目的　对抗肿瘤坏死因子受体超家族成员4（OX40）单克隆抗体Ab18进行结构优化和生物学活性初步鉴定。方法　采用ELISA检测Ab18与不同物种OX40的种属交叉结合活性。用流式细胞术（flow cytometry，FCM）检测Ab18与HEK293-hOX40细胞的结合活性。采用报告基因法检测Ab18的阻断活性和激动活性。采用点突变技术对Ab18抗体Fc段进行工程化改造，改变Fc段与Fc受体的亲和力。用ELISA和FCM检测其与人Fcγ受体ⅡB和人新生儿Fc受体的结合活性，用报告基因法检测改造后的Ab18及其突变体抗体的激动活性、抗体依赖性细胞介导的细胞毒作用（antibody-dependent cell-mediated cytotoxicity，ADCC）活性。结果　Ab18抗体具有与小鼠、大鼠和恒河猴的种属交叉结合活性，相比对照抗体GBR830和KHK4083，Ab18与HEK293-hOX40的结合活性和阻断活性更强，Ab18与HEK293-hOX40的结合活性半数效应浓度（median effect concentration，EC₅₀）值为366.9 ng/ml，阻断活性半数抑制浓度为657.3 ng/ml。此外，Ab18、GBR830和KHK4083均具有激动活性。Ab18的ADCC活性EC₅₀值为25.7 ng/ml，激动活性EC₅₀值为14.9 ng/ml。Ab18经Fc段改造后，激动活性降低、与人新生儿Fc受体的结合活性增强、ADCC活性保持，具有较好的生物学活性。结论　成功优化了Ab18，优化后的抗体具有更好的生物学活性。

Objective　To structurally optimize and preliminarily identify the biological activity of anti-tumor necrosis factor receptor superfamily member 4 (OX40) monoclonal antibody Ab18.Methods　The species cross-binding activity of Ab18 to OX40 of different species was measured by ELISA. The binding activity of Ab18 to HEK293-hOX40 cells was measured by flow cytometry (FCM). The blocking activity and agonistic activity of Ab18 were measured by reporter gene methods. The Fc fragment of Ab18 was engineered by point mutagenesis technology to change the affinity of the Fc fragment with Fc receptors. ELISA and FCM were used to evaluate the binding activity to human Fcγ receptor ⅡB and human neonatal Fc receptor, and the reporter gene method was used to measure the agonistic activity and antibody-dependent cell-mediated cytotoxicity (ADCC) activity of Ab18 and its mutants.Results　The Ab18 antibody had species cross-binding activity with mouse, rat and rhesus monkey OX40s, and stronger binding activity and stronger blocking activity with HEK293-hOX40 than the control antibodies GBR830 and KHK4083. The median effect concentration (EC₅₀) value of binding activity of Ab18 with HEK293-hOX40 was 366.9 ng/ml, and the half maximal inhibitory concentration value of blocking activity was 657.3 ng/ml. In addition, Ab18, GBR830 and KHK4083 showed agonistic activity. The ADCC activity EC₅₀ value of Ab18 was 25.7 ng/ml, and the agonistic activity EC₅₀ value was 14.9 ng/ml. The mutated Ab18 had lower agonistic activity, better binding activity with human neonatal Fc receptor, consistent ADCC activity, and good biological activity.Conclusion　The Ab18 antibody is successfully optimized, showing better biological activity.