T-cell receptors (also known as TCRs) are an incredibly important part of immunology.
One of their key characteristics is their diversity, allowing for recognition of many different antigens.
Similar to B cells, they are produced in the bone marrow, however, differentiate in the thymus by breaking and rearranging their genes (whereas B cells differentiate in the bone marrow). Following exit from the thymus, the T cells are known as naive T cells as they have not yet encountered an antigen, presented to them by an MHC molecules on the surface of APCs. They recirculate via the blood/lymphatics through secondary lymphoid tissue.
Their variable regions are encoded by V, D and J segments, which can arrange in any format, which is what allows them to be so diverse.