Abstract PD4-05: PD4-05 Integrated multi-cohort profiling identifies CCL19+ dendritic cells to potentiate immunotherapy efficacy in triple-negative breast cancer
Authors: Wu Song-Yang , Zhang Si-Wei , Ma Ding , Jin Xi , Jiang Yi-Zhou , Shao Zhi-Ming 
Published: March 2023

Abstract
Background: Immune checkpoint inhibitors (ICIs) targeting the PD-1/PD-L1 axis have emerged as constituting a new pillar for breast cancer; however, they benefit only a subset of patients, and predictive biomarkers are urgently needed. While dendritic cells (DCs) are essential for the orchestration of antitumor immune response, the clinical value of DCs in breast cancer immunotherapy remains unclear. An improved understanding of the functional diversity of DC subsets, as well as their relationship with ICI response, would eventually improve the efficacy of ICIs in breast cancer patients. Objective: We sought to comprehensively characterize DC heterogeneity within the tumor microenvironment, identify distinct DC subsets associated with the response to ICIs, and define clinically applicable predictive biomarkers for ICI therapy. Methods: We performed a comprehensive single-cell RNA sequencing (scRNA-seq) analysis of 53 breast tumors receiving ICIs or chemotherapy in two retrospective studies (NCT03197389 and GSE169246) to identify specific DC populations associated with ICI responsiveness. Next, we harnessed multiplex immunohistochemistry (n = 186), multiparametric flow cytometry of fresh tissues (n = 87), large consecutive transcriptomic datasets (The Cancer Genome Atlas [TCGA] and Fudan University Shanghai Cancer Center [FUSCC]), and in vivo experiments to illustrate the molecular portraits and clinical relevance of the identified DC subsets. Additionally, except for the two scRNA-seq datasets, we leveraged another four independent cohorts (NCT03805399, NCT04613674, NCT04129996, GSE124821) and assessed the clinical utility of the established clinically applicable biomarkers derived from prior analyses to predict response following treatment with ICIs or chemotherapy. Results: By obtaining single-cell transcriptome data of 1,955 high-quality DCs, we identified five distinct DC subpopulations (CLEC9A+, CD1A+, CLEC10A+, CCL19+, and LILRA4+). We then illustrated that a specific CCL19+ DC population, but not whole DCs or other subsets, was associated with ICI responsiveness, particularly in triple-negative breast cancer (TNBC). Mechanistically, a potent CD8+ T-cell response was unleashed, rendering tumors susceptible to PD-1 blockade in vivo and confirming their putative immunomodulatory capacity. This phenomenon was only observed in CCL19+ DCs but not in CCL19- DCs, indicating CCL19 as a specific marker and could reflect the infiltration and functional phenotype of CCL19+ DCs in breast tumors. Finally, by integrating six independent ICI therapy cohorts, we demonstrated that baseline CCL19 in both tumor and blood could predict better response and survival in TNBC patients receiving ICIs, but not so for chemotherapy. Conclusions: Our results provide important insights into the relationship between the clinical outcome of ICIs and DC heterogeneity at single-cell resolution, support the development of therapies modulating CCL19+ DCs to trigger antitumor CD8+ T-cell immunity, and suggest baseline CCL19 levels as a noninvasive predictive biomarker for patients receiving ICIs, that are potentially applicable in the clinic. In light of these results, we suggest CCL19+ DC modulation as a possible precision immunotherapy approach for cancer patients.
Citation Format: Song-Yang Wu, Si-Wei Zhang, Ding Ma, Xi Jin, Yi-Zhou Jiang, Zhi-Ming Shao. PD4-05 Integrated multi-cohort profiling identifies CCL19+ dendritic cells to potentiate immunotherapy efficacy in triple-negative breast cancer [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 PD4-05.