目的 对靶向唾液酸结合免疫球蛋白样凝集素-15（sialic acid-binding immunoglobulin-like lectin 15, Siglec-15）的全人源单克隆抗体23F4进行关键结合位点鉴定和生物学功能的初步评价。方法 对Siglec-15进行丙氨酸扫描突变，鉴定23F4的关键结合位点，再通过ELISA和流式细胞术对23F4的体外生物学功能进行探究，最后构建2种小鼠肿瘤模型以评价23F4的体内抗肿瘤功能。结果 鉴定得到23F4的关键结合位点（R71/H72残基）。在体外检测中23F4具有较高的结合活性，半数效应浓度为68.42 ng/mL，在中、低浓度下与Siglec-15阳性细胞的结合活性优于对照抗体，并且23F4能够阻断Siglec-15与受体的结合，解除T细胞的增殖抑制，在2种小鼠肿瘤模型中均具有抑制肿瘤生长的功能。结论 靶向Siglec-15的单克隆抗体23F4具有新型结合位点，能够解除Siglec-15介导的免疫抑制。

Objective To identify the key binding sites and preliminarily evaluate the biological functions of fully humanized monoclonal antibody (mAb) 23F4 targeting sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15).Methods Alanine scanning mutagenesis was performed on Siglec-15 to identify key binding sites of 23F4. In vitro biological activity was assessed via ELISA and flow cytometry. In vivo antitumor efficacy was evaluated using 2 murine tumor models.Results The critical binding sites of 23F4 were identified as residue R71/H72. In vitro, 23F4 exhibited superior binding activity with median effective concentration of 68.42 ng/mL, and outperformed control antibodies in binding Siglec-15-positive cells particularly at medium-to-low concentrations. 23F4 blocked Siglec-15-receptor interaction, reversed T-cell proliferation suppression, and suppressed tumor growth in both murine tumor models.Conclusion As a Siglec-15-targeting mAb with novel binding sites, 23F4 effectively alleviates Siglec-15-mediated immunosuppression.