Microbially driven TLR5-dependent signaling governs distal malignant progression through tumor-promoting inflammation

The dominant TLR5(R392X) polymorphism abrogates flagellin responses in >7% of humans. We report that TLR5-dependent commensal bacteria drive malignant progression at extramucosal locations by increasing systemic IL-6, which drives mobilization of myeloid-derived suppressor cells (MDSCs). Mechanistically, expanded granulocytic MDSCs cause γδ lymphocytes in TLR5-responsive tumors to secrete galectin-1, dampening antitumor immunity and accelerating malignant progression. In contrast, IL-17 is consistently upregulated in TLR5-unresponsive tumor-bearing mice but only accelerates malignant progression in IL-6-unresponsive tumors. Importantly, depletion of commensal bacteria abrogates TLR5-dependent differences in tumor growth. Contrasting differences in inflammatory cytokines and malignant evolution are recapitulated in TLR5-responsive/unresponsive ovarian and breast cancer patients. Therefore, inflammation, antitumor immunity, and the clinical outcome of cancer patients are influenced by a common TLR5 polymorphism.

TLR5 mediated regulation of tumor growth in an inducible model of cancer (162.48)

It has been reported that up to 25% of the human population carries a dominant point mutation in TLR5 resulting in the loss of TLR5 signaling. TLR5 expression is paramount in modulating the balance of regulatory FoxP3+ and proinflamatory IL-17+ T cell lineages, two cellular subsets with potentially divergent roles in cancer. However, in the context of cancer, the significance of this mutation remains unknown. Sequencing of cDNA isolated from human ovarian tumor specimens revealed that 6% of tumor specimens harbor a functional mutation in TLR5, suggesting that a loss in TLR5 signaling results in “resistance” to cancer. To further investigate the role of TLR5 signaling in cancer progression, we utilized a novel p53 and KRas dependent model of inducible cancer. TLR5-/- mice had a remarkable delay in tumor onset and a dramatic reduction in tumor burden. Corresponding to the delayed tumor onset, we observed that T cells sorted from the tumor draining lymph nodes of TLR5-/- mice were able to vigorously recall against tumor antigens compared to a profound paralysis of effector function in T cells sorted from the draining lymph nodes of WT mice. These data indicate for the first time that pattern recognition receptors may influence the elimination and/or equilibrium phases of tumor progression at extraintestional locations, pinpointing potentially novel pathways to target for immunotherapy.

Ovarian cancer progression is controlled by phenotypic changes in dendritic cells

We characterized the initiation and evolution of the immune response against a new inducible p53-dependent model of aggressive ovarian carcinoma that recapitulates the leukocyte infiltrates and cytokine milieu of advanced human tumors. Unlike other models that initiate tumors before the development of a mature immune system, we detect measurable anti-tumor immunity from very early stages, which is driven by infiltrating dendritic cells (DCs) and prevents steady tumor growth for prolonged periods. Coinciding with a phenotypic switch in expanding DC infiltrates, tumors aggressively progress to terminal disease in a comparatively short time. Notably, tumor cells remain immunogenic at advanced stages, but anti-tumor T cells become less responsive, whereas their enduring activity is abrogated by different microenvironmental immunosuppressive DCs. Correspondingly, depleting DCs early in the disease course accelerates tumor expansion, but DC depletion at advanced stages significantly delays aggressive malignant progression. Our results indicate that phenotypically divergent DCs drive both immunosurveillance and accelerated malignant growth. We provide experimental support for the cancer immunoediting hypothesis, but we also show that aggressive cancer progression after a comparatively long latency period is primarily driven by the mobilization of immunosuppressive microenvironmental leukocytes, rather than loss of tumor immunogenicity.