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

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, colocalizing in TLS, all express the CXCL13 receptor CXCR5. An ex vivo functional assay determined that only activated, functional Th1-oriented Tfh TIL (PD-1(hiI)COS(int) phenotype) provide help for immunoglobulin and IFN-gamma 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 that 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 glycoprotein A repetitions predominant (GARP)-associated TGF-beta-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.

Automated summary

This study found that T follicular helper (Tfh) cells in breast cancer play a key role in the formation of tertiary lymphoid structures (TLS), with active and functional Tfh TILs in TLS being associated with positive clinical outcomes in patients. The balance between functional Tfh TILs and functional T follicular regulatory (Tfr) TILs dictates the activity of tumor-associated TLS.