In vivo blockade of T cell development reveals alternative pathways for generation of intraepithelial lymphocytes in mice

Intraepithelial lymphocytes (IELs) are resident cells localized within the intestinal epithelia and play an important role in regulating gut inflammations and host defense against pathogens. CD8α⁺ TCRαβ⁺ IELs are heterogeneous populations that are generated from T cell precursors including CD4⁻ CD8α⁻ double-negative (DN) cells and CD4⁺ CD8α⁺ double-positive (DP) cells. However, developmental pathways of TCRαβ⁺ IELs remained unclear. To gain insight into the mechanisms, we generated mice (Bcl11b^ΔDN2 mice) that lack thymic precursors (DN CD5⁺ TCRβ⁺ cells) for CD4⁻ CD8αα⁺ TCRαβ⁺ IELs. Unexpectedly, we found that, in the absence of the precursors in thymi of Bcl11b^ΔDN2 mice, CD4⁻ CD8αα⁺ TCRαβ⁺ IELs were still present in the intestine though the number was reduced. Adoptive transfer experiment showed that their precursors were highly enriched in CD8α⁺ TCRβ⁻ thymocytes. The CD4⁻ CD8αα⁺ TCRαβ⁺ IELs in Bcl11b^ΔDN2 mice are distinguished by Thy1.2 expression and are indeed present in WT mice. Taken together, our study reveal a novel developmental pathway for CD8αα⁺ TCRαβ⁺ IELs.