Cotton rats (Sigmodon hispidus): an animal model to study the pathogenesis of measles virus infection

A neutralizing antibody prevents postfusion transition of measles virus fusion protein

Measles virus (MeV) presents a public health threat that is escalating as vaccine coverage in the general population declines and as populations of immunocompromised individuals, who cannot be vaccinated, increase. There are no approved therapeutics for MeV. Neutralizing antibodies targeting viral fusion are one potential therapeutic approach but have not yet been structurally characterized or advanced to clinical use. We present cryo-electron microscopy (cryo-EM) structures of prefusion F alone [2.1-angstrom (Å) resolution], F complexed with a fusion-inhibitory peptide (2.3-Å resolution), F complexed with the neutralizing and protective monoclonal antibody (mAb) 77 (2.6-Å resolution), and an additional structure of postfusion F (2.7-Å resolution). In vitro assays and examination of additional EM classes show that mAb 77 binds prefusion F, arrests F in an intermediate state, and prevents transition to the postfusion conformation. These structures shed light on antibody-mediated neutralization that involves arrest of fusion proteins in an intermediate state.

Measles Encephalitis: Towards New Therapeutics

Measles remains a major cause of morbidity and mortality worldwide among vaccine preventable diseases. Recent decline in vaccination coverage resulted in re-emergence of measles outbreaks. Measles virus (MeV) infection causes an acute systemic disease, associated in certain cases with central nervous system (CNS) infection leading to lethal neurological disease. Early following MeV infection some patients develop acute post-infectious measles encephalitis (APME), which is not associated with direct infection of the brain. MeV can also infect the CNS and cause sub-acute sclerosing panencephalitis (SSPE) in immunocompetent people or measles inclusion-body encephalitis (MIBE) in immunocompromised patients. To date, cellular and molecular mechanisms governing CNS invasion are still poorly understood. Moreover, the known MeV entry receptors are not expressed in the CNS and how MeV enters and spreads in the brain is not fully understood. Different antiviral treatments have been tested and validated in vitro, ex vivo and in vivo, mainly in small animal models. Most treatments have high efficacy at preventing infection but their effectiveness after CNS manifestations remains to be evaluated. This review describes MeV neural infection and current most advanced therapeutic approaches potentially applicable to treat MeV CNS infection.

Epithelial cell lines of the cotton rat (Sigmodon hispidus) are highly susceptible in vitro models to zoonotic Bunya-, Rhabdo-, and Flaviviruses

Background

Small mammals such as bats and rodents have been increasingly recognized as reservoirs of novel potentially zoonotic pathogens. However, few in vitro model systems to date allow assessment of zoonotic viruses in a relevant host context. The cotton rat (Sigmodon hispidus) is a New World rodent species that has a long-standing history as an experimental animal model due to its unique susceptibility to human viruses. Furthermore, wild cotton rats are associated with a large variety of known or potentially zoonotic pathogens.

Methods

A method for the isolation and culture of airway epithelial cell lines recently developed for bats was applied for the generation of rodent airway and renal epithelial cell lines from the cotton rat. Continuous cell lines were characterized for their epithelial properties as well as for their interferon competence. Susceptibility to members of zoonotic Bunya-, Rhabdo-, and Flaviviridae, in particular Rift Valley fever virus (RVFV), vesicular stomatitis virus (VSV), West Nile virus (WNV), and tick-borne encephalitis virus (TBEV) was tested. Furthermore, novel arthropod-derived viruses belonging to the families Bunya-, Rhabdo-, and Mesoniviridae were tested.

Results

We successfully established airway and kidney epithelial cell lines from the cotton rat, and characterized their epithelial properties. Cells were shown to be interferon-competent. Viral infection assays showed high-titre viral replication of RVFV, VSV, WNV, and TBEV, as well as production of infectious virus particles. No viral replication was observed for novel arthropod-derived members of the Bunya-, Rhabdo-, and Mesoniviridae families in these cell lines.

Conclusion

In the current study, we showed that newly established cell lines from the cotton rat can serve as host-specific in vitro models for viral infection experiments. These cell lines may also serve as novel tools for virus isolation, as well as for the investigation of virus-host interactions in a relevant host species.

Pharmacokinetic study of neural stem cell-based cell carrier for oncolytic virotherapy: targeted delivery of the therapeutic payload in an orthotopic brain tumor model

Oncolytic virotherapy is a promising novel therapy for glioblastoma that needs to be optimized before introduced to clinic. The targeting of conditionally replicating adenoviruses (CRAds) can be improved by relying on the tumor tropic properties of neural stem cells (NSCs). Here, we report the characterization of an FDA approved NSC, HB1.F3-CD, as a cell carrier for CRAd-S-pk7, a glioma-tropic oncolytic adenovirus. We show that NSCs replicate and release infectious CRAd-S-pk7 progeny capable of lysing glioma cell lines. Moreover, ex-vivo loaded NSCs, injected intracranially in nude mice bearing human glioma xenografts (i) retained their tumor-tropism, (ii) continued to replicate CRAd-S-pk7 for more than a week after reaching the tumor site and (iii) successfully handed-off CRAd-S-pk7 to glioma cells in vivo. Delivery via carrier cells reduced non-specific adenovirus distribution in the mouse brain. Moreover, we assessed biodistribution of loaded NSCs after intracranial injection in animal models semi-permissive to adenovirus replication, the Syrian hamster and cotton rat. NSCs did not migrate to distant organs and high levels of CRAd-S-pk7 DNA were observed only in the injected hemisphere. In conclusion, this optimized carrier system, with high efficiency of adenovirus delivery and minimal systemic toxicity, poses considerable advantages for anti-glioma oncolytic virotherapy.

Making it to the synapse: measles virus spread in and among neurons

Measles virus (MV) is one of the most transmissible microorganisms known, continuing to result in extensive morbidity and mortality worldwide. While rare, MV can infect the human central nervous system, triggering fatal CNS diseases weeks to years after exposure. The advent of crucial laboratory tools to dissect MV neuropathogenesis, including permissive transgenic mouse models, the capacity to manipulate the viral genome using reverse genetics, and cell biology advances in understanding the processes that govern intracellular trafficking of viral components, have substantially clarified how MV infects, spreads, and persists in this unique cell population. This review highlights some of these technical advances, followed by a discussion of our present understanding of MV neuronal infection and transport. Because some of these processes may be shared among diverse viruses, comparisons are made to parallel studies with other neurotropic viruses. While a crystallized view of how the unique environment of the neuron affects MV replication, spread, and, ultimately, neuropathogenesis is not fully realized, the tools and ideas are in place for exciting advances in the coming years.

Sindbis virus-based measles DNA vaccines protect cotton rats against respiratory measles: relevance of antibodies, mucosal and systemic antibody-secreting cells, memory B cells, and Th1-type cytokines as correlates of immunity

Measles remains an important cause of pediatric morbidity and mortality in developing countries, especially among infants who are too young to receive the current licensed live attenuated measles vaccine. We developed two Sindbis virus DNA vaccines encoding the measles virus hemagglutinin (pMSIN-H) and fusion proteins (pMSINH-FdU) and examined their immunogenicities and protective efficacies when administered alone or followed by the live measles virus vaccine in cotton rats. Neutralizing antibodies, mucosal and systemic antibody-secreting cells, memory B cells, and gamma interferon-secreting T cells developed after priming and increased after boosting. pMSIN-H priming conferred 100% protection against pulmonary measles, whereas pMSINH-FdU protected only in conjunction with the live measles virus vaccine boost.

Measles virus-induced immunosuppression

Immunosuppression is the major cause of infant death associated with acute measles and therefore of substantial clinical importance. Major hallmarks of this generalized modulation of immune functions are (1) lymphopenia, (2) a prolonged cytokine imbalance consistent with suppression of cellular immunity to secondary infections, and (3) silencing of peripheral blood lymphocytes, which cannot expand in response to ex vivo stimulation. Lymphopenia results from depletion, which can occur basically at any stage of lymphocyte development, and evidently, expression of the major MV receptor CD150 plays an important role in targeting these cells. Virus transfer to T cells is thought to be mediated by dendritic cells (DCs), which are considered central to the induction of T cell silencing and functional skewing. As a consequence of MV interaction, viability and functional differentiation of DCs and thereby their expression pattern of co-stimulatory molecules and soluble mediators are modulated. Moreover, MV proteins expressed by these cells actively silence T cells by interfering with signaling pathways essential for T cell activation.

Measles virus and CD46

Measles virus (MV) was isolated in 1954 (Enders and Peeble 1954). It is among the most contagious of viruses and a leading cause of mortality in children in developing countries (Murray and Lopez 1997; Griffin 2001; Bryce et al. 2005). Despite intense research over decades on the biology and pathogenesis of the virus and the successful development in 1963 of an effective MV vaccine (Cutts and Markowitz 1994), cell entry receptor(s) for MV remained unidentified until 1993. Two independent studies showed that transfection of nonsusceptible rodent cells with human CD46 renders these cells permissive to infection with the Edmonston and Halle vaccine strains of measles virus (Dorig et al. 1993; Naniche et al. 1993). A key finding in these investigations was that MV binding and infection was inhibited by monoclonal and polyclonal antibodies to CD46. These reports established CD46 as a MV cell entry receptor. This chapter summarizes the role of CD46 in measles virus infection.

Disease manifestations of canine distemper virus infection in ferrets are modulated by vitamin A status

The measles virus (MV) causes half a million childhood deaths annually. Vitamin A supplements significantly reduce measles-associated mortality and morbidity. The mechanisms whereby vitamin A acts against MV are not understood and currently there is no satisfactory small animal model for MV infection. We report on the development of a ferret model to study antiviral activity of vitamin A against canine distemper virus (CDV). CDV is closely related to MV at the molecular level and distemper in ferrets mimics measles in humans. We infected vitamin A-replete (control) and vitamin A-depleted ferrets with CDV and assessed the ability of high-dose vitamin A supplements to influence CDV disease. In control ferrets, CDV infection caused fever, rash, conjunctivitis, cough, coryza, and diarrhea. In contrast, control ferrets that were given 30 mg of vitamin A did not develop typical distemper after infection and exhibited only a mild rash. The supplement did not negatively affect ferret health and resulted in a 100% increase in serum and liver vitamin A concentrations. We also found that profound vitamin A deficiency is inducible in ferrets and can be rapidly reversed upon high-dose vitamin A supplementation. Vitamin A deficiency caused anorexia, diarrhea, cataracts, behavioral abnormalities, and ultimately death, with or without CDV infection. All ferrets that received vitamin A supplements, however, recovered uneventfully from CDV infection. These results replicate many aspects of the observations of vitamin A therapy in humans with measles and suggest that CDV infection in ferrets is an appropriate model for the study of the antiviral mechanism of vitamin A.

Probing neutralizing-antibody responses against emerging measles viruses (MVs): immune selection of MV by H protein-specific antibodies?

Measles virus (MV) infection and vaccination induce long-lasting immunity and neutralizing-antibody responses that are directed against the MV haemagglutinin (H) and the fusion (F) protein. A new MV genotype, D7, emerged recently in western Germany and rapidly replaced the long-term endemically circulating genotypes C2 and D6. Analysis of the H gene of C2, D6, D7 and vaccine viruses revealed uniform sequences for each genotype. Interestingly, a consistent exchange of seven distinct amino acids in the D7 H was observed when compared with residues shared between C2, D6 and vaccine viruses, and one exchange (D416→N) in the D7 H was associated with an additionalN-linked glycosylation. In contrast, the F gene is highly conserved between MVs of these genotypes. To test whether the D7 H protein escapes from antibody responses that were raised against earlier circulating or vaccine viruses, the neutralizing capacity of mAbs recognizing seven distinct domains on the H of an Edmonston-related MV was compared. The mAbs revealed a selective and complete loss of two neutralizing epitopes on the D7 H when compared with C2, D6 and vaccine viruses. To assess whether these alterations of the D7 H affect the neutralizing capacity of polyclonal B-cell responses, genotype-specific antisera were produced in cotton rats. However, no significant genotype-dependent difference was found. Likewise, human sera obtained from vaccinees (n=7) and convalescents (n=6) did not distinguish between the MV genotypes. Although the hypothesis of selection of D7 viruses by pre-existing neutralizing antibodies is compatible with the differing pattern of neutralizing epitopes on the H protein, it was not confirmed by the results of MV neutralization with polyclonal sera.

Morbilliviruses and human disease

Morbilliviruses are a group of viruses that belong to the family Paramyxoviridae. The most instantly recognizable member is measles virus (MV) and individuals acutely infected with the virus exhibit a wide range of clinical symptoms ranging from a characteristic mild self-limiting infection to death. Canine distemper virus (CDV) and rinderpest virus (RPV) cause a similar but distinctive pathology in dogs and cattle, respectively, and these, alongside experimental MV infection of primates, have been useful models for MV pathogenesis. Traditionally, viruses were identified because a distinctive disease was observed in man or animals; an infectious agent was subsequently isolated, cultured, and this could be used to recapitulate the disease in an experimentally infected host. Thus, satisfying Koch's postulates has been the norm. More recently, particularly due to the advent of exceedingly sensitive molecular biological assays, many researchers have looked for infectious agents in disease conditions for which a viral aetiology has not been previously established. For these cases, the modified Koch's postulates of Bradford Hill have been developed as criteria to link a virus to a specific disease. Only in a few cases have these conditions been fulfilled. Therefore, many viruses have over the years been definitely and tentatively linked to human diseases and in this respect the morbilliviruses are no different. In this review, human diseases associated with morbillivirus infection have been grouped into three broad categories: (1) those which are definitely caused by the infection; (2) those which may be exacerbated or facilitated by an infection; and (3) those which currently have limited, weak, unsubstantiated or no credible scientific evidence to support any link to a morbillivirus. Thus, an attempt has been made to clarify the published data and separate human diseases actually linked to morbilliviruses from those that are merely anecdotally associated.

Tropism illuminated: lymphocyte-based pathways blazed by lethal morbillivirus through the host immune system

The immunosuppressive properties of morbilliviruses including measles and canine distemper virus (CDV) are well known, but the host cells supporting infection are poorly characterized. To identify these cells, a recombinant CDV expressing green fluorescent protein was produced by reverse genetics based on a wild-type strain lethal for ferrets. This recombinant virus fully retained virulence and blazed three lymphocyte-based pathways through the immune system of its host: first, it infected rapidly and massively circulating B and T cells; second, it took over and damaged secondary lymphatic organs including spleen, lymph nodes, and gut-associated and mucosal lymphoid tissues; third, it infected most thymocytes. In contrast, replication in epithelial cells was initially not detectable, but substantial before host death. Thus, CDV initially infects lymphocytes and massively replicates therein, thereby causing immunosuppression and preparing systemic invasion and host escape.

The cotton rat: an underutilized animal model for human infectious diseases can now be exploited using specific reagents to cytokines, chemokines, and interferons

The cotton rat represents the best or only animal model for a large number of human infectious diseases, and it may be unique among small laboratory animals in its susceptibility to several potential agents of bioterrorism. Although the cotton rat is a reliable model to define pathologic changes produced during infection with human pathogens, the lack of specific reagents has precluded a more extensive analysis of the molecular basis of pathogenesis. Here, we report the cloning of 24 cotton rat genes encoding various cytokines, chemokines, and interferons (IFNs). Analysis of the expression of most of these genes was performed by RT-PCR in cotton rat macrophages during treatment with lipopolysaccharide (LPS) and in cotton rat lungs after infection with influenza virus. The availability of these reagents will provide the tools for molecular analysis of pathogenesis and immune responses to a wide variety of pathogens and set the basis for the development of new prophylactic and therapeutic strategies against human infectious diseases.

Selectively receptor-blind measles viruses: Identification of residues necessary for SLAM- or CD46-induced fusion and their localization on a new hemagglutinin structural model

Measles virus (MV) enters cells either through the signaling lymphocyte activation molecule SLAM (CD150) expressed only in immune cells or through the ubiquitously expressed regulator of complement activation, CD46. To identify residues on the attachment protein hemagglutinin (H) essential for fusion support through either receptor, we devised a strategy based on analysis of morbillivirus H-protein sequences, iterative cycles of mutant protein production followed by receptor-based functional assays, and a novel MV H three-dimensional model. This model uses the Newcastle disease virus hemagglutinin-neuraminidase protein structure as a template. We identified seven amino acids important for SLAM- and nine for CD46 (Vero cell receptor)-induced fusion. The MV H three-dimensional model suggests (i) that SLAM- and CD46-relevant residues are located in contiguous areas in propeller beta-sheets 5 and 4, respectively; (ii) that two clusters of SLAM-relevant residues exist and that they are accessible for receptor contact; and (iii) that several CD46-relevant amino acids may be shielded from direct receptor contacts. It appears likely that certain residues support receptor-specific H-protein conformational changes. To verify the importance of the H residues identified with the cell-cell fusion assays for virus entry into cells, we transferred the relevant mutations into genomic MV cDNAs. Indeed, we were able to recover recombinant viruses, and we showed that these replicate selectively in cells expressing SLAM or CD46. Selectively receptor-blind viruses will be used to study MV pathogenesis and may have applications for the production of novel vaccines and therapeutics.

A ferret model of canine distemper virus virulence and immunosuppression

Canine distemper virus (CDV) infects many carnivores, including ferrets and dogs, and is the member of the Morbillivirus genus most easily amenable to experimentation in a homologous small-animal system. To gain insights into the determinants of CDV pathogenesis, we isolated a strain highly virulent for ferrets by repeated passaging in these animals. Sequence comparison of the genome of this strain with that of its highly attenuated precursor revealed 19 mutations distributed almost evenly in the six genes. We then recovered a virus from a cDNA copy of the virulent CDV strain's consensus sequence by using a modified reverse genetics system based on B cells. We infected ferrets with this virus and showed that it fully retained virulence as measured by the timing of rash appearance, disease onset, and death. Body temperature, leukocyte number, lymphocyte proliferation activity, and cell-associated viremia also had similar kinetics. We then addressed the question of the relative importance of the envelope and other viral constituents for virulence. Viruses in which the envelope genes (matrix, fusion, and hemagglutinin) of the virulent strain were combined with the other genes of the attenuated strain caused severe rash and fever even if the disease onset was delayed. Viruses in which the nucleocapsid, polymerase, and phosphoprotein genes (coding also for the V and C proteins) of the virulent strain were combined with the envelope genes of the attenuated strain caused milder signs of disease. Thus, virulence-inducing mutations have accumulated throughout the genome.

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.

Enhanced protection against the migratory phase, but defective protection against the intestinal phase of Strongyloides venezuelensis infection in cotton rats, Sigmodon hispidus

The protective capacity of the cotton rat, Sigmodon hispidus, against the migratory and intestinal phases of Strongyloides venezuelensis infection was examined. After subcutaneous infection with infective larvae (L(3)), adult worm recovery rates from male and female animals on Day 71 were only 0.10% and 0.06% of initial dose, respectively. To determine whether this enhanced protection was expressed during the migratory phase or the intestinal phase, larval recovery from the lungs of cotton rat was evaluated 3 days after subcutaneous L(3) infection. The larval recovery rate was only 0.5% of initial dose and about 40-fold lower than that from control mice. Protection in the intestine was also evaluated after intraduodenal implantation of adult worms. About 30% of implanted worms became established and worm burden remained constant until Day 28. Despite a high worm burden on Day 28, EPG was about 25-fold lower than the peak count. To evaluate expulsive capacity and monitor the cellular responses in the intestine of cotton rats, adult Nippostrongylus brasiliensis worms were implanted in addition to S. venezuelensis. Cotton rats were unable to expel adult S. venezuelensis worms, even after 21 days of observation. Although the number of mucosal mast cells increased significantly, the intraepithelial migration of mast cells was not observed. In contrast, N. brasiliensis was expelled by Day 6 in association with goblet cell hyperplasia. These results suggest that in cotton rats, the defective intestinal protection against adult S. venezuelensis worms results from dysfunction of mucosal mast cells.

Resistance of cotton rats, Sigmodon hispidus, to primary infection by Nippostrongylus brasiliensis

The resistance of cotton rats, Sigmodon hispidus to Nippostrongylus brasiliensis infection was examined and compared the response to that of the susceptible Indian soft-furred rat, Millardia meltada. After a primary infection with infective third-stage N. brasiliensis larvae (L3), the number of eggs in feces and adult worm recovery rates from the small intestine of cotton rats were significantly lower than in the controls. To determine whether cotton rat resistance was observed during the migratory phase or the intestinal phase, cotton rats and control animals were challenged subcutaneously with L3 or intraduodenally with adult worms, and larval recovery from lungs and adult worm burden were evaluated. The recovery rate of larvae from the lungs of cotton rats was about five-fold lower than from controls. Adult worm recovery from the small intestine of cotton rats was also lower than that from the controls, but the difference (two-fold lower) was smaller than that observed for lung recovery. Carbon treatment at a dose of 250-500 mg/kg effectively increased larval worm recovery from the lungs of cotton rats. However, this treatment had no effect on worm recovery from the intestine after intraduodenal implantation of adult N. brasiliensis. These results suggest that macrophage function have important role in the expression of strong resistance during the migratory phase of N. brasiliensis infection in cotton rats.

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.

Use of cotton rats for preclinical evaluation of measles vaccines

The continued prevalence and medical impact of measles worldwide has created interest in the development of new generations of measles vaccines. Monkeys can be used for preclinical testing of these vaccines. However, a more practical and less expensive animal model is highly desirable, particularly for initial vaccine development and evaluation. Cotton rats have been shown to support the replication of different strains of measles virus (MV), and thus may be useful for these purposes. To test this concept, the immunogenicity and protective efficacy of two standard (Moraten and trivalent measles, mumps, rubella) and four experimental (two recombinant ALVAC, one ISCOM subunit and live attenuated Edmonston-Zagreb) MV vaccines were evaluated in naïve cotton rats, and cotton rats with passively acquired MV-specific neutralizing serum antibodies. All of the test vaccines were immunogenic and protected naíve animals from pulmonary infection and viral dissemination. However, under the conditions utilized, only the Edmonston-Zagreb vaccine provided such protection to animals with significant levels of passively acquired MV-specific neutralizing antibodies. The results of these tests and the potential of using cotton rats as an animal model for preliminary testing of MV vaccines are discussed.

Use of cotton rats to evaluate the efficacy of antivirals in treatment of measles virus infections

No practical animal models for the testing of chemotherapeutic or biologic agents identified in cell culture assays as being active against measles virus (MV) are currently available. Cotton rats may serve this purpose. To evaluate this possibility, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide (EICAR) and poly(acrylamidomethyl propanesulfonate) (PAMPS), two compounds that have been reported to inhibit MV in vitro, and ribavirin, an established antiviral drug with MV-inhibitory activity, were evaluated for their antiviral activities against MV and respiratory syncytial virus (RSV) in tissue culture and in hispid cotton rats. A single administration of PAMPS markedly inhibited pulmonary RSV or MV replication (>3 log(10) reduction in pulmonary titer compared to that for controls), but only if this compound was administered intranasally at about the time of virus inoculation. Both EICAR and ribavirin exhibited therapeutic activity against RSV and MV in cotton rats when they were administered parenterally. However, both of these compounds were less effective against MV. On the basis of the pulmonary virus titers on day 4 after virus inoculation, the minimal efficacious dose of EICAR against MV (120 mg/kg of body weight/day when delivered intraperitoneally twice daily) appeared to be three times lower against this virus than that of ribavirin delivered at a similar dose (i.e., 360 mg/kg/day). These findings correlated with those obtained in vitro. The data obtained suggest that cotton rats may indeed be useful for the initial evaluation of the activities of antiviral agents against MV.

Neutralization of measles virus wild-type isolates after immunization with a synthetic peptide vaccine which is not recognized by neutralizing passive antibodies

The sequence H379-410 of the measles virus haemagglutinin (MV-H) protein forms a surface-exposed loop and contains three cysteine residues (Cys-381, Cys-386 and Cys-394) which are conserved among all measles isolates. It comprises the minimal sequential B cell epitope (BCE) (H386-400) of the neutralizing and protective MAb BH6 that neutralizes all wild-type viruses tested. The aim of this study was to design synthetic peptides which induce neutralizing antibodies against MV wild-type isolates. Peptides containing one or two copies of T cell epitopes (TCE) and BCEs of different lengths (H386-400, B(CC); H379-400, B(CCC)), in different combinations and orientations were produced and iteratively optimized for inducing neutralizing antibodies. Peptides with the shorter BCE induced sera that cross-reacted with MV but did not neutralize. The longer BCE containing the three cysteines (B(CCC)) and two homologous TCE were required for neutralization activity. These sera neutralized wild-type strains of different clades and geographic origins. Neutralizing serum was also obtained after immunization with human promiscuous TCEs. Furthermore B(CCC)-based peptides were fully immunogenic even in the presence of pre-existing MV-specific antibodies. The results suggest that subunit vaccines based on such peptides could potentially be used to actively protect infants against wild-type viruses irrespective of persisting maternal antibodies.