375P Insights from single cell profiling of blood, tumour and lymph nodes: Dysfunctional dendritic cell states in breast cancer drive early immune evasion

Background: Transforming growth factor beta (TGF) contributes to pancreatic ductal adenocarcinoma (PDAC) progression by promoting immune suppression, fibrosis, and metastasis.Its central role in shaping the tumor microenvironment has made TGF an attractive target for immunotherapy.One promising strategy involves TGF-based immune-modulatory vaccines (IMVs) to activate TGF-specific T cells.In this study, we examined the immunogenicity of multiple TGF-derived epitopes and assessed the clinical relevance of TGF-specific T cells in patients with PDAC. Methods:The immunogenicity of the TGF-derived epitopes TGF-15, -33, and -38, as well as the presence, phenotype, and functionality of TGF-specific T cells, was assessed in healthy donors and pancreatic cancer patients using enzyme-linked immunospot (ELISPOT) and intracellular cytokine staining (ICS).We also explored different mRNA constructs to activate these TGF-specific T cells.Finally, we correlated baseline T-cell responses to the epitopes with clinical outcomes in patients with PDAC who received immune checkpoint inhibitors and radiotherapy. Results:We detected T cell responses to TGF-15, -33, and -38 in both healthy donors and PDAC patients, with TGF-33 eliciting robust responses in the patients.These T cells were mainly CD4 + , displayed both proinflammatory and cytotoxic activity, and recognized target cells in a TGF-dependent manner.Additionally, higher baseline frequencies of TGF-33-specific T cells correlated with improved clinical outcomes following combined immune checkpoint inhibitor therapy and radiotherapy.Furthermore, baseline responses to multiple epitopes, compared to responses to only a single epitope, were linked to longer overall and progression-free survival.By using a single mRNA construct encoding multiple TGF-derived epitopes, we demonstrated efficient activation of both CD4 + and CD8 + T cells specific for distinct TGF epitopes. Conclusions:We demonstrated that TGF-specific T cells are present in patients with pancreatic cancer and that baseline responses to multiple TGF-derived epitopes correlate with improved outcomes after immune checkpoint inhibitors and radiotherapy.