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Symmonds J, Gaufin T, Xu C, Raehtz KD, Ribeiro RM, Pandrea I, Apetrei C. Making a Monkey out of Human Immunodeficiency Virus/Simian Immunodeficiency Virus Pathogenesis: Immune Cell Depletion Experiments as a Tool to Understand the Immune Correlates of Protection and Pathogenicity in HIV Infection. Viruses 2024; 16:972. [PMID: 38932264 PMCID: PMC11209256 DOI: 10.3390/v16060972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2024] [Revised: 05/31/2024] [Accepted: 06/12/2024] [Indexed: 06/28/2024] Open
Abstract
Understanding the underlying mechanisms of HIV pathogenesis is critical for designing successful HIV vaccines and cure strategies. However, achieving this goal is complicated by the virus's direct interactions with immune cells, the induction of persistent reservoirs in the immune system cells, and multiple strategies developed by the virus for immune evasion. Meanwhile, HIV and SIV infections induce a pandysfunction of the immune cell populations, making it difficult to untangle the various concurrent mechanisms of HIV pathogenesis. Over the years, one of the most successful approaches for dissecting the immune correlates of protection in HIV/SIV infection has been the in vivo depletion of various immune cell populations and assessment of the impact of these depletions on the outcome of infection in non-human primate models. Here, we present a detailed analysis of the strategies and results of manipulating SIV pathogenesis through in vivo depletions of key immune cells populations. Although each of these methods has its limitations, they have all contributed to our understanding of key pathogenic pathways in HIV/SIV infection.
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Affiliation(s)
- Jen Symmonds
- Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA; (J.S.); (C.X.); (K.D.R.); (I.P.)
- Department of Infectious Diseases and Microbiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Thaidra Gaufin
- Tulane National Primate Research Center, Tulane University, Covington, LA 70433, USA;
| | - Cuiling Xu
- Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA; (J.S.); (C.X.); (K.D.R.); (I.P.)
- Division of Infectious Diseases, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Kevin D. Raehtz
- Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA; (J.S.); (C.X.); (K.D.R.); (I.P.)
- Division of Infectious Diseases, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Ruy M. Ribeiro
- Theoretical Biology and Biophysics Group, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
| | - Ivona Pandrea
- Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA; (J.S.); (C.X.); (K.D.R.); (I.P.)
- Department of Infectious Diseases and Microbiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Cristian Apetrei
- Department of Infectious Diseases and Microbiology, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA
- Division of Infectious Diseases, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA
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Lewis PE, Poteet EC, Liu D, Chen C, LaBranche CC, Stanfield-Oakley SA, Montefiori DC, Ferrari G, Yao Q. CTLA-4 Blockade, during HIV Virus-Like Particles Immunization, Alters HIV-Specific B-Cell Responses. Vaccines (Basel) 2020; 8:E284. [PMID: 32517277 PMCID: PMC7349993 DOI: 10.3390/vaccines8020284] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2020] [Revised: 05/31/2020] [Accepted: 06/03/2020] [Indexed: 12/23/2022] Open
Abstract
Studies have shown that blockade of CTLA-4 promoted the expansion of germinal center B-cells in viral infection or immunization with model antigens. Few studies have evaluated the immunological consequences of CTLA-4 blockade during immunization against relevant vaccine candidates. Here, we investigated the effects of CTLA-4 blockade on HIV virus-like particles (VLPs) vaccination in a C57BL/6J mouse model. We found that CTLA-4 blockade during HIV VLP immunization resulted in increased CD4+ T-cell activation, promoted the expansion of HIV envelope (Env)-specific follicular helper T cell (Tfh) cells, and significantly increased HIV Gag- and Env-specific IgG with higher avidity and antibody-dependent cellular cytotoxicity (ADCC) capabilities. Furthermore, after only a single immunization, CTLA-4 blockade accelerated T-cell dependent IgG class switching and the induction of significantly high serum levels of the B-cell survival factor, A proliferation-inducing ligand (APRIL). Although no significant increase in neutralizing antibodies was observed, increased levels of class-switched Env- and Gag-specific IgG are indicative of increased polyclonal B-cell activation, which demonstrated the ability to mediate and enhance ADCC in this study. Altogether, our findings show that CTLA-4 blockade can increase the levels of HIV antigen-specific B-cell and antigen-specific Tfh cell activity and impact humoral immune responses when combined with a clinically relevant HIV VLP-based vaccine.
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Affiliation(s)
- Phoebe E. Lewis
- Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, TX 77030, USA; (P.E.L.); (E.C.P.); (D.L.); (C.C.)
- Interdepartmental Program in Translational Biology and Molecular Medicine, Baylor College of Medicine, Houston, TX 77030, USA
| | - Ethan C. Poteet
- Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, TX 77030, USA; (P.E.L.); (E.C.P.); (D.L.); (C.C.)
| | - Dongliang Liu
- Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, TX 77030, USA; (P.E.L.); (E.C.P.); (D.L.); (C.C.)
| | - Changyi Chen
- Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, TX 77030, USA; (P.E.L.); (E.C.P.); (D.L.); (C.C.)
| | - Celia C. LaBranche
- Duke Human Vaccine Institute, Departments of Medicine, Immunology, Surgery, and Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, NC 27708, USA; (C.C.L.); (S.A.S.-O.); (D.C.M.); (G.F.)
| | - Sherry A. Stanfield-Oakley
- Duke Human Vaccine Institute, Departments of Medicine, Immunology, Surgery, and Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, NC 27708, USA; (C.C.L.); (S.A.S.-O.); (D.C.M.); (G.F.)
| | - David C. Montefiori
- Duke Human Vaccine Institute, Departments of Medicine, Immunology, Surgery, and Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, NC 27708, USA; (C.C.L.); (S.A.S.-O.); (D.C.M.); (G.F.)
| | - Guido Ferrari
- Duke Human Vaccine Institute, Departments of Medicine, Immunology, Surgery, and Molecular Genetics and Microbiology, Duke University School of Medicine, Durham, NC 27708, USA; (C.C.L.); (S.A.S.-O.); (D.C.M.); (G.F.)
| | - Qizhi Yao
- Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, TX 77030, USA; (P.E.L.); (E.C.P.); (D.L.); (C.C.)
- Center for Translational Research on Inflammatory Diseases (CTRID), Michael E. DeBakey VA Medical Center, Houston, TX 77030, USA
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3
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Gonzalez-Nieto L, Castro IM, Bischof GF, Shin YC, Ricciardi MJ, Bailey VK, Dang CM, Pedreño-Lopez N, Magnani DM, Ejima K, Allison DB, Gil HM, Evans DT, Rakasz EG, Lifson JD, Desrosiers RC, Martins MA. Vaccine protection against rectal acquisition of SIVmac239 in rhesus macaques. PLoS Pathog 2019; 15:e1008015. [PMID: 31568531 PMCID: PMC6791558 DOI: 10.1371/journal.ppat.1008015] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 10/14/2019] [Accepted: 08/02/2019] [Indexed: 02/07/2023] Open
Abstract
A prophylactic vaccine against human immunodeficiency virus (HIV) remains a top priority in biomedical research. Given the failure of conventional immunization protocols to confer robust protection against HIV, new and unconventional approaches may be needed to generate protective anti-HIV immunity. Here we vaccinated rhesus macaques (RMs) with a recombinant (r)DNA prime (without any exogenous adjuvant), followed by a booster with rhesus monkey rhadinovirus (RRV)-a herpesvirus that establishes persistent infection in RMs (Group 1). Both the rDNA and rRRV vectors encoded a near-full-length simian immunodeficiency virus (SIVnfl) genome that assembles noninfectious SIV particles and expresses all nine SIV gene products. This rDNA/rRRV-SIVnfl vaccine regimen induced persistent anti-Env antibodies and CD8+ T-cell responses against the entire SIV proteome. Vaccine efficacy was assessed by repeated, marginal-dose, intrarectal challenges with SIVmac239. Encouragingly, vaccinees in Group 1 acquired SIVmac239 infection at a significantly delayed rate compared to unvaccinated controls (Group 3). In an attempt to improve upon this outcome, a separate group of rDNA/rRRV-SIVnfl-vaccinated RMs (Group 2) was treated with a cytotoxic T-lymphocyte antigen-4 (CTLA-4)-blocking monoclonal antibody during the vaccine phase and then challenged in parallel with Groups 1 and 3. Surprisingly, Group 2 was not significantly protected against SIVmac239 infection. In sum, SIVnfl vaccination can protect RMs against rigorous mucosal challenges with SIVmac239, a feat that until now had only been accomplished by live-attenuated strains of SIV. Further work is needed to identify the minimal requirements for this protection and whether SIVnfl vaccine efficacy can be improved by means other than anti-CTLA-4 adjuvant therapy.
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Affiliation(s)
- Lucas Gonzalez-Nieto
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Isabelle M. Castro
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Georg F. Bischof
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Young C. Shin
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Michael J. Ricciardi
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Varian K. Bailey
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Christine M. Dang
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Nuria Pedreño-Lopez
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Diogo M. Magnani
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Keisuke Ejima
- Department of Epidemiology and Biostatistics, Indiana University School of Public Health-Bloomington, Bloomington, Indiana, United States of America
| | - David B. Allison
- Department of Epidemiology and Biostatistics, Indiana University School of Public Health-Bloomington, Bloomington, Indiana, United States of America
| | - Hwi Min Gil
- Wisconsin National Primate Research Center, University of Wisconsin, Madison, Wisconsin, United States of America
| | - David T. Evans
- Wisconsin National Primate Research Center, University of Wisconsin, Madison, Wisconsin, United States of America
- Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, Wisconsin, United States of America
| | - Eva G. Rakasz
- Wisconsin National Primate Research Center, University of Wisconsin, Madison, Wisconsin, United States of America
| | - Jeffrey D. Lifson
- AIDS and Cancer Virus Program, Frederick National Laboratory for Cancer Research, Frederick, Maryland, United States of America
| | - Ronald C. Desrosiers
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
| | - Mauricio A. Martins
- Department of Pathology, Miller School of Medicine, University of Miami, Miami, Florida, United States of America
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4
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Kleinman AJ, Sivanandham R, Pandrea I, Chougnet CA, Apetrei C. Regulatory T Cells As Potential Targets for HIV Cure Research. Front Immunol 2018; 9:734. [PMID: 29706961 PMCID: PMC5908895 DOI: 10.3389/fimmu.2018.00734] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 03/23/2018] [Indexed: 12/19/2022] Open
Abstract
T regulatory cells (Tregs) are a key component of the immune system, which maintain a delicate balance between overactive responses and immunosuppression. As such, Treg deficiencies are linked to autoimmune disorders and alter the immune control of pathogens. In HIV infection, Tregs play major roles, both beneficial and detrimental. They regulate the immune system such that inflammation and spread of virus through activated T cells is suppressed. However, suppression of immune activation also limits viral clearance and promotes reservoir formation. Tregs can be directly targeted by HIV, thereby harboring a fraction of the viral reservoir. The vital role of Tregs in the pathogenesis and control of HIV makes them a subject of interest for manipulation in the search of an HIV cure. Here, we discuss the origin and generation, homeostasis, and functions of Tregs, particularly their roles and effects in HIV infection. We also present various Treg manipulation strategies, including Treg depletion techniques and interventions that alter Treg function, which may be used in different cure strategies, to simultaneously boost HIV-specific immune responses and induce reactivation of the latent virus.
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Affiliation(s)
- Adam J Kleinman
- Center for Vaccine Research, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Microbiology and Molecular Genetics, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ranjit Sivanandham
- Center for Vaccine Research, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States
| | - Ivona Pandrea
- Center for Vaccine Research, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, United States
| | - Claire A Chougnet
- Division of Immunobiology, Department of Pediatrics, Cincinnati Children's Hospital, Cincinnati University, Cincinnati, OH, United States
| | - Cristian Apetrei
- Center for Vaccine Research, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Microbiology and Molecular Genetics, School of Medicine, University of Pittsburgh, Pittsburgh, PA, United States.,Department of Infectious Diseases and Microbiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, PA, United States
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5
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Nonhuman Primate Models for Studies of AIDS Virus Persistence During Suppressive Combination Antiretroviral Therapy. Curr Top Microbiol Immunol 2017; 417:69-109. [PMID: 29026923 DOI: 10.1007/82_2017_73] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Nonhuman primate (NHP) models of AIDS represent a potentially powerful component of the effort to understand in vivo sources of AIDS virus that persist in the setting of suppressive combination antiretroviral therapy (cART) and to develop and evaluate novel strategies for more definitive treatment of HIV infection (i.e., viral eradication "cure", or sustained off-cART remission). Multiple different NHP models are available, each characterized by a particular NHP species, infecting virus, and cART regimen, and each with a distinct capacity to recapitulate different aspects of HIV infection. Given these different biological characteristics, and their associated strengths and limitations, different models may be preferred to address different questions pertaining to virus persistence and cure research, or to evaluate different candidate intervention approaches. Recent developments in improved cART regimens for use in NHPs, new viruses, a wider array of sensitive virologic assay approaches, and a better understanding of pathogenesis should allow even greater contributions from NHP models to this important area of HIV research in the future.
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6
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Abstract
Co-inhibitory receptors play a key role in regulating T cell responses and maintaining immune homeostasis. Their inhibitory function prevents autoimmune responses but also restricts the ability of T cells to mount effective immune responses against tumors or persistent pathogens. T cells express a module of co-inhibitory receptors, which display great diversity in expression, structure, and function. Here, we focus on the co-inhibitory receptors Tim-3, Lag-3, and TIGIT and how they regulate T cell function, maintenance of self-tolerance, their role in regulating ongoing T cell responses at peripheral tissues, and their synergistic effects in regulating autoimmunity and antitumor responses.
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Affiliation(s)
- Nicole Joller
- Institute for Experimental Immunology, University of Zurich, Zurich, Switzerland
| | - Vijay K Kuchroo
- Harvard Medical School and Brigham & Women's Hospital, Evergrande Center for Immunologic Diseases, Boston, MA, USA.
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7
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Drewes JL, Croteau JD, Shirk EN, Engle EL, Zink MC, Graham DR. Distinct Patterns of Tryptophan Maintenance in Tissues during Kynurenine Pathway Activation in Simian Immunodeficiency Virus-Infected Macaques. Front Immunol 2016; 7:605. [PMID: 28066416 PMCID: PMC5165277 DOI: 10.3389/fimmu.2016.00605] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Accepted: 12/01/2016] [Indexed: 12/02/2022] Open
Abstract
Induction of the kynurenine pathway (KP) of tryptophan (TRP) catabolism has been proposed to contribute to T cell dysfunction during human/simian immunodeficiency virus (SIV) infection via depletion of local TRP levels and production of immunomodulatory KP metabolites. However, while changes in TRP and KP metabolites have been observed in plasma, their levels in lymphoid tissues and levels of enzymes downstream of indoleamine 2,3-dioxygenase (IDO1) have been relatively unexplored. We used our SIV-infected pigtailed macaque model to analyze longitudinal changes in KP metabolites and enzymes by gas chromatography/mass spectrometry and NanoString nCounter gene expression analysis, respectively, in spleen and blood compared to changes previously established in brain and CSF. We found that TRP levels were remarkably stable in tissue sites despite robust depletion in the circulating plasma and CSF. We also demonstrated that intracellular TRP reserves were maintained in cultured cells even in the presence of depleted extracellular TRP levels. Kynurenine (KYN), 3-hydroxykynurenine, quinolinic acid, and the KP enzymes all displayed highly divergent patterns in the sites examined, though IDO1 expression always correlated with local KYN/TRP ratios. Finally, we demonstrated by fluorescence-activated cell sorting that myeloid dendritic cells and cells of monocytic lineage were the highest producers of IDO1 in chronically infected spleens. Overall, our study reveals insights into the tissue-specific regulation of KP enzymes and metabolites and, in particular, highlights the multiple mechanisms by which cells and tissues seek to prevent TRP starvation during inflammation.
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Affiliation(s)
- Julia L Drewes
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - Joshua D Croteau
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - Erin N Shirk
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - Elizabeth L Engle
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - M C Zink
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine , Baltimore, MD , USA
| | - David R Graham
- Department of Molecular and Comparative Pathobiology, Johns Hopkins University School of Medicine , Baltimore, MD , USA
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Hepatitis C virus drives the pathogenesis of hepatocellular carcinoma: from immune evasion to carcinogenesis. Clin Transl Immunology 2016; 5:e101. [PMID: 27867514 PMCID: PMC5099426 DOI: 10.1038/cti.2016.55] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2016] [Revised: 08/23/2016] [Accepted: 08/23/2016] [Indexed: 02/08/2023] Open
Abstract
Persistent hepatitis C virus (HCV) infection is associated with high incidence of hepatocellular carcinoma (HCC), the most common primary malignancy of the liver with over half a million new cases diagnosed annually worldwide. The aryl hydrocarbon receptor (AhR) is a ubiquitously expressed transcription factor and its activation by environmental chemicals and by its endogenous ligand kynurenine (Kyn) has been implicated in a variety of tumour-promoting processes such as transformation, tumorigenesis and in immunosuppression that enables tumour survival and growth. Kyn is generated constitutively by human tumour cells via tryptophan (Trp)-2,3-dioxygenase (TDO), a Trp-degrading enzyme expressed in liver, brain and cancer cells. Notably, it has been shown that TDO-derived Kyn suppresses anti-tumour immune responses, thus promoting tumour-cell survival through activation of the AhR pathway. In the context of HCV infection-associated HCC, it was shown that AhR signalling is increased in HCV-infected hepatocytes, and that modifications in the expression of AhR pathway-specific genes are associated with the progression of HCV infection into HCC. Based on these observations, we present and discuss here the hypothesis that HCV infection promotes HCC by modulation of the TDO-Kyn-AhR pathway, resulting in tumorigenesis as well as in suppression of both anti-HCV and anti-tumour immune responses.
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Combination antiretroviral therapy and indoleamine 2,3-dioxygenase in HIV infections: challenges and new opportunities. AIDS 2016; 30:1839-41. [PMID: 27351927 DOI: 10.1097/qad.0000000000001168] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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10
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Mehraj V, Routy JP. Tryptophan Catabolism in Chronic Viral Infections: Handling Uninvited Guests. Int J Tryptophan Res 2015; 8:41-8. [PMID: 26309411 PMCID: PMC4527356 DOI: 10.4137/ijtr.s26862] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2015] [Revised: 05/17/2015] [Accepted: 05/19/2015] [Indexed: 11/25/2022] Open
Abstract
l-Tryptophan (l-Trp) is an essential amino acid that possesses diverse metabolic, neurological, and immunological roles spanning from the synthesis of proteins, neurotransmitter serotonin, and neurohormone melatonin, to its degradation into immunosuppressive catabolites by indoleamine-2, 3-dioxygenase (IDO) in the kynurenine pathway (KP). Trp catabolites, by activating aryl hydrocarbon receptor (AhR), play an important role in antimicrobial defense and immune regulation. IDO/AhR acts as a double-edged sword by both depleting l-Trp to starve the invaders and by contributing to the state of immunosuppression with microorganisms that were not cleared during acute infection. Pathogens experiencing Trp deprivation by IDO-mediated degradation include certain bacteria, parasites, and less likely viruses. However, chronic viral infections highjack the host immune response to create a state of disease tolerance via kynurenine catabolites. This review covers the latest data involving chronic viral infections such as human immunodeficiency virus (HIV), hepatitis B virus (HBV), hepatitis C virus (HCV), herpes, and cytomegalovirus (CMV) and their cellular interplay with Trp catabolites. Strategies developed by viruses to escape immune control also represent new avenues for therapeutic interventions based on Trp metabolism.
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Affiliation(s)
- Vikram Mehraj
- Chronic Viral Illness Service, McGill University Health Centre, Montreal, QC, Canada. ; Research Institute of the McGill University Health Centre, Montreal, QC, Canada
| | - Jean-Pierre Routy
- Chronic Viral Illness Service, McGill University Health Centre, Montreal, QC, Canada. ; Research Institute of the McGill University Health Centre, Montreal, QC, Canada. ; Division of Hematology, McGill University Health Centre, Montreal, QC, Canada
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Abstract
IDO1 (indoleamine 2,3-dioxygenase 1) is a member of a unique class of mammalian haem dioxygenases that catalyse the oxidative catabolism of the least-abundant essential amino acid, L-Trp (L-tryptophan), along the kynurenine pathway. Significant increases in knowledge have been recently gained with respect to understanding the fundamental biochemistry of IDO1 including its catalytic reaction mechanism, the scope of enzyme reactions it catalyses, the biochemical mechanisms controlling IDO1 expression and enzyme activity, and the discovery of enzyme inhibitors. Major advances in understanding the roles of IDO1 in physiology and disease have also been realised. IDO1 is recognised as a prominent immune regulatory enzyme capable of modulating immune cell activation status and phenotype via several molecular mechanisms including enzyme-dependent deprivation of L-Trp and its conversion into the aryl hydrocarbon receptor ligand kynurenine and other bioactive kynurenine pathway metabolites, or non-enzymatic cell signalling actions involving tyrosine phosphorylation of IDO1. Through these different modes of biochemical signalling, IDO1 regulates certain physiological functions (e.g. pregnancy) and modulates the pathogenesis and severity of diverse conditions including chronic inflammation, infectious disease, allergic and autoimmune disorders, transplantation, neuropathology and cancer. In the present review, we detail the current understanding of IDO1’s catalytic actions and the biochemical mechanisms regulating IDO1 expression and activity. We also discuss the biological functions of IDO1 with a focus on the enzyme's immune-modulatory function, its medical implications in diverse pathological settings and its utility as a therapeutic target.
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Phetsouphanh C, Xu Y, Zaunders J. CD4 T Cells Mediate Both Positive and Negative Regulation of the Immune Response to HIV Infection: Complex Role of T Follicular Helper Cells and Regulatory T Cells in Pathogenesis. Front Immunol 2015; 5:681. [PMID: 25610441 PMCID: PMC4285174 DOI: 10.3389/fimmu.2014.00681] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 12/17/2014] [Indexed: 12/13/2022] Open
Abstract
HIV-1 infection results in chronic activation of cells in lymphoid tissue, including T cells, B-cells, and myeloid lineage cells. The resulting characteristic hyperplasia is an amalgam of proliferating host immune cells in the adaptive response, increased concentrations of innate response mediators due to viral and bacterial products, and homeostatic responses to inflammation. While it is generally thought that CD4 T cells are greatly depleted, in fact, two types of CD4 T cells appear to be increased, namely, regulatory T cells (Tregs) and T follicular helper cells (Tfh). These cells have opposing roles, but may both be important in the pathogenic process. Whether Tregs are failing in their role to limit lymphocyte activation is unclear, but there is no doubt now that Tfh are associated with B-cell hyperplasia and increased germinal center activity. Antiretroviral therapy may reduce the lymphocyte activation, but not completely, and therefore, there is a need for interventions that selectively enhance normal CD4 function without exacerbating Tfh, B-cell, or Treg dysfunction.
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Affiliation(s)
- Chansavath Phetsouphanh
- Centre for Applied Medical Research, Kirby Institute, St Vincent's Hospital, University of New South Wales , Sydney, NSW , Australia
| | - Yin Xu
- Centre for Applied Medical Research, Kirby Institute, St Vincent's Hospital, University of New South Wales , Sydney, NSW , Australia
| | - John Zaunders
- Centre for Applied Medical Research, Kirby Institute, St Vincent's Hospital, University of New South Wales , Sydney, NSW , Australia
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The calcineurin-NFAT axis controls allograft immunity in myeloid-derived suppressor cells through reprogramming T cell differentiation. Mol Cell Biol 2014; 35:598-609. [PMID: 25452304 DOI: 10.1128/mcb.01251-14] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
While cyclosporine (CsA) inhibits calcineurin and is highly effective in prolonging rejection for transplantation patients, the immunological mechanisms remain unknown. Herein, the role of calcineurin signaling was investigated in a mouse allogeneic skin transplantation model. The calcineurin inhibitor CsA significantly ameliorated allograft rejection. In CsA-treated allograft recipient mice, CD11b(+) Gr1(+) myeloid-derived suppressor cells (MDSCs) were functional suppressive immune modulators that resulted in fewer gamma interferon (IFN-γ)-producing CD8(+) T cells and CD4(+) T cells (T(H)1 T helper cells) and more interleukin 4 (IL-4)-producing CD4(+) T cells (T(H2)) and prolonged allogeneic skin graft survival. Importantly, the expression of NFATc1 is significantly diminished in the CsA-induced MDSCs. Blocking NFAT (nuclear factor of activated T cells) with VIVIT phenocopied the CsA effects in MDSCs and increased the suppressive activities and recruitment of CD11b(+) Gr1(+) MDSCs in allograft recipient mice. Mechanistically, CsA treatment enhanced the expression of indoleamine 2,3-dioxygenase (IDO) and the suppressive activities of MDSCs in allograft recipients. Inhibition of IDO nearly completely recovered the increased MDSC suppressive activities and the effects on T cell differentiation. The results of this study indicate that MDSCs are an essential component in controlling allograft survival following CsA or VIVIT treatment, validating the calcineurin-NFAT-IDO signaling axis as a potential therapeutic target in transplantation.
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Schmidt SV, Schultze JL. New Insights into IDO Biology in Bacterial and Viral Infections. Front Immunol 2014; 5:384. [PMID: 25157255 PMCID: PMC4128074 DOI: 10.3389/fimmu.2014.00384] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 07/28/2014] [Indexed: 12/24/2022] Open
Abstract
Initially, indoleamine-2,3-dioxygenase (IDO) has been introduced as a bactericidal effector mechanism and has been linked to T-cell immunosuppression and tolerance. In recent years, evidence has been accumulated that IDO also plays an important role during viral infections including HIV, influenza, and hepatitis B and C. Moreover, novel aspects about the role of IDO in bacterial infections and sepsis have been revealed. Here, we review these recent findings highlighting the central role of IDO and tryptophan metabolism in many major human infections. Moreover, we also shed light on issues concerning human-specific and mouse-specific host–pathogen interactions that need to be considered when studying the biology of IDO in the context of infections.
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Affiliation(s)
- Susanne V Schmidt
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn , Bonn , Germany
| | - Joachim L Schultze
- Genomics and Immunoregulation, LIMES-Institute, University of Bonn , Bonn , Germany
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15
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Del Prete GQ, Lifson JD. Considerations in the development of nonhuman primate models of combination antiretroviral therapy for studies of AIDS virus suppression, residual virus, and curative strategies. Curr Opin HIV AIDS 2013; 8:262-72. [PMID: 23698559 PMCID: PMC3939607 DOI: 10.1097/coh.0b013e328361cf40] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
PURPOSE OF REVIEW Animal models will be critical for preclinical evaluations of novel HIV eradication and/or functional cure strategies in the setting of suppressive combination antiretroviral therapy (cART). Here, the strengths, limitations, and challenges of recent efforts to develop nonhuman primate (NHP) models of cART-mediated suppression for use in studies of persistent virus and curative approaches are discussed. RECENT FINDINGS Several combinations of NHP species and viruses that recapitulate key aspects of human HIV infection have been adapted for cART-mediated suppression studies. Different cART regimens incorporating drugs targeting multiple different steps of the viral replication cycle have provided varying levels of virologic suppression, dependent in part upon the host species, virus, drug regimen and timing, and virologic monitoring assay sensitivity. New, increasingly sensitive virologic monitoring approaches for measurements of plasma viral RNA, cell-associated and tissue-associated viral RNA and DNA, and the replication-competent residual viral pool in the setting of cART in NHP models are being developed to allow for the assessment of persistent virus on cART and to evaluate the impact of viral induction/eradication strategies in vivo. SUMMARY Given the vagaries of each specific virus and host species, and cART regimen, each model will require further development and analysis to determine their appropriate application for addressing specific experimental questions.
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Affiliation(s)
- Gregory Q. Del Prete
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD
| | - Jeffrey D. Lifson
- AIDS and Cancer Virus Program, SAIC-Frederick, Inc., Frederick National Laboratory for Cancer Research, Frederick, MD
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16
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Lei N, Wang Y, Zhang WJ, Duan JZ, Yang GB. Indoleamine 2,3-dioxygenase is differentially expressed by different white blood cell populations of rhesus macaques (Macaca mulatta
). J Med Primatol 2013; 42:192-203. [DOI: 10.1111/jmp.12054] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/25/2013] [Indexed: 01/28/2023]
Affiliation(s)
- N. Lei
- National Center for AIDS/STD Control and Prevention; China-CDC; Beijing China
| | - Y. Wang
- National Center for AIDS/STD Control and Prevention; China-CDC; Beijing China
| | - W.-J. Zhang
- National Center for AIDS/STD Control and Prevention; China-CDC; Beijing China
| | - J.-Z. Duan
- National Center for AIDS/STD Control and Prevention; China-CDC; Beijing China
| | - G.-B. Yang
- National Center for AIDS/STD Control and Prevention; China-CDC; Beijing China
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17
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Nzowa LK, Teponno RB, Tapondjou LA, Verotta L, Liao Z, Graham D, Zink MC, Barboni L. Two new tryptophan derivatives from the seed kernels of Entada rheedei: effects on cell viability and HIV infectivity. Fitoterapia 2013; 87:37-42. [PMID: 23537889 DOI: 10.1016/j.fitote.2013.03.017] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 03/12/2013] [Accepted: 03/14/2013] [Indexed: 10/27/2022]
Abstract
Two new tryptophan derivatives, N-sulfonyl-L-tryptophan (tryptorheedei A) (1) and 3-(N-sulfonylindolyl)-D-lactic acid (tryptorheedei B) (2) together with the known 5-O-β-D-glucopyranosyl-2-hydroxyphenylacetic acid (3), 1-O-methylglucopyranoside, entadamide A, homogentisic acid and 3-O-β-D-glucopyranosyl-β-sitosterol, were isolated from the seed kernels of Entada rheedei (Mimosaceae). Their structures were established using 1D and 2D NMR spectroscopy, mass spectrometry and by comparison with spectroscopic data reported in the literature. Compounds 1 and 2 showed no toxicity to TZM and Human PBMC cells. Both compounds 1 and 2 were found to promote early infection events in HIV, likely by inhibiting the enzyme indolamine 2,3-dioxygenase (IDO) and preventing tryptophan depletion. Inhibition of IDO acutely in HIV infection inhibits viral replication, but chronic activation of IDO leads to immune impairment in AIDS. IDO is also the gatekeeper enzyme for kynurenine metabolism, a pathway involved in serotonin and melatonin biosynthesis and the regulation of glutamate and dopamine levels in the brain. Therefore inhibition of IDO might explain both the reported medicinal and neuropsychiatric effects of E. rheedei.
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Affiliation(s)
- L K Nzowa
- Department of Chemistry, Faculty of Science, University of Dschang, Dschang, Cameroon
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18
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Sun JK, Mu XW, Li WQ, Tong ZH, Li J, Zheng SY. Effects of early enteral nutrition on immune function of severe acute pancreatitis patients. World J Gastroenterol 2013; 19:917-922. [PMID: 23431120 PMCID: PMC3574890 DOI: 10.3748/wjg.v19.i6.917] [Citation(s) in RCA: 89] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/28/2012] [Revised: 11/02/2012] [Accepted: 12/18/2012] [Indexed: 02/07/2023] Open
Abstract
AIM: To investigate the effects of early enteral nutrition (EEN) on the immune function and clinical outcome of patients with severe acute pancreatitis (SAP).
METHODS: Patients were randomly allocated to receive EEN or delayed enteral nutrition (DEN). Enteral nutrition was started within 48 h after admission in EEN group, whereas from the 8th day in DEN group. All the immunologic parameters and C-reactive protein (CRP) levels were collected on days 1, 3, 7 and 14 after admission. The clinical outcome variables were also recorded.
RESULTS: Sixty SAP patients were enrolled to this study. The CD4+ T-lymphocyte percentage, CD4+/CD8+ ratio, and the CRP levels in EEN group became significantly lower than in DEN group from the 7th day after admission. In contrast, the immunoglobulin G (IgG) levels and human leukocyte antigen-DR expression in EEN group became significantly higher than in DEN group from the 7th day after admission. No difference of CD8+ T-lymphocyte percentage, IgM and IgA levels was found between the two groups. The incidences of multiple organ dysfunction syndrome, systemic inflammatory response syndrome, and pancreatic infection as well as the duration of intensive care unit stay were significantly lower in EEN group than in DEN group. However, there was no difference of hospital mortality between the two groups.
CONCLUSION: EEN moderates the excessive immune response during the early stage of SAP without leading to subsequent immunosuppression. EEN can improve the clinical outcome, but not decrease the hospital mortality of SAP patients.
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19
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Dunham RM, Gordon SN, Vaccari M, Piatak M, Huang Y, Deeks SG, Lifson J, Franchini G, McCune JM. Preclinical evaluation of HIV eradication strategies in the simian immunodeficiency virus-infected rhesus macaque: a pilot study testing inhibition of indoleamine 2,3-dioxygenase. AIDS Res Hum Retroviruses 2013; 29:207-14. [PMID: 22924680 DOI: 10.1089/aid.2012.0162] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Even in the setting of maximally suppressive antiretroviral therapy (ART), HIV persists indefinitely. Several mechanisms might contribute to this persistence, including chronic inflammation and immune dysfunction. In this study, we have explored a preclinical model for the evaluation of potential interventions that might serve to eradicate or to minimize the level of persistent virus. Given data that metabolic products of the inducible enzyme indoleamine 2,3-dioxygeanse (IDO) might foster inflammation and viral persistence, chronically simian immunodeficiency virus (SIV)-infected, ART-treated rhesus macaques were treated with the IDO inhibitor 1-methyl tryptophan (1mT). Orally administered 1mT achieved targeted plasma levels, but did not impact tryptophan metabolism or decrease viral RNA or DNA in plasma or in intestinal tissues beyond levels achieved by ART alone. Animals treated with 1mT showed no difference in the levels of T cell activation or differentiation, or in the kinetics or magnitude of viral rebound following cessation of ART. Notwithstanding these negative results, our observations suggest that the chronically SIV-infected rhesus macaque on suppressive ART can serve as a tractable model in which to test and to prioritize the selection of other potential interventions designed to eradicate HIV in vivo. In addition, this model might be used to optimize the route and dose by which such interventions are administered and the methods by which their effects are monitored.
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Affiliation(s)
- Richard M. Dunham
- Department of Medicine, University of California, San Francisco, California
| | - Shari N. Gordon
- Animal Models and Retroviral Vaccines Section, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Monica Vaccari
- Animal Models and Retroviral Vaccines Section, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Michael Piatak
- AIDS and Cancer Virus Program, Science Applications International Corporation Frederick, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland
| | - Yong Huang
- Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, California
| | - Steven G. Deeks
- Department of Medicine, University of California, San Francisco, California
| | - Jeffrey Lifson
- AIDS and Cancer Virus Program, Science Applications International Corporation Frederick, Inc., Frederick National Laboratory for Cancer Research, Frederick, Maryland
| | - Genoveffa Franchini
- Animal Models and Retroviral Vaccines Section, National Cancer Institute, National Institutes of Health, Bethesda, Maryland
| | - Joseph M. McCune
- Department of Medicine, University of California, San Francisco, California
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20
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Frebel H, Oxenius A. The risks of targeting co-inhibitory pathways to modulate pathogen-directed T cell responses. Trends Immunol 2013; 34:193-9. [PMID: 23333205 PMCID: PMC7106470 DOI: 10.1016/j.it.2012.12.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2012] [Revised: 12/18/2012] [Accepted: 12/21/2012] [Indexed: 12/22/2022]
Abstract
The identification of T cell co-inhibition as a central mechanism in the regulation of adaptive immunity during infectious diseases provides new opportunities for immunotherapeutic interventions. However, the fact that T cell activity is frequently downregulated during pathogen-directed responses suggests a pivotal physiological role of co-inhibitory pathways during infectious disease. Reports of exacerbated immunopathology in conditions of impaired co-inhibition foster the view that downregulation of T cell activity is an essential negative feedback mechanism that protects from excessive pathogen-directed immunity. Thus, targeting co-inhibitory pathways can bear detrimental potential through the deregulation of physiological processes. Here, we summarize recent preclinical and clinical interventions that report immune-related adverse events after targeting co-inhibitory pathways.
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Affiliation(s)
- Helge Frebel
- Institute of Microbiology, ETH Zurich, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland
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21
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Barth H, Raghuraman S. Persistent infectious diseases say - IDO. Role of indoleamine-2,3-dioxygenase in disease pathogenesis and implications for therapy. Crit Rev Microbiol 2012; 40:360-8. [PMID: 23174025 DOI: 10.3109/1040841x.2012.742037] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Indoleamine-2,3-dioxygenase (IDO) is an enzyme that catabolises tryptophan - an essential amino acid critical for T cell proliferation. Initially recognized as a first line of host defense against infectious pathogens, IDO has been subsequently identified as an important immune-regulator inhibiting T-cell responses and promoting immune tolerance. Research over the past few years has demonstrated a crucial role for IDO in the pathogenesis of persistent infections that place an enormous burden on public health. In this review, we summarize current knowledge about IDO's role in causing pathogen persistence and progression to clinical disease. We conclude with a perspective on the potential benefits and risks of therapeutic IDO manipulation.
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22
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Regulatory T cells in HIV infection: can immunotherapy regulate the regulator? Clin Dev Immunol 2012; 2012:908314. [PMID: 23251223 PMCID: PMC3509372 DOI: 10.1155/2012/908314] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2012] [Accepted: 08/28/2012] [Indexed: 12/25/2022]
Abstract
Regulatory T cells (Tregs) have a dominant role in self-tolerance and control of autoimmune diseases. These cells also play a pivotal role in chronic viral infections and cancer by limiting immune activation and specific immune response. The role of Tregs in HIV pathogenesis remains poorly understood as their function, changes according to the phases of infection. Tregs can suppress anti-HIV specific responses and conversely can have a beneficial role by reducing the deleterious impact of immune activation. We review the frequency, function and homing potential of Tregs in the blood and lymphoid tissues as well as their interaction with dendritic cells in the context of HIV infection. We also examine the new insights generated by recombinant IL-2 and IL-7 clinical trials in HIV-infected adults, including the immunomodulatory effects of Tregs. Based on their detrimental role in limiting anti-HIV responses, we propose Tregs as potential targets for immunotherapeutic strategies aimed at decreasing Tregs frequency and/or immunosuppressive function. However, such approaches require a better understanding of the time upon infection when interfering with Treg function may not cause a deleterious state of hyperimmune activation.
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23
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Orabona C, Pallotta MT, Grohmann U. Different partners, opposite outcomes: a new perspective of the immunobiology of indoleamine 2,3-dioxygenase. Mol Med 2012; 18:834-42. [PMID: 22481272 DOI: 10.2119/molmed.2012.00029] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2012] [Accepted: 03/30/2012] [Indexed: 01/07/2023] Open
Abstract
Indoleamine 2,3-dioxygenase (IDO), a metabolic enzyme that catalyzes tryptophan conversion into kynurenines, is a crucial regulator of immunity. Altered IDO activity is often associated with pathology, including neoplasia and autoimmunity. IDO is highly expressed in dendritic cells (DCs) that exploit the enzyme's activity and the production of tryptophan catabolites to regulate immune responses by acting on several cell types, including T lymphocytes, of which they promote a regulatory phenotype. IDO also contains immunoreceptor tyrosine-based inhibitory motifs (ITIMs) that, once bound by distinct molecular partners, will either promote degradation or initiate signaling activity and self-maintenance of the enzyme. We here discuss how ITIM-dependent molecular events can affect the functional plasticity of IDO by modifying the protein half-life and its enzymic and nonenzymic functions.
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Affiliation(s)
- Ciriana Orabona
- Department of Experimental Medicine and Biochemical Sciences, University of Perugia, Perugia, Italy.
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24
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Li L, Huang L, Lemos HP, Mautino M, Mellor AL. Altered tryptophan metabolism as a paradigm for good and bad aspects of immune privilege in chronic inflammatory diseases. Front Immunol 2012; 3:109. [PMID: 22593757 PMCID: PMC3350084 DOI: 10.3389/fimmu.2012.00109] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2012] [Accepted: 04/17/2012] [Indexed: 01/01/2023] Open
Abstract
The term "immune privilege" was coined to describe weak immunogenicity (hypo-immunity) that manifests in some transplant settings. We extended this concept to encompass hypo-immunity that manifests at local sites of inflammation relevant to clinical diseases. Here, we focus on emerging evidence that enhanced tryptophan catabolism is a key metabolic process that promotes and sustains induced immune privilege, and discuss the implications for exploiting this knowledge to improve treatments for hypo-immune and hyper-immune syndromes using strategies to manipulate tryptophan metabolism.
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Affiliation(s)
- Lingqian Li
- Immunotherapy Center, Georgia Health Sciences University Augusta, GA, USA
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