目的：制备新型人源化抗CD20单克隆抗体并检测其与CD20抗原的亲和力和抗肿瘤活性。方法通过计算机模建技术，在蛋白质结构数据库中找到与利妥昔单抗（ rituximab）空间结构最相近的人IgG1为骨架，将利妥昔单抗的互补决定区（ complementarity determining region ，CDR）进行移植和改造，通过重叠PCR方法，扩增出目的基因片段。分别将轻链（L）、重链（H）基因片段克隆到载体pcDNA3．3、pOptiVEC质粒上。瞬时转染至293F细胞，收取细胞上清，用rProteinA亲和层析法纯化目的抗体，并用十二烷基硫酸钠（SDS）-聚丙烯酰胺凝胶电泳（PAGE）检验抗体的纯度和表达量，采用Fortebio技术检测抗体与抗原的结合能力，最后通过裸鼠移植瘤生长抑制实验检测抗体的抗肿瘤活性。结果构建了3种抗CD20人源化抗体。抗体在还原SDS-PAGE中表现为两条相对分子质量约为25×103和55×103的条带，与预计条带大小相符；Fortebio实验结果表明，3组抗体与抗原具有良好的亲和活性：利妥昔单抗、L4H7抗体、L5H5抗体和L5H7抗体的Kd值分别为6．48×10－9、1．91×10－9、7．35×10－10和1．91×10－9 mol／L。裸鼠移植瘤生长抑制实验表明，L5H7抗体的抗肿瘤活性优于利妥昔单抗。结论成功构建并表达了3种抗CD20人源化抗体，其中L5H7抗体具有良好的抗原结合能力和抗肿瘤活性。%Objective To construct humanized monoclonal antibodies against CD 20 and check their affinity to CD 20 antigen and their anti-tumor activity.Methods Based on the computer model , human IgG1 candidates closest to rituximab in crystal structure were selected in the Protein Data Bank ( PDB) .With the selected human IgG 1 candidates as the frame , we modified and transplanted the complementarity determining region ( CDR) of rituximab .First,the target gene fragments were obtained by overlapping PCR.Then, the sequences of the light chains(L) and the heavy chains(H) were inserted in-to the pcDNA3.3 and pOptiVEC vectors.Next, the constructed clones were transfected into 293F cells through transient transfection.After a large-scale cell culture, the mAb was purified by affinity chromatography rProtein A column.The puri-ty and expression level of the humanized antibodies was tested by sodium dodecyl sulfate ( SDS)-polyacrylamide gelelectro-phoresis(PAGE).The affinity of the humanized antibodies to CD20 was assessed with Fortebio assay.Finally, the anti-tumor activity of the constructed antibodies was detected by checking the tumor growth inhibition of the nude mice transplan-ted with tumor .Results Three humanized monoclonal antibodies against CD 20 were expressed and purified successfully . In reducing SDS-PAGE, the antibodies exhibited two bands of approximately 25 ×103 and 55 ×103 , respectively.The band size of the antibodies matched the expected value.Fortebio assay revealed that the humanized antibodies could bind to CD20 with high affinity (rituximab:6.48 ×10 -9mol/L, L4H7:1.91 ×10 -9mol/L, L5H5:7.35 ×10 -10mol/L,and L5H7:1.91 ×10 -9mol/L).The tumor growth inhibition experiment showed that the anti-tumor activity of L5H7 mAb was better than that of rituximab .Conclusion Three humanized monoclonal antibodies against CD 20 have been successfully construc-ted and expressed.L5H7 mAb possesses high affinity for CD20 and a good ability to kill tumor cells.
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