Project description:Melanoma is the deadliest form of skin cancer showing rising incidence over the past years. New insights into the mechanisms of melanoma progression contributed to the development of novel treatment options, such as immunotherapies. However, acquiring resistance to treatment poses a big problem to therapy success. Therefore, understanding the mechanisms underlying resistance could improve therapy efficacy. By conducting transcriptional analysis between SCG2-overexpressing (OE) and control melanoma cells, we detected a downregulation of components of the antigen presenting machinery (APM), which is important for the assembly of the MHC class I complex.
Project description:Melanoma is the deadliest form of skin cancer showing rising incidence over the past years. New insights into the mechanisms of melanoma progression contributed to the development of novel treatment options, such as immunotherapies. However, acquiring resistance to treatment poses a big problem to therapy success. Therefore, understanding the mechanisms underlying resistance could improve therapy efficacy. Correlating expression levels in tissue samples of primary melanoma and metastases revealed that secretogranin 2 (SCG2) is highly expressed in advanced melanoma patients with poor overall survival (OS) rates. By conducting transcriptional analysis between SCG2-overexpressing (OE) and control melanoma cells, we detected a downregulation of components of the antigen presenting machinery (APM), which is important for the assembly of the MHC class I complex. Flow cytometry analysis revealed a downregulation of surface MHC class I expression on melanoma cells that showed resistance towards the cytotoxic activity of melanoma-specific T cells. IFNγ treatment partially reversed these effects. Based on our findings, we suggest that SCG2 might stimulate mechanisms of immune evasion and therefore be associated with resistance to checkpoint blockade and adoptive immunotherapy.
Project description:Oligodendrocytes and their progenitors upregulate MHC pathways in response to inflammation, but the frequency of this phenotypic change is unknown and the features of these immune oligodendroglia are poorly defined. We generated MHC class I and II transgenic reporter mice to define their dynamics in response to inflammatory demyelination, providing a means to monitor MHC activation in diverse cell types in living mice and define their roles in aging, injury and disease.
Project description:OIS is characterized by a stable proliferation arrest and secretion of pro-inflammatory cytokines and chemokines, the senescence-associated secretory phenotype (SASP). Proliferation arrest and the SASP collaborate to enact tumor suppression, the former by blocking cell proliferation and the latter by recruiting immune cells to clear damaged cells. However, the interactions of OIS cells with the immune system are still poorly defined. Here we show that engagement of OIS in primary human melanocytes, specifically by melanoma driver mutations NRASQ61K and BRAFV600E, causes expression of the MHC class II antigen presentation apparatus, via secreted IL1ß signaling and expression of CIITA, a master regulator of MHC class II gene transcription.
Project description:Immune checkpoint inhibitors interfere with T cell exhaustion but often fail to cure or control cancer long-term in patients. Using a genetic screen in C57BL/6J mice, we discovered a mutation in host H2-Aa that caused strong immune-mediated resistance to mouse melanomas. H2-Aa encodes an MHC class II α chain, and its absence in C57BL/6J mice eliminates all MHC-II expression. H2-Aa deficiency, specifically in dendritic cells (DC), led to a quantitative increase in type 2 conventional DC (cDC2) and a decrease in cDC1. H2-Aa–deficient cDC2, but not cDC1, were essential for melanoma suppression and effectively cross-primed and recruited CD8 T cells into tumors. Lack of T regulatory cells, also observed in H2-Aa deficiency, contributed to melanoma suppression. Acute disruption of H2-Aa was therapeutic in melanoma-bearing mice, particularly when combined with checkpoint inhibition, which had no therapeutic effect by itself. Our findings suggest that inhibiting MHC-II may be an effective immunotherapeutic approach to enhance immune responses to cancer.
Project description:Unleashing the immune anti-tumor response through immune checkpoint blockade (ICB) has been successful in treating many solid-tumor malignancies, including metastatic melanoma. When successful, the ICB response can be potent; however, half of patients fail to respond. ICB responsiveness is impacted by the harsh solid tumor microenvironment (TME), which is characterized by metabolic stress. The TME impacts tumor antigenicity, with ICB-responsive melanomas exhibiting increased major histocompatibility complex class I (MHC-I) expression. Further investigation of tumor immunogenicity in the context of the TME may improve cellular therapies. Here, we define and characterize an epigenetic mechanism regulating melanoma antigen presentation driven by prolonged metabolic stress. Murine and human melanoma cell lines were cultured under prolonged metabolic stress, forcing cells to adapt to the absence of glucose. Melanoma cells adapted to the absence of glucose have IFN-gamma-independent increases in MHC-I and an increased sensitivity to T cell-mediated killing. Proteomic analysis revealed dysregulation of histone epigenetic modifiers under prolonged metabolic stress, specifically loss of histone methyltransferase EZH2 (Enhancer of Zeste Homolog 2). EZH2 directly silences gene transcription via catalyzing H3K27me3. Following metabolic adaptation, ChIP-sequencing and ChIP-PCR revealed H3K27me3 loss at genes specific to MHC-I antigen presentation. Prolonged metabolic stress in melanoma cells blunt EZH2 levels and H3K27me3 levels at promoters of genes regulating MHC-I presentation, resulting in elevated MHC-I antigenicity and increased CD8+ T cell killing. This demonstrates potential for EZH2 abundance and mutational status as a prognostic indicators of ICB-responsiveness in metastatic melanoma and supports EZH2 inhibition as adjuvant for immunotherapies