STAT1-associated intratumoural TH1 immunity predicts chemotherapy resistance in high-grade serous ovarian cancer

Abstract

High-grade serous ovarian carcinoma (HGSC) accounts for 70% of all epithelial ovarian cancers but clinical management is challenged by a lack of accurate prognostic and predictive biomarkers of chemotherapy response. This study evaluated the role of Signal Transducer and Activator of Transcription 1 (STAT1) as an independent prognostic and predictive biomarker and its correlation with intratumoural CD8⁺ T cells in a second independent biomarker validation study. Tumour STAT1 expression and intratumoural CD8⁺ T cell infiltration were assessed by immunohistochemistry as a multicentre validation study conducted on 734 chemotherapy-naïve HGSCs. NanoString-based profiling was performed to correlate expression of STAT1 target genes CXCL9, CXCL10 and CXCL11 with CD8A transcript expression in 143 primary tumours. Multiplexed cytokine analysis of pre-treatment plasma from resistant and sensitive patients was performed to assess systemic levels of STAT1-induced cytokines. STAT1 was validated as a prognostic and predictive biomarker in both univariate and multivariate models and its expression correlated significantly with intra-epithelial CD8⁺ T cell infiltration in HGSC. STAT1 levels increased the prognostic and predictive value of intratumoural CD8⁺ T cells, confirming their synergistic role as biomarkers in HGSC. In addition, expression of STAT1 target genes (CXCL9, CXCL10 and CXCL11) correlated significantly with levels of, and CD8A transcripts from intratumoural CD8⁺ T cells within the resistant and sensitive tumours. Our findings provide compelling evidence that high levels of STAT1, STAT1-induced chemokines and CD8⁺ T cells correlate with improved chemotherapy response in HGSC. These results identify STAT1 and its target genes as novel biomarkers of chemosensitivity in HGSC. These findings provide new translational opportunities for patient stratification for immunotherapies based on emerging biomarkers of inflammation in HGSC. An improved understanding of the role of interferon-inducible genes will be foundational for developing immunomodulatory therapies in ovarian cancer.

Keywords: STAT1; chemoresistance; interferon; intratumoural CD8+ T cell; ovarian cancer.

Figure 1

STAT1 expression associates with progression free survival in HGSC. Kaplan–Meier estimates showing significant association between high STAT1 expression and increased progression free survival (p = 0.017) (A) and response to chemotherapy (p = 0.018) (B) in the Phase II COEUR validation cohort. STAT1 expression in duplicate tumour cores on a HGSC TMA was evaluated using immunohistochemistry using a previously validated antibody 7.

Figure 2

STAT1 expression correlates with intratumoural CD8⁺ T cell density. (A) Immunohistochemical analysis of STAT1 expression and CD8⁺ T cells in HGSCs (B) Spearman correlation analysis showing significant association between STAT1 expression and intratumoural CD8⁺ T cell numbers.

Figure 3

Prognostic relevance of intratumoural CD8⁺ T cell density in HGSC. Kaplan–Meier analysis was performed using intratumoural CD8⁺ T cell density (using average of two cores) dichotomised with the threshold of ≤ 5 vs >5 as established for ovarian cancer. Tumour samples were derived from two HGSC retrospective cohorts; (A) CHUM cohort, (n= 184) and (B) TFRI‐COEUR cohort, (n = 515). Analysis performed on optimally debulked cases on two independent retrospective HGSC patient cohorts (C, CHUM and D, TFRI‐COEUR) showed significant prognostic relevance of intratumoural CD8⁺ T cells. Log‐rank test was applied to determine statistical significance (p < 0.05).

Figure 4

STAT1 expression enhances the prognostic and predictive value of intratumoural CD8⁺ T cells in HGSC. Average intratumoural CD8⁺ T cell numbers and STAT1 expression levels in corresponding tumour cores from CHUM (A & B) and TFRI‐COEUR (C & D) cohorts were included in the Kaplain Meier survival analysis. Log‐rank test was applied to derive statistical significance (p < 0.05).

Figure 5

Differential expression of STAT1 target genes in chemoresistant and sensitive HGSC. NanoString based expression profiling of a customised gene panel of 34 genes including those induced by STAT1 as well as immune phenotypic markers in 77 sensitive and 66 resistant HGSCs. NanoString Data analysis was performed using nSolver software from NanoString and R Bioconductor NanoStringnorm package. Statistical significance (p < 0.05) between the two groups was determined using Welch's t‐test.

Figure 6

STAT1 target chemokine genes exhibit significant correlation with CD8A expression. Spearman correlation analysis was performed between STAT1, CD8A, CXCL9, CXCL10 and CXCL11 gene expression in the sensitive and resistant tumours. Significant positive correlation was noted between STAT1 and CXCL9 (A), STAT1 and CD8A (B) as well as CXCL9 and CD8A (C) gene expression (measured as house keeping gene normalised NanoString counts) within the two groups.