Abstract 6150: Intramammary gland activation of invariant natural killer T cells with anti-tumor CD4Th1 cells prevents the development of invasive mammary carcinoma

Breast cancer (BC) remains one of the most prevalent cancers in the world thus prompting efforts in risk reduction and prevention. Current strategies for prevention are limited to hormone therapy or prophylactic surgery, which are not without complication. Patients with preinvasive malignant lesions of the breast, including ductal carcinoma in situ (DCIS), if left untreated or after surgical resection, have a higher risk of developing invasive BC (IBC). In addition, clinical studies have shown that a subset of DCIS patients who did not progress to invasive disease died from recurrence or distant metastasis. These findings highlight the need for an effective prevention strategy to halt IBC progression and recurrence. Recently, we reported the critical role of anti-tumor CD4Th1 cells in preventing early BC progression. Other studies have shown that enhancement of invariant natural killer T (iNKT) cells plays a role in preventing mammary carcinoma. However, loss of CD1d expression on mammary epithelial cells can suppress iNKT cells, leading to mammary carcinoma and progression of invasive disease. We tested the efficacy of combined activation of iNKT and CD4Th1 cells with intratumoral delivery of type 1 polarized dendritic cells targeting tumor antigen (HER2-DC1) and α-galactosylceramide (α-GalCer-DC1) in BALB-HER2/neu transgenic mice bearing spontaneous invasive mammary lesions. The intratumoral activation of iNKT-CD4Th1 cells with systemic anti-HER2 antibody therapy resulted in eradication of invasive mammary lesions with improved survival of BALB-neuT mice. We then investigated the efficacy of iNKT-CD4Th1 cells in a BALB-neuT mice preventive model. The combined activation of iNKT-CD4Th1 cells in one mammary gland (mammary gland 5) with systemic delivery of anti-HER2 antibody in BALB-neuT mice before the onset of a preinvasive malignant mammary lesion induced a strong anti-tumor response. Complete prevention of mammary carcinoma was observed in all ten mammary glands (up to 27 weeks of mice age) with improved survival. We further demonstrated that activation of iNKT-CD4Th1 cells in all ten mammary glands of BALB-neuT mice in a preventive model displayed a superior anti-tumor immunity and prolonged tumor prevention with survival benefits. The immune profiling revealed an increased infiltration of iNKT, CD4T, CD4T effector memory, CD4T central memory, CD4T effector, NK, and B cells in the mammary glands of BALB-neuT mice. Importantly, iNKT-CD4Th1 combined activation strategy also decreased the level of myeloid derived suppressor cells and tumor associated macrophages in the mammary glands of BALB-neuT mice. Collectively, these results suggest that iNKT-CD4Th1 cell mediated anti-tumor immunity is an effective strategy for BC prevention. Citation Format: Camille C. Baumrucker, Ganesan Ramamoorthi, William Dominguez-Viqueira, Brian J. Czerniecki. Intramammary gland activation of invariant natural killer T cells with anti-tumor CD4Th1 cells prevents the development of invasive mammary carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 6150.