Gas-filled microvesicles comprising an antigen bound thereto and to aqueous suspensions containing said microvesicles, for use in immunomodulating formulations, in particular as a vaccine. The antigen is covalently bound to a component of the microvesicles envelope. The microvesicles of the invention, comprising a molar excess of fatty acids in the stabilizing envelope, are particularly effective in the uptake by antigen-presenting cells, in particular dendritic cells.
