Role of immune-checkpoint LAG3 as a biomarker finding tool in patient-derived organoid cultures of breast cancer.

LAG3 plays a regulatory role in immunity and emerged as an inhibitory immune checkpoint molecule comparable to PD-L1 and CTLA-4 and a potential target for enhancing anti-cancer immune responses. We generated 3D cancer cultures as a model to identify novel molecular biomarkers for the selection of patients suitable for α-LAG3 treatment and simultaneously the possibility to perform an early diagnosis due to its higher presence in breast cancer, also to achieve a theragnostic approach. Our data confirm the extreme dysregulation of LAG3 in breast cancer with significantly higher expression in tumor tissue specimens, compared to non-cancerous tissue controls. LAG3 blockade inhibited proliferation of in vitro and ex vivo 3D human organoids and immune micro-environment through both a decrease of PD-L1, TIM-3 and CTLA4 expression and an increased production of several pro-inflammatory cytokines (IFNγ, IL-12, IL-6, IL-1β, TNFα) and EMT markers. These effects trigger a more permissive anti-tumor immune reaction, recruiting immune cells to the tumor sites, boosting the anti-tumor response. LAG3 acts as an immunosuppressive molecule in breast cancer, inhibiting T CD8 + cell proliferation and cytokine production by T cells. We proposed the modulation of a novel checkpoint molecule, such as LAG3, as potential biomarkers associated to a rapid diagnosis.