Abstract 2367: Hedgehog signaling influences tumor immunogenicity by the modulation of T cell populations in breast cancer

Abstract

Abstract Breast cancer is becoming more prevalent as it now makes up 30% of all new cancer cases yearly for U.S. women. Additionally, highly aggressive triple-negative breast cancer (TNBC) presents with immunologically “cold” tumors characterized by limited infiltration of anti-tumorigenic lymphocytes and the promotion of immunosuppressive cell populations. Therefore, it is essential to consider possible combinational therapies in treating primary tumors and in preventing metastases and recurrence. In the breast tumor microenvironment (TME), the presence and activity of regulatory T cells (Tregs) have been associated with poorer prognoses in breast cancer due to their ability to promote the progression of tumor growth and metastasis. Our group has extensively studied how the Hedgehog (Hh) signaling pathway can modulate the aggressiveness and the immune portfolio of the mammary TME, and we have recently reported the role of this pathway in regulating Treg activity and abundance. We have discovered that Hh inhibition can influence Treg-to-Th17 plasticity, promoting Tregs into a pro-inflammatory Th17-like phenotype (Tr17), therefore, affecting the immunogenicity of the mammary TME. As Tregs are highly influential to other immune populations of the TME, it is imperative to determine how this phenotypic change in Tregs after Hh inhibition influences other T cell populations of the mammary TME. We hypothesize that systemic Hh inhibition reshapes the tumor-immune microenvironment to be tumor-eradicating by influencing key immune populations of the mammary TME. Therefore, we further investigated how CD4+ and CD8+ T cells are influenced by systemic Hh blockade in a mammary carcinoma mouse model using single-cell RNA-Sequencing (scRNA-Seq), multiparameter flow cytometry, and R programming for data analyses and visualization. We sought to interpret how Hh inhibition influences key T cell populations that can dictate the immunogenicity of the primary tumor and to determine if these changes may be a result of the Treg-to-Th17 transition in response to Hh manipulation. In these investigations, we found that systemic Hh inhibition modified the abundance, metabolic signatures, and effector functions of CD4+ and CD8+ T cell populations within the primary tumor. As Tregs can impair essential tumor-infiltrating lymphocytes and promote the recruitment of other immunosuppressive constituents to the primary mammary tumor and Th17s can promote inflammatory and cytotoxic immune populations, these studies will expand on the mechanism by which Hh signaling modulates mammary tumorigenesis holistically, as well as specifically, through Tregs. This comprehensive work revealing the mechanistic role of Hh signaling in Treg plasticity and other T cell subsets will also inform innovative combinational therapeutic strategies to treat highly aggressive TNBC. Citation Format: Courtney A. Swain, Dominique C. Hinshaw, Brandon J. Metge, Heba M. Alsheikh, Lalita A. Shevde-Samant. Hedgehog signaling influences tumor immunogenicity by the modulation of T cell populations in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2367.