Introduction: Peptide immunotherapy has been shown to be a simple and effective method of restoring tolerance and reversing disease in animal models of type 1 diabetes. It is highly important to administer the peptide interadermally into an environment in which antigen presenting cells such as dendritic cells are maintained in a tolerogenic state.
Objective: Our aim was to determine whether topical pre-treatment of the skin has the potential to enhance tolerogenic immunity during peptide immunotherapy.
Methods: Healthy volunteers received one of three pre-treatment regimes twice daily for 4 days to the skin of a small area of the arm: 0.05% betamethasone (S), 50 μg/mg calcipotriol (D), 0.05% betamethasone+calcipotriol (S+D). 12 h later, all subjects had a 1015 mm suction blister raised at the site of treatment. Blister fluid was then withdrawn for the measurement of cytokine production. The blister roof was removed and epidermal cells isolated for study using 9-colour flow cytometry and for functional analysis in a mixed lymphocyte reaction (MLR) using allogeneic PBMC.
Results: Epidermal cells comprised around 2% of the CD1a+ dendritic cells (EDC). In S subjects MLR proliferation was markedly suppressed with an associated reduction in interferon-γ (IFN-γ), interleukin 2 (IL2), and IL13 in the blister fluid. However, IL10 remained constant. A reduction in expression of CD86 and HLA-DR was seen in CD1a+EDC from S subjects but ILT3 expression was maintained. In contrast, D had no effect on MLR proliferation, but tended to reduced CD40, CD80 and ILT3 expression on EDCs. S+D had little effect on proliferative responses but reduced expression of CD86 by EDC.
Conclusion: Pretreatment of the skin for as little as 4 days appears to have marked effects on epidermal dendritic cell function. Further functional studies are required to determine which combination will prove optimal for tolerance induction in peptide immunotherapy.