Abstract PR10: Active and quiescent tertiary lymphoid structures, differentiated using FOXP1 expression, play a role in immunity to breast cancer

Abstract

Abstract Interest is growing in active immune responses generated by tertiary lymphoid structures (TLS) arising in solid tumors; however, their clinical impact in breast cancer (BC) remains unclear. Several studies show that transcription factors contribute to TLS formation via their regulation of cytokine and chemokine production. The Forkhead box (FOX) protein 1 (FOXP1) has been shown to play critical roles in regulating immune cells, including our recent work revealing its effects on TIL migration. These data lead us to further investigate FOXP1 expression in tumor-infiltrating lymphocytes (TIL) and TLS. We identify two types of TLS based on FOXP1 expression: 1) those that contain a germinal center (GC+) and those that do not (GC-). Comparative analysis of FOXP1 expression in secondary lymphoid organs, including more immune active tonsils (many GC) and less immune active spleens (primarily without GC), confirms differences in FOXP1 expression associated with GC. In BC, TLS-containing tumors were more frequently GC- than GC+ (n=49), with triple-negative tumors having higher numbers of GC+ TLS compared to luminal or HER2+ tumors. Immunofluorescence and multiplex immunohistochemistry was used to closely examine the GC+ and GC- TLS, finding an immune active profile in the former, characterized by T follicular helper cells (PD1+CD4+ T), mature dendritic cells (CD21+ and CD23+), actively proliferating (Ki67+) B cells undergoing immunoglobulin (Ig) class switch recombination (AID+) and a plasma cell presence (CD138+). Analysis of Igs in primary tumor supernatants revealed that BC with ≥1 GC+ TLS (n=20) were characterized by increases in total Ig, IgG1, IgG2, and IgA, reflecting active humoral immunity, compared to BC containing only GC- TLS (n=29). Gene expression analysis of individual microdissected TLS demonstrated upregulation of Th1, Th2, and Tfh immune genes in the GC+ compared to the GC- TLS, suggesting the former also sustain cell-mediated immune responses. Immune infiltrates in tumors with ≥1 GC+ TLS are specifically characterized by high global TIL, CD3+, CD4+ or CD8+ T cell TIL and CD20+ TIL-B (n=29). Analysis of BC TIL spatial distribution identified increased stromal TIL (all subpopulations) while intratumoral TIL increases were predominantly CD3+ and CD8+ T cell TIL in tumors with GC+ TLS. Overall, our data indicate that GC+ TLS house active immune responses in BC while GC- TLS are quiescent. This abstract is also being presented as Poster B99. Citation Format: Pushpamali De Silva, Soizic Garaud, Cinzia Solinas, Grégory Noël, Mireille Langouo Fontsa, Anaïs Boisson, Alexandre de Wind, David Venet, Gert Van den Eynden, Hugues Duvillier, Céline Naveaux, Ligia Craciun, Dominique Bron, Martine Piccart-Gebhart, Denis Larsimont, Karen Willard-Gallo. Active and quiescent tertiary lymphoid structures, differentiated using FOXP1 expression, play a role in immunity to breast cancer [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr PR10.