Measles is a highly contagious disease that most commonly strikes children. The causative agent, measles virus (MV), is generally transmitted by aerosolized secretions deposited on upper-respiratory-tract mucosal surfaces. Exposure leads to local respiratory tract replication; infection of regional lymphoid tissues then occurs followed by viremia and systemic dissemination as revealed by the characteristic skin rash. Most children recover uneventfully from the illness, but serious complications can occur, including pneumonia and involvement of the central nervous system (17,27,28). Despite the highly contagious nature of the disease, MV can be controlled effectively by immunization with live attenuated vaccines. The effectiveness of MV vaccines is well illustrated by the epidemiology of the disease in the United States. Prior to 1963, before use of the earliest vaccines, there were over 500,000 reported cases per year. Twenty years later, MV incidence was less than 2,000 cases per year (11,28). The availability of these effective vaccines has not eliminated the threat from MV, and measles still causes significant levels of morbidity and mortality in developing countries largely because of inadequate and unsustained vaccination efforts (17).Several effective MV vaccines were derived from a single clinical viral isolate called the Edmonston strain (28, 66). Enders et al. (20) developed the first MV vaccine by the classical approach (1) of propagating the pathogen in heterologous cells and tissues. Specifically, MV was serially propagated in semipermissive chicken embryos and chick fibroblast cells. Variations of the Enders approach have led to the development of a number of independently derived but effective Edmonstonbased vaccines (28,66).MV is a member of the genus Morbillivirus in the Paramyxoviridae family and, like other members of this family, it is an enveloped RNA virus that contains a single-strand, negativesense, nonsegmented genome (28, 47). The 16-kb MV genome encodes eight known proteins from six nonoverlapping cistrons arranged 3Ј-N-P-M-F-H-L-5Ј. The major structural polypeptide is encoded by the N (nucleocapsid) gene. The N protein is essential for packaging the genome into a ribonucleoprotein complex that serves as template for transcription, replication, and packaging into progeny virions. The P cistron specifies three polypeptides: P, C, and V. The P (phosphoprotein) polypeptide is a subunit of the viral RNA polymerase. P protein also acts as a chaperone that interacts with and regulates the cellular localization of N protein and probably assists in nucleocapsid assembly (28,33,70). The C and V polypeptides are nonstructural proteins that are translated from P mRNAs through the use of alternative reading frames; C protein is synthesized from a downstream translation start signal, whereas V protein is translated from an edited mRNA that contains an extra G residue (28,33,70). The M gene encodes the matrix protein that lines the inner surface of the viral envelope and participates in virion matur...

The noncoding sequence of five Edmonston vaccine viruses (AIK-C, Moraten, Rubeovax, Schwarz, and Zagreb) and those of a low-passage Edmonston wild-type (wt) measles virus have been determined and compared. Twenty-one nucleotide positions were identified at which Edmonston wt and one or more vaccine strains differed. The location of some of these nucleotide substitutions suggests that they may influence the efficiency of mRNA synthesis, processing, and translation, as well as genome replication and encapsidation. Five nucleotide substitutions were conserved in all of the vaccine strains. Two of these were in the genomic 3-terminal transcriptional control region and could affect RNA synthesis or encapsidation. Three were found within the 5-untranslated region of the F mRNA, potentially altering translation control sequences. The remaining vaccine virus base changes were found in one to four vaccine strains. Their genomic localization suggests that some may modify cis-acting regulatory domains, including the Kozak consensus element of the P and M genes, the F gene-end signal, and the F mRNA 5-untranslated sequence.

The advent of reverse genetics technology has revolutionized the field of RNA viruses. It is now possible to manipulate even negative-stranded RNA viruses at will, and evaluate the effects of these changes on the biology and pathogenesis of these viruses. The fundamental insights gleaned from the reverse genetics-based studies over the last several years have provided a new momentum for the development of designed therapies for the control and prevention of these viral pathogens. The recombinant viruses have been exploited also as vectors for devising targeted therapies for non-viral diseases such as malignancies, and in gene therapy for inherited disorders. This review provides a brief summary of the stumbling blocks and the successes in the development of the technology for the negative-stranded RNA viruses. The many and varied applications of the recombinant vectors are also outlined.

Nipah virus (NiV) was first recognized in 1998 in a zoonotic disease outbreak associated with highly lethal febrile encephalitis in humans and a predominantly respiratory disease in pigs. Periodic deadly outbreaks, documentation of person-to-person transmission, and the potential of this virus as an agent of agroterror reinforce the need for effective means of therapy and prevention. In this report, we describe the vaccine potential of NiV virus-like particles (NiV VLPs) composed of three NiV proteins G, F and M. Co-expression of these proteins under optimized conditions resulted in quantifiable amounts of VLPs with many virus-like/vaccine desirable properties including some not previously described for VLPs of any paramyxovirus: The particles were fusogenic, inducing syncytia formation; PCR array analysis showed NiV VLP-induced activation of innate immune defense pathways; the surface structure of NiV VLPs imaged by cryoelectron microscopy was dense, ordered, and repetitive, and consistent with similarly derived structure of paramyxovirus measles virus. The VLPs were composed of all the three viral proteins as designed, and their intracellular processing also appeared similar to NiV virions. The size, morphology and surface composition of the VLPs were consistent with the parental virus, and importantly, they retained their antigenic potential. Finally, these particles, formulated without adjuvant, were able to induce neutralizing antibody response in Balb/c mice. These findings indicate vaccine potential of these particles and will be the basis for undertaking future protective efficacy studies in animal models of NiV disease.

Nipah virus is a highly lethal zoonotic paramyxovirus that was first recognized in Malaysia during an outbreak in 1998. During this outbreak, Nipah virus infection caused a severe febrile neurological disease in humans who worked in close contact with infected pigs. The case fatality rate in humans was approximately 40%. Since 2001, NiV has re-emerged in Bangladesh and India where fruit bats (Pteropus spp.) have been identified as the principal reservoir of the virus. Transmission to humans is considered to be bat-to-human via food contaminated with bat saliva, or consumption of contaminated raw date palm sap, although human-to-human transmission of Nipah virus has also been documented. To date, there are no approved prophylactic options or treatment for NiV infection. In this study, we produced mammalian cell-derived native Nipah virus-like particles composed of Nipah virus G, F and M proteins for use as a novel Nipah virus vaccine. Previous studies demonstrated that the virus-like particles were structurally similar to authentic virus, functionally assembled and immunoreactive. In the studies reported here, purified Nipah virus-like particles were utilized either alone or with adjuvant to vaccinate golden Syrian hamsters with either three-dose or one-dose vaccination regimens followed by virus challenge. These studies found that Nipah virus-like particle immunization of hamsters induced significant neutralizing antibody titers and provided complete protection to all vaccinated animals following either single or three-dose vaccine schedules. These studies prove the feasibility of a virus-like particle-based vaccine for protection against Nipah virus infection.