Macrophages are the key regulator of T-cell responses depending on their activation state. C-C motif chemokine receptor-like 2 (CCRL2), a nonsignaling atypical receptor originally cloned from LPS-activated macrophages, has recently been shown to regulate immune responses under several inflammatory conditions. However, whether CCRL2 influences macrophage function and regulates tumor immunity remains unknown. Here, we found that tumoral CCRL2 expression is a predictive indicator of robust antitumor T-cell responses in human cancers. CCRL2 is selectively expressed in tumor-associated macrophages (TAM) with immunostimulatory phenotype in humans and mice. Conditioned media from tumor cells could induce CCRL2 expression in macrophages primarily via TLR4, which is negated by immunosuppressive factors. Ccrl2^−/− mice exhibit accelerated melanoma growth and impaired antitumor immunity characterized by significant reductions in immunostimulatory macrophages and T-cell responses in tumor. Depletion of CD8⁺ T cells or macrophages eliminates the difference in tumor growth between WT and Ccrl2^−/− mice. Moreover, CCRL2 deficiency impairs immunogenic activation of macrophages, resulting in attenuated antitumor T-cell responses and aggravated tumor growth in a coinjection tumor model. Mechanically, CCRL2 interacts with TLR4 on the cell surface to retain membrane TLR4 expression and further enhance its downstream Myd88-NF-κB inflammatory signaling in macrophages. Similarly, Tlr4^−/− mice exhibit reduced CCRL2 expression in TAM and accelerated melanoma growth. Collectively, our study reveals a functional role of CCRL2 in activating immunostimulatory macrophages, thereby potentiating antitumor T-cell response and tumor rejection, and suggests CCLR2 as a potential biomarker candidate and therapeutic target for cancer immunotherapy.

巨噬细胞是 T 细胞反应的关键调节器，取决于它们的激活状态。CC 基序趋化因子受体样 2 (CCRL2) 是一种最初从 LPS 激活的巨噬细胞克隆的非信号非典型受体，最近已被证明可以在几种炎症条件下调节免疫反应。然而，CCRL2 是否影响巨噬细胞功能和调节肿瘤免疫仍然未知。在这里，我们发现肿瘤 CCRL2 表达是人类癌症中强大的抗肿瘤 T 细胞反应的预测指标。CCRL2 在人类和小鼠的具有免疫刺激表型的肿瘤相关巨噬细胞 (TAM) 中选择性表达。来自肿瘤细胞的条件培养基主要通过 TLR4 诱导巨噬细胞中 CCRL2 的表达，而 TLR4 会被免疫抑制因子所抵消。Ccrl2 ^-/-小鼠表现出加速的黑色素瘤生长和受损的抗肿瘤免疫力，其特征是肿瘤中免疫刺激性巨噬细胞和 T 细胞反应显着减少。CD8 ⁺ T 细胞或巨噬细胞的消耗消除了 WT 和Ccrl2 ^-/-小鼠之间肿瘤生长的差异。此外，CCRL2 缺陷会损害巨噬细胞的免疫原性激活，导致抗肿瘤 T 细胞反应减弱并加剧共注射肿瘤模型中的肿瘤生长。在机械上，CCRL2 与细胞表面上的 TLR4 相互作用以保留膜 TLR4 表达并进一步增强其在巨噬细胞中的下游 Myd88-NF-κB 炎症信号传导。类似地，Tlr4 ^-/-小鼠在 TAM 中表现出降低的 CCRL2 表达并加速黑色素瘤的生长。总的来说，我们的研究揭示了 CCRL2 在激活免疫刺激性巨噬细胞中的功能作用，从而增强了抗肿瘤 T 细胞反应和肿瘤排斥反应，并建议 CCLR2 作为癌症免疫治疗的潜在生物标志物候选者和治疗靶点。