An induced thymic epithelial cell‐based high throughput screen for thymus extracellular matrix mimetics

Thymic epithelial cells (TECs) are key effectors of the thymic stroma and are critically required for T‐cell development. TECs comprise a diverse set of related but functionally distinct cell types that are scarce and difficult to isolate and handle. This has precluded TEC‐based screening assays. We previously described induced thymic epithelial cells (iTECs), an artificial cell type produced in vitro by direct reprogramming, raising the possibility that iTECs might provide the basis for functional screens related to TEC biology. Here, we present an iTEC‐based three‐stage medium/high‐throughput in vitro assay for synthetic polymer mimics of thymic extracellular matrix (ECM). Using this assay, we identified, from a complex library, four polymers that bind iTEC as well as or better than gelatin but do not bind mesenchymal cells. We show that these four polymers also bind and maintain native mouse fetal TECs and native human fetal TECs. Finally, we show that the selected polymers do not interfere with iTEC function or T‐cell development. Collectively, our data establish that iTECs can be used to screen for TEC‐relevant compounds in at least some medium/high‐throughput assays and identify synthetic polymer ECM mimics that can replace gelatin or ECM components in TEC culture protocols. Thymic epithelial cells are refractory to medium/high‐throughput screening. Using induced thymic epithelial cells to screen a complex synthetic polymer library, we identified four polymers that selectively maintained this cell type. These polymers also bound native mouse and human fetal thymic epithelial cells and were compatible with in vitro T‐cell development.