The use of conjugation to carrier proteins in order to enhance the immunogenicity of saccharide antigens is well known [e.g., reviewed in refs. 1 to 9 etc.] and is used in particular for paediatric vaccines [10]. Three widely used carrier proteins in present-day vaccines are tetanus toxoid (TT), diphtheria toxoid (DT) and the diphtheria toxoid variant, CRM197. These proteins have been used as carriers for various saccharides, including streptococcal and meningococcal capsular saccharides (see, for example, the use of TT as carrier for saccharides derived from Streptococcus agalactiae serotypes II and III in ref. 11 and for saccharides derived from Neisseria meningitidis serogroups A, C, W135 and Y in ref. 12; and the use of DT and CRM197 as carriers for the same N. meningitidis saccharides in refs. 13 and 14 and for saccharides derived from Streptococcus agalactiae serotypes Ia, Ib and III in ref. 15). Concerns have been raised about the overuse of these carrier proteins in vaccines [see, for example, ref. 16], with various alternative carriers being suggested (e.g. protein D from Haemophilus influenzae in ref. 17). However, many alternative carrier proteins are not as effective as TT, DT and/or CRM197. Accordingly, there remains a need to find alternative and/or better carrier proteins.
It is therefore an object of the invention to provide further and better carrier proteins, particularly carrier proteins for capsular saccharides. The carrier proteins may be used in conjugates to induce protective and/or therapeutic immune responses against infections or drugs.