Innate PLZF+ CD4+ αβ T cells develop and expand in the absence of Itk1

T cell development in the thymus produces multiple lineages of cells, including innate T cells. Studies in mice harboring alterations in TCR signaling proteins or transcriptional regulators have revealed an expanded population of CD4 + innate T cells in the thymus that produce IL-4 and express the transcription factor PLZF. In these mice, IL-4 produced by the CD4 + PLZF + T cell population leads to the conversion of conventional CD8 + thymocytes into innate CD8 + T cells resembling memory T cells expressing Eomesodermin. The expression of PLZF, the signature iNKT cell transcription factor, in these innate CD4 + T cells suggests that they might be a subset of αβ or γδ TCR + NKT cells or MAIT cells. To address these possibilities, we characterized the CD4 + PLZF + innate T cells in itk -/- mice. We show that itk -/- innate PLZF + CD4 + T cells are not CD1d-dependent NKT cells, MR1-dependent MAIT cells, nor γδ T cells. Further, although the itk -/- innate PLZF + CD4 + T cells express αβ TCRs, neither β2m-dependent MHC class I nor any MHC class II molecules are required for their development. In contrast to iNKT cells and MAIT cells, this population has a highly diverse TCRα chain repertoire. Analysis of peripheral tissues indicates that itk -/- innate PLZF + CD4 + T cells preferentially home to spleen and mesenteric lymph nodes due to increased expression of gut-homing receptors, and that their expansion is regulated by commensal gut flora. These data support the conclusion that itk -/- innate PLZF + CD4 + T cells are a novel subset of innate T cells.