Brca2 deficiency leads to T cell loss and immune dysfunction

Towards targeting the breast cancer immune microenvironment

The tumour immune microenvironment is shaped by the crosstalk between cancer cells, immune cells, fibroblasts, endothelial cells and other stromal components. Although the immune tumour microenvironment (TME) serves as a source of therapeutic targets, it is also considered a friend or foe to tumour-directed therapies. This is readily illustrated by the importance of T cells in triple-negative breast cancer (TNBC), culminating in the advent of immune checkpoint therapy in combination with cytotoxic chemotherapy as standard of care for both early and advanced-stage TNBC, as well as recent promising signs of efficacy in a subset of hormone receptor-positive disease. In this Review, we discuss the various components of the immune TME in breast cancer and therapies that target or impact the immune TME, as well as the complexity of host physiology.

BRCA-Mutated Pancreatic Cancer: From Discovery to Novel Treatment Paradigms

Simple Summary

Approximately 10–20% of pancreatic cancer patients will have a mutation in their DNA, passed on in families, that contributes to the development of their pancreatic cancer. These mutations are important in that they effect the biology of the disease as well as contribute to sensitivity to specific treatments. We describe the critical role that these genes play in various cellular processes in the body that contribute to their role in cancer development and normal cellular function. In this review, we aim to describe the role of certain genes (BRCA1 and BRCA2) in the development of pancreatic cancer and the current and future research efforts underway to treat this subtype of disease.

Abstract

The discovery of BRCA1 and BRCA2 in the 1990s revolutionized the way we research and treat breast, ovarian, and pancreatic cancers. In the case of pancreatic cancers, germline mutations occur in about 10–20% of patients, with mutations in BRCA1 and BRCA2 being the most common. BRCA genes are critical in DNA repair pathways, particularly in homologous recombination, which has a serious impact on genomic stability and can contribute to cancerous cell proliferation. However, BRCA1 also plays a fundamental role in cell cycle checkpoint control, ubiquitination, control of gene expression, and chromatin remodeling, while BRCA2 also plays a role in transcription and immune system response. Therefore, mutations in these genes lead to multiple defects in cells that may be utilized when treating cancer. BRCA mutations seem to confer a prognostic benefit with an improved overall survival due to differing underlying biology. These mutations also appear to be a predictive marker, with patients showing increased sensitivity to certain treatments, such as platinum chemotherapy and PARP inhibitors. Olaparib is currently indicated for maintenance therapy in metastatic PDAC after induction with platinum-based chemotherapy. Resistance has been found to these therapies, and with a 10.8% five-year OS, novel therapies are desperately needed.

brca2-mutant zebrafish exhibit context- and tissue-dependent alterations in cell phenotypes and response to injury

Cancer cells frequently co-opt molecular programs that are normally activated in specific contexts, such as embryonic development and the response to injury. Determining the impact of cancer-associated mutations on cellular phenotypes within these discrete contexts can provide new insight into how such mutations lead to dysregulated cell behaviors and subsequent cancer onset. Here we assess the impact of heritable BRCA2 mutation on embryonic development and the injury response using a zebrafish model (Danio rerio). Unlike most mouse models for BRCA2 mutation, brca2-mutant zebrafish are fully viable and thus provide a unique tool for assessing both embryonic and adult phenotypes. We find that maternally provided brca2 is critical for normal oocyte development and embryonic survival in zebrafish, suggesting that embryonic lethality associated with BRCA2 mutation is likely to reflect defects in both meiotic and embryonic developmental programs. On the other hand, we find that adult brca2-mutant zebrafish exhibit aberrant proliferation of several cell types under basal conditions and in response to injury in tissues at high risk for cancer development. These divergent effects exemplify the often-paradoxical outcomes that occur in embryos (embryonic lethality) versus adult animals (cancer predisposition) with mutations in cancer susceptibility genes such as BRCA2. The altered cell behaviors identified in brca2-mutant embryonic and adult tissues, particularly in adult tissues at high risk for cancer, indicate that the effects of BRCA2 mutation on cellular phenotypes are both context- and tissue-dependent.

A Pediatric Case of Transformed Mycosis Fungoides in a BRCA2 Positive Patient

Cutaneous T-cell lymphomas are very rare in children. Although mycosis fungoides is the most common of these rare cutaneous T-cell lymphomas in children, transformation to an aggressive malignancy remains extremely uncommon, and there are no clear guidelines for clinical management in the pediatric population. In addition, the increased usage of next-generation sequencing for pediatric patients with unusual malignancies may result in the discovery of pathogenic germline mutations, though the association between these mutations and the patient's cancer is not always clear. We present here a unique pediatric case of transformed mycosis fungoides in a patient with BRCA2 mutation.

Recent Findings in the Regulation of Programmed Death Ligand 1 Expression

With the recent approvals for the application of monoclonal antibodies that target the well-characterized immune checkpoints, immune therapy shows great potential against both solid and hematologic tumors. The use of these therapeutic monoclonal antibodies elicits inspiring clinical results with durable objective responses and improvements in overall survival. Agents targeting programmed cell death protein 1 (PD-1; also known as PDCD1) and its ligand (PD-L1) achieve a great success in immune checkpoints therapy. However, the majority of patients fail to respond to PD-1/PD-L1 axis inhibitors. Expression of PD-L1 on the membrane of tumor and immune cells has been shown to be associated with enhanced objective response rates to PD-1/PD-L1 inhibition. Thus, an improved understanding of how PD-L1 expression is regulated will enable us to better define its role as a predictive marker. In this review, we summarize recent findings in the regulation of PD-L1 expression.

A STING to inflammation and autoimmunity

Various intracellular pattern recognition receptors (PRRs) recognize cytosolic pathogen-associated molecular patterns (PAMPs) and damage-associated molecular patterns (DAMPs). Cyclic GMP-AMP synthase (cGAS), a cytosolic PRR, recognizes cytosolic nucleic acids including dsDNAs. The recognition of dsDNA by cGAS generates cyclic GMP-AMP (GAMP). The cGAMP is then recognized by STING generating type 1 IFNs and NF-κB-mediated generation of pro-inflammatory cytokines and molecules. Thus, cGAS-STING signaling mediated recognition of cytosolic dsDNA causing the induction of type 1 IFNs plays a crucial role in innate immunity against cytosolic pathogens, PAMPs, and DAMPs. The overactivation of this system may lead to the development of autoinflammation and autoimmune diseases. The article opens with the introduction of different PRRs involved in the intracellular recognition of dsDNA and gives a brief introduction of cGAS-STING signaling. The second section briefly describes cGAS as intracellular PRR required to recognize intracellular nucleic acids (dsDNA and CDNs) and the formation of cGAMP. The cGAMP acts as a second messenger to activate STING- and TANK-binding kinase 1-mediated generation of type 1 IFNs and the activation of NF-κB. The third section of the article describes the role of cGAS-STING signaling in the induction of autoinflammation and various autoimmune diseases. The subsequent fourth section describes both chemical compounds developed and the endogenous negative regulators of cGAS-STING signaling required for its regulation. Therapeutic targeting of cGAS-STING signaling could offer new ways to treat inflammatory and autoimmune diseases.

Foxp3 expression in induced regulatory T cells is stabilized by C/EBP in inflammatory environments

Proper control of immune responses by Foxp3⁺ regulatory T cells at inflamed sites is crucial for the prevention of immunopathology. TGF-β-induced Foxp3⁺ regulatory T (T_reg) cells are generated in inflammatory environments as well as in steady-state conditions. Inflammatory cytokines such as IFN-γ and IL-4 have an antagonistic effect on T_reg cell conversion. However, it is not known how naive CD4⁺ T cells overcome the inhibitory environment in inflamed sites to differentiate into T_reg cells. Here, we show that CCAAT/enhancer-binding protein (C/EBP) functions as a safeguard that enhances T_reg cell generation by dampening the inhibitory effect of IFN-γ and IL-4 on Foxp3 expression. We find that C/EBPβ is induced by retinoic acid and binds to the methyl-CRE sequence in the Foxp3 TSDR to sustain its expression. C/EBPβ-transduced iT_reg cells show more potent suppressive activity in mouse disease models. We also reveal that C/EBPβ-transduced human iT_reg cells exhibit more enhanced suppressor function. These results establish C/EBP as a new molecular target for enhancing the formation and stability of T_reg cells in inflammatory environments.

Toxicity of environmentally-relevant concentrations of arsenic on developing T lymphocyte

Arsenic is a ubiquitous environmental contaminant that exists in many inorganic and organic forms. In particular, arsenite is known to induce immunotoxicity in humans and animals. There are still major gaps in our understanding of the mechanism(s) of the immunotoxicity induced by arsenic at environmentally-relevant concentrations. T cells are an essential part of the immune system required for host resistance to infections and protection from cancer. Developing T cells in the thymus have been shown to be particularly prone to arsenite-induced toxicity at low concentrations. Suppression of DNA repair proteins and oxidative stress have been identified as a mechanism of genotoxicity that occurs at low to moderate concentrations. Inhibition of the IL-7 signaling pathway was thought to be responsible for the non-genotoxicity induced by low to moderate doses of arsenic. Interestingly, T cells at different stages of their development had distinct sensitivities to arsenite, which was regulated by arsenite exporters. The current evidence strongly suggests that low to moderate doses of arsenic induces toxic effects in the developing T cells and accumulates to highest levels in the early cells that are least capable to pump out arsenic, which may be the mechanism of the high arsenic sensitivity. Therefore, quantification of the exposure levels should be encouraged in future arsenic toxicity studies.

DNA repair gene expressions are related to bone marrow cellularity in myelodysplastic syndrome

Objective

To evaluate the expression of genes related to nuclear excision (ERCC8, XPA and XPC), homologous recombination and non-homologous end-joining (ATM, BRCA1, BRCA2 and LIG4) repair mechanisms, using quantitative PCR methodologies, and it relation with bone marrow cellularity in myelodysplastic syndrome (MDS).

Methods and results

A total of 51 adult de novo patients with MDS (3 refractory anaemia (RA), 11 refractory anaemia with ringed sideroblasts (RARS), 28 refractory cytopenia with multilineage dysplasia (RCMD), 3 refractory anaemia with excess blasts type I (RAEB-I), 5 refractory anaemia with excess blasts type II (RAEB-II), and 1 chronic myelomonocytic leukaemia (CMML) were evaluated. For karyotype, 16.2% patients were defined as very low prognosis, 59.5% low risk, 8.1% intermediate risk, 5.4% high risk and 10.8% very high risk. For bone marrow cellularity, 17.6%, 17.6% and 64.7% presented as hypocellular, normocellular and hypercellular, respectively. Patients with hypocellular MDS had significantly decreased expression of ATM (p=0.000), BRCA1 (p=0.014), BRCA2 (p=0.003), LIG4 (p=0.004) and ERCC8 (p=0.000) than those with normocellular/hypercellular bone marrow, whereas XPA (p=0.049) and XPC (p=0.000) genes were increased. In patients with hypoplastic MDS, a low expression of ATM (p=0.0268), LIG4 (p=0.0199) and ERCC8 (p=0.0493) was significantly associated with the presence of chromosomal abnormalities. We detected positive correlations between BRCA1 and BRCA2 (r=0.416; p=0.007), ATM and LIG4 (r=0.472; p=0.001), LIG4 and BRCA1 (r=0.333; p=0.026), LIG4 and BRCA2 (r=0.334; p=0.025), ATM and XPA (r=0.377; p=0.008), ATM and XPC (r=0.287; p=0.046), LIG4 and XPC (r=0.371; p=0.007) and XPA and XPC genes (r=0.895; p=0.0000). We also found among all patients evaluated that correlation with LIG4 occurred most often.

Conclusions

These correlations demonstrate the important intrinsic relations between single and double DNA strand breaks genes in MDS, emphasising that these genes are related to MDS pathogenesis.

Precancer Atlas to Drive Precision Prevention Trials

Cancer development is a complex process driven by inherited and acquired molecular and cellular alterations. Prevention is the holy grail of cancer elimination, but making this a reality will take a fundamental rethinking and deep understanding of premalignant biology. In this Perspective, we propose a national concerted effort to create a Precancer Atlas (PCA), integrating multi-omics and immunity - basic tenets of the neoplastic process. The biology of neoplasia caused by germline mutations has led to paradigm-changing precision prevention efforts, including: tumor testing for mismatch repair (MMR) deficiency in Lynch syndrome establishing a new paradigm, combinatorial chemoprevention efficacy in familial adenomatous polyposis (FAP), signal of benefit from imaging-based early detection research in high-germline risk for pancreatic neoplasia, elucidating early ontogeny in BRCA1-mutation carriers leading to an international breast cancer prevention trial, and insights into the intricate germline-somatic-immunity interaction landscape. Emerging genetic and pharmacologic (metformin) disruption of mitochondrial (mt) respiration increased autophagy to prevent cancer in a Li-Fraumeni mouse model (biology reproduced in clinical pilot) and revealed profound influences of subtle changes in mt DNA background variation on obesity, aging, and cancer risk. The elaborate communication between the immune system and neoplasia includes an increasingly complex cellular microenvironment and dynamic interactions between host genetics, environmental factors, and microbes in shaping the immune response. Cancer vaccines are in early murine and clinical precancer studies, building on the recent successes of immunotherapy and HPV vaccine immune prevention. Molecular monitoring in Barrett's esophagus to avoid overdiagnosis/treatment highlights an important PCA theme. Next generation sequencing (NGS) discovered age-related clonal hematopoiesis of indeterminate potential (CHIP). Ultra-deep NGS reports over the past year have redefined the premalignant landscape remarkably identifying tiny clones in the blood of up to 95% of women in their 50s, suggesting that potentially premalignant clones are ubiquitous. Similar data from eyelid skin and peritoneal and uterine lavage fluid provide unprecedented opportunities to dissect the earliest phases of stem/progenitor clonal (and microenvironment) evolution/diversity with new single-cell and liquid biopsy technologies. Cancer mutational signatures reflect exogenous or endogenous processes imprinted over time in precursors. Accelerating the prevention of cancer will require a large-scale, longitudinal effort, leveraging diverse disciplines (from genetics, biochemistry, and immunology to mathematics, computational biology, and engineering), initiatives, technologies, and models in developing an integrated multi-omics and immunity PCA - an immense national resource to interrogate, target, and intercept events that drive oncogenesis. Cancer Res; 77(7); 1510-41. ©2017 AACR.

Emerging roles of p53 and other tumour-suppressor genes in immune regulation

Tumour-suppressor genes are indispensable for the maintenance of genomic integrity. Recently, several of these genes, including those encoding p53, PTEN, RB1 and ARF, have been implicated in immune responses and inflammatory diseases. In particular, the p53 tumour- suppressor pathway is involved in crucial aspects of tumour immunology and in homeostatic regulation of immune responses. Other studies have identified roles for p53 in various cellular processes, including metabolism and stem cell maintenance. Here, we discuss the emerging roles of p53 and other tumour-suppressor genes in tumour immunology, as well as in additional immunological settings, such as virus infection. This relatively unexplored area could yield important insights into the homeostatic control of immune cells in health and disease and facilitate the development of more effective immunotherapies. Consequently, tumour-suppressor genes are emerging as potential guardians of immune integrity.

Silencing of BRCA2 to Identify Novel BRCA2-regulated Biological Functions in Cultured Human Cells

Silencing of the tumor suppressor protein BRCA2 and its detection by conventional biochemical analyses represent a great technical challenge owing to the large size of the human BRCA2 protein (approximately 390 kDa). We report modifications of standard siRNA transfection and immunoblotting protocols to silence human BRCA2 and detect endogenous BRCA2 protein, respectively, in human epithelial cell lines. Key steps include a high siRNA to transfection reagent ratio and two subsequent rounds of siRNA transfection within the same experiment. Using these and other modifications to the standard protocol we consistently achieve more than 70% silencing of the human BRCA2 gene as judged by immunoblotting analysis with anti-BRCA2 antibodies. In addition, denaturation of the cell lysates at 55 °C instead of the conventional 70-100 °C and other technical optimizations of the immunoblotting procedure allow detection of intact BRCA2 protein even when very low amounts of starting material are available or when BRCA2 protein expression levels are very low. Efficient silencing of BRCA2 in human cells offers a valuable strategy to disrupt BRCA2 function in cells with intact BRCA2, including tumor cells, to examine new molecular pathways and cellular functions that may be affected by pathogenic BRCA2 mutations in tumors. Adaptation of this protocol for efficient silencing and analysis of other 'large' proteins like BRCA2 should be readily achievable.