Immune evasion during foot-and-mouth disease virus infection of swine

miR-361 and miR-34a suppress foot-and-mouth disease virus proliferation by activating immune response signaling in PK-15 cells

Foot-and-mouth disease (FMD) severely impacts cloven-hoofed live-stock production, leading to serious economic losses and international restriction on the trade of animals and animal products worldwide. MiRNAs serve key roles in viral immunity and regulation. However, the knowledge about miRNAs regulation in FMDV infection is still limited. In this study, we found that FMDV infection caused rapid cytopathic in PK-15 cell. To investigate the miRNAs' function in FMDV infection, we performed knockdown of endogenous Dgcr8 using its specific siRNA and found that interference of Dgcr8 inhibited cellular miRNA expression and increased FMDV production, including viral capsid proteins expression, viral genome copies and virus titer, suggesting that miRNAs play an important role in FMDV infection. To obtain a full perspective on miRNA expression profiling after FMDV infection, we performed miRNA sequencing and found that FMDV infection caused inhibition of miRNA expression in PK-15 cells. Together with the target prediction result, miR-34a and miR-361 were screened for further study. Function study showed that no matter plasmid or mimics-mediated overexpression of miR-34a and miR-361 both suppressed FMDV replication, while inhibition of endogenous miR-34a and miR-361 expression using specific inhibitors significantly increased FMDV replication. Further study showed that miR-34a and miR-361 stimulated IFN-β promoter activity and activated interferon-stimulated response element (ISRE). In addition, ELISA test found that miR-361 and miR-34a increased secretion level of IFN-β and IFN-γ, which may contribute to repression of FMDV replication. This study preliminary revealed that miR-361 and miR-34a inhibited FMDV proliferation via stimulating immune response.

Interleukin-10-Mediated Lymphopenia Caused by Acute Infection with Foot-and-Mouth Disease Virus in Mice

Foot-and-mouth disease (FMD) is characterized by a pronounced lymphopenia that is associated with immune suppression. However, the mechanisms leading to lymphopenia remain unclear. In this study, the number of total CD4⁺, CD8⁺ T cells, B cells, and NK cells in the peripheral blood were dramatically reduced in C57BL/6 mice infected with foot-and-mouth disease virus (FMDV) serotype O, and it was noted that mice with severe clinical symptoms had expressively lower lymphocyte counts than mice with mild or without clinical symptoms, indicating that lymphopenia was associated with disease severity. A further analysis revealed that lymphocyte apoptosis and trafficking occurred after FMDV infection. In addition, coinhibitory molecules were upregulated in the expression of CD4⁺ and CD8⁺ T cells from FMDV-infected mice, including CTLA-4, LAG-3, 2B4, and TIGIT. Interestingly, the elevated IL-10 in the serum was correlated with the appearance of lymphopenia during FMDV infection but not IL-6, IL-2, IL-17, IL-18, IL-1β, TNF-α, IFN-α/β, TGF-β, and CXCL1. Knocking out IL-10 (IL-10^-/-) mice or blocking IL-10/IL-10R signaling in vivo was able to prevent lymphopenia via downregulating apoptosis, trafficking, and the coinhibitory expression of lymphocytes in the peripheral blood, which contribute to enhance the survival of mice infected with FMDV. Our findings support that blocking IL-10/IL-10R signaling may represent a novel therapeutic approach for FMD.

Foot-and-Mouth Disease Virus VP3 Protein Acts as a Critical Proinflammatory Factor by Promoting Toll-Like Receptor 4-Mediated Signaling

Foot-and-mouth disease virus (FMDV) infection in cloven-hoofed animals causes severe inflammatory symptoms, including blisters on the oral mucosa, hoof, and breast; however, the molecular mechanism underlying the inflammatory response is unclear. In this study, we provide the first evidence that the FMDV protein VP3 activates lipopolysaccharide-triggered Toll-like receptor 4 (TLR4) signaling. FMDV VP3 increased the expression of TLR4 by downregulating the expression of the lysozyme-related protein Rab7b. Additionally, Rab7b can interact with VP3 to promote the replication of FMDV. Our findings suggested that VP3 regulates the Rab7b-TLR4 axis to mediate the inflammatory response to FMDV.

IMPORTANCE Foot-and-mouth disease virus (FMDV) infection causes a severe inflammatory response in cloven-hoofed animals, such as pigs, cattle, and sheep, with typical clinical manifestations of high fever, numerous blisters on the oral mucosa, hoof, and breast, as well as myocarditis (tigroid heart). However, the mechanism underlying the inflammatory response caused by FMDV is enigmatic. In this study, we identified the VP3 protein of FMDV as an important proinflammatory factor. Mechanistically, VP3 interacted with TLR4 to promote TLR4 expression by inhibiting the expression of the lysozyme-related protein Rab7b. Our findings suggest that FMDV VP3 is a major proinflammatory factor in FMDV-infected hosts.

Foot and Mouth Disease Vaccine Development and Challenges in Inducing Long-Lasting Immunity: Trends and Current Perspectives

Foot and mouth disease (FMD) is an extremely contagious viral disease of livestock caused by foot and mouse disease virus genus: Aphthovirus, which causes a serious economic impact on both individual farmers and the national economy. Many attempts to advance a vaccine for FMD have failed to induce sterile immunity. The classical methods of vaccine production were due to selective accumulation of mutations around antigenic and binding sites. Reversion of the agent by positive selection and quasi-species swarm, use of this method is inapplicable for use in non-endemic areas. Chemical attenuation using binary ethyleneimine (BEI) protected the capsid integrity and produced a pronounced immunity against the challenge strain. Viral antigens which have been chemically synthesized or expressed in viruses, plasmid, or plants were tried in the vaccination of animals. DNA vaccines expressing either structural or nonstructural protein antigens have been tried to immunize animals. Using interleukins as a genetic adjuvant for DNA vaccines have a promising effect. While the challenges of inducing sterile immunity lies on non-structural (NS) proteins of FMDV which are responsible for apoptosis of dendritic cells and have negative effects on lympho-proliferative responses which lead to transient immunosuppression. Furthermore, destruction of host protein trafficking by nonstructural proteins suppressed CD₈⁺ T-cell proliferation. In this review, it tried to address multiple approaches for vaccine development trials and bottle necks of producing sterile immunity.

A Comprehensive Review of the Immunological Response against Foot-and-Mouth Disease Virus Infection and Its Evasion Mechanisms

Foot-and-mouth disease (FMD) is a highly contagious viral disease, which has been reported for over 100 years, and against which the struggle has lasted for the same amount of time. It affects individuals from the order Artiodactyla, such as cattle, swine, sheep, wild animals from this order, and a few non-cloven hoofed species, such as mice and elephants. FMD causes large-scale economic losses for agricultural production systems; morbidity is almost 100% in an affected population, accompanied by a high mortality rate in young animals due to myocarditis or an inability to suckle if a mother is ill. The aetiological agent is an Aphthovirus from the family Picornaviridae, having seven serotypes: A, O, C, SAT1, SAT2, SAT3, and Asia 1. Serotype variability means that an immune response is serospecific and vaccines are thus designed to protect against each serotype independently. A host’s adaptive immune response is key in defence against pathogens; however, this virus uses successful strategies (along with most microorganisms) enabling it to evade a host’s immune system to rapidly and efficiently establish itself within such host, and thus remain there. This review has been aimed at an in-depth analysis of the immune response in cattle and swine regarding FMD virus, the possible evasion mechanisms used by the virus and describing some immunological differences regarding these species. Such aspects can provide pertinent knowledge for developing new FMD control and prevention strategies.

Advances in Foot-and-Mouth Disease Virus Proteins Regulating Host Innate Immunity

Foot-and-mouth disease (FMD) is a highly contagious disease that affects cloven-hoofed animals such as pigs, cattle, and sheep. The disease is caused by the foot-and-mouth disease virus (FMDV) which has a non-enveloped virion with icosahedral symmetry that encapsulates a positive-sense, single-stranded RNA genome of ∼8.4 kb. FMDV infection causes obvious immunosuppressive effects on the host. In recent years, studies on the immunosuppressive mechanism of FMDV have become a popular topic. In addition, studies have shown that many FMDV proteins are involved in the regulation of host innate immunity and have revealed mechanisms by which FMDV proteins mediate host innate immunity. In this review, advances in studies on the mechanisms of interaction between FMDV proteins and host innate immunity are summarized to provide a comprehensive understanding of FMDV pathogenesis and the theoretical basis for FMD prevention and control.

Molecular Mechanisms of Immune Escape for Foot-and-Mouth Disease Virus

Foot-and-mouth disease virus (FMDV) causes a highly contagious vesicular disease in cloven-hoofed livestock that results in severe consequences for international trade, posing a great economic threat to agriculture. The FMDV infection antagonizes the host immune responses via different signaling pathways to achieve immune escape. Strategies to escape the cell immune system are key to effective infection and pathogenesis. This review is focused on summarizing the recent advances to understand how the proteins encoded by FMDV antagonize the host innate and adaptive immune responses.

Type I Interferon Induced and Antagonized by Foot-and-Mouth Disease Virus

Viral infections trigger the innate immune system, serving as the first line of defense, and are characterized by the production of type I interferon (IFN). Type I IFN is expressed in a broad spectrum of cells and tissues in the host and includes various subtypes (IFN-α, IFN-β, IFN-δ, IFN-ε, IFN-κ, IFN-τ, IFN-ω, IFN-ν, and IFN-ζ). Since the discovery of type I IFN, our knowledge of the biology of type I IFN has accumulated immensely, and we now have a substantial amount of information on the molecular mechanisms of the response and induction of type I IFN, as well as the strategies utilized by viruses to evade the type I IFN response. Foot-and-mouth disease virus (FMDV) can selectively alter cellular pathways to promote viral replication and evade antiviral immune activation of type I IFN. RNA molecules generated by FMDV are sensed by the cellular receptor for pathogen-associated molecular patterns (PAMPs). FMDV preferentially activates different sensor molecules and various signal transduction pathways. Based on knowledge of the virus or RNA pathogen specificity as well as the function-structure relationship of RNA sensing, it is necessary to summarize numerous signaling adaptors that are reported to participate in the regulation of IFN gene activation.

Foot-and-mouth disease virus infection stimulates innate immune signaling in the mouse macrophage RAW 264.7 cells

The innate immune system acts as the first line of defense against invasion by bacterial and viral pathogens. The role of macrophages in innate immune responses to foot-and-mouth disease virus (FMDV) is poorly understood. To determine the mechanism underlying activation of innate immunity after FMDV infection in macrophages, we performed FMDV infection in mouse macrophage RAW 264.7 cells and found that FMDV serotype O infection induced a cytopathic effect. We then evaluated the gene expression profile in macrophage RAW 264.7 cells after FMDV infection using systematic microarray analysis. Gene ontology annotation and enrichment analysis revealed that FMDV promoted expression in a group of genes that are enriched in innate immune response and inflammatory response processes. Further research demonstrated that FMDV serotype O infection enhanced NF-κB, Toll-like, and RIG-I-like receptor signaling pathways and proteins expression and increased transcription and expression of a series of cytokines and interferons, as proved by qRT-PCR, Western blot, ELISA, and dual-luciferase reporter assay. Our study concluded that FMDV infection triggers the innate immune response in macrophages after activation of multiple innate immune pathway receptors and proteins by FMDV serotype O, resulting in activation and secretion of a series of cytokines and interferons.

Molecular Mechanisms of Foot-and-Mouth Disease Virus Targeting the Host Antiviral Response

Foot-and-mouth disease virus (FMDV) is the causative agent of an acute vesicular disease affecting pigs, cattle and other domestic, and wild animals worldwide. The aim of the host interferon (IFN) response is to limit viral replication and spread. Detection of the viral genome and products by specialized cellular sensors initiates a signaling cascade that leads to a rapid antiviral response involving the secretion of type I- and type III-IFNs and other antiviral cytokines with antiproliferative and immunomodulatory functions. During co-evolution with their hosts, viruses have acquired strategies to actively counteract host antiviral responses and the balance between innate response and viral antagonism may determine the outcome of disease and pathogenesis. FMDV proteases Lpro and 3C have been found to antagonize the host IFN response by a repertoire of mechanisms. Moreover, the putative role of other viral proteins in IFN antagonism is being recently unveiled, uncovering sophisticated immune evasion strategies different to those reported to date for other members of the Picornaviridae family. Here, we review the interplay between antiviral responses induced by FMDV infection and viral countermeasures to block them. Research on strategies used by viruses to modulate immunity will provide insights into the function of host pathways involved in defense against pathogens and will also lead to development of new therapeutic strategies to fight virus infections.

Foot-and-mouth disease virus structural protein VP3 degrades Janus kinase 1 to inhibit IFN-γ signal transduction pathways

Foot-and-mouth disease is a highly contagious viral disease of cloven-hoofed animals that is caused by foot-and-mouth disease virus (FMDV). To replicate efficiently in vivo, FMDV has evolved methods to circumvent host antiviral defense mechanisms, including those induced by interferons (IFNs). Previous research has focused on the effect of FMDV L(pro) and 3C(pro) on type I IFNs. In this study, FMDV VP3 was found to inhibit type II IFN signaling pathways. The overexpression of FMDV VP3 inhibited the IFN-γ-triggered phosphorylation of STAT1 at Tyr701 and the subsequent expression of downstream genes. Mechanistically, FMDV VP3 interacted with JAK1/2 and inhibited the tyrosine phosphorylation, dimerization and nuclear accumulation of STAT1. FMDV VP3 also disrupted the assembly of the JAK1 complex and degraded JAK1 but not JAK2 via a lysosomal pathway. Taken together, the results reveal a novel mechanism used by which FMDV VP3 counteracts the type II IFN signaling pathways.

Macrophage Polarization in Virus-Host Interactions

Macrophage involvement in viral infections and antiviral states is common. However, this involvement has not been well-studied in the paradigm of macrophage polarization, which typically has been categorized by the dichotomy of classical (M1) and alternative (M2) statuses. Recent studies have revealed the complexity of macrophage polarization in response to various cellular mediators and exogenous stimuli by adopting a multipolar view to revisit the differential process of macrophages, especially those re-polarized during viral infections. Here, through examination of viral infections targeting macrophages/monocytic cells, we focus on the direct involvement of macrophage polarization during viral infections. Type I and type III interferons (IFNs) are critical in regulation of viral pathogenesis and host antiviral infection; thus, we propose to incorporate IFN-mediated antiviral states into the framework of macrophage polarization. This view is supported by the multifunctional properties of type I IFNs, which potentially elicit and regulate both M1- and M2-polarization in addition to inducing the antiviral state, and by the discoveries of viral mechanisms to adapt and modulate macrophage polarization. Indeed, several recent studies have demonstrated effective prevention of viral diseases through manipulation of macrophage immune statuses.

Swine interferon-induced transmembrane protein, sIFITM3, inhibits foot-and-mouth disease virus infection in vitro and in vivo

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Swine IFITM3 (sIFITM3) shares the conserved functional domains and amino acid residues with its human ortholog.

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sIFITM3 restricts FMDV infection in BHK cells.

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sIFITM3 disrupts FMDV viral attachment to the host cell surface.

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sIFITM3 protects suckling mice from FMDV challenge.

The interferon-induced transmembrane protein 3 (IFITM3) is a widely expressed potent antiviral effector of the host innate immune system. It restricts a diverse group of pathogenic, enveloped viruses, by interfering with endosomal fusion. In this report, the swine IFITM3 (sIFITM3) gene was cloned. It shares the functionally conserved CD225 domain and multiple critical amino acid residues (Y19, F74, F77, R86 and Y98) with its human ortholog, which are essential for antiviral activity. Ectopic expression of sIFITM3 significantly inhibited non-enveloped foot-and-mouth disease virus (FMDV) infection in BHK-21 cells. Furthermore, sIFITM3 blocked FMDV infection at early steps in the virus life cycle by disrupting viral attachment to the host cell surface. Importantly, inoculation of 2-day-old suckling mice with a plasmid expressing sIFITM3 conferred protection against lethal challenge with FMDV. These results suggest that sIFITM3 is a promising antiviral agent and that can safeguard the host from infection with FMDV.

Delivery of synthetic RNA can enhance the immunogenicity of vaccines against foot-and-mouth disease virus (FMDV) in mice

We have recently described the antiviral effect in mice of in vitro-transcribed RNAs mimicking structural domains in the non-coding regions of the foot-and-mouth disease virus (FMDV) genome RNA. These small, synthetic and non-infectious RNA molecules (ncRNAs) are potent type-I interferon (IFN) inducers in vivo. In this work, the immunomodulatory effect of the ncRNA corresponding to the internal ribosome entry site (IRES) on immunization with two different FMD vaccine formulations, both based on inactivated virus, including or not a commercial adjuvant, was analyzed in the mice model. The effect of the time interval between RNA inoculation and immunization was also studied. RNA delivery consistently increased the titers of specific anti-FMDV antibodies, including neutralizing antibodies, elicited after vaccination. Moreover, at day 2 after immunization, significant differences in mean antibody titers could be detected between the groups of mice receiving either vaccine co-administered with the RNA and the control group, unlike those immunized with the vaccine alone. When vaccinated mice were challenged with FMDV, the mean values of viral load were lower in the groups receiving the RNA together with the vaccine. Our results show the enhancing effect of the IRES RNA on the immune response elicited after vaccination and suggest the potential of this molecule as an adjuvant for new FMD vaccine design.

Bovine fetal epithelium cells expressing shRNA targeting viral VP1 gene resisted against foot-and-mouth disease virus

RNAi could protect experimental animals from Foot-and-mouth disease virus (FMDV), but pivotal issue is delivery of RNAi. In this study, shRNA recombinant lentiviral plasmid RNAi-LT6 targeting VP1 of FMDV, which strongly suppressed the transient expression of a FLAG-tagged VP1 protein in 293T cells and significantly inhibited viral replication in BHK-21 cells, was screened and transfected into bovine fetal fibroblast cells. With subsequent somatic cell cloning, three 4-month-old transgenic fetuses were obtained, and integration into chromosome and expression of shRNA in primary transgenic tongue epithelium cells were confirmed by Southern hybridization and Northern assay, respectively. shRNA significantly suppressed viral RNA synthesis and viral replication in primary transgenic tongue epithelium cells after inoculation of 200 TCID50 of FMDV. The results suggested that transgenic cloning may be a useful tool for RNAi delivery and RNAi anti-viral strategy, and RNAi-LT6 could be a candidate shRNA used for preparation of transgenic cattle against FMDV.

Foot-and-mouth disease virus 3C protease cleaves NEMO to impair innate immune signaling

Foot-and-mouth disease is a highly contagious viral illness of wild and domestic cloven-hoofed animals. The causative agent, foot-and-mouth disease virus (FMDV), replicates rapidly, efficiently disseminating within the infected host and being passed on to susceptible animals via direct contact or the aerosol route. To survive in the host, FMDV has evolved to block the host interferon (IFN) response. Previously, we and others demonstrated that the leader proteinase (L(pro)) of FMDV is an IFN antagonist. Here, we report that another FMDV-encoded proteinase, 3C(pro), also inhibits IFN-α/β response and the expression of IFN-stimulated genes. Acting in a proteasome- and caspase-independent manner, the 3C(pro) of FMDV proteolytically cleaved nuclear transcription factor kappa B (NF-κB) essential modulator (NEMO), a bridging adaptor protein essential for activating both NF-κB and interferon-regulatory factor signaling pathways. 3C(pro) specifically targeted NEMO at the Gln 383 residue, cleaving off the C-terminal zinc finger domain from the protein. This cleavage impaired the ability of NEMO to activate downstream IFN production and to act as a signaling adaptor of the RIG-I/MDA5 pathway. Mutations specifically disrupting the cysteine protease activity of 3C(pro) abrogated NEMO cleavage and the inhibition of IFN induction. Collectively, our data identify NEMO as a substrate for FMDV 3C(pro) and reveal a novel mechanism evolved by a picornavirus to counteract innate immune signaling.

Use of replication-defective adenoviruses to develop vaccines and biotherapeutics against foot-and-mouth disease

We have developed a replication-defective human adenovirus (Ad5) vectored foot-and-mouth disease (FMD) vaccine platform that protects both swine and cattle from subsequent challenge with homologous virus after a single immunization. This Ad5-FMD vaccine has undergone testing following the requirements of the Center for Veterinary Biologics of the Animal Plant and Health Inspection Service, US Department of Agriculture, and has recently been granted a conditional license for inclusion of the vaccine in the US National Veterinary Vaccine Stockpile. In this review, we will describe the approaches we have taken to improve the potency and efficacy of this vaccine platform. Furthermore, we will discuss the development of Ad5 vector-based biotherapeutics to generate rapid protection against FMD virus prior to vaccine-induced adaptive immunity and describe the use of a combination of these approaches to stimulate both fast and long-lasting immunity.

Cattle remain immunocompetent during the acute phase of foot-and-mouth disease virus infection

Infection of cattle with foot-and-mouth disease virus (FMDV) results in the development of long-term protective antibody responses. In contrast, inactivated antigen vaccines fail to induce long-term protective immunity. Differences between susceptible species have also been observed during infection with FMDV, with cattle often developing persistent infections whilst pigs develop more severe symptoms and excrete higher levels of virus. This study examined the early immune response to FMDV in naïve cattle after in-contact challenge. Cattle exposed to FMDV were found to be viraemic and produced neutralising antibody, consistent with previous reports. In contrast to previous studies in pigs these cattle did not develop leucopenia, and the proliferative responses of peripheral blood mononuclear cells to either mitogen or third party antigen were not suppressed. Low levels of type 1 interferon and IL-10 were detected in the circulation. Taken together, these results suggest that there was no generalised immunosuppression during the acute phase of FMDV infection in cattle.

RNA structural domains in noncoding regions of the foot-and-mouth disease virus genome trigger innate immunity in porcine cells and mice

The induction of type I interferons (alpha/beta interferon [IFN-α/β]) in response to viral infection is a crucial step leading to the antiviral state in the host. Viruses produce double-stranded RNA (dsDNA) during their replication cycle that is sensed as nonself by host cells through different receptors. A signaling cascade then is activated to block viral replication and spread. Foot-and-mouth disease virus (FMDV) is a picornavirus that is highly sensitive to IFN, and it causes one of the world's most important animal diseases. In this study, we showed the ability of structural domains predicted to enclose stable dsRNA regions in the 5'- and 3'-noncoding regions (NCRs) of the FMDV genome to trigger an IFN-α/β response in porcine kidney cultured cells and newborn mice. These RNAs, generated by in vitro transcription, were able to stimulate IFN-β transcription and induce an antiviral state in SK-6 cells. The induction levels elicited by the different NCR RNAs were compared. Among them, the 3'NCR was identified as a potent IFN activator, and the features in this region involved in signaling have been analyzed. To address whether the FMDV NCR transcripts were able to trigger the innate immune response in vivo, Swiss suckling mice were inoculated intraperitoneally with the RNAs. All transcripts induced the innate response in transfected animals, measured as IFN-α/β protein levels, antiviral activity in sera, and reduced susceptibility to FMDV infection. Our work provides new insight into innate responses against FMDV and identifies these small noninfectious RNA molecules as potential adjuvants for vaccine improvement and antiviral strategies against picornaviruses.

Foot-and-mouth disease virus leader proteinase inhibits dsRNA-induced RANTES transcription in PK-15 cells

The chemokine RANTES (regulated upon activation, normal T-cells expressed and secreted) plays an essential role in inflammation and immune response. Infection with wild-type foot-and-mouth disease virus (FMDV) in PK-15 cells strongly inhibits the expression of RANTES compared to infection with a genetically engineered mutant lacking the leader protein (L(pro)) coding region. This suggests that L(pro) is involved in RANTES regulation. However, the underlying molecular mechanism remains unclear. In this study, we show that transfection of PK-15 cells with a plasmid expressing the L(pro) of FMDV, in the absence of other FMDV proteins, inhibited dsRNA-induced RANTES transcription and promoter activity. Promoter mutagenesis experiments revealed that the interferon-stimulated response element (ISRE) was important for the ability of L(pro) to inhibit dsRNA-induced RANTES promoter activity. Furthermore, over-expression of L(pro) also inhibited IRF-3/7-mediated RANTES activation. Screening L(pro) mutants indicated that catalytic activity and a SAP (for SAF-A/B, Acinus, and PIAS) domain of L(pro) were required to suppress dsRNA-induced RANTES transcription.

Induction of foot-and-mouth disease virus-specific cytotoxic T cell killing by vaccination

Foot-and-mouth disease (FMD) continues to be a significant threat to the health and economic value of livestock species. This acute infection is caused by the highly contagious FMD virus (FMDV), which infects cloven-hoofed animals, including large and small ruminants and swine. Current vaccine strategies are all directed toward the induction of neutralizing antibody responses. However, the role of cytotoxic T lymphocytes (CTLs) has not received a great deal of attention, in part because of the technical difficulties associated with establishing a reliable assay of cell killing for this highly cytopathic virus. Here, we have used recombinant human adenovirus vectors as a means of delivering FMDV antigens in a T cell-directed vaccine in pigs. We tested the hypothesis that impaired processing of the FMDV capsid would enhance cytolytic activity, presumably by targeting all proteins for degradation and effectively increasing the class I major histocompatibility complex (MHC)/FMDV peptide concentration for stimulation of a CTL response. We compared such a T cell-targeting vaccine with the parental vaccine, previously shown to effectively induce a neutralizing antibody response. Our results show induction of FMDV-specific CD8(+) CTL killing of MHC-matched target cells in an antigen-specific manner. Further, we confirm these results by MHC tetramer staining. This work presents the first demonstration of FMDV-specific CTL killing and confirmation by MHC tetramer staining in response to vaccination against FMDV.

Dendritic Cells and HIV-1 Trans-Infection

Dendritic cells initiate and sustain immune responses by migrating to sites of pathogenic insult, transporting antigens to lymphoid tissues and signaling immune specific activation of T cells through the formation of the immunological synapse. Dendritic cells can also transfer intact, infectious HIV-1 to CD4 T cells through an analogous structure, the infectious synapse. This replication independent mode of HIV-1 transmission, known as trans-infection, greatly increases T cell infection in vitro and is thought to contribute to viral dissemination in vivo. This review outlines the recent data defining the mechanisms of trans-infection and provides a context for the potential contribution of trans-infection in HIV-1 disease.