Distinct cellular interactions in the TNBC tumor microenvironment in association with PD-L1 expression and pathologic complete response based on spatial analysis.

Abstract

e12544 Background: Immune-activated tumor microenvironments (TMEs), characterized by PD-L1 positivity or an abundance of tumor-infiltrating lymphocytes, are associated with pathologic complete response (pCR) in patients with triple-negative breast cancer (TNBC) treated with neoadjuvant systemic therapies (NAST). We performed a spatial analysis of the TME using a highly multiplexed imaging technique in treatment-naïve TNBC tumor samples treated with NAST. Methods: We collected 28 biopsied tumor samples before NAST. Of these, 6 patients underwent preoperative immunochemotherapy with pembrolizumab. Spatial analysis of the TME was performed using CO-Detection by indexing (CODEX). Physical cell-to-cell interactions were analyzed by assessing the rate of direct contact and the closest distance between different cell types. PD-L1 expression was evaluated using the Ventana SP142 PD-L1 assay. Results: The rate of PD-L1 positivity and pCR were 42.8% and 53.6%, respectively. CD8+ T cells were classified into two groups by immune checkpoint (IC) markers (PD1, LAG3, CXCL13): CD8+IC high and CD8+IC low . Direct contact between CD8+IC high and CD4+FoxP3 low T cells was enriched in tumors with PD-L1-negative or non-pCR. In PD-L1-positive tumors, podoplanin exhibited direct interactions with various immune cell types, including CD8+IC low , CD4, CD8, and myeloid cells. When analyzing cell-to-cell distances, the distances between B cells and various cells including tumor epithelial cells were significantly shorter in cases with pCR compared to those without pCR. Conclusions: Direct interaction between CD8+IC high and CD4+FoxP3 low cells may be associated with PD-L1-negative TNBC. Podoplain potentially plays a role in the PD-L1-expressing TME in TNBC. Active physical interaction between B cells and neighbor cells was observed in tumors with pCR. Our findings, based on spatial analysis of TME, may enhance our understanding of immune-cold TNBC and its lack of response to immunochemotherapy.