Immune profiling of the tumor microenvironment for optimizing Treg-targeted antibody-based immunotherapy

Regulatory T cells (Tregs) are suppressive immune cells abundant in many types of solid tumors. They actively promote the suppressive immune state of the tumor microenvironment (TME), which could lead to a poor prognosis and failure to respond to conventional therapies. Therefore, Tregs have become a potent target for immunotherapies using cytotoxic antibodies to deplete them from the TME, potentiating the patient`s immune system to selectively target cancer cells. A major limitation of this approach is the lack of a known Treg-specific membrane marker as a selective target for antibody-mediated elimination. Our preliminary data demonstrate that antibodies developed to deplete Tregs, including antibodies in clinical evaluation, cause unwanted elimination of effector cells in addition to their Treg depletion activity. This non-selective activity is further enhanced when the antibodies are Fc-optimized for their depletion activity, and causes a significant hurdle in the therapeutic translation of this approach. This study addresses this translational challenge and aims to improve the Treg selectivity of currently available antibodies. We utilize high-dimensional immune profiling of the TME of MC-38 colorectal carcinoma mouse tumor and spleens through mass-cytometry (cyToF) and flow cytometry, to identify unique properties and expression markers on immune cells in the TME, specifically tumor Tregs in an attempt to develop highly-specifically targeted antibodies.