HLA-G expression in human ovarian carcinoma counteracts NK cell function

Enhancing the therapeutic efficacy of NK cells in the treatment of ovarian cancer (Review)

Ovarian cancer is a prevalent gynecological malignancy associated with a high mortality rate and a low 5‑year survival rate. Typically, >70% of patients present with an advanced stage of the disease, resulting in a high number of ovarian cancer‑associated deaths worldwide. Over the past decade, adoptive cellular immunotherapy has been investigated in clinical trials, and the results have led to the increased use in cancer treatment. Natural killer (NK) cells are cytotoxic lymphoid cells that recognize and lyse transformed cells, thereby impeding tumor growth. Thus, NK cells exhibit potential as a form of immunotherapy in the treatment of cancer. However, some patients with ovarian cancer treated with NK cells have experienced unsatisfactory outcomes. Therefore, further optimization of NK cells is required to increase the number of patients achieving long‑term remission. In the present review article, studies focusing on improving NK cell function were systematically summarized, and innovative strategies that augment the anticancer properties of NK cells were proposed.

Immune Evasion Through Human Leukocyte Antigen Implications and Its Impact on Targeted Therapy

The malfunctioning of human leukocyte antigen (HLA) class I antigens has a substantial negative impact on the effectiveness of leukemia treatment, particularly in the development of immunotherapies that rely on T-cell activation. HLA-G, a molecule that suppresses the immune response, plays a role in repressing the activation and proliferation of T cells, natural killer cells, and antigen-presenting cells. The expression of HLA-G is associated with various pathological conditions. Tumor cells exploit the immune evasion capabilities of HLA, allowing them to evade detection and elimination by the immune system. Understanding and modifying the HLA molecules is crucial for the advancement of innovative immunotherapies targeting chronic lymphocytic leukemia. Numerous mechanisms have been investigated to elucidate how HLA facilitates tumor evasion in patients with chronic lymphocytic leukemia and other malignancies. These mechanisms include inhibiting immune cell cytolysis, altering cytokine production levels, promoting immune cell programmed cell death, and impairing chemotaxis. This review provides a comprehensive overview of immune evasion mediated by HLA and its implications for targeted therapy.

Diversity of immune checkpoints in cancer immunotherapy

Finding effective treatments for cancer remains a challenge. Recent studies have found that the mechanisms of tumor evasion are becoming increasingly diverse, including abnormal expression of immune checkpoint molecules on different immune cells, in particular T cells, natural killer cells, macrophages and others. In this review, we discuss the checkpoint molecules with enhanced expression on these lymphocytes and their consequences on immune effector functions. Dissecting the diverse roles of immune checkpoints in different immune cells is crucial for a full understanding of immunotherapy using checkpoint inhibitors.

A Novel Prognostic Risk Model for Cervical Cancer Based on Immune Checkpoint HLA-G-Driven Differentially Expressed Genes

Human leukocyte antigen G (HLA-G) is a potential checkpoint molecule that plays a key role in cervical carcinogenesis. The purpose of this study was to construct and validate a prognostic risk model to predict the overall survival (OS) of cervical cancer patients, providing a reference for individualized clinical treatment that may lead to better clinical outcomes. HLA-G-driven differentially expressed genes (DEGs) were obtained from two cervical carcinoma cell lines, namely, SiHa and HeLa, with stable overexpression of HLA-G by RNA sequencing (RNA-seq). The biological functions of these HLA-G-driven DEGs were analysed by GO enrichment and KEGG pathway using the “clusterProfiler” package. The protein-protein interactions (PPIs) were assessed using the STRING database. The prognostic relevance of each DEG was evaluated by univariate Cox regression using the TCGA-CESC dataset. After the TCGA-CESC cohort was randomly divided into training set and testing set, and a prognostic risk model was constructed by LASSO and stepwise multivariate Cox regression analysis in training set and validated in testing set or in different types of cervical cancer set. The predictive ability of the prognostic risk model or nomogram was evaluated by a series of bioinformatics methods. A total of 1108 candidate HLA-G-driven DEGs, including 391 upregulated and 717 downregulated genes, were obtained and were enriched mostly in the ErbB pathway, steroid biosynthesis, and MAPK pathway. Then, an HLA-G-driven DEG signature consisting of the eight most important prognostic genes CD46, LGALS9, PGM1, SPRY4, CACNB3, PLIN2, MSMO1, and DAGLB was identified as a key predictor of cervical cancer. Multivariate Cox regression analysis showed that this signature is an independent risk factor for the overall survival of CESC patients. Kaplan-Meier survival analysis showed that the 5-year overall survival rate is 23.0% and 84.6% for the high-risk and low-risk patients, respectively (P<0.001). The receiver operating characteristic (ROC) curve of this prognostic model with an area under the curve (AUC) was 0.896 for 5 years, which was better than that of other clinical traits. This prognostic risk model was also successfully validated in different subtypes of cervical cancer, including the keratinizing squamous cell carcinoma, non-keratinizing squamous cell carcinoma, squamous cell neoplasms, non-squamous cell neoplasms set. Single-sample gene set enrichment (ssGSEA) algorithm and Tumor Immune Dysfunction and Exclusion (TIDE) analysis confirmed that this signature influence tumour microenvironment and immune checkpoint blockade. A nomogram that integrated risk score, age, clinical stage, histological grade, and pathological type was then built to predict the overall survival of CESC patients and evaluated by calibration curves, AUC, concordance index (C-index) and decision curve analysis (DCA). To summarize, we developed and validated a novel prognostic risk model for cervical cancer based on HLA-G-driven DEGs, and the prognostic signature showed great ability in predicting the overall survival of patients with cervical cancer.

The Human Leukocyte Antigen G as an Immune Escape Mechanism and Novel Therapeutic Target in Urological Tumors

The non-classical human leukocyte antigen G (HLA-G) is a potent regulatory protein involved in the induction of immunological tolerance. This is based on the binding of membrane-bound as well as soluble HLA-G to inhibitory receptors expressed on various immune effector cells, in particular NK cells and T cells, leading to their attenuated functions. Despite its restricted expression on immune-privileged tissues under physiological conditions, HLA-G expression has been frequently detected in solid and hematopoietic malignancies including urological cancers, such as renal cell and urothelial bladder carcinoma and has been associated with progression of urological cancers and poor outcome of patients: HLA-G expression protects tumor cells from anti-tumor immunity upon interaction with its inhibitory receptors by modulating both the phenotype and function of immune cells leading to immune evasion. This review will discuss the expression, regulation, functional and clinical relevance of HLA-G expression in urological tumors as well as its use as a putative biomarker and/or potential therapeutic target for the treatment of renal cell carcinoma as well as urothelial bladder cancer.

Prognostic significance of high circulating sHLA-G in ovarian carcinoma

HLA-G is a non-classical major histocompatibility complex class Ib molecule. Its expression has been described in various cancer types, including ovarian cancer. HLA-G molecule has been implicated in immune escape and in progression of ovarian tumor cells. Our goal was to assess if total soluble (s)HLA-G molecules or HLA-G5 and sHLA-G1 isoforms could be considered as circulating ovarian tumor biomarkers, we measured the concentration of these molecules in ovarian carcinoma patients stratified according with their clinicopathological parameters. sHLA-G, sHLA-G1 and HLA-G5 concentrations were dosed in plasma samples by sandwich-ELISA. The sHLA-G dimerization was analyzed after immunoprecipitation and SDS-PAGE migration. Total sHLA-G and sHLA-G1 levels were significantly represented in plasma of ovarian carcinoma patients compared to healthy controls. sHLA-G1 isoform concentration was highly represented in ovarian carcinoma compared to HLA-G5 isoforms. Additionally, high sHLA-G molecules have been found in aged patients, as well as in patients with advanced stages, and those with metastatic lymph nodes and those with distant metastasis. Elsewhere, sHLA-G monomers were highly represented in ovarian carcinoma patients compared to controls. sHLA-G plasmatic protein was highly represented in ovarian carcinoma. In effect, HLA-G might be considered as a new checkpoint molecule that could be used to assess progression and recurrence of the disease, thus placing it as a potential biomarker for advanced and complicated ovarian carcinoma.

Comprehensive Transcriptomic Analysis Reveals the Role of the Immune Checkpoint HLA-G Molecule in Cancers

Human leukocyte antigen G (HLA-G) is known as a novel immune checkpoint molecule in cancer; thus, HLA-G and its receptors might be targets for immune checkpoint blockade in cancer immunotherapy. The aim of this study was to systematically identify the roles of checkpoint HLA-G molecules across various types of cancer. ONCOMINE, GEPIA, CCLE, TRRUST, HAP, PrognoScan, Kaplan-Meier Plotter, cBioPortal, LinkedOmics, STRING, GeneMANIA, DAVID, TIMER, and CIBERSORT were utilized. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed. In this study, we comprehensively analysed the heterogeneous expression of HLA-G molecules in various types of cancer and focused on genetic alterations, coexpression patterns, gene interaction networks, HLA-G interactors, and the relationships between HLA-G and pathological stage, prognosis, and tumor-infiltrating immune cells. We first identified that the mRNA expression levels of HLA-G were significantly upregulated in both most tumor tissues and tumor cell lines on the basis of in-depth analysis of RNAseq data. The expression levels of HLA-G were positively associated with those of the other immune checkpoints PD-1 and CTLA-4. Abnormal expression of HLA-G was significantly correlated with the pathological stage of some but not all tumor types. There was a significant difference between the high and low HLA-G expression groups in terms of overall survival (OS) or disease-free survival (DFS). The results showed that HLA-G highly expressed have positive associations with tumor-infiltrating immune cells in the microenvironment in most types of tumors (P<0.05). Additionally, we identified the key transcription factor (TF) targets in the regulation of HLA-G expression, including HIVEP2, MYCN, CIITA, MYC, and IRF1. Multiple mutations (missense, truncating, etc.) and the methylation status of the HLA-G gene may explain the differential expression of HLA-G across different tumors. Functional enrichment analysis showed that HLA-G was primarily related to T cell activation, T cell regulation, and lymphocyte-mediated immunity. The data may provide novel insights for blockade of the HLA-G/ILT axis, which holds potential for the development of more effective antitumour treatments.

Double Insurance for OC: miRNA-Mediated Platinum Resistance and Immune Escape

Ovarian cancer (OC) is still the leading cause of death among all gynecological malignancies, despite the recent progress in cancer therapy. Immune escape and drug resistance, especially platinum-based chemotherapy, are significant factors causing disease progression, recurrence and poor prognosis in OC patients. MicroRNAs(miRNAs) are small noncoding RNAs, regulating gene expression at the transcriptional level. Accumulating evidence have indicated their crucial roles in platinum resistance. Importantly, they also act as mediators of tumor immune escape/evasion. In this review, we summarize the recent study of miRNAs involved in platinum resistance of OC and systematically analyses miRNAs involved in the regulation of OC immune escape. Further understanding of miRNAs roles and their possible mechanisms in platinum resistance and tumor escape may open new avenues for improving OC therapy.

Tackling HLA Deficiencies Head on with Oncolytic Viruses

Dysregulation of HLA (human leukocyte antigen) function is increasingly recognized as a common escape mechanism for cancers subject to the pressures exerted by immunosurveillance or immunotherapeutic interventions. Oncolytic viruses have the potential to counter this resistance by upregulating HLA expression or encouraging an HLA-independent immunological responses. However, to achieve the best therapeutic outcomes, a prospective understanding of the HLA phenotype of cancer patients is required to match them to the characteristics of different oncolytic strategies. Here, we consider the spectrum of immune competence observed in clinical disease and discuss how it can be best addressed using this novel and powerful treatment approach.

HLA-G expression in melanomas

OBJECTIVE

Human leukocyte antigen G (HLA-G) is a non-classical HLA class I molecule involved in inducing tolerance at the feto-maternal interface and in escape of immune response by tumor cells. The aim of the study is to review the published literature on the expression of HLA-G in malignant melanomas and its clinicopathological and prognostic correlates.

METHODS

A systematic search was carried out in electronic databases. Studies dealing with HLA-G expression in surgically-removed human samples were retrieved and analyzed.

RESULTS

Of 1737 retrieved articles, 16 were included. The main themes regarded HLA-G expression in malignant melanocytic lesions, assessed by immunohistochemistry (IHC), soluble or molecular techniques, and its relationship with clinicopathological features, such as tumor thickness and malignant behavior. Overall significant HLA-G expression was found in 460/843 tumors (55%), and specifically in 251/556 melanomas (45%) evaluated with IHC, in 208/250 cases (83%) examined with soluble methods and in 13/23 melanoma lesions (57%) tested with polymerase chain reaction. Despite the correlation with parameters indicating an aggressive behavior, no studies demonstrated any prognostic value of HLA-G expression. Furthermore, uveal melanomas were constantly negative for this biomarker.

CONCLUSION

Overall, published data indicate that while HLA-G is involved in the interactions between melanomas and the immune system, it is unlikely to be the only factor to play such a role, therefore making it difficult to designate it as a prognostically relevant molecule. Evidence further suggests that HLA-G is not implicated in the immunobiology of uveal melanomas.

The microRNA-152/human leukocyte antigen-G axis affects proliferation and immune escape of non-small cell lung cancer cells

Objective

To investigate the role of human leukocyte antigen (HLA-G) on proliferation, invasion, and immune escape in non-small cell lung cancer (NSCLC).

Methods

The relationship between HLA-G and overall survival (OS) of NSCLC patients was analyzed using the KMPlot database. The expression of micro (mi)R-152 or HLA-G was modulated by transfecting synthetic oligonucleotides, and the impact of the miR-152/HLA-G axis on proliferation, invasion, colony formation in soft agar, and tolerance to natural killer (NK) cell cytolysis was measured.

Results

Bioinformatics analysis showed that high HLA-G expression was correlated with poor OS in NSCLC patients. The tolerance of NSCLC cells to NK cytotoxicity was negatively correlated with HLA-G and positively correlated with miR-152 expression. Over-expressing miR-152 inhibited HLA-G expression in A549 cells and attenuated cell proliferation, migration, colony formation ability, and tolerance to NK cells. However, blocking HLA-G expression by small interfering RNA did not affect migration or colony formation, but only proliferation and tolerance to NK cells in vitro and in vivo. Blocking Ig-like transcript 2 on the surface of NK cells increased their killing effect in the presence of high HLA-G expression.

Conclusions

miR-152/HLA-G axis plays an oncogenic role in NSCLC by affecting cell proliferation and immune escape.

The Molecular and Functional Characteristics of HLA-G and the Interaction with Its Receptors: Where to Intervene for Cancer Immunotherapy?

Human leukocyte antigen G (HLA-G) mediates maternal-fetal immune tolerance. It is also considered an immune checkpoint in cancer since it may mediate immune evasion and thus promote tumor growth. HLA-G is, therefore, a potential target for immunotherapy. However, existing monoclonal antibodies directed against HLA-G lack sufficient specificity and are not suitable for immune checkpoint inhibition in a clinical setting. For this reason, it is essential that alternative approaches are explored to block the interaction between HLA-G and its receptors. In this review, we discuss the structure and peptide presentation of HLA-G, and its interaction with the receptors Ig-like transcript (ILT) 2, ILT4, and Killer cell immunoglobulin-like receptor 2DL4 (KIR2DL4). Based on our findings, we propose three alternative strategies to block the interaction between HLA-G and its receptors in cancer immunotherapy: (1) prevention of HLA-G dimerization, (2) targeting the peptide-binding groove of HLA-G, and (3) targeting the HLA-G receptors. These strategies should be an important focus of future studies that aim to develop immune checkpoint inhibitors to block the interaction between HLA-G and its receptors for the treatment of cancer.

HLA-G Neo-Expression on Tumors

HLA-G is known to modulate the immune system activity in tissues where physiological immune-tolerance is necessary (i.e., maternal-fetal interface, thymus, and cornea). However, the frequent neo-expression of HLA-G in many cancer types has been previously and extensively described and is correlated with a bad prognosis. Despite being an MHC class I molecule, HLA-G is highly present in tumor context and shows unique characteristics of tissue restriction of a Tumor Associated Antigen (TAA), and potent immunosuppressive activity of an Immune CheckPoint (ICP). Consequently, HLA-G appears to be an excellent molecular target for immunotherapy. Although the relevance of HLA-G in cancer incidence and development has been proven in numerous tumors, its neo-expression pattern is still difficult to determine. Indeed, the estimation of HLA-G's actual expression in tumor tissue is limited, particularly concerning the presence and percentage of the new non-canonical isoforms, for which detection antibodies are scarce or inexistent. Here, we summarize the current knowledge about HLA-G neo-expression and implication in various tumor types, pointing out the need for the development of new tools to analyze in-depth the HLA-G neo-expression patterns, opening the way for the generation of new monoclonal antibodies and cell-based immunotherapies.

HLA-G: A New Immune Checkpoint in Cancer?

Human leukocyte antigen G (HLA-G), known as a central protein in providing immune tolerance to the fetus in pregnant women, is also studied for a possible role in tumor development. Many studies have claimed HLA-G as a new immune checkpoint in cancer. Therefore, HLA-G and its receptors might be targets for immune checkpoint blockade in cancer immunotherapy. In order to substantiate that HLA-G is indeed an immune checkpoint in cancer, two important questions need to be answered: (1) To what extent is HLA-G expressed in the tumor by cancer cells? and (2) What is the function of HLA-G in cancer immune evasion? In this review, we discuss these questions. We agree that HLA-G is a potentially new immune checkpoint in cancer, but additional evidence is required to show the extent of intra-tumor and inter-tumor expression. These studies should focus on tumor expression patterns of the seven different HLA-G isoforms and of the receptors for HLA-G. Furthermore, specific roles for the different HLA-G isoforms should be established.

Soluble HLA-G expression levels and HLA-G/irinotecan association in metastatic colorectal cancer treated with irinotecan-based strategy

We here explore the soluble Human Leukocyte Antigen-G (sHLA-G) expression level as clinical biomarker in metastatic colorectal cancer (mCRC). To this aim the sHLA-G protein was measured in plasma samples of 40 patients with mCRC treated with the FOLFIRI (irinotecan (CPT-11) plus 5-fluorouracil (5-FU) and leucovorin (LV)) regimen. The results suggest a link between HLA-G levels and irinotecan (CPT-11) pharmacokinetic, leading to hypothesize a molecular interaction between sHLA-G and CPT-11. This interaction was confirmed experimentally by fluorescence spectroscopy. HLA-G is known to exist in a number of polymorphs that affect both the protein expression levels and its peptide-binding cleft. The interaction between HLA-G polymorphs and CPT-11 was explored by means of computational modelling, confirming the hypothesis that CPT-11 could actually target the peptide binding cleft of the most common HLA-G polymorphs.

NK Cell-Based Immune Checkpoint Inhibition

Immunotherapy, with an increasing number of therapeutic dimensions, is becoming an important mode of treatment for cancer patients. The inhibition of immune checkpoints, which are the source of immune escape for various cancers, is one such immunotherapeutic dimension. It has mainly been aimed at T cells in the past, but NK cells are a newly emerging target. Simultaneously, the number of checkpoints identified has been increasing in recent times. In addition to the classical NK cell receptors KIRs, LIRs, and NKG2A, several other immune checkpoints have also been shown to cause dysfunction of NK cells in various cancers and chronic infections. These checkpoints include the revolutionized CTLA-4, PD-1, and recently identified B7-H3, as well as LAG-3, TIGIT & CD96, TIM-3, and the most recently acknowledged checkpoint-members of the Siglecs family (Siglec-7/9), CD200 and CD47. An interesting dimension of immune checkpoints is their candidacy for dual-checkpoint inhibition, resulting in therapeutic synergism. Furthermore, the combination of immune checkpoint inhibition with other NK cell cytotoxicity restoration strategies could also strengthen its efficacy as an antitumor therapy. Here, we have undertaken a comprehensive review of the literature to date regarding NK cell-based immune checkpoints.

Flow cytometry-based assessment of direct-targeting anti-cancer antibody immune effector functions

Monoclonal antibody-based therapies are increasingly being used to treat cancer. Some mediate their therapeutic effects through modifying the function of immune cells globally, while others bind directly to tumor cells and can recruit immune effector cells through their Fc regions. As new direct-binding agents are developed, having the ability to test their Fc-mediated functions in a high-throughput manner is important for selecting antibodies with immune effector properties. Here, using monoclonal anti-CD20 antibody (rituximab) as an example and the CD20⁺ Raji cell line as tumor target, we describe flow cytometry-based assays for determining an antibody's capacity for mediating antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP) and complement-dependent cytotoxicity (CDC). These assays are sensitive, reliable, affordable and avoid the use of radioactivity.

The HLA-G 14 bp insertion/deletion polymorphism and its association with soluble HLA-G levels in women with recurrent miscarriages

HLA-G, a nonclassical class-Ib gene is mainly expressed on extravillous trophoblasts at the fetal-maternal interface. HLA-G molecule is considered to play an important role in maternal immune suppression during pregnancy. The 14 bp insertion/deletion polymorphism (rs66554220) in exon eight of the HLA-G gene influences HLA-G mRNA stability and isoform splicing patterns. In this study, 202 recurrent miscarriage (RM) women with two or more than two consecutive miscarriages, their 202 partners and 204 fertile control women with at least one live birth and no miscarriages were analyzed for 14 bp insertion/deletion polymorphism. Soluble HLA-G (sHLA-G) levels were also determined and compared between randomly selected 111 RM women and 111 control women using QAYEE-Bio ELISA kits. Student's t test and χ² test were used to depict the statistical differences. The results showed no significant differences for 14 bp allele and genotype frequencies between the study groups. However, our study showed a significant difference (P = .0107) for sHLA-G levels in RM women and control women. Furthermore, a significant difference (P = .0135) for sHLA-G levels in relation to +/-14 bp heterozygous genotype was seen between the two groups. The 14 bp allele sharing between the partners did not show any significant association with the number of miscarriages in RM couples. The association of 14 bp polymorphism and recurrent miscarriages was not significant in our study.

European Patent in Immunoncology: From Immunological Principles of Implantation to Cancer Treatment

The granted European patent EP 2 561 890 describes a procedure for an immunological treatment of cancer. It is based on the principles of the HLA-supported communication of implantation and pregnancy. These principles ensure that the embryo is not rejected by the mother. In pregnancy, the placenta, more specifically the trophoblast, creates an “interface” between the embryo/fetus and the maternal immune system. Trophoblasts do not express the “original” HLA identification of the embryo/fetus (HLA-A to -DQ), but instead show the non-classical HLA groups E, F, and G. During interaction with specific receptors of NK cells (e.g., killer-immunoglobulin-like receptors (KIR)) and lymphocytes (lymphocyte-immunoglobulin-like receptors (LIL-R)), the non-classical HLA groups inhibit these immunocompetent cells outside pregnancy. However, tumors are known to be able to express these non-classical HLA groups and thus make use of an immuno-communication as in pregnancies. If this occurs, the prognosis usually worsens. This patent describes, in a first step, the profiling of the non-classical HLA groups in primary tumor tissue as well as metastases and recurrent tumors. The second step comprises tailored antibody therapies, which is the subject of this patent. In this review, we analyze the underlying mechanisms and describe the currently known differences between HLA-supported communication of implantation and that of tumors.

Similarities Between Embryo Development and Cancer Process Suggest New Strategies for Research and Therapy of Tumors: A New Point of View

Here, I propose that cancer stem cells (CSCs) would be equivalent to para-embryonic stem cells (p-ESCs), derived from adult cells de-re-programmed to a ground state. p-ESCs would differ from ESCs by the absence of genomic homeostasis. A p-ESC would constitute the cancer cell of origin (i-CSC or CSC0), capable of generating an initial tumor, corresponding to a pre-implantation blastocyst. In a niche with proper signals, it would engraft as a primary tumor, corresponding to a post-implantation blastocyst. i-CSC progeny would form primary pluripotent and slow self-renewing CSCs (CSC1s), blocked in an undifferentiated state, corresponding to epiblast cells; CSC1s would be tumor-initiating cells (TICs). CSC1s would generate secondary CSCs (CSC2s), corresponding to hypoblast cells; CSC2s would be tumor growth cells (TGCs). CSC1s/CSC2s would generate tertiary CSCs (CSC3s), with a mesenchymal phenotype; CSC3s would be tumor migrating cells (TMCs), corresponding to mesodermal precursors at primitive streak. CSC3s with more favorable conditions (normoxia), by asymmetrical division, would differentiate into cancer progenitor cells (CPCs), and these into cancer differentiated cells (CDCs), thus generating a defined cell hierarchy and tumor progression, mimicking somito-histo-organogenesis. CSC3s with less favorable conditions (hypoxia) would delaminate and migrate as quiescent circulating micro-metastases, mimicking mesenchymal cells in gastrula morphogenetic movements. In metastatic niches, these CSC3s would install and remain dormant in the presence of epithelial/mesenchymal transition (EMT) signals and hypoxia. But, in the presence of mesenchymal/epithelial transition (MET) signals and normoxia, they would revert to self-renewing CSC1s, reproducing the same cell hierarchy of the primary tumor as macro-metastases. Further similarities between ontogenesis and oncogenesis involving crucial factors, such as ID, HSP70, HLA-G, CD44, LIF, and STAT3, are strongly evident at molecular, physiological and immunological levels. Much experimental data about these factors led to considering the cancer process as ectopic rudimentary ontogenesis, where CSCs have privileged immunological conditions. These would consent to CSC development in an adverse environment, just like an embryo, which is tolerated, accepted and favored by the maternal organism in spite of its paternal semi-allogeneicity. From all these considerations, novel research directions, potential innovative tumor therapy and prophylaxis strategies might, theoretically, result.

Tropheryma whipplei Increases Expression of Human Leukocyte Antigen-G on Monocytes to Reduce Tumor Necrosis Factor and Promote Bacterial Replication

BACKGROUND & AIMS

Infection with Tropheryma whipplei has a range of effects-some patients can be chronic carriers without developing any symptoms, whereas others can develop systemic Whipple disease, characterized by a lack a protective inflammatory immune response. Alterations in HLA-G function have been associated with several diseases. We investigated the role of HLA-G during T whipplei infection.

METHODS

Sera, total RNA, and genomic DNA were collected from peripheral blood from 22 patients with classic Whipple's disease, 19 patients with localized T whipplei infections, and 21 asymptomatic carriers. Levels of soluble HLA-G in sera were measured by enzyme-linked immuosorbent assay, and expressions of HLA-G and its isoforms were monitored by real-time polymerase chain reaction. HLA-G alleles were identified and compared with a population of voluntary bone marrow donors. Additionally, monocytes from healthy subjects were stimulated with T whipplei, and HLA-G expression was monitored by real-time polymerase chain reaction and flow cytometry. Bacterial replication was assessed by polymerase chain reaction in the presence of HLA-G or inhibitor of tumor necrosis factor (TNF) (etanercept).

RESULTS

HLA-G mRNAs and levels of soluble HLA-G were significantly increased in sera from patients with chronic T whipplei infection compared with sera from asymptomatic carriers and control individuals. No specific HLA-G haplotypes were associated with disease or T whipplei infection. However, T whipplei infection of monocytes induced expression of HLA-G, which was associated with reduced secretion of TNF compared with noninfected monocytes. A neutralizing antibody against HLA-G increased TNF secretion by monocytes in response to T whipplei, and a TNF inhibitor promoted bacteria replication.

CONCLUSIONS

Levels of HLA-G are increased in sera from patients with T whipplei tissue infections, associated with reduced production of TNF by monocytes. This might promote bacteria colonization in patients.

Heterogeneity of HLA-G Expression in Cancers: Facing the Challenges

Phenotypic heterogeneity has been observed in most malignancies, which represents a considerable challenge for tumor therapy. In recent decades, the biological function and clinical significance of the human leukocyte antigen (HLA)-G have been intensively explored. It is now widely accepted that HLA-G is a critical marker of immunotolerance in cancer cell immune evasion and is strongly associated with disease progress and prognosis for cancer patients. Moreover, it has recently been emphasized that the signaling pathway linking HLA-G and immunoglobulin-like transcripts (ILTs) is considered an immune checkpoint. In addition, HLA-G itself can generate at least seven distinct isoforms, and intertumor and intratumor heterogeneity of HLA-G expression is common across different tumor types. Furthermore, HLA-G heterogeneity in cancers has been related to disease stage and outcomes, metastatic status and response to different therapies. This review focuses on the heterogeneity of HLA-G expression in malignant lesions, and clinical implications of this heterogeneity that might be relevant to personalized treatments are also discussed.

Clinical Significance of Potential Unidentified HLA-G Isoforms Without α1 Domain but Containing Intron 4 in Colorectal Cancer Patients

The ectopic HLA-G expression in malignancies has been extensively explored and clinical significance of the molecule was widely acknowledged. Besides previously well-documented seven isoforms (HLA-G1~-G7), other novel isoforms of HLA-G have been reported but their clinical relavenace remians evaluated. In this study, lesion HLA-G expression in 379 case-matched serial section primary colorectal cancers (CRC) were evaluated with mAb 4H84 (recognizing an epitope in HLA-G α1 domain), and mAb 5A6G7 (recognizing an epitope encoded by intron 4), respectively. Data showed that HLA-G positive staining with mAbs 4H84 and 5A6G7 was 70.7 and 60.4%, respectively. When percentage of HLA-G expression detected with mAb 4H84 subtracted that with mAb 5A6G7, the difference (_ΔHLA-G) with negative (_ΔHLA-G_neg), comparable (_ΔHLA-G_com) and positive (_ΔHLA-G_pos) were observed in 64 (16.9%), 159 (42.0%), and 156 (41.2%) cases, respectively. Noteworthy, unexpected immunostaining was observed in 44 (11.6%) lesions that no staining was detected with mAb 4H84 but positive with mAb 5A6G7 (4H84^neg5A6G7^pos). This staining pattern was unpredictable because all seven known HLA-G isoforms containing the α 1 domain could be recognized by the mAb 4H84. Moreover, patients with _ΔHLA-G_neg had obviously better survival than those with _ΔHLA-G_com and _ΔHLA-G_pos (p = 0.017), and _ΔHLA-G could be an independent prognostic factor for CRC patients (p = 0.008). Our findings provides the first report that potential unidentified HLA-G isoforms is of distinct clinical significance in CRC patients.

Clinicopathologic significance of HLA-G and HLA-E molecules in Tunisian patients with ovarian carcinoma

BACKGROUND

The human leukocyte antigen (HLA)-G and HLA-E, non classical HLA class I molecules, have been highly implicated in immune tolerance. HLA-G and HLA-E molecules were proposed as putative markers of several advanced cancers. As a step towards a better understanding of ovarian carcinoma, we evaluated the expression of both HLA-G and HLA-E molecules and explored their prognostic implication.

METHODS

HLA-G and HLA-E expression were studied by immunohistochemistry on ovarian carcinoma tissues. This expression was semi-quantitatively scored into four expression groups and correlated to clinicopathological parameters and patients' survival.

RESULTS

HLA-G and HLA-E have been found to be highly expressed in ovarian carcinoma tissues (Respectively, 72.4% and 96.8%). They are frequently co-expressed. Univariate and multivariate analysis revealed that a positive HLA-G expression status in tumor tissue is a promising candidate parameter to predict disease recurrence in addition to the disease status in Tunisian patients with ovarian carcinoma. Moreover, the elevated HLA-E expression was associated with serous ovarian carcinoma subtype as well as with advanced stages of ovarian carcinoma.

CONCLUSION

HLA-G and HLA-E are highly represented in ovarian carcinoma suggesting a potential association with progressive disease mechanism. HLA-G and HLA-E molecules might be new candidates' markers for ovarian carcinoma progression.

Chimeric Small Antibody Fragments as Strategy to Deliver Therapeutic Payloads

Antibody-drug conjugates (ADCs) represent an innovative class of biopharmaceuticals, which aim at achieving a site-specific delivery of cytotoxic agents to the target cell. The use of ADCs represents a promising strategy to overcome the disadvantages of conventional pharmacotherapy of cancer or neurological diseases, based on cytotoxic or immunomodulatory agents. ADCs consist of monoclonal antibodies attached to biologically active drugs by means of cleavable chemical linkers. Advances in technologies for the coupling of antibodies to cytotoxic drugs promise to deliver greater control of drug pharmacokinetic properties and to significantly improve pharmacodelivery applications, minimizing exposure of healthy tissue. The clinical success of brentuximab vedotin and trastuzumab emtansine has led to an extensive expansion of the clinical ADC pipeline. Although the concept of an ADC seems simple, designing a successful ADC is complex and requires careful selection of the receptor antigen, antibody, linker, and payload. In this review, we explore insights in the antibody and antigen requirements needed for optimal payload delivery and support the development of novel and improved ADCs for the treatment of cancer and neurological diseases.

Epigenetic Changes of the Immune System with Role in Tumor Development

Tumor development is closely related to chronic inflammation and to evasion of immune defense mechanisms by neoplastic cells. The mediators of the inflammatory process as well as proteins involved in immune response or immune response evasion can be subject to various epigenetic changes such as methylation, acetylation, or phosphorylation. Some of these, such as cytokine suppressors, are undergoing repression through epigenetic changes, and others such as cytokines or chemokines are undergoing activation through epigenetic changes, both modifications having as a result tumor progression. The activating changes can affect the receptor molecules involved in immune response and these promote inflammation and subsequently tumor development while the inactivating changes seem to be related to the tumor regression process. The proteins involved in antigen presentation, and, therefore in immune response escape, such as classical HLA proteins and related APM (antigen presentation machinery) with their epigenetic changes contribute to the tumor development process, either to tumor progression or regression, depending on the immune effector cells that are in play.

Sestrin2 and sestrin3 suppress NK-92 cell-mediated cytotoxic activity on ovarian cancer cells through AMPK and mTORC1 signaling

Ovarian cancer is one of the major cancer types. NK-92 cell line, which has consistently and reproducibly high anti-tumor cytotoxicity, may be used for immunotherapy against ovarian cancer. Understanding the mechanisms that regulate the anti-tumor activity of NK-92 cells is important for developing novel therapeutic strategies. In the current study, using an ovarian cancer xenograft mouse model, we identified the up-regulation of sestrin2 (SESN2) and sestrin3 (SESN3) in intratumoral NK-92 cells. Lentivirus-transduced NK-92 cells, which overexpressed SESN2 or SESN3 after doxycycline treatment, exhibited less expression of activating receptors, perforin and granzyme B. Overexpression of SESN2 and SESN3 impaired tumoricidal effect of NK-92 cells both in vitro and in vivo. Furthermore, overexpression of SESN2 and SESN3 inhibited mTORC1 signaling while promoting AMPK signaling in NK-92 cells. Taken together, our data highlights the crucial effects of SESN2 and SESN3 on NK-92 cell-mediated anti-ovarian cancer activity. This study might be valuable for designing a novel therapeutic strategy for ovarian cancer.

Tumour and placenta establishment: The importance of antigen processing and presentation

Classical and non-classical MHC class I (MHC I) molecules displayed at the cell surface are essential for the induction of innate and adaptive immune responses. Classical MHC I present endogenously derived peptides to CD8⁺ T cells for immunosurveillance of infected or malignant cells. By contrast, non-classical MHC I, in particular HLA-G, also display peptides, but primarily act as immunomodulatory ligands for the innate immune response and are an important component for extravillous trophoblast invasion to form the placenta in pregnancy. Endoplasmic Reticulum AminoPeptidase 1 (ERAP1), which trims peptides in the ER to generate ligands for MHC I loading, is a key regulator of the peptide repertoire and has a significant impact on the formation of stable MHC I at the cell surface. ERAP1 also plays a role in angiogenesis, cell cycle progression and migration, events that are shared between tumour cells and placenta formation. Here we discuss the similarities between tumour and extravillous trophoblast cells in their immune modulatory, invasion, migration and proliferation properties in the context of ERAP1 and its role in establishment of solid tumours and placenta formation.

IL-15 super-agonist (ALT-803) enhances natural killer (NK) cell function against ovarian cancer

OBJECTIVE

Natural killer (NK) cells represent a powerful immunotherapeutic target as they lyse tumors directly, do not require differentiation, and can elicit potent inflammatory responses. The objective of these studies was to use an IL-15 super-agonist complex, ALT-803 (Altor BioScience Corporation), to enhance the function of both normal and ovarian cancer patient derived NK cells by increasing cytotoxicity and cytokine production.

METHODS

NK cell function from normal donor peripheral blood mononuclear cells (PBMCs) and ovarian cancer patient ascites was assessed using flow cytometry and chromium release assays ±ALT-803 stimulation. To evaluate the ability of ALT-803 to enhance NK cell function in vivo against ovarian cancer, we used a MA148-luc ovarian cancer NOD scid gamma (NSG) xenogeneic mouse model with transferred human NK cells.

RESULTS

ALT-803 potently enhanced functionality of NK cells against all ovarian cancer cell lines with significant increases seen in CD107a, IFNγ and TNFα expression depending on target cell line. Function was also rescued in NK cells derived from ovarian cancer patient ascites. Finally, only animals treated with intraperitoneal ALT-803 displayed an NK dependent significant decrease in tumor.

CONCLUSIONS

ALT-803 enhances NK cell cytotoxicity against ovarian cancer in vitro and in vivo and is able to rescue functionality of NK cells derived from ovarian cancer patient ascites. These findings suggest that ALT-803 has the potential to enhance NK cell-based immunotherapeutic approaches for the treatment of ovarian cancer.

Lesion HLA-G5/-G6 isoforms expression in patients with ovarian cancer

HLA-G is an immune tolerant with seven isoforms. HLA-G expression was observed to be associated with tumor cell immune escaping, invasion and metastasis, and with poor prognosis in cancer patients. Different types of HLA-G isoforms could be expressed in clinical settings when meet different cellular and environmental conditions. Lesion total HLA-G expression detected by the monoclonal antibody (mAb) 4H84 was widely investigated in previous studies, while specific HLA-G isoforms such as HLA-G5/-G6 remains to be clarified. In this study, 118 primary ovarian cancer lesions were probed with mAb 5A6G7 which recognizes HLA-G5/-G6 was performed by immunohistochemistry. Data showed that HLA-G5/-G6 was expressed in 79.7% (94/118) of these ovarian cancer lesions, where HLA-G5/-G6 expression was observed in 75.7% (53/70) serous, 63.6% (7/11) mucinous cystadenocarcinoma and in 100% (11/11) endometrioid adenocarcinoma, in 85.7% (6/7) clear cell carcinoma, 100% (10/10) sex cord-stromal tumor and 77.8% (7/9) germ cell tumors. However, lesion HLA-G5/-G6 expression was unrelated to histological type, patient age, FIGO stage and patient survival. Unlike total HLA-G expression, no clinical significance of HLA-G5/-G6 expression in ovarian cancer lesion was observed in this study. Our findings indicated that different HLA-G isoforms might have different biological functions in malignancies.

Human Leukocyte Antigen-G (HLA-G) Expression in Cancers: Roles in Immune Evasion, Metastasis and Target for Therapy

Aberrant induction of human leukocyte antigen-G (HLA-G) expression has been observed in various malignancies and is strongly associated with tumor immune escape, metastasis and poor prognosis. To date, great achievements have been made in understanding the underlying mechanisms of HLA-G involved in tumor progression. HLA-G could lead to tumor evasion by inhibition of immune cell cytolysis, differentiation and proliferation and inhibition of cytokine production, induction of immune cell apoptosis, generation of regulatory cells and expansion of myeloid-derived suppressive cells and by impairment of chemotaxis. Moreover, HLA-G could arm tumor cells with a higher invasive and metastatic potential with the upregulation of tumor-promoting factor expression such as matrix metalloproteinases (MMPs), indicating that ectopic HLA-G expression could render multiple effects during the progression of malignancies. In this review, we summarized the mechanisms of HLA-G involved in promoting tumor cell immune escaping, metastasis and disease progression. Special attention will be paid to its significance as an attractive therapeutic target in cancers.

Intracellular antigens as targets for antibody based immunotherapy of malignant diseases

This review discusses the potential use of intracellular tumor antigens as targets of antibody-based immunotherapy for the treatment of solid tumors. In addition, it describes the characteristics of the intracellular tumor antigens targeted with antibodies which have been described in the literature and have been identified in the authors' laboratory. Finally, the mechanism underlying the trafficking of the intracellular tumor antigens to the plasma membrane of tumor cells are reviewed.

Significance of tumour cell HLA-G5/-G6 isoform expression in discrimination for adenocarcinoma from squamous cell carcinoma in lung cancer patients

Human leucocyte antigen (HLA)-G has seven isoforms, of which HLA-G1-G4 are membrane-bound and HLA-G5-G7 are soluble. Previous studies reinforced HLA-G expression was strongly related to poor prognosis in different types of cancers. Among these studies, the monoclonal antibody (mAb) 4H84 was used which detects all HLA-G isoform heavy chain; unfortunately, leaves the specific types of isoforms expressed in lesions undistinguished and its clinical significance needs to be clarified. To explore clinical significance of lesion soluble HLA-G (sHLA-G) in non-small-cell lung cancer (NSCLC), mAb 5A6G7 recognizing HLA-G5/-G6 molecules was used. Tumour cell sHLA-G expression in 131 primary NSCLC lesions (66 squamous cell carcinoma, 55 adenocarcinoma and 10 adenosquamous carcinoma) were analysed with immunohistochemistry. Data showed that sHLA-G expression was observed in 34.0% (45/131) of the NSCLC lesions, which was unrelated to patient age, sex, lymph nodal status, tumour-node-metastasis stage and patient survival. However, tumour cell sHLA-G expression in lesions was predominately observed in adenocarcinoma lesions (73.0%, 40/55) which was significantly higher than that in squamous cell carcinoma (6.0%, 4/66) and adenosquamous carcinoma lesions (10.0%, 1/10, P < 0.001). The area under the receiver operating characteristic curve for lesion sHLA-G was 0.833 (95% CI: 0.754-0.912, P < 0.001) for adenocarcinoma versus squamous cell carcinoma. Our findings for the first time showed that tumour cell sHLA-G was predominately expressed in lung adenocarcinoma, which could be a useful biomarker to discriminate adenocarcinoma from squamous cell carcinoma in NSCLC patients.

Recent Advancements in Prognostic Factors of Epithelial Ovarian Carcinoma

Ovarian cancer remains the most common cause of gynecologic cancer-related death among women in developed countries. Nevertheless, subgroups of ovarian cancer patients experience relatively longer survival. Efforts to identify prognostic factors that characterize such patients are ongoing, with investigational areas including tumor characteristics, surgical management, inheritance patterns, immunologic factors, and genomic patterns. This review discusses various demographic, clinical, and molecular factors implicating longevity and ovarian cancer survival. Continued efforts at identifying these prognosticators may result in invaluable adjuncts to the treatment of ovarian cancer, with the ultimate goal of advancing patient care.

Non-classical MHC-I human leukocyte antigen (HLA-G) in hepatotropic viral infections and in hepatocellular carcinoma

The human leukocyte antigen (HLA)-G is a "nonclassical" major histocompatibility complex (MHC) class Ib gene, located at chromosome 6, in the 6p21.3 region. The HLA-G presents immunomodulatory functions essential in pregnancy for the tolerance of the semi-allogenic fetus, but an abnormal expression of HLA-G has been observed in numerous pathological conditions, such as tumors, autoimmune diseases and viral infections. In recent years, numerous studies have assessed the clinical relevance of HLA-G expression in different types of cancer: in general, a higher HLA-G expression correlates with a lower survival rate or a shorter disease-free survival. Altered expression of HLA-G has been found in both HCV and HBV infection, and some genetic polymorphisms have been associated with altered susceptibility/disease development for these infections, however, whether the biologic role of HLA-G in HCV and HBV infection is beneficial or hazardous, it is not completely clear. In the context of hepatocellular carcinoma, HLA-G has shown a potential diagnostic role, moreover a prognostic value in HCC patients has been also attributed to HLA-G molecules. We revise here the role of HLA-G in hepatotropic HBV/HCV infections and in hepatocellular carcinoma (HCC).

HLA-G expression is an independent predictor for improved survival in high grade ovarian carcinomas

Aberrant expression of human leukocyte antigens (HLA) class I has prognostic importance in various cancers. Here, we evaluated the prognostic value of classical (A/B/C) and nonclassical (G/E) HLA expression in 169 high grade epithelial ovarian cancer samples and linked that to clinicopathological characteristics and survival. Expression of HLA-A, -B/C, or -E was not correlated with survival. Survival was prolonged when tumours expressed HLA-G (P = 0.008) and HLA-G was an independent predictor for better survival (P = 0.011). In addition, HLA-G expression was associated with longer progression-free survival (P = 0.036) and response to chemotherapy (P = 0.014). Accordingly, high expression of HLA-G mRNA was associated with prolonged disease-free survival (P = 0.037) in 65 corresponding samples. Elevated serum-soluble HLA-G levels as measured by enzyme-linked immunosorbent assay in 50 matched patients were not correlated to HLA-G protein expression or gene expression nor with survival. During treatment, sHLA-G levels declined (P = 0.038). In conclusion, expression of HLA-G is an independent prognostic factor for improved survival in high grade epithelial ovarian cancer and a predictor for platinum sensitivity.

Overexpression of HLA-G Is positively associated with Kazakh esophageal squamous cell carcinoma in Xinjiang, China

HLA-G is a class I HLA that has gained much attention due to its multiple functions in the immune system. More important, some studies found HLA-G may be detrimental in tumors and viral infections, and the detection of HLA-G expression might serve as a clinical marker in the prediction of clinical outcomes for certain types of carcinoma. We assessed the association between the development of Kazakh esophageal squamous cell carcinoma (ESCC) harboring high-risk HPV infection and the expression of HLA-G. The expression of HLA-G was detected by S-P immunohistochemical staining in 60 cases of Kazakh ESCC tissues and 40 cases of Kazakh tumor adjacent normal tissues. HPV16 infection in ESCC was detected by genotype-specific polymerase chain reaction. HPV16 infection rate in Kazakh ESCC was 35.0%, significantly higher than that of the infection rate of the adjacent normal tissues 15% (p<0.05, OR=3.051; 95% CI: 1.103-8.438). The expression of HLA-G in Kazakh ESCC was 75.0% (45/60), significantly higher than that of tumor adjacent normal tissues (17.5%; p<0.05); expression of HLA-G was slightly higher in HPV16-positive than HPV16-negative ESCC, but the difference was not statistically significant (p>0.05). The positive expression rate of HLA-G was closely related to depth of invasion and clinical stage (p<0.05 for all), but was not related to age, sex, tumor location, histologic grade, and nodal status (p>0.05 for all). Overexpression of HLA-G was a characteristic feature of Kazakh ESCC; HLA-G may be involved in Kazakh ESCC carcinogenesis and HPV infection.

Ovarian cancer molecular pathology

Ovarian cancer (OVC) is the fourth leading cause of cancer mortality among women in Europe and the United States. Its early detection is difficult due to the lack of specificity of clinical symptoms. Unfortunately, late diagnosis is a major contributor to the poor survival rates for OVC, which can be attributed to the lack of specific sets of markers. Aside from patients sharing a strong family history of ovarian and breast cancer, including the BRCA1 and BRCA2 tumor suppressor genes mutations, the most used biomarker is the Cancer-antigen 125 (CA-125). CA-125 has a sensitivity of 80 % and a specificity of 97 % in epithelial cancer (stage III or IV). However, its sensitivity is 30 % in stage I cancer, as its increase is linked to several physiological phenomena and benign situations. CA-125 is particularly useful for at-risk population diagnosis and to assess response to treatment. It is clear that alone, CA-125 is inadequate as a biomarker for OVC diagnosis. There is an unmet need to identify additional biomarkers. Novel and more sensitive proteomic strategies such as MALDI mass spectrometry imaging studies are well suited to identify better markers for both diagnosis and prognosis. In the present review, we will focus on such proteomic strategies in regards to OVC signaling pathways, OVC development and escape from the immune response.

In vivo identification of an HLA-G complex as ubiquitinated protein circulating in exosomes

The nonclassical human leukocyte antigen-G (HLA-G) is a tolerogenic molecule that can be released to the circulation by expressing cells. This molecule can form dimers but some other complexed HLA-G forms have been proposed to be present in vivo. Here, we further characterized these other complexed HLA-G forms in vivo. Ascitic and pleural exudates from patients were selected based on positivity for HLA-G by ELISA. Complexed HLA-G was detected in exosomes, which indicates an intracellular origin of these forms. 2D-PAGE analysis of exudates and isolated exosomes showed that these high molecular weight complexes were more heterogeneous than the HLA-G1 expressed by cell cultures. Treatment with deglycosylating enzymes did not change the molecular weight of HLA-G complexes. Immunoblot analysis of exudates and exosomes with an anti-ubiquitin antibody showed that at least some of these structures correspond to ubiquitinated HLA-G. HLA-G ubiquitination could be reproduced in vitro in HLA-G1-transfected cell lines, although with a lower modified/nonmodified protein proportion than in exudates. In summary, we demonstrate new circulating HLA-G forms in vivo that open a new perspective in the study of HLA-G function and analysis.

Monoclonal antibodies for the treatment of cancer

Over the past decade, the clinical utility of monoclonal antibodies has been realized and antibodies are now a mainstay for the treatment of cancer. Antibodies have the unique capacity to target and kill tumor cells while simultaneously activating immune effectors to kill tumor cells through the complement cascade or antibody-dependent cellular cytotoxicity (ADCC). This multifaceted mechanism of action combined with target specificity underlies the capacity of antibodies to elicit anti-tumor responses while minimizing the frequency and magnitude of adverse events. This review will focus on mechanisms of action, clinical applications and putative mechanisms of resistance to monoclonal antibody therapy in the context of cancer.