Transient decreases in human T cell proliferative responses following vaccinia immunization

Immune modulation in primary vaccinia virus zoonotic human infections

In 2010, the WHO celebrated the 30th anniversary of the smallpox eradication. Ironically, infections caused by viruses related to smallpox are being increasingly reported worldwide, including Monkeypox, Cowpox, and Vaccinia virus (VACV). Little is known about the human immunological responses elicited during acute infections caused by orthopoxviruses. We have followed VACV zoonotic outbreaks taking place in Brazil and analyzed cellular immune responses in patients acutely infected by VACV. Results indicated that these patients show a biased immune modulation when compared to noninfected controls. Amounts of B cells are low and less activated in infected patients. Although present, T CD4⁺ cells are also less activated when compared to noninfected individuals, and so are monocytes/macrophages. Similar results were obtained when Balb/C mice were experimentally infected with a VACV sample isolated during the zoonotic outbreaks. Taking together, the data suggest that zoonotic VACVs modulate specific immune cell compartments during an acute infection in humans.

Cytokine-armed vaccinia virus infects the mesothelioma tumor microenvironment to overcome immune tolerance and mediate tumor resolution

Intratumoral (i.t.) administration of cytokine genes expressed by viral vectors represents a rational approach that induces cytokine secretion at the site they are needed, and i.t. vaccinia virus (VV) has shown promise in mesothelioma patients. However, we and others have shown that the mesothelioma tumor microenvironment includes macrophages, dendritic cells (DCs), and T cells. Therefore, we investigated which of these cell types are infected after exposure to VV or Fowlpox virus (FPV)-cytokine gene constructs. In vitro studies showed that mesothelioma tumor cells were resistant to FPV infection yet highly permissive to infection by VV vectors resulting in significant cytokine production and impaired proliferation. Macrophages secreted low levels of cytokine suggestive of resistance to overt infection. DCs transiently secreted virally derived cytokines, but did not mature during VV infection. VV inhibition of T cell proliferation was rescued by the interleukin (IL)-2 and IL-12 VV constructs. In vivo studies of murine mesotheliomas showed that i.t. injection of the parent VV could not hinder tumor progression. In contrast, the VV-cytokine constructs induced profound tumor regression. These data suggest that i.t. VV-cytokine gene constructs retard tumor growth by infecting mesothelioma cells and targeting the immune system through tumor-infiltrating DC and T cells.

Diminished intracellular invariant chain expression after vaccinia virus infection

Vaccinia virus (VV) has been used as a vaccine to eradicate smallpox and as a vaccine for HIV and tumors. However, the immunoevasive properties of VV have raised safety concerns. VV infection of APCs perturbs MHC class II-mediated Ag presentation. Exposure of human B cell lines to VV induced a substantial reduction in cellular expression of the class II chaperone, invariant chain (Ii), during the late stages (i.e., 8-10 h) of infection. Yet, cell viability and surface expression of MHC class II molecules were maintained up to 24 h after exposure to virus. Reductions in Ii and class II mRNA levels were detected as early as 6 h after VV infection of APCs. To examine whether VV was acting solely to disrupt host protein synthesis, B cells were treated with an inhibitor of translation, cycloheximide (CHX). Within 1 h of B cell CHX treatment, Ii protein expression decreased coupled with a loss of class II presentation. Analysis of Ii degradation in VV- or CHX-treated cells, revealed ongoing Ii proteolysis contributing to reduced steady-state Ii levels in these APC. Yet in contrast with CHX, VV infection of APCs altered lysosomal protease expression and Ii degradation. Virus infection induced cellular cathepsin L expression while reducing the levels of other lysosomal proteases. These results demonstrate that at late stages of VV infection, reductions in cellular Ii levels coupled with changes in lysosomal protease activity, contribute in part to defects in class II presentation.

Human CD8+ T cell memory generation in Puumala hantavirus infection occurs after the acute phase and is associated with boosting of EBV-specific CD8+ memory T cells

The induction and maintenance of T cell memory is incompletely understood, especially in humans. We have studied the T cell response and the generation of memory during acute infection by the Puumala virus (PUUV), a hantavirus endemic to Europe. It causes a self-limiting infection with no viral persistence, manifesting as hemorrhagic fever with renal syndrome. HLA tetramer staining of PBMC showed that the CD8(+) T cell response peaked at the onset of the clinical disease and decreased within the next 3 wk. Expression of activation markers on the tetramer-positive T cells was also highest during the acute phase, suggesting that the peak population consisted largely of effector cells. Despite the presence of tetramer-positive T cells expressing cytoplasmic IFN-gamma, PUUV-specific cells producing IFN-gamma in vitro were rare during the acute phase. Their frequency, as well as the expression of IL-7R alpha mRNA and surface protein, increased during a follow-up period of 6 wk and probably reflected the induction of memory T cells. Simultaneously with the PUUV-specific response, we also noted in seven of nine patients an increase in EBV-specific T cells and the transient presence of EBV DNA in three patients, indicative of viral reactivation. Our results show that in a natural human infection CD8(+) memory T cells are rare during the peak response, gradually emerging during the first weeks of convalescence. They also suggest that the boosting of unrelated memory T cells may be a common occurrence in human viral infections, which may have significant implications for the homeostasis of the memory T cell compartment.

Vaccinia virus infection induces dendritic cell maturation but inhibits antigen presentation by MHC class II

Vaccinia virus (VV) infection is known to inhibit dendritic cells (DC) functions in vitro. Paradoxically, VV is also highly immunogenic and thus has been used as a vaccine. In the present study, we investigated the effects of an in vivo VV infection on DC function by focusing on early innate immunity. Our data indicated that DC are activated upon in vivo VV infection of mice. Splenic DC from VV-infected mice expressed elevated levels of MHC class I and co-stimulatory molecules on their cell surface and exhibited the enhanced potential to produce cytokines upon LPS stimulation. DC from VV-infected mice also expressed a high level of interferon-beta. However, a VV infection resulted in the down-regulation of MHC class II expression and the impairment of antigen presentation to CD4 T cells by DC. Thus, during the early stage of a VV infection, although DC are impaired in some of the critical antigen presentation functions, they can promote innate immune defenses against viral infection.

Immune responses to vaccinia and influenza elicited during primary versus recent or distant secondary smallpox vaccination of adults

The kinetics and frequency of the primary response to human smallpox vaccine was compared to that among subjects re-vaccinated within the last 2 years, or after several decades. Vaccination induced local and systemic reactions that were mildest in the distant cohort and more severe in the primary vaccinees. The timing of IFN-gamma responses was similar in all three groups, but of higher frequency in the primary vaccinees. Responses to vaccinia re-immunization between those immunized <2 years ago and those immunized >10 years ago were not significantly different. Neutralizing antibodies were boosted in all groups, with the highest titers observed among the distant cohort. However, the antibody and IFN-gamma responses did not correlate strongly with the local reactions at the vaccine site. This suggests that local immune events in the tissue are distinct from the parameters measured in the peripheral blood.

Disruption of MHC class II-restricted antigen presentation by vaccinia virus

Vaccinia virus (VV), currently used in humans as a live vaccine for smallpox, can interfere with host immunity via several discrete mechanisms. In this study, the effect of VV on MHC class II-mediated Ag presentation was investigated. Following VV infection, the ability of professional and nonprofessional APC to present Ag and peptides to CD4+ T cells was impaired. Viral inhibition of class II Ag presentation could be detected within 1 h, with diminished T cell responses dependent upon the duration of APC infection and virus titer. Exposure of APC to replication-deficient virus also diminished class II Ag presentation. Virus infection of APC perturbed Ag presentation by newly synthesized and recycling class II molecules, with disruptions in both exogenous and cytoplasmic Ag presentation. Virus-driven expression of an endogenous Ag, failed to restore T cell responsiveness specific for this Ag in the context of MHC class II molecules. Yet, both class II protein steady-state and cell surface expression were not altered by VV. Biochemical and functional analysis revealed that VV infection directly interfered with ligand binding to class II molecules. Together, these observations suggest that disruption of MHC class II-mediated Ag presentation may be one of multiple strategies VV has evolved to escape host immune surveillance.

Perspectives on cancer immuno-epidemiology

Estimating human cancer risk based on host-environment interaction is one task of epidemiology, and it has provided indispensable knowledge for prevention of cancer. The recent develop-ment of gene-engineered mice has also provided solid evidence about the relationship between cancer development and immunity. The aim of this review is to discuss the possible contribution of epidemiology to understanding the role of immunity in host defense against cancer, and also to assess the involvement of inflammation in the occurrence of selected cancers. Here we look at the concepts of cancer immunosurveillance and infection-inflammation-cancer, and include a brief introduction to recent studies in humans and experimental animal models. It has been postulated for many years that the immune system has the ability to recognize and eliminate nascent transformed cells in the body (so-called cancer immunosurveillance hypothesis), and this idea has recently obtained strong support from animal experiments. In humans, follow-up studies among immunosuppressed transplant recipients revealed a remarkably increased risk of not only selected malignancies, but also cancers with no known viral etiology. On the other hand, a prospective cohort study among the general population revealed that individuals with low natural cytotoxic activity of peripheral blood lymphocytes had an increased risk of cancer development. More studies are warranted to allow the construction of a model for the interaction between host immunity, aging, and the environment. The host immune system is also involved in inflammatory responses to pathogen infection: insufficient immune function of the host, or repeated infection, may result in persistent inflammation, where growth/survival factors continuously act on initiated cells. The combined use of biomarkers will be necessary to define low-grade persistent inflammation in future cohort studies; and, in addition to these phenotype marker-based cohort studies, one plausible future direction will be a genomic approach that can be undertaken within cohort studies, looking at the genetic background underlying individual variations in phenotype markers.

Inability to induce tolerance through direct antigen presentation

Both the direct and indirect antigen presentation pathways are important mechanisms for T cell-mediated allograft rejection. Studies using knockout mice and monoclonal antibodies have demonstrated that CD4+ T cells are both necessary and sufficient for the rejection of allogeneic tissues, including skin, heart, and islet. Furthermore, combined blockade of the CD28/B7 and CD154/CD40 costimulatory pathways induces tolerance in multiple CD4+ T-cell dependent allograft models. In this study, we addressed the T-cell requirement for costimulation in direct antigen presentation. We demonstrated that class II-specific alloreactive T-cell receptor transgenic T cells were sufficient to mediate allograft rejection independent of costimulatory blockade. Analysis of the costimulatory capacity of different antigen presenting cell (APC) populations demonstrated that APCs resident within the donor skin, Langerhans cells, are potent stimulators not requiring CD28- or CD154-dependent costimulation for direct major histocompatibility complex (MHC) antigen presentation. These results complement previous work examining the role of costimulation on CD8+ T cells, supporting a model in which the effectiveness of costimulatory blockade in the setting of transplantation may be selective for the indirect pathway of MHC alloantigen presentation.