Biological effects of recombinant vaccinia virus-expressed interleukin 4

Application of Parallel Reaction Monitoring to the Development and Validation of a Quantitative Assay for ST-246 in Human Plasma

In this work, we developed and validated a robust and sensitive method of liquid chromatography with high-resolution mass spectrometry in parallel reaction monitoring (PRM) mode for ST-246 (tecovirimat) quantification in human blood plasma. The method was compared with the multiple reaction monitoring (MRM) technique and showed better selectivity and similar sensitivity in a wider concentration range (10–5000 ng/mL). Within this range, intra- and interday variability of precision and accuracy were within acceptable ranges in accordance with the European Medicines Agency guidelines, and recovery was 87.9–100.6%. Samples were stable at 4 °C within 48 h and at −20 °C up to 3 months. The recovery and matrix effects in the proposed HRMS method were about 5% higher than those reported for the MRM method, but the PRM method showed better accuracy with comparable precision. It was found that the ST-246 concentration shown by the PRM method is approximately 24% higher than the output of the MRM one. Nonetheless, the high selectivity with similar sensitivity, as compared with traditional MRM methods, makes the proposed approach attractive for research and clinical use.

Select agent program impact on the IBC

Stringent, exacting and local oversight for the control and use of Select Agents and Toxins is crucial to ensuring biosecurity. However, review of research involving Select Agents and Toxins can present particular challenges to the Institutional Biosafety Committee (IBC). Institutional review for biosecurity programs focuses on security assessments and access control, whereas most IBCs primarily focus on occupational exposure assessment, biohazard control, and biosafety practices. Determining how and where to interweave biosecurity program requirements into programs based on occupational health priorities is the key to integrated and effective compliance management. Recent new or pending regulations on dual use or gain of function research suggests or mandates additional duties for the IBC. This chapter explores challenges and strategies for institutional oversight and support of Select Agent program compliance.

Fowlpox virus as a recombinant vaccine vector for use in mammals and poultry

Live vaccines against fowlpox virus, which causes moderate pathology in poultry and is the type species of the Avipoxvirus genus, were developed in the 1920s. Development of recombinant fowlpox virus vector vaccines began in the 1980s, for use not only in poultry, but also in mammals including humans. In common with other avipoxviruses, such as canarypox virus, fowlpox virus enters mammalian cells and expresses proteins, but replicates abortively. The use of fowlpox virus as a safe vehicle for expression of foreign antigens and host immunomodulators, is being evaluated in numerous clinical trials of vaccines against cancer, malaria, tuberculosis and AIDS, notably in heterologous prime-boost regimens. In this article, technical approaches to, and issues surrounding, the use of fowlpox virus as a recombinant vaccine vector in poultry and mammals are reviewed.

Development of the small-molecule antiviral ST-246 as a smallpox therapeutic

Naturally occurring smallpox has been eradicated, yet it remains as one of the highest priority pathogens due to its potential as a biological weapon. The majority of the US population would be vulnerable in a smallpox outbreak. SIGA Technologies, Inc. has responded to the call of the US government to develop and supply to the Strategic National Stockpile a smallpox antiviral to be deployed in the event of a smallpox outbreak. ST-246(®) (tecovirimat) was initially identified via a high-throughput screen in 2002, and in the ensuing years, our drug-development activities have spanned in vitro analysis, preclinical safety, pharmacokinetics and efficacy testing (all according to the 'animal rule'). Additionally, SIGA has conducted Phase I and II clinical trials to evaluate the safety, tolerability and pharmacokinetics of ST-246, bringing us to our current late stage of clinical development. This article reviews the need for a smallpox therapeutic and our experience in developing ST-246, and provides perspective on the role of a smallpox antiviral during a smallpox public health emergency.

Poxvirus interleukin-4 expression overcomes inherent resistance and vaccine-induced immunity: pathogenesis, prophylaxis, and antiviral therapy

In 2001, Jackson et al. reported that murine IL-4 expression by a recombinant ectromelia virus caused enhanced morbidity and lethality in resistant C57BL/6 mice as well as overcame protective immune memory responses. To achieve a more thorough understanding of this phenomenon and to assess a variety of countermeasures, we constructed a series of ECTV recombinants encoding murine IL-4 under the control of promoters of different strengths and temporal regulation. We showed that the ECTV-IL-4 recombinant expressing the highest level of IL-4 was uniformly lethal for C57BL/6 mice even when previously immunized. The lethality of the ECTV-IL-4 recombinants resulted from virus-expressed IL-4 signaling through the IL-4 receptor but was not due to IL-4 toxicity. A number of treatment approaches were evaluated against the most virulent IL-4 encoding virus. The most efficacious therapy was a combination of two antiviral drugs (CMX001(®) and ST-246(®)) that have different mechanisms of action.

Immune responses to the smallpox vaccine given in combination with ST-246, a small-molecule inhibitor of poxvirus dissemination

The re-emerging threat of smallpox and the emerging threat of monkeypox highlight the need for effective poxvirus countermeasures. Currently approved smallpox vaccines have unacceptable safety profiles and, consequently, the general populace is no longer vaccinated, leading to an increasingly susceptible population. ST-246, a small-molecule inhibitor of poxvirus dissemination, has been demonstrated in various animal models to be safe and effective in preventing poxviral disease. This suggests that it may also be used to improve the safety of the traditional smallpox vaccine provided that it does not inhibit vaccine-induced protective immunity. In this study, we compared the immune responses elicited by the smallpox vaccine alone or in combination with ST-246 in mice. Normal lesion formation following dermal scarification with the attenuated New York City Board of Health strain (Dryvax), commonly referred to as a vaccine “take”, was not inhibited although severe lesions and systemic disease due to vaccination with the virulent Western Reserve (VV-WR) strain were prevented. The vaccine given with ST-246 did not affect cellular immune responses or neutralizing antibody titers although anti-vaccinia ELISA titers were slightly reduced. Vaccination in combination with ST-246 provided equivalent short- and long-term protection against lethal intranasal challenge with VV-WR when compared to vaccine alone. These results suggest that ST-246 does not compromise protective immunity elicited by the vaccine and provide the basis for future studies examining the efficacy of ST-246 in preventing or treating adverse events due to vaccination.

Initiation of primary anti-vaccinia virus immunity in vivo

The primary focus of our work is the initiation of an antiviral immune response. While we employ many experimental systems to address this fundamental issue, much of our work revolves around the use of vaccinia virus. Concerns over the negative effects of vaccination have prevented the return of the smallpox immunization program to the general population and underscored the importance of understanding the primary immune response to vaccinia virus. This response is comprised of a complex symphony of immune system components employing a variety of different mechanisms. In this review, we will both highlight the roles of many of these components and touch on the applications of vaccinia virus in the laboratory and the clinic.

The ‘supervirus’? Lessons from IL-4-expressing poxviruses

Members of the Poxviridae family are particularly adept at avoiding the host immune system, encoding a plethora of immunomodulatory proteins that subvert host defense. With their large genome, poxviruses are also useful for studying the effect of exogenous genes on virus-host interactions and immune responses. The insertion of the Th2 cytokine interleukin-4 (IL-4) into several poxviruses significantly increases the efficiency of the recombinant virus as a pathogen by directly inhibiting the development of Th1 immunity, which is crucial for viral clearance. In an age in which the fear of genetically modified weaponized pathogens exists, the understanding of how to make viruses more pathogenic further blurs the distinction between fundamental academic research and bioweapons development. Here, the extent of immune evasion by IL-4-expressing poxviruses will be explored, as will the consequences of this increased pathogenicity on protective immune responses.

Expression of rabbit IL-4 by recombinant myxoma viruses enhances virulence and overcomes genetic resistance to myxomatosis

Rabbit IL-4 was expressed in the virulent standard laboratory strain (SLS) and the attenuated Uriarra (Ur) strain of myxoma virus with the aim of creating a Th2 cytokine environment and inhibiting the development of an antiviral cell-mediated response to myxomatosis in infected rabbits. This allowed testing of a model for genetic resistance to myxomatosis in wild rabbits that have undergone 50 years of natural selection for resistance to myxomatosis. Expression of IL-4 significantly enhanced virulence of both virulent and attenuated virus strains in susceptible (laboratory) and resistant (wild) rabbits. SLS-IL-4 completely overcame genetic resistance in wild rabbits. The pathogenesis of SLS-IL-4 was compared in susceptible and resistant rabbits. The results support a model for resistance to myxomatosis of an enhanced innate immune response controlling virus replication and allowing an effective antiviral cell-mediated immune response to develop in resistant rabbits. Expression of IL-4 did not overcome immunity to myxomatosis induced by immunization.

A new member of the interleukin 10-related cytokine family encoded by a poxvirus

Poxviruses express numerous proteins involved in manipulating the host immune response. Analysis of the primary sequence and predicted structure of the 134R protein of Yaba-like disease virus (Y134R) indicated that it is similar to cellular proteins of the IL-10 family, specifically IL-19, IL-20 and IL-24. A flag-tagged Y134R was expressed from mammalian cells and identified as a secreted, monomeric glycoprotein that stimulated signal transduction from class II cytokine receptors IL-20Ralpha/IL-20Rbeta (IL-20R type1) and IL-22R/IL-20Rbeta (IL-20R type 2). Y134R induced phosphorylation of signal transducers and activators of transcription, their translocation to the nucleus and the induction of reporter gene expression. In contrast, Y134R was unable to induce similar responses from either the IL-22 or IFN-lambda (IL-28A, IL-28B, IL-29) class II cytokine receptors. To examine the role Y134R plays during a poxvirus infection, a vaccinia virus recombinant expressing Y134R was constructed and tested in a murine intranasal infection model. Compared with control viruses, the virus expressing Y134R had a reduced virulence, manifested by reduced weight loss, signs of illness and virus titres in infected organs. These results demonstrate that Y134R is a new viral member of the IL-10-related cytokine family and that its activity in vivo affects virus virulence.

Smallpox infections during pregnancy, lessons on pathogenesis from nonpregnant animal models of infection

Both vaccinated and unvaccinated women during pregnancy who contract variola virus, the causative agent of smallpox, suffer much higher mortality rates than nonpregnants. Furthermore, acute maternal smallpox leads to spontaneous abortion, premature termination of pregnancy and early postnatal infant mortality. The mechanisms governing the abortifacient activity of smallpox, as well as the enhanced susceptibility of gestating women to lethal disease, have remained largely unexamined. Experimental poxvirus infections in nonpregnant small animal models have revealed that T helper type 1 (TH1) cytokines promote efficient resolution of these infections whereas type 2 (TH2) cytokines enhance viral pathogenesis. These data, combined with recent understanding of how the immune system is modulated by pregnancy, may offer important clues as to the increased pathogenesis of variola in pregnant women. The aim of this review is to bring together the current literature on the effects of poxvirus infections in nonpregnant hosts, as well as the effects of pregnancy on the immune system, in order to develop unifying concepts that may provide insight into the pathogenesis of variola during pregnancy and why prior vaccination with vaccinia virus the live anti-variola vaccine offers less protection to pregnant women and their unborn children.

NK T cells contribute to expansion of CD8(+) T cells and amplification of antiviral immune responses to respiratory syncytial virus

CD1d-deficient mice have normal numbers of T lymphocytes and natural killer cells but lack Valpha14(+) natural killer T cells. Respiratory syncytial virus (RSV) immunopathogenesis was evaluated in 129xC57BL/6, C57BL/6, and BALB/c CD1d(-/-) mice. CD8(+) T lymphocytes were reduced in CD1d(-/-) mice of all strains, as shown by cell surface staining and major histocompatibility complex class I tetramer analysis, and resulted in strain-specific alterations in illness, viral clearance, and gamma interferon (IFN-gamma) production. Transient activation of NK T cells in CD1d(+/+) mice by alpha-GalCer resulted in reduced illness and delayed viral clearance. These data suggest that early IFN-gamma production and efficient induction of CD8(+)-T-cell responses during primary RSV infection require CD1d-dependent events. We also tested the ability of alpha-GalCer as an adjuvant to modulate the type 2 immune responses induced by RSV glycoprotein G or formalin-inactivated RSV immunization. However, immunized CD1-deficient or alpha-GalCer-treated wild-type mice did not exhibit diminished disease following RSV challenge. Rather, some disease parameters, including cytokine production, eosinophilia, and viral clearance, were increased. These findings indicate that CD1d-dependent NK T cells play a role in expansion of CD8(+) T cells and amplification of antiviral responses to RSV.

Expression of mouse interleukin-4 by a recombinant ectromelia virus suppresses cytolytic lymphocyte responses and overcomes genetic resistance to mousepox

Genetic resistance to clinical mousepox (ectromelia virus) varies among inbred laboratory mice and is characterized by an effective natural killer (NK) response and the early onset of a strong CD8(+) cytotoxic T-lymphocyte (CTL) response in resistant mice. We have investigated the influence of virus-expressed mouse interleukin-4 (IL-4) on the cell-mediated response during infection. It was observed that expression of IL-4 by a thymidine kinase-positive ectromelia virus suppressed cytolytic responses of NK and CTL and the expression of gamma interferon by the latter. Genetically resistant mice infected with the IL-4-expressing virus developed symptoms of acute mousepox accompanied by high mortality, similar to the disease seen when genetically sensitive mice are infected with the virulent Moscow strain. Strikingly, infection of recently immunized genetically resistant mice with the virus expressing IL-4 also resulted in significant mortality due to fulminant mousepox. These data therefore suggest that virus-encoded IL-4 not only suppresses primary antiviral cell-mediated immune responses but also can inhibit the expression of immune memory responses.

Local IL-4 expression in the lung reduces pulmonary influenza-virus-specific secondary cytotoxic T cell responses

We studied the effect of lung-specific IL-4 expression on the T cell response during primary and secondary heterologous infection with influenza virus by using transgenic mice that express IL-4 under a lung-specific promoter. Subsequent to primary infection with a type A/H1N1 influenza virus these transgenic mice exhibited similar local recruitment of CD4(+) and CD8(+) T cells and only slightly decreased virus-specific CTL activity. However, during secondary challenge with a heterologous influenza virus, the local infiltration with virus-specific, MHC class I-restricted CD8(+) T cells was significantly decreased compared to that of nontransgenic littermates. The ability of IL-4 transgenic mice to clear the heterologous infection was delayed but not abrogated. This was associated with a faster virus-neutralizing antibody response in IL-4 transgenic mice and with their ability to mount significant Th1 responses even in the presence of increased local IL-4 expression. Our observations demonstrate a negative regulatory effect of IL-4 on memory Tc1/CD8(+) T cells, but are also consistent with complementary mechanisms important for virus clearance such as virus-neutralizing antibodies. The reduction of memory CTL in the presence of IL-4 might have consequences for understanding the course of influenza infection in situations where T(H)2 immunity is increased.

Insertion sites for recombinant vaccinia virus construction: effects on expression of a foreign protein

The expression of antigens or other molecules from recombinant vaccinia viruses requires the insertion of coding sequence at specific sites in the viral genome. Here we investigate the influence of two different sites on the level of protein expressed during a viral infection. The level of immune response in mice to vaccinia virus-expressed murine interleukin 2 (IL-2) or IL-4 varied depending on whether the coding sequence was inserted into the vaccinia virus thymidine kinase (tk) gene or into the HindIII F fragment of the viral genome where herpes simplex virus (HSV) tk was used as a selectable marker. In each case the intensity of the response was greater when the relevant gene was expressed from the HindIII F insertion site. In order to quantify these differences a series of recombinant viruses expressing luciferase was constructed. Luciferase activity from coding sequence inserted into the HindIII F fragment was significantly higher than that from the tk gene insertion, provided HSV tk(+) constructs were compared. Insertion of a marker gene (HSV tk) into the HindIII F site with disruption of the F7L open reading frame led to a reduced level of luciferase expressed from the tk insert, despite more than 45 kb of intervening sequence. In mice, luciferase expression was higher from the HindIII F inserted gene than from the tk insert in both lungs and ovaries.

Recombinant vaccinia virus coexpressing the F protein of respiratory syncytial virus (RSV) and interleukin-4 (IL-4) does not inhibit the development of RSV-specific memory cytotoxic T lymphocytes, whereas priming is diminished in the presence of high levels of IL-2 or gamma interferon

In order to investigate if immune responses to the fusion (F) protein of respiratory syncytial virus (RSV) could be influenced by cytokines, recombinant vaccinia viruses (rVV) carrying both the F gene of RSV and the gene for murine interleukin-2 (IL-2), IL-4, or gamma interferon (IFN-gamma) were constructed. In vitro characterization of rVV revealed that insertion of the cytokine gene into the VP37 locus of the vaccinia virus genome resulted in 100- to 1,000-fold higher expression than insertion of the same gene into the thymidine kinase (TK) locus. In comparison, only a two- to fivefold difference in the level of expression of the F protein was observed when the gene was inserted into either of these two loci. Mice vaccinated with rVV expressing the F protein and high levels of IL-2 or IFN-gamma cleared rVV more rapidly than mice inoculated with a control rVV and developed only low levels of RSV-specific serum antibody. In addition, these recombinants were much less effective at priming RSV-specific memory cytotoxic T lymphocytes (CTL) and IFN-gamma production by spleen cells than rVV expressing the F protein alone. In contrast, mice vaccinated with rVV expressing high levels of IL-4 showed signs of delayed rVV clearance. RSV-specific serum antibody responses were biased in favor of immunoglobulin G1 (IgG1) in these mice, as there was a significant reduction in IgG2a antibody responses compared with serum antibody responses in mice vaccinated with rVV expressing the F protein alone. However, vaccination with rVV expressing the F protein together with high levels of IL-4 did not alter the development of RSV-specific memory CTL or IFN-gamma production by RSV-restimulated splenocytes.

Interleukin-4 mediates down regulation of antiviral cytokine expression and cytotoxic T-lymphocyte responses and exacerbates vaccinia virus infection in vivo

Interleukin-4 (IL-4) promotes the growth of Th2-type cells while down regulating the development of Th1-type cells. It has been suggested that the actions of this factor inhibit Th1-type effector activity in vivo and may underlie the development of diseases normally controlled by cell-mediated immune responses. Here, we show that clearance of recombinant vaccinia viruses (VV) engineered to express the gene for murine IL-4 is markedly delayed in mice compared with control recombinant VV. While antiviral antibody levels and NK activity in mice given control virus or IL-4-expressing virus were similar, antiviral cytotoxic T-lymphocyte responses were profoundly suppressed throughout the course of infection with the latter. Limiting dilution analysis of IL-4-virus-infected spleens revealed a marked reduction in numbers of cytotoxic T-lymphocyte precursors. Furthermore, reverse transcriptase PCR analysis of splenic mRNA prepared from mice infected with the IL-4-expressing VV showed a marked down regulation of IL-12, gamma interferon, and IL-2 gene expression compared with that from mice given control virus. IL-4 also inhibited the production of nitric oxide (NO), a potent mediator of antimicrobial activity. Together, these data show that IL-4 markedly suppresses the development of antiviral cell-mediated immune responses in vivo with deleterious effects on virus clearance.

Increased susceptibility of mice infected with Schistosoma mansoni to recombinant vaccinia virus: association of viral persistence with egg granuloma formation

BALB/c mice infected 7 weeks previously with Schistosoma mansoni and challenged with a recombinant vaccinia virus vPE16 expressing the human immunodeficiency virus envelope protein gp160 show a marked delay in hepatic viral clearance as compared to mice infected with vPE16 alone. This increase in viral persistence is accompanied by reduced gp120-specific Th1-associated cytokine responses as well as by impaired cytotoxic T lymphocyte (CTL) activity against targets expressing epitopes of the same antigen. To investigate the contribution of these defects to the observed delay in clearance of recombinant vaccinia virus, animals were challenged with vPE16 at different times following S. mansoni infection, and virus titers in tissues and viral-specific immune responses were measured simultaneously in the same animals. While normal resolution of virus occurred in schistosome-infected mice prior to parasite egg deposition, persistence within the liver was observed in animals challenged during the onset and peak phase of granuloma formation (6 to 8 weeks after S. mansoni infection). At later times, when schistosomiasis is in its chronic phase, normal viral clearance returned. This time course of viral resolution correlated in part with the observed pattern of decreased Th1 cytokine production toward viral antigens but was clearly less temporally related to the defect in virus-specific CTL activity. Immunohistochemical staining of liver sections from vaccinia/S. mansoni co-infected mice with polyclonal anti-vaccinia antibodies revealed that viral epitopes are localized primarily within granulomas. These experiments suggest that egg granulomas, by providing a microenvironment for viral expression, in combination with the cytokine imbalance present during schistosome infection, can promote the expansion of vaccinia virus and possibly other viral agents.

In vivo delivery of interleukin-4 by a recombinant vaccinia virus prevents tumor development in mice

To study the immunotherapeutic potential of interleukin-4 (IL-4) delivered in vivo via a recombinant vaccinia virus, a thymidine kinase-negative (TK-) vaccinia virus that expressed the murine IL-4 gene (VV1/IL-4) was constructed. When mice were inoculated with 10(7) plaque-forming units (pfu) of VV1/IL-4 subcutaneously (s.c.), 10(5) pfu/cm2 were found in skin, and smaller numbers in liver and kidney between 1 and 7 days after infection; few viral pfu were found in spleen and lung, or in any organ after intravenous infection. This suggested that recombinant vaccinia viruses might be most efficient at delivery of cytokine genes to the skin. Because IL-4 has recently been found to have potent anti-tumor activity, the effect of recombinant virus infection on the development of s.c. tumors was studied. A single s.c. inoculation with VV1/IL-4 delayed the development of NCTC 2472 tumors, but when VV1/IL-4 was inoculated s.c. weekly for 8 weeks, tumor development was completely prevented in 93% of mice. Similarly, the development of M-3 melanoma tumors was also prevented by weekly s.c. inoculations of VV1/IL-4. About 40% of mice treated with control VV2/beta gal by the same regimen also failed to develop tumors. Weekly virus treatment did not prevent NCTC 2472 tumor development in athymic nu/nu mice, suggesting that mature T cells are required for expression of VV1/IL-4 induced antitumor activity. Thus, recombinant vaccinia viruses may be especially well suited for convenient therapeutic delivery of immunomodulator genes to skin-related sites.