IgG‐single chain Fv fusion protein therapeutic for alzheimer's disease: Expression in CHO cells and pharmacokinetics and brain delivery in the rhesus monkey

Monoclonal antibodies (MAb) directed against the Abeta amyloid peptide of Alzheimer's disease (AD) are potential new therapies for AD, since these antibodies disaggregate brain amyloid plaque. However, the MAb is not transported across the blood–brain barrier (BBB). To enable BBB transport, a single chain Fv (ScFv) antibody against the Abeta peptide of AD was re‐engineered as a fusion protein with the MAb against the human insulin receptor (HIR). The HIRMAb acts as a molecular Trojan horse to ferry the ScFv therapeutic antibody across the BBB. Chinese hamster ovary (CHO) cells were stably transfected with a tandem vector encoding the heavy and light chains of the HIRMAb–ScFv fusion protein. A high secreting line was isolated following methotrexate amplification and dilutional cloning. The HIRMAb–ScFv fusion protein in conditioned serum‐free medium was purified by protein A affinity chromatography. The fusion protein was stable as a liquid formulation, and retained high‐affinity binding of both the HIR and the Abeta amyloid peptide. The HIRMAb–ScFv fusion protein was radiolabeled with the ¹²⁵I‐Bolton–Hunter reagent, followed by measurement of the pharmacokinetics of plasma clearance and brain uptake in the adult Rhesus monkey. The HIRMAb–ScFv fusion protein was rapidly cleared from plasma and was transported across the primate BBB in vivo. In conclusion, the HIRMAb–ScFv fusion protein is a new class of antibody‐based therapeutic for AD that has been specifically engineered to cross the human BBB. Biotechnol. Bioeng. 2010; 105: 627–635. © 2009 Wiley Periodicals, Inc.     

Genetic engineering, expression, and activity of a fusion protein of a human neurotrophin and a molecular Trojan horse for delivery across the human blood-brain barrier

Neurotrophins, such as brain derived neurotrophic factor (BDNF), do not cross the blood-brain barrier (BBB). Certain monoclonal antibodies (MAb) to the human insulin receptor (HIR) do cross the BBB via receptor-mediated transport, and can act as a molecular Trojan horse to ferry across the BBB an attached drug. A genetically engineered fusion protein was produced whereby the amino terminus of human BDNF is fused to the carboxyl terminus of the heavy chain of a chimeric HIRMAb. The HIRMAb-BDNF fusion protein reacted equally with antibodies to human IgG and BDNF. The bi-functionality of the fusion protein was retained as the affinity of the fusion protein for the HIR was identical to that of the chimeric HIRMAb, and the affinity of the fusion protein for the trkB receptor was identical to that of BDNF. The fusion protein was equi-potent with BDNF in a neuroprotection assay in human neural cells. The pharmacokinetics (PK) of the fusion protein was examined in the adult Rhesus monkey. The mean residence time (MRT) of the fusion protein in blood was >100-fold longer than the MRT of BDNF. Therapeutic levels of BDNF were produced in primate brain following the intravenous administration of the fusion protein. A fusion protein tandem vector was engineered that allowed for isolation of a CHO cell line that produced the fusion protein at high levels in serum free medium. Neurotrophins, such as BDNF, can be re-formulated to enable these molecules to cross the human BBB, and such fusion proteins represent a new class of human neurotherapeutics.     

Genetic engineering of a lysosomal enzyme fusion protein for targeted delivery across the human blood-brain barrier

Mucopolysaccharidosis Type I, Hurler's Syndrome, is a lysosomal storage disorder that affects the brain. The missing enzyme, alpha-L-iduronidase (IDUA), does not cross the blood-brain barrier (BBB). To enable BBB transport of the enzyme, human IDUA was fused to the carboxyl terminus of the heavy chain of a chimeric monoclonal antibody (MAb) to the human insulin receptor (HIR). The HIRMAb crosses the BBB on the endogenous insulin receptor, and acts as a molecular Trojan horse to ferry into brain the IDUA. Transfection of COS cells resulted in high levels of IDUA enzyme activity both in the medium and in the intracellular space. The size of the fusion heavy chain, as measured with Western blotting and antibodies to either human IDUA or human IgG, was increased about 80 kDa, relative to the size of the heavy chain of the parent HIRMAb. The IDUA enzyme specific activity of the affinity purified HIRMAb-IDUA fusion protein was 363 +/- 37 U/microg protein, which is comparable to specific activity of recombinant IDUA. The accumulation of glycosoaminoglycans in Hurler fibroblasts was decreased 70% by treatment with the HIRMAb-IDUA fusion protein. Confocal microscopy showed targeting of the fusion protein to the lysosome. The HIRMAb-IDUA fusion protein bound with high affinity to the HIR, and was rapidly transported into the brain of the adult Rhesus monkey following intravenous administration. The HIRMAb-IDUA fusion protein is a new treatment for Hurler's syndrome, which has been specifically engineered to cross the human BBB.     

Pharmacokinetics and brain uptake in the rhesus monkey of a fusion protein of arylsulfatase a and a monoclonal antibody against the human insulin receptor

Metachromatic leukodystrophy (MLD) is a lysosomal storage disorder of the brain caused by mutations in the gene encoding the lysosomal sulfatase, arylsulfatase A (ASA). It is not possible to treat the brain in MLD with recombinant ASA, because the enzyme does not cross the blood‐brain barrier (BBB). In the present investigation, a BBB‐penetrating IgG‐ASA fusion protein is engineered and expressed, where the ASA monomer is fused to the carboxyl terminus of each heavy chain of an engineered monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb crosses the BBB via receptor‐mediated transport on the endogenous BBB insulin receptor, and acts as a molecular Trojan horse to ferry the ASA into brain from blood. The HIRMAb‐ASA is expressed in stably transfected Chinese hamster ovary cells grown in serum free medium, and purified by protein A affinity chromatography. The fusion protein retains high affinity binding to the HIR, EC50 = 0.34 ± 0.11 nM, and retains high ASA enzyme activity, 20 ± 1 units/mg. The HIRMAb‐ASA fusion protein is endocytosed and triaged to the lysosomal compartment in MLD fibroblasts. The fusion protein was radio‐labeled with the Bolton–Hunter reagent, and the [¹²⁵I]‐HIRMAb‐ASA rapidly penetrates the brain in the Rhesus monkey following intravenous administration. Film and emulsion autoradiography of primate brain shows global distribution of the fusion protein throughout the monkey brain. These studies describe a new biological entity that is designed to treat the brain of humans with MLD following non‐invasive, intravenous infusion of an IgG‐ASA fusion protein. Biotechnol. Bioeng. 2013; 110: 1456–1465. © 2012 Wiley Periodicals, Inc.     

Biologic TNFα-inhibitors that cross the human blood-brain barrier

Tumor necrosis factor (TNF)α inhibitors (TNFI) are a major class of biologic therapeutics, and include decoy receptor and monoclonal antibody (MAb) therapeutics that block TNFα action. TNFα is a pro-inflammatory cytokine in brain disease, such as stroke, brain or spinal cord injury, or Alzheimer disease. However, the biologic TNFIs cannot be developed for the brain, because these large molecules do not cross the blood-brain barrier (BBB). Brain penetrating forms of TNFα decoy receptors or anti-TNFα antibody therapeutics can be re-engineered as IgG fusion proteins with a BBB molecular Trojan horse, such as the mAb against the human insulin receptor (HIR). The HIRMAb undergoes receptor-mediated transport across the BBB via the endogenous insulin receptor, and carries into brain the fused biologic TNFI. A fusion protein of the HIRMAb and the type II TNF receptor (TNFR) extracellular domain, designated the HIRMAb-TNFR fusion protein, has been engineered and expressed in stably transfected Chinese hamster ovary (CHO) cells. The HIRMAb-TNFR fusion protein binds both the HIR and TNFα with low nM affinity. The HIRMAb cross reacts with the Rhesus monkey insulin receptor, and the HIRMAb-TNFR is rapidly, and selectively, taken up by primate brain at concentrations that inhibit TNFα. In addition, a fusion protein of the HIRMAb and a therapeutic single chain Fv (ScFv) antibody has been engineered and also expressed in stably transfected CHO cells. The BBB molecular Trojan horse platform technology allows for the engineering of brain-penetrating recombinant proteins as new biologic therapeutics for the human brain.     

Engineering and expression of a chimeric transferrin receptor monoclonal antibody for blood-brain barrier delivery in the mouse

Protein therapeutics may be delivered across the blood-brain barrier (BBB) by genetic fusion to a BBB molecular Trojan horse. The latter is an endogenous peptide or a peptidomimetic monoclonal antibody (MAb) against a BBB receptor, such as the insulin receptor or the transferrin receptor (TfR). Fusion proteins have been engineered with the MAb against the human insulin receptor (HIR). However, the HIRMAb is not active against the rodent insulin receptor, and cannot be used for drug delivery across the mouse BBB. The rat 8D3 MAb against the mouse TfR is active as a drug delivery system in the mouse, and the present studies describe the cloning and sequencing of the variable region of the heavy chain (VH) and light chain (VL) of the rat 8D3 TfRMAb. The VH and VL were fused to the constant region of mouse IgG1 heavy chain and mouse kappa light chain, respectively, to produce a new chimeric TfRMAb. The chimeric TfRMAb was expressed in COS cells following dual transfection with the heavy and light chain expression plasmids, and was purified by protein G affinity chromatography. The affinity of the chimeric TfRMAb for the murine TfR was equal to the 8D3 MAb using a radio-receptor assay and mouse fibroblasts. The chimeric TfRMAb was radio-labeled and injected into mice for a pharmacokinetics study of the clearance of the chimeric TfRMAb. The chimeric TfRMAb was rapidly taken up by mouse brain in vivo at a level comparable to the rat 8D3 MAb. In summary, these studies describe the genetic engineering, expression, and validation of a chimeric TfRMAb with high activity for the mouse TfR, which can be used in future engineering of therapeutic fusion proteins for BBB drug delivery in the mouse.     

Expression in CHO cells and pharmacokinetics and brain uptake in the Rhesus monkey of an IgG-iduronate-2-sulfatase fusion protein

Sulfatases are potential therapeutic biopharmaceuticals, as mutations in sulfatase genes leads to inherited disease. Mucopolysaccharidosis (MPS) Type II is caused by mutations in the lysosomal enzyme, iduronate-2-sulfatase (IDS). MPS-II affects the brain and enzyme replacement therapy is ineffective for the brain, because IDS does not cross the blood-brain barrier (BBB). To deliver IDS across the human BBB, the sulfatase has been re-engineered as an IgG-sulfatase fusion protein with a genetically engineered monoclonal antibody (MAb) against the human insulin receptor (HIR). The HIRMAb part of the HIRMAb-IDS fusion protein acts as a molecular Trojan horse to ferry the fused IDS across the BBB. Chinese hamster ovary (CHO) cells were stably transfected to produce the HIRMAb-IDS fusion protein. The fusion protein was triaged to the lysosomal compartment of MPS-II fibroblasts based on confocal microscopy, and 300 ng/mL medium concentrations normalized IDS enzyme activity in the cells. The HIRMAb-IDS fusion protein was tritiated and injected intravenously into the adult Rhesus monkey at a low dose of 0.1 mg/kg. The IDS enzyme activity in plasma was elevated 10-fold above the endogenous level, and therapeutic plasma concentrations were generated in vivo. The uptake of the HIRMAb-IDS fusion protein in the brain was sufficiently high to produce therapeutic concentrations of IDS in the brain following IV administration of the fusion protein.     

CHO cell expression,long‐term stability,and primate pharmacokinetics and brain uptake of an IgG–paroxonase‐1 fusion protein

Paraoxonase (PON)‐1 is the most potent human organophosphatase known, but recombinant forms of human PON1 have been difficult to produce owing to poor secretion by host cells. In the present investigation, human PON1 is re‐engineered as an IgG–PON1 fusion protein. The 355 amino acid human PON1 is fused to the carboxyl terminus of the heavy chain of a chimeric monoclonal antibody (MAb) against the human insulin receptor (HIR), and this fusion protein is designated HIRMAb–PON1. The HIRMAb part of the fusion protein enables brain penetration of the PON1, which was considered important, because organophosphate toxicity causes death via a central nervous system site of action. A high producing line of stably transfected Chinese hamster ovary (CHO) cells secreting the HIRMAb–PON1 fusion protein in the absence of serum or lipid acceptors was cloned. The bioreactor generated fusion protein was purified to homogeneity with low impurities by protein A affinity chromatography and anion exchange chromatography. The HIRMAb–PON1 fusion protein was stable as a sterile liquid formulation stored at 4°C for at least 1 year. The plasma pharmacokinetics (PK) of the HIRMAb–PON1 fusion protein was evaluated in Rhesus monkeys, which is the first PK evaluation of a recombinant PON1 protein. The fusion protein was rapidly removed from blood, primarily by the liver. The blood–brain barrier permeation of the HIRMAb–PON1 fusion protein was high and comparable to other HIRMAb fusion proteins. Re‐engineering human PON1 as the HIRMAb fusion protein allows for production of a stable, field‐deployable formulation of the enzyme that is brain‐penetrating. Biotechnol. Bioeng. 2011; 108:186–196. © 2010 Wiley Periodicals, Inc.     

Nucleotide sequence of a cDNA clone encoding a rabbit immunoglobulin-lambda light chain: the V lambda region differs markedly from that of other species

A cDNA clone (pDH7) has been isolated which encodes the entire leader peptide and variable (V) region and most of the constant (C) region of a rabbit lambda-light chain. Although similar to amino acid sequences derived from fragments of isolated lambda-chains from several Basilea rabbits, differences in the first framework region (FR1) suggest that at least two germ-line V lambda genes are expressed. There are major differences between rabbit V lambda sequences and light chains of other species: in particular, rabbit lambda-chains have an additional four amino acids in the vicinity of the FR2-CDR2 junction. The same region also has significant homology with the human D2 germ-line mini-gene sequence, especially with a 14-nucleotide sequence previously shown to be homologous to human and rabbit heavy chain CDR2 sequences. Similar homologies in other heavy and light chain sequences suggest that D-gene segments may be derived from VH genes, perhaps by transposition. The framework regions of the rabbit lambda-chain encoded by clone pDH7 show the greatest homologies with those of human kappa- and lambda-sequences (46 to 54% homology), with that of chicken sequence (55%), and least with murine V lambda sequences (40%).     

Genetic engineering, expression, and activity of a chimeric monoclonal antibody-avidin fusion protein for receptor-mediated delivery of biotinylated drugs in humans

The genetic engineering, expression, and validation of a fusion protein of avidin (AV) and a chimeric monoclonal antibody (mAb) to the human insulin receptor (HIR) is described. The 15 kDa avidin monomer was fused to the carboxyl terminus of the heavy chain of the HIRMAb. The fusion protein heavy chain reacted with antibodies specific for human IgG and avidin, and had the same affinity for binding to the HIR extracellular domain as the original chimeric HIRMAb. The fusion protein qualitatively bound biotinylated ligands, but was secreted fully saturated with biotin by COS cells, owing to the high level of biotin in tissue culture medium. Chinese hamster ovary (CHO) cells were permanently transfected with a tandem vector expressing the fusion protein genes, and high expressing cell lines were isolated by methotrexate amplification and dilutional cloning. The product expressed by CHO cells had high binding to the HIR, and migrated as a homogeneous species in size exclusion HPLC and native polyacrylamide gel electrophoresis. The CHO cells were adapted to a 4 week culture in biotin depleted medium, and the HIRMAb-AV fusion protein expressed under these conditions had 1 unoccupied biotin binding site per molecule, based on a [3H]-biotin ultrafiltration assay. The HIRMAb-AV increased biotin uptake by human cells >15-fold, and mediated the endocytosis of fluorescein-biotin, as demonstrated by confocal microscopy. In summary, the HIRMAb-AV fusion protein is a new drug targeting system for humans that can be adapted to monobiotinylated drugs or nucleic acids.     

Construction, expression and characterization of humanized antibodies directed against the human alpha/beta T cell receptor.

Completely humanized antibodies with specificity for the human alpha/beta TCR have been produced by genetic engineering. The L and H chain V region exons encoding the murine mAb BMA 031 CD regions and human EU framework regions were synthesized and replaced into previously isolated genomic fragments. These fragments were inserted into mammalian expression vectors containing the human kappa and gamma 1 C region exons. Two variants were constructed each containing selected BMA 031 amino acids within the human frameworks. The humanized genes were transfected into Sp2/0 hybridoma cells by electroporation and transfectomas secreting humanized antibody were isolated. Levels of antibody expression up to 7 pg/cell/24 h were obtained. The humanized antibody, BMA 031-EUCIV2, competed poorly with murine BMA 031 for binding to T cells. BMA 031-EUCIV3, however, bound specifically to T cells and competed effectively with both the murine BMA 031 antibody and a previously constructed chimeric BMA 031 antibody for binding to these cells. The relative affinity of BMA 031-EUCIV3 was about 2.5 times lower than BMA 031. The ability to promote antibody dependent cell-mediated cytolysis was significantly enhanced with the engineered antibodies as compared to murine BMA 031. Humanized BMA 031 is a clinically relevant, genetically engineered antibody with potential uses in transplantation, graft vs host disease, and autoimmunity.     

Characterization and humanization of a monoclonal antibody that neutralizes human leukocyte interferon: a candidate therapeutic for IDDM and SLE

We have developed a panel of murine monoclonal antibodies that recognize human interferon alpha. One of these mononclonal antibodies binds and neutralizes, with high affinity, all of seven tested recombinant human interferon alphas. This mononclonal antibody also neutralizes the interferon activity present in two independent pools of interferon alphas prepared following stimulation of human peripheral blood leukocytes. The complementary determining regions from this murine mononclonal antibody were transferred to a human IgG2 heavy chain and to a human kappa1 light chain. In addition, six (heavy chain) and two (light chain) amino acids were transferred from the framework regions. This generated a humanized mononclonal antibody that retained the specificity of the mouse parent. The humanized anti-interferon alpha antibody is a candidate therapeutic for those diseases, such as insulin-dependent diabetes, systemic lupus erythematosis, psoriasis and Crohn's disease, which are all characterized by pathological expression of interferon alpha.     

Design and synthesis of germline-based hemi-humanized single-chain Fv against the CD18 surface antigen

The 6.7 murine monoclonal antibody (mAb) recognizes the human CD18 antigen and is therefore of interest as an anti-inflammatory agent. The 6.7 heavy variable chain (VH) was humanized using the closest human germline sequence as the template on to which to graft the murine complementary determining regions (CDRs). Two versions were proposed, one in which the residue proline 45 of the murine form was maintained and another in which this framework residue was changed to the leucine found in the human sequence. These VH humanized versions were expressed in the yeast Pichia pastoris as hemi-humanized single-chain Fv (scFvs), with the VL from the murine antibody. The scFv from the murine antibody was also expressed. The binding activities of the murine and both hemi-humanized scFvs were determined by flow cytometry analysis. All the constructions were able to recognize human lymphocytes harboring CD18, indicating successful humanization with transfer of the original binding capability. Some differences between the two hemi-humanized versions were observed. The method used was simple and straightforward, with no need for refined structural analyses and could be used for the humanization of other antibodies.     

Predicting regional mutability in antibody V genes based solely on di- and trinucleotide sequence composition.

Somatic mutations are not distributed randomly throughout Ab V region genes. A sequence-specific target bias is revealed by a defined hierarchy of mutability among di- and trinucleotide sequences located within Ig intronic DNA. Here we report that the di- and trinucleotide mutability preference pattern is shared by mouse intronic JH and Jkappa clusters and by human VH genes, suggesting that a common mutation mechanism exists for all Ig V genes of both species. Using di- and trinucleotide target preferences, we performed a comprehensive analysis of human and murine germline V genes to predict regional mutabilities. Heavy chain genes of both species exhibit indistinguishable patterns in which complementarity-determining region 1 (CDR1), CDR2, and framework region 3 (FR3) are predicted to be more mutable than FR1 and FR2. This prediction is borne out by empirical mutation data from nonproductively rearranged human VH genes. Analysis of light chain genes in both species also revealed a common, but unexpected, pattern in which FR2 is predicted to be highly mutable. While our analyses of nonfunctional Ig genes accurately predicts regional mutation preferences in VH genes, observed relative mutability differences between regions are more extreme than expected. This cannot be readily accounted for by nascent mRNA secondary structure or by a supplemental gene conversion mechanism that might favor nucleotide replacements in CDR. Collectively, our data support the concept of a common mutation mechanism for heavy and light chain genes of mice and humans with regional bias that is qualitatively, but not quantitatively, accounted for by short nucleotide sequence composition.     

Guided selection of human antibody light chains against TAG-72 using a phage display chain shuffling approach

To enhance therapeutic potential of murine monoclonal antibody, humanization by CDR grafting is usually used to reduce immunogenic mouse residues. Most humanized antibodies still have mouse residues critical for antigen binding, but the mouse residues may evoke immune responses in humans. Previously, we constructed a new humanized version (AKA) of mouse CC49 antibody specific for tumor-associated glycoprotein, TAG-72. In this study, to select a completely human antibody light chain against TAG-72, guided selection strategy using phage display was used. The heavy chain variable region (VH) of AKA was used to guide the selection of a human TAG-72-specific light chain variable region (VL) from a human VL repertoire constructed from human PBL. Most of the selected VLs were identified to be originated from the members of the human germline VK1 family, whereas the VL of AKA is more homologous to the VK4 family. Competition binding assay of the selected Fabs with mouse CC49 suggested that the epitopes of the Fabs overlap with that of CC49. In addition, they showed better antigen-binding affinity compared to parental AKA. The selected human VLs may be used to guide the selection of human VHs to get completely human anti-TAG72 antibody.     

An immunoglobulin heavy chain variable region gene is generated from three segments of DNA: VH, D and JH

We have determined the sequences of separate germline genetic elements which encode two parts of a mouse immunglobulin heavy chain variable region. These elements, termed gene segments, are heavy chain counterparts of the variable (V) and joining (J) gene segments of immunoglobulin light chains. The VH gene segment encodes amino acids 1-101 and the JH gene segment encodes amino acids 107-123 of the S107 phosphorylcholine-binding VH region. This JH gene segment and two other JH gene segments are located 5' to the mu constant region gene (Cmu) in germline DNA. We have also determined the sequence of a rearranged VH gene encoding a complete VH region, M603, which is closely related to S107. In addition, we have partially determined the VH coding sequences of the S107 and M167 heavy chain mRNAs. By comparing these sequences to the germline gene segments, we conclude that the germline VH and JH gene segments do not contain at least 13 nucleotides which are present in the rearranged VH genes. In S107, these nucleotides encode amino acids 102-106, which form part of the third hypervariable region and consequently influence the antigen-binding specificity of the immunoglobulin molecule. This portion of the variable region may be encoded by a separate germline gene segment which can be joined to the VH and JH gene segments. We term this postulated genetic element the D gene segment, referring to its role in the generation of heavy chain diversity. Essentially the same noncoding sequences are found 3' to the VH gene segment and as inverse complements 5' to two JH gene segments. These are the same conserved nucleotides previously found adjacent to light chain V and J gene segments. Each conserved sequence consists of blocks of seven and ten conserved nucleotides which are separated by a spacer of either 11 or 22 nonconserved nucleotides. The highly conserved spacing, corresponding to one or two turns of the DNA helix, maintains precise spatial orientations between blocks of conserved nucleotides. Gene segments which can join to one another (VK and JK, for example) always have spacers of different lengths. Based on these observations, we propose a model for variable region gene rearrangement mediated by proteins which recognize the same conserved sequences adjacent to both light and heavy chain immunoglobulin gene segments.     

Complete heavy and light chain variable region sequence of anti-arsonate monoclonal antibodies from BALB/c and A/J mice sharing the 36-60 idiotype are highly homologous

Structural and serologic studies on murine A/J monoclonal anti-arsonate antibodies resulted in the identification of a second idiotype family (Id36-60) in addition to the predominant idiotype family (IdCR). Id36-60, unlike IdCR, is a dominant idiotype in the BALB/c strain but is a "minor" idiotype in the A/J strain. The complete heavy and light chain variable region (VH and VL) amino acid sequences of a representative Id36-60 hybridoma protein from both the A/J and BALB/c strains have been determined. There are only four amino acid sequence differences between the VH of antibody 36-60 (A/J) and antibody 1210.7 (BALB/c). Two of these differences arise from single nucleotide changes in which the A/J and BALB/c Id36-60 VH germline gene sequences differ. The two other differences are the result of somatic mutation in hybridoma protein 36-60. In addition, Id36-60 heavy chains employ the same D and JH3 segments in both strains. The entire Vk2 VL of 36-60 and 1210.7 differ by only two amino acids, suggesting that like the heavy chains, they are derived from highly homologous VL genes. The same Jk segment is used in both antibodies. A comparison of the amino acid sequence data from Id36-60-bearing hybridomas suggests that a heavy chain amino acid difference accounts for the diminished arsonate binding by the 1210.7 hybridoma protein. Because the 1210.7 heavy chain is the unmutated product of the BALB/c VH gene, somatic mutation in VH may be required to enhance Ars affinity in this system.     

抗人前列腺干细胞抗原单克隆抗体可变区基因的5＇RACE扩增及序列分析

目的：克隆并分析抗人前列腺干细胞抗原单克隆抗体轻链和重链的可变区基因。方法：从分泌抗人前列腺干细胞抗原单克隆抗体的杂交瘤细胞株中提取总RNA,根据小鼠IgG恒定区序列设计特异性引物,通过5’RACE法扩增其轻链和重链的可变区基因,克隆入pMD18-T载体,测序并分析其可变区序列。结果：3株抗人前列腺干细胞抗原单克隆抗体的重链可变区基因序列全长均为423bp,编码141个氨基酸残基;轻链可变区基因序列全长均为393bp,编码131个氨基酸残基;在GenBank中对氨基酸序列进行比对分析,均符合小鼠IgG可变区基因的特征;根据Kabat法则对3株抗体轻链和重链可变区氨基酸序列进行分析,确定了3个抗原互补决定区、4个框架区和前导肽。结论：通过5＇RACE法得到了3株抗人前列腺干细胞抗原单克隆抗体轻链与重链可变区基因,为进一步研究抗体三维结构、人源化改造奠定了基础。     

Molecular Basis for the Interaction of the Hepatitis B Virus Core Antigen with the Surface Immunoglobulin Receptor on Naive B Cells

The nucleocapsid of the hepatitis B virus (HBV) is composed of 180 to 240 copies of the HBV core (HBc) protein. HBc antigen (HBcAg) capsids are extremely immunogenic and can activate naive B cells by cross-linking their surface receptors. The molecular basis for the interaction between HBcAg and naive B cells is not known. The functionality of this activation was evidenced in that low concentrations of HBcAg, but not the nonparticulate homologue HBV envelope antigen (HBeAg), could prime naive B cells to produce anti-HBc in vitro with splenocytes from HBcAg- and HBeAg-specific T-cell receptor transgenic mice. The frequency of these HBcAg-binding B cells was estimated by both hybridoma techniques and flow cytometry (B7-2 induction and direct HBcAg binding) to be approximately 4 to 8% of the B cells in a naive spleen. Cloning and sequence analysis of the immunoglobulin heavy- and light-chain variable (VH and VL) domains of seven primary HBcAg-binding hybridomas revealed that six (86%) were related to the murine and human VH1 germ line gene families and one was related to the murine VH3 family. By using synthetic peptides spanning three VH1 sequences, one VH3 sequence, and one VLkappaV sequence, a linear motif in the framework region 1 (FR1)complementarity-determining region 1 (CDR1) junction of the VH1 sequence was identified that bound HBcAg. Interestingly, the HBcAg-binding motif was present in the VL domain of the HBcAg-binding VH3-encoded antibody. Finally, two monoclonal antibodies containing linear HBcAg-binding motifs blocked HBcAg presentation by purified naive B cells to purified HBcAg-primed CD4(+) T cells. Thus, the ability of HBcAg to bind and activate a high frequency of naive B cells seems to be mediated through a linear motif present in the FR1-CDR1 junction of the heavy or light chain of the B-cell surface receptor.     

Molecular characterization of a human anti-Rh(D) antibody with a DH segment encoded by a germ-line sequence.

The lambda-light-chain and lambda-heavy-chain variable-region genes of an anti-Rh(D) (Rh, Rhesus; D, heavy-chain diversity region) human monoclonal antibody secreted by lymphocytes transformed by the Epstein-Barr virus have been cloned and sequenced. Sequence comparison of the anti-Rh(D)mAb lambda-chain variable region with those of the other available human lambda chains revealed that it belonged to the human V lambda I (V lambda, variable region of lambda chain) subgroup. The greatest sequence similarity (80%) was observed with that of another anti-Rh antibody lambda-chain directed against the Rh(c) antigen. For the VH (VH, variable region of heavy chain) sequence, the highest similarity (86%) was observed with the germline VHG3 gene which belongs to the VHI subgroup. The expressed DH sequence of the anti-Rh(D) antibody is also of germline origin and complementarity-determining region 3 is thus produced by VH-DH and DH-JH (J, joining region) joining without recombination of multiple DH gene segments.