Functional Th1-oriented T follicular helper cells that infiltrate human breast cancer promote effective adaptive immunity.

Noël, Grégory; Langouo Fontsa, Mireille; Garaud, Soizic; De Silva, Pushpamali; de Wind, Alexandre; Van den Eynden, Gert G; Salgado, Roberto; Boisson, Anaïs; Locy, Hanne; Thomas, Noémie; Solinas, Cinzia; Migliori, Edoardo; Naveaux, Celine; Duvillier, Hugues; Lucas, Sophie; Craciun, Ligia; Thielemans, Kris; Larsimont, Denis; Willard-Gallo, Karen

We previously demonstrated that tumor infiltrating lymphocytes (TIL) in human breast cancer sometimes form organized tertiary lymphoid structures (TLS) characterized by CXCL13-producing T follicular helper (Tfh) cells. The present study found that CD4+ Tfh TIL, CD8+ TIL and TIL-B, co-localizing in TLS, all express the CXCL13 receptor CXCR5. An ex vivo functional assay determined that only activated, functional Th1-oriented Tfh TIL (PD-1hiICOSint phenotype) provide help for immunoglobulin and IFNγ production. A functional Tfh TIL presence signals an active TLS, characterized by humoral (immunoglobulins, Ki-67+ TIL-B in active germinal centers) and cytotoxic (GZMB+CD8+ and GZMB+CD68+ TIL plus Th1 gene expression) immune responses. Analysis of active versus inactive TLS in untreated patients revealed the former are associated with positive clinical outcomes. TLS also contain functional T follicular regulatory (Tfr) TIL, which are characterized by a CD25+CXCR5+GARP+FOXP3+ phenotype and a demethylated FOXP3 gene. Functional Tfr inhibited functional Tfh activities via a GARP-associated TGFβ-dependent mechanism. The activity of tumor-associated TLS was dictated by the relative balance between functional Tfh TIL and functional Tfr TIL. These data provide mechanistic insight into TLS processes orchestrated by functional Th1-oriented Tfh TIL, including TIL-B and CD8+ TIL activation and immunological memory generation. Tfh TIL, regulated by functional Tfr TIL, are an expected key target of PD-1/PD-L1 blockade.