Heterogeneity of Tertiary Lymphoid Structures and Plasma Cells in PDAC with and Without Lymph Node Metastasis

Background/Objectives: TLSs are favorable PDAC prognostic biomarkers. However, the mechanisms underlying TLSs formation and their contribution to the humoral antitumor immune response remain poorly understood. Methods: We used mIF staining combined with AI-based pathological image analysis software to assess the heterogeneity in the distribution of TLSs, B cells, plasma cells, and tumor cells between N0 and N1/2 PDAC. Three scRNA-seq datasets and the TCGA-PAAD database were utilized to investigate the functional heterogeneity in B cells and plasma cells. Results: The TLS area and maturity in N0 PDAC were higher than those in N1/2 PDAC. The densities of memory B cells and germinal-center B cells in intratumoral mTLSs, as well as plasma cells in stromal imTLSs, were associated with the density of intratumoral plasma cells. Moreover, plasma cells in N0 PDAC exhibited stronger IgG antibody production than those in N1/2 PDAC. IgG⁺ tumor cells congregated within 40 μm of IgG⁺ plasma cells, forming an IgG⁺ plasma cell-related immune hotspot in N0 PDAC, which was not observed in N1/2 PDAC. The distance between IgG⁺ plasma cells and the nearest IgG⁺ tumor cells was a new prognosis biomarker. Conclusions: The TLS formation and development in N0 PDAC were better than those in N1/2 PDAC, and there is an IgG⁺ plasma cell-related immune hotspot in N0 PDAC. The TLS area and maturity and the distance between IgG⁺ plasma cells and the nearest IgG⁺ tumor cells could be PDAC prognostic biomarkers.