Inhibition of FGFR3 upregulates MHC‐I and PD‐L1 via TLR3/NF‐kB pathway in muscle‐invasive bladder cancer

Improving the potency of immune response is paramount among issues concerning immunotherapy of muscle-invasive bladder cancer (MIBC).On the basis of immune subtypes, we investigated possible molecular mechanisms involved in tumor immune escape in MIBC. According to the 312 immune-related genes, three MIBC immune subtypes were clustered.Cluster 2 subtype is characterized by FGFR3 mutations and has a better clinical prognosis. However, the expression levels of MHC-I and immune checkpoints genes were the lowest, indicating that this subtype is subject to immune escape and has a low response rate to immunotherapy. Bioinformatics analysis and immunofluorescence staining of clinical samples revealed that the FGFR3 is involved in the immune escape in MIBC. Besides, after FGFR3 knockout with siRNA in RT112 and UMUC14 cells, the TLR3/NF-kB pathway was significantly activated and was accompanied by upregulation of MHC-I and PD-L1 gene expression. Furthermore, the use of TLR3 agonists poly(I:C) can further improve the effect.Together, our results suggest that FGFR3 might involve in immunosuppression by inhibition of NF-kB pathway in BC. Considering that TLR3 agonists are currently approved for clinical treatment as immunoadjuvants, our study might provide more insights for improving the efficacy of immunotherapy in MIBC.