Abstract B036: Micromechanical regulation of tumor immune microenvironment
Authors: Peura Aino , Turpin Rita , Salmela Maria , Liu Ruixian , Mikkonen Piia , Klefström Juha , Munne Pauliina M 
Published: February 2024

Abstract
Although the prognosis of primary breast cancer (BC) is considerably good, the prognosis of therapy-resistant, metastatic BC remains rather poor, thus being the major cause of BC-related deaths. Due to the undifferentiated and heterogenous nature of this disease, immunotherapies have been among the most promising therapeutic strategies for metastatic BC. However, in recent clinical trials, immunotherapies have had a poor success rate for breast cancer. Therefore, new therapeutic strategies and more profound knowledge of BC-specific immune-evasion mechanisms are urgently needed. We have developed a patient-derived explant model (PDEC), that allows us to cultivate patient-derived primary tumor samples. Moreover, the model also maintains alive the tumor resident immune cells, hence providing us with a unique platform for researching immunological drugs in vivo. In our model, tumor cells and tumor-derived immune cells are embedded in a 3D scaffold matrix with altering biological and physical properties. By altering the material in which the tumor cells are embedded we can also research the effect of microenvironmental factors such as stiffness and growth factors on the tumor cells. Microenvironmental stiffness is a well-known regulator of BC identity; in stiff 3D microenvironment breast cancer cells maintain their original identity, while in a softer microenvironment, they dedifferentiate towards more undifferentiated, therapy-resistant, and metastasis-mimicking subtype (Munne et al, 2021). In this study, we observed for the first time how the alterations in breast tumor microenvironmental stiffness also alter the phenotype in the breast tumor immune microenvironment concomitantly. In the soft microenvironment, the cytokine profile is polarized towards more tumor suppressing via upregulation of TGFB and downregulation of IL1B. Moreover, immune response and antigen presentation are heavily downregulated. Lastly, macrophages are depolarized from M1-like toward more tumor-promoting. This effect is induced and mediated by tumor cells and fresh immune cells embedded in similar 3D conditions that fail to secrete tumor suppressive cytokines or silence antitumor immunity. Manipulation of the tumor cell identity and tumor immune microenvironment via alteration of 3D matrices provides us a unique perspective for observing new methods of how metastatic breast cancer creates immune evasion. Moreover, the model allows us to develop novel treatments against metastatic, theraphy resistant breast cancer and test them easily in ex vivo conditions.
Citation Format: Aino Peura, Rita Turpin, Maria Salmela, Ruixian Liu, Piia Mikkonen, Juha Klefström, Pauliina M Munne. Micromechanical regulation of tumor immune microenvironment [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 B036.