Pancreatic ductal adenocarcinoma (PDA) resists immunotherapy of adoptive cell transfer (ACT) and immune checkpoint inhibitors. Understanding the mechanisms underlying this resistance will improve PDA immunotherapy. This study investigated therapeutic effects and underlying mechanisms of anticoagulants on immunotherapy in PDA.
The antitumor activity of immunotherapy was evaluated in mouse models of desert, excluded, and inflamed tumors. The underlying mechanisms were investigated by analyzing immune cell infiltration by immunofluorescence imaging and tumor microcirculation by interstitial fluid pressure and coagulation status measurement.
Combined use of heparin and ACT inhibited tumor growth and metastasis, whereas neither heparin nor ACT had any therapeutic effect. The combination of heparin and ACT significantly increased the intratumor infiltration of CD8+ T cells and M1 macrophages and reduced the infiltration of immunosuppressive M2 macrophages and FOXP3+/CD4+ regulatory T cells (Treg). Assessments of tumor microenvironment revealed that heparin promoted tumor vascular regression and normalized the remaining blood vessels, facilitating the extravasation and perivascular accumulation of activated CD8+ T cells in tumors. Mechanistically, tumor microvessel hemodynamic properties were significantly improved by heparin, which is consistent with its inhibitory effects on tumor angiogenesis. Similarly, the combination of heparin and anti-PD1 also produced a pronounced antitumor activity, whereas neither heparin nor anti-PD1 treatment had appreciable antitumor activity.
Combined treatment of heparin and ACT or anti-PD1 produced synergistic antitumor effects, which were at least in part through tumor vascular normalization, hence increased antitumor T-cell responses due to reduced Treg infiltration and increased M1 macrophage polarization. This synergistic combination therapy warrants clinical evaluation.