Regulatory T Cells in Tumor-Associated Tertiary Lymphoid Structures Suppress Anti-tumor T Cell Responses

• TA-TLSs form adjacent to advanced lung tumors
• TA-TLSs have features and functions of lymph nodes
• Treg cells in TA-TLSs actively suppress immune responses
• Therapeutic Treg cell depletion causes immune-mediated tumor destruction

SummaryInfiltration of regulatory T (Treg) cells into many tumor types correlates with poor patient prognoses. However, mechanisms of intratumoral Treg cell function remain to be elucidated. We investigated Treg cell function in a genetically engineered mouse model of lung adenocarcinoma and found that Treg cells suppressed anti-tumor responses in tumor-associated tertiary lymphoid structures (TA-TLSs). TA-TLSs have been described in human lung cancers, but their function remains to be determined. TLSs in this model were spatially associated with >90% of tumors and facilitated interactions between T cells and tumor-antigen-presenting dendritic cells (DCs). Costimulatory ligand expression by DCs and T cell proliferation rates increased in TA-TLSs upon Treg cell depletion, leading to tumor destruction. Thus, we propose that Treg cells in TA-TLSs can inhibit endogenous immune responses against tumors, and targeting these cells might provide therapeutic benefit for cancer patients.

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