A stabilized glycomimetic conjugate vaccine inducing protective antibodies against Neisseria meningitidis serogroup A

Abstract

Neisseria meningitidis serogroup A capsular polysaccharide (MenA CPS) consists of (1 → 6)-2-acetamido-2-deoxy-α-D-mannopyranosyl phosphate repeating units, O-acetylated at position C3 or C4. Glycomimetics appear attractive to overcome the CPS intrinsic lability in physiological media, due to cleavage of the phosphodiester bridge, and to develop a stable vaccine with longer shelf life in liquid formulation. Here, we generate a series of non-acetylated carbaMenA oligomers which are proven more stable than the CPS. An octamer (DP8) inhibits the binding of a MenA specific bactericidal mAb and polyclonal serum to the CPS, and is selected for further in vivo testing. However, its CRM197 conjugate raises murine antibodies towards the non-acetylated CPS backbone, but not the natural acetylated form. Accordingly, random O-acetylation of the DP8 is performed, resulting in a structure (Ac-carbaMenA) showing improved inhibition of anti-MenA CPS antibody binding and, after conjugation to CRM197, eliciting anti-MenA protective murine antibodies, comparably to the vaccine benchmark.

Rational design of a hydrolysis-resistant mycobacterial phosphoglycolipid antigen presented by CD1c to T cells

“…This finding is consistent with the conclusion that hydrolysis of MPM to PM reduces the amount of available antigen, while MPM-3 is not sensitive to hydrolysis. This favored interpretation is separately supported by plate-bound antigen presentation assays that distinguish responses to PM and MPM ( 12 ), the known susceptibility of this type of glycosyl phosphate diesters to hydrolysis ( 28 ), the demonstrated hydrolysis of MPM, and the overcoming of antigen loss by substituting the link between sugar and phosphate with alternatives that are not subject to hydrolysis.…”

Carbohydrate based meningococcal vaccines: past and present overview

“…The resulting conjugates showed induction of antibodies capable of recognizing the native MenA polysaccharide, but with very poor immunogenicity. More recently, oligomers up to 8 repeating units in length were generated [ 77 ]. Particularly, the octamer showed a unique capacity to recognize a bactericidal murine monoclonal antibody that has been mapped by Saturation Transfer NMR and X-ray crystallography, showing that it binds to an O-acetylated trisaccharide epitope [ 78 ].…”

“…Particularly, the octamer showed a unique capacity to recognize a bactericidal murine monoclonal antibody that has been mapped by Saturation Transfer NMR and X-ray crystallography, showing that it binds to an O-acetylated trisaccharide epitope [ 78 ]. While initial studies with a conjugate of the non-O-acetylated octamer provided unsatisfactory results, introduction of O-acetylation at a level up to 75 %, similar to the natural polysaccharide, generated an antigen which upon conjugation induced bactericidal antibodies similarly to the MenA polysaccharide vaccine benchmark [ 77 ]. This work represented a proof-of-principle that glycomimetic vaccines can be used as more stable alternatives to polysaccharide-derived ones.…”

Semi- and fully synthetic carbohydrate vaccines against pathogenic bacteria: recent developments

“…A rapid and cost-effective chemoenzymatic synthesis of oligosaccharides from N. meningitidis serogroup X produced glycans that elicited functional antibodies in mice ( Figure 7 bottom) [ 63 ]. A vaccine candidate involving glycomimetics that stabilizes the natural CPS of N. meningitis serogroup A after conjugation to CRM 197 elicited in mice high levels of protective antibodies with bactericidal activity [ 64 ], which advanced previous work that had used the synthetic tetrasaccharide conjugate of TT [ 65 ]. The structural epitopes of N. meningitidis serogroup A revealed the importance of acetylation of the respective CPS [ 66 ].…”