SummaryRespiratory syncytial virus (RSV) is a worldwide public health concern for which no vaccine is available. Elucidation of the prefusion structure of the RSV F glycoprotein and its identification as the main target of neutralizing antibodies have provided new opportunities for development of an effective vaccine. Here, we describe the structure-based design of a self-assembling protein nanoparticle presenting a prefusion-stabilized variant of the F glycoprotein trimer (DS-Cav1) in a repetitive array on the nanoparticle exterior. The two-component nature of the nanoparticle scaffold enabled the production of highly ordered, monodisperse immunogens that display DS-Cav1 at controllable density. In mice and nonhuman primates, the full-valency nanoparticle immunogen displaying 20 DS-Cav1 trimers induced neutralizing antibody responses ∼10-fold higher than trimeric DS-Cav1. These results motivate continued development of this promising nanoparticle RSV vaccine candidate and establish computationally designed two-component nanoparticles as a robust and customizable platform for structure-based vaccine design.
The challenges of evolution in a complex biochemical
environment—coupling genotype to phenotype and protecting the genetic
material—are solved elegantly in biological systems by nucleic acid
encapsulation. In the simplest examples, viruses use capsids to surround their
genomes. While these naturally occurring systems have been modified to change
their tropism1 and to display
proteins or peptides2–4, billions of years of evolution
have favored efficiency at the expense of modularity, making viral capsids
difficult to engineer. Synthetic systems composed of non-viral proteins could
provide a “blank slate” to evolve desired properties for drug
delivery and other biomedical applications, while avoiding the safety risks and
engineering challenges associated with viruses. Here we create synthetic
nucleocapsids—computationally designed icosahedral protein
assemblies5, 6 with positively charged inner surfaces
capable of packaging their own full-length mRNA genomes—and explore
their ability to evolve virus-like properties by generating diversified
populations using Escherichia coli as an expression host.
Several generations of evolution resulted in drastically improved genome
packaging (>133-fold), stability in whole murine blood (from less than
3.7% to 71% of packaged RNA protected after 6 hours of
treatment), and in vivo circulation time (from less than 5
minutes to 4.5 hours). The resulting synthetic nucleocapsids package one
full-length RNA genome for every 11 icosahedral assemblies, similar to the best
recombinant adeno-associated virus (AAV) vectors7, 8.
Our results show that there are simple evolutionary paths through which protein
assemblies can acquire virus-like genome packaging and protection. Considerable
effort has been directed at “top-down” modification of viruses
to be safe and effective for drug delivery and vaccine applications1, 9, 10; the ability
to computationally design synthetic nanomaterials and to optimize them through
evolution now enables a complementary “bottom-up” approach with
considerable advantages in programmability and control.
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