Measles Virus: Identification in the M Protein Primary Sequence of a Potential Molecular Marker for Subacute Sclerosing Panencephalitis.

Subacute Sclerosing Panencephalitis (SSPE), a rare lethal disease of children and young adults due to persistence of measles virus (MeV) in the brain, is caused by wild type (wt) MeV. Why MeV vaccine strains never cause SSPE is completely unknown. Hypothesizing that this phenotypic difference could potentially be represented by a molecular marker, we compared glycoprotein and matrix (M) genes from SSPE cases with those from the Moraten vaccine strain, searching for differential structural motifs. We observed that all known SSPE viruses have residues P64, E89, and A209 (PEA) in their M proteins whereas the equivalent residues for vaccine strains are either S64, K89, and T209 (SKT) as in Moraten or PKT. Through the construction of MeV recombinants, we have obtained evidence that the wt MeV-M protein PEA motif, in particular A209, is linked to increased viral spread. Importantly, for the 10 wt genotypes (of 23) that have had their M proteins sequenced, 9 have the PEA motif, the exception being B3, which has PET. Interestingly, cases of SSPE caused by genotype B3 have yet to be reported. In conclusion, our results strongly suggest that the PEA motif is a molecular marker for wt MeV at risk to cause SSPE.

Mutations in the H, F, or M Proteins Can Facilitate Resistance of Measles Virus to Neutralizing Human Anti-MV Sera.

Although there is currently no evidence of emerging strains of measles virus (MV) that can resist neutralization by the anti-MV antibodies present in vaccinees, certain mutations in circulating wt MV strains appear to reduce the efficacy of these antibodies. Moreover, it has been hypothesized that resistance to neutralization by such antibodies could allow MV to persist. In this study, we use a novel in vitro system to determine the molecular basis of MV's resistance to neutralization. We find that both wild-type and laboratory strain MV variants that escape neutralization by anti-MV polyclonal sera possess multiple mutations in their H, F, and M proteins. Cytometric analysis of cells expressing viral escape mutants possessing minimal mutations and their plasmid-expressed H, F, and M proteins indicates that immune resistance is due to particular mutations that can occur in any of these three proteins that affect at distance, rather than directly, the native conformation of the MV-H globular head and hence its epitopes. A high percentage of the escape mutants contain mutations found in cases of Subacute Sclerosing Panencephalitis (SSPE) and our results could potentially shed light on the pathogenesis of this rare fatal disease.

Lentiviral vectors displaying modified measles virus gp overcome pre-existing immunity in in vivo-like transduction of human T and B cells.

Gene transfer into quiescent T and B cells is important for gene therapy and immunotherapy approaches. Previously, we generated lentiviral vectors (LVs) pseudotyped with Edmonston (Ed) measles virus (MV) hemagglutinin (H) and fusion (F) glycoproteins (H/F-LVs), which allowed efficient transduction of quiescent human T and B cells. However, a major obstacle in the use of H/F-LVs in vivo is that most of the human population is vaccinated against measles. As the MV humoral immune response is exclusively directed against the H protein of MV, we mutated the two dominant epitopes in H, Noose, and NE. LVs pseudotyped with these mutant H-glycoproteins escaped inactivation by monoclonal antibodies (mAbs) but were still neutralized by human serum. Consequently, we took advantage of newly emerged MV-D genotypes that were less sensitive to MV vaccination due to a different glycosylation pattern. The mutation responsible was introduced into the H/F-LVs, already mutated for Noose and NE epitopes. We found that these mutant H/F-LVs could efficiently transduce quiescent lymphocytes in the presence of high concentrations of MV antibody-positive human serum. Finally, upon incubation with total blood, mimicking the in vivo situation, the mutant H/F-LVs escaped MV antibody neutralization, where the original H/F-LVs failed. Thus, these novel H/F-LVs offer perspectives for in vivo lymphocyte-based gene therapy and immunotherapy.

Measles virus glycoprotein-pseudotyped lentiviral vector-mediated gene transfer into quiescent lymphocytes requires binding to both SLAM and CD46 entry receptors.

Gene transfer into quiescent T and B cells is of importance for gene therapy and immunotherapy approaches to correct hematopoietic disorders. Previously, we generated lentiviral vectors (LVs) pseudotyped with the Edmonston measles virus (MV) hemagglutinin and fusion glycoproteins (Hgps and Fgps) (H/F-LVs), which, for the first time, allowed efficient transduction of quiescent human B and T cells. These target cells express both MV entry receptors used by the vaccinal Edmonston strain, CD46 and signaling lymphocyte activation molecule (SLAM). Interestingly, LVs pseudotyped with an MV Hgp, blind for the CD46 binding site, were completely inefficient for resting-lymphocyte transduction. Similarly, SLAM-blind H mutants that recognize only CD46 as the entry receptor did not allow stable LV transduction of resting T cells. The CD46-tropic LVs accomplished vector-cell binding, fusion, entry, and reverse transcription at levels similar to those achieved by the H/F-LVs, but efficient proviral integration did not occur. Our results indicate that both CD46 and SLAM binding sites need to be present in cis in the Hgp to allow successful stable transduction of quiescent lymphocytes. Moreover, the entry mechanism utilized appears to be crucial: efficient transduction was observed only when CD46 and SLAM were correctly engaged and an entry mechanism that strongly resembles macropinocytosis was triggered. Taken together, our results suggest that although vector entry can occur through the CD46 receptor, SLAM binding and subsequent signaling are also required for efficient LV transduction of quiescent lymphocytes to occur.

Nipah virus entry can occur by macropinocytosis.

Nipah virus (NiV) is a zoonotic biosafety level 4 paramyxovirus that emerged recently in Asia with high mortality in man. NiV is a member, with Hendra virus (HeV), of the Henipavirus genus in the Paramyxoviridae family. Although NiV entry, like that of other paramyxoviruses, is believed to occur via pH-independent fusion with the host cell's plasma membrane we present evidence that entry can occur by an endocytic pathway. The NiV receptor ephrinB2 has receptor kinase activity and we find that ephrinB2's cytoplasmic domain is required for entry but is dispensable for post-entry viral spread. The mutation of a single tyrosine residue (Y304F) in ephrinB2's cytoplasmic tail abrogates NiV entry. Moreover, our results show that NiV entry is inhibited by constructions and drugs specific for the endocytic pathway of macropinocytosis. Our findings could potentially permit the rapid development of novel low-cost antiviral treatments not only for NiV but also HeV.

Acute Hendra virus infection: Analysis of the pathogenesis and passive antibody protection in the hamster model.

Hendra virus (HeV) and Nipah virus (NiV) are recently-emerged, closely related and highly pathogenic paramyxoviruses. We have analysed here the pathogenesis of the acute HeV infection using the new animal model, golden hamster (Mesocricetus auratus), which is highly susceptible to HeV infection. HeV-specific RNA and viral antigens were found in multiple organs and virus was isolated from different tissues. Dual pathogenic mechanism was observed: parenchymal infection in various organs, including the brain, with vasculitis and multinucleated syncytia in many blood vessels. Furthermore, monoclonal antibodies specific for the NiV fusion protein neutralized HeV in vitro and efficiently protected hamsters from HeV if given before infection. These results reveal the similarities between HeV and NiV pathogenesis, particularly in affecting both respiratory and neuronal system. They demonstrate that hamster presents a convenient novel animal model to study HeV infection, opening new perspectives to evaluate vaccine and therapeutic approaches against this emergent infectious disease.

Evidence of a potential receptor-binding site on the Nipah virus G protein (NiV-G): identification of globular head residues with a role in fusion promotion and their localization on an NiV-G structural model.

As a preliminary to the localization of the receptor-binding site(s) on the Nipah virus (NiV) glycoprotein (NiV-G), we have undertaken the identification of NiV-G residues that play a role in fusion promotion. To achieve this, we have used two strategies. First, as NiV and Hendra virus (HeV) share a common receptor and their cellular tropism is similar, we hypothesized that residues functioning in receptor attachment could be conserved between their respective G proteins. Our initial strategy was to target charged residues (which can be expected to be at the surface of the protein) conserved between the NiV-G and HeV-G globular heads. Second, we generated NiV variants that escaped neutralization by anti-NiV-G monoclonal antibodies (MAbs) that neutralize NiV both in vitro and in vivo, likely by blocking receptor attachment. The sequencing of such "escape mutants" identified NiV-G residues present in the epitopes to which the neutralizing MAbs are directed. Residues identified via these two strategies whose mutation had an effect on fusion promotion were localized on a new structural model for the NiV-G protein. Our results suggest that seven NiV-G residues, including one (E533) that was identified using both strategies, form a contiguous site on the top of the globular head that is implicated in ephrinB2 binding. This site commences near the shallow depression in the center of the top surface of the globular head and extends to the rim of the barrel-like structure on the top loops of beta-sheet 5. The topology of this site is strikingly similar to that proposed to form the SLAM receptor site on another paramyxovirus attachment protein, that of the measles virus hemagglutinin.

High pathogenicity of wild-type measles virus infection in CD150 (SLAM) transgenic mice.

Measles virus (MV) infection causes an acute childhood disease, associated in certain cases with infection of the central nervous system and development of a severe neurological disease. We have generated transgenic mice ubiquitously expressing the human protein SLAM (signaling lymphocytic activation molecule), or CD150, recently identified as an MV receptor. In contrast to all other MV receptor transgenic models described so far, in these mice infection with wild-type MV strains is highly pathogenic. Intranasal infection of SLAM transgenic suckling mice leads to MV spread to different organs and the development of an acute neurological syndrome, characterized by lethargy, seizures, ataxia, weight loss, and death within 3 weeks. In addition, in this model, vaccine and wild-type MV strains can be distinguished by virulence. Furthermore, intracranial MV infection of adult transgenic mice generates a subclinical infection associated with a high titer of MV-specific antibodies in the serum. Finally, to analyze new antimeasles therapeutic approaches, we created a recombinant soluble form of SLAM and demonstrated its important antiviral activity both in vitro and in vivo. Taken together, our results show the high susceptibility of SLAM transgenic mice to MV-induced neurological disease and open new perspectives for the analysis of the implication of SLAM in the neuropathogenicity of other morbilliviruses, which also use this molecule as a receptor. Moreover, this transgenic model, in allowing a simple readout of the efficacy of an antiviral treatment, provides unique experimental means to test novel anti-MV preventive and therapeutic strategies.

Immunization with plasmid DNA encoding the hemagglutinin and the nucleoprotein confers robust protection against a lethal canine distemper virus challenge.

We have investigated the protective effect of immunization of a highly susceptible natural host of canine distemper virus (CDV) with DNA plasmids encoding the viral nucleoprotein (N) and hemagglutinin (H). The combined intradermal and intramuscular routes of immunization elicited high virus-neutralizing serum antibody titres in mink (Mustela vison). To mimic natural exposure, we also conducted challenge infection by horizontal transmission from infected contact animals. Other groups received a lethal challenge infection by administration to the mucosae of the respiratory tract and into the muscle. One of the mink vaccinated with N plasmid alone developed severe disease after challenge. In contrast, vaccination with the H plasmid together with the N plasmid conferred solid protection against disease and we were unable to detect CDV infection in PBMCs or in different tissues after challenge. Our findings show that DNA immunization by the combined intradermal and intramuscular routes can confer solid protective immunity against naturally transmitted morbillivirus infection and disease.

Measles virus (MV) hemagglutinin: evidence that attachment sites for MV receptors SLAM and CD46 overlap on the globular head.

Measles virus hemagglutinin (MVH) residues potentially responsible for attachment to the wild-type (wt) MV receptor SLAM (CD150) have been identified and localized on the MVH globular head by reference to a revised hypothetical structural model for MVH (www.pepscan.nl/downloads/measlesH.pdb). We show that the mutation of five charged MVH residues which are conserved among morbillivirus H proteins has major effects on both SLAM downregulation and SLAM-dependent fusion. In the three-dimensional surface representation of the structural model, three of these residues (D505, D507, and R533) align the rim on one side of the cavity on the top surface of the MVH globular head and form the basis of a single continuous site that overlaps with the 546-548-549 CD46 binding site. We show that the overlapping sites fall within the footprint of an anti-MVH monoclonal antibody that neutralizes both wt and laboratory-vaccine MV strains and whose epitope contains R533. Our study does not exclude the possibility that Y481 binds CD46 directly but suggests that the N481Y mutation of wt MVH could influence, at a distance, the conformation of the overlapping sites so that affinity to CD46 increases. The relevance of these results to present concepts of MV receptor usage is discussed, and an explanation is proposed as to why morbillivirus attachment proteins are H, whereas those from the other paramyxoviruses are HN (hemagglutinin-neuraminidase).

Specific detection of Nipah virus using real-time RT-PCR (TaqMan).

Nipah and Hendra viruses belong to the novel Henipavirus genus of the Paramyxoviridae family. Its zoonotic circulation in bats and recent emergence in Malaysia with fatal consequences for humans that were in close contact with infected pigs, has made the reinforcement of epidemiological and clinical surveillance systems a priority. In this study, TaqMan RT-PCR of the Nipah nucleoprotein has been developed so that Nipah virus RNA in field specimens or laboratory material can be characterized rapidly and specifically and quantitated. The linearity of the standard curve allowed quantification of 10(3) to 10(9) RNA transcripts. The sensitivity of the test was close to 1 pfu. The kinetics of Nipah virus production in Vero cells was monitored by the determination of infectious virus particles in the supernatant fluid and by quantitation of the viral RNA. Approximately, 1000 RNA molecules were detected per virion, suggesting the presence of many non-infectious particles, similar to other RNA viruses. TaqMan real-time RT-PCR failed to detect Hendra virus DNA. Importantly, the method was able to detect virus despite a similar ratio in viremic sera from hamsters infected with Nipah virus. This standardized technique is sensitive and reliable and allows rapid detection and quantitation of Nipah RNA in both field and experimental materials used for the surveillance and specific diagnosis of Nipah virus.

Identification of a second major site for CD46 binding in the hemagglutinin protein from a laboratory strain of measles virus (MV): potential consequences for wild-type MV infection.

Natural or wild-type (wt) measles virus (MV) infection in vivo which is restricted to humans and certain monkeys represents an enigma in terms of receptor usage. Although wt MV is known to use the protein SLAM (CD150) as a cell receptor, many human tissues, including respiratory epithelium in which the infection initiates, are SLAM negative. These tissues are CD46 positive, but wt MV strains, unlike vaccinal and laboratory MV strains, are not thought to use CD46 as a receptor. We have identified a novel CD46 binding site at residues S548 and F549, in the hemagglutinin (H) protein from a laboratory MV strain, which is also present in wt H proteins. Our results suggest that although wt MV interacts with SLAM with high affinity, it also possesses the capacity to interact with CD46 with low affinity.

The terminal six amino-acids of the carboxy cytoplasmic tail of CD36 contain a functional domain implicated in the binding and capture of oxidized low-density lipoprotein.

CD36, a major adhesion molecule expressed by monocytes/macrophages, plays a key role in the binding and internalization of oxidized low-density lipoprotein (OxLDL). This adhesion molecule, a member of an important scavenger receptor family, contains a very short C-terminal cytoplasmic tail that is known to induce intracellular signalling events. However, the domains on the cytoplasmic tail involved in such signal transduction are unknown. In this study, we have investigated the functional components of the cytoplasmic tail by site-directed mutagenesis coupled with functional OxLDL and monoclonal antibody (mAb) binding studies. Seven truncated or punctual CD36 constructs, localized in the cytoplasmic tail, were produced by site-directed mutagenesis. Each construct was stably expressed in HEK293 cells. We used a quantitative and a qualitative method, labelling OxLDL with either iodine or rhodamine, to determine the functional importance of the cytoplasmic domains in OxLDL internalization. Results indicate that: (1) a deletion of the last amino-acid (construct K472STOP) significantly reduces, compared with wild-type, the binding, internalization and degradation of OxLDL; (2) truncation of the last six amino-acids (construct R467STOP) significantly reduces OxLDL binding; (3) the above two constructs (K472STOP and R467STOP) showed a reduced rate of OxLDL internalization compared with wild-type; (4) the binding and rate of internalization of an anti-CD36 monoclonal antibody (10/5) was not affected by the above mentioned mutants (K472STOP and R467STOP), compared with wild-type. This study shows, for the first time, a specific site on the CD36 cytoplasmic tail that is critical for the binding, endocytosis and targeting of OxLDL.