¹University Medical Center Groningen, Department of Medical Microbiology, Molecular Virology Section, University of Groningen, Groningen, The Netherlands

Correspondence: Dr A Huckriede, University Medical Center Groningen, Department of Medical Microbiology, Molecular Virology Section, A. Deusinglaan 1, Groningen 9713 AV, The Netherlands. E-mail: a.l.w.huckriede@med.umcg.nl

Received 26 March 2005; Revised 12 August 2005; Accepted 19 September 2005; Published online 3 November 2005.

Abstract

Application of RNA interference for in vivo evaluation of gene function or for therapeutic interventions has been hampered by a lack of suitable delivery methods for small interfering RNA (siRNA). Here, we present reconstituted viral envelopes (virosomes) derived from influenza virus as suitable vehicles for in vitro as well as in vivo delivery of siRNAs. Virosomes are vesicles that bear in their membrane the influenza virus spike protein hemagglutinin (HA). This protein mediates binding of native virus to and fusion with cellular target membranes. Accordingly, virosomes with membrane-incorporated HA bind to cells, are taken up by receptor-mediated endocytosis, and fuse with the endosomal membrane to release their contents into the cytoplasm. When complexed to cationic lipids, siRNA was successfully encapsulated in virosomes. Virosomes with encapsulated siRNA fused with target membranes in a pH-dependent manner and delivered the encapsulated siRNA to several cell lines in vitro. Virosome-delivered siRNA markedly downregulated the synthesis of newly induced and constitutively expressed green fluorescent protein. Moreover, intraperitoneal injection of siRNA-loaded virosomes resulted in delivery of the nucleotides to cells in the peritoneal cavity. Our results indicate that virosomes are a promising delivery device for in vivo application, especially where topical administration of siRNA, for example, to the respiratory tract is envisaged.