T cells mature in the thymus. They originate from hematopoietic stem cells in the bone marrow, but the critical development and maturation steps occur in the thymus gland, which provides a specialized microenvironment for T-cell differentiation
. In detail, T-cell precursors migrate from the bone marrow to the thymus, where they undergo a series of developmental stages, including selection processes that ensure functional and self-tolerant T cells. The thymus is divided into the cortex and medulla, with most T-cell development occurring in the cortex and mature T cells found in the medulla before they leave to populate peripheral tissues
. Thus, while T cells start their lineage in the bone marrow, their maturation is thymus-dependent, which is why they are called T cells (thymus-derived lymphocytes)
