MHC class II-mediated antigen presentation by melanoma cells

Dual molecule targeting HDAC6 leads to intratumoral CD4+ cytotoxic lymphocytes recruitment through MHC-II upregulation on lung cancer cells

BACKGROUND

Despite the current therapeutic treatments including surgery, chemotherapy, radiotherapy and more recently immunotherapy, the mortality rate of lung cancer stays high. Regarding lung cancer, epigenetic modifications altering cell cycle, angiogenesis and programmed cancer cell death are therapeutic targets to combine with immunotherapy to improve treatment success. In a recent study, we uncovered that a molecule called QAPHA ((E)-3-(5-((2-cyanoquinolin-4-yl)(methyl)amino)-2-methoxyphenyl)-N-hydroxyacrylamide) has a dual function as both a tubulin polymerization and HDAC inhibitors. Here, we investigate the impact of this novel dual inhibitor on the immune response to lung cancer.

METHODS

To elucidate the mechanism of action of QAPHA, we conducted a chemical proteomics analysis. Using an in vivo mouse model of lung cancer (TC-1 tumor cells), we assessed the effects of QAPHA on tumor regression. Tumor infiltrating immune cells were characterized by flow cytometry.

RESULTS

In this study, we first showed that QAPHA effectively inhibited histone deacetylase 6, leading to upregulation of HSP90, cytochrome C and caspases, as revealed by proteomic analysis. We confirmed that QAPHA induces immunogenic cell death (ICD) by expressing calreticulin at cell surface in vitro and demonstrated its efficacy as a vaccine in vivo. Remarkably, even at a low concentration (0.5 mg/kg), QAPHA achieved complete tumor regression in approximately 60% of mice treated intratumorally, establishing a long-lasting anticancer immune response. Additionally, QAPHA treatment promoted the infiltration of M1-polarized macrophages in treated mice, indicating the induction of a pro-inflammatory environment within the tumor. Very interestingly, our findings also revealed that QAPHA upregulated major histocompatibility complex class II (MHC-II) expression on TC-1 tumor cells both in vitro and in vivo, facilitating the recruitment of cytotoxic CD4+T cells (CD4+CTL) expressing CD4+, NKG2D+, CRTAM+, and Perforin+. Finally, we showed that tumor regression strongly correlates to MHC-II expression level on tumor cell and CD4+ CTL infiltrate.

CONCLUSION

Collectively, our findings shed light on the discovery of a new multitarget inhibitor able to induce ICD and MHC-II upregulation in TC-1 tumor cell. These two processes participate in enhancing a specific CD4+ cytotoxic T cell-mediated antitumor response in vivo in our model of lung cancer. This breakthrough suggests the potential of QAPHA as a promising agent for cancer treatment.

Identification of neoantigens for individualized therapeutic cancer vaccines

Somatic mutations in cancer cells can generate tumour-specific neoepitopes, which are recognized by autologous T cells in the host. As neoepitopes are not subject to central immune tolerance and are not expressed in healthy tissues, they are attractive targets for therapeutic cancer vaccines. Because the vast majority of cancer mutations are unique to the individual patient, harnessing the full potential of this rich source of targets requires individualized treatment approaches. Many computational algorithms and machine-learning tools have been developed to identify mutations in sequence data, to prioritize those that are more likely to be recognized by T cells and to design tailored vaccines for every patient. In this Review, we fill the gaps between the understanding of basic mechanisms of T cell recognition of neoantigens and the computational approaches for discovery of somatic mutations and neoantigen prediction for cancer immunotherapy. We present a new classification of neoantigens, distinguishing between guarding, restrained and ignored neoantigens, based on how they confer proficient antitumour immunity in a given clinical context. Such context-based differentiation will contribute to a framework that connects neoantigen biology to the clinical setting and medical peculiarities of cancer, and will enable future neoantigen-based therapies to provide greater clinical benefit.

Myron Gordon Award paper: Microbes, T-cell diversity and pigmentation

Melanocytes are static, minimally proliferative cells. This leaves them vulnerable in vitiligo. Yet upon malignant transformation, they form vicious tumors. This profound switch in physiology is accompanied by genetic change and is driven by environmental factors. If UV exposure in younger years supports malignant transformation and melanoma formation, it can likewise impart mutations on melanocytes that reduce their viability, to initiate vitiligo. A wide variety of microbes can influence these diametrically opposed outcomes before either disease takes hold. These microbes are vehicles of change that we are only beginning to study. Once a genetic modification occurs, there is a wide variety of immune cells ready to respond. Though it does not act alone, the T cell is among the most decisive responders in this process. The same biochemical process that offered the skin protection by producing melanin can become an Achilles heel for the cell when the T cells target melanosomal enzymes or, on occasion, neoantigens. T cells are precise, determined, and consequential when they strike. Here, we probe the relationship between the microbiome and its metabolites, epithelial integrity, and the activation of T cells that target benign and malignant melanocytes in vitiligo and melanoma.

Lipid Metabolism and Tumor Antigen Presentation

Tumors always evade immune surveillance and block T cell activation in a poorly immunogenic and immunosuppressive environment. Cancer cells and immune cells exhibit metabolic reprogramming in the tumor microenvironment (TME), which intimately links immune cell function and edits tumor immunology. In addition to glucose metabolism, amino acid and lipid metabolism also provide the materials for biological processes crucial in cancer biology and pathology. Furthermore, lipid metabolism is synergistically or negatively involved in the interactions between tumors and the microenvironment and contributes to the regulation of immune cells. Antigen processing and presentation as the initiation of adaptive immune response play a critical role in antitumor immunity. Therefore, a relationship exists between antigen-presenting cells and lipid metabolism in TME. This chapter introduces the updated understandings of lipid metabolism of tumor antigen-presenting cells and describes new directions in the manipulation of immune responses for cancer treatment.

Pre-clinical modeling of cutaneous melanoma

Metastatic melanoma is challenging to manage. Although targeted- and immune therapies have extended survival, most patients experience therapy resistance. The adaptability of melanoma cells in nutrient- and therapeutically-challenged environments distinguishes melanoma as an ideal model for investigating therapy resistance. In this review, we discuss the current available repertoire of melanoma models including two- and three-dimensional tissue cultures, organoids, genetically engineered mice and patient-derived xenograft. In particular, we highlight how each system recapitulates different features of melanoma adaptability and can be used to better understand melanoma development, progression and therapy resistance.

Despite the new targeted and immunotherapies for metastatic melanoma, several patients show therapeutic plateau. Here, the authors review the current pre-clinical models of cutaneous melanoma and discuss their strengths and limitations that may help with overcoming therapeutic plateau.

Conservation of immune gene signatures in solid tumors and prognostic implications

Background

Tumor-infiltrating leukocytes can either limit cancer growth or facilitate its spread. Diagnostic strategies that comprehensively assess the functional complexity of tumor immune infiltrates could have wide-reaching clinical value. In previous work we identified distinct immune gene signatures in breast tumors that reflect the relative abundance of infiltrating immune cells and exhibited significant associations with patient outcomes. Here we hypothesized that immune gene signatures agnostic to tumor type can be identified by de novo discovery of gene clusters enriched for immunological functions and possessing internal correlation structure conserved across solid tumors from different anatomic sites.

Methods

We assembled microarray expression datasets encompassing 5,295 tumors of the breast, colon, lung, ovarian and prostate. Unsupervised clustering methods were used to determine number and composition of gene clusters within each dataset. Immune-enriched gene clusters (signatures) identified by gene ontology enrichment were analyzed for internal correlation structure and conservation across tumors then compared against expression profiles of: 1) flow-sorted leukocytes from peripheral blood and 2) >300 cancer cell lines from solid and hematologic cancers. Cox regression analysis was used to identify signatures with significant associations with clinical outcome.

Results

We identified nine distinct immune-enriched gene signatures conserved across all five tumor types. The signatures differentiated specific leukocyte lineages with moderate discernment overall, and naturally organized into six discrete groups indicative of admixed lineages. Moreover, seven of the signatures exhibit minimal and uncorrelated expression in cancer cell lines, suggesting that these signatures derive predominantly from infiltrating immune cells. All nine immune signatures achieved statistically significant associations with patient prognosis (p<0.05) in one or more tumor types with greatest significance observed in breast and skin cancers. Several signatures indicative of myeloid lineages exhibited poor outcome associations that were most apparent in brain and colon cancers.

Conclusions

These findings suggest that tumor infiltrating immune cells can be differentiated by immune-specific gene expression patterns that quantify the relative abundance of multiple immune infiltrates across a range of solid tumor types. That these markers of immune involvement are significantly associated with patient prognosis in diverse cancers suggests their clinical utility as pan-cancer markers of tumor behavior and immune responsiveness.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2948-z) contains supplementary material, which is available to authorized users.

CD4+ T cell-mediated cytotoxicity eliminates primary tumor cells in metastatic melanoma through high MHC class II expression and can be enhanced by inhibitory receptor blockade

Metastatic melanoma is a rapidly progressing disease with high mortality rate and limited treatment options. Immunotherapy based on tumor-targeting cytotoxic T cell responses represents a promising strategy. To assist in its development, we examined the possibility and efficacy of using CD4+ cytotoxic T cells. The regulatory mechanisms controlling CD4+ T cell-mediated cytotoxicity were also investigated. We found that naturally occurring granzyme B and perforin-expressing CD4+ cytotoxic T cells can be recovered from metastatic melanoma patients at significantly elevated frequencies compared to those from healthy controls. These CD4+ cytotoxic T cells were also capable of killing autologous tumor cells harvested from metastatic melanoma, independent of CD8+ T cells or any other cell types. However, several restricting factors were observed. First, the cytolytic activity by CD4+ T cells required high MHC class II expression on melanoma cells, which was not satisfied in a subset of melanomas. Second, the granzyme B and perforin release by activated CD4+ cytotoxic T cells was reduced after coculturing with autologous melanoma cells, characterized by low LAMP-1 expression and low granzyme B and perforin secretion in the supernatant. This suggested that inhibitory mechanisms were present to suppress CD4+ cytotoxic T cells. Indeed, blockade of PD-1 and CTLA-4 had increased the cytolytic activity of CD4+ T cells but was only effective in MHC class II high but not MHC class II low melanomas. Together, our study showed that CD4+ T cell-mediated cytotoxicity could eliminate primary melanoma cells but the efficacy depended on MHC class II expression.

MHC class II presentation of gp100 epitopes in melanoma cells requires the function of conventional endosomes and is influenced by melanosomes

Many human solid tumors express MHC class II (MHC-II) molecules, and proteins normally localized to melanosomes give rise to MHC-II-restricted epitopes in melanoma. However, the pathways by which this response occurs have not been defined. We analyzed the processing of one such epitope, gp100(44-59), derived from gp100/Pmel17. In melanomas that have down-regulated components of the melanosomal pathway, but constitutively express HLA-DR*0401, the majority of gp100 is sorted to LAMP-1(high)/MHC-II(+) late endosomes. Using mutant gp100 molecules with altered intracellular trafficking, we demonstrate that endosomal localization is necessary for gp100(44-59) presentation. By depletion of the AP-2 adaptor protein using small interfering RNA, we demonstrate that gp100 protein internalized from the plasma membrane to such endosomes is a major source for gp100(44-59) epitope production. The gp100 trapped in early endosomes gives rise to epitopes that are indistinguishable from those produced in late endosomes but their production is less sensitive to inhibition of lysosomal proteases. In melanomas containing melanosomes, gp100 is underrepresented in late endosomes, and accumulates in stage II melanosomes devoid of MHC-II molecules. The gp100(44-59) presentation is dramatically reduced, and processing occurs entirely in early endosomes or stage I melanosomes. This occurrence suggests that melanosomes are inefficient Ag-processing compartments. Thus, melanoma de-differentiation may be accompanied by increased presentation of MHC-II restricted epitopes from gp100 and other melanosome-localized proteins, leading to enhanced immune recognition.

An epigenetic vaccine model active in the prevention and treatment of melanoma

Background

Numerous immune genes are epigenetically silenced in tumor cells and agents such as histone deacetylase inhibitors (HDACi), which reverse these effects, could potentially be used to develop therapeutic vaccines. The conversion of cancer cells to antigen presenting cells (APCs) by HDACi treatment could potentially provide an additional pathway, together with cross-presentation of tumor antigens by host APCs, to establish tumor immunity.

Methods

HDACi-treated B16 melanoma cells were used in a murine vaccine model, lymphocyte subset depletion, ELISpot and Cytotoxicity assays were employed to evaluate immunity. Antigen presentation assays, vaccination with isolated apoptotic preparations and tumorigenesis in MHC-deficient mice and radiation chimeras were performed to elucidate the mechanisms of vaccine-induced immunity.

Results

HDACi treatment enhanced the expression of MHC class II, CD40 and B7-1/2 on B16 cells and vaccination with HDACi-treated melanoma cells elicited tumor specific immunity in both prevention and treatment models. Cytotoxic and IFN-γ-producing cells were identified in splenocytes and CD4⁺, CD8⁺ T cells and NK cells were all involved in the induction of immunity. Apoptotic cells derived from HDACi treatments, but not H₂O₂, significantly enhanced the effectiveness of the vaccine. HDACi-treated B16 cells become APCs in vitro and studies in chimeras defective in cross presentation demonstrate direct presentation in vivo and short-term but not memory responses and long-term immunity.

Conclusion

The efficacy of this vaccine derives mainly from cross-presentation which is enhanced by HDACi-induced apoptosis. Additionally, epigenetic activation of immune genes may contribute to direct antigen presentation by tumor cells. Epigenetically altered cancer cells should be further explored as a vaccine strategy.

Immunohistochemical characterization of tumor cells and inflammatory infiltrate associated with cutaneous melanocytic tumors of Duroc and Iberian swine

The immunophenotype of tumor cells and inflammatory infiltrate associated with cutaneous melanocytic lesions (29 melanocytomas, two malignant melanomas, and 23 residual lesions) from 54 adult Iberian and Iberian x Duroc pigs were examined using a panel of nine antibodies. All neoplastic cells were vimentin+, cytokeratin-, and alpha-1-antitrypsin- and the majority were S100+, whereas all pigmented macrophages were vimentin+, cytokeratin-, and S100- and most expressed alpha-1-antitrypsin. Regressing tumors were characterized by zones with low density of neoplastic cells accompanied by heavy infiltration of CD3+ T lymphocytes, whereas zones with high density of neoplastic cells showed very low numbers of CD3+ T lymphocytes. The infiltrate of CD79a+ B cells and IgG, IgM, and IgA plasma cells was low. The majority of lymphocytes of the peri- and intratumoral infiltrate were major histocompatibility complex class II+, but neoplastic cells did not express class II antigen. The 17 residual lesions examined were composed of macrophages containing abundant melanin pigment and low to moderate numbers of CD3+ T lymphocytes. The results of the present study suggest that the local cellular immune response plays a crucial role in the host response that induces regression of cutaneous melanomas and melanocytomas of the Iberian and crossbred Iberian x Duroc pigs.

T-cell-directed cancer vaccines: mechanisms of immune escape and immune tolerance

Recent clinical trials using vaccines directed toward tumour-associated antigens (TA) have shown the increasing capacity of vaccines to cause immunologic responses. In fact, strongly reactive TA-specific cytolytic T-lymphocytes and tumour-infiltrating lymphocytes (TIL) can be identified and expanded ex vivo from patients with metastatic melanoma vaccinated with melanoma-associated antigens. Paradoxically, this strong immunological response does not correlate with clinical tumour regression. Proposed mechanisms responsible for this glaring inconsistency are numerous and varied; systemic immunosuppressive as well as local mechanistic factors are implicated. In this review we will critically evaluate the possible mechanisms that allow tumours to escape immune destruction and be tolerated by the immune system. In addition, strategies that may allow further insight into the biology of tumour rejection are discussed, in the hope of deepening the understanding of this phenomenon and enhancing its therapeutic potential.

Restoration of alloreactivity of melanoma by transduction with B7.1

Melanoma cells are unusual because, unlike most epithelial tumors, constitutive expression of human leukocyte antigen (HLA) class II molecules is common. To elucidate the role of HLA class II expression in the immunopathogenesis of melanoma, the authors compared HLA class II+ melanoma cells to autologous B cells with respect to their ability to stimulate primary (naïve) histoincompatible lymphocytes and T-cell clones (antigen experienced). Using primary lymphocytes (peripheral blood lymphocytes [PBLs]), melanoma cells were nonstimulatory when compared to autologous B cells. To determine whether this was caused by defective antigen processing, the authors used alloreactive T-cell clones, which require alloantigen presentation by a histocompatible stimulator cell but not costimulation. Melanoma cells stimulated the alloreactive T-cell clones in two of three clones tested, indicating that they processed and presented alloantigen. To determine whether the failure of melanoma cells to stimulate primary lymphocytes was caused by their inability to costimulate the T cells, the authors transduced the melanoma cells with B7.1 and achieved stable expression in more than 95% of the cells. The transduced cells were highly stimulatory, eliciting a 17- to 25-fold increase in proliferation by the peripheral blood lymphocytes compared with controls. Indeed, B7-expressing melanoma cells were more stimulatory than autologous B cells, which elicited an 11- to 15-fold increase compared with controls. These data indicate that melanoma cells fail to stimulate primary lymphocytes because they do not deliver costimulatory signals. Engineering HLA class II+ melanoma cells to express high levels of B7.1 may provide a way to elicit primary T-cell responses to melanoma-associated antigens.

HLA-DQB1*0303 and *0301 alleles influence susceptibility to and prognosis in cutaneous malignant melanoma in the British Caucasian population

The presence of lymphocytic infiltrates within primary cutaneous malignant melanoma (CMM), documented spontaneous tumour regression and genetic linkage with chromosome six in familial cases all suggest that immunogenetic factors may modulate disease progression. An association has been suggested between HLA DQB1*0301 and CMM in US patients but no such investigation has been performed in the UK population. Polymerase chain reaction-based HLA class II DRB1, DQA1 and DQB1 typing of 99 UK-based CMM patients was performed using DNA extracted from archival formalin-fixed and paraffin wax-embedded surgical biopsies, enabling retrospective access to clinical follow-up data. An increase in frequency of the HLA DQB1*0303 genotype among CMM patients was identified compared to control subjects (19.2% vs 5.8%; Pc=0.003; RR=3.9) while HLA DQB1*0301 was associated with more advanced and therefore poorer prognosis primary tumours (e.g. HLA DQB1*0301 allele frequency: 20.1% vertical growth phase vs 4.0% horizontal growth phase; Pc=0.03; RR=6.1). These findings suggest that the HLA DQB1 locus, and in particular the HLA DQB1*0303 and *0301 alleles, may play an important role in determining the risk of development and the prognosis of CMM within the UK population.