Tumor Microenvironment–Derived R-spondins Enhance Antitumor Immunity to Suppress Tumor Growth and Sensitize for Immune Checkpoint Blockade Therapy

Abstract

Natural killer (NK) cells and T cells are key effectors of antitumor immune responses and major targets of checkpoint inhibitors. In multiple cancer types, we find that the expression of Wnt signaling potentiator R-spondin genes (e.g., RSPO3) is associated with favorable prognosis and positively correlates with gene signatures of both NK cells and T cells. Although endothelial cells and cancer-associated fibroblasts comprise the R-spondin 3–producing cells, NK cells and T cells correspondingly express the R-spondin 3 receptor LGR6 within the tumor microenvironment (TME). Exogenous expression or intratumor injection of R-spondin 3 in tumors enhanced the infiltration and function of cytotoxic effector cells, which led to tumor regression. NK cells and CD8+ T cells independently and cooperatively contributed to R-spondin 3–induced control of distinct tumor types. The effect of R-spondin 3 was mediated in part through upregulation of MYC and ribosomal biogenesis. Importantly, R-spondin 3 expression enhanced tumor sensitivity to anti–PD-1 therapy, thereby highlighting new therapeutic avenues. Significance: Our study identifies novel targets in enhancing antitumor immunity and sensitizing immune checkpoint inhibition, which provides a rationale for developing new immunotherapies against cancers. It also offers mechanistic insights on Wnt signaling–mediated modulation of anticancer immunity in the TME and implications for a putative R-spondin–LGR6 axis in regulating NK-cell biology. This article is highlighted in the In This Issue feature, p. 2945

R-spondin family biology and emerging linkages to cancer

“…found that the expression of the Wnt signaling booster gene RSPO3 was linked to a better prognosis. Exogenous expression of RSPO3 in tumors can increase the cytotoxic effector cells infiltration and function, resulting in tumor regression [ 9 ].…”

“…Bioinformatic analyses such as gene enrichment found that RSPOs are widely involved in immune regulation. For example, the latest study reported that RSPO increased tumor sensitivity to anti-PD-1 therapy, highlighting an unprecedented treatment approach [ 9 , 10 ]. Immune checkpoint blockade has been widely used in the clinical treatment of tumors, but the lack of tumor antigens and the failure to effectively initiate adaptive immunity led to poor efficacy of immunotherapy.…”

Cancer stem cell‐immune cell collusion in immunotherapy

“…As a crucial immune cells, natural killer (NK) cells are an important immune factor in the body's antitumor and anti‐infection processes. Increased infiltration of NK cells and cytotoxic cells leads to enhanced immune system function, increased efficacy of anti‐PD‐1/PD‐L1 therapy and improved prognosis 68 . Due to the reduced expression of MHC I molecules on the surface of CSCs and the dysregulation of excitation and inhibition signals on the surface of NK cells, CSCs can be specifically targeted to enable NK cells to exert killing effects 69 .…”

“…The expression of the Wnt signaling protein BCL9L in soft tumors correlates positively with worsening clinicopathological features in advanced stages, which may be related to Wnt signaling promotion of epithelial cell proliferation and EMT 78 . However, it has been found that increased expression of R‐spondin 3 in the Wnt pathway in NK cells and CD8 + T cells could exert antitumor effects by activating the immune system with enhanced efficacy of ICB 68 . Therefore, the role of Wnt signaling expression and its sites in tumor therapy remain to be further clarified (Figure 2).…”

“…Increased infiltration of NK cells and cytotoxic cells leads to enhanced immune system function, increased efficacy of anti-PD-1/PD-L1 therapy and improved prognosis. 68 Due to the reduced expression of MHC I molecules on the surface of CSCs and the dysregulation of excitation and inhibition signals on the surface of NK cells, CSCs can be specifically targeted to enable NK cells to exert killing effects. 69 Major histocompatibility complex class I-related molecule A (MICA) is a ligand for NKG2D, which is not found in normal tissues and mainly expressed on the surface of some tumor cells.…”