A healthy immune system produces T cells that can recognize and react against foreign molecules (antigens) to protect against infection, while leaving normal host cells with “self antigens” undamaged. All T cells are produced in the thymus from blood stem cells that migrate from the bone marrow. “Tolerant” T cells are those that have been “educated” to not react against self antigen on host cells. The key cells in the thymic microenvironment that control T cell production and tolerance are the thymic epithelial cells (TECs). When TECs are lost or become dysfunctional, T cell production is poor and patients are at risk for a wide range of infections. When tolerance is lost, T cells react to host tissues as if they were foreign, producing inflammation and damage and causing autoimmune diseases such as Type I Diabetes, multiple sclerosis, rheumatoid arthritis and systemic lupus erythematosus. The goal of our studies is to develop a method for engineering and transplanting new, healthy thymus tissue into patients, thus creating a way to generate healthy T cells.
A major problem with regenerating the thymus ex vivo is that the TECs, which are so important for T cell growth and differentiation, tend to die during culture. Through this grant support we have developed a method to engineer one component of the thymic microenvironment (the thymic mesenchyme) to produce specific growth factors that we propose will protect TECs. We have developed specific culture conditions that allow us to grow the thymic mesenchyme separately to the TECs. We then take the mesenchyme and TECs out of culture and spin them together to form a cluster of cells called a thymic “aggregate” or “organoid”. We have shown that when we combine these thymic organoids with cord blood stem cells (also known as “hematopoietic” stem cells) we can produce T cells from the cord blood. We can make T cells in the organoids either in culture or after implantation of the organoids into immune deficient mice. During the final phase of support, we have focused on understanding what kind of T cells we produce in the organoids using mouse thymus. In addition we have developed a gene signature of normal thymus which can be used as a comparison for testing of our engineered organoids.