Reconstitution of a functional human thymus by postnatal stromal progenitor cells and natural whole-organ scaffolds

Abstract

The thymus is a primary lymphoid organ, essential for T cell maturation and selection. There has been long-standing interest in processes underpinning thymus generation and the potential to manipulate it clinically, because alterations of thymus development or function can result in severe immunodeficiency and autoimmunity. Here, we identify epithelial-mesenchymal hybrid cells, capable of long-term expansion in vitro, and able to reconstitute an anatomic phenocopy of the native thymus, when combined with thymic interstitial cells and a natural decellularised extracellular matrix (ECM) obtained by whole thymus perfusion. This anatomical human thymus reconstruction is functional, as judged by its capacity to support mature T cell development in vivo after transplantation into humanised immunodeficient mice. These findings establish a basis for dissecting the cellular and molecular crosstalk between stroma, ECM and thymocytes, and offer practical prospects for treating congenital and acquired immunological diseases.

Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects

“…In the mouse, a common bipotent precursor for cTEC and mTEC compartments has long been described (37)(38)(39). Recent characterization of expanding human mTECs and cTECs, which lose their compartmental signature, is in keeping with this (35). Finally, the whole structure is supported by a scaffold of extracellular matrix (ECM), comprising, among other things, collagen and fibronectin, which facilitates thymocyte migration and cellular interaction (40)(41)(42).…”

“…This method cannot be used to obtain human natural scaffolds, as it cannot be applied to the much larger human thymi. The very recent development of a novel whole-organ perfusion system has made it possible to obtain a natural decellularized ECM from human thymi, despite the lack of major vascular access ( 35 ). This has made it possible to obtain an engineered thymus after reconstitution with in vitro expanded human thymic stromal progenitor cells.…”

“…When transplanted into a humanized small animal model, the engineered thymi demonstrated the capacity to re-organize into a recognizable thymus with cortex and medulla, including Hassall’s bodies. This reconstituted human thymus had the ability to support thymopoiesis, both ex vivo and in vivo ( 35 ). Having overcome important obstacles, given the possibility of expanding large numbers of thymic stromal cells and of perfusing a whole thymus organ, this approach can be scaled up, thus facilitating translation into the clinic.…”

“…TECs are the hallmark cells of the thymus being classed broadly into two groups with distinct functions, cortical (cTEC) and medullary (mTEC). The cellular complexity of the thymic stroma with higher TEC heterogeneity is becoming increasingly evident (31,35,36). In the mouse, a common bipotent precursor for cTEC and mTEC compartments has long been described (37)(38)(39).…”

Dynamics of thymus function and T cell receptor repertoire breadth in health and disease

“…Therefore one approach that has shown some promise is to build what has been called an artificial thymic organoid (ATO) entirely for regenerating immunity [ 238 – 241 ]. ATO tissues have been made by decellularizing endogenous thymic tissue, as well as generating synthetic matrices to support T cell development, though in vivo evidence of therapeutic efficacy of these approaches is still limited [ 189 , 241 , 242 ]. However, given the extensive requirement for cellular micornvironmental support for T cell development, these approaches still require cellular input to generate a fully functional thymus, namely the thymic epithelial microenvironment would need to be recapitulated.…”