TUMORAL PD-L1 ORCHESTRATES DIFFERENT TUMOR-INDUCED IMMUNOSUPPRESSION MECHANISMS DURING BREAST CANCER PROGRESSION

PAULA AGUIRRE; MARCOS PALAVECINO; LILIAN CASTILLO; SABRINA ALDANA VALLONE; ROBERTO MEISS; ADRIANO BERTELLI; AGUSTINA SUBAN; SANTIAGO RODRIGUEZ.- SEGUÍ; OMAR COSO; EVA WERTHEIMER; EDITH KORDON; MARINA SIMIAN; ANDREA ERRASTI; MANUEL DE LA MATA; ALBANA GATTELLI; ANTONIO CARRERA-SILVA; JUAN PABLO FEDEDA

VIRTUAL

Congreso; LXVI REUNIÓN ANUAL DE LA SOCIEDAD ARGENTINA DE INVESTIGACIÓN CLÍNICA (SAIC); 2021

One of the main immunosuppressive mechanisms by which cancer avoids eradication by the immune system is the expression of PD-L1, the ligand for T-cell inhibitory receptor PD-1. PD-1 activation leads to cytotoxic CD8+ lymphocyte exhaustion, which is the major immunoediting pathway triggered by PD-L1. However, little is known about which other aspects of immunosuppression are exerted by tumor-intrinsic PD-L1 expression. To genetically address tumor-immune system interactions in a triple negative breast cancer (TNBC) model, we developed a CRISPR/Cas9 expressing TNBC-like EO771 cell line platform. Using flow cytometry, we characterized the immune response associated with the progression of EO771 tumor growth, which elicited immunosuppression signatures associated with poor prognosis in TNBC patients: an increase in pro-tumoral M2 macrophage polarization, a decrease in MHCII+ Antigen Presenting Cells (APCs) and a marked increase in T-cell exhaustion. To test the role of tumoral PD-L1 in tumor-mediated immune escape, we generated PD-L1 KO EO771 cell lines. Using CRISPR/Cas9 edited EO771 line KO for PD-L1, we found that tumor intrinsic PD-L1 expression is required for tumor growth. Interestingly, we found that PD-L1 expressed by tumor cell is also necessary to establish several suppressive immune cell hallmarks: a) in the myeloid compartment it is required for the differentiation of macrophages to a M2 phenotype and for the generation of myeloid derived suppressor cells and b) in the T-cell compartment, unexpectedly, tumoral PD-L1 is needed to exhaustion of regulatory CD4+ but not CD8+ cytotoxic cells. All together, these data suggests that tumor-intrinsic PD-L1 plays a key role on TNBC tumor growth by triggering different immunosuppressive mechanisms in the tumor immune landscape.Using this editable EO771 model platform, we will be able to massively test tumoral PD-L1 synthetic interactions to identify candidate genetic targets to overcome PD-1/PD-L1 resistance in TNBC.