探究宿主TLR5信号如何调控FLT3配体治疗卵巢癌的疗效

Ovarian cancer continues to be the most fatal gynecological malignancy, and survival rates of individuals with this disease have remained relatively unchanged for the past 30 years. Though immunotherapies such as immune checkpoint blockades have drastically improved survival outcomes for other cancers, they rarely induce a therapeutic response for ovarian cancer. We have identified toll-like receptor 5 (TLR5) signaling, the only known ligand of which is bacterial flagellin, as a host- intrinsic factor that orchestrates the failure of checkpoint therapy for ovarian cancer. Mechanistically, ovarian tumors induce chronic gut leakage, enabling dissemination of flagellin into the ovarian tumor microenvironment (TME). Chronic TLR5 signaling disrupts the accumulation of IL-12+ anti-tumorigenic dendritic cells (DCs) in the ovarian TME and promotes expansion of PD-L1 expressing immature myeloid populations, culminating in failure of immune checkpoint blockade. One strategy to overcome this deficit is to promote further expansion of DCs via administration of the DC growth factor fms-like tyrosine kinase receptor 3 ligand (FLT3L). Although no benefit was observed for wild type (WT) mice with intact TLR5 signaling, an observation consistent with poor clinical efficacy of FLT3L therapy, FLT3L administration in TLR5-deficient (TLR5KO) mice resulted in prolonged and durable survival for over 80% of animals when combined with PD-L1 blockade. These data suggest that in the absence of TLR5 signaling, the ovarian TME becomes more responsive to immunotherapy, and justifies further investigation into how TLR5 signaling is disrupting FLT3L expanded DCs. High dimensional flow cytometry data show that in the absence of ovarian tumors, FLT3L significantly expands the proportion of DCs in multiple tissues, including the peritoneal cavity, in both TLR5KO and WT mice. Phenotypic profiling of tumor nodules and the peritoneal cavity in ovarian tumor- bearing TLR5KO and WT animals 24 hours after FLT3L treatment ceases shows significantly higher frequencies of DCs in the peritoneal cavity of TLR5KO mice as compared to WT. Analysis of tumor nodules also reflects a significant increase in the frequency of dendritic cells infiltrating tumors as compared to WT mice. These preliminary results suggest TLR5 signaling is impacting the expansion and/or recruitment of dendritic cells into the ovarian tumor microenvironment. Ongoing and future experiments will assess chemokines and cytokines the periphery, peritoneal washes, and tumor lysates to define TLR5-mediated signaling pathways that inhibit DC maturation and recruitment. Our results aim to mechanistically define how chronic TLR5 signaling is impacting FLT3L efficacy, and further elucidate how TLR5 signaling is a host intrinsic process whereby the microbiome is driving resistance to immune therapies.