CD137 agonists in mice suppress germinal center responses by increasing the immunosuppressive activity of follicular regulatory T-cells

Abstract

Humoral immune responses rely on germinal center (GC) reactions to generate long-lasting antibody responses with affinity maturation. CD137 (4-1BB) agonists are known to exert inhibitory effects on B-cell responses; however, the underlying mechanisms remain unclear. Here, we show that agonistic anti-CD137 monoclonal antibodies target multiple CD137-expressing cell types, including activated CD8⁺ T-cells, regulatory T-cells, follicular regulatory T-cells, and follicular dendritic cells. Anti-CD137 antibodies strongly disrupt GC reactions upon vaccination, preventing the development of anti-drug antibodies, and suppress ectopic B-cell responses within tumor-associated tertiary lymphoid structures in mice. Mechanistic analyses demonstrate that GC disruption occurs independently of IFN-γ, IL-12, and CD8⁺ T-cells, but is critically dependent on Foxp3⁺ T-cells. Combined transcriptomic profiling, immune phenotyping, and functional GC suppression assays reveal that anti-CD137 treatment increases the abundance and immunosuppressive activity of regulatory and follicular regulatory T-cells in vaccinated mice. Our results uncover the cellular basis of CD137-mediated suppression of humoral immunity and provide insight into rational combinatorial immunotherapeutic strategies incorporating CD137 agonists under active clinical development. Agonistic CD137 (4-1BB) antibodies are promising cancer immunotherapies, but their inhibitory effects on humoral immunity remain poorly understood. This study shows that CD137 agonists abolish germinal center (GC) responses by enhancing the suppressive activity of follicular regulatory T-cells, thereby inhibiting B-cell responses after vaccination, in tumor-associated tertiary lymphoid structures, and against therapeutic antibodies. A single dose of an agonistic anti-CD137 antibody completely abolishes GC responses after vaccination. Agonistic anti-CD137 antibodies bind primarily to activated CD8⁺ T-cells, follicular regulatory T-cells, regulatory T-cells, and follicular dendritic cells. The inhibitory effect is independent of IFN-γ, IL-12, and CD8⁺ T-cells, but depends on a radiosensitive hematopoietic compartment. GC suppression is mediated, at least in part, by the expansion of Foxp3⁺ CD4⁺ T-cells (regulatory and follicular regulatory T-cells) and their enhanced suppressive activity. CD137 agonists also suppress B-cell responses in tumor-associated tertiary lymphoid structures and reduce anti-drug antibody formation. A single dose of an agonistic anti-CD137 antibody completely abolishes GC responses after vaccination. Agonistic anti-CD137 antibodies bind primarily to activated CD8⁺ T-cells, follicular regulatory T-cells, regulatory T-cells, and follicular dendritic cells. The inhibitory effect is independent of IFN-γ, IL-12, and CD8⁺ T-cells, but depends on a radiosensitive hematopoietic compartment. GC suppression is mediated, at least in part, by the expansion of Foxp3⁺ CD4⁺ T-cells (regulatory and follicular regulatory T-cells) and their enhanced suppressive activity. CD137 agonists also suppress B-cell responses in tumor-associated tertiary lymphoid structures and reduce anti-drug antibody formation. Agonistic anti-CD137 (4-1BB) monoclonal antibodies target multiple cell types and suppress B-cell responses through the expansion of Foxp3⁺ CD4⁺ T-cells.