Calculation of monoclonal antibody affinity constants directly from antibody dilution curves

A method for estimating the affinity constants of monoclonal antibody directly from antibody dilution curves is described.     

一对高亲和力抗人肌钙蛋白Ⅰ单克隆抗体的制备及鉴定

目的 获取抗人肌钙蛋白Ⅰ（cTnI）的单克隆抗体（McAb）.方法 以人cTnI作为抗原,免疫Balb/c小鼠,通过杂交瘤技术制备了抗人cTnI高亲和力、高特异性单克隆抗体.随后采用间接ELISA法测定抗血清效价,用protein G亲和纯化法纯化抗体,抗原竞争ELISA法鉴定抗体亲和力,SDS-PAGE法鉴定纯度,Western blotting鉴定抗cTnI单克隆抗体的特异性,竞争ELISA法分析抗原结合位点.结果 筛选出9株稳定分泌抗cTnI的单抗杂交瘤细胞株,其中A3、A9两株免疫球蛋白亚类均为IgG2a,分泌的抗体纯度高,与CK-MB、cTnT无交叉反应,效价均为：1：1024000,亲和力分别为4.21×10^8mol/L、1.07×10^8mol/L,抗原结合位点不同.结论 成功制备出了一对高亲和力、高特异性抗人cTnI单克隆抗体.     

Theoretical analysis of the reaction of multivalent antigen with heterogeneous antibody: a model of soluble phase antibody assays

The theoretical characteristics of soluble phase antibody assays were analyzed using a computer model of antigen-antibody interaction which allowed antibody to be heterogeneous and antigen multivalent. Studies show that when antibody is heterogeneous with respect to affinity, the high affinity antibody will usually mask the low affinity antibody. If the reaction of multivalent antigen with multispecific antibody is studied in antigen excess, the reaction closely approximates a one to one binding reaction. Several characteristics of the soluble phase antibody assay are determined by the affinity-antigen product or the product of the antibody affinity constant multiplied by the molar antigen concentration. When the product is high, the sensitivity of the assay will vary with antigen concentration and titers will be independent of antibody affinity. If the affinity-antigen product is low, sensitivity is dependent upon antibody affinity and titers will reflect antibody affinity as well as antibody concentration.     

Theoretical Analysis of the Reaction of Moltivalent Antigen with Heterogeneous Antibody: A Model of Soluble Phase Antibody Assays

Abstract

The theoretical characteristics of soluble phase antibody assays were analyzed using a computer model of antigen-antibody interaction which allowed antibody to be heterogeneous and antigen multivalent. Studies show that when antibody is heterogeneous with respect to affinity, the high affinity antibody will usually mask the low affinity antibody. If the reaction of multivalent antigen with multispecific antibody is studied in antigen excess, the reaction closely approximates a one to one binding reaction. Several characteristics of the soluble phase antibody assay are determined by the affinity-antigen product or the product of the antibody affinity constant multiplied by the molar antigen concentration. When the product is high, the sensitivity of the assay will vary with antigen concentration and titers will be independent of antibody affinity. If the affinity-antigen product is low, sensitivity is dependent upon antibody affinity and titers will reflect antibody affinity as well as antibody concentration.     

Sweeping antibody as a novel therapeutic antibody modality capable of eliminating soluble antigens from circulation

Monoclonal antibodies have become a general modality in therapeutic development, and a variety of monoclonal antibodies targeting soluble antigens have been developed. However, even with infinite binding affinity to an antigen, a conventional antibody can bind to the antigen only once and results in an increase in total plasma antigen concentration in vivo. This antibody-mediated antigen accumulation generally occurs because the clearance from circulation of an antibody–antigen complex is much slower than that of a free antigen. This limitation has recently been overcome by sweeping antibodies, which are capable of actively eliminating soluble antigens from circulation. A sweeping antibody incorporates two antibody engineering technologies: one is variable region engineering to enable the antibody to bind to an antigen in plasma and dissociate from the antigen in endosome (after which the antigen undergoes lysosomal degradation), and the other is constant region engineering to increase the cellular uptake of the antibody–antigen complex into endosome. By enhancing the elimination of soluble antigens from circulation, sweeping antibodies can therapeutically target soluble antigens that conventional antibodies cannot. This review discusses the features, engineering technologies, advantages, and applications of sweeping antibodies that target soluble antigens.     

改良ELISA测定腹水中单克隆抗体的亲和常数

抗体亲和力对体内外免疫反应有重要影响,为阐明抗体亲和力在免疫学检测及疾病发生发展机理中的作用,需要建立简单准确的测定抗体亲和力的方法。本实验参照Friguet氏利用酶联免疫吸附试验(ELISA)测定抗体亲和力的基本原理,建立了改良测定法,能准确且方便地直接测得腹水中单克隆抗体的亲和力常数。     

基因工程双价抗体在肿瘤中的研究进展

基因工程抗体技术的发展加速了单链抗体的应用,但其稳定性差,亲和力低,功能单一,体内清除过快等特点影响了它的广泛应用。双价抗体作为一种新型小分子抗体,具有双价的结合位点,能够使抗原分子上的两个表位交联或使两个分子连接,可以模拟完整的单克隆抗体的抗原抗体反应,其构建方法有亮氨酸拉链法、利用部分抗体恒定区法、连接肽法、利用双聚化结构法、knobs into holes技术等,在乳腺癌、 直肠癌、淋巴瘤等的诊治方面均有很好的应用价值。     

Improving antibody affinity through in vitro mutagenesis in complementarity determining regions

High-affinity antibodies are widely used in diagnostics and for the treatment of human diseases. However, most antibodies are isolated from semi-synthetic libraries by phage display and do not possess in vivo affinity maturation, which is triggered by antigen immunization. It is therefore necessary to engineer the affinity of these antibodies by way of in vitro assaying. In this study, we optimized the affinity of two human monoclonal antibodies which were isolated by phage display in a previous related study. For the 42A1 antibody, which targets the liver cancer antigen glypican-3, the variant T57H in the second complementarity-determining region of the heavy chain (CDR-H2) exhibited a 2.6-fold improvement in affinity, as well as enhanced cell-binding activity. For the I4A3 antibody to severe acute respiratory syndrome coronavirus 2, beneficial single mutations in CDR-H2 and CDR-H3 were randomly combined to select the best synergistic mutations. Among these, the mutation S53P-S98T improved binding affinity (about 3.7 fold) and the neutralizing activity (about 12 fold) compared to the parent antibody. Taken together, single mutations of key residues in antibody CDRs were enough to increase binding affinity with improved antibody functions. The mutagenic combination of key residues in different CDRs creates additive enhancements. Therefore, this study provides a safe and effective in vitro strategy for optimizing antibody affinity.     

单克隆抗体相对亲和力和特异性的测定

在单克隆抗体的制备中,亲和力和特异性的测定是非常重要的。实验证明单抗的特异性不是绝对的,我们也发现在免疫酶组化染色过程中,当单抗浓度达到一定水平时会出现交叉反应,即抗3型(或7型)腺病毒单抗与7型(或3型)腺病毒出现反应。因此有必要测定单抗特异性,以便筛选高特异性的单抗。     

抗人红细胞膜抗原非凝集型单克隆抗体的研制及特性鉴定

目的:制备抗人红细胞膜抗原的非凝集型单克隆抗体(mAb)并鉴定其特性。方法:应用杂交瘤技术,以人O型红细胞膜抗原免疫BALB/c小鼠。取免疫小鼠的脾细胞与Sp2/0骨髓瘤细胞融合,用聚凝胺试管法筛选识别红细胞表面共同抗原的抗体,玻片凝集实验剔除凝集型抗体(完全抗体),再将分泌非凝集型mAb(不完全抗体)的杂交瘤细胞株用有限稀释法克隆化3次。对杂交瘤细胞的稳定性和mAb的特性进行鉴定。结果:获得1株可稳定分泌mAb的杂交瘤细胞2E8。mAb2E8为IgG1类,可特异性地识别红细胞膜上的H抗原,没有种属交叉血凝反应。杂交瘤细胞的培养上清与人的A、B、AB和O型红细胞均能产生强凝集,凝集效价为1∶1024,腹水mAb的凝集效价达到1∶64×106。mAb的亲和力用凝集试验检测,出现血凝的时间为7s,3min以内凝块>1mm。结论:成功地制备了针对红细胞膜H抗原的非凝集性mAb,此mAb的凝集效价、相对亲和力及特异性均较良好,为构建双特异性抗体奠定了基础。     

Determination by ellipsometry of the affinity of monoclonal antibodies

The reaction between monoclonal antibodies and surface-immobilised hapten was studied by ellipsometry, a method allowing absolute measurement of the surface concentration of proteins. Monoclonal antibodies against 2-phenyloxazolone were used and their affinity for the antigen in solution was determined by calculations of the equilibrium constant from data obtained by measuring fluorescence quenching of the hapten due to antibody binding. The binding rate of antibody to surface-immobilised hapten and the dissociation rate of the complex were measured by ellipsometry. The equilibrium constant of the heterogeneous antigen-antibody reaction was determined by a Scatchard plot. The affinity of the antibodies for the antigen was found to be higher in the heterogeneous than in the homogeneous reaction by a factor which varied between different monoclonal antibodies.     

抗人大肠癌单克隆抗体的制备及应用

目的制备和纯化抗人大肠癌单克隆抗体(ND-1),分析其在大肠癌诊断中的应用价值。方法常规免疫小鼠制备腹水,腹水经离心和过滤后,应用G蛋白亲和层析法进行纯化。采用SDS-PAGE、间接免疫荧光(IFA)、间接ELISA检测纯化后抗体的纯度、活性、效价和特异性。并用免疫组织化学SP法检测在大肠癌组织中的表达。结果经SDS-PAGE分离可见两条相对分子质量(Mr)分别为55 000和25 000明显的两条蛋白条带。间接ELISA检测抗体效价为1∶1 000 000,ND-1抗体对表达相应抗原的大肠癌细胞株具有特异结合活性。人大肠癌组织切片经ND-1抗体免疫组织化学染色阳性率为82.9%,其中高分化腺癌阳性率为100%。结论应用G蛋白亲和层析法可以很好分离纯化鼠腹水中的IgG1亚型的单克隆抗体,抗体的纯度高,特异性强,生物学活性好,可望成为有效的肿瘤诊断和治疗的手段。     

胃癌单抗MGd1的噬菌体呈现型ScFv的制备

目的 制备胃癌单抗MGd1的单链可变区片段（single chain variable fragment,ScFv),为胃癌体内诊疗研究提供候选靶向载体分子。方法 从MGd1杂交瘤分离mRNA,RT-PCR分别扩增抗体重、轻链可变区基因（VH和VLDNA）,二者经linkerDNA连接形成ScFvDNA,将ScFvDNA与载体pCANTAB5E的连接产物转化于大肠杆菌TG1,经M13KO7感染后,获得重组噬菌体抗体ScFv,以高表达MGd1结合抗原的细胞株KATOⅢ对重组噬菌体抗体ScFv进行峡谷轮筛选后;随机挑取克隆经ELISA筛选MGd1ScFv单克隆,并对其结合抗原的能力进行鉴定。结果 VH、VL和ScFvDNA分别约为340、320和750bp,经两轮亲和筛选后,在随机筛检的30个克隆中得到12个噬菌体呈现型MGd1ScFv单克隆,其中结合抗原能力强的克隆有5个。结论 用噬菌体呈现技术成功地获得了单抗MGd1的ScFv,为拓展该抗体的应用范围奠定了基础。     

A rapid one-step radiometric assay for hepatitis B surface antigen utilising monoclonal antibodies

A two-site antigen assay for HBsAg has been developed that employs 3 monoclonal antibodies. The antibodies were selected for their high affinity and their particular epitope specificity to establish an assay with a sensitivity for the antigen comparable with that of a conventional assay with heterologous antisera. In addition, by selecting a monoclonal antibody for use as a tracer which does not compete for antigenic binding sites with the solid-phase monoclonal antibodies, it has been possible to perform a two-site assay in a single 1 h incubation step, achieving the same degree of sensitivity. This principle of using monoclonal antibodies in a one-step assay therefore gives advantages of speed and simplicity over assays using heterologous antisera and would be applicable to a variety of antigen assays for which appropriate monoclonal antibodies are available.     

Cloning,expression and characterization of a single‐chain antibody specific for the herbicide atrazine

The antigen‐binding domain of an antibody specific for the herbicide atrazine was cloned from hybridoma 4063–21–1 and expressed as a single‐chain antibody (scAb) in the vector pPM1‐His. The observed heavy and light chain gene sequences were consistent with those in subgroup VH I (B) and VK TV, as defined by the Kabat database of sequences. Subsequent expression in Escherichia coli strain XL‐1 Blue produced up to 0.3 μg of functional single‐chain antibody, from periplasmic protein preparations, per millilitre of culture. The scAb was purified as a monomer by immobilized metal chelate affinity chromatography via a hexa‐histidine tail or as a dimer by antibody affinity chromatography. The functionality and specificity of the recombinant antibody was confirmed by binding to an atrazine‐bovine serum albumin conjugate and free atrazine and simazine in a competition ELISA. This is the first example of the production and purification of a recombinant antibody that retains antigen binding for a triazine herbicide.     

A simple method for ranking the affinities of monoclonal antibodies

Measurement of the binding of constant trace amounts of labelled antigen by increasing dilutions of culture supernatant allows the ranking of monoclonal antibodies in the order of their affinity for the antigen. The theoretical basis for this method is discussed and it is illustrated with data from a set of anti-alphafoetoprotein monoclonal antibodies. Hybridomas secreting antibodies of desired affinity for immunoassay, histochemistry or antigen purification can thus be selected at an early stage after fusion.     

Screening human antibody libraries against carcinoma cells by affinity purification and polymerase chain reaction

Bacterial scFv clones from a naïve antibody library have been isolated against cancer cell antigens with AffiSelect, a novel screening method that indirectly identifies candidate library members via an antigen reporter gene. The first step is the coating of carcinoma cell surface epitopes (antigen) with either mAbs, scFvs or phages (library members). Upon binding to a cell surface ligand, the library member generates a linking moiety. This facilitates magnetic affinity purification of the antibody–cancer cell complexes, detected by the polymerase chain reaction (PCR) using the β-actin gene of the cancer cell as the target. Combining these well-known methods resulted in a higher resolution than a comparable cell-based ELISA method of detection. We have isolated human scFv antibodies against surface antigens of a lung carcinoma cell line. These were identified from a polyclonal mixture of phage display-enriched library clones comparing PCR patterns of the carcinoma cell line with the two negative cell types, HUVEC and peripheral blood cells (PBLs). The positive clones were sequenced and verified by FACS.     

抗CEA嵌合小分子抗体的构建与表达

目的 构建表达抗CEA小分子抗体,以利于放射免疫诊断及导向治疗。方法 构建CEA单链抗体基因,克隆入载体pKpL-3a,在大肠杆蓖中包涵体表达,ELISA检测活性,将轻重链基因克隆入分泌型表达载体pSCMH,在大肠杆菌中表达。ELISA检测活性,钭CEA嵌合抗体的轻链和Fd基因克隆入杆状病毒表达载体pAcUW51中,在sf9细胞中分泌表达,ELISA检测活性及测定产量,竞争抑制ELISA测定其识别的抗原表位。结果 多种方法复性的包涵体及原核分泌表达的单链相同的表位。结论 该CEA抗体基因在大肠杆菌中不能表达出有功能的分子。而在昆虫细胞中表达了具自学成才性抗体分子,某些抗体基因只有在真核细胞中才能表达出有功能的抗体分子。     

The effect of epitope density and antibody affinity on the ELISA as analysed by monoclonal antibodies

The antibody titre and the optical density values in an ELISA are influenced by the epitope density of the antigen and the affinity of the antibody tested. This has major implications in the interpretation of ELISA results.