All hematopoietic cells, including T lymphocytes, originate from stem cells that reside in the
bone marrow. Most hematopoietic lineages also mature in the bone marrow, but in this
respect, T lymphocytes differ. Under normal circumstances, most T lymphocytes are
produced in the thymus from marrow-derived progenitors that circulate in the blood. Cells
that home to the thymus from the marrow possess the potential to generate multiple T and
non-T lineages. However, there is little evidence to suggest that, once inside the thymus …