Annette Hadley

Polyomavirus-Infected Dendritic Cells Induce Antiviral CD8+ T Lymphocytes

ABSTRACT CD8+ T cells are critical for the clearance of acute polyomavirus infection and the prevention of polyomavirus-induced tumors, but the antigen-presenting cell(s) involved in generating polyomavirus-specific CD8+ T cells have not been defined. We investigated whether dendritic cells and macrophages are permissive for polyomavirus infection and examined their potential for inducing antiviral CD8+ T cells. Although dendritic cells and macrophages both supported productive polyomavirus infection, dendritic cells were markedly more efficient at presenting the immunodominant viral epitope to CD8+ T cells. Additionally, infected dendritic cells, but not infected macrophages, primed anti-polyomavirus CD8+ T cells in vivo. Treatment with Flt3 ligand, a hematopoietic growth factor that dramatically expands the number of dendritic cells, markedly enhanced the magnitude of virus-specific CD8+ T-cell responses during acute infection and the pool of memory anti-polyomavirus CD8+ T cells. These findings suggest that virus-infected dendritic cells induce polyomavirus-specific CD8+ T cells in vivo and raise the potential for their use as cellular adjuvants to promote CD8+ T cell surveillance against polyomavirus-induced tumors.

An MHC class Ib–restricted CD8 T cell response confers antiviral immunity

Although immunity against intracellular pathogens is primarily provided by CD8 T lymphocytes that recognize pathogen-derived peptides presented by major histocompatibility complex (MHC) class Ia molecules, MHC class Ib–restricted CD8 T cells have been implicated in antiviral immunity. Using mouse polyoma virus (PyV), we found that MHC class Ia–deficient (Kb−/−Db−/−) mice efficiently control this persistently infecting mouse pathogen. CD8 T cell depletion mitigates clearance of PyV in Kb−/−Db−/− mice. We identified the ligand for PyV-specific CD8 T cells in Kb−/−Db−/− mice as a nonamer peptide from the VP2 capsid protein presented by Q9, a member of the β2 microglobulin–associated Qa-2 family. Using Q9-VP2 tetramers, we monitored delayed but progressive expansion of these antigen-specific CD8αβ T cells in Kb−/−Db−/− mice. Importantly, we demonstrate that Q9-VP2–specific CD8 T cells more effectively clear wild-type PyV than a VP2 epitopenull mutant PyV. Finally, we show that wild-type mice also generate Q9-restricted VP2 epitope–specific CD8 T cells to PyV infection. To our knowledge, this is the first evidence for a defined MHC class Ib–restricted antiviral CD8 T cell response that contributes to host defense. This study motivates efforts to uncover MHC class Ib–restricted CD8 T cell responses in other viral infections, and given the limited polymorphism of MHC class Ib molecules, it raises the possibility of developing peptide-based viral vaccines having broad coverage across MHC haplotypes.

Characterization of corneal endothelium cell cultured on microporous membrane filters

In these experiments we characterize rabbit and bovine corneal endothelia cell cultured on microporous membrane filters (0.6cm2). Cell cultured bovine or rabbit corneal endothelial cells (subcultures 1-3) were seeded onto Millicell-HA filter inserts. Electrical resistance measured across the cultured monolayers increased steadily through 14 days of culture, reaching 34.2 +/- 0.8 ohm-cm2 (mean +/- SE) for rabbit cells and 33.1 +/- 1.1 ohm-cm2 for bovine cells. Alizarin red staining of the monolayers showed a polygonal morphology comparable to that observed in situ. Transmission electron microscopy showed well developed apical junctional complexes and flaps. Exposure of the monolayers to calcium-free medium resulted in the disruption of intercellular junctions, rounding-up of the cells and a decrease in electrical resistance (to near 0). Transmonolayer fluxes of inulin and dextran correlated well to the resistance measurements. Results of this study demonstrate that corneal endothelium, both bovine and rabbit, grown on filter inserts is comparable in morphology and ultrastructure to corneal endothelium in situ. The cells cultured in this system form functional apical junctional complexes that effect a barrier function comparable to that of the endothelium in situ.

Heterogeneity among viral antigen-specific CD4+ T cells and their de novo recruitment during persistent polyomavirus infection

Virus-specific CD4+ T cells optimize antiviral responses by providing help for antiviral humoral responses and CD8+ T cell differentiation. Although CD4+ T cell responses to viral infections that undergo complete clearance have been studied extensively, less is known about virus-specific CD4+ T cell responses to viruses that persistently infect their hosts. Using a mouse polyomavirus (MPyV) infection model, we previously demonstrated that CD4+ T cells are essential for recruiting naive MPyV-specific CD8+ T cells in persistently infected mice. In this study, we defined two dominant MPyV-specific CD4+ T cell populations, one directed toward an epitope derived from the nonstructural large T Ag and the other from the major viral capsid protein of MPyV. These MPyV-specific CD4+ T cells vary in terms of their magnitude, functional profile, and phenotype during acute and persistent phases of infection. Using a minimally myeloablative-mixed bone marrow chimerism approach, we further show that naive virus-specific CD4+ T cells, like anti-MPyV CD8+ T cells, are primed de novo during persistent virus infection. In summary, these findings reveal quantitative and qualitative differences in the CD4+ T cell response to a persistent virus infection and demonstrate that naive antiviral CD4+ T cells are recruited during chronic polyomavirus infection.

Gamma Interferon Controls Mouse Polyomavirus Infection In Vivo

ABSTRACT Human polyomaviruses are associated with substantial morbidity in immunocompromised patients, including those with HIV/AIDS, recipients of bone marrow and kidney transplants, and individuals receiving immunomodulatory agents for autoimmune and inflammatory diseases. No effective antipolyomavirus agents are currently available, and no host determinants have been identified to predict susceptibility to polyomavirus-associated diseases. Using the mouse polyomavirus (MPyV) infection model, we recently demonstrated that perforin-granzyme exocytosis, tumor necrosis factor alpha (TNF-α), and Fas did not contribute to control of infection or virus-induced tumors. Gamma interferon (IFN-γ) was recently shown to inhibit replication by human BK polyomavirus in primary cultures of renal tubular epithelial cells. In this study, we provide evidence that IFN-γ is an important component of the host defense against MPyV infection and tumorigenesis. In immortalized and primary cells, IFN-γ reduces expression of MPyV proteins and impairs viral replication. Mice deficient for the IFN-γ receptor (IFN-γR−/−) maintain higher viral loads during MPyV infection and are susceptible to MPyV-induced tumors; this increased viral load is not associated with a defective MPyV-specific CD8+ T cell response. Using an acute MPyV infection kidney transplant model, we further show that IFN-γR−/− donor kidneys harbor higher MPyV levels than donor kidneys from wild-type mice. Finally, administration of IFN-γ to persistently infected mice significantly reduces MPyV levels in multiple organs, including the kidney, a major reservoir for persistent mouse and human polyomavirus infections. These findings demonstrate that IFN-γ is an antiviral effector molecule for MPyV infection.

CD8 T Cells Recruited Early in Mouse Polyomavirus Infection Undergo Exhaustion

Repetitive Ag encounter, coupled with dynamic changes in Ag density and inflammation, imparts phenotypic and functional heterogeneity to memory virus-specific CD8 T cells in persistently infected hosts. For herpesvirus infections, which cycle between latency and reactivation, recent studies demonstrate that virus-specific T cell memory is predominantly derived from naive precursors recruited during acute infection. Whether functional memory T cells to viruses that persist in a nonlatent, low-level infectious state (smoldering infection) originate from acute infection-recruited naive T cells is not known. Using mouse polyomavirus (MPyV) infection, we previously showed that virus-specific CD8 T cells in persistently infected mice are stably maintained and functionally competent; however, a sizeable fraction of these memory T cells are short-lived. Further, we found that naive anti-MPyV CD8 T cells are primed de novo during persistent infection and contribute to maintenance of the virus-specific CD8 T cell population and its phenotypic heterogeneity. Using a new MPyV-specific TCR-transgenic system, we now demonstrate that virus-specific CD8 T cells recruited during persistent infection possess multicytokine effector function, have strong replication potential, express a phenotype profile indicative of authentic memory capability, and are stably maintained. In contrast, CD8 T cells recruited early in MPyV infection express phenotypic and functional attributes of clonal exhaustion, including attrition from the memory pool. These findings indicate that naive virus-specific CD8 T cells recruited during persistent infection contribute to preservation of functional memory against a smoldering viral infection.

Induction of Polyomavirus-Specific CD8+T Lymphocytes by Distinct Dendritic Cell Subpopulations

ABSTRACT Dendritic cells are pivotal antigen-presenting cells for generating adaptive T-cell responses. Here, we show that dendritic cells belonging to either the myeloid-related or lymphoid-related subset are permissive for infection by mouse polyomavirus and, when loaded with a peptide corresponding to the immunodominant anti-polyomavirus CD8+T-cell epitope or infected by polyomavirus, are each capable of driving expansion of primary polyomavirus-specific CD8+ T-cell responses in vivo.

MHC class Ib-restricted CD8 T cells differ in dependence on CD4 T cell help and CD28 costimulation over the course of mouse polyomavirus infection

We recently identified a protective MHC class Ib-restricted CD8 T cell response to infection with mouse polyomavirus. These CD8 T cells recognize a peptide from aa 139–147 of the VP2 viral capsid protein bound to the nonpolymorphic H-2Q9 molecule, a member of the Qa-2 family of β2m-associated MHC class Ib molecules. Q9:VP2.139-specific CD8 T cells exhibit an unusual inflationary response characterized by a gradual expansion over 3 mo followed by a stable maintenance phase. We previously demonstrated that Q9:VP2.139-specific CD8 T cells are dependent on Ag for expansion, but not for long-term maintenance. In this study, we tested the hypothesis that the expansion and maintenance components of the Q9:VP2.139-specific T cell response are differentially dependent on CD4 T cell help and CD28 costimulation. Depletion of CD4+ cells and CD28/CD40L blockade impaired expansion of Q9:VP2.139-specific CD8 T cells, and intrinsic CD28 signaling was sufficient for expansion. In contrast, CD4 T cell insufficiency, but not CD28/CD40L blockade, resulted in a decline in frequency of Q9:VP2.139-specific CD8 T cells during the maintenance phase. These results indicate that the Q9:VP2.139-specific CD8 T cell response to mouse polyomavirus infection depends on CD4 T cell help and CD28 costimulation for inflationary expansion, but only on CD4 T cell help for maintenance.

Attrition of memory CD8 T cells during sepsis requires LFA-1

CD8 T cell loss and dysfunction have been implicated in the increased susceptibility to opportunistic infections during the later immunosuppressive phase of sepsis, but CD8 T cell activation and attrition in early sepsis remain incompletely understood. With the use of a CLP model, we assessed CD8 T cell activation at 5 consecutive time points and found that activation after sepsis results in a distinct phenotype (CD69+CD25intCD62LHI) independent of cognate antigen recognition and TCR engagement and likely through bystander‐mediated cytokine effects. Additionally, we observed that sepsis concurrently results in the preferential depletion of a subset of memory‐phenotype CD8 T cells that remain “unactivated” (i.e., fail to up‐regulate activation markers) by apoptosis. Unactivated CD44HI OT‐I cells were spared from sepsis‐induced attrition, as were memory‐phenotype CD8 T cells of mice treated with anti‐LFA‐1 mAb, 1 h after CLP. Perhaps most importantly, we demonstrate that attrition of memory phenotype cells may have a pathologic significance, as elevated IL‐6 levels were associated with decreased numbers of memory‐phenotype CD8 T cells in septic mice, and preservation of this subset after administration of anti‐LFA‐1 mAb conferred improved survival at 7 d. Taken together, these data identify potentially modifiable responses of memory‐phenotype CD8 T cells in early sepsis and may be particularly important in the application of immunomodulatory therapies in sepsis.

CXCR4 blockade decreases CD4+ T cell exhaustion and improves survival in a murine model of polymicrobial sepsis

Sepsis is a dysregulated systemic response to infection involving many inflammatory pathways and the induction of counter-regulatory anti-inflammatory processes that results in a state of immune incompetence and can lead to multi-organ failure. CXCR4 is a chemokine receptor that, following ligation by CXCL12, directs cells to bone marrow niches and also plays an important role in T cell cosignaling and formation of the immunological synapse. Here, we investigated the expression and function of CXCR4 in a murine model of polymicrobial sepsis. Results indicate that CXCR4 is selectively upregulated on naïve CD4+ and CD8+ T cells and CD4+ central memory T cells following the induction of sepsis, and that CXCR4 antagonism resulted in a significant decrease in sepsis-induced mortality. We probed the mechanistic basis for these findings and found that CXCR4 antagonism significantly increased the number of peripheral CD4+ and CD8+ T cells following sepsis. Moreover, mice treated with the CXCR4 antagonist contained fewer PD-1+ LAG-3+ 2B4+ cells, suggesting that blockade of CXCR4 mitigates CD4+ T cell exhaustion during sepsis. Taken together, these results characterize CXCR4 as an important pathway that modulates immune dysfunction and mortality following sepsis, which may hold promise as a target for future therapeutic intervention in septic patients.