Attenuation of human respiratory syncytial virus by genome-scale codon-pair deoptimization

Significance Human respiratory syncytial virus (RSV) is the most important viral agent of serious pediatric respiratory-tract disease. We designed new live attenuated RSV vaccine candidates by codon-pair deoptimization (CPD). Specifically, viral ORFs were recoded to increase the usage of underrepresented codon pairs, leaving amino acid coding unchanged. CPD viruses were temperature-sensitive and grew less efficiently in vitro than wild-type RSV. In addition, the CPD viruses exhibited a range of restriction in mice and African green monkeys that compared favorably with existing attenuated strains presently in clinical studies. This study produced examples of a new type of vaccine candidate for RSV and showed that CPD of a nonsegmented negative-strand RNA virus can rapidly generate vaccine candidates with a range of attenuation.