Recombinant Hepatitis E virus like particles can function as RNA nanocarriers

Abstract

Background: Assembled virus-like particles (VLPs) without genetic material, with structure similar to infectious virions, have been successfully used as vaccines. We earlier described in vitro assembly, characterisation and tissue specific receptor dependent Clathrin mediated entry of empty HEV VLPs, produced from Escherichia coli expressed HEV capsid protein (pORF2). Similar VLP's have been described as a potential candidate vaccine (Hecolin) against HEV. Findings:We have attempted to use such recombinant assembled Hepatitis E virus (HEV) VLPs as a carrier for heterologous RNA with protein coding sequence fused in-frame with HEV 5′ region (containing cap and encapsidation signal) and investigated, if the relevant protein could be expressed and elicit an immune response in vivo. In vitro transcribed red fluorescent protein (RFP)/Hepatitis B virus surface antigen (HBsAg) RNA, fused to 5′-HEV sequence with cap and encapsidation signal (1-249 nt), was packaged into the recombinant HEV-VLPs and incubated with five different cell lines (Huh7, A549, Vero, HeLa and SiHa). The pORF2-VLPs could specifically transfer exogenous coding RNA into Huh7 and A549 cells. In vivo, Balb/c mice were immunized (intramuscular injections) with 100 µg pORF2-VLP encapsidated with 5′-methyl-G-HEV (1-249 nt)-HBsAg RNA, blood samples were collected and screened by ELISA for anti-pORF2 and anti-HBsAg antibodies. Humoral immune response could be elicited in Balb/c mice against both HEV capsid protein and cargo RNA encoded HBsAg protein. Conclusions:These findings suggest that other than being a possible vaccine, HEV pORF2-VLPs can be used as a promising non-replicative tissue specific gene delivery system. FindingsVLPs inherit most of the properties of parent virus, like capability of self-assembly into organised structure, specific interaction with nucleic acid/protein, and cell-specific entry. These replication-deficient, non-infectious, nano-structured particles can be useful if they can effectively deliver therapeutically useful nucleic acid, drug, targeting peptide or a conjugated imaging molecule.We had described generation of HEV VLP's from Escherichia coli produced capsid protein Here, we investigate whether (1) empty VLPs of HEV could encapsidate heterologous RNA fused with encapsidation signal and deliver the exogenous RNA in a cell specific manner as a nanocarrier? (2) Can the foreign gene be translated from delivered chimeric RNA? and (3) If injected to animals, can the RNA-VLP complex induce immunity to both the carrier HEV capsid protein and the protein expressed from delivered RNA? To study the above possibilities, we generated a chimeric RNA where reporter/antigen producing gene/coding sequence (RFP/