Phenotypical characterization of epithelial cells from normal thymus and tumors IntroductionThe thymus gland, one of the primary organs of the lymphatic system, is located in the mediastinum, behind the sternum. Anatomically, the thymus extends inferiorly to the fourth intercostal space and superiorly to the lower edge of the thyroid gland. The thymus is larger and more active during puberty than adulthood, after this period the organ begins to atrophy and is replaced by adipose tissue. The thymus is a specialized primary lymphoid organ that develops from the third pharyngeal pouch of the anterior gut and provides the necessary environment for thymopoiesis, the process by which thymocytes differentiate into mature T lymphocytes.Main function of the thymus is the production of immunologically competent T cells that can recognize and eliminate foreign antigens but that tolerate the body’s own components. T cell ‘education’ in the thymus is mainly orchestrated by thymic epithelial cells. \cite{Kadouri2020} \cite{Manley2003}\cite{Boehm_2008}\cite{Anderson_2007}. The thymus is composed by two pyramid-shaped lobes. Each lobe is divided into a central medulla and a peripheral cortex and is covered by a capsule of loose connective tissue and divided interiorly by connective tissue septa called cortico-medullary junction (CMJ). The cortex is the outer region, where a stromal meshwork houses densely packed immature thymocytes, while the medulla is the inner region with less densely localized mature thymocytes and enriched stromal cells. The thymic stroma is composed by mesenchyme, pericytes and endothelial cells, but the predominant component of postnatal thymus stroma are thymic epithelial cells (TECs) divided into cortical (cTEC) and medullary (mTEC) based on their physical position in the organ\cite{Bautista_2021}. There is a functional as well anatomical difference between the two regions, infact each region is composed of different cell types producing soluble and non-soluble molecules that can modulate different stages of thymocytes migration and maturation \cite{Savino2002}\cite{Savino2004}. The cortex microenvironment is filled with cTECs, thymic nurse cells (TNC, thymic epithelial-thymocyte forming lymphoepithelial complexes), macrophages, migratory dendritic cells (DCs), and fibroblasts. The medullary region contains mTECs, macrophages, resident and migratory conventional DCs, plasmacytoid DCs, fibroblasts, and B cells \cite{Takada_2013}.