Development of an Adenovirus-Based Respiratory Syncytial Virus Vaccine: Preclinical Evaluation of Efficacy, Immunogenicity, and Enhanced Disease in a Cotton Rat Model

Abstract

The lack of a vaccine against respiratory syncytial virus (RSV) is a challenging and serious gap in preventive medicine. Herein, we characterize the immunogenicity of an adenovirus serotype 5-based RSV vaccine encoding the fusion (F) protein (Ad5.RSV-F) and the protection provided following immunization with Ad5.RSV-F and assess its potential for producing enhanced disease in a cotton rat (CR) model. Animals were immunized intranasally (i.n.) and/or intramuscularly (i.m.) and subsequently challenged with RSV/A/Tracy (i.n.) to assess protection. Robust immune responses were seen in CRs vaccinated with Ad5.RSV-F given i.m. or i.n., and these responses correlated with reduced replication of the virus in noses and lungs after challenge. Neutralizing antibody responses following immunization with a single dose of Ad5.RSV-F at 1 ؋ 10 11 viral particles (v.p.) elicited antibody titers 64-to 256-fold greater than those seen after natural infection. CRs boosted with Ad5.RSV-F i.n. 28 days after an i.m. dose also had significant increases in neutralizing antibody titers. Antibody affinity for different F-protein antigenic sites revealed substantial differences between antibodies elicited by Ad5.RSV-F and those seen after RSV infection; differences in antibody profiles were also seen between CRs given Ad5.RSV-F i.m. and CRs given Ad5.RSV-F i.n. Ad5.RSV-F priming did not result in enhanced disease following live-virus challenge, in contrast to the histopathology seen in CRs given the formalin-inactivated RSV/A/Burnett vaccine. IMPORTANCERespiratory syncytial virus (RSV) is the most common cause of acute lower respiratory infection in infants and young children and a serious health threat in the immunocompromised and the elderly. Infection severity increased in children in an immunization trial, hampering the over 4-decade-long quest for a successful RSV vaccine. In this study, we show that a genetically engineered RSV-F-encoding adenoviral vector provides protective immunity against RSV challenge without enhanced lung disease in cotton rats (CRs). CRs were vaccinated under a number of different regimens, and the immunity induced by the recombinant adenoviral RSV vaccine administered by use of an intramuscular prime-intranasal boost regimen may provide the best protection for young infants and children at risk of RSV infection, since this population is naive to adenoviral preformed immunity. Overall, this report describes a potential RSV vaccine candidate that merits further evaluation in a phase I clinical study in humans.

Recombinant measles virus incorporating heterologous viral membrane proteins for use as vaccines

“…A similar result, i.e. effective protection from challenge in the lung but persistent RSV in the upper respiratory tract, was also observed in cotton rats vaccinated intra-muscularly with a single dose of up to 10 11 viral particles of a recombinant replication-defective adenovirus vaccine (Kim et al, 2014;Widjojoatmodjo et al, 2015). Interestingly, a single dose of the same vaccine administered intra-nasally resulted in a more robust protection, further supporting the hypothesis that local immunity is an important determinant of protection that future vaccine strategies should consider.…”

Novel recombinant DNA vaccine candidates for human respiratory syncytial virus: Preclinical evaluation of immunogenicity and protection efficiency

“…Significant levels of F protein were identified in HEp-2 cells using ELISA and immunofluorescence with a higher abundance of the secretory form. The proper expression of these constructs is consistent with the previous trials of DNA immunization using codon optimized and truncated F protein forms 17,23,26,37 It was expected that the secretory form should have the lowest intracellular concentration due to its rapid secretion in the cell supernatant. Harvesting the expressed proteins 48 hr posttransfection, which may be insufficient for protein secretion, can justify this unexpected finding.…”

“…11 The F protein was highly recommended for use in the development of vaccine candidates due to its conserved nature and ability to induce neutralizing antibodies and cytotoxic T lymphocytes. 12,13 A number of HRSV vaccine candidates were generated and tested in preclinical and/or clinical trials including FI-RSV, 14 live-attenuated, 15 subunit 16 and viral vector-based 17 vaccines. FI-RSV was prohibited due to its hazardous effect, which resulted in disease enhancement and the death of 2 vaccine recipients.…”

Recombinant influenza virus expressing a fusion protein neutralizing epitope of respiratory syncytial virus (RSV) confers protection without vaccine-enhanced RSV disease

“…We chose a dose of 2x10 5 PFU that was recently reported to be sufficient to assess the efficacy of RSV vaccines (Garg et al, 2014; Johnson et al, 2014; Kim et al, 2014; Murata and Catherman, 2012; Nguyen et al, 2012; Schmidt et al, 2012). We also found that the PBS or PR8 WT group of mice that were infected with 2x10 5 PFU RSV showed a high titer of approximately up to 10 4 PFU from lungs at day 5 post infection (Fig.…”