Formaldehyde inactivation of measles virus abolishes CD46-dependent presentation of nucleoprotein to murine class I-restricted CTLs but not to class II-restricted helper T cells

Assessment and verification of chemical inactivation of peste des petits ruminants virus by virus isolation following virus capture using Nanotrap magnetic virus particles

IMPORTANCE

Research including diagnosis on highly contagious viruses at the molecular level such as PCR and next-generation sequencing requires complete inactivation of the virus to ensure biosafety and biosecurity so that any accidental release of the virus does not compromise the safety of the susceptible population and the environment. In this work, peste des petits ruminants virus (PPRV) was inactivated with chemical agents, and the virus inactivation was confirmed by virus isolation (VI) using Vero cells. Since the chemical agents are cytotoxic, inactivated virus (PPRV) was diluted 1:100 to neutralize cytotoxicity, and the residual viruses (if any) were captured using Nanotrap magnetic virus particles (NMVPs). The NMVPs and the captured viruses were subjected to VI. No CPE was observed, indicating complete inactivation, and the results were further supported by real-time RT-PCR. This new protocol to verify virus inactivation can be applicable to other viruses.

Biotechnological Applications of an Insect-Specific Alphavirus

The coupling of viral and arthropod host diversity, with evolving methods of virus discovery, has resulted in the identification and classification of a growing number of novel insect-specific viruses (ISVs) that appear to be evolutionarily related to many human pathogens but have either lost or have yet to gain the ability to replicate in vertebrates. The discovery of ISVs has raised many questions as to the origin and evolution of many human pathogenic viruses and points to the role that arthropods may play in this evolutionary process. Furthermore, the use of ISVs to control the transmission of arthropod-borne viruses has been proposed and demonstrated experimentally. Previously, our laboratory reported on the discovery and characterization of Eilat virus (EILV), an insect-specific alphavirus that phylogenetically groups within the mosquito-borne clade of medically relevant alphaviruses, including eastern equine encephalitis virus (EEEV) and Venezuelan equine encephalitis virus (VEEV), as well as chikungunya virus (CHIKV). Despite its evolutionary relationship to these human pathogens, EILV is unable to replicate in vertebrate cells due to blocks at attachment/entry and RNA replication. We recently demonstrated that, using a chimeric virus approach, EILV could be utilized as a platform for vaccine and diagnostic development, serving as a proof-of-concept for other ISVs. Due to the vast abundance of ISVs, there is an untapped resource for the development of vaccines and diagnostics for a variety of human pathogens and further work in this area is warranted.

A chikungunya fever vaccine utilizing an insect-specific virus platform

Traditionally, vaccine development involves tradeoffs between immunogenicity and safety. Live-attenuated vaccines typically offer rapid and durable immunity but have reduced safety when compared to inactivated vaccines. In contrast, the inability of inactivated vaccines to replicate enhances safety at the expense of immunogenicity, often necessitating multiple doses and boosters. To overcome these tradeoffs, we developed the insect-specific alphavirus, Eilat virus (EILV), as a vaccine platform. To address the chikungunya fever (CHIKF) pandemic, we used an EILV cDNA clone to design a chimeric virus containing the chikungunya virus (CHIKV) structural proteins. The recombinant EILV/CHIKV was structurally identical at 10 Å to wild-type CHIKV, as determined by single-particle cryo-electron microscopy, and it mimicked the early stages of CHIKV replication in vertebrate cells from attachment and entry to viral RNA delivery. Yet the recombinant virus remained completely defective for productive replication, providing a high degree of safety. A single dose of EILV/CHIKV produced in mosquito cells elicited rapid (within 4 d) and long-lasting (>290 d) neutralizing antibodies that provided complete protection in two different mouse models. In nonhuman primates, EILV/CHIKV elicited rapid and robust immunity that protected against viremia and telemetrically monitored fever. Our EILV platform represents the first structurally native application of an insect-specific virus in preclinical vaccine development and highlights the potential application of such viruses in vaccinology.

The preclinical testing of a formaldehyde inactivated Ross River virus vaccine designed for use in humans

Ross River virus was grown in industrial facilities in vaccine-certified Vero cells in the absence of serum, inactivated using standard formalin-inactivation protocols, treated with Benzonase to digest host cell DNA and purified on a sucrose gradient. Mice given two subcutaneous injections of 0.625 microg of this vaccine or two doses of 0.156 microg vaccine with aluminium hydroxide adjuvant failed to develop a detectable viraemia after intravenous challenge with 10(6)TCID50 of the prototype strain of Ross River virus (T48). Guinea pigs immunised with one or two10 microg doses of vaccine with adjuvant also failed to develop a detectable viraemia following a similar challenge. The levels of neutralising antibody (neutralisation index 1.9-3.1) in the mice protected against challenge with 10(6)TCID50 Ross River virus were similar to those in 16 former epidemic polyarthritis patients (1.1-3.5) who had not experienced a second clinical infection with Ross River virus in the 20 years following their initial infection.

[Cellular tropism and adaptation of the measles virus]

Measles virus (MV) is a member of the genus Morbillivirus in the family Paramyxoviridae. Clinical isolates of MV use signaling lymphocyte activating molecule (SLAM) as a cellular receptor. SLAM is mainly expressed on immune cells such as immature thymocytes, activated lymphocytes and mature dendritic cells. This distribution of SLAM can account for the lymphotropism of MV. On the other hand, laboratory strains of MV use CD46 as an alternative receptor, through amino acid change(s) in the receptor binding hemagglutinin protein. Recently, several reports imply the existence of the cellular receptor(s) other than SLAM and CD46. In this review, we discuss the receptor usage of MV and its adaptation to cultured cells.

Emerging roles and new functions of CD46

In the past 20 years, our understanding of the workings of complement regulatory protein, CD46 (membrane cofactor protein), has grown as has the impressive list of pathogens interacting with this membrane-bound complement inhibitor. Referred to as a "pathogen magnet," CD46 serves as a receptor for seven human pathogens. Initially discovered as a widely expressed C3b- and C4b-binding protein, it was subsequently shown to be a cofactor for the serine protease factor I to inactivate by limited proteolysis these two opsonins and components of the convertases. The involvement of CD46 in reproductive processes continues to be an emerging story. It is a protector of placental tissue, but it may also play a more direct role in reproduction through its expression on the inner acrosomal membrane of spermatozoa. Cross-linking CD46 with antibodies or natural or pathogenic ligands induces rapid turnover and signaling events. In this regard, much attention is currently focused on generating human T lymphocyte regulatory cells by cross-linking CD46. Finally, highlighting its importance in protecting cells against excessive complement activation is the discovery that even a heterozygous deficiency of CD46 predisposes to hemolytic uremic syndrome.

CD46: A complement regulator and pathogen receptor that mediates links between innate and acquired immune function

In the last 10 years, the human cell-surface molecule, CD46, has evolved from 'just another complement regulator' to a receptor for a striking array of pathogens. CD46 not only protects cells from complement-mediated attack and facilitates infection by a large number of pathogens, but also exerts complex effects on cellular immune function. It has been proposed that CD46 links innate and adaptive immunity by affecting cellular immune function in response to complement binding, and the role of CD46 in the pathogenesis of many infectious pathogens is now the subject of intense investigation. So far, the flood of information that implicates CD46 in modifying a host response to measles, Neisseria, human herpes virus 6, and pathogens that activate complement has not yet been matched with a comprehensive understanding of the molecular mechanisms by which CD46 affects immune function. This review summarizes the evidence that points to a significant role for CD46 in a range of pathological processes and describes how CD46 might exert its effects by altering signal transduction and antigen presentation pathways.

Ligand binding determines whether CD46 is internalized by clathrin-coated pits or macropinocytosis

CD46 is a ubiquitous human cell surface receptor for the complement components C3b and C4b and for various pathogens, including the measles virus and human herpes virus 6. Ligand binding to CD46 affects (i) protection of autologous cells from complement attack by breakdown of complement components, (ii) intracellular signals that affect the regulation of immune cell function, (iii) antigen presentation, and (iv) down-regulation of cell surface CD46. Recent evidence indicates that CD46 signaling can link innate and acquired immune function. The molecular mechanisms for these processes and the importance of intracellular trafficking of the receptor have not yet been elucidated. We demonstrate here that, in nonlymphoid cells, CD46 is constitutively internalized via clathrin-coated pits, traffics to multivesicular bodies, and is recycled to the cell surface. However, cross-linking of CD46 at the cell surface, by either multivalent antibody or by measles virus, induces pseudopodia that engulf the ligand in a process similar to macropinocytosis, and leads to the degradation of cell surface CD46. Thus, we have elucidated two pathways for CD46 internalization, which are regulated by the valence of cross-linking of CD46 and which utilize either clathrin-coated pits or pseudopodial extension. This has important implications for CD46 signaling, antigen presentation, CD46 down-regulation, and engulfment of pathogens.

T cell responses in acute measles

Immune containment of measles virus (MV) infection has long been a focus of interest for investigators. An emerging theme is that MV immunity is conferred by appropriately polarized antiviral CD4+ and CD8+ T cell populations. Recent technological advances permit the analysis of the composition and dynamics of these CD4+ and CD8+ T cell responses at the single cell level, and of the molecular events responsible for their induction. Novel insights into these issues for measles are discussed in the light of their importance for the development of an improved vaccine.

West Nile virus-induced bax-dependent apoptosis

The mechanism of cell death induced by West Nile virus (WNV), a causative agent of human febrile syndrome and encephalitis, was investigated. WNV-infected K562 and Neuro-2a cells manifested the typical features of apoptosis, including cell shrinkage, chromatin condensation and subdiploid DNA content by flow cytometry. DNA fragmentation into nucleosomal size and changes in outer cell membrane phospholipid composition were also observed in K562 cells. UV-inactivated virus failed to induce the above-mentioned characteristics, suggesting that viral replication may be required for the induction of apoptosis by WNV. Additionally, signals involved in WNV-induced apoptosis are associated with the up-regulation of bax gene expression.

Production of atypical measles in rhesus macaques: evidence for disease mediated by immune complex formation and eosinophils in the presence of fusion-inhibiting antibody

The severe disease atypical measles occurred when individuals immunized with a poorly protective inactivated vaccine contracted measles, and was postulated to be due to a lack of fusion-inhibiting antibodies. Here, rhesus macaques immunized with formalin-inactivated measles vaccine developed transient neutralizing and fusion-inhibiting antibodies, but no cytotoxic T-cell response. Subsequent infection with measles virus caused an atypical rash and pneumonitis, accompanied by immune complex deposition and an increase in eosinophils. Fusion-inhibiting antibody appeared earlier in these monkeys than in non-immunized monkeys. These data indicate that atypical measles results from previous priming for a nonprotective type 2 CD4 T-cell response rather than from lack of functional antibody against the fusion protein.

Requirements for measles virus induction of RANTES chemokine in human astrocytoma-derived U373 cells

Interferons and chemokines play a critical role in regulating the host response to viral infection. Measles virus, a member of the Paramyxoviridae family, induces RANTES expression by astrocytes. We have examined the mechanism of this induction in U373 cells derived from a human astrocytoma. RANTES was induced in a dose- and time-dependent manner by measles virus infection. Inhibition of receptor binding by the anti-CD46 antibody TRA-2.10 and of virus-membrane fusion by the tripeptide X-Phe-Phe-Gly reduced RANTES expression. Formalin-inactivated virus, which can bind but not fuse, and extensively UV-irradiated virus, which can bind and fuse, were both ineffective. Therefore, virus binding to the cellular receptor CD46 and subsequent membrane fusion were necessary, but not sufficient, to induce RANTES. UV irradiation of virus for less than 10 min proportionally inhibited viral transcription and RANTES expression. RANTES induction was decreased in infected cells treated with ribavirin, which inhibits measles virus transcription. However, RANTES mRNA was superinduced by measles virus in the presence of cycloheximide. These data suggest that partial transcription of the viral genome is sufficient and necessary for RANTES induction, whereas viral protein synthesis and replication are not required. This hypothesis was supported by the fact that RANTES was induced through transient expression of the measles virus nucleocapsid gene but not by measles genes encoding P or L proteins or by leader RNA in A549 cells. Thus, transcription of specific portions of measles virus RNA, such as the nucleocapsid gene, appears able to generate the specific signaling required to induce RANTES gene expression.

Processing of the DRB1*1103-restricted measles virus nucleoprotein determinant 185-199 in the endosomal compartment

MHC class II molecules present to CD4+ T cells protein fragments which mostly derive from the extracellular and from the endosomal compartments. Determinants of cytosolic proteins are, however, also displayed by MHC class II molecules following pathways which are still not yet fully characterized. Here we describe the isolation of DRB1*1103-restricted T cell clones specific for the measles virus (MV) nucleoprotein peptide 185-199 (N185). Experiments were then conducted to delineate how this determinant is assembled with DR molecules. In vitro binding analyses indicated that complexes between the N185 peptide and DRB1*1103 protein are optimally constituted at pH 4-4.5. In cellular experiments it was observed that chloroquine, leupeptin and emetine, which are classical inhibitors of presentation of MHC class II-restricted antigens, when added during infection of B cells with MV, prevent presentation of the N185 determinant. In addition, it was found that the N185 determinant is efficiently presented when the nucleoprotein is exogenously provided to B cells, either by blocking MV fusion with the peptide FFG or by the use of purified nucleoprotein. In contrast, it was observed that nucleoprotein recombinant vaccinia virus (vv-N)-infected B cells weakly stimulated N185-specific T cells, indicating that the restricted localization of the nucleoprotein in the cytosol resulted in a poor presentation of the N185 determinant. Taken together, these findings suggest that it is prior to delivery of the nucleoprotein into the cytosol that the N185 determinant is efficiently assembled with newly synthesized DR molecules in the acidic environment of the endosomal compartment.

A candidate Ross River virus vaccine: preclinical evaluation

A killed Ross River virus vaccine is being developed in an effort to prevent the, ca 5000 cases of epidemic polyarthritis which occur in Australia each year. The symptoms of epidemic polyarthritis commonly last 30-40 weeks and 25% of patients have symptoms for a year or more. There is no cure. Although there was some strain to strain variation, particularly after a single injection, outbred and inbred strains of mice all produced significant levels of anti-Ross River virus antibody after intramuscular (i.m.) injection with 24 h BEI inactivated, sucrose gradient purified, Ross River virus vaccine. Mice immunized i.m. with two 20 micrograms doses of vaccine or live virus produced similar levels of neutralizing antibody but the reaction of IgG 2a and IgG 2b antibody from these two groups of mice to Ross River virus proteins in western blots differed. Antibody from BALB/c mice immunized with this vaccine neutralized all strains of Ross River virus tested, in vitro, albeit to different degrees.