Iron overload in HFE-related hemochromatosis severely impairs Vδ2 γδ T-cell homeostasis

• Iron overload in HFE-related hemochromatosis and thalassemia leads to reversal of the Vδ2+/Vδ2- ratio in the γδ-T-cell compartment

• Iron overload promotes constant Vδ2+TCR ligand availability by inhibiting pyrophosphatases, leading to Vδ2+T cell exhaustion and cell death

HFE-related hemochromatosis (HH) induces systemic iron overload. Although extensive studies indicate a pivotal role for iron homeostasis in αβ-T-cell immunity, its effect on γδ-T cells is unknown. Here we show a reversal of the Vδ2+/Vδ2- ratio in the γδ-T-cell compartment as a feature of hemochromatosis, which is associated with a Vδ2+ population that cannot be enriched by ZOL-stimulation, despite evidence of TCR-ligand formation and strong proliferative behavior. Already in vivo, ROS production and exhaustion marker expression are significantly increased on Vδ2+-T-cells in hemochromatosis compared with healthy individuals. Ex vivo, hemochromatosis-donor-derived Vδ2+-cells are hyporesponsive to TCR stimulation in terms of ROS production, but significantly increase their paramount expression of exhaustion markers further. Fas-Fas Ligand coexpression indicates their high susceptibility to activation-induced cell death. Consistent therewith FeSO4 alone induces Vδ2+ subset-specific proliferation in healthy PBMCs comparable to stimulation by ZOL, and blocking experiments identify FeSO4-induced proliferation as BTN3A1/TCR-mediated. Pyrophosphates are key for Vδ2+-TCR-ligand formation. Iron, by suppressing pyrophosphatase ALP promotes their stability. In light of this our data suggest that the transcriptional repression of pyrophosphatases - as under the conditions of iron overload in hemochromatosis in vivo - leads to the constitutive availability of stress-signaling Vδ2+-TCR ligand thus permanent TCR-triggering in Vδ2+-T-cells even under homeostatic conditions, ultimately leading to their subset-specific activation-induced cell death. A similar phenotype was observed in patients with iron overload due to inborn hemoglobinopathies, suggesting an inverted Vδ2+/Vδ2- ratio in the γδ-T-cell compartment as a hallmark of iron overload.