Abstract P5-04-13: Toll like receptor-9 and CD73 may act on the same pathway to induce immunosuppression in triple negative breast cancer cells
Authors: Selander Katri S , Tuomela Johanna M , Mella Mikko , Kauppila Joonas , Sandholm Jouko , Yegutkin Gennady , Karihtala Peeter , Jukkola-Vuorinen Arja , Haapasaari Kirsi-Maria , Vuopala Katri S , Harris Kevin W 
Published: May 2015

Toll like-receptor-9 (TLR9) is an innate immune system DNA-receptor which is also widely expressed in breast cancer cell lines and in clinical breast cancer specimens. Although TLR9 ligands (such as bacterial DNA and synthetic, CpG-sequence containing oligonucleotides) induce TLR9-mediated invasion in breast cancer cells in vitro, the contribution of this protein to breast cancer pathophysiology remains unclear. We showed previously that tumor TLR9 expression is a highly significant prognostic factor in breast cancer, but only in tumors that are triple negative (TNBC). Specifically, low tumor TLR9 expression in TNBC is associated with a significantly shortened disease-specific survival. Our published, preclinical results further suggest that tumor TLR9 expression may be an important determinant of tumor immunophenotype and that patients with low-TLR9 TNBC may not gain the immunogenic benefit from chemotherapy. A possible mechanistic explanation for the change in the immunophenotype of low TLR9-TNBC tumors involves CD73, which is a 5’ectonucleotidase that converts extracellular adenosine monophosphate (AMP) into the highly immunosuppressive adenosine. CD73 is also expressed in breast cancer cells and in clinical specimens. High CD73 expression has been associated with poor prognosis, but similar with TLR9 expression, the prognostic significance was specific only for TNBC. There are no previous reports on TLR9 regulation of CD73 in any cancer. Interestingly, however, TLR9 deficiency was shown to promote CD73 expression of T-cells in a mouse model of diabetes. To begin to test the hypothesis that TLR9 affects CD73 expression in TNBC, we studied CD73 mRNA and protein expression in control and TLR9 siRNA TNBC cells in vitro. We discovered that TLR9 siRNA TNBC cells express significantly higher CD73 mRNA concentrations than control siRNA cells specifically in hypoxia. Similar findings were observed with immunofluorescence. Our results suggest that the lack or TLR9 in TNBC may allow high CD73 expression and through this mechanism result in an immunosuppressive phenotype of the tumors. The immunosuppression then would explain the poor prognosis associated with low TLR9-TNBC tumors. We are currently studying this with clinical TNBC specimens.

Citation Format: Katri S Selander, Johanna M Tuomela, Mikko Mella, Joonas Kauppila, Jouko Sandholm, Gennady Yegutkin, Peeter Karihtala, Arja Jukkola-Vuorinen, Kirsi-Maria Haapasaari, Katri S Vuopala, Kevin W Harris. Toll like receptor-9 and CD73 may act on the same pathway to induce immunosuppression in triple negative breast cancer cells [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-04-13.