Immunohistological analysis of peptide-induced delayed-type hypersensitivity in advanced melanoma patients treated with melanoma antigen-pulsed mature monocyte-derived dendritic cell vaccination

SummaryBackgroundIn melanoma patients vaccinated with monocyte-derived melanoma peptide-pulsed dendritic cells (DC), the delayed-type hypersensitivity (DTH) reactions have been examined as a surrogate marker to determine if acquired immunity is induced by DC vaccination. To date, however, only limited information has been reported as for histopathological analyses of DTH.ObjectiveTo evaluate tumor-specific immunomonitoring histopathologically after DC vaccination in melanoma patients.MethodsSeven patients previously vaccinated with monocyte-derived melanoma peptide-pulsed DCs were challenged with recall antigenic peptide injection in the skin of the forearm. Using immunohistochemical techniques, the presence of immune cells and the expression of CD4, CD8, interleukin (IL)-2, IL-4, IL-10, Foxp3, CD1a, CD1d, and interferon (IFN)-γ was investigated at the site of injection where a DTH reaction developed.ResultsStrong DTH reactions from infiltrated erythema to bullae formation were detected in all 7 cases. Biopsies taken from the DTH site revealed heavy infiltration of mononuclear cells and eosinophils in the dermis and subcutaneous tissue. Cells staining positively for CD4, CD8, IL-2, IL-4, Foxp3, CD1d, and IFN-γ were increased at the site 48 h after antigen injection in all cases. Cells positive for IL-10 were never found in any patient. Regulatory T cells appeared 6 h after injection and reached their maximum at day 7.ConclusionsThe significant induction of CD8+T cells as well as both Th1 and Th2-type cells at the site of DTH suggests that effective antigen presentation leading to anti-tumor immune responses has taken place. Inhibitory mechanisms may also develop as the disappearance of the DTH response could be related to an increase in Foxp3+ cells.