Liposomes with lipids having an advantageous pka-value for rna delivery

Abstract

RNA encoding an immunogen is delivered in a liposome for the purposes of immunisation. The liposome includes lipids which have a pKa in the range of 5.0 to 7.6 and, preferably, a tertiary amine. These liposomes can have essentially neutral surface charge at physiological pH and are effective for immunisation.

1 . A liposome having a lipid bilayer encapsulating an aqueous core, wherein: (i) the lipid bilayer comprises a lipid having a pKa in the range of 5.0 to 7.6; and (ii) the aqueous core includes a RNA which encodes an immunogen. 
     
     
         2 . The liposome of  claim 1 , wherein the lipid having a pKa in the range of 5.0 to 7.6 has a tertiary amine. 
     
     
         3 . The liposome of  claim 1 , wherein pKa in the range of 5.0 to 7.6 is between 5.7-5.9. 
     
     
         4 . The liposome of  claim 1 , wherein the lipid having a pKa in the range of 5.0 to 7.6 has the formula shown herein for RV01, RV02, RV03, RV04, RV05, RV06, RV07, RV08, RV09, RV11, RV12, RV16 or RV17. 
     
     
         5 . The liposome of  claim 1 , having a diameter in the range of 20-220 nm. 
     
     
         6 . The liposome of  claim 1 , wherein the RNA molecule encodes (i) a RNA-dependent RNA polymerase which can transcribe RNA from the RNA molecule and (ii) an immunogen. 
     
     
         7 . The liposome of  claim 5 , wherein the RNA molecule has two open reading frames, the first of which encodes an alphavirus replicase and the second of which encodes the immunogen. 
     
     
         8 . The liposome of  claim 1 , wherein the RNA molecule is 9000-12000 nucleotides long. 
     
     
         9 . The liposome of  claim 1 , wherein the immunogen can elicit an immune response in vivo against a bacterium, a virus, a fungus or a parasite. 
     
     
         10 . The liposome of  claim 1 , wherein the immunogen can elicit an immune response in vivo against respiratory syncytial virus glycoprotein F. 
     
     
         11 . A pharmaceutical composition comprising the liposome of  claim 1 . 
     
     
         12 . A method for raising a protective immune response in a vertebrate, comprising the step of administering to the vertebrate an effective amount of the liposome of  claim 1 . 
     
     
         13 . A process for preparing a RNA-containing liposome, comprising steps during liposome formation of: (a) mixing RNA with a lipid at a pH which is below the lipid's pKa but is above 4.5; then (b) increasing the pH to be above the lipid's pKa. 
     
     
         14 . The process of  claim 13 , wherein: RNA used in step (a) is in aqueous solution, for mixing with an organic solution of the lipid to give a mixture which is then diluted to form liposomes; and the pH is increased in step (b) after liposome formation.