Abstract 4000: A DNA damage response deficiency (DDRD) group in breast cancer is associated with activation of the STING innate immune pathway and PD-L1 expression
Authors: Parkes Eileen E. , Walker Steven M. , McCabe Nuala , Taggart Laura E. , Hill Laura , Buckley Niamh E. , Savage Kienan I. , Salto-Tellez Manuel , McQuaid Stephen , Harte Mary T. , Mullan Paul B. , Harkin D Paul , Kennedy Richard D. 
Published: July 2016

We have previously identified a DNA damage response deficient (DDRD) subgroup in breast cancer, associated with loss of the Fanconi Anemia/BRCA DNA repair pathway. The 44-gene DDRD signature developed to prospectively identify this subgroup has been validated as predictive of response to DNA damaging chemotherapy in the treatment of breast cancer. This subgroup is defined by immune signalling, with immune genes, such as the chemokines CXCL10 and CCL5, and immune checkpoints IDO1 and PD-L1 (CD274) overexpressed within the signature and subgroup. Here we report innate immune pathway activation in this subgroup, and association with PD-L1 expression.

Methods: We used isogenic cell line models to identify and model pathways constitutively active in DDRD cancer cells. CD4+, CD8+ T-cell infiltration and PD-L1 expression was identified by immunohistochemistry (IHC) on a previously described breast TMA of 191 breast tumor samples, of which 65 were in the DDRD subgroup. DNA microarray data from FFPE samples was used to identify other immune checkpoints associated with this subgroup.

Results: CD4+ and CD8+ T-cell infiltration, and PD-L1 expression were significantly associated with DDRD breast tumors on IHC analysis. In addition, expression of immune checkpoints such as IDO1, TIM-3 and LAG-3 were associated with the DDRD subgroup. Increased migration of peripheral blood mononuclear cells was identified into media conditioned by DDRD cells, this was dependent on chemokines secreted by DDRD cells. Endogenous activation of the innate immune pathway STING/TBK1/IRF3 was identified in DDRD cancer cells, and required for expression of chemokines CXCL10 and CCL5. This chemokine expression was associated with cytosolic DNA detected by cGAS and activation of the innate immune pathway STING/TBK1/IRF3. Importantly, this pathway was cell cycle related with upregulation of chemokine expression in S-phase of the cell cycle. Chemokine expression could be induced by S-phase DNA damaging chemotherapy but not by taxanes. Similarly, PD-L1 was induced by treatment with DNA damaging agents in cancer cells dependent on STING.

Conclusions: We have identified constitutive activation of the innate immune STING pathway in a DNA damage response deficient subgroup of breast cancer, which is associated with CD4+, CD8+ infiltration and PD-L1 expression. We propose activation of the STING pathway as an important signal for lymphocytic infiltration, independent of tumor-associated neoantigens. The DDRD signature could identify patients with innate immune activation in response to endogenous DNA damage, which may allow stratification for immune checkpoint targeted treatments. Moreover, S-phase DNA damaging agents activate PD-L1 expression, and a combination approach of immune checkpoint inhibitors and S-phase specific chemotherapy may be synergistic in the clinic.

Citation Format: Eileen E. Parkes, Steven M. Walker, Nuala McCabe, Laura E. Taggart, Laura Hill, Niamh E. Buckley, Kienan I. Savage, Manuel Salto-Tellez, Stephen McQuaid, Mary T. Harte, Paul B. Mullan, D Paul Harkin, Richard D. Kennedy. A DNA damage response deficiency (DDRD) group in breast cancer is associated with activation of the STING innate immune pathway and PD-L1 expression. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4000.