Fig. 3 |. Engineering thymus tissue.

a | Thymic dysfunction leads to thymic involution, causing a decrease in the production of T cells, b | A schematic of thymic structure is presented, showing key cell types and microenvironmental cues, including thymic epithelial cells (TECs), haematopoietic stem cells (HSCs), thymocytes (that is, lymphocytes in the thymus), cortical epithelial cells and Notch ligands (delta-like ligand 4 (DLL4)). Negative and positive selection processes, as determined by the reactivity of thymocytes to self-peptides on the major histocompatibility complexes (MHCs) of cortical epithelial cells, are required to establish a diverse set of MHC-restricted yet self-tolerant mature T cells, c | Progenitor cells can be differentiated into T cells using different strategies: Notch signalling can be activated by co-culturing HSCs and bone marrow stromal cells (OP9), which are genetically engineered to present the Notch ligand DLL1. Magnetic polystyrene beads can be functionalized with DLL4 at a specific density and orientation. A stromal cell-free thymic niche can be designed by culturing HSCs with both DLL1 and vascular cell adhesion protein 1 (VCAM1). d | Organoid cultures can be engineered by aggregating and centrifuging HSCs and MS5-hDLL1 cells — a genetically engineered bone marrow stromal cell line expressing human DLL1 (hDLL1). Decellularized extracellular matrices (ECMs) can be used to culture TECs and HSCs. Self-assembling hydrogels based on amphiphilic peptides can be applied to encapsulate HSCs and TECs, enabling precise control of the microenvironment. Anti-histidine (His) and TEC-specific anti-epithelial cell adhesion molecule (EpCAM) antibodies can be bound to protein A/G adaptor complexes to promote binding to histidinylated amphiphilic peptides and for 3D aggregation of TECs, respectively. TCR, T cell receptor.