Premature expression of T cell receptor (TCR)alphabeta suppresses TCRgammadelta gene rearrangement but permits development of gammadelta lineage T cells.

The T cell receptor (TCR)gammadelta and the pre-TCR promote survival and maturation of early thymocyte precursors. Whether these receptors also influence gammadelta versus alphabeta lineage determination is less clear. We show here that TCRgammadelta gene rearrangements are suppressed in TCRalphabeta transgenic mice when the TCRalphabeta is expressed early in T cell development. This situation offers the opportunity to examine the outcome of gammadelta versus alphabeta T lineage commitment when only the TCRalphabeta is expressed. We find that precursor thymocytes expressing TCRalphabeta not only mature in the alphabeta pathway as expected, but also as CD4(-)CD8(-) T cells with properties of gammadelta lineage cells. In TCRalphabeta transgenic mice, in which the transgenic receptor is expressed relatively late, TCRgammadelta rearrangements occur normally such that TCRalphabeta(+)CD4(-)CD8(-) cells co-express TCRgammadelta. The results support the notion that TCRalphabeta can substitute for TCRgammadelta to permit a gammadelta lineage choice and maturation in the gammadelta lineage. The findings could fit a model in which lineage commitment is determined before or independent of TCR gene rearrangement. However, these results could be compatible with a model in which distinct signals bias lineage choice and these signaling differences are not absolute or intrinsic to the specific TCR structure.