Neoadjuvant chemotherapy remodels the three-dimensional vascular architecture and immune microenvironment in pancreatic ductal adenocarcinoma.

BACKGROUND: Pancreatic ductal adenocarcinoma (PDAC) is characterized by a highly immunosuppressive tumor microenvironment (TME) and poor treatment responsiveness. Although neoadjuvant chemotherapy (NAC) can improve clinical outcomes, its effects on the TME, particularly the interplay between vascular remodeling and immune reprogramming, remain poorly understood. This study examined the impact of NAC on both the immune cell composition and vascular structure of PDAC. METHODS: Immunohistochemistry of immune cell infiltration was performed in PDAC tissues resected from 56 patients. In a separate cohort of 26 patients, three-dimensional vascular analysis using tissue clearing and confocal imaging was performed alongside immunohistochemistry-based evaluation of vessel proportions. Immunohistochemistry was used to evaluate CD4+ T cells, CD8+ T cells, FoxP3+ regulatory T cells, CD163+ macrophages, CD34+ pan-endothelial cells, and CD105+ tumor-associated endothelial cells. Vascular morphology, including vessel length, surface area, and volume, was quantified by three-dimensional reconstruction. All comparisons were performed at the patient level. RESULTS: NAC-treated tissues exhibited increased CD4+ and stromal CD8+ T cell infiltration, a reduced FoxP3+/CD4+ ratio, and an increased tumoral CD8+/CD163+ ratio. NAC was associated with shorter vessel length and a selective reduction in CD105+ tumor-associated vessels, with unchanged total CD34+ vessel density. These changes were generally more pronounced in patients with a better treatment response. CONCLUSION: NAC was associated with coordinated TME remodeling involving both immune and vascular components. This integrated remodeling might contribute to the development of an immunologically activated tumor phenotype and support the rationale for combination strategies with immunotherapy in PDAC.