Genetic evidence supporting selection of the Vα14i NKT cell lineage from double-positive thymocyte precursors

Invariant V alpha 14i NKT (iNKT) cells are a specialized subset of T lymphocytes with regulatory functions. They coexpress TCR alpha beta and natural killer cell markers. They differentiate through interaction of their V alpha 14-J alpha 18 invariant TCR alpha chains with CD1d expressed on double-positive (DP) thymocytes. Although their development has been shown to be thymus dependent, their developmental pathway has not been definitively established. By using genetic analyses, we show here that all iNKT cells are selected from a pool of DP thymocytes. Their development is absolutely dependent on Runx1 and ROR gamma t, transcription factors that influence, but are not required for, development of conventional T cells. Our results indicate that even though CD1d binding DP thymocytes have yet to be observed, V alpha 14-J alpha 18 rearrangement in these cells is required for development of iNKT cells.