Distinct Molecular Mechanisms of Altered HLA Class II Expression in Malignant Melanoma.

Stefanie Meyer,Maria-Filothei Lazaridou,Diana Handke,Chiara Massa,André Steven,Mark Berneburg,Katharina Biehl,Anja Mueller,Markus Kreuz,Barbara Seliger,Jürgen Bukur,Ulrike Koehl

doi:10.3390/cancers13153907

Abstract

Simple SummaryThere exists limited knowledge about the underlying molecular processes controlling the expression of HLA class II APM components and their prognostic significance in melanoma. Therefore, this study analyzed the basal and regulated expression of HLA class II antigens and components in melanoma cell lines and patients’ lesions in conjunction to T-cell infiltration. The heterogeneous constitutive HLA class II APM expression was caused by distinct molecular mechanisms and was partially linked to immune cell infiltration and clinical parameters. These results contribute not only to a better understanding of the regulation of HLA class II expression in melanoma, but might have an impact on the design of novel (immuno)therapies for the treatment of this disease.Background: The human leukocyte antigen (HLA) class II molecules are constitutively expressed in some melanoma, but the underlying molecular mechanisms have not yet been characterized. Methods: The expression of HLA class II antigen processing machinery (APM) components was determined in melanoma samples by qPCR, Western blot, flow cytometry and immunohistochemistry. Immunohistochemical and TCGA datasets were used for correlation of HLA class II expression to tumor grading, T-cell infiltration and patients’ survival. Results: The heterogeneous HLA class II expression in melanoma samples allowed us to characterize four distinct phenotypes. Phenotype I totally lacks constitutive HLA class II surface expression, which is inducible by interferon-gamma (IFN-γ); phenotype II expresses low basal surface HLA class II that is further upregulated by IFN-γ; phenotype III lacks constitutive and IFN-γ controlled HLA class II expression, but could be induced by epigenetic drugs; and in phenotype IV, lack of HLA class II expression is not recovered by any drug tested. High levels of HLA class II APM component expression were associated with an increased intra-tumoral CD4+ T-cell density and increased patients’ survival. Conclusions: The heterogeneous basal expression of HLA class II antigens and/or APM components in melanoma cells is caused by distinct molecular mechanisms and has clinical relevance.

Highlights

The implementation of high-throughput technologies led to the identification of a large series of mutations, which appeared to be involved in the development, maintenance and progression of malignant melanoma (MM), but might serve as suitable targets for T-cell-based immunotherapies, due to the creation of neo-antigens [1,2,3]
Gene transfer of class II transactivator protein (CIITA) into tumor cells resulted in a stimulation of tumor specific CD4+ T cells in vivo associated with a long-lasting protective immunity [34], as well as an increased repertoire of tumor-associated human leukocyte antigen (HLA) class II antigens [35]
Since the role of HLA class II antigens in melanoma is controversially discussed, a Tissue Microarrays (TMAs) consisting of 368 melanoma lesions was stained with an anti-pan-HLA class II-specific monoclonal antibodies (mAb) antibody

Summary

Introduction

The implementation of high-throughput technologies led to the identification of a large series of mutations, which appeared to be involved in the development, maintenance and progression of malignant melanoma (MM), but might serve as suitable targets for T-cell-based immunotherapies, due to the creation of neo-antigens [1,2,3]. Despite that tumor-associated antigens (TAA) can be recognized by CD8+ cytotoxic T lymphocytes (CTL) in the context of HLA class I antigens, T-cell-based immunotherapies of melanoma might exhibit a lower efficacy than expected [4], and patients often develop resistances to these treatments [5] This impaired response of MM patients is often associated with a downregulation or loss of HLA class I antigens and/or components of the HLA class I antigen-processing machinery (APM), leading to evasion from immune surveillance [6,7,8], disease progression and/or poor patients’ outcome [9,10], but their expression could be frequently upregulated by interferon (IFN)-α and IFN-γ [11,12]. Conclusions: The heterogeneous basal expression of HLA class II antigens and/or APM components in melanoma cells is caused by distinct molecular mechanisms and has clinical relevance

Methods

Results

Conclusion