Abstract P5-02-51: Single-cell transcriptome reveals distinct peripheral blood immune landscapes associated with sensitivity to anti-HER2 treatment in HER2-positive metastatic breast cancer patients
Authors: Lee Jongwon , Choi Jungmin , Park In Hae 
Published: March 2023

Abstract
Background: Different immune cell states reflect distinct tumor microenvironment and led to various clinical outcomes for cancer patients. However, very few studies examined the contribution of peripheral blood (PB) immune landscapes to the treatment response due to the limited applications. This study aimed to explore the circulating immune cell landscapes associated the sensitivity to cytotoxic chemotherapy with trastuzumab in HER2 positive metastatic breast cancer patients. Methods: Whole blood were drawn at baseline and after 2 cycles of trastuzumab plus cytotoxic chemotherapy from six patients (3 responders and 3 non-responders). Approximately 3,500 to 10,000 peripheral blood mononuclear cells per patients were profiled using single-cell RNA sequencing (scRNA-seq). scRNA-seq data were further processed and analyzed using Seurat package version 3.1. Cell populations were clustered using the Louvain algorithm and subsequently annotated using known marker genes. Differential abundance in cell population was quantified using MiloR and differentially expressed genes were detected using MAST between responders and non-responders. Results: After removing low quality cells, a total of 65,295 cells were clustered into 18 clusters. CD8 Effector T, CD4 Naïve T, CD4 Effector T, Cytotoxic NK, Naïve B, Plasma B and Monocytes were significantly enriched in responders compared to non-responders. Especially, CD8 Effector T, NK, Plasma B and Classical Monocytes showed distinct patterns that those cells were enriched in pre-treatment than post-treatment of responder but not in non-responder. From the differentially expressed gene analysis, cytotoxic or costimulatory marker genes (GZMK, GZMA, GNLY, CCL5, NKG7, PRF1) were enriched in responders. While, exhausted or coinhibitory marker genes (DNAJB1, LGALS9, HAVCR2) were enriched in non-responders. Gene set enrichment analysis revealed four pathways associated with T cell, B cell receptor signaling, NK cell mediated cytotoxicity and Cytokine-cytokine receptor interaction which showed differences between responders and non-responders following chemotherapy. Finally, validation with flow cytometry using independent cohort showed that constant expression manner in HAVCR2, LGALS9 and LGALS3 genes. Conclusions: Single-cell transcriptome analysis identified distinct PB immune landscapes associated with treatment response in HER2-positive metastatic breast cancer patients. Differential abundance and unique gene expression programs of immune cell populations could serve as potential predictive biomarkers for anti-HER2 therapy.
Citation Format: Jongwon Lee, Jungmin Choi, In Hae Park. Single-cell transcriptome reveals distinct peripheral blood immune landscapes associated with sensitivity to anti-HER2 treatment in HER2-positive metastatic breast cancer patients [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-51.