Icosavax raises $51M to take VLP RSV vaccine into humans

Icosavax co-founder Neil King (University of Washington)

Icosavax has raised a $51 million series A round to take respiratory syncytial virus (RSV) vaccine IVX-121 through phase 1b in older adults. The vaccine is built on computationally designed self-assembling viruslike particle (VLP) technology Icosavax thinks can eliminate some of the barriers to protecting people against RSV.

VLPs have the potential to generate humoral and cellular immune responses without exposing patients to an actual virus, either in an attenuated or inactivated form. However, while VLP vaccines such as GlaxoSmithKline’s Engerix-B and Merck’s Gardasil have come to market, technical issues have stopped the application of the approach to complex antigens.

“It’s really a protein folding and manufacturing problem. The complex antigens displayed on the VLP need to be properly folded to provide a protective immune response, without interfering with the assembly or manufacturability of the macromolecular structure itself,” Icosavax CEO Adam Simpson said. 


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Icosavax thinks it has addressed that problem. The Seattle-based startup licensed technology from the University of Washington that enables the computational design of candidates.

“We are able to manufacture the properly folded antigens with traditional recombinant technologies and the individual antigens then self assemble into the VLP structure themselves,” Simpson said.

A team featuring Icosavax co-founder Neil King, an assistant professor at the University of Washington, published a paper describing the technology and an RSV vaccine derived from it in Cell earlier this year.

Icosavax plans to build on that work using $51 million in series A funds from an investor syndicate led by Qiming Venture Partners USA. Adams Street Partners, Sanofi Ventures and NanoDimension also participated in the round, as did Icosavax’s seed investors.  

The money will enable Icosavax to gather data on the safety of IVX-121 and its ability to generate high-quality antibody titers in a phase 1b trial. Icosavax is yet to commit publicly to a timeline for getting the RSV vaccine into the clinic. The series A will also support work on the development of at least one other vaccine against a significant unmet medical need. 

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