Thymic selection: a matter of life and death.

Mice transgenic for the T-cell receptor (TCR) were instrumental to the understanding that developing alpha beta T cells undergo programmed cell death unless the TCR beta gene properly rearranges and produces receptors of appropriate specificity. The delineation of developmental pathways for 'conventional' alpha beta T cells has resulted in the recognition of a different lineage of alpha beta T cells that develop in the thymus, the function of which remains to be elucidated.