Highly sensitive immunoassay for rapid quantification of meningococcal capsular polysaccharide antigens
The present disclosure relates to the field of immunoassays for Gram negative bacteria, in particular N. meningitidis . The disclosure provides a simple and affordable immunoassay to quantitate polysaccharides in meningococcal vaccines for the evaluation of antigen content and lot-to-lot manufacturing consistency. The inventors have found a Sandwich ELISA that can be applicable for the quantitation and identification of N. meningitidis serogroup X polysaccharide in a multivalent meningococcal polysaccharide-protein conjugate vaccine as well as in a multivalent meningococcal plain polysaccharide vaccine. Said assay employs a polyclonal antibody as capture antibody and a novel monoclonal antibody against serogroup X polysaccharide as detection antibody. Further the assay is rapid, robust and reproducible.
1. A method for quantification of conjugated N. meningitidis serogroup X capsular polysaccharide in a sample using an immunological assay, the method comprising:
providing a solid support coated with a capture polyclonal antibody;
providing a sample including N. meningitidis serogroup X capsular polysaccharide-TT conjugate and unconjugated N. meningtitidis serogroup X capsular polysaccharide, wherein the sample is lyophilized and resuspended in phosphate buffer saline having pH 7.2±0.2 comprising KCl at a concentration from 75 mM to 140 mM followed by further dilution or the sample is liquid and directly diluted with phosphate buffer saline having pH 7.2±0.2 comprising KCl at a concentration from 75 mM to 140 mM;
applying the sample to the solid support coated with capture polyclonal antibody;
removing unbound sample;
providing a detection monoclonal antibody;
applying the detection monoclonal antibody to the solid support;
removing unbound detection monoclonal antibody;
applying labeled secondary antibody with a label; and
detecting the label;
wherein the assay does not show any interference due to presence of sucrose and glucose excipients.
2. The method according to claim 1 , wherein the capture polyclonal antibody is obtained from rabbit antisera and the detection monoclonal antibody is obtained from fusion of mice splenocyte cells and mouse myeloma cells.
3. The method according to claim 1 , wherein
dilution of capture polyclonal capture antibody is between 1:5000 to 1:15000 in carbonate buffer, pH 9.6;
dilution of the detection monoclonal antibody is between 1:3000 to 1:10000 in phosphate-buffered saline (PBS), pH 7.2; and
dilution of the labeled secondary antibody is between 1:5000 to 1:15000 in phosphate-buffered saline (PBS), pH 7.2.
4. The method according to claim 1 , wherein said detection monoclonal antibody does not show cross-reactivity with N. meningitidis serogroup polysaccharides A, C, W and Y.
5. The method according to claim 1 , wherein limit of detection (LOD) is 0.4 ng/ml for N. meningitidis X.
6. The method according to claim 1 , wherein the solid support is selected from the group consisting of polyvinyl chloride (PVC), polystyrene, agarose and sepharose.
7. The method according to claim 6 , wherein the solid support is polystyrene.
8. The method according to claim 6 , wherein the support is formed as a microtitration plate, tube or bead.
9. The method according to claim 8 , wherein the microtitration plate is an activated immuno-assay plate.
10. The method according to claim 1 , wherein the label is selected from the group consisting of an enzyme label, fluorescent label, a radioactive label and biotin.
11. The method according to claim 10 , wherein the enzyme label is selected from the group consisting of a single enzyme, an oligomeric form of an enzyme, and an enzyme/antienzyme complex.
12. The method according to claim 11 , wherein the enzyme label is coupled to an alternative detection system.
13. The method according to claim 11 , wherein the enzyme label is selected from the group consisting of alkaline phosphatase, horse radish peroxidase, beta-galactosidase and urease.
14. The method according to claim 11 , wherein the label enzyme is horse radish peroxidase.
15. The method according to claim 1 , wherein the sample comprises a monovalent N. meningitidis serogroup X capsular polysaccharide.
16. The method according to claim 15 , wherein the sample comprises at least one additional N. meningitidis serogroup capsular polysaccharide selected from the group consisting of N. meningitidis serogroup A, N. meningitidis serogroup C, N. meningitidis serogroup W and N. meningitidis serogroup Y.
17. The method according to claim 15 , wherein the sample comprises at least one additional N. meningitidis serogroup capsular polysaccharide-protein conjugate selected from the group consisting of N. meningitidis serogroup A, N. meningitidis serogroup C, N. meningitidis serogroup W and N. meningitidis serogroup Y.
18. The method according to claim 1 , wherein the sample comprises at least one non N. meningitidis antigen selected from the group consisting of S. pneumoniae and H. influenzae.
19. The method according to claim 1 , wherein the sample includes Neisseria meningitidis X polysaccharide from N. meningitidis X8210 strain and tetanus toxoid protein.