Abstract 4618: Biomarkers of functionally active tertiary lymphoid structures in human breast cancer
Authors: Sofronii Doïna , Padonou Francine , Langouo Mireille , Thomas Noemie , Boisson Anais , De Wind Alexandre , Larsimont Denis , Awada Ahmad , Garaud Soizic , Willard-Gallo Karen 
Published: April 2023

Abstract
The clinical relevance of tumor infiltrating lymphocytes (TIL) in breast cancer (BC) is now widely accepted and being implemented in clinical practice. Our lab previously demonstrated that 60% of BC organize some of their TIL in tertiary lymphoid structures (TLS). TLS have been detected in a wide variety of solid tumors with their prognostic value and importance in the response to immunotherapy increasingly accepted. Reliable biomarkers to identify and characterize TLS and their immune activities in tumors are needed. The specific aim of this project was to perform a comprehensive analysis across the spectrum of TLS states to identify biomarkers associated with active and inactive TLS, where the former are associated with functional anti-tumor immunity and improved responses to treatment and long-term survival. This study analyzed FFPE tissues from 38 primary untreated HER2+ and triple negative (TN) BC patients. Patients were divided into two groups based on a TLS score evaluating CD3/CD20 and PD-1/Ki-67 dual IHC-stained tumor tissues: 1) BC containing a majority of active TLS (tumors with only active TLS have never been observed), defined by the presence of a germinal center (GCpos ; Ki-67+ follicular B cells) and 2) BC with only inactive TLS (GCneg ; Ki-67− follicular B cells). Controls included normal breast tissues, BC without TLS and lymphoid tissues (reactive tonsils for GCpos and spleens for GCneg TLS). RNA extracts from microdissected tissues (N=100), including active TLS, inactive TLS and lymphoid B follicles, were sequenced. DESeq2 and CIBERSORT were employed to quantify differentially expressed genes and immune cell subpopulations, respectively. Gene Set Enrichment Analysis was used for additional data interpretation and pathway identification. Tumors from patients with active TLS were characterized by increased naïve and plasma B cell TIL compared to tumors with only inactive TLS. Preliminary analysis of the differentially expressed genes in active TLS (vs inactive TLS) revealed upregulation of key B cell differentiation, somatic hypermutation and class switch recombination genes, which paralleled their respective lymphoid controls. These gene upregulations were linked with a GC presence in active TLS. A specific set of immunoglobulin genes were also differentially expressed in active TLS. Continued analysis of the TLS data, including their cellular composition, location, maturation and functionality, along with data confirmation (RT-PCR and multiplex IHC), and assessment of their functional and clinical relevance is ongoing. Our preliminary results suggest that active B cell differentiation and Ig production contribute to TLS functionality. In lymphoid tissues, the GC plays important roles in orchestrating the molecular and cellular programs of humoral immunity. Our data suggest that active GC-containing TLS foster an immune microenvironment in BC that favors positive clinical outcomes.
Citation Format: Doïna Sofronii, Francine Padonou, Mireille Langouo, Noemie Thomas, Anais Boisson, Alexandre De Wind, Denis Larsimont, Ahmad Awada, Soizic Garaud, Karen Willard-Gallo. Biomarkers of functionally active tertiary lymphoid structures in human breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4618.