Varicella zoster-specific CD₄+Foxp₃+ T cells accumulate after cutaneous antigen challenge in humans

We investigated the relationship between varicella zoster virus (VZV)-specific memory CD4+ T cells and CD4+Foxp3+ regulatory T cells (Tregs) that accumulate after intradermal challenge with a VZV skin test Ag. VZV-specific CD4+ T cells were identified with a MHC class II tetramer or by intracellular staining for either IFN-g or IL-2 after Ag rechallenge in vitro. VZV-specific T cells, mainly of a central memory (CD45RA2CD27+) phenotype, accumulate at the site of skin challenge compared with the blood of the same individuals. This resulted in part from local proliferation because >50% of tetramer defined Ag-specific CD4+ T cells in the skin expressed the cell cycle marker Ki67. CD4+Foxp3+ T cells had the characteristic phenotype of Tregs, namely CD₂₅hiCD1₂₇loCD39hi in both unchallenged and VZV challenged skin and did not secrete IFN-g or IL-2 after antigenic restimulation. The CD₄+Foxp3+ T cells from unchallenged skin had suppressive activity, because their removal led to an increase in cytokine secretion after activation. After VZVAg injection, Foxp3+CD25hiCD127loCD39hi T cells were also found within the VZV tetramer population. Their suppressive activity could not be directly assessed by CD25 depletion because activated T cells in the skin were also CD₂₅+. Nevertheless, there was an inverse correlation between decreased VZV skin responses and proportion of CD₄+Foxp ₃+ T cells present, indicating indirectly their inhibitory activity in vivo. These results suggest a linkage between the expansion of Ag-specific CD4+ T cells and CD4+ Tregs that may provide controlled responsiveness during Ag-specific stimulation in tissues.