Generation of a CRISPR/Cas9 EO771-tumor platform to study breast cancer cell - immune system interactions

AGUIRRE PAULA; PALAVECINO MARCOS; CASTILLO LILIAN; MEISS ROBERTO; RODRIGUEZ SEGUI SANTIAGO; COSO OMAR; WERTHEIMER EVA; KORDON EDITH; ERRASTI ANDREA; GATTELLI ALBANA; DE LA MATA MANUEL; CARRERA SILVA EUGENIO; FEDEDA JUAN PABLO

CABA

Simposio; BA-BCS 2021; 2021

The main immunosuppressive mechanism by which canceravoids eradication by the immune system is the expressionof PD-L1, the ligand for T-cell inhibitory receptor PD-1.Despite their success in the treatment of different types ofsolid tumors, PD-1/PD-L1 blockade therapies have beenineffective in triple negative breast cancer (TNBC). Thus, itremains unclear which is the role of tumor PD-L1 and otherimmune checkpoint ligands in TNBC immune evasion. To addressthis, we developed a CRISPR/Cas9 expressing EO771cell line as a platform to genetically study tumor-immunesystem interactions. As a first step, we confirmed the TNBCbehavior of the EO771 model and characterized the immuneresponse associated with the progression of EO771 tumorgrowth using flow cytometry. We found that EO771 tumorprogression is hormone-independent and correlates withan increase in M2 macrophage polarization, a decrease inMHCII+ Antigen Presenting Cells (APCs), a marked increasein the CD4+/CD8+ ratio and CD4+ T cell exhaustion, whichare consistent with tumor-mediated immunosuppression associatedwith poor prognosis in TNBC patients. In preliminaryexperiments, PD-L1 KO EO771 tumors show a significant butpartial reduction in tumor growth rates, consistent with tumorPD-L1 being not sufficient to suppress anti-tumor immunity.By screening this platform, we will be able to massively testtumoral PD-L1 synthetic interactions to identify candidategenetic targets to overcome PD-1/PD-L1 resistance in TNBC.