This review briefly describes the last decades of experimental work on the thymus. Given the histological complexity of this organ, the multiple embryological origins of its cellular components and its role in carefully regulating T lymphocyte maturation and function, methods to dissect and understand this complexity have been developed through the years. The possibility to study ex vivo the thymus organ function has been achieved by developing Fetal Thymus Organ Cultures (FTOC). Subsequently, the combination of organ disaggregation and reaggregation in vitro represented by Reaggregate Thymus Organ cultures (RTOC) allowed mixing cellular components from different genetic backgrounds. Moreover, RTOC allowed dissecting the different stromal and hematological components to study the interactions between Major Histocompatibility Complex (MHC) molecules and the T-cell receptors during thymocytes selection. In more recent years, prospective isolation of stromal cells and thymocytes at different stages of development made it possible to explore and elucidate the molecular and cellular players in both the developing and adult thymus. Finally, the appearance of novel cell sources such as embryonic stem (ES) cells and more recently induced pluripotent stem (iPS) cells has opened new scenarios in modelling thymus development and regeneration strategies. Most of the work described was carried out in rodents and the current challenge is to develop equivalent or even more informative assays and tools in entirely human model systems.
We thank Giulio Cossu, Peter W. Zandstra, Anna Cariboni and Sara Campinoti for critical reading.
P.B. is supported by the European Research Council (ERC-2014-Stg), the Rosetrees Trust Foundation, the UCL Excellence Fellowship Program and the NIHR Biomedical Research Centre at Great Ormond Street Hospital for Children NHS Foundation Trust; E.P. was supported by the New Ideas Grant provided by the Ontario Institute for Regenerative Medicine (OIRM). S.C. is supported by a GOSH Charity studentship (V6116).