Evaluation of attenuation, immunogenicity and efficacy of a bovine parainfluenza virus type 3 (PIV-3) vaccine and a recombinant chimeric bovine/human PIV-3 vaccine vector in rhesus monkeys

The contribution of bovines to human health against viral infections

In the last 40 years, novel viruses have evolved at a much faster pace than other pathogens. Viral diseases pose a significant threat to public health around the world. Bovines have a longstanding history of significant contributions to human nutrition, agricultural, industrial purposes, medical research, drug and vaccine development, and livelihood. The life cycle, genomic structures, viral proteins, and pathophysiology of bovine viruses studied in vitro paved the way for understanding the human counterparts. Calf model has been used for testing vaccines against RSV, papillomavirus vaccines and anti-HCV agents were principally developed after using the BPV and BVDV model, respectively. Some bovine viruses-based vaccines (BPIV-3 and bovine rotaviruses) were successfully developed, clinically tried, and commercially produced. Cows, immunized with HIV envelope glycoprotein, produced effective broadly neutralizing antibodies in their serum and colostrum against HIV. Here, we have summarized a few examples of human viral infections for which the use of bovines has contributed to the acquisition of new knowledge to improve human health against viral infections covering the convergence between some human and bovine viruses and using bovines as disease models. Additionally, the production of vaccines and drugs, bovine-based products were covered, and the precautions in dealing with bovines and bovine-based materials.

RNA-based viral vectors

The advent of reverse genetic approaches to manipulate the genomes of both positive (+) and negative (-) sense RNA viruses allowed researchers to harness these genomes for basic research. Manipulation of positive sense RNA virus genomes occurred first largely because infectious RNA could be transcribed directly from cDNA versions of the RNA genomes. Manipulation of negative strand RNA virus genomes rapidly followed as more sophisticated approaches to provide RNA-dependent RNA polymerase complexes coupled with negative-strand RNA templates were developed. These advances have driven an explosion of RNA virus vaccine vector development. That is, development of approaches to exploit the basic replication and expression strategies of RNA viruses to produce vaccine antigens that have been engineered into their genomes. This study has led to significant preclinical testing of many RNA virus vectors against a wide range of pathogens as well as cancer targets. Multiple RNA virus vectors have advanced through preclinical testing to human clinical evaluation. This review will focus on RNA virus vectors designed to express heterologous genes that are packaged into viral particles and have progressed to clinical testing.

Evaluation of a novel immunogenic vaccine platform based on a genome replication-deficient Sendai vector

We developed a novel vaccine platform based on a paramyxoviral, genome replication-deficient Sendai virus vector that can express heterologous genes inserted into the genome. To validate the novel approach in vivo, we generated a combined vaccine candidate against human respiratory syncytial virus (RSV) and human parainfluenza virus type 3 (PIV3). The present study compares two different methods of displaying heterologous antigens: (i) the RSV fusion (F) protein, encoded as a secretable version in an additional transcription unit, serves as an antigen only after being expressed in infected cells; (ii) PIV3 fusion (F) and hemagglutinin-neuraminidase (HN) genes, replacing Sendai counterparts in the vector genome, are also expressed as structural components on the surface of vaccine particles. The efficacy of this prototype vaccine was assessed in a mouse model after mucosal administration. The vaccine candidate was able to elicit specific mucosal, humoral and T cell-mediated immune responses against RSV and PIV3. However, PIV3 antigen display on the vaccine particles' surface induced higher antibody titers than the RSV antigen, being expressed only after cell infection. Consequently, this construct induced an adequate neutralizing antibody response only to PIV3. Finally, replicating virus particles were not detected in the lungs of immunized mice, confirming the genome stability and replication deficiency of this vaccine vector in vivo. Both factors can contribute substantially to the safety profile of vaccine candidates. In conclusion, this replication-deficient Sendai vector represents an efficient platform that can be used for vaccine developments against various viral pathogens.

Complete genome sequence and pathogenicity of two swine parainfluenzavirus 3 isolates from pigs in the United States

Two novel paramyxoviruses, 81-19252 (Texas81) and 92-7783 (ISU92), isolated from the brains of pigs in the United States in the 1980s and 1990s, were characterized. The complete genome of Texas81 virus was 15,456 nucleotides (nt) in length, that of ISU92 was 15,480 nt, and both genomes consisted of six nonoverlapping genes, predicted to encode nine proteins, with conserved and complementary 3' leader and 5' trailer regions and conserved gene starts, gene stops, and trinucleotide intergenic sequences similar to those in paramyxoviruses. The corresponding genes from these two viruses were similar in length, except for the F genes, of which the ISU92 form had an additional 24-nt U-rich 3' untranslated region. The P genes of swine viruses were predicted to produce V and D mRNAs by RNA editing (one to four G insertions in Texas81 and one to nine G insertions in ISU92) or C mRNA by alternative translation initiation. Sequence-specific features related to virus replication and host-specific amino acid signatures indicated that these viruses originated from bovine parainfluenzavirus 3 (bPIV3). Phylogenetic analysis of individual genes suggested that these viruses are novel members of the genus Respirovirus of the Paramyxovirinae subfamily and may be grouped into two subgenotypes of genotype A of bPIV3. Our comprehensive studies revealed that these swine PIV3 are variants of bPIV3 and were possibly transferred from cattle to pigs but failed to establish an active enzootic state. These two viruses were mildly pathogenic to conventionally reared pigs, and results from a limited enzyme-linked immunosorbent assay-based serosurvey of swine farms in Minnesota and Iowa in 2007 and 2008 were negative.

Development of recombinant Sendai virus vaccines for prevention of human parainfluenza and respiratory syncytial virus infections

Respiratory syncytial virus (RSV) and human parainfluenza viruses (hPIVs) are the most important causes of hospitalization for viral respiratory tract diseases in infants and young children. Unfortunately, there are currently no licensed vaccines for prevention of these infections. Researchers at St. Jude Children's Research Hospital are now developing Sendai virus (SV), a natural respiratory pathogen of mice, as a Jennerian vaccine for hPIV-1, and as a vaccine backbone for the prevention of RSV and other hPIVs. Unmodified SV is currently being tested in the clinic. Thus far, the vaccine has been well tolerated. Preclinical studies also continue and have demonstrated that intranasal vaccinations with recombinant SV expressing an RSV antigen are sufficient to activate high-magnitude RSV-specific neutralizing B- and T-cell activities in a cotton rat system. Furthermore, vaccinated animals are completely protected against RSV challenges. As clinical safety studies progress, St. Jude Children's Research Hospital researchers are also working to formulate a SV-based cocktail vaccine designed to prevent several hPIV and RSV infections in humans.

Sendai virus recombinant vaccine expressing hPIV-3 HN or F elicits protective immunity and combines with a second recombinant to prevent hPIV-1, hPIV-3 and RSV infections

The human parainfluenza viruses (hPIVs) and respiratory syncytial virus (RSV) are the leading causes of serious respiratory illness in the human pediatric population. Despite decades of research, there are currently no licensed vaccines for either the hPIV or RSV pathogens. Here we describe the testing of hPIV-3 and RSV candidate vaccines using Sendai virus (SeV, murine PIV-1) as a vector. SeV was selected as the vaccine backbone, because it has been shown to elicit robust and durable immune activities in animal studies, and has already advanced to human safety trials as a xenogenic vaccine for hPIV-1. Two new SeV-based hPIV-3 vaccine candidates were first generated by inserting either the fusion (F) gene or hemagglutinin-neuraminidase (HN) gene from hPIV-3 into SeV. The resultant rSeV-hPIV3-F and rSeV-hPIV3-HN vaccines expressed their inserted hPIV-3 genes upon infection. The inoculation of either vaccine into cotton rats elicited binding and neutralizing antibody activities, as well as interferon-gamma-producing T cells. Vaccination of cotton rats resulted in protection against subsequent challenges with either homologous or heterologous hPIV-3. Furthermore, vaccination of cotton rats with a mixture of rSeV-hPIV3-HN and a previously described recombinant SeV expressing the F protein of RSV resulted in protection against three different challenge viruses: hPIV-3, hPIV-1 and RSV. Results encourage the continued development of the candidate recombinant SeV vaccines to combat serious respiratory infections of children.

Viral antigen production in cell cultures on microcarriers Bovine parainfluenza 3 virus and MDBK cells

Viral antigens can be obtained from infected mammalian cells cultivated on microcarriers. We have worked out parameters for the production of bovine parainfluenza 3 (PI-3) virus by Mandin-Darby Bovine Kidney (MDBK) cells cultivated on Cytodex 1 microcarriers (MCs) in spinners flasks and bioreactor using fetal bovine serum (FBS) supplemented Eagle minimal essential medium (Eagle-MEM). Medium renewal during the cell culture was shown to be crucial for optimal MCs loading (>90% MCs with confluent cell monolayers) and cell growth (2.5 x 10(6)cells/mL and a micro(x) (h(-1)) 0.05). Since cell cultures performed with lower amount of MCs (1g/L), showed good performances in terms of cell loading, we designed batch experiments with a lower concentration of MCs in view of optimizing the cell growth and virus production. Studies of cell growth with lower concentrations of MCs (0.85 g/L) showed that an increase in the initial cell seeding (from 7 to 40 cells/MC) led to a different kinetic of initial cell growth but to comparable final cell concentrations ((8-10)x10(5)cells/mL at 120 h) and cell loading (210-270 cells/MC). Upon infection with PI-3 virus, cultures showed a decrease in cell growth and MC loading directly related to the multiplicity of infection (moi) used for virus infection. Infected cultures showed also a higher consumption of glucose and production of lactate. The PI-3 virus and PI-3 antigen production among the cultures was not significantly different and attained values ranging from, respectively, 7-9 log(10) TCID(50)/mL and 1.5-2.2 OD. The kinetics of PI-3 virus production showed a sharp increase during the first 24h and those of PI-3 antigen increased after 24h. The differential kinetics of PI-3 virus and PI-3 antigen can be explained by the virus sensitivity to temperature. In view of establishing a protocol of virus production and based on the previous experiments, MDBK cell cultures performed under medium perfusion in a bioreactor of 1.2L were infected and the PI-3 virus production in 12L attained 12 log(10) TCID(50). Other than establishing a protocol for PI-3 production in MDBK cell cultures on Cytodex 1, the experiments are proposed as a basis for approaching the development of a virus production protocol in mammalian cells cultivated on microcarriers in bioreactors.

The cell biology of acute childhood respiratory disease: therapeutic implications

Respiratory syncytial virus (RSV), the recently identified human metapneumovirus (HMPV), and the human parainfluenza viruses (HPIVs), cause most cases of childhood croup, bronchiolitis, and pneumonia. Influenza virus also causes a significant burden of disease in young children, although its significance in children was not fully recognized until recently. This article discusses pathogens that have been studied for several decades, including RSV and HPIVs, and also explores the newly identified viral pathogens HMPV and human coronavirus NL63. The escalating rate of emergence of new infectious agents, fortunately meeting with equally rapid advancements in molecular methods of surveillance and pathogen discovery, means that new organisms will soon be added to the list. A section on therapies for bronchiolitis addresses the final common pathways that can result from infection with diverse pathogens, highlighting the mechanisms that may be amenable to therapeutic approaches. The article concludes with a discussion of the overarching impact of new diagnostic strategies.

A host-range restricted parainfluenza virus type 3 (PIV3) expressing the human metapneumovirus (hMPV) fusion protein elicits protective immunity in African green monkeys

Human metapneumovirus (hMPV) infection causes respiratory tract disease similar to that observed during human respiratory syncytial virus infection (hRSV). hMPV infections have been reported across the entire age spectrum although the most severe disease occurs in young children. No vaccines, chemotherapeutics or antibodies are presently available for preventing or treating hMPV infections. In this study, a bovine/human chimeric parainfluenza virus type 3 (b/h PIV3) expressing the human parainfluenza type 3 (hPIV3) fusion (F) and hemagglutinin-neuraminidase (HN) proteins was engineered to express hMPV fusion (F) protein from the second genome position (b/h PIV3/hMPV F2) with the goal of generating a novel hMPV vaccine. b/h PIV3/hMPV F2 was previously shown to protect hamsters from challenge with wt hMPV (Tang RS, Schickli JH, Macphail M, Fernandes F, Bicha L, Spaete J, et al. Effects of human metapneumovirus and respiratory syncytial virus antigen insertion in two 3' proximal genome positions of bovine/human parainfluenza virus type 3 on virus replication and immunogenicity. J Virol 2003;77:10819-28) and is here further evaluated for efficacy and immunogenicity in African green monkeys (AGMs). AGMs immunized intranasally and intratracheally with b/h PIV3/hMPV F2 generated hMPV- and hPIV3-specific humoral and cellular immune responses and were protected from wt hMPV infection. In a separate study, the host-range restriction of b/h PIV3/hMPV F2 replication relative to wt hPIV3 was performed in rhesus monkeys to demonstrate attenuation. These studies showed that b/h PIV3/hMPV F2 was immunogenic, protective and attenuated in non-human primates and warrants further evaluation in humans as a vaccine candidate for prevention of hMPV-associated respiratory tract diseases.

Parainfluenza virus type 3 expressing the native or soluble fusion (F) Protein of Respiratory Syncytial Virus (RSV) confers protection from RSV infection in African green monkeys

Respiratory syncytial virus (RSV) causes respiratory disease in young children, the elderly, and immunocompromised individuals, often resulting in hospitalization and/or death. After more than 40 years of research, a Food and Drug Administration-approved vaccine for RSV is still not available. In this study, a chimeric bovine/human (b/h) parainfluenza virus type 3 (PIV3) expressing the human PIV3 (hPIV3) fusion (F) and hemagglutinin-neuraminidase (HN) proteins from an otherwise bovine PIV3 (bPIV3) genome was employed as a vector for RSV antigen expression with the aim of generating novel RSV vaccines. b/h PIV3 vaccine candidates expressing native or soluble RSV F proteins were evaluated for efficacy and immunogenicity in a nonhuman primate model. b/h PIV3 is suited for development of pediatric vaccines since bPIV3 had already been evaluated in clinical studies in 1- and 2-month-old infants and was found to be safe, immunogenic, and nontransmissible in a day care setting (Karron et al., Pediatr. Infect. Dis. J. 15:650-654, 1996; Lee et al., J. Infect. Dis. 184:909-913, 2001). African green monkeys immunized with b/h PIV3 expressing either the native or soluble RSV F protein were protected from challenge with wild-type RSV and produced RSV neutralizing and RSV F-protein specific immunoglobulin G serum antibodies. The PIV3-vectored RSV vaccines evaluated here further underscore the utility of this vector system for developing safe and immunogenic pediatric respiratory virus vaccines.

Identification of small-animal and primate models for evaluation of vaccine candidates for human metapneumovirus (hMPV) and implications for hMPV vaccine design

Human metapneumovirus (hMPV), a recently identified paramyxovirus, is the causative agent of respiratory tract disease in young children. Epidemiological studies have established the presence of hMPV in retrospective as well as current clinical samples in Europe, USA, Canada, Hong Kong and Australia. The hMPV disease incidence rate varied from 7 to 12 %. This rate of disease attack places hMPV in severity between respiratory syncytial virus and human parainfluenza virus type 3, two common respiratory pathogens of young children, the elderly and immunosuppressed individuals. To evaluate the effectiveness and safety of future hMPV antiviral drugs, therapeutic and prophylactic monoclonal antibodies (mAbs), and vaccine candidates, it was necessary to identify small-animal and primate models that efficiently supported hMPV replication in the respiratory tract and produced neutralizing serum antibodies, commonly a clinical correlate of protection in humans. In this study, various rodents (mice, cotton rats, hamsters and ferrets) and two primate species, rhesus macaques and African green monkeys (AGMs), were evaluated for hMPV replication in the respiratory tract. The results showed that hamsters, ferrets and AGMs supported hMPV replication efficiently and produced high levels of hMPV-neutralizing antibody titres. Hamsters vaccinated with subgroup A hMPV were protected from challenge with subgroup A or subgroup B hMPV, which has implications for hMPV vaccine design. Although these animal models do not mimic human hMPV disease signs, they will nevertheless be invaluable for the future evaluation of hMPV antivirals, mAbs and vaccines.