Hypo- and hyper-acetylated meningococcal capsular saccharides
Capsular saccharides derived from serogroups W135 and Y of Neisseria meningitidis have altered levels of O-acetylation at the 7 and 9 positions of their sialic acid residues, and can be used to make immunogenic compositions. Relative to unmodified native saccharides, derivatives of the invention are preferentially selected during conjugation to carrier proteins, and conjugates of the derivatives show improved immunogenicity compared to native polysaccharides.
1. A modified serogroup Y meningococcal capsular saccharide, conjugated to a carrier protein, wherein (a) between 2-9% of the sialic acid residues in the saccharide are O-acetylated at the 7 position; and/or (b) between 35-55% of the sialic acid residues in the saccharide are O-acetylated at the 9 position.
2. The modified meningococcal capsular saccharide of claim 1 wherein between 4-8% of the sialic acid residues in the saccharide are O-acetylated at the 7 position.
3. The modified meningococcal capsular saccharide of claim 1 , wherein between 40-50% of the sialic acid residues in the saccharide are O-acetylated at the 9 position.
4. A modified meningococcal capsular saccharide conjugated to a carrier protein, wherein the saccharide comprises n or more repeating units of the disaccharide unit:
[sialic acid]-[hexose]
wherein the hexose is glucose and n is an integer from 1 to 100, and wherein:
(a) x % of the sialic acid residues in said n or more repeating units are O-acetylated at the 7 position; and/or
(b) y % of the sialic acid residues in said n or more repeating units are O-acetylated at the 9 position,
wherein x is between 2-9 and y is between 35-55.
5. The saccharide of claim 4 , wherein 6%±0.6% of the sialic acid residues in said n or more repeating units are O-acetylated at the 7 position, and 45%±4.5% of the sialic acid residues in said n or more repeating units are O-acetylated at the 9 position.
6. A composition comprising a molecules of serogroup Y meningococcal capsular saccharide, wherein (i) the average number of sialic acid residues per capsular saccharide molecule is b, and wherein: (a) between 2-9% of the a·b serogroup Y sialic acid residues in the composition are O-acetylated at the 7 position; and/or (b) between 35-55% of the a·b serogroup Y sialic acid residues in the composition are O-acetylated at the 9 position, (ii) the saccharide is conjugated to a carrier protein.
7. A saccharide comprising n or more repeats of the following disaccharide unit:
n is an integer from 1 to 100,
X and Y are different groups selected from —H and —OH,
R 1 is independently selected from —H and —COCH 3 and may be the same or different in each disaccharide unit,
R 2 is independently selected from —H and —COCH 3 and may be the same or different in each disaccharide unit, and,
X is —H and Y is —OH, (a) 2-9% of R 1 are —COCH 3 and/or (b) 35-55% of R 2 are —COCH 3 ,
and wherein the saccharide is conjugated to a carrier protein.
8. The saccharide of claim 1 , wherein the saccharide has an average degree of polymerisation of less than 30.
9. The saccharide of claim 1 , wherein the carrier protein is selected from the group consisting of: diphtheria toxoid, tetanus toxoid, H. influenzae protein D, and CRM 197 .
10. An immunogenic composition comprising (a) a modified capsular saccharide conjugate of claim 1 , and (b) a pharmaceutically acceptable carrier.
11. The composition of claim 10 , in aqueous form.
12. The composition of claim 10 , in lyophilised form.
13. The composition of claim 10 , further comprising a capsular saccharide antigen from serogroup C of N. meningitidis.
14. The composition of claim 10 , further comprising a capsular saccharide antigen from serogroup A of N. meningitidis.
15. The composition of claim 10 , further comprising a capsular saccharide antigen from serogroup W135 of N. meningitidis.
16. The composition of claim 14 , wherein the serogroup A antigen is a modified saccharide in which one or more of the hydroxyl groups on the native saccharide has/have been replaced by a blocking group.
17. The composition of claim 10 , further comprising an antigen from serogroup B of N. meningitidis.
18. The composition of claim 10 , further comprising a saccharide antigen from Haemophilus influenzae type B.
19. The composition of claim 10 , further comprising an antigen from Streptococcus pneumoniae.
20. The composition of claim 10 , further comprising one or more of: an antigen from hepatitis A virus; an antigen from hepatitis B virus; an antigen from Bordetella pertussis ; a diphtheria toxoid; a tetanus toxoid; or a poliovirus antigen.
21. A method for raising an antibody response in a mammal, comprising administering a composition of claim 10 to the mammal.
22. A process for preparing a modified serogroup Y meningococcal capsular saccharide conjugated to a carrier protein comprising the steps of: (1) providing a starting serogroup Y meningococcal capsular saccharide and the carrier protein, either or both of which is/are optionally modified to render it/them reactive towards the other; (2) forming a covalent bond between the saccharide and the carrier protein; and (3) purifying the resulting serogroup Y meningococcal capsular saccharide conjugated to a carrier protein, wherein, between steps (1) and (3), the degree of O-acetylation at the 9 position of sialic acid residues in the starting saccharide increases to 35-55% and/or the degree of O-acetylation at the 7-position of the sialic acid residues decreases to 2-9% to generate the modified serogroup Y meningococcal capsular saccharide.