Methods: The LAV “DB1” was generated from recombinant A2 strain RSV by deleting the small hydrophobic (SH) protein gene; recoding the genes for non-structural proteins NS1 and NS2 with the least used codons by humans; and replacing the A2 fusion (F) gene with an RSV subgroup B F gene consensus sequence of the Buenos Aires clade. Viral growth kinetics were measured in Vero cells, BEAS-2B cells, and in BALB/c mice. Immunogenicity was determined by measuring serum neutralizing antibody titers in BALB/c mice and cotton rats. Efficacy was determined by lung viral loads in mice and cotton rats on day 4 post-RSV challenge.
Results: DB1 was attenuated in BEAS-2B cells and BALB/c mice compared to A2-line19F. In Vero cells, a cell line approved for vaccine production, DB1 growth was equivalent to A2-line19F. In BALB/c mice, DB1 generated broad neutralizing antibody responses against a panel of RSV A and B viruses and completely protected against RSV challenge. In cotton rats, DB1 generated similar neutralizing antibody responses to RSV/A/Tracy and RSV/B/18537 that were sustained at 6 weeks post-vaccination. When vaccinated cotton rats were challenged with RSV, DB1 reduced lung and nasal wash titers by 2.68 log10 PFU/g tissue and 3.76 log10 total PFU respectively compared to untreated controls (P<0.00001; Student’s t-test, two-tailed).
Conclusion: DB1 is a highly attenuated RSV LAV candidate which generates broad neutralizing antibody responses against RSV A and B and protects against RSV challenge in mice and cotton rats.
A. Hotard, None
J. Meng, None
B. Gilbert, None
P. Piedra, None
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