Immune Monitoring in Metastatic Melanoma

Despite recent breakthroughs in the treatment of melanoma, the prognosis in the advanced stage of the disease continues to be very poor. 45-50% of all melanomas carry a point mutation in codon 600 of the BRAF gene encoding a serine-threonine kinase. The two most common BRAF mutations (V600E and V600K) constitutively activate the MAP kinase signaling pathway that drives the proliferation and survival of cancer cells. Specific BRAF V600 inhibitors such as vemurafenib, dabrafenib and encorafenib and inhibitors of the downstream target MEK such as trametinib, binimetinib and cobimetinib are very effective regimens in BRAF-positive metastatic melanoma. Recent studies have shown that these inhibitors in addition to the effects on the tumor cells also have an influence on cells of the immune system. For example, vemurafenib leads to a loss of peripheral blood lymphocytes. Thus, the number of peripheral CD4 + positive cells decreases with vemurafenib therapy, while the number of natural killer cells (NK cells) increases. On the other hand, initial studies show that B cells and CD8 + positive cells are not affected numerically by vemurafenib. It has been demonstrated that vemurafenib but not dabrafenib reduces the number of peripheral lymphocytes in melanoma patients and changes the function and phenotype of CD4 + positive cells, although both drugs show comparable clinical efficacy. Selective inhibition of BRAF by inhibitors such as vemurafenib or dabrafenib thus has a significant influence on the peripheral lymphocyte populations of melanoma patients. Studies have been demonstrated that inhibition of BRAF can induce increased invasion of tumor-infiltrating lymphocytes into melanoma metastases. Tumor infiltration of CD4 + and CD8 + positive lymphocytes is surprisingly enhanced by therapy with a BRAF inhibitor. Furthermore, it could be shown in this study that the number of immunoreactive cells correlated with a reduction in tumor size and an increased necrosis in the tumor areas. The data obtained so far suggest that treatment with BRAF inhibitors increases melanoma antigen expression and thus facilitates T cell cytotoxicity. This results in a more favorable tumor microenvironment for a synergistic BRAF-targeted therapy and immunotherapy. This therapeutic strategy is currently being evaluated in clinical trials. The group of immunotherapeutics is a second new class of drugs, in which great hope for the treatment of metastatic melanoma is placed. Ipilimumab is an antibody that binds the cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), thereby stimulating T-cell activation and proliferation. The drug has been approved for the treatment of metastatic melanoma since July 2011 and significantly increases survival in some patients. In addition, at the end of 2015, a monoclonal antibody directed against the Programmed Death Receptor (PD1) was approved by the European Medicines Commission for the treatment of unresectable or metastatic melanoma. PD1 is a receptor that is expressed on T cells and inhibits T cell activation upon binding of a ligand. Study results have shown that blocking this T-cell inhibition with PD1 or PD-L1 antagonists is a very effective therapeutic strategy for melanoma and other tumor entities. Current data show that targeted therapy has a major impact on the tumor microenvironment and on the regulatory and effector cells of the immune system. However, the impact of the therapy on the immune system as a whole is largely unknown. A comprehensive understanding of these effects is crucial to be able to further develop the therapy and to evaluate useful combination therapies with other immunomodulatory agents. In the context of this study, the immune status, e.g. the number and the activation state of different immune cells at the beginning and in the course of a systemic therapy for metastatic melanoma should be determined. For this purpose, 10 ml of EDTA blood is taken as part of the guideline-compliant routine care (The blood samples taken in the study are given every 4 weeks for therapy with kinase inhibitors and every 2 weeks for therapy with checkpoint inhibitors). The blood samples taken before and during therapy will be analyzed by flow cytometry and the changes in the immunophenotype will be correlated with the response to therapy. In this way, the investigator want to identify both predictive and prognostic markers. The assessment of the immune status should help to optimize the effectiveness of melanoma therapy. Therefore, it would be important to identify suitable markers and to characterize subgroups of immune cells that have an impact on the tumor microenvironment. The evaluation of the immune status in melanoma patients could thus be incorporated into the treatment strategies in the future in order to combine a targeted therapy with immunomodulating substances or also from enriched sub-populations of immune cells in order to increase the effectiveness of the treatment.