Modified spike proteins and uses thereof

A nucleic acid comprising:

• (i) a sequence coding for the S1 domain of a Spike protein from a virus of the Orthocoronavirinae subfamily, or a variant thereof;
• (ii) a sequence coding for the S2 domain of a Spike protein from a virus of the Orthocoronavirinae subfamily, or a variant thereof;
• and
• (iii) a sequence coding for a pilot peptide which interacts with ESCRT proteins,
• wherein the sequences (i) and (ii) are from Spike proteins from a different virus of the Orthocoronavirinae subfamily, or from Spike proteins from different strains of the same virus of the Orthocoronavirinae subfamily.

An extracellular vesicle harboring at its external surface a Spike protein from a virus of the Orthocoronavirinae subfamily, or a variant thereof, wherein said Spike protein comprises:

• (i) a sequence of the S1 domain of a Spike protein from a virus of the Orthocoronavirinae subfamily, or a variant thereof;
• (ii) a sequence of the S2 domain of a Spike protein from a virus of the Orthocoronavirinae subfamily, or a variant thereof;
• and
• wherein the sequences (i) and (ii) are from Spike proteins from a different virus of the Orthocoronavirinae subfamily, or from Spike proteins from different strains of the same virus of the Orthocoronavirinae subfamily.

A method of screening antibodies against the S2 domain of a Spike protein of a virus of the Orthocoronavirinae subfamily comprising the steps of:

• (a) contacting the antibodies to be screened with a first extracellular vesicle, or a first population of extracellular vesicle harboring a Spike protein at the extracellular vesicle surface,
• (b) selecting the antibodies which bind to the Spike protein harbored at the extracellular vesicle surface,
• (c) contacting the antibodies selected in step (b) with a second extracellular vesicle or a second population of extracellular vesicle, wherein the extracellular vesicle(s) used in step (c) harbor(s) a Spike protein comprising the same S2 domain but a different S1 domain than the Spike protein harbored at the surface of the extracellular vesicle(s) used in step (a),
• (d) selecting the antibodies which bind to the Spike protein harbored at the extracellular vesicle surface, thereby identifying antibodies which bind specifically to the S2 domain of Spike protein.