Dr. Mark Pezzano
RESEARCH (Focus of the Lab)
Fully understanding the signaling pathways and cellular interactions which contribute to TEC development and organization will be critical to designing rational therapeutic strategies to counteract age associated thymic involution and thymic architecture defects associated with autoimmunity. These strategies will also significantly impact the effectiveness of bone marrow transplantation for cancer treatment by counteracting the severe premature thymic degeneration associated with preparative cytoablative treatments including chemotherapy and radiation, as well as post transplant GVHD.
Crosstalk Control of Thymic Epithelial Development (NIH/NIAID)
A common endoderm derived fetal TEC progenitor was recently shown to give rise to both cortical and medullary TEC subsets, however, the signaling pathways and cell-to-cell interactions that regulate this process are poorly defined. TEC development and organization is dependent on crosstalk signals received from developing thymocytes as they migrate through the epithelial network. The goal of this study is to define both the nature and function of the SP thymocyte/TEC interactions that regulate development of the thymic medulla, the thymic microenvironment that is critically responsible for central tolerance. The medullary reconstitution induced by adoptive transfer of mature T cells into mice with blocks in T cell development, is being used to test the contribution of specific T cell/TEC interactions to development of functional mTECs. In addition, newly developed KO and conditional transgenic models are being utilized to examine the role of Wnt signaling in both TEC development and the maintenance of postnatal TEC microenvironments. Recent progress in this study has demonstrated that tetracycline-regulated expression of the Wnt inhibitor DKK1 in cTECs and mTECs of adult mice, results in rapid thymic degeneration characterized by a reduced Foxn1 expression, loss of K5K8DP putative TEC progenitors, decreased proliferation and the development of cystic structures, similar to an aged thymus. Removal of DKK1 from DKK1-involuted mice results in full recovery, suggesting that canonical Wnt signaling is required for the differentiation or proliferation of TEC populations needed for maintenance of properly organized adult thymic epithelial microenvironments. The results of this study demonstrate that canonical Wnt signaling within TECs is required for the maintenance of epithelial microenvironments in the postnatal thymus, possibly through effects on TEC progenitor/stem cell populations. Current efforts are focused on characterizing these progenitor populations and the molecular interactions that promote their survival and differentiation.
Characterization of Thymic Epithelial Progenitors and their Capacity to Reconstitute Thymic Function (NIH/NCI Collaborative Project with MSKCC)
Hematopoietic stem cell transplantation (HSCT) can cure many forms of blood-derived cancers. Unfortunately, particularly in adult patients, HSCT is associated with a period of immune incompetence due to a loss of capacity to generate functional T cells. The structural and functional changes in thymic epithelial cells (TECs), induced by HSCT, directly impact the capacity of the thymus to facilitate T cell development. Clinical treatment strategies that enhance T cell reconstitution could significantly improve the survival of HSCT recipients through reduced incidence of fatal infectious complications and enhanced T-cell mediated tumor activity. The goal of this study is to identify thymic epithelial stem cells/progenitors and test the capacity of grafting of these populations to speed the recovery of thymic function after HSCT.
Due to their slow turnover rate, stem cells in a variety of tissues have been identified by their capacity to retain labeled nucleotides, so called “label retaining cells” (LRCs). A novel transgenic model, which utilizes a histone2B-GFP fusion protein (H2B-GFP), under control of a tetracycline response element driven by a K5 promoter, was used by Elaine Fuch’s group at Rockefeller to identify epithelial stem cells in the hair follicle bulge. This model is unique because it allows sorting of viable stem cells, in the absence of defining cell surface markers. Since putative thymic epithelial progenitors also express K5, we have obtained this transgenic model and are currently applying the method to identify potential thymic epithelial stem/progenitor populations. Further separation of putative stem cell populations will be performed using previously characterized epithelial stem cell surface characteristics. Sorted subsets will be assayed for progenitor potential based on their capacity to reform a functional thymus after transfer under the kidney capsule of nude mice. Once functional TEC progenitor/stem cells have been identified, their ex vivo growth potential and their subsequent capacity to enhance immune reconstitution following hematopoietic stem cell transplantation (HSCT) will be further assessed.
Dr. Mark Pezzano
Department of Biology, Room MR-526
City College of New York
138th Street & Convent Avenue
New York, NY 10031
t. 212.650.8577 (Lab)
Other Locations: MR-501 (main office), MR-609 (Lab), and MR-632 (office)