The　immunosuppressive　microenvironment　in　pancreatic　cancer,　characterized　by　low　tumor-specific　T　cells　and　excessive　fibrosis,　limits　the　effectiveness　of　immunotherapy.　Here,　three　datasets　and　multi-immunofluorescence　staining　of　tissue　microarrays　in　pancreatic　cancer　indicate　that　mesothelin　(MSLN)　expression　negatively　correlates　with　cytotoxic　T　cells　in　tumor.　Anti-MSLN　antibody　(alpha　MSLN)　treatment　of　pancreatic　cancer　in　vivo　can　significantly　increase　T　cell　infiltration.　Meanwhile,　the　combination　of　alpha　MSLN　and　neoantigen　peptide　vaccine　identified　from　pancreatic　cancer　cell　lines　is　demonstrated　to　be　more　effective　in　inducing　neoantigen-specific　T　cell　generation　and　infiltration　at　subcutaneous　and　orthotopic　pancreatic　cancer　models　for　enhancing　antitumor　efficacy.　Single-cell　transcriptome　analysis　shows　that　the　combined　treatment　significantly　reduces　the　proportion　of　fibroblasts,　improves　the　infiltration　of　IFN-gamma+CD4+　and　GZMK+CD8+　T　cells,　as　well　as　reduces　the　interaction　of　antigen　presentation-associated　ligands　and　receptors　between　antigen-presenting　Cancer-Associated　Fibroblasts　(apCAFs)　and　naive　CD4+　T　cells.　The　negative　correlations　between　apCAFs　and　CD8+　T　cells/IFN-gamma+CD4+　T　cells　are　further　confirmed　in　human　pancreatic　cancer　tissues.　Overall,　this　study　demonstrates　that　targeting　MSLN　can　improve　neoantigen　vaccine　induced　immune　efficacy　by　reducing　apCAFs　to　interrupt　the　conversion　of　naive　CD4+　T　cells　to　Tregs,　and　therefore　increase　the　infiltration　of　tumor-specific　T　cells.