P29 - An immunosuppression gauge for indicating metastatic risk and therapeutic response in breast cancer

Introduction: : Immunosuppression drives metastatic outgrowth and therapy resistance in cancer. Gauging its level can provide valuable insights into cancer progression and therapy responses. However, the absence of robust biomarkers has hindered the development of such a gauge. We recently found that in breast cancer, the systematic immunosuppression is negatively related to the abundance of CXCL1, CXCL2, and CXCL5 chemokines in major organs. These chemokines can actively recruit pro-inflammatory immune cells, creating an immune-active anti-tumor environment to inhibit metastatic outgrowth. In contrast, organs lacking these chemokines exhibit significant immunosuppression and are vulnerable to secondary tumor growth. Based on this novel finding, we developed CXCR2-guided cell imaging to quantify the abundance of CXCL1, CXCL2, and CXCL5 in major organs as a method to gauge immunosuppression in breast cancer.

Materials and

Methods: : Mesenchymal stem cells (MSCs) have been widely studied for their application in cell-based therapy and imaging. We developed a MSC cell line stably overexpressing CXCR2. Notably, CXCR2 is the receptor of CXCL1, CXCL2, and CXCL5. These CXCR2+ MSCs were fluorescently labeled and then intravenously injected into mice. Whole-body imaging was conducted at 24 hours after injection to quantify the accumulation of fluorescent CXCR2+ MSCs in the lungs and livers. This accumulation is expected to be CXCL-dependent, with a high accumulation in major organs correlating with a low level of immunosuppression and a low risk of metastatic outgrowth in breast cancer. We subsequently evaluated the effectiveness of this cell imaging-based immunosuppression gauge in (1) distinguishing non-aggressive from aggressive breast cancers based on their ability to induce systemic immunosuppression during progression, (2) detecting the early onset of metastatic outgrowth in aggressive breast cancers, and (3) predicting response or resistance to anti-PD-1 immune checkpoint therapy in aggressive breast cancer models.

Results, Conclusions, and Discussions:: First, we observed a high accumulation of CXCR2+ MSCs in mice with non-aggressive 67NR breast cancer and a low accumulation of these cells in those with aggressive 4T1 breast cancer when both models have primary tumors of comparable size. Additionally, systematic immunosuppression increased exponentially over time in 4T1 model. Resecting 4T1 tumors at an early cancer stage cannot stop the progression of immunosuppression. Therefore, mice receiving tumor resection treatment showed no survival advantage compared to untreated controls. Second, we observed that as cancer progressed to a stage when major organs failed to recruit intravenously injected CXCR2+ MSCs, indicating an extremely low abundance of CXCL1, CXCL2, and CXCL5, myeloid cells isolated from these organs showed T cell suppression activity and the metastatic outgrowth in hosts initiated. The onset of metastasis indicated by our immunosuppression gauge is much earlier than detection by CT scans, which typically identify >4 mm tumor masses that contain millions of proliferating tumor cells. Third, in 4T1 mice receiving neoadjuvant or adjuvant anti-PD1 antibody therapy, those exhibiting alleviated immunosuppression, represented by increased accumulation of CXCR2+ MSCs in major organs, responded favorably and achieved longer survival than those exhibiting persistent immunosuppression. Overall, our results demonstrated CXCR2+ MSC-based imaging as a sensitive and accurate tool for gauging immunosuppression. It can outperform CT scans to detect the metastatic risk and monitor therapy responses in breast cancer. In the future, we will develop a CXCL-targeted, nanoparticle-based imaging system to gauge immunosuppression, offering a safer, more cost-effective, and user-friendly alternative to cell-based imaging.

Acknowledgements and/or References (Optional)::