Defective Human Leukocyte Antigen Class I-associated Antigen Presentation Caused by a Novel β2-Microglobulin Loss-of-function in Melanoma Cells

A diversity of novel type-2 innate lymphoid cell subpopulations revealed during tumour expansion

Type 2 innate lymphoid cells (ILC2s) perform vital functions in orchestrating humoral immune responses, facilitating tissue remodelling, and ensuring tissue homeostasis. Additionally, in a role that has garnered considerably less attention, ILC2s can also enhance Th1-related cytolytic T lymphocyte immune responses against tumours. Studies have thus far generally failed to address the mystery of how one ILC2 cell-type can participate in a multiplicity of functions. Here we utilized single cell RNA sequencing analysis to create the first comprehensive atlas of naïve and tumour-associated lung ILC2s and discover multiple unique subtypes of ILC2s equipped with developmental gene programs that become skewed during tumour expansion favouring inflammation, antigen processing, immunological memory and Th1-related anti-tumour CTL responses. The discovery of these new subtypes of ILC2s challenges current paradigms of ILC2 biology and provides an explanation for their diversity of function.

Heterotypic communication as the promoter of phenotypic plasticity of cancer cells: The role of cancer secretomes

Cellular communication relies on signaling circuits whose statuses are mainly modulated by soluble biomolecules such as carbohydrates, lipids, proteins, and metabolites as well as extracellular vesicles (EVs). Therefore, the active secretion of such biomolecules is critical for both cell homeostasis and proper pathophysiological responses in a timely fashion. In this context, proteins are among the main modulators of such biological responses. Hence, profiling cell line secretomes may be an opportunity for the identification of "signatures" of specific cell types (i.e., stromal or metastatic cells) with important prognostic/therapeutic value. This review will focus on the biological implications of cell secretomes in the context of cancer, as well as their functional roles in shaping the tumoral microenvironment (TME) and communication status of participating cells.

A novel cell-based screen identifies chemical entities that reverse the immune-escape phenotype of metastatic tumours

Genetic and epigenetic events have been implicated in the downregulation of the cellular antigen processing and presentation machinery (APM), which in turn, has been associated with cancer evasion of the immune system. When these essential components are lacking, cancers develop the ability to subvert host immune surveillance allowing cancer cells to become invisible to the immune system and, in turn, promote cancer metastasis. Here we describe and validate the first high-throughput cell-based screening assay to identify chemical extracts and unique chemical entities that reverse the downregulation of APM components in cell lines derived from metastatic tumours. Through the screening of a library of 480 marine invertebrate extracts followed by bioassay-guided fractionation, curcuphenol, a common sesquiterpene phenol derived from turmeric, was identified as the active compound of one of the extracts. We demonstrate that curcuphenol induces the expression of the APM components, TAP-1 and MHC-I molecules, in cell lines derived from both metastatic prostate and lung carcinomas. Turmeric and curcumins that contain curcuphenol have long been utilized not only as a spice in the preparation of food, but also in traditional medicines for treating cancers. The remarkable discovery that a common component of spices can increase the expression of APM components in metastatic tumour cells and, therefore reverse immune-escape mechanisms, provides a rationale for the development of foods and advanced nutraceuticals as therapeutic candidates for harnessing the power of the immune system to recognize and destroy metastatic cancers.

The immune-related role of beta-2-microglobulin in melanoma

Despite the remarkable success of immunotherapy in the treatment of melanoma, resistance to these agents still affects patient prognosis and response to therapies. Beta-2-microglobulin (β2M), an important subunit of major histocompatibility complex (MHC) class I, has important biological functions and roles in tumor immunity. In recent years, increasing studies have shown that B2M gene deficiency can inhibit MHC class I antigen presentation and lead to cancer immune evasion by affecting β2M expression. Based on this, B2M gene defect and T cell-based immunotherapy can interact to affect the efficacy of melanoma treatment. Taking into account the many recent advances in B2M-related melanoma immunity, here we discuss the immune function of the B2M gene in tumors, its common genetic alteration in melanoma, and its impact on and related improvements in melanoma immunotherapy. Our comprehensive review of β2M biology and its role in tumor immunotherapy contributes to understanding the potential of B2M gene as a promising melanoma therapeutic target.

Tim-3 adapter protein Bat3 acts as an endogenous regulator of tolerogenic dendritic cell function

Dendritic cells (DCs) sense environmental cues and adopt either an immune-stimulatory or regulatory phenotype, thereby fine-tuning immune responses. Identifying endogenous regulators that determine DC function can thus inform the development of therapeutic strategies for modulating the immune response in different disease contexts. Tim-3 plays an important role in regulating immune responses by inhibiting the activation status and the T cell priming ability of DC in the setting of cancer. Bat3 is an adaptor protein that binds to the tail of Tim-3; therefore, we studied its role in regulating the functional status of DCs. In murine models of autoimmunity (experimental autoimmune encephalomyelitis) and cancer (MC38-OVA-implanted tumor), lack of Bat3 expression in DCs alters the T cell compartment-it decreases TH1, TH17 and cytotoxic effector cells, increases regulatory T cells, and exhausted CD8+ tumor-infiltrating lymphocytes, resulting in the attenuation of autoimmunity and acceleration of tumor growth. We found that Bat3 expression levels were differentially regulated by activating versus inhibitory stimuli in DCs, indicating a role for Bat3 in the functional calibration of DC phenotypes. Mechanistically, loss of Bat3 in DCs led to hyperactive unfolded protein response and redirected acetyl-coenzyme A to increase cell intrinsic steroidogenesis. The enhanced steroidogenesis in Bat3-deficient DC suppressed T cell response in a paracrine manner. Our findings identified Bat3 as an endogenous regulator of DC function, which has implications for DC-based immunotherapies.

Specific cannabinoids revive adaptive immunity by reversing immune evasion mechanisms in metastatic tumours

Emerging cancers are sculpted by neo-Darwinian selection for superior growth and survival but minimal immunogenicity; consequently, metastatic cancers often evolve common genetic and epigenetic signatures to elude immune surveillance. Immune subversion by metastatic tumours can be achieved through several mechanisms; one of the most frequently observed involves the loss of expression or mutation of genes composing the MHC-I antigen presentation machinery (APM) that yields tumours invisible to Cytotoxic T lymphocytes, the key component of the adaptive cellular immune response. Fascinating ethnographic and experimental findings indicate that cannabinoids inhibit the growth and progression of several categories of cancer; however, the mechanisms underlying these observations remain clouded in uncertainty. Here, we screened a library of cannabinoid compounds and found molecular selectivity amongst specific cannabinoids, where related molecules such as Δ9-tetrahydrocannabinol, cannabidiol, and cannabigerol can reverse the metastatic immune escape phenotype in vitro by inducing MHC-I cell surface expression in a wide variety of metastatic tumours that subsequently sensitizing tumours to T lymphocyte recognition. Remarkably, H3K27Ac ChIPseq analysis established that cannabigerol and gamma interferon induce overlapping epigenetic signatures and key gene pathways in metastatic tumours related to cellular senescence, as well as APM genes involved in revealing metastatic tumours to the adaptive immune response. Overall, the data suggest that specific cannabinoids may have utility in cancer immunotherapy regimens by overcoming immune escape and augmenting cancer immune surveillance in metastatic disease. Finally, the fundamental discovery of the ability of cannabinoids to alter epigenetic programs may help elucidate many of the pleiotropic medicinal effects of cannabinoids on human physiology.

Biomimetic Nanoparticles Enabled by Cascade Cell Membrane Coating for Direct Cross-Priming of T Cells

Despite the activation of T lymphocytes by antigen-presenting cells being responsible for eliciting antigen-specific immune responses, their crosstalking suffers from temporospatial limitations and endogenous influencing factors, which restrict the generation of a strong antitumor immunity. Here, cascade cell membrane coating is reported to prepare biomimetic nanoparticles (BNs) that can manipulate the cross-priming of T cells. BNs are obtained from coating nanoparticulate substrates with cell membranes extracted from dendritic cells (DCs) that are pre-pulsed with cancer cell membrane-coated nanoparticles. With a DC membrane that presents an array of cancer cell membrane antigen epitopes, BNs inherit the intrinsic membrane function of DCs, which can directly cross-prime T cells and provoke robust yet antigen-specific antitumor responses in multiple mouse models. Combination with clinical anti-programmed death-1 antibodies demonstrates a robust way of BNs to achieve desirable tumor regression and survival rate. This work spotlights the impact of nanoparticles on direct cross-priming of T cells and supports a unique yet modulate platform for boosting an effective adaptive immunity for immunotherapy.

Artificial Mini Dendritic Cells Boost T Cell-Based Immunotherapy for Ovarian Cancer

Ovarian cancer is the most lethal gynecological malignancy with high recurrence rates and low survival rates, remaining a disease of high unmet need. Cancer immunotherapy, which harnesses the potential of the immune system to attack tumors, has emerged as one of the most promising treatment options in recent years. As an important form of immunotherapy, dendritic cell (DC)-based vaccines have demonstrated the ability to induce an immune response, while clinical efficacy of DC vaccines remains unsubstantiated as long-term benefit is only reported in a restricted proportion of patients. Here, a biomimetic nanovaccine derived from DCs is developed through cell membrane coating nanotechnology. This nanovaccine, denoted "mini DC," inherits the ability of antigen presentation and T cells' stimulation from DCs and is shown to elicit enhanced activation of T cells both in vitro and in vivo. In a mouse model of ovarian cancer, mini DCs exhibit superior therapeutic and prophylactic efficacy against cancer including delayed tumor growth and reduced tumor metastasis compared with DC vaccine. These findings suggest that mini DCs may serve as a facile and potent vaccine to boost anticancer immunotherapy.

Gemcitabine alters the proteasome composition and immunopeptidome of tumour cells

The antigenic makeup of tumour cells can have a profound effect on the progression of cancer and success of immunotherapies. Therefore, one strategy to improve the efficacy of cancer treatments is to augment the antigens displayed by tumours. The present study explores how the recognition of tumour cells may be altered by non-cytotoxic concentrations of gemcitabine (GEM). Testing a panel of chemotherapeutics in human cancer cell lines in vitro, it was found that GEM increased surface expression of HLA-A,B,C and that underlying this were specific increases in β-2-microglobulin and immunoproteasome subunit proteins. Furthermore, the peptide antigen repertoire displayed on HLA class I was altered, revealing a number of novel antigens, many of which that were derived from proteins involved in the DNA-damage response. Changes in the nature of the peptide antigens eluted from HLA-A,B,C after GEM treatment consisted of amino acid anchor-residue modifications and changes in peptide length which rendered peptides likely to favour alternative HLA-alleles and increased their predicted immunogenicity. Signalling through the MAPK/ERK and NFκB/RelB pathways was associated with these changes. These data may explain observations made in previous in vivo studies, advise as to which antigens should be used in future vaccination protocols and reinforce the idea that chemotherapy and immunotherapy could be used in combination.

Oncogenic growth factor signaling mediating tumor escape from cellular immunity

Unrestrained growth factor signals can promote carcinogenesis, as well as other hallmarks of cancer such as immune evasion. Our understanding of the function and complex regulation of HER family of receptors has led to the development of targeted therapeutic agents that suppress tumor growth. However, these receptors also mediate escape from recognition by the host immune system. We discuss how HER family of oncogenic receptors downregulate tumor antigen presentation and upregulate suppressive membrane-bound or soluble secreted inhibitory molecules that ultimately lead to impaired cellular immunity mediated by cytotoxic T lymphocyte (CTL) recognition. Implementing this knowledge into new therapeutic strategies to enhance tumor immunogenicity may restore effector cell mediated immune clearance of tumors and clinical efficacy of tumor-targeted immunotherapy against HER receptor overexpression.

Dendritic cell-based immunotherapy

Immunotherapy using dendritic cell (DC)-based vaccination is an approved approach for harnessing the potential of a patient's own immune system to eliminate tumor cells in metastatic hormone-refractory cancer. Overall, although many DC vaccines have been tested in the clinic and proven to be immunogenic, and in some cases associated with clinical outcome, there remains no consensus on how to manufacture DC vaccines. In this review we will discuss what has been learned thus far about human DC biology from clinical studies, and how current approaches to apply DC vaccines in the clinic could be improved to enhance anti-tumor immunity.

Position 97 of HLA-B, a residue implicated in pathogenesis of ankylosing spondylitis, plays a key role in cell surface free heavy chain expression

Objective

Association of position 97 (P97) residue polymorphisms in human leucocyte antigen (HLA)-B, including HLA-B*27, with ankylosing spondylitis (AS) has recently been reported. We studied the effect of P97 variations on cell surface expression of the AS-associated HLA-B*27 and HLA-B*51, and the AS-protective HLA-B*7.

Methods

Flow cytometry was used to measure surface expression of HLA-B*27 in C1R/HeLa cells expressing HLA-B*27 (N97) and six mutants at P97 (N97T, N97S, N97V, N97R, N97W and N97D). Transporter associated with antigen processing-deficient T2, tapasin-deficient 220, β2m-deficient HCT15 and endoplasmic reticulum aminopeptidase 1 or β2m-clustered regularly interspaced short palindromic repeats/Cas9-knockout HeLa cells were used to provide evidence for specific protein interactions. Surface expression of HLA-B*7/HLA-B*51 P97 mutants was also studied.

Results

Mutation of HLA-B*27 P97 to the AS risk residue threonine increased cell surface free heavy chain (FHC) expression. Protective residues (serine or valine) and non-AS-associated residues (arginine or tryptophan) did not alter FHC expression. The N97D mutation reduced expression of conventional and FHC forms of HLA-B*27. Differences in FHC expression levels between HLA-B*27, HLA-B*27-N97T and HLA-B*27-N97D were dependent on the presence of functional β2m. HLA-B*7, which has an AS-protective serine at P97, expressed lower levels of FHC than HLA-B*27 or HLA-B*51. Introduction of asparagine at P97 of both HLA-B*7 and HLA-B*51 increased FHC expression.

Conclusions

The nature of P97 residue affects surface expression of HLA-B*27, B*7 and B*51, with AS-associated residues giving rise to higher FHC expression levels. The association of P97 amino acid polymorphisms with AS could be, at least in part, explained by its effect on HLA-B*27 FHC cell surface expression.

Diversification of Antitumour Immunity in a Patient with Metastatic Melanoma Treated with Ipilimumab and an IDO-Silenced Dendritic Cell Vaccine

Indoleamine 2,3-dioxygenase (IDO) expression in dendritic cells (DCs) inhibits T-cell activation and promotes T-cell differentiation into regulatory T-cells. Moreover, IDO expression promotes resistance to immunotherapies targeting immune checkpoints such as the cytotoxic T lymphocyte antigen-4 (CTLA-4). Here, a patient with metastatic melanoma pretreated with ipilimumab, an anti-CTLA-4 blocking antibody, was vaccinated with IDO-silenced DCs cotransfected with mRNA for survivin or hTERT tumour antigens. During vaccination, T-cell responses to survivin and hTERT tumour antigens were generated, and a certain degree of clinical benefit was achieved, with a significant reduction in lung, liver, and skin metastases, along with a better performance status. T-cell responses against MART-1 and NY-ESO-1 tumour antigens were also detected in the peripheral blood. The patient also mounted an antibody response to several melanoma proteins, indicating diversification of the antitumour immunity in this patient. The identification of such serum antibody-reacting proteins could facilitate the discovery of tumour neoantigens.

Improvement of the cytotoxic T lymphocyte response against hepatocellular carcinoma by transduction of cancer cells with an adeno-associated virus carrying the interferon-γ gene

Dendritic cell (DC)-based antigen-targeted immunotherapy may offer effective adjuvant therapy for hepatocellular carcinoma (HCC), in which cytotoxic T lymphocytes (CTLs) are key. However, in a number of cases, the activity of CTLs is completely inhibited due to the downregulated expression of major human leukocyte antigen (HLA) class I molecules by HCC cells. The aim of the present study was to overcome this issue. Hep3B cells were transduced by HCC‑specific recombinant adeno‑associated virus (rAAV) carrying human α‑fetoprotein promoter (AFPp) and the interferon‑γ (IFN‑γ) gene (rAAV/AFPp‑IFN‑γ). rAAV carrying the cytomegalovirus promoter (CMVp) and human α‑fetoprotein (AFP) gene (rAAV/CMVp‑AFP) was used to transduce professional antigen‑presenting DCs for the purpose of stimulating a CTL response. It was observed that transduction of DCs with rAAV/CMVp‑AFP resulted in: (i) AFP and interleukin‑12 expression; (ii) high expression levels of cluster of differentiation (CD)80, CD83, CD86, CD40, HLA‑death receptor and CD1a; (iii) T cell populations with marked IFN‑γ expression; (iv) a high percentage of CD69+/CD8+ T cells; and (v) the activity of CTLs against HLA‑A2‑expressing Hep3B cells. The transduction of Hep3B cells with rAAV/AFPp‑IFN‑γ resulted in: (i) IFN‑γ expression; (ii) upregulated expression of HLA‑A2; and (iii) an improved CTL response against HLA‑A2‑deficient Hep3B cells. rAAV/CMVp‑AFP‑transduced DCs elicited an AFP‑specific and HLA‑class I‑restricted CTL response against Hep3B cells. In conclusion, it was shown that the transduction of Hep3B with rAAV/AFPp-IFN-γ upregulated the expression of HLA-A2 and improved the sensitivity to CTL response.

Multiple structural and epigenetic defects in the human leukocyte antigen class I antigen presentation pathway in a recurrent metastatic melanoma following immunotherapy

Scant information is available about the molecular basis of multiple HLA class I antigen-processing machinery defects in malignant cells, although this information contributes to our understanding of the molecular immunoescape mechanisms utilized by tumor cells and may suggest strategies to counteract them. In the present study we reveal a combination of IFN-γ-irreversible structural and epigenetic defects in HLA class I antigen-processing machinery in a recurrent melanoma metastasis after immunotherapy. These defects include loss of tapasin and one HLA haplotype as well as selective silencing of HLA-A3 gene responsiveness to IFN-γ. Tapasin loss is caused by a germ-line frameshift mutation in exon 3 (TAPBP(684delA)) along with a somatic loss of the other gene copy. Selective silencing of HLA-A3 gene and its IFN-γ responsiveness is associated with promoter CpG methylation nearby site-α and TATA box, reversible after DNA methyltransferase 1 depletion. This treatment combined with tapasin reconstitution and IFN-γ stimulation restored the highest level of HLA class I expression and its ability to elicit cytotoxic T cell responses. These results represent a novel tumor immune evasion mechanism through impairing multiple components at various levels in the HLA class I antigen presentation pathway. These findings may suggest a rational design of combinatorial cancer immunotherapy harnessing DNA demethylation and IFN-γ response.

Epigenetic changes within the promoter regions of antigen processing machinery family genes in Kazakh primary esophageal squamous cell carcinoma

The esophageal squamous cell carcinoma (ESCC) is thought to develop through a multi-stage process. Epigenetic gene silencing constitutes an alternative or complementary mechanism to mutational events in tumorigenesis. Posttranscriptional regulation of human leukocyte antigen class I (HLA-I) and antigen processing machinery (APM) proteins expression may be associated with novel epigenetic modifications in cancer development. In the present study, we determined the expression levels of HLA-I antigen and APM components by immunohistochemistry. Then by a bisulfite-sequencing PCR (BSP) approach, we identified target CpG islands methylated at the gene promoter region of APM family genes in a ESCC cell line (ECa109), and further quantitative analysis of CpG site specific methylation of these genes in cases of Kazakh primary ESCCs with corresponding non-cancerous esophageal tissues using the Sequenom MassARRAY platform. Here we showed that the development of ESCCs was accompanied by partial or total loss of protein expression of HLA-B, TAP2, LMP7, tapasin and ERp57. The results demonstrated that although no statistical significance was found of global target CpG fragment methylation level sof HLA-B, TAP2, tapasin and ERp57 genes between ESCC and corresponding non-cancerous esophageal tissues, there was significant differences in the methylation level of several single sites between the two groups. Of thesse only the global methylation level of LMP7 gene target fragments was statistically higher (0.0517±0.0357) in Kazakh esophageal cancer than in neighboring normal tissues (0.0380±0.0214, p<0.05). Our results suggest that multiple CpG sites, but not methylation of every site leads to down regulation or deletion of gene expression. Only some of them result in genetic transcription, and silencing of HLA-B, ERp57, and LMP7 expression through hypermethylation of the promoters or other mechanisms may contribute to mechanisms of tumor escape from immune surveillance in Kazakh esophageal carcinogenesis.

Cytokeratin 8-MHC class I interactions: a potential novel immune escape phenotype by a lymph node metastatic carcinoma cell line

Defective human leukocyte antigen (HLA) class I expression in malignant cells facilitates their escape from destruction by CD8(+) cytotoxic T lymphocytes. In this study, a post-translational mechanism of HLA class I abnormality that does not involve defects in the HLA subunits and antigen processing machinery components was identified and characterized. The marked HLA class I downregulation phenotype of a metastatic carcinoma cell line can be readily reversed by trypsin, suggesting a masking effect by serine protease-sensitive HLA class I-interacting factors. Co-immunoprecipitation, combined with LC-tandem mass spectrometry and immunoblotting identified these factors as cytokeratin (CK) 8 and its heterodimeric partners CK18 and CK19. Ectopic CK8/18 or CK8/19 expression in HEK293 cells resulted in surface CK8 expression with an HLA class I downregulation phenotype, while redirecting CK8/18 and CK8/19 to the endoplasmic reticulum (ER) had no such effect. This observation and the failure to constrain CK8/18 and CK8/19 membrane trafficking by an ER-Golgi transport inhibitor suggested an ER-independent route for CK8 access to HLA class I molecules. Monoclonal antibody mapping revealed a potential CK8 blockade of HLA class I-CD8 and -TCR contacts. These findings, along with the emerging role of cell surface CK8 in cancer metastasis, may imply a dual strategy for tumor cell survival in the host.

The two sides of HER2/neu: immune escape versus surveillance

The oncogene HER2 is one of the prototypes for targeted immunotherapy of cancer using both monoclonal antibodies as well as T cell based immunotherapies. Effective humoral and cellular immune responses against HER2 can be induced, but these responses can be influenced by the effects of this oncogene on the target tumor cells. The processes involved in HER2-mediated adaptive and innate immunity and the molecular mechanisms underlying the escape of HER2-expressing tumor cells from immune surveillance, particularly from cytotoxic T cells, are discussed. Implementing this knowledge in clinical trials to revert immune evasion may help optimize immunotherapies directed against HER2-expressing tumors.

Immune escape of cancer cells with beta2-microglobulin loss over the course of metastatic melanoma

Cancer cells escape T-cell-mediated destruction by losing human leukocyte antigen (HLA) class I expression via various mechanisms, including loss of beta2-microglobulin (β2m). Our study illustrates the immune escape of HLA class I-negative tumor cells and chronological sequence of appearance of tumor β2m gene mutation in successive lesions obtained from a patient with metastatic melanoma. We observed a gradual decrease in HLA expression in consecutive lesions with few HLA-negative nodules in the primary tumor and the emergence of a totally negative lesion at later stages of the disease. We detected loss of β2m in β2m-negative nests of the primary tumor caused by a combination of two alterations: (i) a mutation (G to T substitution) in codon 67 in exon 2 of β2m gene, producing a stop codon and (ii) loss of the second gene copy by loss of heterozygosity (LOH) in chromosome 15. The same β2m mutation was found in a homogeneously β2m-negative metastasis 10 months later and in a cell line established from a biopsy of a postvaccination lymph node. Microsatellite analysis revealed the presence of LOH in chromosomes 6 and 15 in tumor samples, showing an accumulation of chromosomal loss at specific short tandem repeats in successive metastases during disease progression. HLA loss correlated with decreased tumor CD8+ T-cell infiltration. Early incidence of β2m defects can cause an immune selection and expansion of highly aggressive melanoma clones with irreversible genetic defects causing total loss of HLA class I expression and should be taken into consideration as a therapeutic target in the development of cancer immunotherapy protocols.

Prevalence of heterotypic tumor/immune cell-in-cell structure in vitro and in vivo leading to formation of aneuploidy

Cell-in-cell structures refer to a unique phenomenon that one living cell enters into another living cell intactly, occurring between homotypic tumor cells or tumor (or other tissue cells) and immune cells (named as heterotypic cell-in-cell structure). In the present study, through a large scale of survey we observed that heterotypic cell-in-cell structure formation occurred commonly in vitro with host cells derived from different human carcinomas as well as xenotypic mouse tumor cell lines. Most of the lineages of human immune cells, including T, B, NK cells, monocytes as well as in vitro activated LAK cells, were able to invade tumor cell lines. Poorly differentiated stem cells were capable of internalizing immune cells as well. More significantly, heterotypic tumor/immune cell-in-cell structures were observed in a higher frequency in tumor-derived tissues than those in adjacent tissues. In mouse hepatitis models, heterotypic immune cell/hepatocyte cell-in-cell structures were also formed in a higher frequency than in normal controls. After in vitro culture, different forms of internalized immune cells in heterotypic cell-in-cell structures were observed, with one or multiple immune cells inside host cells undergoing resting, degradation or mitosis. More strikingly, some internalized immune cells penetrated directly into the nucleus of target cells. Multinuclear cells with aneuploid nucleus were formed in target tumor cells after internalizing immune cells as well as in situ tumor regions. Therefore, with the prevalence of heterotypic cell-in-cell structures observed, we suggest that shielding of immune cells inside tumor or inflammatory tissue cells implies the formation of aneuploidy with the increased multinucleation as well as fine-tuning of microenvironment under pathological status, which may define distinct mechanisms to influence the etiology and progress of tumors.

Newer developments in the immunotherapy of malignant melanoma

Individuals with malignant melanoma present a variety of immune abnormalities including but not limited to cellular immune dysfunction, antigen presentation deficits, and cytokine production defects. Therefore, enhancing the immune system potential represents an appealing avenue for melanoma therapy. The authors review the immune therapies currently in clinical use as well as the most promising immunotherapy candidates. Ipilimumab, a monoclonal antibody against the CTLA-4, was approved for the therapy of advanced melanoma in 2011. In addition, sizeable anti-melanoma activity has recently been shown with the use of other agents including anti-PD-1/anti-PD-1 ligand antibodies. Consequently, these experimental immunotherapy agents may soon become important items in the anti-melanoma armamentarium.

Implication of the β2-microglobulin gene in the generation of tumor escape phenotypes

Classical MHC molecules present processed peptides from endogenous protein antigens on the cell surface, which allows CD8(+) cytotoxic T lymphocytes (CTLs) to recognize and respond to the abnormal antigen repertoire of hazardous cells, including tumor cells. The light chain, β2-microglobulin (β2m), is an essential constant component of all trimeric MHC class I molecules. There is convincing evidence that β2m deficiency generates immune escape phenotypes in different tumor entities, with an exceptionally high frequency in colorectal carcinoma (CRC) and melanoma. Damage of a single β2m gene by LOH on chromosome 15 may be sufficient to generate a tumor cell precommitted to escape. In addition, this genetic lesion is followed in some tumors by a mutation of the second gene (point mutation or insertion/deletion), which produces a tumor cell unable to express any HLA class I molecule. The pattern of mutations found in microsatellite unstable colorectal carcinoma (MSI-H CRC) and melanoma showed a striking similarity, namely the predominance of frameshift mutations in repetitive CT elements. This review emphasizes common but also distinct molecular mechanisms of β2m loss in both tumor types. It also summarizes recent studies that point to an acquired β2m deficiency in response to cancer immunotherapy, a barrier to successful vaccination or adoptive cellular therapy.

Novel insights into the molecular mechanisms of HLA class I abnormalities

Alterations in the MHC class I surface antigens represent one mechanism of tumor cells to escape from natural or immunotherapy-induced antitumor immune responses. In order to restore MHC class I expression, knowledge about the underlying molecular mechanisms of MHC class I defects in different tumor types is required. In most cases, abnormalities of MHC class I expression are reversible by cytokines suggesting a deregulation rather than structural abnormalities of members of the antigen-processing and presentation machinery (APM). The impaired expression of APM components could be controlled at the epigenetic, transcriptional and/or posttranscriptional level. Furthermore, a direct link between altered transcription factor binding, interferon signal transduction and MHC class I APM component expression has been shown, which might be further associated with cell cycle progression. This information will not only give novel insights into the (patho) physiology of the antigen-processing and presenting pathway, but will help in the future to design effective T cell-based immunotherapies.

TroVax® vaccine therapy for renal cell carcinoma

Renal cell carcinoma (RCC) is the most common primary malignancy affecting the kidney. In the past decade, several well-designed clinical trials have shifted the treatment paradigm for RCC to favor targeted therapies as first-line agents. Recognition of the immunogenic nature of RCC has also resulted in the development of immunotherapy approaches with high-dose IL-2 treatment being the best established and associated with durable disease control. The lack of defined antigens in RCC has hindered more specific vaccine development. TroVax® is a novel vaccine based on a modified vaccinia virus Ankara vector engineered to express the 5T4 tumor-associated antigen, found on over 95% of clear cell and papillary RCC tumors. The safety and efficacy of TroVax has been evaluated in several Phase I/II clinical trials and in a multicenter Phase III trial. This article will discuss the clinical background of RCC, the rationale for TroVax development, results of several TroVax clinical trials and future directions for optimizing TroVax therapy in patients with RCC and other cancers.

Immunotherapy for prostate cancer: biology and therapeutic approaches

Although prostate cancer was not historically considered to be a particularly immune-responsive cancer, recent clinical trials have demonstrated that immunotherapy for prostate cancer can lead to improvements in overall survival (OS). These studies include randomized controlled trials with sipuleucel-T and another with PROSTVAC-VF, both of which rely on stimulating the immune system to target prostate proteins. This review discusses the most promising developments over the past year in immune-based therapy for prostate cancer and the opportunities that lie ahead. Recent randomized immunotherapy trials in prostate cancer have demonstrated improvements in OS but without the concomitant improvements in progression-free survival. This uncoupling of survival from clinical response poses challenges to clinical management, because conventional measures of objective response cannot be used to identify patients benefiting from treatment. There is a significant need to identify immunologic or clinical surrogates for survival so that clinical benefit can be assessed in a timely manner. Immunotherapy is now an established treatment approach for prostate cancer, with multiple clinical trials demonstrating improvements in OS. Significant challenges to this modality remain, including determining best clinical setting for immunotherapy, identifying patients who benefit, and defining relevant clinical and immunologic end points. Nevertheless, the broader availability of novel immunotherapies will provide opportunities not only to target different components of the immune system but also to combine immunotherapies with other treatments for improved clinical efficacy.

Directing dendritic cell immunotherapy towards successful cancer treatment

The use of dendritic cells (DCs) for tumor immunotherapy represents a powerful approach for harnessing the patient's own immune system to eliminate tumor cells. However, suboptimal conditions for generating potent immunostimulatory DCs, as well as the induction of tolerance and suppression mediated by the tumors and its microenvironment have contributed to limited success. Combining DC vaccines with new approaches that enhance immunogenicity and overcome the regulatory mechanisms underlying peripheral tolerance may be the key to achieving effective and durable anti-tumor immune responses that translate to better clinical outcomes.

Identification of E2F1 as an important transcription factor for the regulation of tapasin expression

HER-2/neu overexpression in tumor cells caused abnormalities of MHC class I surface expression due to impaired expression of components of the antigen-processing machinery (APM) including the low molecular weight proteins, the transporter associated with antigen processing (TAP), and the chaperone tapasin, whereas the expression of MHC class I heavy chain as well as β(2)-microglobulin was only marginally affected. This oncogene-mediated deficient APM component expression could be reverted by interferon-γ treatment, suggesting a deregulation rather than structural alterations as underlying molecular mechanisms. To determine the level of regulation, the transcriptional activity of APM components was analyzed in HER-2/neu(-) and HER-2/neu(+) cells. All major APM components were transcriptionally down-regulated in HER-2/neu(+) when compared with HER-2/neu(-) cells, which was accompanied by a reduced binding of RNA polymerase II to the APM promoters. Site-directed mutagenesis of the p300- and E2F-binding sites in the APM promoters did not reconstitute the oncogene-mediated decreased transcription rate with the exception of tapasin, which was restored in HER-2/neu(+) cells to levels of wild type tapasin promoter activity in HER-2/neu(-) fibroblasts. The E2F-directed control of tapasin expression was further confirmed by chromatin immunoprecipitation analyses showing that E2F1 and p300 bind to the tapasin and APM promoters in both cell lines. Moreover, siRNA-mediated silencing of E2F1 was associated with an increased tapasin expression, whereas transient overexpression of E2F1 launch a reduced tapasin transcription, suggesting that E2F1 is an essential transcription factor for tapasin.

Immunotherapy for melanoma: current status and perspectives

Immunotherapy is an important modality in the therapy of patients with malignant melanoma. As our knowledge about this disease continues to expand, so does the immunotherapeutic armamentarium. Nevertheless, successful preclinical models do not always translate into clinically meaningful results. The authors give a comprehensive analysis of most recent advances in the immune anti-melanoma therapy, including interleukins, interferons, other cytokines, adoptive immunotherapy, biochemotherapy, as well as the use of different vaccines. We also present the fundamental concepts behind various immune enhancement strategies, passive immunotherapy, as well as the use of immune adjuvants. This review brings into discussion the results of newer and older clinical trials, as well as potential limitations and drawbacks seen with the utilization of various immune therapies in malignant melanoma. Development of novel therapeutic approaches, along with optimization of existing therapies, continues to hold a great promise in the field of melanoma therapy research. Use of anti-CTLA4 and anti-PD1 antibodies, realization of the importance of co-stimulatory signals, which translated into the use of agonist CD40 monoclonal antibodies, as well as activation of innate immunity through enhanced expression of co-stimulatory molecules on the surface of dendritic cells by TLR agonists are only a few items on the list of recent advances in the treatment of melanoma. The need to engineer better immune interactions and to boost positive feedback loops appear crucial for the future of melanoma therapy, which ultimately resides in our understanding of the complexity of immune responses in this disease.

Constitutive expression of the alpha4 integrin correlates with tumorigenicity and lymph node metastasis of the B16 murine melanoma

The lymphatic system plays a critical role in melanoma metastasis, and yet, virtually no information exists regarding the cellular and molecular mechanisms that take place between melanoma cells and the lymphatic vasculature. Here, we generated B16-F1 melanoma cells that expressed high (B16alpha(4)+) and negligible (B16alpha(4)-) levels of alpha(4) integrin to determine how the expression of alpha(4) integrins affects tumor cell interactions with lymphatic endothelial cells in vitro and how it impacts lymphatic metastasis in vivo. We found a direct correlation between alpha(4) integrin expression on B16-F1 melanoma cells and their ability to form adhesive interactions with monolayers of lymphatic endothelial cells. Adhesion of B16-F1 melanoma cells to lymphatic endothelial cells was mediated by the melanoma cell alpha(4) integrin binding to its counterreceptor, vascular cell adhesion molecule 1 (VCAM-1), that was constitutively expressed on the lymphatic endothelial cells. VCAM-1 was also expressed on the tumor-associated lymphatic vessels of B16-F1 and B16alpha(4)+ tumors growing in the subcutaneous space of C57BL/6J mice. B16-F1 tumors metastasized to lymph nodes in 30% of mice, whereas B16alpha(4)+ tumors generated lymph node metastases in 80% of mice. B16-F1 melanoma cells that were deficient in alpha(4) integrins (B16alpha(4)-) were nontumorigenic. Collectively, these data show that the alpha(4) integrin expressed by melanoma cells contributes to tumorigenesis and may also facilitate metastasis to regional lymph nodes by promoting stable adhesion of melanoma cells to the lymphatic vasculature.

Association of HLA class I antigen abnormalities with disease progression and early recurrence in prostate cancer

Defects in HLA class I antigen processing machinery (APM) component expression often have a negative impact on the clinical course of tumors and on the response to T cell-based immunotherapy. Since only scant information is available about the frequency and clinical significance of HLA class I APM component abnormalities in prostate cancer, the APM component expression pattern was analyzed in 59 primary prostate carcinoma, adjacent normal tissues, as well as in prostate carcinoma cell lines. The IFN-gamma inducible proteasome subunits LMP2 and LMP7, TAP1, TAP2, calnexin, calreticulin, ERp57, and tapasin are strongly expressed in the cytoplasm of normal prostate cells, whereas HLA class I heavy chain (HC) and beta(2)-microglobulin are expressed on the cell surface. Most of the APM components were downregulated in a substantial number of prostate cancers. With the exception of HLA class I HC, TAP2 and ERp57 not detectable in about 0.5% of tumor lesions, all other APM components were not detected in at least 21% of lesions analyzed. These APM component defects were associated with a higher Gleason grade of tumors and an early disease recurrence. Prostate carcinoma cell lines also exhibit a heterogeneous, but reduced constitutive APM component expression pattern associated with lack or reduced HLA class I surface antigens, which could be upregulated by IFN-gamma. Our results suggest that HLA class I APM component abnormalities are mainly due to regulatory mechanisms, play a role in the clinical course of prostate cancer and on the outcome of T cell-based immunotherapies.

Different regulation of MHC class I antigen processing components in human tumors

In recent years, progress has been made in understanding how peptides presented by MHC Class I molecules were generated, in particular which proteases are involved in this process and how intracellular pathways influence antigen presentation in professional antigen-presenting cells and various types of tumor cells. This review will give an overview of MHC Class I abnormalities in malignancies and their underlying molecular mechanisms. Dependent on the tumor types structural alterations in particular of the MHC Class I heavy chain, beta(2)-m and the TAP1 subunit have been found at a low frequency, whereas dysregulation of MHC Class I antigen processing components appears to be the major mechanism of MHC Class I down-regulation in tumors of distinct origin. This could occur at the epigenetic, transcriptional and/or post-transcriptional level. The lack or suppression of MHC Class I surface expression due to antigen-processing deficiencies are accompanied by reduced recognition and lysis by antigen-specific cytotoxic T-lymphocytes, which is further often associated with disease progression.

Strategies to overcome obstacles to successful immunotherapy of melanoma

The immunogenicity of malignant melanomas has been recognized by the observed recruitment of tumor-specific cytotoxic T-cells (CTL), leading to the identification of several melanoma associated antigen (MAA). However, numerous strategies to treat melanoma with immunotherapy have resulted in only partial success. In this editorial, we discuss recent data related to the ability of tumors to elude immune responses. We therefore discuss different strategies to induce a clinically effective immune response. These approaches include 1) immunostimulation: including peptide/protein based vaccines, dendritic cell vaccines, and adoptive cell transfer; and 2) overcoming immunosuppression, including targeting of checkpoint molecules such as CTLA-4, circumventing the activity of Tregs, and assuring antigen expression by tumor cells (thwarting antigen silencing). Finally, we discuss recent advances in gene therapy, including adoptive therapy with engineered T cell receptors (TCRs). These issues lead to the conclusion that successful immunotherapy in malignant melanoma requires a combination of strategies aimed at both inducing immunostimulation and blocking immunosuppression.

Molecular mechanisms of MHC class I abnormalities and APM components in human tumors

Tumor immune escape plays a critical role in cancer, but the mechanisms involved in this process have still to be defined. In the recent years, progress has been made in understanding how peptides presented by MHC class I molecules were generated, in particular which proteases are involved in this process and how intracellular pathways influence antigen presentation in professional antigen-presenting cells and in various types of malignancies. Different MHC class I abnormalities have been found in solid tumors of distinct origin, but also in hematopoietic diseases. These include structural alterations such as total, haplotype and allelic loss of the MHC class I heavy chain, deletions and point mutations, in particular in beta2-microglobulin and TAP1 as well as dysregulation of various components of the MHC class I antigen processing machinery (APM), which could occur at the epigenetic, transcriptional and posttranscriptional level. The lack or downmodulation of the expression of single or multiple components of the MHC class I antigen processing pathway may avoid the recognition of tumor cells by tumor-specific CD8+ cytotoxic T lymphocytes. This review will give an overview of the underlying molecular mechanisms of MHC class I abnormalities in human tumors of distinct histology, which also might have an impact on the design of T cell-based immunotherapies.

Next generation of immunotherapy for melanoma

PURPOSE

Immunotherapy has a long history with striking but limited success in patients with melanoma. To date, interleukin-2 and interferon-alfa2b are the only approved immunotherapeutic agents for melanoma in the United States.

DESIGN

Tumor evasion of host immune responses, and strategies for overcoming tumor-induced immunosuppression are reviewed. Several novel immunotherapies currently in worldwide phase III clinical testing for melanoma are discussed.

RESULTS

The limitations of immunotherapy for melanoma stem from tumor-induced mechanisms of immune evasion that render the host tolerant of tumor antigens. For example, melanoma inhibits the maturation of antigen-presenting cells, preventing full T-cell activation and downregulating the effector antitumor immune response. New immunotherapies targeting critical regulatory elements of the immune system may overcome tolerance and promote a more effective antitumor immune response. These include monoclonal antibodies that block the cytotoxic T lymphocyte-associated antigen 4 (CTLA4) and toll-like receptor 9 (TLR9) agonists. Blockade of CTLA4 prevents inhibitory signals that downregulate T-cell activation. TLR9 agonists stimulate dendritic cell maturation and ultimately induce a more effective immune response. These approaches have been shown to stimulate acute immune activation with concomitant appearance of transient adverse events mediated by the immune system. The pattern and duration of immune responses associated with these new modalities differ from those associated with cytokines and cytotoxic agents. In addition, vaccines are being developed that may ultimately target melanoma either alone or in combination with these immunomodulatory therapies.

CONCLUSION

The successes of cytokine and interferon therapy of melanoma, coupled with an array of new approaches, are generating new enthusiasm for the immunotherapy of melanoma.

Histone deacetylase inhibitors induce TAP, LMP, Tapasin genes and MHC class I antigen presentation by melanoma cells

Histone deacetylase inhibitors (HDACi), including trichostatin A (TSA) and valproic acid, can alter the acetylation of histones in chromatin and enhance gene transcription. Previously we demonstrated that HDACi-treated tumor cells are capable of presenting antigen via the MHC class II pathway. In this study, we show that treatment with HDACi enhances the expression of molecules (TAP1, TAP2, LMP2, LMP7, Tapasin and MHC class I) involved in antigen processing and presentation via the MHC class I pathway in melanoma cells. HDACi treatment of B16F10 cells also enhanced cell surface expression of class I and costimulatory molecules CD40 and CD86. Enhanced transcription of these genes is associated with a significant increase in direct presentation of whole protein antigen and MHC class I-restricted peptides by TSA-treated B16F10 cells. Our data indicate that epigenetic modification can convert a tumor cell to an antigen presenting cell capable of activating IFN-gamma secreting T cells via the class I pathway. These findings suggest that the abnormalities, observed in some tumors in the expression of MHC class I antigen processing and presentation molecules, may result from epigenetic repression.

Dynamic cross-talk between tumor and immune cells in orchestrating the immunosuppressive network at the tumor microenvironment

Accumulating evidence indicates that a dynamic cross-talk between tumors and the immune system can regulate tumor growth and metastasis. Increased understanding of the biochemical nature of tumor antigens and the molecular mechanisms responsible for innate and adaptive immune cell activation has revolutionized the fields of tumor immunology and immunotherapy. Both the protective effects of the immune system against tumor cells (immunosurveillance) and the evasion of tumor cells from immune attack (tumor-immune escape) have led to the concept of cancer immunoediting, a proposal which infers that a bidirectional interaction between tumor and inflammatory/regulatory cells is ultimately responsible for orchestrating the immunosuppressive network at the tumor site. In this context, a major challenge is the potentiation or redirection of tumor antigen-specific immune responses. The success in reaching this goal is highly dependent on an improved understanding of the interactions and mechanisms operating during the different phases of the cancer immunoediting process. In this review, we discuss the multiple defense and counterattack strategies that tumors have devised in order to evade immune attack and to thwart the effectiveness of several immunotherapeutic approaches.

Tumor immunoediting and immunosculpting pathways to cancer progression

Recent studies have suggested that a natural function of the immune system is to respond and destroy aberrant, dysfunctional cells by a process called immunosurveillance. These studies also suggest that the tumors that arise despite immunosurveillance have been immunosculpted by the immune system. The purported abilities of tumors to induce immune tolerance and suppression, the increased pathogenic behavior of the tumor cells following exposure to immune effectors and the loss of immunogenicity (i.e. immunoediting) often observed in advanced stage tumors could be the result of immunosculpting. In some cases, these immunosculpting features may be permanent and irreversible. However, in other cases, reversible epigenetic mechanisms may underlie the immune resistant tumor phenotype. Regardless, these immune-induced alterations could contribute to cancer pathogenesis. Understanding the mechanisms by which tumors evade immunity will be important for disease prevention and therapeutics.

Attenuation of the Glucocorticoid Response during Ad5IL-12 Adenovirus Vector Treatment Enhances Natural Killer Cell–Mediated Killing of MHC Class I–Negative LNCaP Prostate Tumors

Tumor cells can evolve to evade immune responses by down-modulating surface MHC class I expression and become refractory to T cell-directed immunotherapy. We employed a strategy to bypass this escape mechanism using a recombinant adenovirus vector expressing interleukin-12 (Ad5IL-12) to target natural killer (NK) cell-mediated killing of human prostate tumors in NOD.scid mice. Fluorescence-activated cell sorting analysis revealed that LNCaP tumor cells bear negligible levels of MHC class I molecules; yet, they express MICA/B molecules, ligands for the NKG2D receptors found on NK cells. Transduction of LNCaP cells with the Ad5IL-12 vector prevented tumor formation in NOD.scid mice, indicating that NK cells alone can conduct tumor immunosurveillance and mediate protection. Intratumor injection of the Ad5IL-12 vector to established LNCaP tumors in NOD.scid mice resulted in a significant delay of tumor growth mediated by NK cell killing activity. The dependency of NK cells in this protective response was shown by the complete loss of Ad5IL-12 therapeutic efficacy on LNCaP tumors established in NOD.Cg-Rag1(tm1Mom)Prf1(tm1Sdz) congenic mice, which are devoid of NK cell activity. More pronounced attenuation of tumor growth and enhanced NK killing activity was observed when pharmacologic adrenalectomy with mitotane was done in combination with Ad5IL-12 vector treatment. The Ad5IL-12 vector treatment also induced killing of MICA/B-negative MHC class I-positive PC3 tumors formed in NOD.scid mice. Together, these results indicate that a targeted NK cell response could provide a generic approach for cancer immunotherapy, and that enhancing the NK cell response via control of cortisol levels may provide an additional therapeutic avenue in cancer.