Virology
Abstract
HIV-2 infection in the majority of infected subjects follows an attenuated disease course that distinguishes it from infection with HIV-1. Antigen-specific T cells are pivotal in the management of chronic viral infections but are not sufficient to control viral replication in HIV-1–positive subjects, and their function in HIV-2 infection is not fully established. In a community-based cohort of HIV-2 long-term nonprogressors in rural Guinea-Bissau, we performed what we believe is the first comprehensive analysis of HIV-2–specific immune responses. We demonstrate that Gag is the most immunogenic protein. The magnitude of the IFN-γ immune response to the HIV-2 proteome was inversely correlated with HIV-2 viremia, and this relationship was specifically due to the targeting of Gag. Furthermore, patients with undetectable viremia had greater Gag-specific responses compared with patients with high viral replication. The most frequently recognized peptides clustered within a defined region of Gag, and responses to a single peptide in this region were associated with low viral burden. The consistent relationship between Gag-specific immune responses and viremia control suggests that T cell responses are vital in determining the superior outcome of HIV-2 infection. A better understanding of how HIV-2 infection is controlled may identify correlates of effective protective immunity essential for the design of HIV vaccines.
Authors
Aleksandra Leligdowicz, Louis-Marie Yindom, Clayton Onyango, Ramu Sarge-Njie, Abraham Alabi, Matthew Cotten, Tim Vincent, Carlos da Costa, Peter Aaby, Assan Jaye, Tao Dong, Andrew McMichael, Hilton Whittle, Sarah Rowland-Jones
Abstract
CD137 is expressed on activated T cells and ligands to this costimulatory molecule have clinical potential for amplifying CD8 T cell immunity to tumors and viruses, while suppressing CD4 autoimmune T cell responses. To understand the basis for this dichotomy in T cell function, CD4 and CD8 antiviral immunity was measured in lymphocytic choriomeningitis virus (LCMV) Armstrong– or A/PR8/34 influenza–infected mice injected with anti-CD137 mAbs. We found that the timing of administration of anti-CD137 mAbs profoundly altered the nature of the antiviral immune response during acute infection. Antiviral immunity progressed normally for the first 72 hours when the mAb was administered early in infection before undergoing complete collapse by day 8 postinfection. Anti-CD137–injected LCMV-infected mice became tolerant to, and persistently infected with, LCMV Armstrong. Elevated levels of IL-10 early in the response was key to the loss of CD4+ T cells, whereas CD8+ T cell deletion was dependent on a prolonged TNF-α response, IL-10, and upregulation of Fas. Blocking IL-10 function rescued CD4 antiviral immunity but not CD8+ T cell deletion. Anti-CD137 treatment given beyond 72 hours after infection significantly enhanced antiviral immunity. Mice treated with anti-CD137 mAb 1 day before infection with A/PR8/34 virus experienced 80% mortality compared with 40% mortality of controls. When treatment was delayed until day 1 postinfection, 100% of the infected mice survived. These data show that anti-CD137 mAbs can induce T cell activation–induced cell death or enhance antiviral immunity depending on the timing of treatment, which may be important for vaccine development.
Authors
Benyue Zhang, Charles H. Maris, Juergen Foell, Jason Whitmire, Liguo Niu, Jing Song, Byoung S. Kwon, Anthony T. Vella, Rafi Ahmed, Joshy Jacob, Robert S. Mittler
Abstract
The adenoviral protein E3-14.7K (14.7K) is an inhibitor of TNF-induced apoptosis, but the molecular mechanism underlying this protective effect has not yet been explained exhaustively. TNF-mediated apoptosis is initiated by ligand-induced recruitment of TNF receptor–associated death domain (TRADD), Fas-associated death domain (FADD), and caspase-8 to the death domain of TNF receptor 1 (TNFR1), thereby establishing the death-inducing signaling complex (DISC). Here we report that adenovirus 14.7K protein inhibits ligand-induced TNFR1 internalization. Analysis of purified magnetically labeled TNFR1 complexes from murine and human cells stably transduced with 14.7K revealed that prevention of TNFR1 internalization resulted in inhibition of DISC formation. In contrast, 14.7K did not affect TNF-induced NF-κB activation via recruitment of receptor-interacting protein 1 (RIP-1) and TNF receptor–associated factor 2 (TRAF-2). Inhibition of endocytosis by 14.7K was effected by failure of coordinated temporal and spatial assembly of essential components of the endocytic machinery such as Rab5 and dynamin 2 at the site of the activated TNFR1. Furthermore, we found that the same TNF defense mechanisms were instrumental in protecting wild-type adenovirus–infected human cells expressing 14.7K. This study describes a new molecular mechanism implemented by a virus to escape immunosurveillance by selectively targeting TNFR1 endocytosis to prevent TNF-induced DISC formation.
Authors
Wulf Schneider-Brachert, Vladimir Tchikov, Oliver Merkel, Marten Jakob, Cora Hallas, Marie-Luise Kruse, Peter Groitl, Alexander Lehn, Eberhard Hildt, Janka Held-Feindt, Thomas Dobner, Dieter Kabelitz, Martin Krönke, Stefan Schütze
Abstract
Topical microbicides represent a promising new approach to preventing HIV and other sexually transmitted infections. TLR agonists are ideal candidates for microbicides, as they trigger a multitude of antiviral genes effective against a broad range of viruses. Although vaginal application of CpG oligodeoxynucleotides (ODNs) and poly I:C has been shown to protect mice from genital herpes infection, the mechanism by which these agents provide protection remains unclear. Here, we show that plasmacytoid DCs (pDCs) are required for CpG ODN–mediated protection against lethal vaginal challenge with herpes simplex virus type 2 (HSV-2). Moreover, we demonstrate that cells of both the hematopoietic and stromal compartments must respond to CpG ODN via TLR9 and to type I IFNs through IFN-αβ receptor (IFN-αβR) for protection. Thus, crosstalk between pDCs and vaginal stromal cells provides for optimal microbicide efficacy. Our results imply that temporally and spatially controlled targeting of CpG ODN to pDCs and epithelial cells can potentially maximize their effectiveness as microbicides while minimizing the associated inflammatory responses.
Authors
Hong Shen, Akiko Iwasaki
Abstract
To develop an animal model of Kaposi sarcoma–associated herpesvirus (KSHV) infection uniquely suited to evaluate longitudinal patterns of viral gene expression, cell tropism, and immune responses, we injected NOD/SCID mice intravenously with purified virus and measured latent and lytic viral transcripts in distal organs over the subsequent 4 months. We observed sequential escalation of first latent and then lytic KSHV gene expression coupled with electron micrographic evidence of virion production within the murine spleen. Using novel technology that integrates flow cytometry with immunofluorescence microscopy, we found that the virus establishes infection in murine B cells, macrophages, NK cells, and, to a lesser extent, dendritic cells. To investigate the potential for human KSHV–specific immune responses within this immunocompromised host, we implanted NOD/SCID mice with functional human hematopoietic tissue grafts (NOD/SCID-hu mice) and observed that a subset of animals produced human KSHV–specific antibodies. Furthermore, treatment of these chimeric mice with ganciclovir at the time of inoculation led to prolonged but reversible suppression of KSHV DNA and RNA levels, suggesting that KSHV can establish latent infection in vivo despite ongoing suppression of lytic replication.
Authors
Christopher H. Parsons, Laura A. Adang, Jon Overdevest, Christine M. O’Connor, J. Robert Taylor, David Camerini, Dean H. Kedes
Abstract
Failure to clear persistent viral infections results from the early loss of T cell activity. A pertinent question is whether the immune response is programmed to fail or if nonresponsive T cells can specifically be fixed to eliminate infection. Although evidence indicates that T cell expansion is permanently programmed during the initial priming events, the mechanisms that determine the acquisition of T cell function are less clear. Herein we show that in contrast to expansion, the functional programming of T cell effector and memory responses in vivo in mice is not hardwired during priming but is alterable and responsive to continuous instruction from the antigenic environment. As a direct consequence, dysfunctional T cells can be functionally reactivated during persistent infection even after an initial program of inactivation has been instituted. We also show that early therapeutic reductions in viral replication facilitate the preservation of antiviral CD4+ T cell activity, enabling the long-term control of viral replication. Thus, dysfunctional antiviral T cells can regain activity, providing a basis for future therapeutic strategies to treat persistent viral infections.
Authors
David G. Brooks, Dorian B. McGavern, Michael B.A. Oldstone
Abstract
HIV infection selectively targets CD4+ effector memory T (TEM) cells, resulting in dramatic depletion of CD4+ T cells in mucosal effector sites in early infection. Regeneration of the TEM cell compartment is slow and incomplete, even when viral replication is controlled by antiretroviral therapy (ART). Here, we demonstrate that IL-15 dramatically increases in vivo proliferation of rhesus macaque (RM) CD4+ and CD8+ TEM cells with little effect on the naive or central memory T (TCM) cell subsets, a response pattern that is quite distinct from that of either IL-2 or IL-7. TEM cells produced in response to IL-15 did not accumulate in blood. Rather, 5-bromo-2′-deoxyuridine (BrdU) labeling studies suggest that many of these cells rapidly disperse to extralymphoid effector sites, where they manifest (slow) decay kinetics indistinguishable from that of untreated controls. In RMs with uncontrolled SIV infection and highly activated immune systems, IL-15 did not significantly increase CD4+ TEM cell proliferation, but with virologic control and concomitant reduction in immune activation by ART, IL-15 responsiveness was again observed. These data suggest that therapeutic use of IL-15 in the setting of ART might facilitate specific restoration of the CD4+ T cell compartment that is the primary target of HIV with less risk of exhausting precursor T cell compartments or generating potentially deleterious regulatory subsets.
Authors
Louis J. Picker, Edward F. Reed-Inderbitzin, Shoko I. Hagen, John B. Edgar, Scott G. Hansen, Alfred Legasse, Shannon Planer, Michael Piatak, Jeffrey D. Lifson, Vernon C. Maino, Michael K. Axthelm, Francois Villinger
Abstract
CD8+ T cells play a key role in clearing primary virus infections and in protecting against subsequent challenge. The potent antiviral effects of these cells make them important components of vaccine-induced immunity and, because of this, peptide vaccines often contain epitopes designed to induce strong CD8+ T cell responses. However, the same effector functions that protect the host also can be harmful if they are not tightly regulated, and virus-specific CD8+ T cells are a frequent cause of immunopathology. Here, we report that the administration of peptide to virus-immune recipient mice can lead to the synchronous activation of preexisting virus-specific CD8+ T cells with serious, and even lethal, consequences. Mice infected with LCMV or vaccinia virus developed rapid and profound hypothermia following injection of cognate synthetic peptides, and LCMV-infected mice frequently died within hours. Detailed analyses of the LCMV infected mice revealed enterocyte apoptosis and implicated TNF produced by peptide-specific CD8+ T cells as the major mediator of disease. The caspase inhibitor zVADfmk had no demonstrable effect on the development of hypothermia, but diminished enterocyte apoptosis and greatly reduced the number of deaths. These findings, if similarly observed in patients, counsel caution when administering powerful immunogens such as peptide vaccines to individuals who may have a large preexisting pool of epitope-specific CD8+ T cells.
Authors
Fei Liu, Ralph Feuer, Daniel E. Hassett, J. Lindsay Whitton
Abstract
Depletion or dysfunction of CD4+ T lymphocytes profoundly perturbs host defenses and impairs immunogenicity of vaccines. Here, we show that plasmid DNA vaccination with a cassette encoding antigen (OVA) and a second cassette encoding full-length CD40 ligand (CD40L), a molecule expressed on activated CD4+ T lymphocytes and critical for T cell helper function, can elicit significant titers of antigen-specific immunoglobulins in serum and Tc1 CD8+ T cell responses in CD4-deficient mice. To investigate whether this approach leads to CD4+ T cell–independent vaccine protection against a prototypic AIDS-defining infection, Pneumocystis (PC) pneumonia, we used serum from mice vaccinated with PC-pulsed, CD40L-modifed DCs to immunoprecipitate PC antigens. Kexin, a PC antigen identified by this approach, was used in a similar DNA vaccine strategy with or without CD40L. CD4-deficient mice receiving DNA vaccines encoding Kexin and CD40L showed significantly higher anti-PC IgG titers as well as opsonic killing of PC compared with those vaccinated with Kexin alone. Moreover, CD4-depleted, Kexin-vaccinated mice showed a 3-log greater protection in a PC challenge model. Adoptive transfer of CD19+ cells or IgG to SCID mice conferred protection against PC challenge, indicating a role of humoral immunity in the protection. The results of these studies show promise for CD4-independent vaccination against HIV-related or other opportunistic pathogens.
Authors
Mingquan Zheng, Alistair J. Ramsay, Myles B. Robichaux, Karen A. Norris, Corrine Kliment, Christopher Crowe, Rekha R. Rapaka, Chad Steele, Florencia McAllister, Judd E. Shellito, Luis Marrero, Paul Schwarzenberger, Qiu Zhong, Jay K. Kolls
Abstract
Reovirus induces apoptosis in cultured cells and in vivo. In cell culture models, apoptosis is contingent upon a mechanism involving reovirus-induced activation of transcription factor NF-κB complexes containing p50 and p65/RelA subunits. To explore the in vivo role of NF-κB in this process, we tested the capacity of reovirus to induce apoptosis in mice lacking a functional nfkb1/p50 gene. The genetic defect had no apparent effect on reovirus replication in the intestine or dissemination to secondary sites of infection. In comparison to what was observed in wild-type controls, apoptosis was significantly diminished in the CNS of p50-null mice following reovirus infection. In sharp contrast, the loss of p50 was associated with massive reovirus-induced apoptosis and uncontrolled reovirus replication in the heart. Levels of IFN-β mRNA were markedly increased in the hearts of wild-type animals but not p50-null animals infected with reovirus. Treatment of p50-null mice with IFN-β substantially diminished reovirus replication and apoptosis, which suggests that IFN-β induction by NF-κB protects against reovirus-induced myocarditis. These findings reveal an organ-specific role for NF-κB in the regulation of reovirus-induced apoptosis, which modulates encephalitis and myocarditis associated with reovirus infection.
Authors
Sean M. O’Donnell, Mark W. Hansberger, Jodi L. Connolly, James D. Chappell, Melissa J. Watson, Janene M. Pierce, J. Denise Wetzel, Wei Han, Erik S. Barton, J. Craig Forrest, Tibor Valyi-Nagy, Fiona E. Yull, Timothy S. Blackwell, Jeffrey N. Rottman, Barbara Sherry, Terence S. Dermody
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ISSN: 0021-9738 (print), 1558-8238 (online)