Cloning, Expression and Characterization of a Peptibody To Deplete Myeloid Derived Suppressor Cells in a Murine Mammary Carcinoma Model

Myeloid derived suppressor cells (MDSCs) are an immature heterogeneous population of myeloid lineage that attenuate the anti-tumor immune responses. Depletion of MDSCs has been shown to improve efficacy of cancer immunotherapeutic approaches. Here, we produced and characterized a recombinant peptibody capable of recognizing and depleting murine MDSCs. Using SOE-PCR, the coding sequence of the MDSC binding peptide and linker were synthesized and then ligated into a home-made expression plasmid containing mouse IgG2a Fc. The peptibody construct was transfected into CHO-K1 cells by lipofectamine 3000 reagent and the resulting fusion protein was purified with protein G column and subsequently characterized by ELISA, SDS-PAGE and immunoblotting. The binding profile of the peptibody to splenic MDSCs and its MDSC depletion ability were then tested by flow cytometry. The purified peptibody appeared as a 70 kDa band in Western blot. It could bind to 98.8% of splenic CD11b + /Gr-1 + MDSCs. In addition, the intratumoral MDSCs were significantly depleted after peptibody treatment compared to their PBS-treated negative control counterparts (P <0.05). In this study, a peptibody capable of depleting intratumoral MDSCs, was produced. Our results imply that it could be considered as a potential drug effective for immunotherapy of cancers.