Immune alterations in malignant melanoma and current immunotherapy concepts

INTRODUCTION

Malignant melanoma is a highly aggressive, immunogenic tumor that has the ability to modulate the immune system to its own advantage. Patients with melanoma present numerous cellular immune defects and cytokine abnormalities, all leading to suppression of the host anti-tumor immune response. Innovative treatment strategies can be achieved through employing our knowledge of the melanoma-induced immune alterations.

AREAS COVERED

The authors review comprehensively the immune abnormalities in individuals with melanoma, and provide a summary of currently available melanoma immunotherapy agents that are currently on the market or undergoing clinical trials.

EXPERT OPINION

Ipilimumab, a monoclonal antibody directed against the CTLA-4, is one of the current forefront treatment strategies in malignant melanoma. Novel immunomodulating agents have shown clear activity in patients with malignant melanoma. These include anti-PD-1 and anti-PD-1 ligand antibodies that may soon become important items in the anti-melanoma armamentarium. Combinations of different immunotherapy agents, between themselves or with other agents, are currently being studied in an attempt to further enhance the antineoplastic effect in patients with malignant melanoma.

Cytokine-Based Therapy and Biochemotherapy for Advanced Melanoma

A variety of immunotherapeutic approaches have shown activity in patients with metastatic melanoma with the best results being observed with interleukin 2 (IL-2). Follow-up data through 2004 confirm the durability of responses produced by the Food and Drug Administration-approved high-dose IL-2 regimen in this patient population. Efforts to develop more tolerable and/or effective IL-2-based treatment regimens by either prolonged administration of lower doses or the combination of IL-2 with other cytokines, monoclonal antibodies, or vaccines have yet to produce results superior to those seen with high-dose IL-2 alone. Recent investigations have suggested that, in some patients, IL-2 may expand regulatory T-cell populations leading to immune tolerance rather than antitumor immunity. Efforts to shift this balance in favor of immune rejection by reducing the confounding effects of regulatory T cells on IL-2 therapy or the use of novel and potentially more purely immunostimulatory cytokines are ongoing. Despite promising phase 2 data, phase 3 studies have failed to show meaningful clinical benefit for the combination of cytokines with cytotoxic chemotherapy, so-called "biochemotherapy." Nonetheless, recent investigations with biochemotherapy followed by maintenance immunotherapy suggest that biochemotherapy may still have a role as a "bridge to immunotherapy" in some patients with rapidly progressive disease. Given the low number of patients achieving durable benefit with cytokine-based immunotherapy, considerable recent effort has focused on identifying predictors of therapeutic response. Investigations suggest that immune responsiveness may be predetermined by a tumor microenvironment conducive to immune recognition and the host propensity to develop autoimmunity. Efforts to understand and further define pretreatment predictors of response through the use of gene expression and proteomic techniques are ongoing and raise the potential for eventually limiting cytokine-based immunotherapy to those most likely to benefit.

Randomized Trials in Melanoma: An Update

No effective therapy for metastatic melanoma exists. Polychemotherapy or chemoimmunotherapy have not shown survival benefits. Vaccines have shown little activity in stage IV disease. To advance the identification of effective agents, new drugs can and should be offered as first-line treatment. Efforts must be made to improve understanding of the biology of malignant melanoma. Too many phase III trials have been conducted with a poor understanding of the mechanism of action of the involved drugs.