Targeting immune cell-specific sphingosine-1-phosphate receptor 4 to restore antitumor immunity resulting in improved therapy response

The inflammatory tumor microenvironment is a critical element of tumor development and progression, as well as a parameter predicting the response to cancer treatment. An increased abundance of suppressive immune cells such as tumor-associated macrophages (TAMs) and regulatory T-cells (Tregs) appears thereby as a limiting factor for a successful treatment due to the inhibition of tumoricidal lymphocytes such as cytotoxic CD8+ T-cells. The bioactive lipid sphingosine-1-phosphate (S1P), which signals mainly through its five G-protein-coupled receptors (S1PR1-5), emerges as an important regulator of carcinogenesis that promotes tumor growth, angiogenesis and metastasis, among others, by affecting tumor immunity. We investigated S1PR4, which is exclusively expressed by immune cells, as a potential regulator of antitumor immunity. Using a transgenic mouse model of spontaneous invasive ductal mammary carcinoma (PyMT mice) and the AOM/DSS model of colitis-associated cancer, we show that S1PR4 deficiency (S1PR4-/-) leads to a significant decrease in lung metastasis and a delay of tumor growth in case of the PyMT breast cancer model and reduced colon tumor incidence and size in S1PR4-/- mice subjected to the AOM/DSS model. S1PR4-/- PyMT tumors contained macrophages with an altered activation profile, characterized by reduced IL-10, IL-1β and IL-6 production. Likely as a consequence, S1PR4-/- mice showed a less immunosuppressive lymphocyte infiltrate composed of reduced Tregs and Th17 cells, but increased cytotoxic CD8+ T-cell numbers. Interestingly, AOM/DSS-treated colons of S1PR4-/- mice also displayed a marked increase in CD8+ intestinal epithelial lymphocytes, underlining the negative impact of S1PR4 signaling on CD8+ T-cell abundance during tumor development. Next, we asked whether increased CD8+ T-cell numbers in S1PR4-/- tumors would increase the efficacy of chemotherapy or immunotherapy. Indeed, S1PR4-/- PyMT mice exhibited a significantly improved response to treatment with doxorubicin (DXR), characterized by the absence of relapse, whereas WT PyMT tumors relapsed after DXR treatment. This enhanced tumor control was strictly CD8+ T-cell dependent, as shown by experiments utilizing CD8 antibody depletion in combination with DXR treatment. Finally, using a MC38 colon adenocarcinoma model, where MC38 cells were engrafted into the flanks of WT and S1PR4-/- mice, we demonstrate a synergistic effect of S1PR4 depletion and anti-PD-1 immunotherapy reflected by reduced tumor growth and an increased survival rate of tumor-bearing S1PR4-/- compared to WT mice. A similar effect of additional tumor growth reduction by combinatorial anti-PD-1 treatment was seen in S1PR4-/- PyMT mice compared to their WT counterpart, although less pronounced compared to the MC38 allograft model. Taken together, our data indicate that S1PR4 depletion restores antitumor immunity by, among other mechanisms, increasing CD8+ T-cell abundance, translating into enhanced response to chemotherapy and anti-PD-1 immunotherapy. Thus, we reveal the potential of S1PR4 as a target to improve cancer therapy. Citation Format: Catherine Olesch, Evelyn Sirait-Fischer, Bernhard Brune, Andreas Weigert. Targeting immune cell-specific sphingosine-1-phosphate receptor 4 to restore antitumor immunity resulting in improved therapy response [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A209.