LIPOSOMES WITH LIPIDS HAVING AN ADVANTAGEOUS PKA-VALUE FOR RNA DELIVERY
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.