ABSTRACT
A diverse, yet self-tolerant T-cell repertoire is essential for adaptive immunity. Negative selection is a key checkpoint in T-cell development that is responsible for the elimination of T-cell clones that express T-cell receptors (TCRs) with high affinity to self-peptide, MHC complexes (pMHCs). Both medullary thymic epithelial cells (mTECs) and thymic antigen presenting cells of hematopoietic origin (e.g., thymic dendritic cells, macrophages, and B-cells) contribute to the clonal deletion process. Advances over the past decade have highlighted the critical roles of tissue-restricted antigen (TRA) expression in mTECs in defining “immunological self” and establishing immune tolerance of peripheral tissues and organs. Although numerous genetic tools and mouse models, such as TCR transgenic strains, targeted mutagenic mouse models, and reaggregate thymus organ culture (RTOC), have been developed to study various aspects of negative selection, its underlying mechanism remains not fully understood, primarily due to the complexity of the process. We have 54recently developed a tissue engineering technique that allows us to reconstruct a functional thymus organoid by repopulating a decellularized thymus scaffold with TECs and other thymic stromal cells. The bioengineered thymus organoid can recapitulate the function of a thymus, support the development of a complex T-cell repertoire, and reestablish T-cell adaptive immunity in athymic nude mice. This bottom-up approach enables us to further delineate the roles of different thymic stromal components in negative selection. Here, using islet cell autoantigen 69 (ICA69), a known pancreatic beta cell autoantigen in the pathogenesis of type 1 diabetes, as a model antigen, we show that ICA69-reactive T-cells can escape clonal deletion in athymic nude mice transplanted with thymus organoids constructed with ICA69-deficient mTECs. Thymus bioengineering could be a useful approach for further understanding and modulating thymic negative selection.
