DLL1 orchestrates CD8+ T cells to induce long-term vascular normalization and tumor regression.

The immunosuppressive and hypoxic tumor microenvironment (TME) remains a major obstacle to impede cancer immunotherapy. Here, we showed that elevated levels of Delta-like 1 (DLL1) in the breast and lung TME induced long-term tumor vascular normalization to alleviate tumor hypoxia and promoted the accumulation of interferon γ (IFN-γ)-expressing CD8+ T cells and the polarization of M1-like macrophages. Moreover, increased DLL1 levels in the TME sensitized anti-cytotoxic T lymphocyte-associated protein 4 (anti-CTLA4) treatment in its resistant tumors, resulting in tumor regression and prolonged survival. Mechanically, in vivo depletion of CD8+ T cells or host IFN-γ deficiency reversed tumor growth inhibition and abrogated DLL1-induced tumor vascular normalization without affecting DLL1-mediated macrophage polarization. Together, these results demonstrate that elevated DLL1 levels in the TME promote durable tumor vascular normalization in a CD8+ T cell- and IFN-γ-dependent manner and potentiate anti-CTLA4 therapy. Our findings unveil DLL1 as a potential target to persistently normalize the TME to facilitate cancer immunotherapy.

Increased vessel perfusion predicts the efficacy of immune checkpoint blockade.

Immune checkpoint blockade (ICB) has demonstrated curative potential in several types of cancer, but only for a small number of patients. Thus, the identification of reliable and noninvasive biomarkers for predicting ICB responsiveness is an urgent unmet need. Here, we show that ICB increased tumor vessel perfusion in treatment-sensitive EO771 and MMTV-PyVT breast tumor as well as CT26 and MCA38 colon tumor models, but not in treatment-resistant MCaP0008 and 4T1 breast tumor models. In the sensitive tumor models, the ability of anti-cytotoxic T lymphocyte-associated protein 4 or anti-programmed cell death 1 therapy to increase vessel perfusion strongly correlated with its antitumor efficacy. Moreover, globally enhanced tumor vessel perfusion could be detected by Doppler ultrasonography before changes in tumor size, which predicted final therapeutic efficacy with more than 90% sensitivity and specificity. Mechanistically, CD8+ T cell depletion, IFN-γ neutralization, or implantation of tumors in IFN-γ receptor knockout mice abrogated the vessel perfusion enhancement and antitumor effects of ICB. These results demonstrated that ICB increased vessel perfusion by promoting CD8+ T cell accumulation and IFN-γ production, indicating that increased vessel perfusion reflects the successful activation of antitumor T cell immunity by ICB. Our findings suggest that vessel perfusion can be used as a novel noninvasive indicator for predicting ICB responsiveness.

Myeloid-derived suppressor cell and macrophage exert distinct angiogenic and immunosuppressive effects in breast cancer.

The immunosuppressive tumor microenvironment is a key obstacle to hinder a cancer immunotherapy. Myeloid-derived suppressor cells (MDSCs) have been considered as a major player in immunosuppression. In this study, we find that tumor-infiltrating MDSCs (tiMDSCs) are less immunosuppressive than tumor-associated macrophages (TAMs) in multiple murine orthotopic breast tumor models. Compared to TAMs, tiMDSCs produce higher levels of pro-inflammatory factors and lower levels of anti-inflammatory factors. Furthermore, tiMDSCs are preferentially located in hypoxic areas and are more pro-angiogenic than TAMs. Consistent with these functional disparities, a shift from tiMDSCs to TAMs is observed during the progression of breast cancer. Moreover, infiltration of tiMDSCs is also noted in distal colonization of breast cancer cells in the lung. Taken together, our findings indicate that tiMDSCs are more pro-angiogenic and promote tumor initiation, while TAMs are more immunosuppressive and facilitate tumor immune evasion. This study suggests that selectively targeting on TAMs could alleviate the immunosuppressive tumor microenvironment and potentiate cancer immunotherapy.