Melanie R. Rutkowski

TLR5 Signaling Causes Dendritic Cell Dysfunction and Orchestrates Failure of Immune Checkpoint Therapy against Ovarian Cancer

Abstract Ovarian cancer accounts for more deaths than any other cancer of the female reproductive system. Patients who have ovarian tumors infiltrated with high frequencies of T cells are associated with a greater survival probability. However, therapies to revitalize tumor-associated T cells, such as PD-L1/PD-1 or CTLA4 blockade, are ineffective for the treatment of ovarian cancer. In this study, we demonstrate that for ovarian cancer, Toll-like receptor 5 (TLR5) signaling, for which the only known ligand is bacterial flagellin, governed failure of PD-L1 and CTLA4 blockade. Mechanistically, chronic TLR5 signaling on CD11c+ cells in vivo and in vitro impaired the differentiation of functional IL-12–producing XCR1+CD103+ conventional type 1 dendritic cells, biasing CD11c+ precursor cells toward myeloid subsets expressing high levels of PD-L1. This culminated in impaired activation of CD8+ T cells, reducing CD8+ T-cell function and ability to persist within the ovarian tumor microenvironment. Expansion of XCR1+CD103+ conventional type 1 dendritic cells in situ using Flt3L-Ig in combination with PD-L1 blockade achieved significant survival benefit in TLR5 knockout mice bearing ovarian tumors, whereas no benefit was observed in the presence of TLR5 signaling. Thus, we have identified a host-intrinsic mechanism leading to the failure of PD-L1 blockade for ovarian cancer, demonstrating that chronic TLR5 signaling on CD11c+ cells is a barrier limiting the efficacy of checkpoint therapy.

Ovarian cancer drives TLR5-dependent expansion of myeloid progenitors through systemic ligand dissemination

Abstract Ovarian cancer remains the most lethal gynecologic malignancy, due in part to the establishment of a profoundly immunosuppressive tumor microenvironment (TME). While toll-like receptor 5 (TLR5) signaling has previously been implicated in promoting myeloid cell recruitment to the ovarian TME, source(s) of ligand and systemic effects on hematopoiesis remain poorly understood. Here, we demonstrate that ovarian cancer disrupts gut barrier integrity, leading to systemic translocation of TLR5 ligands into the peritoneum, blood, and bone marrow. This translocation correlates with enhanced expansion of myeloid progenitors in the bone marrow of wild-type (WT) but not TLR5-deficient (TLR5 KO) mice, leading to enhanced accumulation of monocytes and macrophages into the TME. In the bone marrow, direct TLR5 signaling induced expansion of TLR5-expressing granulocyte-monocyte progenitors, a phenotype recapitulated both using an in vitro colony-forming assay and in a mixed bone marrow chimera model. Acute pharmacologic blockade of TLR5 in tumor-bearing mice altered the composition of tumor-associated myeloid populations, reducing the frequency of monocytes and CCR2-expressing macrophages accumulating within the TME of WT mice. These data reveal that chronic TLR5 signaling, driven by tumor-induced loss of gut barrier integrity, promotes expansion of myeloid cells within the bone marrow and is a host-intrinsic mechanism driving accumulation of immature monocytes and macrophages into the TME.