Vaccination with recombinant modified vaccinia virus Ankara protects against measles virus infection in the mouse and cotton rat model

Current approaches to evaluate the function of cytotoxic T-cells in non-human primates

Cytotoxic T-lymphocytes (CTL) are a subset of T-cells that play a critical role in protecting against intracellular infections and cancer, and have the ability to identify and kill infected or transformed cells expressing non-self peptides associated with major histocompatibility (MHC) Class I molecules. Conversely, aberrant CTL activity can contribute to immune-related pathology under conditions of overwhelming infection or autoimmunity. Disease-modifying therapeutics can have unintended effects on CTL, and a growing number of therapeutics are intended to either suppress or enhance CTL or their functions. The susceptibility of CTL to unintended effects from common therapeutic modalities underscores the need for a better understanding of the impact that such therapies have on CTL function and the associated safety implications. While there are reliable ways of quantifying CTL, notably via flow cytometric analysis of specific CTL markers, it has been a greater challenge to implement fit-for-purpose methods measuring CTL function in the context of safety studies of therapeutics. This review focuses on methods for measuring CTL responses in the context of drug safety and pharmacology testing, with the goals of informing the reader about current approaches, evaluating their pros and cons, and providing perspectives on the utility of these approaches for safety evaluation.

Viral Vector Vaccines against Bluetongue Virus

Bluetongue virus (BTV), the prototype member of the genus Orbivirus (family Reoviridae), is the causative agent of an important livestock disease, bluetongue (BT), which is transmitted via biting midges of the genus Culicoides. To date, up to 29 serotypes of BTV have been described, which are classified as classical (BTV 1–24) or atypical (serotypes 25–27), and its distribution has been expanding since 1998, with important outbreaks in the Mediterranean Basin and devastating incursions in Northern and Western Europe. Classical vaccine approaches, such as live-attenuated and inactivated vaccines, have been used as prophylactic measures to control BT through the years. However, these vaccine approaches fail to address important matters like vaccine safety profile, effectiveness, induction of a cross-protective immune response among serotypes, and implementation of a DIVA (differentiation of infected from vaccinated animals) strategy. In this context, a wide range of recombinant vaccine prototypes against BTV, ranging from subunit vaccines to recombinant viral vector vaccines, have been investigated. This article offers a comprehensive outline of the live viral vectors used against BTV.

Newcastle Disease Virus as a Vaccine Vector for 20 Years: A Focus on Maternally Derived Antibody Interference

It has been 20 years since Newcastle disease virus (NDV) was first used as a vector. The past two decades have witnessed remarkable progress in vaccine generation based on the NDV vector and optimization of the vector. Protective antigens of a variety of pathogens have been expressed in the NDV vector to generate novel vaccines for animals and humans, highlighting a great potential of NDV as a vaccine vector. More importantly, the research work also unveils a major problem restraining the NDV vector vaccines in poultry, i.e., the interference from maternally derived antibody (MDA). Although many efforts have been taken to overcome MDA interference, a lack of understanding of the mechanism of vaccination inhibition by MDA in poultry still hinders vaccine improvement. In this review, we outline the history of NDV as a vaccine vector by highlighting some milestones. The recent advances in the development of NDV-vectored vaccines or therapeutics for animals and humans are discussed. Particularly, we focus on the mechanisms and hypotheses of vaccination inhibition by MDA and the efforts to circumvent MDA interference with the NDV vector vaccines. Perspectives to fill the gap of understanding concerning the mechanism of MDA interference in poultry and to improve the NDV vector vaccines are also proposed.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Prevention of measles virus infection by intranasal delivery of fusion inhibitor peptides

Measles virus (MV) infection is undergoing resurgence and remains one of the leading causes of death among young children worldwide despite the availability of an effective measles vaccine. MV infects its target cells by coordinated action of the MV H and the fusion (F) envelope glycoprotein; upon receptor engagement by H, the prefusion F undergoes a structural transition, extending and inserting into the target cell membrane and then refolding into a postfusion structure that fuses the viral and cell membranes. By interfering with this structural transition of F, peptides derived from the heptad-repeat (HR) regions of F can potently inhibit MV infection at the entry stage. We show here that specific features of H's interaction with its receptors modulate the susceptibility of MV F to peptide fusion inhibitors. A higher concentration of inhibitory peptides is required to inhibit F-mediated fusion when H is engaged to its nectin-4 receptor than when H is engaged to its CD150 receptor. Peptide inhibition of F may be subverted by continued engagement of receptor by H, a finding that highlights the ongoing role of H-receptor interaction after F has been activated and that helps guide the design of more potent inhibitory peptides. Intranasal administration of these peptides results in peptide accumulation in the airway epithelium with minimal systemic levels of peptide and efficiently prevents MV infection in vivo in animal models. The results suggest an antiviral strategy for prophylaxis in vulnerable and/or immunocompromised hosts.

IMPORTANCE

Measles virus (MV) infection causes an acute illness that may be associated with infection of the central nervous system (CNS) and severe neurological disease. No specific treatment is available. We have shown that parenterally delivered fusion-inhibitory peptides protect mice from lethal CNS MV disease. Here we show, using established small-animal models of MV infection, that fusion-inhibitory peptides delivered intranasally provide effective prophylaxis against MV infection. Since the fusion inhibitors are stable at room temperature, this intranasal strategy is feasible even outside health care settings, could be used to protect individuals and communities in case of MV outbreaks, and could complement global efforts to control measles.

Maternal antibodies: clinical significance, mechanism of interference with immune responses, and possible vaccination strategies

Neonates have an immature immune system, which cannot adequately protect against infectious diseases. Early in life, immune protection is accomplished by maternal antibodies transferred from mother to offspring. However, decaying maternal antibodies inhibit vaccination as is exemplified by the inhibition of seroconversion after measles vaccination. This phenomenon has been described in both human and veterinary medicine and is independent of the type of vaccine being used. This review will discuss the use of animal models for vaccine research. I will review clinical solutions for inhibition of vaccination by maternal antibodies, and the testing and development of potentially effective vaccines. These are based on new mechanistic insight about the inhibitory mechanism of maternal antibodies. Maternal antibodies inhibit the generation of antibodies whereas the T cell response is usually unaffected. B cell inhibition is mediated through a cross-link between B cell receptor (BCR) with the Fcγ-receptor IIB by a vaccine-antibody complex. In animal experiments, this inhibition can be partially overcome by injection of a vaccine-specific monoclonal IgM antibody. IgM stimulates the B cell directly through cross-linking the BCR via complement protein C3d and antigen to the complement receptor 2 (CR2) signaling complex. In addition, it was shown that interferon alpha binds to the CD21 chain of CR2 as well as the interferon receptor and that this dual receptor usage drives B cell responses in the presence of maternal antibodies. In lieu of immunizing the infant, the concept of maternal immunization as a strategy to protect neonates has been proposed. This approach would still not solve the question of how to immunize in the presence of maternal antibodies but would defer the time of infection to an age where infection might not have such a detrimental outcome as in neonates. I will review successful examples and potential challenges of implementing this concept.

Synergistic induction of interferon α through TLR-3 and TLR-9 agonists stimulates immune responses against measles virus in neonatal cotton rats

Immunization of neonates is problematic because of the immaturity of their immune system and the presence of maternal antibodies, both of which affect B cell responses. We tested the effects of co-administration of measles vaccine with a combination of TLR-3 (pI:C) and TLR-9 (ODN2216, optimized for human TLR-9) agonists on the ability to induce an effective immune response in neonatal cotton rats. TLR-9 expression in cotton rat lymphocytes was at the same low level as in human lymphocytes, which is in contrast to mice that express higher levels. TLR-3 expression levels were comparable between cotton rats, mice, and humans. A combination of TLR-3 and TLR-9 agonists synergistically induced high levels of type I interferon in neonatal spleen cells and higher levels of IL-10 as compared to adult spleen cells. Previously, it was shown that type I interferon stimulates B cell generation and antibody secretion in vitro and in vivo, and that IL-10 has immunomodulatory effects. The simultaneous induction of both type I interferon and IL-10 indicated that this immunization regimen could be both effective and safe. Neonatal cotton rats did not generate neutralizing antibodies after measles vaccination in the first week of life (although a T cell response was detectable). However, co-administration of the TLR-3 and TLR-9 agonist combination with measles vaccine in neonatal cotton rats induced neutralizing antibody responses comparable to those after adult immunization. This immunization regimen was also effective in neonatal cotton rats in the presence of natural maternal antibodies, although antibody titers were lower than those after immunization in the absence of maternal antibodies.

Pulmonary vaccination as a novel treatment for lung fibrosis

Pulmonary fibrosis is an untreatable, uniformly fatal disease of unclear etiology that is the result of unremitting chronic inflammation. Recent studies have implicated bone marrow derived fibrocytes and M2 macrophages as playing key roles in propagating fibrosis. While the disease process is characterized by the accumulation of lymphocytes in the lung parenchyma and alveolar space, their role remains unclear. In this report we definitively demonstrate the ability of T cells to regulate lung inflammation leading to fibrosis. Specifically we demonstrate the ability of intranasal vaccinia vaccination to inhibit M2 macrophage generation and fibrocyte recruitment and hence the accumulation of collagen and death due to pulmonary failure. Mechanistically, we demonstrate the ability of lung Th1 cells to prevent fibrosis as vaccinia failed to prevent disease in Rag−/− mice or in mice in which the T cells lacked IFN-γ. Furthermore, vaccination 3 months prior to the initiation of fibrosis was able to mitigate the disease. Our findings clearly demonstrate the role of T cells in regulating pulmonary fibrosis as well as suggest that vaccinia-induced immunotherapy in the lung may prove to be a novel treatment approach to this otherwise fatal disease.

Joint production of prime/boost pairs of Fowlpox Virus and Modified Vaccinia Ankara recombinants carrying the same transgene

Pairs of recombinant MVA (Modified Vaccinia Ankara) and FPV (Fowlpox Virus) expressing the same transgene are reasonable candidates for prime/boost regimens, because cross-reacting immune responses between the two vectors, both non-replicative in mammalian hosts, are very limited. The acceptor virus FPD-Red, a derivative of FPV, carrying a red fluorescent protein gene flanked by the homology regions of MVA deletion III, was constructed. The same MVA Transfer Plasmid Green, designed to insert transgenes into the MVA deletion III locus, can therefore be used to transfer transgenes into both acceptor viruses MVA-Red and FPD-Red with the described recently Red-to-Green gene swapping method. Cells infected by either recombinant virus can be sorted differentially by a simple and reliable FACS-based purification protocol. The procedure is carried out in primary chick embryo fibroblasts grown in serum-free media and was applied to the production of three rMVA/rFPV pairs expressing the H5N1 avian influenza antigens M1, M2 and NP. The viral genes were human codon-optimized and expressed at high levels in both chick and mammalian cells. Both single-step and multiple-step growth analyses showed no significant differences in growth due to the transgenes in either rMVA or rFPV derivatives.

Measles virus neurovirulence and host immunity

Measles virus is highly neuroinvasive, yet host immune responses are highly effective at limiting neurovirulence in humans. We know that neurons are an important target of infection and that both IFN-γ and -β expression are observed in the measles virus-infected human brain. Rodent models can be used to understand how this response is orchestrated. Constitutive expression of the major inducible 70-kDa heat-shock protein is a feature of primate tissues that is lacking in mice. This article examines the importance of addressing this difference when modeling outcomes of brain infection in mice, particularly in terms of understanding how infected neurons may activate uninfected brain macrophages to produce IFN-β and support T-cell production of IFN-γ, a mediator of noncytolytic viral clearance. New and historical data suggest that the virus heat-shock protein 70 relationship is key to a protective host immune response and has potential broad relevance.

Effect of maternal HIV infection on measles susceptibility during early infancy: implications for optimizing protection of the infant

The measles virus was first isolated as the causative pathogen of measles approximately 50 years ago by John Enders and Thomas Peebles. Despite a safe and effective vaccine extant for nearly the same amount of time, control of measles nevertheless remains a challenge in developing countries. This article investigates the possible contribution of maternal HIV infection on measles susceptibility in infants. The current WHO position on measles vaccination in HIV-infected children recommends vaccinating asymptomatic HIV-infected infants as early as 6 months of age, followed with two additional doses at 9 and 18 months. This is rarely implemented due to logistical constraints related to early HIV diagnosis in infants and access to vaccines in low-resource settings. In addition, measles vaccine safety and immunogenicity in HIV-infected children are based on very low levels of scientific evidence. There are no specific recommendations for measles immunization of HIV-uninfected children born to HIV-infected mothers. We reviewed the available data on transplacental transfer of measles antibody and the influence of HIV, the findings of which suggest that consideration should be given to extending early measles immunization to all infants born to HIV-infected women.

The combination of marker gene swapping and fluorescence-activated cell sorting improves the efficiency of recombinant modified vaccinia virus Ankara vaccine production for human use

Modified vaccinia virus Ankara (MVA) is employed as a human vaccine vector for the high expression of heterologous genes and the lack of replication in mammalian cells. This study demonstrates that cells infected by recombinant viruses can be obtained by fluorescence-activated cell sorting. Recombinant viruses are generated by a swapping event between a red fluorescent protein gene in the acceptor virus and a plasmid cassette coding for both a green fluorescent marker and a transgene. To prevent the carry-over of parental virus, due to superinfection of the cells harbouring recombinant viruses, the sorting is performed on cells infected at low m.o.i. in the presence of a reversible inhibitor of viral particle release. Terminal dilution cloning is then used to isolate both green and marker-free recombinant viruses, which can be identified by whole-plate fluoroimaging. The differential visualization of all the viral types involved allows a stepwise monitoring of all recombinations and leads to a straightforward and efficient flow cytometry-based cell sorting purification protocol. As an example of the efficacy of this sorting procedure, the construction of rMVA's coding for the rat nuclear protein HMGB1 and H5N1 influenza A virus hemagglutinin is reported. The entire recombinant MVA production process is carried out in serum-free media employing primary chicken embryo fibroblasts (CEF), which are certified for the preparation of human vaccines. This rMVA production method is faster, simpler and more reliable than any other available procedure for obtaining safe vaccine stocks for human use.

Current animal models: cotton rat animal model

The cotton rat (Sigmodon hispidus) model has proven to be a suitable small animal model for measles virus pathogenesis to fill the niche between tissue culture and studies in macaques. Similar to mice, inbred cotton rats are available in a microbiologically defined quality with an ever-increasing arsenal of reagents and methods available for the study of infectious diseases. Cotton rats replicate measles virus in the respiratory tract and (depending on virus strain) in lymphoid organs. They can be infected with vaccine, wild-type, and recombinant measles viruses and have been used to study viruses with genetic modifications. Other areas of study include efficacy testing of antivirals and vaccines. The cotton rat also has been an informative animal model to investigate measles virus-induced immune suppression and suppression of vaccination by maternal antibodies. In addition, the cotton rat promises to be a useful model for the study of polymicrobial disease (interaction between measles virus and secondary pathogens).

Marker gene swapping facilitates recombinant Modified Vaccinia Virus Ankara production by host-range selection

Modified Vaccinia Virus Ankara (MVA) is employed widely as an experimental and human vaccine vector for its lack of replication in mammalian cells and high expression of heterologous genes. Recombinant MVA technology can be improved greatly by combining transient host-range selection (based on the restoration in MVA of the deleted vaccinia gene K1L) with the differential expression of fluorescent proteins. Recombinant virus results from swapping a red protein gene (in the acceptor virus) with a cassette of the transfer plasmid comprising the transgene and the green marker K1Lgfp (a chimeric gene comprising K1L and EGFP). Recombinant selection is performed in the selective host RK13. Finally, in the non-selective host BHK-21, a single crossover between identical flanking regions excises the marker gene. The three types of viruses involved (red parental, green intermediate and colourless final recombinant) are visualized differentially by fluorescence microscopy or fluoro-imaging of terminal dilution microcultures, leading to a straightforward and efficient purification protocol. This method (Red-to-Green gene swapping) reduces greatly the time needed to obtain marker-free recombinant MVA and increases the reliability of the construction process.

MVA E2 recombinant vaccine in the treatment of human papillomavirus infection in men presenting intraurethral flat condyloma: a phase I/II study

BACKGROUND

Human papillomavirus (HPV) is the etiologic agent for warts and cervical cancer. In Mexico, the death rate from cervical cancer is extremely high, and statistical data show that since 1990 the number of deaths is increasing. Condylomas and cancer of the penis are the most common lesions presented in men; bladder and prostate cancer in men are also associated with the presence of HPV. Since HPV is transmitted by sexual intercourse, treating both partners is necessary in order to eliminate the virus in the population. Approaches to this include preventative vaccines such as Gardasil, and therapeutic vaccines to treat established infections in both men and women. This will be the only way to decrease the numbers of deaths due to this malignancy.

PATIENTS AND METHODS

We conducted a phase I/II clinical trial to evaluate the potential use of the recombinant vaccinia viral vaccine MVA E2 (composed of modified vaccinia virus Ankara [MVA] expressing the E2 gene of bovine papillomavirus) to treat flat condyloma lesions associated with oncogenic HPV in men. Fifty male patients with flat condyloma lesions were treated with either MVA E2 therapeutic vaccine or fluorouracil (5-fluorouracil). Thirty men received the therapeutic vaccine, at a total of 10(6) virus particles per dose, administered directly into the urethra once every week over a 4-week period. Twenty control patients were treated with 5% fluorouracil 1mL twice weekly over a 4-week period directly into the urethra. Reduction of lesions or absence of papillomavirus infection was monitored by colposcopy and histologic analysis. The immune response after MVA E2 treatment was determined by measuring the antibodies against the MVA E2 virus and by analyzing the lymphocyte cytotoxic activity against cancer cells bearing oncogenic papillomavirus. Presence of papillomavirus was determined by the Hybrid Capture method.

RESULTS

Twenty-eight of 30 patients showed no lesion or presence of papillomavirus as diagnosed by colposcopy and brush histologic examination after 4 weeks of MVA E2 treatment. These patients showed complete elimination of flat condyloma in the urethra and no acetowhite spots were detected over the prepuce. In two other patients the acetowhite spots and flat condyloma did not diminish. All patients developed antibodies against the MVA E2 vaccine and E2 protein, and generated a specific cytotoxic response against papilloma-transformed cells. Viral DNA was not detected in MVA E2-treated patients. In the control group, 13 of 20 patients were free of lesions. Three of these patients had recurrence of lesions after 3 months of treatment and none of the patients developed specific antibodies against cancer cells. In contrast, patients treated with MVA E2 did not show any recurrence of lesions after 1 year of treatment. In addition, none of the patients had local or systemic adverse effects according to the WHO classification 1-4.

CONCLUSIONS

Therapeutic vaccination with MVA E2 proved to be very effective in stimulating the immune system against papillomavirus, and in generating regression of flat condyloma lesions in men.

A phase I vaccination study with tyrosinase in patients with stage II melanoma using recombinant modified vaccinia virus Ankara (MVA-hTyr)

A significant percentage of patients with stage II melanomas suffer a relapse after surgery and therefore need the development of adjuvant therapies. In the study reported here, safety and immunological response were analyzed after vaccination in an adjuvant setting with recombinant modified vaccinia virus Ankara carrying the cDNA for human tyrosinase (MVA-hTyr). A total of 20 patients were included and vaccinated three times at 4-week intervals with 5x10(8) IU of MVA-hTyr each time. The responses to the viral vector, to known HLA class I-restricted tyrosinase peptides, and to dendritic cells transfected with tyrosinase mRNA, were investigated by ELISpot assay on both ex vivo T cells and on T cells stimulated in vitro prior to testing. The delivery of MVA-hTyr was safe and did not cause any side effects above grade 2. A strong response to the viral vector was achieved, indicated by an increase in the frequency of MVA-specific CD4+ and CD8+ T cells and an increase in virus-specific antibody titers. However, no tyrosinase-specific T-cell or antibody response was observed with MVA-hTyr in any of the vaccinated patients. Although MVA-hTyr provides a safe and effective antigen-delivery system, it does not elicit a measurable immune response to its transgene product in patients with stage II melanoma after repeated combined intradermal and subcutaneous vaccination. We presume that modification of the antigen and/or prime-boost vaccination applying different approaches to antigen delivery may be required to induce an effective tyrosinase-specific immune response.

Therapeutic Vaccination of HIV-1-Infected Patients on Haart with a Recombinant HIV-1 Nef-Expressing Mva: Safety, Immunogenicity and Influence on Viral Load during Treatment Interruption

The safety and immunogenicity of an HIV-1 nef-expressing modified vaccinia virus Ankara (MVA) was investigated in 14 HIV-1-positive patients (CD4 >400/μl) on highly active antiretroviral therapy (HAART). Patients were vaccinated at weeks 0, 4 and 16, followed by interruption of HAART at week 18. MVA- nef was well-tolerated except for local reactions, with only mild systemic side effects reported in a few patients. Vaccination with MVA- nef was associated with recognition of new HIV-1 T-cell epitopes (cytotoxic T-lymphocyte epitopes in 9/14 patients, CD4 epitope/recombinant Nef protein in 2/14) and an increase in CD4+ and CD8+ T cells. All patients had been vaccinated against smallpox and a strong T-cell and antibody response to MVA was induced in all patients. After interruption of HAART, viral load rebounded in all patients, but after a median time of 36 (4–76) weeks in 9/14 patients, viraemia remained below the pre-HAART viral load and CD4 counts stayed above the pre-HAART levels. While six patients have remained off therapy for a median time of 64 (57–76) weeks, HAART was resumed in 8/14 patients after a median treatment interruption time of 15 (4–38) weeks. This study has demonstrated that MVA- nef is safe and immunogenic in HIV-1-infected subjects and has provided encouraging data on the potential of therapeutic vaccinations.

Hyperthermic pre-conditioning promotes measles virus clearance from brain in a mouse model of persistent infection

Nervous tissue subjected to hyperthermic pre-conditioning is resistance to numerous insults although in vitro, the same treatment can increase gene expression and cytopathic effect of neurotropic paramyxoviruses, including measles virus (MV). The present work determined whether the in vivo relationship between hyperthermic pre-conditioning and MV infection would be to increase neuropathogenicity or, conversely, to promote clearance. Balb/c mice 36 h of age were exposed to a 41 degrees C hyperthermic treatment for 30 min. Intracranial inoculation of mice with Edmonston MV was performed at 6 h following the heat treatment, a time point exhibiting elevated levels of the major inducible 70-kDa heat shock protein in brain, a hallmark of pre-conditioning. Forty-seven percent of the non-heated animals supported a persistent cytopathic infection at 21-day post infection (PI) based upon the quantitative detection of viral RNA in brain using real time RT-PCR. Cytopathic effect in the infected brains was proportionate to viral RNA burden. In contrast, infected stress conditioned mice lacked significant cytopathic effect and clearance was demonstrated in 95% of the animals. Analysis of shorter post-infection intervals showed that levels of viral RNA in brain were equivalent between stress conditioned and non-conditioned mice at 2 and 7 days PI, with clearance being first evident in both groups at 14 days. The temporal onset and progression of clearance was correlated to splenocyte blastogenic responsiveness to purified MV antigen but not the production of MV-specific antibody. Collectively, these results support the hypothesis that stress conditioning enhances the efficacy of cell-mediated immune responses known to mediate viral clearance from brain.

Replication of modified vaccinia virus Ankara in primary chicken embryo fibroblasts requires expression of the interferon resistance gene E3L

Highly attenuated modified vaccinia virus Ankara (MVA) serves as a candidate vaccine to immunize against infectious diseases and cancer. MVA was randomly obtained by serial growth in cultures of chicken embryo fibroblasts (CEF), resulting in the loss of substantial genomic information including many genes regulating virus-host interactions. The vaccinia virus interferon (IFN) resistance gene E3L is among the few conserved open reading frames encoding viral immune defense proteins. To investigate the relevance of E3L in the MVA life cycle, we generated the deletion mutant MVA-DeltaE3L. Surprisingly, we found that MVA-DeltaE3L had lost the ability to grow in CEF, which is the first finding of a vaccinia virus host range phenotype in this otherwise highly permissive cell culture. Reinsertion of E3L led to the generation of revertant virus MVA-E3rev and rescued productive replication in CEF. Nonproductive infection of CEF with MVA-DeltaE3L allowed viral DNA replication to occur but resulted in an abrupt inhibition of viral protein synthesis at late times. Under these nonpermissive conditions, CEF underwent apoptosis starting as early as 6 h after infection, as shown by DNA fragmentation, Hoechst staining, and caspase activation. Moreover, we detected high levels of active chicken alpha/beta IFN (IFN-alpha/beta) in supernatants of MVA-DeltaE3L-infected CEF, while moderate IFN quantities were found after MVA or MVA-E3rev infection and no IFN activity was present upon infection with wild-type vaccinia viruses. Interestingly, pretreatment of CEF with similar amounts of recombinant chicken IFN-alpha inhibited growth of vaccinia viruses, including MVA. We conclude that efficient propagation of MVA in CEF, the tissue culture system used for production of MVA-based vaccines, essentially requires conserved E3L gene function as an inhibitor of apoptosis and/or IFN induction.

Successful mucosal immunization of cotton rats in the presence of measles virus-specific antibodies depends on degree of attenuation of vaccine vector and virus dose

After passive transfer of measles virus (MV)-specific antibodies, vaccine-induced seroconversion and subsequent protection is inhibited in cotton rats (Sigmodon hispidus). In this system, an attenuated, recombinant vesicular stomatitis virus expressing the MV haemagglutinin (VSV-H) was found previously to induce neutralizing antibodies and protection against MV challenge after intranasal (i.n.) immunization. Here it is demonstrated that, after i.n. immunization, VSV-H is found in both lung and brain tissue in the absence of clinical signs. Intratracheal inoculation, which does not lead to infection of the brain, proved that immunization via the lung mucosa is sufficient to protect. To reduce or eliminate infection of the brain after i.n. inoculation, stepwise-attenuated VSV-H mutants with truncated cytoplasmic tails of the G protein were tested in cotton rats. A mutant with 9 aa in the G cytoplasmic tail was found at much lower levels in the brain and was protective in the absence or presence of MV-specific antibodies. A more attenuated mutant containing only 1 aa in its tail was not found in brain tissue after inoculation, but it still induced protective antibody to measles in the absence of MV-specific antibody. However, its ability to induce MV-neutralizing antibodies in the presence of passively transferred MV-specific antibodies and its protective capacity was abolished unless higher-dose immunizations were used. This study demonstrates that a lower degree of attenuation is required to be able to immunize in the presence of MV-specific antibodies.

Enhanced immunogenicity and protective efficacy against Mycobacterium tuberculosis of bacille Calmette-Guérin vaccine using mucosal administration and boosting with a recombinant modified vaccinia virus Ankara

Heterologous prime-boost immunization strategies can evoke powerful T cell immune responses and may be of value in developing an improved tuberculosis vaccine. We show that recombinant modified vaccinia virus Ankara, expressing Mycobacterium tuberculosis Ag 85A (M.85A), strongly boosts bacille Calmette-Guérin (BCG)-induced Ag 85A specific CD4(+) and CD8(+) T cell responses in mice. A comparison of intranasal (i.n.) and parenteral immunization of BCG showed that while both routes elicited comparable T cell responses in the spleen, only i.n. delivery elicited specific T cell responses in the lung lymph nodes, and these responses were further boosted by i.n. delivery of M.85A. Following aerosol challenge with M. tuberculosis, i.n. boosting of BCG with either BCG or M.85A afforded unprecedented levels of protection in both the lungs (2.5 log) and spleens (1.5 log) compared with naive controls. Protection in the lung correlated with the induction of Ag 85A-specific, IFN-gamma-secreting T cells in lung lymph nodes. These findings support further evaluation of mucosally targeted prime-boost vaccination approaches for tuberculosis.

Experimental vaccines against measles in a world of changing epidemiology

Vaccination with the current live attenuated measles vaccine is one of the most successful and cost-effective medical interventions. However, as a result of persisting maternal antibodies and immaturity of the infant immune system, this vaccine is poorly immunogenic in children <9 months old. Immunity against the live vaccine is less robust than natural immunity and protection less durable. There may also be some concern about (vaccine) virus spread during the final stage of an eventual measles eradication program. Opinions may differ with respect to the potential threat that some of these concerns may be to the World Health Organisation goal of measles elimination, but there is a consensus that the development of new measles vaccines cannot wait. Candidate vaccines are based on viral or bacterial vectors expressing recombinant viral proteins, naked DNA, immune stimulating complexes or synthetic peptides mimicking neutralising epitopes. While some of these candidate vaccines have proven their efficacy in monkey studies, aerosol formulated live attenuated measles vaccine are evaluated in clinical trials.

Attenuated Salmonella enterica serovar Typhi and Shigella flexneri 2a strains mucosally deliver DNA vaccines encoding measles virus hemagglutinin, inducing specific immune responses and protection in cotton rats

Measles remains a leading cause of child mortality in developing countries. Residual maternal measles antibodies and immunologic immaturity dampen immunogenicity of the current vaccine in young infants. Because cotton rat respiratory tract is susceptible to measles virus (MV) replication after intranasal (i.n.) challenge, this model can be used to assess the efficacy of MV vaccines. Pursuing a new measles vaccine strategy that might be effective in young infants, we used attenuated Salmonella enterica serovar Typhi CVD 908-htrA and Shigella flexneri 2a CVD 1208 vaccines to deliver mucosally to cotton rats eukaryotic expression plasmid pGA3-mH and Sindbis virus-based DNA replicon pMSIN-H encoding MV hemagglutinin (H). The initial i.n. dose-response with bacterial vectors alone identified a well-tolerated dosage (1 x 10(9) to 7 x 10(9) CFU) and a volume (20 micro l) that elicited strong antivector immune responses. Animals immunized i.n. on days 0, 28, and 76 with bacterial vectors carrying DNA plasmids encoding MV H or immunized parenterally with these naked DNA vaccine plasmids developed MV plaque reduction neutralizing antibodies and proliferative responses against MV antigens. In a subsequent experiment of identical design, cotton rats were challenged with wild-type MV 1 month after the third dose of vaccine or placebo. MV titers were significantly reduced in lung tissue of animals immunized with MV DNA vaccines delivered either via bacterial live vectors or parenterally. Since attenuated serovar Typhi and S. flexneri can deliver measles DNA vaccines mucosally in cotton rats, inducing measles immune responses (including neutralizing antibodies) and protection, boosting strategies can now be evaluated in animals primed with MV DNA vaccines.

Immunogenicity and safety of defective vaccinia virus lister: comparison with modified vaccinia virus Ankara

Potent and safe vaccinia virus vectors inducing cell-mediated immunity are needed for clinical use. Replicating vaccinia viruses generally induce strong cell-mediated immunity; however, they may have severe adverse effects. As a vector for clinical use, we assessed the defective vaccinia virus system, in which deletion of an essential gene blocks viral replication, resulting in an infectious virus that does not multiply in the host. The vaccinia virus Lister/Elstree strain, used during worldwide smallpox eradication, was chosen as the parental virus. The immunogenicity and safety of the defective vaccinia virus Lister were evaluated without and with the inserted human p53 gene as a model and compared to parallel constructs based on modified vaccinia virus Ankara (MVA), the present "gold standard" of recombinant vaccinia viruses in clinical development. The defective viruses induced an efficient Th1-type immune response. Antibody and cytotoxic-T-cell responses were comparable to those induced by MVA. Safety of the defective Lister constructs could be demonstrated in vitro in cell culture as well as in vivo in immunodeficient SCID mice. Similar to MVA, the defective viruses were tolerated at doses four orders of magnitude higher than those of the wild-type Lister strain. While current nonreplicating vectors are produced mainly in primary chicken cells, defective vaccinia virus is produced in a permanent safety-tested cell line. Vaccines based on this system have the additional advantage of enhanced product safety. Therefore, a vector system was made which promises to be a valuable tool not only for immunotherapy for diseases such as cancer, human immunodeficiency virus infection, or malaria but also as a basis for a safer smallpox vaccine.

Current overview of the pathogenesis and prophylaxis of measles with focus on practical implications

Measles is one of the most important diseases of mankind, which is so highly contagious and evokes such persistent immunity that the virus cannot be sustained in a population of less than about 500,000 persons. The first of the licensed live virus vaccines against measles was developed empirically and was approved in 1963. It provides high level and lasting immunity and is a paradigm for solving major medical problems without really understanding them. In spite of means for control by prophylactic immunization, research on measles infection continues to be part of the effort to understand the pathogenesis of many different viruses, which may have important similarities and differences and provide important insights. Measles, usually, is spontaneously reversible and is a prime model for understanding virus-induced immunodeficiency disease (AIDS) which is rarely reversible. Much has been learned of basic immunology and vaccinology in measles through observation of the inappropriate use of vaccines of appropriate composition, and through inappropriate host response to measles vaccines of inappropriate composition. This review provides a current overview of selected highlights of measles, the virus, its immunopathogenesis, and its control by use of live virus vaccine which may lead to elimination of the disease and eventually to eradication of the virus.