DC Vaccination Against the Vascular Antigen DLK1 Reduces Triple-Negative Breast Cancer Burden and Metastasis 2299544

Abstract Introduction Despite treatment advancements for triple-negative breast cancer (TNBC) utilizing immune checkpoint blockade (ICB) in combination with chemotherapy, the lack of druggable targets such as receptors for estrogen, progesterone, and HER2 yields high recurrence and metastasis rates. A promising immunotherapeutic strategy involves exploiting the tumor microenvironment’s (TME) dependence on a functional vasculature for growth and progression. Methods We hypothesize that alpha-type-1 dendritic cell (αDC1) vaccination against the conserved tumor blood vessel antigen (TBVA) DLK1, which we found is expressed by abluminal pericytes in the TME of 75% of TNBC patients, can provide therapeutic protection against TNBC. To assess in vivo tumor inhibition and changes in immunologic milieu in two murine models, strain-specific DLK1 peptides were pulsed with αDC1 cells to generate vaccines (αDC-DLK1) that were administered on days 5 and 7 alongside ICB on days 8, 11, and 14 in pre-clinical E0771 and 4T1 TNBC models. Tumors and draining lymph nodes were harvested after euthanasia (E0771) or survival surgery (4T1) around day 17 for analysis by histology, immunohistochemistry, immunofluorescence, TUNEL assay, immunoblotting, qPCR, and/or T cell co-culture activation studies. Lungs and vital organs were harvested for evaluation of metastasis and toxicity. Results Our results demonstrated the ability of therapeutic αDC-DLK1 vaccination to safely provoke anti-angiogenic T cell activation, increased TME infiltration, and enhanced effector function that resulted in significant reduction of primary and metastatic tumor burden. Interestingly, ex vivo analyses demonstrated that vaccine-mediated DLK1 responses initiated polyclonal T cell activation against TNBC cellular antigens through cross-priming effects that likely fortified tumor protection. Conclusion Overall, our data support the clinical relevance of DLK1 as an immunotherapeutic target and the development of TBVA-based DC therapies for TNBC patient treatment. Funding Source n/a Topic Categories Tumor Immunology: Checkpoints, Prevention, and Treatment (TIPT)