Abstract 23P
Background
Immune checkpoint inhibitors exhibit limited response rates in patients with triple-negative breast cancer (TNBC), suggesting that additional immune escape mechanisms may exist. Here, we aimed to observe the function shifts of immune-related genes across various tumor microenvironments and identify previously undescribed regulators of TNBC immunity.
Methods
We performed two-step customized in vivo CRISPR screens targeting disease-related immune genes using different mouse models with multi-dimensional immune deficiency characteristics. Functional screening and transcriptomics analysis identified Lgals2 as a candidate regulator in TNBC involving immune escape. The distribution of tumor-infiltrating immune cells were analyzed through flow cytometry and single-cell RNA sequencing of tumors isolated from mouse xenograft models. We further conducted in vitro co-culture experiments to investigate the crosstalk between tumor-associated macrophages and TNBC cells mediated by Lgals2. Blockade of LGALS2 using an inhibitory antibody were also applied to assess its clinical significance in TNBC.
Results
The in vivo CRISPR screens characterized gene functions in the different tumor microenvironments and recovered canonical immunotherapy targets. Lgals2 was consistently correlated with immune escape in two-step screens and its expression was significantly higher in tumor tissues from TNBC patients compared with normal tissues. In addition, deletion of Lgals2 in tumor cells have no effect on tumor proliferation in vitro, but attenuated tumor growth in vivo. We further demonstrated that tumor cell-intrinsic Lgals2 resulted in the immunosuppressive phenotype of the TNBC microenvironment and induced the significantly increased number of tumor-associated macrophages in tumor tissues. Mechanistic studies revealed that Lgasl2 facilitated M2-like polarization and proliferation of macrophages through CSF1/CSF1R axis. Moreover, anti-LGALS2 antibody arrested tumor growth and reversed the immune suppression.
Conclusions
Lgals2 plays a critical role in the immunosuppressive nature of the TNBC microenvironment. We provide a theoretical basis for LGALS2 as a potential immunotherapy target in TNBC.
Legal entity responsible for the study
Fudan University Shanghai Cancer Center.
Funding
National Natural Science Foundation of China.
Disclosure
All authors have declared no conflicts of interest.