# Alterations in PD-L1+ Myeloid Cells and Immune Infiltration Are Associated with Atezolizumab and Paclitaxel Therapy Success in a Triple-Negative Breast Cancer Model

## TL;DR

This study shows that PD-L1+ myeloid cells and immune infiltration are linked to successful treatment with atezolizumab and paclitaxel in a model of triple-negative breast cancer.

## Contribution

The study identifies PD-L1+ myeloid cells and immune infiltration as potential biomarkers for successful immunotherapy in triple-negative breast cancer.

## Key findings

- Granulocytes, monocytes, and macrophages showed significantly higher PD-L1 expression compared to tumor cells.
- CD206+ TAMs had the highest PD-L1 expression and were also PD-L1 positive in multiple organs.
- Combining paclitaxel and atezolizumab significantly reduced tumor growth and lung metastasis in late-stage TNBC.

## Abstract

Background and Objectives: A combination of chemotherapy and immunotherapy may improve cancer treatment outcomes; however, determining which patient groups will benefit from immunotherapy is critical. Triple-negative breast cancer (TNBC) achieves limited benefit from immune checkpoint inhibitors (ICIs) and anti-PD-L1 blockade therapy. Materials and Methods: In this study, PD-L1 expression levels in myeloid-derived cells in the tumor microenvironment were determined in an experimental TNBC model. Results: Compared with tumor cells, granulocytes, monocytes, and macrophages had significantly higher PD-L1 expression. CD206+ tumor-associated macrophages (TAMs) expressed the highest level of PD-L1. PD-L1 positivity in TAMs was also significantly high in the lung, liver, lymph node, and spleen. Despite treatment initiation in late-stage tumorigenesis, the combination of paclitaxel and the anti-PD-L1 monoclonal antibody atezolizumab significantly reduced tumor growth. In addition, lung metastasis burden was reduced with combined treatment compared with chemotherapy or anti-PD-L1 monotherapy alone. Conclusions: As a result, alterations in PD-L1+ myeloid cells and immune infiltration can be associated with atezolizumab and paclitaxel therapy success in triple-negative breast cancer.