelevant lymph nodes, spleen and peripheral blood.
While this project is confined to in vitro and in vivo murine studies, it is our expectation that it will provide the basis for a clinical trial in the near future. The ability to perform allogeneic islet cell transplants without immunosuppression would represent a quantum leap in the current management of diabetes mellitus.