A TCR α chain transgene induces maturation of CD4− CD8− α β+ T cells from γ δ T cell precursors

The proportion of CD4⁻ CD8⁻ double-negative (DN) α β T cells is increased both in the thymus and in peripheral lymphoid organs of TCR α chain-transgenic mice. In this report we have characterized this T cell population to elucidate its relationship to α β and γ δ T cells. We show that the transgenic DN cells are phenotypically similar to γ δ T cells but distinct from DN NK T cells. The precursors of DN cells have neither rearranged endogenous TCRα genes nor been negatively selected by the Mls^a antigen, suggesting that they originate from a differentiation stage before the onset of TCR α chain rearrangements and CD4/CD8 gene expression. Neither in-frame VδDδJδ nor VγJγ rearrangements are over-represented in this population. However, since peripheral γ δ T cells with functional TCRβ gene rearrangements have been depleted in the transgenics, we propose that the transgenic DN population, at least partially, originates from the precursors of those cells. The present data lend support to the view that maturation signals to γ δ lineage-committed precursors can be delivered via TCR α β heterodimers.