Janice M. Moser

Yellow fever vaccine induces integrated multilineage and polyfunctional immune responses

Correlates of immune-mediated protection to most viral and cancer vaccines are still unknown. This impedes the development of novel vaccines to incurable diseases such as HIV and cancer. In this study, we have used functional genomics and polychromatic flow cytometry to define the signature of the immune response to the yellow fever (YF) vaccine 17D (YF17D) in a cohort of 40 volunteers followed for up to 1 yr after vaccination. We show that immunization with YF17D leads to an integrated immune response that includes several effector arms of innate immunity, including complement, the inflammasome, and interferons, as well as adaptive immunity as shown by an early T cell response followed by a brisk and variable B cell response. Development of these responses is preceded, as demonstrated in three independent vaccination trials and in a novel in vitro system of primary immune responses (modular immune in vitro construct [MIMIC] system), by the coordinated up-regulation of transcripts for specific transcription factors, including STAT1, IRF7, and ETS2, which are upstream of the different effector arms of the immune response. These results clearly show that the immune response to a strong vaccine is preceded by coordinated induction of master transcription factors that lead to the development of a broad, polyfunctional, and persistent immune response that integrates all effector cells of the immune system.

CD94-NKG2A receptors regulate antiviral CD8+ T cell responses

CD8+ T lymphocytes mediate immunosurveillance against persistent virus infections and virus-induced neoplasia. Polyoma virus, a highly oncogenic natural mouse DNA virus, establishes persistent infection, but only a few mice are highly susceptible to tumors induced by the virus. Mature antiviral CD8+ T cells expand in tumor-susceptible mice, but their cytotoxic effector activity is nonfunctional in vivo. Here we show that the natural killer cell inhibitory receptor, CD94-NKG2A, is up-regulated by antiviral CD8+ T cells during acute polyoma infection and is responsible for down-regulating their antigen-specific cytotoxicity during both viral clearance and virus-induced oncogenesis.

CD8 Binding to MHC Class I Molecules Is Influenced by T Cell Maturation and Glycosylation

CD8 serves both as an adhesion molecule for class I MHC molecules and as a coreceptor with the TCR for T cell activation. Here we study the developmental regulation of CD8-mediated binding to noncognate peptide/MHC ligands (i.e., those not bound by the TCR). We show that CD8s ability to bind soluble class I MHC tetramers and to mediate T cell adhesion under shear flow conditions diminishes as double-positive thymocytes mature into CD8(+) T cells. Furthermore, we provide evidence that this decreased CD8 binding results from increased T cell sialylation upon T cell maturation. These data suggest that CD8s ability to interact with class I MHC is not fixed and is developmentally regulated through the T cells glycosylation state.

Cutting Edge: Rapid In Vivo CTL Activity by Polyoma Virus-Specific Effector and Memory CD8+ T Cells

For viruses that establish persistent infection, continuous immunosurveillance by effector-competent antiviral CD8+ T cells is likely essential for limiting viral replication. Although it is well documented that virus-specific memory CD8+ T cells synthesize cytokines after short term in vitro stimulation, there is limited evidence that these T cells exhibit cytotoxicity, the dominant antiviral effector function. Here, we show that antiviral CD8+ T cells in mice acutely infected by polyoma virus, a persistent mouse pathogen, specifically eliminate viral peptide-pulsed donor spleen cells within minutes after adoptive transfer and do so via a perforin-dependent mechanism. Antiviral memory CD8+ T cells were similarly capable of rapidly mobilizing potent Ag-specific cytotoxic activity in vivo. These findings strongly support the concept that a cytotoxic effector-memory CD8+ T cell population operates in vivo to control this persistent viral infection.

Inhibition of NF-κB Activation In Vivo Impairs Establishment of Gammaherpesvirus Latency

A critical determinant in chronic gammaherpesvirus infections is the ability of these viruses to establish latency in a lymphocyte reservoir. The nuclear factor (NF)-κB family of transcription factors represent key players in B-cell biology and are targeted by gammaherpesviruses to promote host cell survival, proliferation, and transformation. However, the role of NF-κB signaling in the establishment of latency in vivo has not been addressed. Here we report the generation and in vivo characterization of a recombinant murine gammaherpesvirus 68 (γHV68) that expresses a constitutively active form of the NF-κB inhibitor, IκBαM. Inhibition of NF-κB signaling upon infection with γHV68-IκBαM did not affect lytic replication in cell culture or in the lung following intranasal inoculation. However, there was a substantial decrease in the frequency of latently infected lymphocytes in the lung (90% reduction) and spleens (97% reduction) 16 d post intranasal inoculation. Importantly, the defect in establishment of latency in lung B cells could not be overcome by increasing the dose of virus 100-fold. The observed decrease in establishment of viral latency correlated with a loss of activated, CD69hi B cells in both the lungs and spleen at day 16 postinfection, which was not apparent by 6 wk postinfection. Constitutive expression of Bcl-2 in B cells did not rescue the defect in the establishment of latency observed with γHV68-IκBαM, indicating that NF-κB–mediated functions apart from Bcl-2–mediated B-cell survival are critical for the efficient establishment of gammaherpesvirus latency in vivo. In contrast to the results obtained following intranasal inoculation, infection of mice with γHV68-IκBαM by the intraperitoneal route had only a modest impact on splenic latency, suggesting that route of inoculation may alter requirements for establishment of virus latency in B cells. Finally, analyses of the pathogenesis of γHV68-IκBαM provides evidence that NF-κB signaling plays an important role during multiple stages of γHV68 infection in vivo and, as such, represents a key host regulatory pathway that is likely manipulated by the virus to establish latency in B cells.

DNA Vaccines for Influenza Virus: Differential Effects of Maternal Antibody on Immune Responses to Hemagglutinin and Nucleoprotein

ABSTRACT Maternal antibody is the major form of protection from disease in early life when the neonatal immune system is still immature; however, the presence of maternal antibody also interferes with active immunization, placing infants at risk for severe bacterial and viral infection. We tested the ability of intramuscular and gene gun immunization with DNA expressing influenza virus hemagglutinin (HA) and nucleoprotein (NP) to raise protective humoral and cellular responses in the presence or absence of maternal antibody. Neonatal mice born to influenza virus-immune mothers raised full antibody responses to NP but failed to generate antibody responses to HA. In contrast, the presence of maternal antibody did not affect the generation of long-lived CD8+ T-cell responses to both HA and NP. Thus, maternal antibody did not affect cell-mediated responses but did affect humoral responses, with the ability to limit the antibody response correlating with whether the DNA-expressed immunogen was localized in the plasma membrane or within the cell.

A gammaherpesvirus-secreted activator of Vβ4+ CD8+ T cells regulates chronic infection and immunopathology

Little is known about herpesvirus modulation of T cell activation in latently infected individuals or the implications of such for chronic immune disorders. Murine gammaherpesvirus 68 (MHV68) elicits persistent activation of CD8+ T cells bearing a Vβ4+ T cell receptor (TCR) by a completely unknown mechanism. We show that a novel MHV68 protein encoded by the M1 gene is responsible for Vβ4+ CD8+ T cell stimulation in a manner reminiscent of a viral superantigen. During infection, M1 expression induces a Vβ4+ effector T cell response that resists functional exhaustion and appears to suppress virus reactivation from peritoneal cells by means of long-term interferon-γ (IFNγ) production. Mice lacking an IFNγ receptor (IFNγR−/−) fail to control MHV68 replication, and Vβ4+ and CD8+ T cell activation by M1 instead contributes to severe inflammation and multiorgan fibrotic disease. Thus, M1 manipulates the host CD8+ T cell response in a manner that facilitates latent infection in an immunocompetent setting, but promotes disease during a dysregulated immune response. Identification of a viral pathogenecity determinant with superantigen-like activity for CD8+ T cells broadens the known repertoire of viral immunomodulatory molecules, and its function illustrates the delicate balance achieved between persistent viruses and the host immune response.

A Gammaherpesvirus 68 Gene 50 Null Mutant Establishes Long-Term Latency in the Lung but Fails To Vaccinate against a Wild-Type Virus Challenge

ABSTRACT The gammaherpesvirus immediate-early genes are critical regulators of virus replication and reactivation from latency. Rta, encoded by gene 50, serves as the major transactivator of the lytic program and is highly conserved among all the gammaherpesviruses, including Epstein-Barr virus, Kaposis sarcoma-associated herpesvirus, and murine gammaherpesvirus 68 (γHV68). Introduction of a translation stop codon in γHV68 gene 50 (gene 50.stop γHV68) demonstrated that Rta is essential for virus replication in vitro. To investigate the role that virus replication plays in the establishment and maintenance of latency, we infected mice with gene 50.stop γHV68. Notably, the gene 50.stop virus established a long-term infection in lung B cells following intranasal infection of mice but was unable to establish latency in the spleen. This complete block in the establishment of latency in the spleen was also seen when lytic virus production was inhibited by treating mice infected with wild-type virus with the antiviral drug cidofovir, implicating virus replication and not an independent function of Rta in the establishment of splenic latency. Furthermore, we showed that gene 50.stop γHV68 was unable to prime the immune system and was unable to protect against a challenge with wild-type γHV68, despite its ability to chronically infect lung B cells. These data indicate gammaherpesviruses that are unable to undergo lytic replication in vivo may not be viable vaccine candidates despite the detection of cells harboring viral genome at late times postinfection.

Optimization of a dendritic cell-based assay for the in vitro priming of naïve human CD4+ T cells.

Methods to prime human CD4(+) T cells in vitro would be of significant value for the pre-clinical evaluation of vaccine candidates and other immunotherapeutics. However, to date, there is no reliable method for the induction of primary human T cell responses in the laboratory. Here, we optimized a culture strategy incorporating highly purified lymphocytes and dendritic cells, in the absence of any exogenous growth factors, for the in vitro sensitization of naïve CD4(+) T cells against a variety of protein antigens. This fully autologous approach, which was superior to the more traditional PBMC assay for supporting the induction of primary human T helper cell responses in culture, elicited effector cells capable of producing a variety of Th cytokines, including IFNgamma, TNFalpha, IL-2, IL-5, IL-17 and IL-21, and memory cells that could be restimulated multiple times with a specific antigen. Through simple modifications to this culture method, we evaluated the role of dendritic cell maturation state and regulatory T cells on the sensitization of naïve T helper cells, which highlights its utility for addressing basic questions of human immunobiology. Finally, using the formulated yellow fever vaccine, YF-VAX (R), we provide a proof-of-concept demonstration of the utility of the system for evaluating the T cell immunogenicity of vaccine candidates in a pre-clinical setting.

Role for MyD88 Signaling in Murine Gammaherpesvirus 68 Latency

ABSTRACT Toll-like receptors (TLRs) are known predominantly for their role in activating the innate immune response. Recently, TLR signaling via MyD88 has been reported to play an important function in development of a B-cell response. Since B cells are a major latency reservoir for murine gammaherpesvirus 68 (MHV68), we investigated the role of TLR signaling in the establishment and maintenance of MHV68 latency in vivo. Mice deficient in MyD88 (MyD88−/−) or TLR3 (TLR3−/−) were infected with MHV68. Analysis of splenocytes recovered at day 16 postinfection from MyD88−/− mice compared to those from wild-type control mice revealed a lower frequency of (i) activated B cells, (ii) germinal-center B cells, and (iii) class-switched B cells. Accompanying this substantial defect in the B-cell response was an approximately 10-fold decrease in the establishment of splenic latency. In contrast, no defect in viral latency was observed in TLR3−/− mice. Analysis of MHV68-specific antibody responses also demonstrated a substantial decrease in the kinetics of the response in MyD88−/− mice. Analysis of wild-type × MyD88−/− mixed-bone-marrow chimeric mice demonstrated that there is a selective failure of MyD88−/− B cells to participate in germinal-center reactions as well as to become activated and undergo class switching. In addition, while MHV68 established latency efficiently in the MyD88-sufficient B cells, there was again a ca. 10-fold reduction in the frequency of MyD88−/− B cells harboring latent MHV68. This phenotype indicates that MyD88 is important for the establishment of MHV68 latency and is directly related to the role of MyD88 in the generation of a B-cell response. Furthermore, the generation of a B-cell response to MHV68 was intrinsic to B cells and was independent of the interleukin-1 receptor, a cytokine receptor that also signals through MyD88. These data provide evidence for a unique role for MyD88 in the establishment of MHV68 latency.