Development of highly sensitive MSD assays for the detection of anti-phospho Tau-specific antibodies in human serum
 
M. Vukicevic*, E. Fiorini*, D. Knittel*, N. Chuard*, V. Giriens*, A. Pfeifer*, E. Ramsburg**, M. Pihlgren* and A. Muhs*
*AC Immune SA, Lausanne, Switzerland
 
We have been developing a phospho-Tau (pTau) vaccine for the treatment of Alzheimer Disease (AD). In order to detect antibodies induced by the vaccine, robust and reliable methods are needed. We have developed highly sensitive Meso Scale Discovery (MSD) assays for the detection of free (assay 1) and target-bound IgG (assay 2) antibodies specific for the pTau antigen present in our vaccine (pS396/pS404). Those assays aim to help better understanding of the nature of antibody response induced by anti-pTau vaccination. In the assay 1, streptavidin MSD plates have been coated with the biotinylated pTau peptide. Serum from monkeys immunized with vaccine was used as positive control. The reaction was revealed with an anti-IgG antibody. In the assay 2, streptavidin MSD plates were coated with the biotinylated capturing anti-Tau monoclonal antibody, with the epitope outside the antigenic pTau peptide of the vaccine. Bound pTau-specific antibodies were further captured by an anti-IgG antibody. In vitro formed complexes between the pTau protein and the antibodies from the vaccine-immunized monkeys were used as a positive control. In the assay 1, matrix effect of naïve sera was reduced by saturating the plates and diluting the samples in BSA. The developed assay showed a very high sensitivity (at least ten times higher than the equivalent ELISA method), good precision and a very high dynamic range with serum minimal required dilution (MRD) of 1:50. While the assay 2 was very difficult to setup in ELISA, in MSD configuration it showed a very specific detection of the complexes, a very high sensitivity and a high dynamic range. In addition, the assay had a good precision without a matrix effect at MRD of 1:50. Both assays showed a good robustness, reproducibility in time and among different operators. We have optimized the MSD assays for the detection of free and bound pTau-specific IgG, which were more sensitive than the ELISA assays. This suggested the suitability of the MSD technology for the evaluation of anti-pTau antibodies, which could be further used for the evaluation of the potential therapeutic effect of anti-pTau immunotherapy in humans.