Hypo- and Hyper- Acetylated Meningococcal Capsular Saccharides

Abstract

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 unmodifed 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 W135 meningococcal capsular saccharide, wherein: (a) ≦29% of the sialic acid residues in the saccharide are O-acetylated at the 7 position; and/or (b) ≧26% of the sialic acid residues in the saccharide are O-acetylated at the 9 position. 
     
     
         2 . A modified serogroup Y meningococcal capsular saccharide, wherein (a) ≦9% of the sialic acid residues in the saccharide are O-acetylated at the 7 position; and/or (b) ≧29% or ≦27% of the sialic acid residues in the saccharide are O-acetylated at the 9 position. 
     
     
         3 . The modified meningococcal capsular saccharide of  claim 1  or  claim 2 , wherein >0% of the sialic acid residues in the saccharide are O-acetylated at the 7 position. 
     
     
         4 . The modified meningococcal capsular saccharide of  claim 1  or  claim 2 , wherein >0% of the sialic acid residues in the saccharide are O-acetylated at the 9 position. 
     
     
         5 . A modified meningococcal capsular saccharide, optionally conjugated to a carrier protein, wherein the saccharide comprises n or more repeating units of the disaccharide unit:
 [sialic acid]-[hexose]   where the hexose is either galactose or 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) when hexose is galactose, ≧y % of the sialic acid residues in said n or more repeating units are O-acetylated at the 9 position, and when hexose is glucose, ≧y % or ≦z % of the sialic acid residues in said n or more repeating units are O-acetylated at the 9 position, 
   where: when hexose is galactose, x is 29 and y is 26; and when hexose is glucose, x is 9, y is 29 and z is 27.   
     
     
         6 . The saccharide of  claim 5 , wherein hexose is galactose, about 6% of the sialic acid residues in said n or more repeating units are O-acetylated at the 7 position, and about 43% of the sialic acid residues in said n or more repeating units are O-acetylated at the 9 position. 
     
     
         7 . The saccharide of  claim 5 , wherein hexose is glucose, about 6% of the sialic acid residues in said n or more repeating units are O-acetylated at the 7 position, and about 45% of the sialic acid residues in said n or more repeating units are O-acetylated at the 9 position. 
     
     
         8 . A composition comprising a molecules of serogroup W135 meningococcal capsular saccharide, wherein the average number of sialic acid residues per capsular saccharide molecule is b, and wherein: (a) ≦29% of the a·b serogroup W135 sialic acid residues in the composition are O-acetylated at the 7 position; and/or (b) ≧26% of the a·b serogroup W135 sialic acid residues in the composition are O-acetylated at the 9 position. 
     
     
         9 . A composition comprising a molecules of serogroup Y meningococcal capsular saccharide, wherein the average number of sialic acid residues per capsular saccharide molecule is b, and wherein: (a) ≦9% of the a·b serogroup Y sialic acid residues in the composition are O-acetylated at the 7 position; and/or (b) ≧29% or ≦27% of the a·b serogroup Y sialic acid residues in the composition are O-acetylated at the 9 position. 
     
     
         10 . The composition of  claim 8  or  claim 9 , wherein the capsular saccharide is conjugated to a protein carrier. 
     
     
         11 . A saccharide comprising n or more repeats of the following disaccharide unit: 
       
         
           
           
               
               
           
         
       
       wherein:
 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,
 when X is —OH and Y is —H, (a) ≦29% of R 1  are —COCH 3  and/or (b) ≧26% of R 2  are —COCH 3 . 
 when X is —H and Y is —OH, (a) ≦9% of R 1  are —COCH 3  and/or (b) ≧29% or ≦27% of R 2  are —COCH 3 . 
 
 
     
     
         12 . The saccharide of any preceding claim, wherein the saccharide has an average degree of polymerisation of less than 30. 
     
     
         13 . The conjugation product of (i) a saccharide of any preceding claim, and (ii) a carrier protein selected from the group consisting of: diphtheria toxoid, tetanus toxoid,  H. influenzae  protein D, and CRM 197 . 
     
     
         14 . An immunogenic composition comprising (a) a modified capsular saccharide or conjugate of any preceding claim, and (b) a pharmaceutically acceptable carrier. 
     
     
         15 . The composition of  claim 14 , in aqueous form. 
     
     
         16 . The composition of  claim 14 , in lyophilised form. 
     
     
         17 . The composition of any one of  claims 14  to  16 , further comprising a capsular saccharide antigen from serogroup C of  N. meningitidis.    
     
     
         18 . The composition of any one of  claims 14  to  17 , further comprising a capsular saccharide antigen from serogroup A of  N. meningitidis.    
     
     
         19 . The composition of  claim 18 , wherein the serogroup A antigen 
     
     
         20 . The composition of any one of  claims 14  to  19 , further comprising an antigen from serogroup B of  N. meningitidis.    
     
     
         21 . The composition of any one of  claims 14  to  20 , further comprising a saccharide antigen from  Haemophilus influenzae  type B. 
     
     
         22 . The composition of any one of  claims 14  to  21 , further comprising an antigen from  Streptococcus pneumoniae.    
     
     
         23 . The composition of any one of  claims 14  to  22 , 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; and/or a poliovirus antigen. 
     
     
         24 . The composition of any one of  claims 14  to  23 , for use as a medicament. 
     
     
         25 . A method for raising an antibody response in a mammal, comprising administering a composition of any one of  claims 14  to  23  to the mammal. 
     
     
         26 . The use of a modified serogroup W135 meningococcal capsular saccharide and/or a modified serogroup Y meningococcal capsular saccharide as defined in any one of  claims 1  to  13 , in the manufacture of a medicament for protecting against meningococcal meningitis. 
     
     
         27 . A process for preparing an immunogenic conjugate comprising the steps of: (1) providing a starting serogroup W135 or serogroup Y meningococcal capsular saccharide and a 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 glycoconjugates, wherein, between steps (1) and (3), the degree of O-acetylation at the 9 position of sialic acid residues in the starting saccharide increases.