Absence of Toll-like receptor 5 confers survival in mice bearing ovarian tumors treated with anti-PD-L1

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Abstract Ovarian cancer accounts for more deaths than any other cancer of the female reproductive system. Patients bearing ovarian tumors infiltrated with high frequencies of T cells associate with a greater survival probability. However, therapies targeting T cells in ovarian cancers are ineffective. We observed in models of late-stage murine ovarian cancer that in absence of Toll-Like Receptor 5 (TLR5) signaling, anti-PD-L1 promotes significant survival and protection against tumor rechallenge. Ovarian tumors from rechallenged TLR5KO mice exhibited significantly higher frequency/number of CD8 T cells expressing functional and activation markers. Thus, in the absence of TLR5 signaling, T cells mount/maintain a stronger response to ovarian tumors after inhibitory receptor blockade. Furthermore, protection against tumor progression in TLR5KO mice corresponds with a significant increase in tumor infiltrating cross presenting and IL-12 producing Dendritic cells (DCs). Additionally, in CD11c Cre x TLR5 fl/fl mice, whose DCs lack TLR5 expression, PD-L1-blockade mediated extended survival in ovarian tumor-bearing mice. Using a mixed bone marrow chimera approach, we demonstrate that direct TLR5 signaling functionally alters DCs to become more suppressive in the tumor microenvironment, impacting T cell differentiation and anti-tumor activity, thereby reducing survival during aPD-L1 therapy. Clinically, roughly 7.5% of the general population harbor a TLR5 SNP that diminishes TLR5 signaling and is associated with increased long-term survival for ovarian cancer patients. Therefore, patients who express the TLR5 SNP may immediately benefit from anti-PDL1 therapy and those without the SNP, TLR5 antagonism. NIH/NCI 1R01CA253285 UVA Farrow Fellowship