Examining the impact of TGF-ß activity on fibroblast infiltration and immune exclusion in MIBC.

851 Background: In urothelial cancer, transforming growth factor β (TGF-β) signaling in fibroblasts has been correlated with poor respose to immunotherapy (IO). We examined TGF- β activity scores in relation to the tumor micro-environment (TME) from muscle invasive bladder cancer (MIBC) patients and whether this correlated to response to neoadjuvant chemoIO utilized in the BLASST-01 trial. Methods: We assessed a prospective commercial cohort (PCC) consisting of the de-identified and anonymized transcriptome-wide expression profiles of N = 604 MIBC patients from the clinical use of the Decipher Bladder TURBT test that were available in the Decipher GRID registry (NCT02609269). Molecular subtypes were categorized by the consensus-MIBC subtyping model. Using GRID signatures, we applied the molecular signatures database hallmark gene set collection to quantify TGF-β hallmark signaling scores. Furthermore, we used TIDE (a computational framework on Tumor Immune Dysfunction and Exclusion) to quantify TME-related scores for cancer associated fibroblasts (CAF), immune exclusion, T regulatory cells and cytotoxic T-lymphocytes. The BLASST-01 trial investigated 4 cycles of neoadjuvant gemciatine, cisplatin, and nivoumab followed by radical cystectomy (RC). Pre-treament tumor specimens were examined for associations between molecular scores and pathological response (≤ypT1N0) at RC. Multivariable logistic regression analyses for pathologic response were adjusted for patient age and sex. Results: Intersection of TGF-β hallmark signaling scores with consensus molecular subtypes in the PCC cohort, we found elevated scores for the stroma-rich molecular subtype (p 0.31, p < 0.001) For BLASST-01, transcriptome data were available for 37/43 (86%); median age was 65 (IQR, 58-70), 41% were female, 89% were cT2N0 and 35% had pathological complete response. Higher scores for TGF-β signaling (OR 0.03, p < 0.005), immune exclusion (OR 0.37, p < 0.03) and CAFs (OR 0.41, p < 0.03) were associated with no pathological response, whereas cytotoxic T lymphocytes were significantly associated with pathological complete response (OR 7.04, p < 0.02). Conclusions: The present study demonstrates that molecular TGF-β activity scores are associated with fibroblast infiltration and immune exclusion, suggesting TGF-β attenuates response to neoadjuvant IO for MIBC.