A fetal wave of human type-3 γδ T cells with restricted TCR diversity persists into adulthood

Abstract

Accumulating evidence suggests that the human embryonic thymus produces distinct waves of innate effector {gamma}{delta} T cells. However, it is unclear whether this process comprises a dedicated subset of IL-17-producing {gamma}{delta} T ({gamma}{delta}T17) cells, like reported in mice. Here we present a novel protocol for high-throughput paired {gamma}{delta} TCR-sequencing, which in combination with single-cell RNA-sequencing revealed a high heterogeneity of effector {gamma}{delta} T cell clusters. While immature {gamma}{delta} T cell clusters displayed mixed and diverse TCR, effector cell types in neonatal and adult blood segregated according to {gamma}{delta}TCR usage. In adult samples, mature V{delta}1+ T cells segregated into exhausted PD-1hi and active PD-1low clusters. Among V{gamma}9V{delta}2+ T cell subsets, we identified distinct PLZF-positive effector {gamma}{delta} T cell clusters with innate type-1 and type-3 T cell signatures that were already detectable in a public dataset of early embryonic thymus organogenesis. Together, this suggests that functionally distinct waves of human innate effector {gamma}{delta} T cells including CCR6+ {gamma}{delta}T17 cells develop in the early fetal thymus and persist into adulthood.