T cell progenitors are known to arise from the foetal liver in embryos and the bone marrow in
adults; however different studies have shown that a pool of T cell progenitors may also exist in the
periphery. Here, we identified a lymphoid population resembling peripheral T cell progenitors which
transiently seed the epidermis during late embryogenesis in both wild-type and T cell-deficient
mice. We named these cells ELCs (Epidermal Lymphoid Cells). ELCs expressed Thy1 and CD2, but
lacked CD3 and TCRαβ/γδ at their surface, reminiscent of the phenotype of extra- or intra- thymic
T cell progenitors. Similarly to Dendritic Epidermal T Cells (DETCs), ELCs were radioresistant and
capable of self-renewal. However, despite their progenitor-like phenotype and expression of T cell
lineage markers within the population, ELCs did not differentiate into conventional T cells or DETCs
in in vitro, ex vivo or in vivo differentiation assays. Finally, we show that ELC expressed NK markers
and secreted IFN-γ upon stimulation. Therefore we report the discovery of a unique population of
lymphoid cells within the murine epidermis that appears related to NK cells with as-yet-unidentified
functions.