IFN-Á Responses in Peptide-treated Melanoma Patients Measured by an ELISPOT Assay Using Allogeneic Dendritic Cells

Abstract

Background: Several melanoma-specific peptides are currently used in clinical trials. However, the monitoring of the T cell response remains non-standardised and is often limited by shortage of cells. Materials and Methods: We established an IFN-Á ELISPOT assay to detect the CD8⁺ T cell response in HLA-A2-positive melanoma patients using pre-frozen, peptide-loaded HLA-A2-positive but otherwise allogeneic, monocyte-derived dendritic cells (DC) as antigen-presenting cells. We tested HLA-A2-positive stage III or IV melanoma patients before and after peptide immunotherapy. Results: The number of EBV and influenza-specific IFN-γ-spots were comparable irrespective of the use of autologous or allogeneic HLA-A2 immature DCs when using purified CD8⁺ cells as responder cells, but a high allogeneic background was seen when using PBMC. We observed modifications of the in vitro response to the melanoma peptides in three out of four responding patients, while virus responses remained constant; however, similar results were seen in the group with progressive disease. Conclusion: This demonstrates the possibility of monitoring an immune response by using allogeneic DCs, reducing the consumption of patient cells. The in vitro IFN-Á responses increased in response to the peptide therapy, however this could not be correlated to clinical outcome.