Selection and Evaluation of Specific Single Chain Antibodies against CD90, a Marker for Mesenchymal and Cancer Stem Cells

Background: CD90, a membrane-associated glycoprotein is a marker used to identify mesenchymal stem cells (MSCs). Recent studies have introduced CD90, which induces tumorigenic activity, as a cancer stem cell (CSC) marker in various malignancies. Blocking CD90 activity with anti-CD90 monoclonal antibodies enhanced anti-tumor effects. To date, highly specific antibody single-chain variable fragments (scFvs) have been isolated against various targets and showed promising results in cancer immunotherapy. Methods: A phage antibody was produced from a scFv library using M13KO7 helper phage. The phage library was panned against a CD90 epitope. To select specific clones, PCR and DNA fingerprinting were performed and common patterns were identified. The panning results were confirmed by phage ELISA. Results: Of 20 clones selected after panning, 16 shared identical fingerprints. One clone from this group reacted specifically with the epitope in phage ELISA. The average absorbance of wells coated with the CD90 peptide was significantly greater than that of wells containing no peptide (p=0.03). Conclusions: Currently, recombinant antibodies are used not only as highly specific detection tools, but due to their specific characteristics, are applied in targeted cancer therapies. The anti-CD90 scFv selected in this study has the potential to be used to detect MSCs and target CSCs and offers promising strategies for treatment of various cancers.