Abstract 723: Reduction of immunosuppressive function of regulatory T cells enhances antigen-specific T cell mediated cytotoxicity against tumor cells

Abstract Regulatory T cells (Tregs) maintain immune homeostasis by suppressing abnormal immune response to self and non-self-antigens. Tregs are also involved in tumor development and progression by inhibiting anti-tumor immunity. Infiltration of Tregs in the tumor microenvironment (TME) inhibit anti-tumor immunity by suppressing tumor antigen-specific T cell responses. This results in tumor progression and poor prognosis in patients with various types of cancers. Therefore, depletion of Tregs could be a promising immunotherapy target to augment the anti-tumor immune response. Molecules highly expressed by Tregs such as CD25, immune checkpoint molecules, and chemokine receptors have been targeted by antibodies or small molecules to deplete Tregs and its immunosuppressive function has been tested in the clinic. However, a thin line exists between augmenting effective immunity and inducing autoimmunity, posing difficulties in harnessing Tregs modulation in cancer treatment. Thus, additional strategies to selectively control Tregs are urgently needed for the effective treatment of cancer. In this study we evaluated the role of Tregs in suppressing the effector function of antigen-specific T cells and targeted killing of cancer cells in vitro. We observed Tregs mediated suppression of antigen-specific cytotoxicity against cancer cells. When Tregs were treated with cyclophosphamide, CD25 depleting antibody and anti-CTLA4 antibody alone or in combination, we observed enhanced killing of cancer cells in vitro as a result of potentiated effector function of antigen-specific T cells. This study provides a path forward to fine-tune and optimize strategies to target various molecules that are highly expressed on Tregs and augment anti-tumor immunity by antigen-specific T cells to achieve therapeutic outcome. Citation Format: Arif Azam Khan, Jaehyung Park, Nate LaVoy, Chris Tompkins, Jeff Bellinder, Tisha San Miguel, Neal Lawrence, Brianna Schoen. Reduction of immunosuppressive function of regulatory T cells enhances antigen-specific T cell mediated cytotoxicity against tumor cells abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 723.