Association of high CD4-positive T cell infiltration with mutations in HLA class II-regulatory genes in microsatellite-unstable colorectal cancer

Global analysis of T-cell groups reveals immunological features and common antigen targets of digestive tract tumors

BACKGROUND

T cells are key players in the tumor immune microenvironment (TIME), as they can recognize and eliminate cancer cells that express neoantigens derived from somatic mutations. However, the diversity and specificity of T-cell receptors (TCRs) that recognize neoantigens are largely unknown, due to the high variability of TCR sequences among individuals.

METHODS

To address this challenge, we applied GLIPH2, a novel algorithm that groups TCRs based on their predicted antigen specificity and HLA restriction, to cluster the TCR repertoire of 1,702 patients with digestive tract cancer. The patients were divided into five groups based on whether they carried tumor-infiltrating or clonal-expanded TCRs and calculated their TCR diversity. The prognosis, tumor subtype, gene mutation, gene expression, and immune microenvironment of these groups were compared. Viral specificity inference and immunotherapy relevance analysis performed for the TCR groups.

RESULTS

This approach reduced the complexity of TCR sequences to 249 clonally expanded and 150 tumor-infiltrating TCR groups, which revealed distinct patterns of TRBV usage, HLA association, and TCR diversity. In gastric adenocarcinoma (STAD), patients with tumor-infiltrating TCRs (Patients-TI) had significantly worse prognosis than other patients (Patients-nonTI). Patients-TI had richer CD8+ T cells in the immune microenvironment, and their gene expression features were positively correlated with immunotherapy response. We also found that tumor-infiltrating TCR groups were associated with four distinct tumor subtypes, 26 common gene mutations, and 39 gene expression signatures. We discovered that tumor-infiltrating TCRs had cross-reactivity with viral antigens, indicating a possible link between viral infections and tumor immunity.

CONCLUSION

By applying GLIPH2 to TCR sequences from digestive tract tumors, we uncovered novel insights into the tumor immune landscape and identified potential candidates for shared TCRs and neoantigens.

Advances in vaccine development for cancer prevention and treatment in Lynch Syndrome

Lynch Syndrome (LS) is one of the most common hereditary cancer syndromes, and is caused by mutations in one of the four DNA mismatch repair (MMR) genes, namely MLH1, MSH2, MSH6 and PMS2. Tumors developed by LS carriers display high levels of microsatellite instability, which leads to the accumulation of large numbers of mutations, among which frameshift insertion/deletions (indels) within microsatellite (MS) loci are the most common. As a result, MMR-deficient (MMRd) cells generate increased rates of tumor-specific neoantigens (neoAgs) that can be recognized by the immune system to activate cancer cell killing. In this context, LS is an ideal disease to leverage immune-interception strategies. Therefore, the identification of these neoAgs is an ongoing effort for the development of LS cancer preventive vaccines. In this review, we summarize the computational methods used for in silico neoAg prediction, including their challenges, and the experimental techniques used for in vitro validation of their immunogenicity. In addition, we outline results from past and on-going vaccine clinical trials and highlight avenues for improvement and future directions.

Strategies for overcoming bottlenecks in allogeneic CAR-T cell therapy

Patient-derived autologous chimeric antigen receptor (CAR)-T cell therapy is a revolutionary breakthrough in immunotherapy and has made impressive progress in both preclinical and clinical studies. However, autologous CAR-T cells still have notable drawbacks in clinical manufacture, such as long production time, variable cell potency and possible manufacturing failures. Allogeneic CAR-T cell therapy is significantly superior to autologous CAR-T cell therapy in these aspects. The use of allogeneic CAR-T cell therapy may provide simplified manufacturing process and allow the creation of 'off-the-shelf' products, facilitating the treatments of various types of tumors at less delivery time. Nevertheless, severe graft-versus-host disease (GvHD) or host-mediated allorejection may occur in the allogeneic setting, implying that addressing these two critical issues is urgent for the clinical application of allogeneic CAR-T cell therapy. In this review, we summarize the current approaches to overcome GvHD and host rejection, which empower allogeneic CAR-T cell therapy with a broader future.

Microsatellite Instability and Immune Response: From Microenvironment Features to Therapeutic Actionability-Lessons from Colorectal Cancer

Microsatellite instability (MSI) can be found in 15-20% of all colorectal cancers (CRC) and is the key feature of a defective DNA mismatch repair (MMR) system. Currently, MSI has been established as a unique and pivotal biomarker in the diagnosis, prognosis, and treatment of CRC. MSI tumors display a strong lymphocytic activation and a shift toward a tumoral microenvironment restraining metastatic potential and ensuing in a high responsiveness to immunotherapy of MSI CRC. Indeed, neoplastic cells with an MMR defect overexpress several immune checkpoint proteins, such as programmed death-1 (PD-1) and programmed death-ligand 1(PD-L1), that can be pharmacologically targeted, allowing for the revival the cytotoxic immune response toward the tumor. This review aims to illustrate the role of MSI in the tumor biology of colorectal cancer, focusing on the immune interactions with the microenvironment and their therapeutic implications.

Exosomal non-coding RNAs' role in immune regulation and potential therapeutic applications

Exosomes are now significant players in both healthy and unhealthy cell-to-cell communication. Exosomes can mediate immune activation or immunosuppression, which can influence the growth of tumors. Exosomes affect the immune responses to malignancies in various ways by interacting with tumor cells and the environment around them. Exosomes made by immune cells can control the growth, metastasis, and even chemosensitivity of tumor cells. In contrast, exosomes produced by cancer cells can encourage immune responses that support the tumor. Exosomes carry circular RNAs, long non-coding RNAs, and microRNAs (miRNAs), all involved in cell-to-cell communication. In this review, we focus on the most recent findings concerning the role of exosomal miRNAs, lncRNAs, and circRNAs in immune modulation and the potential therapeutic implications of these discoveries.

Lynch Syndrome: From Carcinogenesis to Prevention Interventions

Simple Summary

Promoting proper preventive interventions to reduce morbidity and mortality is one of the most important challenges pertaining to inherited conditions. Lynch syndrome (LS) is an inherited disorder that predisposes to several kinds of tumor and is responsible for a relevant proportion of human colorectal and endometrial cancers. Recent knowledge has allowed for a better understanding of the genetic cause, pathogenesis, underlying immunological mechanisms, epidemiological distribution, and prevalence of this disease. This opens up unpredictable perspectives of translating such knowledge into validated programs for prevention and surveillance, in order to reduce the health impact of this disease through medical interventions before cancer development. In our review, we summarize the updated guidelines of the screening, surveillance, and risk-reducing strategies for LS patients. Moreover, we present novel opportunities in the treatment and prevention of LS patients through harnessing the immune system using immunocheckpoint inhibitors and vaccines.

Abstract

Lynch syndrome (LS) is the most common inherited disorder responsible for an increased risk of developing cancers at different sites, most frequently in the gastrointestinal and genitourinary tracts, caused by a germline pathogenic variant affecting the DNA mismatch repair system. Surveillance and risk-reducing procedures are currently available and warranted for LS patients, depending on underlying germline mutation, and are focused on relevant targets for early cancer diagnosis or primary prevention. Although pharmacological approaches for preventing LS-associated cancer development were started many years ago, to date, aspirin remains the most studied drug intervention and the only one suggested by the main surveillance guidelines, despite the conflicting findings. Furthermore, we also note that remarkable advances in anticancer drug discovery have given a significant boost to the application of novel immunological strategies such as immunocheckpoint inhibitors and vaccines, not only for cancer treatment, but also in a preventive setting. In this review, we outline the clinical, biologic, genetic, and morphological features of LS as well as the recent three-pathways carcinogenesis model. Furthermore, we provide an update on the dedicated screening, surveillance, and risk-reducing strategies for LS patients and describe emerging opportunities of harnessing the immune system.

Regulation of the antigen presentation machinery in cancer and its implication for immune surveillance

Evading immune destruction is one of the hallmarks of cancer. A key mechanism of immune evasion deployed by tumour cells is to reduce neoantigen presentation through down-regulation of the antigen presentation machinery. MHC-I and MHC-II proteins are key components of the antigen presentation machinery responsible for neoantigen presentation to CD8⁺ and CD4⁺ T lymphocytes, respectively. Their expression in tumour cells is modulated by a complex interplay of genomic, transcriptomic and post translational factors involving multiple intracellular antigen processing pathways. Ongoing research investigates mechanisms invoked by cancer cells to abrogate MHC-I expression and attenuate anti-tumour CD8⁺ cytotoxic T cell response. The discovery of MHC-II on tumour cells has been less characterized. However, this finding has triggered further interest in utilising tumour-specific MHC-II to harness sustained anti-tumour immunity through the activation of CD4⁺ T helper cells. Tumour-specific expression of MHC-I and MHC-II has been associated with improved patient survival in most clinical studies. Thus, their reactivation represents an attractive way to unleash anti-tumour immunity. This review provides a comprehensive overview of physiologically conserved or novel mechanisms utilised by tumour cells to reduce MHC-I or MHC-II expression. It outlines current approaches employed at the preclinical and clinical trial interface towards reversing these processes in order to improve response to immunotherapy and survival outcomes for patients with cancer.

Current Advances and Trends in KRAS Targeted Therapies for Colorectal Cancer

Kirsten Rat Sarcoma (KRAS) gene somatic point mutations is one of the most prominently mutated proto-oncogenes known to date, and accounts for approximately 60% of all colorectal cancer cases. One of the most exciting drug development areas against colorectal cancer is the targeting of undruggable kinases and kinase-substrate molecules, although whether and how they can be integrated with other therapies remains a question. Current clinical trial data have provided supporting evidence on the use of combination treatment involving MEK inhibitors and either one of the PI3K inhibitors for patients with metastatic colorectal cancer to avoid the development of resistance and provide effective therapeutic outcome rather than using a single agent alone. Many clinical trials are also ongoing to evaluate different combinations of these pathway inhibitors in combination with immunotherapy for patients with colorectal cancer whose current palliative treatment options are limited. Nevertheless, continued assessment of these targeted cancer therapies will eventually allow patients with colorectal cancer to be treated using a personalized medicine approach. In this review, the most recent scientific approaches and clinical trials targeting KRAS mutations directly or indirectly for the management of colorectal cancer are discussed.

Human leukocyte antigen class II-based immune risk model for recurrence evaluation in stage I-III small cell lung cancer

Background

Immunotherapy has revolutionized therapeutic patterns of small cell lung cancer (SCLC). Human leukocyte antigen class II (HLA class II) is related to antitumor immunity. However, the implications of HLA class II in SCLC remain incompletely understood.

Materials and methods

We investigated the expression patterns of HLA class II on tumor cells and tumor-infiltrating lymphocytes (TILs) by immunohistochemistry staining and its association with clinical parameters, immune markers, and recurrence-free survival (RFS) in 102 patients with stage I–III SCLC with radical surgery. Additionally, an HLA class II-based immune risk model was established by least absolute shrinkage and selection operator regression. With bioinformatics methods, we investigated HLA class II-related enrichment pathways and immune infiltration landscape in SCLC.

Results

HLA class II on tumor cells and TILs was positively expressed in 9 (8.8%) and 45 (44.1%) patients with SCLC, respectively. HLA class II on TILs was negatively associated with lymph node metastasis and positively correlated with programmed death-ligand 1 (PD-L1) on TILs (p<0.001) and multiple immune markers (CD3, CD4, CD8, FOXP3; p<0.001). Lymph node metastasis (OR 0.314, 95% CI 0.118 to 0.838, p=0.021) and PD-L1 on TILs (OR 3.233, 95% CI 1.051 to 9.95, p=0.041) were independent predictive factors of HLA class II on TILs. HLA class II positivity on TILs prompted a longer RFS (40.2 months, 95% CI 31.7 to 48.7 vs 28.8 months, 95% CI 21.4 to 36.3, p=0.014). HLA class II on TILs, PD-L1 on TILs, CD4, and FOXP3 were enrolled in the immune risk model, which categorized patients into high-risk and low-risk groups and had better power for predicting the recurrence than tumor stage. Pathway enrichment analyses showed that patients with high HLA class II expression demonstrated signatures of transmembrane transportation, channel activity, and neuroactive ligand–receptor interaction. High-risk SCLC patients had a higher proportion of T follicular helper cells (p=0.034) and a lower proportion of activated memory CD4-positive T cells (p=0.040) and resting dendritic cells (p=0.045) versus low-risk patients.

Conclusions

HLA class II plays a crucial role in tumor immune microenvironment and recurrence prediction. This work demonstrates the prognostic and clinical values of HLA class II in patients with SCLC.

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

BACKGROUND

The human leukocyte antigen (HLA) class II molecules are constitutively expressed in some melanoma, but the underlying molecular mechanisms have not yet been characterized.

METHODS

The expression of HLA class II antigen processing machinery (APM) components was determined in melanoma samples by qPCR, Western blot, flow cytometry and immunohistochemistry. Immunohistochemical and TCGA datasets were used for correlation of HLA class II expression to tumor grading, T-cell infiltration and patients' survival.

RESULTS

The heterogeneous HLA class II expression in melanoma samples allowed us to characterize four distinct phenotypes. Phenotype I totally lacks constitutive HLA class II surface expression, which is inducible by interferon-gamma (IFN-γ); phenotype II expresses low basal surface HLA class II that is further upregulated by IFN-γ; phenotype III lacks constitutive and IFN-γ controlled HLA class II expression, but could be induced by epigenetic drugs; and in phenotype IV, lack of HLA class II expression is not recovered by any drug tested. High levels of HLA class II APM component expression were associated with an increased intra-tumoral CD4+ T-cell density and increased patients' survival.

CONCLUSIONS

The heterogeneous basal expression of HLA class II antigens and/or APM components in melanoma cells is caused by distinct molecular mechanisms and has clinical relevance.

Targeting Neoepitopes to Treat Solid Malignancies: Immunosurgery

Successful outcome of immune checkpoint blockade in patients with solid cancers is in part associated with a high tumor mutational burden (TMB) and the recognition of private neoantigens by T-cells. The quality and quantity of target recognition is determined by the repertoire of ‘neoepitope’-specific T-cell receptors (TCRs) in tumor-infiltrating lymphocytes (TIL), or peripheral T-cells. Interferon gamma (IFN-γ), produced by T-cells and other immune cells, is essential for controlling proliferation of transformed cells, induction of apoptosis and enhancing human leukocyte antigen (HLA) expression, thereby increasing immunogenicity of cancer cells. TCR αβ-dependent therapies should account for tumor heterogeneity and availability of the TCR repertoire capable of reacting to neoepitopes and functional HLA pathways. Immunogenic epitopes in the tumor-stroma may also be targeted to achieve tumor-containment by changing the immune-contexture in the tumor microenvironment (TME). Non protein-coding regions of the tumor-cell genome may also contain many aberrantly expressed, non-mutated tumor-associated antigens (TAAs) capable of eliciting productive anti-tumor immune responses. Whole-exome sequencing (WES) and/or RNA sequencing (RNA-Seq) of cancer tissue, combined with several layers of bioinformatic analysis is commonly used to predict possible neoepitopes present in clinical samples. At the ImmunoSurgery Unit of the Champalimaud Centre for the Unknown (CCU), a pipeline combining several tools is used for predicting private mutations from WES and RNA-Seq data followed by the construction of synthetic peptides tailored for immunological response assessment reflecting the patient’s tumor mutations, guided by MHC typing. Subsequent immunoassays allow the detection of differential IFN-γ production patterns associated with (intra-tumoral) spatiotemporal differences in TIL or peripheral T-cells versus TIL. These bioinformatics tools, in addition to histopathological assessment, immunological readouts from functional bioassays and deep T-cell ‘adaptome’ analyses, are expected to advance discovery and development of next-generation personalized precision medicine strategies to improve clinical outcomes in cancer in the context of i) anti-tumor vaccination strategies, ii) gauging mutation-reactive T-cell responses in biological therapies and iii) expansion of tumor-reactive T-cells for the cellular treatment of patients with cancer.

HLA class I loss in colorectal cancer: implications for immune escape and immunotherapy

T cell-mediated immune therapies have emerged as a promising treatment modality in different malignancies including colorectal cancer (CRC). However, only a fraction of patients currently respond to treatment. Understanding the lack of responses and finding biomarkers with predictive value is of great importance. There is evidence that CRC is a heterogeneous disease and several classification systems have been proposed that are based on genomic instability, immune cell infiltration, stromal content and molecular subtypes of gene expression. Human leukocyte antigen class I (HLA-I) plays a pivotal role in presenting processed antigens to T lymphocytes, including tumour antigens. These molecules are frequently lost in different types of cancers, including CRC, resulting in tumour immune escape from cytotoxic T lymphocytes during the natural history of cancer development. The aim of this review is to (i) summarize the prevalence and molecular mechanisms behind HLA-I loss in CRC, (ii) discuss HLA-I expression/loss in the context of the newly identified CRC molecular subtypes, (iii) analyze the HLA-I phenotypes of CRC metastases disseminated via blood or the lymphatic system, (iv) discuss strategies to recover/circumvent HLA-I expression/loss and finally (v) review the role of HLA class II (HLA-II) in CRC prognosis.

Fisetin inhibits proliferation of pancreatic adenocarcinoma by inducing DNA damage via RFXAP/KDM4A-dependent histone H3K36 demethylation

Pancreatic adenocarcinoma (PDAC) is an extremely malignant tumor that is associated with low survival rates. Fisetin is a natural flavonoid that shows diverse antitumor effects, including DNA damage, in various cancers. Increasing studies have demonstrated that epigenetic modifications play critical roles in DNA-damage response. However, the epigenetic regulation mechanism of fisetin in cancers is hardly studied. RFXAP is a critical transcription factor for MHC II molecules, however, its transcriptional role in PDAC is poorly understood. The anti-PDAC effect of fisetin was measured by CCK-8, flow cytometry, xenograft tumor nude mice model. DNA-damage levels were examined by immunofluorescence. Bioinformatics analysis was used to examine the expression of RFXAP and other genes involved in DNA-damage response. ChIP sequencing was used to explore the transcriptional role of RFXAP. The expression of target gene KDM4A was measured by qRT-PCR and western blots. KDM4A promoter activity was analyzed using dual-luciferase reporter assay. RFXAP overexpressing or silencing of PDAC cells was used to explore the effect of RFXAP in DNA damage induced by fisetin. We found that fisetin inhibited cell proliferation and induced DNA damage and S-phase arrest in PDAC. Expression of RFXAP and other DNA-damage response genes were upregulated by fisetin. We revealed that RFXAP expression was relatively low in PDAC and correlated with tumor stage and poor prognosis. Then we explored the transcriptional role of RFXAP and found that RFXAP targeted KDM4A, a special demethylase specific for tri- and dimethylated histone H3K36. We found that overexpression of RFXAP upregulated KDM4A and attenuated methylation of H3K36, thereby impairing DNA repair and enhancing the DNA damage induced by fisetin, while RFXAP silencing showed the opposite effect. We also found the function of fisetin in enhancing the effect of chemotherapy on pancreatic cancer cells. Our findings revealed that fisetin induced DNA damage via RFXAP/KDM4A-dependent histone H3K36 demethylation, thus causing inhibition of proliferation in PDAC.

Implications of Hereditary Origin on the Immune Phenotype of Mismatch Repair-Deficient Cancers: Systematic Literature Review

Microsatellite instability (MSI) represents one of the major types of genomic instability in human cancers and is most common in colorectal cancer (CRC) and endometrial cancer (EC). MSI develops as a consequence of DNA mismatch repair (MMR) deficiency, which can occur sporadically or in the context of Lynch syndrome (LS), the most common inherited tumor syndrome. MMR deficiency triggers the accumulation of high numbers of somatic mutations in the affected cells, mostly indel mutations at microsatellite sequences. MSI tumors are among the most immunogenic human tumors and are often characterized by pronounced local immune responses. However, so far, little is known about immunological differences between sporadic and hereditary MSI tumors. Therefore, a systematic literature search was conducted to comprehensively collect data on the differences in local T cell infiltration and immune evasion mechanisms between sporadic and LS-associated MSI tumors. The vast majority of collected studies were focusing on CRC and EC. Generally, more pronounced T cell infiltration and a higher frequency of B2M mutations were reported for LS-associated compared to sporadic MSI tumors. In addition, phenotypic features associated with enhanced lymphocyte recruitment were reported to be specifically associated with hereditary MSI CRCs. The quantitative and qualitative differences clearly indicate a distinct biology of sporadic and hereditary MSI tumors. Clinically, these findings underline the need for differentiating sporadic and hereditary tumors in basic science studies and clinical trials, including trials evaluating immune checkpoint blockade therapy in MSI tumors.

Novel Immune-Related Gene Signature for Risk Stratification and Prognosis of Survival in Lower-Grade Glioma

Objective

Despite several clinicopathological factors being integrated as prognostic biomarkers, the individual variants and risk stratification have not been fully elucidated in lower grade glioma (LGG). With the prevalence of gene expression profiling in LGG, and based on the critical role of the immune microenvironment, the aim of our study was to develop an immune-related signature for risk stratification and prognosis prediction in LGG.

Methods

RNA-sequencing data from The Cancer Genome Atlas (TCGA), Genome Tissue Expression (GTEx), and Chinese Glioma Genome Atlas (CGGA) were used. Immune-related genes were obtained from the Immunology Database and Analysis Portal (ImmPort). Univariate, multivariate cox regression, and Lasso regression were employed to identify differentially expressed immune-related genes (DEGs) and establish the signature. A nomogram was constructed, and its performance was evaluated by Harrell’s concordance index (C-index), receiver operating characteristic (ROC), and calibration curves. Relationships between the risk score and tumor-infiltrating immune cell abundances were evaluated using CIBERSORTx and TIMER.

Results

Noted, 277 immune-related DEGs were identified. Consecutively, 6 immune genes (CANX, HSPA1B, KLRC2, PSMC6, RFXAP, and TAP1) were identified as risk signature and Kaplan–Meier curve, ROC curve, and risk plot verified its performance in TCGA and CGGA datasets. Univariate and multivariate Cox regression indicated that the risk group was an independent predictor in primary LGG. The prognostic signature showed fair accuracy for 3- and 5-year overall survival in both internal (TCGA) and external (CGGA) validation cohorts. However, predictive performance was poor in the recurrent LGG cohort. The CIBERSORTx algorithm revealed that naïve CD4⁺ T cells were significant higher in low-risk group. Conversely, the infiltration levels of M1-type macrophages, M2-type macrophages, and CD8⁺T cells were significant higher in high-risk group in both TCGA and CGGA cohorts.

Conclusion

The present study constructed a robust six immune-related gene signature and established a prognostic nomogram effective in risk stratification and prediction of overall survival in primary LGG.

Relationships Between Immune Landscapes, Genetic Subtypes and Responses to Immunotherapy in Colorectal Cancer

Colorectal cancer (CRC) is highly heterogeneous at the genetic and molecular level, which has major repercussions on the efficacy of immunotherapy. A small subset of CRCs exhibit microsatellite instability (MSI), a molecular indicator of defective DNA mismatch repair (MMR), but the majority are microsatellite-stable (MSS). The high tumor mutational burden (TMB) and neoantigen load in MSI tumors favors the infiltration of immune effector cells, and antitumor immune responses within these tumors are strong relative to their MSS counterparts. MSI has emerged as a major predictive marker for the efficacy of immune checkpoint blockade over the last few years and nivolumab or pembrolizumab targeting PD-1 has been approved for patients with MSI refractory or metastatic CRC. However, some MSS tumors show DNA polymerase epsilon (POLE) mutations that also confer a very high TMB and may also be heavily infiltrated by immune cells making them amenable to respond to immune checkpoint inhibitors (ICI). In this review we discuss the role of the different immune landscapes in CRC and their relationships with defined CRC genetic subtypes. We discuss potential reasons why immune checkpoint blockade has met with limited success for the majority of CRC patients, despite the finding that immune cell infiltration of primary non-metastatic tumors is a strong predictive, and prognostic factor for relapse and survival. We then consider in which ways CRC cells develop mechanisms to resist ICI. Finally, we address the latest advances in CRC vaccination and how a personalized neoantigen vaccine strategy might overcome the resistance of MSI and MSS tumors in patients for whom immune checkpoint blockade is not a treatment option.

Exosomes and pancreatic diseases: status, challenges, and hopes

Pancreatic disease, including pathologies such as acute pancreatitis (AP), chronic pancreatitis (CP), and pancreatic cancer (PC), is a complicated and dangerous clinical condition involving the disruption of exocrine or endocrine function. PC has one of the highest mortality rates among cancers due to insufficient diagnosis in early stages. Furthermore, efficient treatment options for the disease etiologies of AP and CP are lacking. Thus, the identification of new therapeutic targets and reliable biomarkers is required. As essential couriers in intercellular communication, exosomes have recently been confirmed to play an important role in pancreatic disease, but the specific underlying mechanisms are unknown. Herein, we summarize the current knowledge of exosomes in pancreatic disease with respect to diagnosis, molecular mechanisms, and treatment, proposing new ideas for the study of pancreatic disease.

Functions and clinical implications of exosomes in pancreatic cancer

Pancreatic cancer is one of the most aggressive human malignancies and is associated with a dismal prognosis, which can be contributed to its atypical symptoms, metastatic propensity, and significant chemoresistance. Emerging evidence shows that pancreatic cancer cell-derived exosomes (PEXs) play critical roles in tumorigenesis and tumor development, as they are involved in drug resistance, immune evasion and metabolic reprograming, and distant metastasis of pancreatic cancer. Their numerous differentially expressed and functional contents make PEXs promising screening tools and therapeutic targets, which require further exploration. In this review, we focus on the functions of PEX contents and their clinical implications in pancreatic cancer.

Lynch syndrome - cancer pathways, heterogeneity and immune escape

Recent work has provided evidence for genetic and molecular heterogeneity in colorectal cancers (CRCs) arising in patients with Lynch syndrome (LS), dividing these into two groups: G1 and G2. In terms of mutation and gene expression profile, G1 CRCs bear resemblance to sporadic CRCs with microsatellite instability (MSI), whereas G2 CRCs are more similar to microsatellite-stable CRCs. Here we review the current state of knowledge on pathways of precursor progression to CRC in LS and how these might tie in with the new findings. Immunotherapies are an active field of research for MSI cancers and their potential use for cancer therapy for both sporadic and LS MSI cancers is discussed. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

IFN-γ induces the upregulation of RFXAP via inhibition of miR-212-3p in pancreatic cancer cells: A novel mechanism for IFN-γ response

Previous studies have demonstrated that pancreatic cancer-derived microRNA (miR)-212-3p can inhibit the expression of regulatory factor X-associated protein (RFXAP), an important transcription factor for major histocompatibility complex (MHC) class II, and thereby lead to downregulation of MHC class II in dendritic cells. It has also been established that interferon (IFN)-γ can increase the expression of MHC class II in immune cells. It was therefore hypothesized that IFN-γ can inhibit miR-212-3p expression in pancreatic cancer, leading to the upregulation of RFXAP and MHC class II expression. This may represent a novel molecular mechanism underlying the use of IFN-γ in immunotherapy. Data from the present study revealed that miR-212-3p was inhibited by IFN-γ in a dose and time-dependent manner in the pancreatic ductal adenocarcinoma cell line PANC-1. RFXAP and MHC class II expression were increased following IFN-γ stimulation. A luciferase assay was performed to validate RFXAP as a target gene of miR-212-3p. The expression levels of RFXAP and MHC class II were decreased by miR-212-3p mimics and increased by miR-212-3p inhibitors. In PANC-1 cells transfected with miR-212-3p mimics, IFN-γ stimulation could not increase the RFXAP and MHC class II. The results from the present study suggest that IFN-γ increases RFXAP and MHC class II expression by inhibiting miR-212-3p. To the best of our knowledge, this is the first report of this novel molecular mechanism underlying the effects of IFN-γ on pancreatic cancer, which may aid with the development of immunotherapies for patients with pancreatic cancer.

High numbers of PDCD1 (PD-1)-positive T cells and B2M mutations in microsatellite-unstable colorectal cancer

DNA mismatch repair (MMR)-deficient cancers accumulate high numbers of coding microsatellite mutations, which lead to the generation of highly immunogenic frameshift peptide (FSP) neoantigens. MMR-deficient cells can grow out to clinically manifest cancers either if they evade immune cell attack or if local T-cells get exhausted. Therefore, a subset of MSI cancer patients responds particularly well to treatment with immune checkpoint inhibitors. We analyzed whether immune evasion in MMR-deficient cancer mediated by loss of HLA class I or II antigens is related to local immune cell activation status. Microsatellites located in Beta2-microglobulin (B2M) and the HLA class II-regulatory genes RFX5 and CIITA were analyzed for mutations in MMR-deficient colorectal cancers (n = 53). The results were related to CD3-positive and PDCD1 (PD-1)-positive T-cell infiltration. PDCD1 (PD-1)-positive T-cell counts were significantly higher in B2M-mutant compared to B2M-wild type tumors (median: 22.2 cells per 0.25 mm² vs. 2.0 cells per 0.25 mm², Wilcoxon test p = 0.002). Increasing PDCD1 (PD-1)-positive T-cell infiltration was significantly related to an increased likelihood of B2M mutations (OR = 1.81). HLA class II antigen expression status was significantly associated with enhanced overall T-cell infiltration, but not related to PDCD1 (PD-1)-positive T-cells. These results suggest that immune evasion mediated by B2M mutation-induced loss of HLA class I antigen expression predominantly occurs in an environment of activated PDCD1 (PD-1)-positive T cell infiltration. If B2M mutations interfere with anti-PDCD1 (PD-1)/CD274 (PD-L1) therapy success, we predict that resistance towards anti-PDCD1 (PD-1) therapy may - counterintuitively - be particularly common in patients with MMR-deficient cancers that show high PDCD1 (PD-1)-positive T cell infiltration.

CD4 and CD8 T lymphocyte interplay in controlling tumor growth

The outstanding clinical success of immune checkpoint blockade has revived the interest in underlying mechanisms of the immune system that are capable of eliminating tumors even in advanced stages. In this scenario, CD4 and CD8 T cell responses are part of the cancer immune cycle and both populations significantly influence the clinical outcome. In general, the immune system has evolved several mechanisms to protect the host against cancer. Each of them has to be undermined or evaded during cancer development to enable tumor outgrowth. In this review, we give an overview of T lymphocyte-driven control of tumor growth and discuss the involved tumor-suppressive mechanisms of the immune system, such as senescence surveillance, cancer immunosurveillance, and cancer immunoediting with respect to recent clinical developments of immunotherapies. The main focus is on the currently existing knowledge about the CD4 and CD8 T lymphocyte interplay that mediates the control of tumor growth.

Spontaneous regression of transverse colon cancer: a case report

Spontaneous regression (SR) of many malignant tumors has been well documented, with an approximate incidence of one per 60,000–100,000 cancer patients. However, SR of colorectal cancer (CRC) is very rare, accounting for less than 2% of such cases. We report a case of SR of transverse colon cancer in an 80-year-old man undergoing outpatient follow-up after surgical treatment of early gastric cancer. Colonoscopy (CS) revealed a Borrmann type II tumor in the transverse colon measuring 30 × 30 mm. Because the patient underwent anticoagulant therapy, we did not perform a biopsy at that time. A second CS was performed 1 week after the initial examination and revealed tumor shrinkage to a diameter of 20 mm and a shift to the Borrmann type III morphology. Biopsy revealed a poorly differentiated adenocarcinoma. One week after the second CS, we performed a partial resection of the transverse colon and D2 lymph node dissection. Histopathology revealed inflammatory cell infiltration and fibrosis from the submucosal to muscularis propria layers in the absence of cancer cells, leading to pathological staging of pStage 0 (T0N0). The patient had an uneventful recovery, and CS performed at 5 months postoperatively revealed the absence of a tumor in the colon and rectum. The patient continues to be followed up as an outpatient at 12 months postoperatively, and no recurrence has been observed.

HLA class II antigen-processing pathway in tumors: Molecular defects and clinical relevance

The human leukocyte antigen (HLA) class II antigen-processing machinery (APM) presents to cognate CD4⁺ T-cells antigenic peptides mainly generated from exogeneous proteins in the endocytic compartment. These CD4⁺ T cells exert helper function, but may also act as effector cells, thereby recognizing HLA class II antigen-expressing tumor cells. Thus, HLA class II antigen expression by tumor cells influences the tumor antigen (TA)-specific immune responses and, depending on the cancer type, the clinical course of the disease. Many types of human cancers express HLA class II antigens, although with marked differences in their frequency. Some types of cancer lack HLA class II antigen expression, which could be due to structural defects or deregulation affecting different components of the complex HLA class II APM and/or from lack of cytokine(s) in the tumor microenvironment. In this review, we have summarized the information about HLA class II antigen distribution in normal tissues, the structural organization of the HLA class II APM, their expression and regulation in malignant cells, the defects, which have been identified in malignant cells, and their functional and clinical relevance.

Transfer of Allogeneic CD4+ T Cells Rescues CD8+ T Cells in Anti-PD-L1-Resistant Tumors Leading to Tumor Eradication

Adoptively transferred CD8⁺ T cells can stabilize the size of solid tumors over long periods of time by exclusively recognizing antigen cross-presented on tumor stroma. However, these tumors eventually escape T-cell-mediated growth control. The aim of this study was to eradicate such persistent cancers. In our model, the SIYRYYGL antigen is expressed by cancer cells that lack the MHC-I molecule K^b needed for direct presentation, but the antigen is picked up and cross-presented by tumor stroma. A single injection of antigen-specific 2C CD8⁺ T cells caused long-term inhibition of tumor growth, but without further intervention, tumors started to progress after approximately 3 months. Escape was associated with reduced numbers of circulating 2C cells. Tumor-infiltrating 2C cells produced significantly less TNFα and expressed more of the "exhaustion" markers PD-1 and Tim-3 than T cells from lymphoid organs. High-dose local ionizing radiation, depletion of myeloid-derived suppressor cells, infusions of additional 2C cells, and antibodies blocking PD-L1 did not prevent tumor escape. In contrast, adoptive transfer of allogeneic CD4⁺ T cells restored the numbers of circulating Ag-specific CD8⁺ T cells and their intratumoral function, resulting in tumor eradication. These CD4⁺ T cells had no antitumor effects in the absence of CD8⁺ T cells and recognized the alloantigen cross-presented on tumor stroma. CD4⁺ T cells might also be effective in cancer patients when PD-1/PD-L1 blockade does not rescue intratumoral CD8⁺ T-cell function and tumors persist. Cancer Immunol Res; 5(2); 127-36. ©2017 AACR.

Pancreatic cancer-derived exosomes transfer miRNAs to dendritic cells and inhibit RFXAP expression via miR-212-3p

It has been reported tumor-derived exosomes can transfer miRNAs to recipient cells in the tumor microenvironment, promoting tumor invasion and metastasis. The present research aimed to explore how pancreatic cancer (PC) derived exosomal miRNAs inhibited mRNA expression of dendritic cells and induced immune tolerance. Our study revealed that 9 PC-related miRNAs were increased and 208 mRNAs were inhibited in exosome-stimulated dendritic cells (exo-iDCs) compared to immature dendritic cells (iDCs). A target prediction between the 9 miRNAs and 208 mRNAs was performed by bioinformatics database analysis. From the target prediction, it was predicted and validated that regulatory factor X-associated protein (RFXAP), an important transcription factor for MHC II, was inhibited by miR-212-3p transferred from PC-secreted exosomes, resulting in decreased MHC II expression. Moreover, a clinical study showed a negative correlation between miR-212-3p and RFXAP in PC tissue. From these data, we concluded that PC-related miRNAs can be transferred to dendritic cells via exosome and inhibit target mRNA expression. More importantly, PC-derived exosomes inhibit RFXAP expression via miR-212-3p, which decrease MHC II expression and induce immune tolerance of dendritic cells. RFXAP deficiency has never been reported in solid tumors. The functions and mechanisms of RFXAP in tumors deserve future explorations.

Opportunities for immunotherapy in microsatellite instable colorectal cancer

Microsatellite instability (MSI), the somatic accumulation of length variations in repetitive DNA sequences called microsatellites, is frequently observed in both hereditary and sporadic colorectal cancer (CRC). It has been established that defects in the DNA mismatch repair (MMR) pathway underlie the development of MSI in CRC. After the inactivation of the DNA MMR pathway, misincorporations, insertions and deletions introduced by DNA polymerase slippage are not properly recognized and corrected. Specific genomic regions, including microsatellites, are more prone for DNA polymerase slippage and, therefore, more susceptible for the introduction of these mutations if the DNA MMR capacity is lost. Some of these susceptible genomic regions are located within the coding regions of genes. Insertions and deletions in these regions may alter their reading frame, potentially resulting in the transcription and translation of frameshift peptides with c-terminally altered amino acid sequences. These frameshift peptides are called neoantigens and are highly immunogenic, which explains the enhanced immunogenicity of MSI CRC. Neoantigens contribute to increased infiltration of tumor tissue with activated neoantigen-specific cytotoxic T lymphocytes, a hallmark of MSI tumors. Currently, neoantigen-based vaccination is being studied in a clinical trial for Lynch syndrome and in a trial for sporadic MSI CRC of advanced stage. In this Focussed Research Review, we summarize current knowledge on molecular mechanisms and address immunological features of tumors with MSI. Finally, we describe their implications for immunotherapeutic approaches and provide an outlook on next-generation immunotherapy involving neoantigens and combinatorial therapies in the setting of MSI CRC.

The Immune Biology of Microsatellite-Unstable Cancer

Deficient DNA mismatch repair (MMR) boosts the accumulation of frameshift mutations in genes encompassing coding microsatellites (cMS). This results in the translation of proteins with mutation-induced frameshift peptides (neoantigens) rendering microsatellite-unstable (MSI) cancers highly immunogenic. MSI cancers express a defined set of neoantigens resulting from functionally relevant driver mutations, which are shared by most MSI cancers. Patients with MSI cancers and healthy individuals affected by Lynch syndrome, an inherited predisposition for MSI cancers, develop specific immune responses against these neoantigens. In this review, we summarize our current understanding of the immune biology of MSI cancers and outline new concepts and research directions to develop not only therapeutic treatments, but also preventive vaccines based on the MSI cancer genome landscapes.

Low density of FOXP3-positive T cells in normal colonic mucosa is related to the presence of beta2-microglobulin mutations in Lynch syndrome-associated colorectal cancer

Microsatellite instability (MSI-H) is caused by DNA mismatch repair deficiency and occurs in 15% of colorectal cancers. MSI-H cancers generate highly immunogenic frameshift peptide (FSP) antigens, which elicit pronounced local immune responses. A subset of MSI-H colorectal cancers develops in frame of Lynch syndrome, which represents an ideal human model for studying the concept of immunoediting. Immunoediting describes how continuous anti-tumoral immune surveillance of the host eventually leads to the selection of tumor cells that escape immune cell recognition and destruction. Between 30 and 40% of Lynch syndrome-associated colorectal cancers display loss of HLA class I antigen expression as a result of Beta2-microglobulin (B2M) mutations. Whether B2M mutations result from immunoediting has been unknown. To address this question, we related B2M mutation status of Lynch syndrome-associated colorectal cancer specimens (n = 30) to CD3-positive, CD8-positive and FOXP3-positive T cell infiltration in both tumor and normal mucosa. No significant correlation between B2M mutations and immune cell infiltration was observed in tumor tissue. However, FOXP3-positive T cell infiltration was significantly lower in normal mucosa adjacent to B2M-mutant (mt) compared to B2M-wild type (wt) tumors (mean: 0.98% FOXP3-positive area/region of interest (ROI) in B2M-wt vs. 0.52% FOXP3-positive area/ROI in B2M-mt, p = 0.023). Our results suggest that in the absence of immune-suppressive regulatory T cells (Treg), the outgrowth of less immunogenic B2M-mt tumor cells is favored. This finding supports the immunoediting concept in human solid cancer development and indicates a critical role of the immune milieu in normal colonic mucosa for the course of disease.