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Live-Attenuated Respiratory Syncytial Virus Vaccine Candidate With Deletion of RNA Synthesis Regulatory Protein M2-2 is Highly Immunogenic in Children.

ABSTRACT: Background:Live respiratory syncytial virus (RSV) candidate vaccine LIDΔM2-2 is attenuated by deletion of the RSV RNA regulatory protein M2-2, resulting in upregulated viral gene transcription and antigen expression but reduced RNA replication. Methods:RSV-seronegative children ages 6-24 months received a single intranasal dose of 105 plaque forming units (PFU) of LIDΔM2-2 (n = 20) or placebo (n = 9) (NCT02237209, NCT02040831). RSV serum antibodies, vaccine infectivity, and reactogenicity were assessed. During the following RSV season, participants were monitored for respiratory illness and pre- and post-RSV season serum antibodies. Results:Vaccine virus was shed by 95% of vaccinees (median peak titers of 3.8 log10 PFU/mL by quantitative culture and 6.3 log10 copies/mL by PCR); 90% had ≥4-fold rise in serum neutralizing antibodies. Respiratory symptoms and fever were common in vaccine (95%) and placebo (78%). One vaccinee had grade 2 rhonchi concurrent with vaccine shedding, rhinovirus, and enterovirus. Eight of 19 vaccinees versus 2 of 9 placebo recipients had substantially increased RSV antibody titers after the RSV season without medically attended RSV disease, indicating anamnestic vaccine responses to wild-type RSV without significant illness. Conclusion:LIDΔM2-2 had excellent infectivity and immunogenicity, encouraging further study of vaccine candidates attenuated by M2-2 deletion. Clinical Trials Registration:NCT02237209, NCT02040831.

SUBMITTER: McFarland EJ

PROVIDER: S-EPMC5894092 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Human respiratory syncytial virus (RSV) is the most important viral cause of serious pediatric respiratory illness worldwide. Currently, the most promising live-attenuated vaccine candidate is a temperature-sensitive (ts) cDNA-derived virus named rA2cp248/404/1030ΔSH, in reference to its set of attenuating mutations. In a previous clinical study, more than one-third of postvaccination nasal wash isolates exhibited partial loss of the ts phenotype. Most of this instability appeared to be due to reversion at a missense point mutation called 1030. This 1030 mutation is a single-nucleotide tyrosine-to-asparagine substitution at position 1321 (Y1321N) of the polymerase L protein that contributes to the ts and attenuation phenotypes of the vaccine candidate. The goals of the present study were to identify a reversion-resistant codon at position 1321 conferring a comparable level of attenuation and to use this to develop a genetically stable version of the vaccine virus. We modified wild-type (wt) RSV to insert each of the 20 possible amino acids at position 1321; 19 viruses were recoverable. We also investigated small deletions at or near this position, but these viruses were not recoverable. Phenotypic analysis identified alternative attenuating amino acids for position 1321. Several of these amino acids were predicted, based on the genetic code, to be refractory to deattenuation. Classical genetics, using temperature stress tests in vitro combined with nucleotide sequencing, confirmed this stability but identified a second site with a compensatory mutation at position 1313. It was possible to stabilize the 1313 site as well, providing a stable 1030 mutation. Further stress tests identified additional incidental mutations, but these did not reverse the ts/attenuation phenotype. An improved version of the vaccine candidate virus was constructed and validated in vitro by temperature stress tests and in vivo by evaluation of attenuation in seronegative chimpanzees. In addition to developing an improved version of this promising live-attenuated RSV vaccine candidate, this study demonstrated the propensity of an RNA virus to escape from attenuation but also showed that, through systematic analysis, genetics can be used to cut off the routes of escape.

Project description:UnlabelledAlthough respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in infants, a safe and effective vaccine is not yet available. Live-attenuated vaccines (LAVs) are the most advanced vaccine candidates in RSV-naive infants. However, designing an LAV with appropriate attenuation yet sufficient immunogenicity has proven challenging. In this study, we implemented reverse genetics to address these obstacles with a multifaceted LAV design that combined the codon deoptimization of genes for nonstructural proteins NS1 and NS2 (dNS), deletion of the small hydrophobic protein (ΔSH) gene, and replacement of the wild-type fusion (F) protein gene with a low-fusion RSV subgroup B F consensus sequence of the Buenos Aires clade (BAF). This vaccine candidate, RSV-A2-dNS-ΔSH-BAF (DB1), was attenuated in two models of primary human airway epithelial cells and in the upper and lower airways of cotton rats. DB1 was also highly immunogenic in cotton rats and elicited broadly neutralizing antibodies against a diverse panel of recombinant RSV strains. When vaccinated cotton rats were challenged with wild-type RSV A, DB1 reduced viral titers in the upper and lower airways by 3.8 log10 total PFU and 2.7 log10 PFU/g of tissue, respectively, compared to those in unvaccinated animals (P < 0.0001). DB1 was thus attenuated, highly immunogenic, and protective against RSV challenge in cotton rats. DB1 is the first RSV LAV to incorporate a low-fusion F protein as a strategy to attenuate viral replication and preserve immunogenicity.ImportanceRSV is a leading cause of infant hospitalizations and deaths. The development of an effective vaccine for this high-risk population is therefore a public health priority. Although live-attenuated vaccines have been safely administered to RSV-naive infants, strategies to balance vaccine attenuation with immunogenicity have been elusive. In this study, we introduced a novel strategy to attenuate a recombinant RSV vaccine by incorporating a low-fusion, subgroup B F protein in the genetic background of codon-deoptimized nonstructural protein genes and a deleted small hydrophobic protein gene. The resultant vaccine candidate, DB1, was attenuated, highly immunogenic, and protective against RSV challenge in cotton rats.

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Live-Attenuated Respiratory Syncytial Virus Vaccine Candidate With Deletion of RNA Synthesis Regulatory Protein M2-2 is Highly Immunogenic in Children.

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