Abstract LB100: Dickkopf-1 induces breast cancer progression by limiting T cell infiltration into the tumor microenvironment

Abstract Activation of Wnt/β-catenin signaling pathway in the tumor cells has been shown to promote cell proliferation and correlate with cancer progression. Therefore, dickkopf-1 (Dkk1), a soluble Wnt/β-catenin inhibitor, has been considered as a tumor suppressor. However, contradicting evidence demonstrated that high levels of circulating Dkk1 correlate with poor prognosis in various cancers. Although Dkk1 is best known to modulate bone remodeling, we recently reported that Dkk1 supports the growth of subcutaneous B16 melanomas by creating an immune-suppressive environment. However, the detailed mechanism by which Dkk1 alters anti-tumor immune responses remains to be elucidated. In this study, we used mice orthotopically injected with hormone-resistant luminal B, ER+ PyMT, EO771 and triple-negative 4T1 cell lines. We find that Dkk1 is upregulated in all models and its neutralization reduces tumor growth. To our surprise, Dkk1 was barely expressed by each tumor lines tested. However, we found elevated expression of Dkk1 in the bone by the osteoblasts (OBs) and in the breast tumor stroma by cancer-associated fibroblasts (CAFs), although at a much lower level compared to the OBs. To address the role of bone-derived versus tumor stroma-derived Dkk1 during tumor progression, we generated mouse models specifically deleting Dkk1 from OBs (OsxCre;Dkk1fl/fl), and from CAFs (Fsp1Cre;Dkk1fl/fl and aSMACreERT2;Dkk1fl/fl). To our surprise, all our mouse models reduced orthotopic PyMT tumor growth significantly, suggesting that Dkk1 could act both systemically and locally to modulate tumor progression. Interestingly, however, deletion of Dkk1 in the bone or in the CAFs did not appear to change the immune composition in the bone marrow, spleen, or at the tumor site. Next, we orthotopically injected PyMT cells into the severely immune-compromised NSG mice treated with anti-Dkk1 or IgG. Strikingly, Dkk1 neutralization did not reduce tumor growth in NSG mice, suggesting that Dkk1 modulates breast cancer growth by altering anti-tumor immune responses. Similar to mice with deletion of Dkk1 in the bone or in the CAFs, Dkk1 neutralization did not alter the percentage of the myeloid and lymphoid cell subsets or the activation status of T cells in bone marrow, spleen, or tumor site compared to IgG control mice. However, by IHC we observed that tumors from anti-Dkk1-treated mice or with deletion of Dkk1 in the CAFs had increased numbers of CD4+ and CD8+ T cells infiltrating the center of tumor mass while these immune populations remained at the edges of the tumors in control mice. In summary, we provide evidence that Dkk1 exerts local and systemic effects to promote tumor progression by modulating the infiltration of immune cells into the TME. Citation Format: Seunghyun Lee, Biancamaria Ricci, Roberta Faccio. Dickkopf-1 induces breast cancer progression by limiting T cell infiltration into the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB100.