Active immunization with Tocilizumab mimotopes induces specific immune responses

BACKGROUND: Tocilizumab is a humanized monoclonal antibody showing high-affinity binding to both soluble interleukin-6 receptor (sIL-6R) and membrane bound IL-6R (mIL-6R), thereby preventing pro-inflammatory effects of IL-6. However, therapeutic antibodies still have practical limitations. To overcome these limitations, we generated Tocilizumab specific epitope mimics by using the phage display technology and tested whether the peptide mimics could induce similar humoral responses in mice immunized with the peptides. RESULTS: Seven phage mimics were obtained by using phage display peptide library. Four phage mimics (YHTTDKLFYMMR, YSAYEFEYILSS, KTMSAEEFDNWL and LTSHTYRSQADT) were shown to mimic Tocilizumab epitope using immunoassays. The mimotopes were conjugated to immunogenic carrier proteins and used to intraperitoneally immunize BALB/c mice. Sera from the mimotopes immunized mice not only showed specific binding to recombinant IL-6R, but can also IL-6R expressed in Hela, U-937, Jurkat cell lines and in fibroblast-like synoviocytes from patients with RA (FLS-RA). Furthermore, sera from mice immunized with mimotopes-KLH conjugate could reduce the level of phosphorylated- signal transducers and activator of transcription (STAT3), STAT3, phosphorylated- extracellular signal-regulated kinase (Erk) 1/2 and Erk1/2 in HeLa and Jurkat cells. Antibody-dependent cellular cytotoxicity (ADCC) assay showed that antibodies induced by mimotopes-KLH conjugate could elicit specific lysis in Hela and U-937 cells. CONCLUSIONS: From phage display library, we successfully isolated four Tocilizumab mimotopes which induced specific humoral and cellular reponses in vitro and in vivo.