ChAdOx1 COVID vaccines express RBD open prefusion SARS-CoV-2 spikes on the cell surface

Area of Science:

• Structural biology
• Vaccinology
• Virology

Background:

• Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines reduce COVID-19 mortality, hospitalization, and transmission.
• ChAdOx1 nCoV-19 vaccine utilizes an adenovirus vector for SARS-CoV-2 spike protein expression on cell surfaces.

Purpose of the Study:

• To determine the native structures of ChAdOx1 nCoV-19 vaccine products expressed in situ.
• To evaluate the impact of HexaPro stabilization on spike protein expression and conformation.

Main Methods:

• Cryo-electron tomography and subtomogram averaging were employed to visualize vaccine antigens on cell surfaces.
• Structural analysis focused on prefusion spike conformation, cell surface expression levels, and S1 shedding.

Main Results:

• ChAdOx1-vectored Beta variant spikes exhibit abundant prefusion conformations, predominantly in a one-RBD-up state.
• HexaPro-stabilized spikes on ChAdOx1 vectors show increased cell surface expression, enhanced RBD exposure, and reduced S1 shedding compared to wild-type.

Conclusions:

• In situ structural determination is a valuable tool for assessing antigen design in vaccine development.
• Findings provide insights for designing improved vaccines against SARS-CoV-2 variants and other viral threats.