抗程序性死亡受体-1纳米抗体的制备及鉴定

Preparation and identification of the nano antibodies of anti-programmed death receptor-1

目的 制备能与程序性死亡受体-1（PD-1）抗原高亲和力结合的骆驼源纳米抗体,为后续开展其功能性研究提供实验基础.方法 采用真核表达的PD-1-Fc重组蛋白对新疆双峰驼进行6次免疫,采集其外周血并从中分离得到淋巴细胞,进行巢式PCR扩增获取骆驼重链抗体可变区（VHH）基因,并构建噬菌体展示文库.然后采用固相酶联免疫吸附测定（ELISA）法筛选噬菌体展示文库,包被质量浓度依次降低（5.00、2.50、1.00 μg/ml）的PD-1抗原于ELISA板中,对噬菌体展示文库进行3轮亲和淘选.接着采用可溶性单克隆ELISA法进一步筛选与PD-1结合的单个克隆.根据DNA测序结果挑选具有多次重复序列的3个VHH单克隆构建至pET22b载体,转化大肠杆菌BL21 （DE3）感受态细胞后采用异丙基-β-D-硫代半乳糖苷进行诱导表达.最后采用镍柱亲和层析纯化重组VHH抗体蛋白,蛋白质印迹法（Western Blot）和ELISA法检测其与PD-1抗原的结合活性和亲和力.结果 采用重组蛋白PD-1-Fc对双峰驼免疫6次后,激发了高滴度的特异抗体,免疫血清效价达到1∶32 000.从免疫后的骆驼淋巴细胞构建了库容大小为2.6× 108 cfu/ml的VHH噬菌体展示文库.经3轮亲和筛选后,采用可溶性单克隆ELISA法进一步筛选获得46个吸光度（A600）值在0.6以上的单个VHH克隆.其中VHH-B7、VHH-H5和VHH-H12三个克隆序列具有较高重复,表明获得了显著富集.Western Blot及ELISA法检测结果显示,纯化的B7、H5和H12纳米抗体均与PD-1抗原具有较好的结合活性,且具有较高的亲和力,亲和力常数分别为1.19×1011、1.63×1011、1.59×1011 L/mol.结论 通过对VHH噬菌体展示文库进行亲和筛选,获得了能与PD-1抗原高亲和力结合的抗PD-1骆驼源纳米抗体,为后续开展其功能性研究提供了实验基础.

Objective To prepare camelid-derived nano antibodies with high affinity binding to programmed death receptor-1 （PD-1） antigen,and to provide experimental basis for subsequent functional studies.Methods The PD-1-Fc recombinant protein expressed in eukaryotic expression was used to immunize Xinjiang Bactrian camel 6 times.The peripheral blood was collected and the lymphocytes were isolated.Nested PCR amplification was performed to obtain the genes in variable region of camelid heavy chain antibody （VHH）,and to construct a phage display library.The phage display library was screened by solid phase enzyme-linked immunosorbent assay （ELISA）.The PD-1 antigen,which was sequentially reduced in mass concentration （5.00、2.50、1.00 μg/ml）,was coated in an ELISA plate,and the phage display library was subjected to 3 rounds of affinity selection.Individual clones that bind to PD-1 were further screened by soluble monoclonal ELISA.According to the results of DNA sequencing,three VHH monoclonals with multiple repeats were selected and ligated into pET22b vector,and transformed into E.coli BL21 （DE3） competent cells,and then induced by isopropyl-β3-D-thiogalactoside.The recombinant VHH antibody protein was purified by nickel column affinity chromatography,and its binding activity and affinity to PD-1 antigen were detected by Western Blot and ELISA.Results After immunization of Bactrian camel 6 times with recombinant protein PD-1-Fc,high titer specific antibody was stimulated,and the immune serum titer reached 1∶32 000.A VHH phage display library with a reservoir size of 2.6×108 cfu/ml was constructed from the immunized camel lymphocytes.After 3 rounds of affinity selection,46 VHH monoclonals with absorbance （A600） values above 0.6 were obtained by soluble monoclonal ELISA.Among them,three clones of VHH-B7,VHH-H5 and VHH-H12 had higher repeats,indicating that significant enrichment was obtained.The results of Western Blot and ELISA showed that the purified B7,H5 and H12 nanobodies had good binding activity to PD-1 antigen and had high affinity.Their affinity constants were 1.19×1011 and 1.63×1011,1.59×1011 L/mol,respectively.Conclusion The anti-PD-1 camelid-derived nanobodies were obtained by affinity selection of VHH phage display library,which can bind to the PD-1 antigen with high affinity.This study can provide an experimental basis for subsequent functional studies.