December 19, 2014
Editor: Andrew H. Lichtman, MD, PhD, Brigham & Women's Hospital
Editorial Board: Abul K. Abbas, MD, University of California, San Francisco | Carla J. Greenbaum, MD, Benaroya Research Institute | Andrew H. Lichtman, MD, PhD, Brigham & Women's Hospital
|Highlights from Recent Literature|
A review of Singhal A., et al. Metformin as adjunct antituberculosis therapy. Sci. Transl. Med. 6, 263ra159 (2014).Sci Transl Med 6, 246ra99 (2014). PMID: 25411472
Tuberculosis (TB) remains one of the biggest killers worldwide and the emergence of drug-resistant strains has complicated therapy. Novel agents that control TB by enhancing host immune responses are urgently needed. In this study, authors report that the anti-diabetic medication metformin enhanced anti-TB immune responses via multiple pathways and may be a powerful new weapon in the war against drug-resistant tuberculosis.
The authors found that metformin modulates several aspects of host immune responses to TB, acidifying the phagosome to enhance microbial killing, inducing autophagy and reducing overt inflammation which helps to ameliorate tissue damage. This comprehensive study, including in vitro analyses, animal models and retrospective analysis of patient responses, sets the stage for adoption of metformin as a new and powerful adjuvant therapy for TB.
Reviewed by Rachael A. Clark, MD, PhD, Brigham and Women's Hospital
A review of Simpson LJ., et al. Epigenomic analysis of primary human T cells reveals enhancers associated with Th2 memory cell differentiation and asthma susceptibility. Nature Immunology. (2014) 15: 777. doi: 10.1038/ni.3026. PMID: 25362490
Asthma is a chronic inflammatory disease characterized by episodes of airflow limitation and bronchial hyperreactivity and is the most common chronic disease of childhood. While there is an increasing appreciation that there are multiple phenotypes within asthma, T helper 2 cells play a clear role in a subset of patients. In this study, Simpson et al profile miRNA expression in human airway T cells in asthma patients versus healthy controls.
This group was able to use profiling of miRNA in airway infiltrating T cells to identify a miRNA, miR-19a, that plays a mechanistic role in encouraging Th2 polarization of T cells, which may contribute to pathogenesis in a subset of asthmatics. While this is fascinating, it will require additional confirmation and mechanistic studies to further elucidate the details of this process (including possible roles in using this mediator to predict prognosis, define phenotype and even possibly provide a therapeutic target for asthmatics with Th2 predominant disease).
Reviewed by Sarah Henrickson, MD, PhD, Children's Hospital of Philadelphia
A review of Alsina L., et al. A narrow repertoire of transcriptional modules responsive to pyogenic bacteria is impaired in patients carrying loss-of-function mutations in MYD88 or IRAK4. Nature Immunology. (2014) 15: 1134-42. PMID: 25344726
Many components of innate and adaptive immunity have been implicated in primary immunodeficiency syndromes, including selective pathogen associated molecular pattern recognition abrogation due to Toll-like receptor (TLR) pathway dysfunction due to MyD88 and IRAK4 loss of function mutations. Of the 10 TLRs in humans, all but one signals via MyD88, and IRAK4 is recruited by MyD88 to signal downstream of those receptors. Interestingly, patients with these defects do not have the broad increased susceptibility to pathogens that might be expected, and instead have a relatively narrow range of pathogens that they are susceptible to (i.e. pyogenic gram positive and gram negative bacteria) and they show clinical improvement in adolescence. Rather than use a traditional panel approach, this team compares responses of patients to purified TLR ligands and whole pathogens using transcriptional readouts and cutting edge systems analysis.
This group is able to use whole transcriptome analysis of responses of whole blood from IRAK4 or MyD88 deficient patients to demonstrate that while responses to purified TLR ligands is blocked, as expected, they retain the ability to respond to selective whole pathogens (even to the pathogens that they are clinically susceptible to), likely secondary to compensatory inflammatory responses (e.g. inflammasome). This application of genome wide transcriptional analysis to individualized pathogen susceptibility in primary immunodeficiency is interesting and could be broadened to the more detailed assessment of responses to immune stimuli in other patient groups (i.e. autoimmunity or malignancy) or other infectious agents. If feasible for broader application, it might yield a more nuanced view of the mechanisms underlying susceptibility in a given patient and potentially more individualized prophylaxis or treatment regimens in those patients.
Reviewed by Sarah Henrickson, MD, PhD, Children's Hospital of Philadelphia
A review of Erusalnov EB., et al. Tumor-associated neutrophils stimulate T cell responses in early stage human lung cancer. J. Clin. Invest. 2014 Dec. 124(12)5466-5480. PMID:25384214
While several recent studies have highlighted the role of adaptive immunity and the value of enhancing cytotoxic T cell function with checkpoint inhibitors such as those targeting PD1 or CTLA4 in oncogenesis, the role of the innate immune system in modulating human malignancy is less well characterized. A recent study by Eruslanov, Signhal, and colleagues sheds new light on a potential role for tumor-associated neutrophils (TANs) in the cancer microenvironment. Most prior studies employing immunohistochemistry have suggested that TAN infiltrates are associated with a poor prognosis in human cancers. However, studies in murine models have suggested that TANs could have both pro-tumor as well as anti-tumor effects. Moreover, in human gastric cancer, neutrophils were associated with a good prognosis. To address these conflicting results, the authors employed both immunohistochemical as well as functional studies of TANs in early stage human lung cancer. Contrary to the investigators initial hypothesis, TANs surprisingly appear to have an anti-tumor effect by stimulating T cells in early stage lung cancer. There are several intriguing findings from this work.
Naughty or nice? These findings suggest that TANs may potentially play a nice role in early stages of lung cancer by stimulating T cell responses to the tumor. While quite intriguing, additional work is clearly needed. Although the impact of TANs on T cells suggests an anti-tumor effect, it is conceivable that other TAN functions could simultaneously serve a pro-tumor function. For example, do TANs have a direct impact on tumor cell proliferation, metastasis, or other aspects of the tumor microenvironment such as angiogenesis or infiltration of other immune cell populations? It will also be important to test whether the functional properties of TANs change during tumor progression or at relapse to a more immunosuppressive phenotype and whether these findings are generalizable to other tumor subtypes. If this is the case, TANs could become another target in the immuno-oncology arsenal.
Reviewed by Michelle L. Hermiston, MD, PhD, University of California, San Francisco
A review of Di Mitri, et al. Tumor- infiltrating Gr-1+ myeloid cells antagonize senescence in cancer. Nature. 2014 (Nov 6) 515:134-137. Nat. Med. 2014 Sep;20(9):1043-1049. Epub 2014 Aug 17. PMID:25156255
Cellular senescence is the induction of permanent loss of the ability of a cell to divide. It can be induced by a variety of mechanisms including aberrant activation of oncogenes or loss of tumor suppressor genes such as Pten or exposure to chemotherapy. In this regard, stable cell growth arrest due to cellular senescence is an important anti-cancer mechanism for the host. Recent work by Di Mitri, Tosso, Alimonti, and colleagues addresses the question of whether tumor-infiltrating immune cells can modulate whether tumor cells become senescent. The authors had previously demonstrated that loss of Pten in the mouse prostate epithelium induces the formation of benign tumors characterized by a strong senescence response that opposed tumor progression. Over time, these tumors overcame this senescence and adopted an aggressive and invasive phenotype. In the current work, the authors address the hypothesis that immune cells might enable Pten deficient tumor cells to evade senescence in a non-cell autonomous manner. Using both mouse models and human prostate cancer samples, they find a new role for the innate immune system in regulating cellular senescence and chemotherapy resistance. There are several intriguing findings from this work.
Are innate immune cells naughty or nice? In this context, they are naughty. Taken together, these data are consistent with a model whereby infiltrating innate immune cells are detrimental, promoting tumor progression by opposing senescence, perhaps via production of IL-1RA. It will be important to determine whether these findings can be expanded to other tumor types. If validated, these data suggest that blocking recruitment of Gr-1+ myeloid cells or inhibiting IL-1RA may be of therapeutic benefit.
Reviewed by Michelle L. Hermiston, MD, PhD, University of California, San Francisco
A review of Duan, F., et al. Genomic and bioinformatic profiling of mutational neoepitopes reveals new rules to predict anticancer immunogenicity. J Exp Med. 2014; 211(11):2231-48. PMID:25245761
Cancer cells carry tens to hundreds of unique mutations. Each mutation has the potential to generate a neoepitope capable of being recognized by T cells and contributing to anti-tumor immunity; but in reality, only a small fraction of the total pool of mutations are immunoprotective. Despite the relative ease of identifying tumor-specific mutations using next-generation sequencing, predicting which mutations generate immunogenic neoepitopes that can drive protective antitumor responses has proven to be challenging. While NetMHC and other algorithms capable of predicting MHC:peptide binding affinities provide promising screening tools, they only tell part of the story. Screens using predicted MHC binding affinity as a sole metric omit contributions of the TCR, as well as tolerance mechanisms which may be preventing anti-tumor immunity. Duan et al. examine this problem by testing the efficacy of vaccines targeting putative neoepitopes selected based either on NetMHC scores alone (which predicts MHC:peptide binding affinities), or based on the authors’ newly proposed differential agretopicity index (DAI, which compares the MHC affinity of the mutant peptide to the wild-type peptide).
Duan et al. suggests that MHC:peptide affinities, predicted or calculated, are insufficient for predicting the immunogenicity of putative mutant neoepitopes. They identify two new principles which will likely guide future work in this field: first, the affinity of the mutant peptide must be considered relative to the wild type peptide; and second, increases in the structural rigidity of the peptide resulting from mutations may increase immunogenicity. These insights provide a foothold for the development of more reliable neoepitope prediction methods, which could have far reaching implications for the clinical development of mutant neoepitope-targeted immunotherapy.
Reviewed by Alexander Hopkins and Eric Lutz, PhD, Johns Hopkins University
A review of Kvistborg, P. et al., Anti-CTLA-4 therapy broadens the melanoma-reactive CD8+ T cell response, Science Translational Medicine 6, 254ra128–254ra128 (2014). PMID:25232180
Treatment of melanoma patients with the T cell checkpoint inhibitor ipilimumab (an anti-CTLA-4 antibody) has led to improved patient survival; however, it is unclear whether this benefit is derived from an increased magnitude of pre-existing T cell responses, or the induction of novel tumor-specific T cell responses, resulting in a broader tumor-specific CD8+ T cell repertoire. Kvistborg et al. show that patients with advanced-stage melanoma who received ipilimumab had an increase in the number of different T cell responses while the overall magnitude of pre-existing T cell responses was on average unchanged.
The T cell checkpoint inhibitor ipilimumab has shown a survival benefit for patients with advanced melanoma, but the mechanism by which targeting CTLA-4 confers a survival benefit remains to be determined. Kvistborg et al. demonstrate that while the magnitude of pre-existing melanoma-specific CD8+ T cell responses remains constant, new melanoma antigen-specific T cell responses arise shortly after the induction of ipilimumab therapy. Thus, these data suggest that anti-CTLA-4 works by priming new T cell responses and broadening the repertoire of the tumor-specific T cell response, rather than by amplifying pre-existing T cell responses. Likewise, other strategies capable of broadening the tumor-specific T cell response may induce similar antitumor effects as anti-CTLA-4.
Reviewed by Heather Kinkead and Eric Lutz, PhD, John Hopkins University
|Human Immunophenotyping Update|
Salah-Eddine Bentebibel and Hideki Ueno, MD, PHD, Baylor Institute for Immunology Research
T follicular helper (TFH) cells represent the subset of CD4+ T cells that helps B cells in germinal centers (GCs) and supports their differentiation into memory B cells or long-lived plasma cells. GC TFH cells express the chemokine receptor 5 (CXCR5), which guides their migration into B cell follicles. They express inducible co-stimulator (ICOS), a molecule essential for their development and function. GC TFH cells also express high levels of immune-regulatory molecule PD-1, signaling adaptor SLAM-associated protein (SAP), and the transcription repressor B cell lymphoma 6 (Bcl-6).
CXCR5+ CD4+ T cells are also found in human blood, and share functional properties with GC TFH cells in secondary lymphoid organs. Recent multiple lines of evidence shows that blood CXCR5+ CD4+ T cells are likely a memory compartment of TFH cells. Accordingly these cells have been termed as blood (or circulating) TFH cells (1). Blood TFH cells are defined as CD4+CD45RA-CXCR5+ and constitute 15-20% of memory CD4+ T cells in humans. The majority of these cells express CD62L, CCR7, and CD45RO and thus belong to central memory cells. In contrast to GC TFH cells, a vast majority of blood TFH cells do not express activation markers such as CD69 and ICOS, and express PD1 only at low levels. Blood memory TFH cells also lack the expression of Bcl-6. Thus, while TFH cells in secondary lymphoid organs are in active state, blood TFH cells are generally in resting state. Recent studies show that human blood memory TFH are composed of heterogeneous subsets with different phenotypes and functions. Currently, there are two main approaches to identify human blood TFH cell subsets.
The first approach consists of using the chemokine receptors CXCR3 and CCR6 (2). This approach permits the dissection of blood memory TFH cells into three major subsets: CXCR3+CCR6- cells, CXCR3-CCR6- cells, and CXCR3-CCR6+ cells. The CXCR3+CCR6- cells resembles to TH1 cells (hereafter called blood TFH1 cells). The CXCR3-CCR6- subset resembles to TH2 cells (hereafter called blood TFH2 cells). The CXCR3-CCR6+ cells resembles to TH17 cells (hereafter called blood TFH17 cells). An example of the analysis of peripheral blood mononuclear cells (PBMCs) from a healthy individual is shown in Figure 1. While TFH2 and TFH17 cells produce interleukin-21 (IL-21) upon interactions with naïve B cells, and are capable of inducing B cell differentiation into immunoglobulin-producing cells, TFH1 cells lack this capacity (2).
The second approach consists of using the immune-regulatory molecule PD1, the inducible co-stimulatory molecule ICOS, and the chemokine receptor CCR7. This approach permits the dissection of another three subsets, one activated subset (ICOS+PD-1++CCR7lo), and two quiescent subsets (ICOS-PD-1+CCR7int, and ICOS-PD-1-CCR7hi) (3, 4). ICOS expression defines blood memory TFH cells with activated phenotype that highly express PD-1 and the cell cycle marker Ki-67. ICOS- cells are further divided into PD-1+CCR7int cells and PD-1-CCR7hi cells, both of which lack the expression of Ki-67 and therefore are in a quiescent state.
We propose that human blood memory TFH cells are composed of nine distinct subsets (1), which are defined by combining the two approaches. It is feasible to construct a flow cytometry panel containing CD3, CD4, CD8, CXCR5, CD45RA, CXCR3, CCR6, ICOS, PD1, and CCR7. A damp channel to exclude any contamination of other cells such as CD8+ T cells, dendritic cells, and natural killer cells and a viability dye such as Live/Dead also can be added to the panel. In order to assess whether CXCR3 and CCR6 staining is properly working, we recommend to compare the expression of these two chemokine receptors between naïve CD4+ T cells and blood memory TFH cells, as naïve CD4+ T cells do not contain cells that highly express CXCR3 or CCR6. When a 10-color flow cytometer is not available, the panel can be simplified by removing CCR7. CCR6 can also removed from the panel as the usage of CXCR3 alone can separate TFH1 (non-efficient helpers) and non-TFH1 cells (efficient helpers).
An increasing number of studies have already demonstrated that analyses of human blood TFH cell subsets provide insights regarding the type and the magnitude of ongoing Tfh and antibody response in patients with autoimmune or infectious diseases, and in subjects after vaccinations. For instance, patients with juvenile dermatomyositis, a pediatric autoimmune disease, are found to display an alteration in the balance of blood memory TFH1, TFH2, and TFH17 subsets (less TFH1 and more TFH2 and/or TFH17), which correlates with disease activity and circulating plasmablast (2). Similar finding was reported in studies of adult SLE, Sjogren’s syndrome, and multiple sclerosis (1). In a study with a large cohort of HIV infected subjects, subjects with broadly neutralizing antibodies against HIV are found to display relatively higher frequency of ICOS-PD-1+ TFH2 and TFH17 cells among blood TFH cells (4). Influenza vaccine was found to induce the emergence of the ICOS+CXCR3+ TFH1 cells at 7 days post-vaccination, which positively correlates with the generation of protective antibody responses (5).
|Developments in Basic Immunology and Novel Therapies|
Abul K. Abbas, MD, University of California San Francisco
The development of placentation in eutherian mammals enabled the fetus to mature and remain in a protected environment for much longer than was possible in less evolved species. But the free vascular connections between the fetus and the pregnant mother enabled the maternal immune system to readily access fetal tissues, including paternal antigens that were expressed in the fetus. These antigens are obviously foreign for the mother but have to be tolerated to prevent rejection of the fetus. The problem of tolerance of the fetus has fascinated immunologists for over fifty years, and has been addressed by a variety of experimental and clinical studies. Many explanations have been proposed, with varying degrees of experimental and clinical support. Recent discoveries implicating a central role of regulatory T cells promise to give meaningful answers that may not only solve a biological riddle but may also suggest approaches for elucidating the basis of spontaneous fetal loss in humans, and ultimately to provide therapies for this condition.
Mechanisms of fetal tolerance: the early findings
A role for Foxp3+ regulatory T cells: the evolutionary perspective
A role for Foxp3+ regulatory T cells: experimental studies
A role for Foxp3+ regulatory T cells: observations in humans
Perspectives and future prospects
Finally, the contribution of defective Treg generation or maintenance to recurrent abortions is a question of obvious clinical importance. As methods for inducing and expanding Tregs are entering clinical testing, this question becomes one of increasing significance. Preventing fetal loss by promoting Treg-mediated suppression without compromising protective immunity against infections remains a distant goal, but the recent basic research raises hopes that one day, the goal may be achieved.
Click here to send your comments and suggestions for future Translational Immunology Updates.
Translational Immunology Update is the official publication of the Federation of Clinical Immunology Societies. Scope: Translational Immunology Update aims to provide a knowledge-sharing forum for basic, clinical and translational scientists around all aspects of human immunology including normal and cross-disease physiology, communication between laboratory-based and clinically-based scientists, the lack of negative results that are published and the difficulty for readers to keep up with important literature.
Advertising: Inquiries concerning advertising should be addressed to Sarah Martis, FOCIS Executive Director.
Permissions: Copyright © 2013 Federation of Clinical Immunology Societies
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patent Act 1988, this publication may be reproduced, stored or transmitted, in any form or by any means, only with the prior permission in writing of the publishers, or in the case of reprographic reproduction, in accordance with the terms and licenses issued by the Copyright Licensing Agency.
Translational Immunology Update is published bimonthly by the Federation of Clinical Immunology Societies. You may opt-out of receiving the publication at any time by clicking the unsubscribe link in the email.