Abstract B022: Targeting epithelial-mesenchymal plasticity and CD73 to enhance responses of breast cancers to immune checkpoint blockade therapies

Abstract

Abstract Immune checkpoint blockade (ICB) therapy has generated dramatic responses in certain types of human tumors however, the response of breast cancers has been largely limited. Epithelial-mesenchymal plasticity (EMP) enables carcinoma cells to metastasize, gain tumor-initiating ability and mount resistance to chemotherapies. In addition, we have demonstrated that this plasticity program also contributes to the establishment of an immunosuppressive tumor microenvironment and confers resistance to ICB therapy (Dongre and Weinberg 2019). By establishing novel, preclinical models of more-epithelial or more-mesenchymal breast tumors, we observed that epithelial tumors recruit CD8+ T-cells to their microenvironment and are sensitive to anti-CTLA4 ICB. In contrast, mesenchymal tumors recruit Tregs and M2-like macrophages and are resistant to the same treatment (Dongre et al., 2017). Strikingly, abrogation of CD73 from more-mesenchymal cells completely sensitizes otherwise refractory tumors to anti-CTLA4 ICB (Dongre et al., 2021). These findings demonstrated for the first time that more-mesenchymal breast cancer cells can be completely sensitized to anti-tumor immunity by interrupting certain cell-intrinsic signaling channels. However, the underlying mechanisms of such sensitization remain elusive. Additionally, the regulatory networks that control the expression of CD73 itself in more-mesenchymal but not epithelial breast cancer cells are not well defined. To determine the subset of T-cells that is functionally important in sensitizing mesenchymal tumors lacking CD73, we depleted either conventional CD4+ T-cells or CD8+ cytotoxic T-cells in combinatoin with ICB. While responding mice recruited both T-cells to their tumors, only CD4+ T-cells (and not CD8+ T-cells) were functionally important in driving sensitization. Along these lines, more-mesenchymal cancer cells lacking CD73 failed to respond to anti-CTLA4 ICB when propagated in genetically engineered mice lacking CD4+ T-cells relative to wild type controls. Importantly, depletion of CD4+ T-cells also prevented the recruitment of peripheral CD8+ T-cells to responding tumors, thereby driving resistance to ICB. In addition, we observed that human triple negative breast cancer cell lines expressed the highest amount of CD73 relative to hormone receptor-positive cell lines. Most importantly, activating EMP in human breast cancer cells by doxycycline-controlled expression of various transcription factors, induced the expression of CD73. Taken together, our work demonstrates that (i) the phenotypic plasticity of breast cancer cells can predict responses to ICB (ii) targeting CD73 can completely sensitize more-mesenchymal tumors to anti-CTLA4 ICB in a CD4+ T-cell dependent fashion and; (iii) altering the cellular plasticity of cancer cells can regulate CD73 expression. Given the highly refractory nature of more-mesenchymal cancer cells, our findings hold tremendous potential in aiding translational efforts to target cancer plasticity to enhance responses of breast cancers to ICB therapy. Citation Format: Anushka Dongre. Targeting epithelial-mesenchymal plasticity and CD73 to enhance responses of breast cancers to immune checkpoint blockade therapies [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B022.