Innate-like CD27+CD45RBhigh γδ T Cells Require TCR Signaling for Homeostasis in Peripheral Lymphoid Organs

TCR signaling is required for homeostasis of naive αβ T cells. However, whether such a signal is necessary for γδ T cell homeostasis in the periphery remains unknown. In this study, we present evidence that a portion of Vγ2 + γδ T cells, one of the major γδ T cell subsets in the secondary lymphoid organs, requires TCR signaling for homeostasis. To attenuate γδTCR signals, we generated mice lacking Eγ4 (Eγ4 -/- ), an enhancer located at the 3'-most end of the TCRγ locus. Overall, we found that in thymus, Eγ4 loss altered V-J rearrangement, chromatin accessibility, and transcription of the TCRγ locus in a distance-dependent manner. Vγ2 + γδ T cells in Eγ4 -/- mice developed normally both fetal and adult mouse thymi but were relatively reduced in number in spleen and lymph nodes. Although Vγ2 TCR transcription decreased in all subpopulations of Eγ4 -/- mice, the number of Vγ2 + γδ T cells decreased and TCR signaling was attenuated only in the innate-like CD27 + CD45RB high subpopulation in peripheral lymphoid organs. Consistently, CD27 + CD45RB high Vγ2 + γδ T cells from Eγ4 -/- mice transferred into Rag2-deficient mice were not efficiently recovered, suggesting that continuous TCR signaling is required for their homeostasis. Finally, CD27 + CD45RB high Vγ2 + γδ T cells from Eγ4 -/- mice showed impaired TCR-induced activation and antitumor responses. These results suggest that normal homeostasis of innate-like CD27 + CD45RB high Vγ2 + γδ T cells in peripheral lymphoid organs requires TCR signaling.