Depletion of bovine CD8+ T cells with chCC63, a chimaeric mouse-bovine antibody.

In order to investigate the role of T cells in immune responses to infectious pathogens, depletion of individual T cell subsets using monoclonal antibodies (mAbs) is commonly undertaken. Since most mAbs are of murine origin, such depletion studies in cattle are restricted by the bovine anti-mouse antibody (BAMA) response to the mouse mAbs used for the depletions. In this study, we describe the use of antibody engineering to overcome the BAMA response. The variable region cDNA from CC63, a monoclonal mouse anti-bovine CD8 antibody, has been expressed in conjunction with bovine constant region genes to produce a mouse-bovine chimaeric antibody (chCC63). Characterisation of chCC63 showed that the antibody contained a bovine constant region and specifically bound bovine CD8+ T cells. Furthermore, chCC63 blocked the binding of the original mouse antibody, CC63, and mediated complement-dependent lysis of bovine CD8+ cells in vitro. In vivo, chCC63 depleted calves of CD8+ T cells as effectively as CC63 and provoked a BAMA response that was about one-tenth of that seen with the mouse antibody.

A fully human antibody neutralising biologically active human TGFbeta2 for use in therapy.

Phage display provides a methodology for obtaining fully human antibodies directed against human transforming growth factor-beta (TGFbeta) suitable for the treatment of fibrotic disorders. The strategy employed was to isolate a human single chain Fv (scFv) fragment that neutralises human TGFbeta2 from a phage display repertoire, convert it into a human IgG4 and then determine its TGFbeta binding and neutralisation properties and its physical characteristics. Several scFv fragments binding to TGFbeta2 were isolated by panning of an antibody phage display repertoire, and subsequent chain shuffling of the selected V(H) domains with a library of V(L) domains. The three most potent neutralising antibodies were chosen for conversion to IgG4 format. The IgG4 antibodies were ranked for their ability to neutralise TGFbeta2 and the most potent, 6B1 IgG4, was chosen for further characterisation. 6B1 IgG4 has a high affinity for TGFbeta2 with a dissociation constant of 0.89 nM as determined using the BIAcore biosensor and only 9% cross-reactivity with TGFbeta3 (dissociation constant, 10 nM). There was no detectable binding to TGFbeta1. 6B1 IgG4 strongly neutralises (IC50 = 2 nM) the anti-proliferative effect of TGFbeta2 in bioassays using TF1 human erythroleukaemia cells. Similarly, there was strong inhibition of binding of TGFbeta2 to cell surface receptors in a radioreceptor assay using A549 cells. 6B1 IgG4 shows no detectable cross-reactivity with related or unrelated antigens by immunocytochemistry or ELISA. The 6B1 V(L) domain has entirely germline framework regions and the V(H) domain has only three non-germline framework amino acids. This, together with its fully human nature, should minimise any potential immunogenicity of 6B1 IgG4 when used in therapy of fibrotic diseases mediated by TGFbeta2.

Human antibodies by design.

Monoclonal antibodies (Mabs) have long been considered a good class of natural drugs, both because they mimic their natural role in the body and because they have no inherent toxicity. Although rodent Mabs are readily generated, their widespread use as therapeutic agents has been hampered because they are recognized as foreign by the patient. Evidently, clinical Mabs should be as human as possible and results with some of the more recently developed chimerized and humanized Mabs are testimony to this. Mabs that are entirely human are now being produced from phage display and transgenic mice. The first fully human Mabs generated by phage display have already entered clinical trials, and together with recent advances in these technologies, may finally realize the full potential of antibodies.

Construction and characterization of a humanized anti-gamma-Ig receptor type I (Fc gamma RI) monoclonal antibody.

The murine mAb 22 (M22) binds to the human high affinity receptor for the Fc portion of IgG (Fc gamma RI). This mAb recognizes an epitope on Fc gamma RI that is distinct from the natural ligand (Fc) binding site, and, therefore, can bind to Fc gamma RI in the presence of saturating levels of IgG found in vivo. Fc gamma RI is expressed only on cytotoxic effector cells and it acts as an efficient mediator (trigger molecule) of effector functions. Directing tumor cells or other pathogens to Fc gamma RI utilizing M22 conjugated to an anti-tumor- or to an anti-pathogen-specific mAb may represent an effective method to enhance their removal and destruction under physiologic conditions. Humanization of M22 may improve the therapeutic potential of the mAb since murine mAbs normally elicit a human anti-mouse Ab response. In this report we describe the humanization of M22 by CDR-grafting onto human V region frameworks based on KOL VH and REI V kappa attached to human IgG1 and kappa constant domains. This humanized mAb, H22, displays equivalent binding specificity and affinity as its murine counterpart. In addition, H22 is able to trigger superoxide release from Fc gamma RI-bearing cells, a finding that demonstrates that H22 triggers Fc gamma RI functions. The successful humanization of mAb 22 is an important step in the development of Fc gamma RI-directed immunotherapy.

Identification of framework residues required to restore antigen binding during reshaping of a monoclonal antibody against the glycoprotein gB of human cytomegalovirus.

Introduction of the complementary determining regions (CDRs) from a murine antibody to a human monoclonal antibody is an important technique (humanization) in the development of human immunotherapeutics. We have humanized murine monoclonal antibody HCMV37 which binds to the gB envelope glycoprotein of human cytomegalovirus. Simple transfer of the murine HCMV37 CDRs into heavy- and light-chain framework regions (FRs) based on human NEW and REI, respectively, together with human IgGI and K constant regions, abolished antigen binding because of a suboptimal heavy chain. Replacement of human VH amino acids Leu70, Val71 and Arg94 with murine residues Thr70, Arg71 and Asn94 was insufficient to improve affinity. However, significant restoration of binding was obtained by substitution of human VH amino acids Thr28, Phe29, Ser30 with murine residues Ser28, Ile29, Thr30, in conjunction with the position 94 change. Residue 71, often regarded as critical for antigen binding, was not a major factor.

Efficient generation of a reshaped human mAb specific for the alpha toxin of Clostridium perfringens.

We have used the technique of antibody reshaping to produce a humanized antibody specific for the alpha toxin of Clostridium perfringens. The starting antibody was from a mouse hybridoma from which variable (V) region nucleotide sequences were determined. The complementarity-determining regions (CDRs) from these V regions were then inserted into human heavy and light chain V region genes with human constant region gene fragments subsequently added. The insertion of CDRs alone into human frameworks did not produce a functional reshaped antibody and modifications to the V region framework were required. With minor framework modifications, the affinity of the original murine mAb was restored and even exceeded. Where affinity was increased, an altered binding profile to overlapping peptides was observed. Computer modelling of the reshaped heavy chain V regions suggested that amino acids adjacent to CDRs can either contribute to, or distort, CDR loop conformation and must be adjusted to achieve high binding affinity.

Sequences of heavy and light chain variable regions from four bovine immunoglobulins.

Oligodeoxyribonucleotide primers based on the 5' ends of bovine IgG1/2 and lambda constant (C) region genes, together with primers encoding conserved amino acids at the N-terminus of mature variable (V) regions from other species, have been used in cDNA and polymerase chain reactions (PCRs) to amplify heavy and light chain V region cDNA from bovine heterohybridomas. The amino acid sequences of VH and V lambda from four bovine immunoglobulins of different specificities are presented.

A humanized anti-tumor necrosis factor-alpha monoclonal antibody that acts as a partial, competitive antagonist of the template antibody.

We have constructed several humanized versions of a monoclonal antibody (MAb78) against human tumor necrosis factor-alpha (huTNF-alpha) retaining the complementarity-determining regions (CDR) of the original mouse MAb with or without a variable number of original framework region (FR) residues. All versions, except one, showed a loss of binding affinity and neutralizing potency of at least 10-fold compared to the original mouse MAb or its chimeric equivalent. In some cases, however, the decrease in neutralizing potency was significantly greater than the decrease in binding affinity. Two humanized versions showing the greatest dissociation between these two parameters were studied for their capacity to inhibit the neutralizing activity of chimeric or murine MAb78 when used at concentrations that bound but only partially neutralized huTNF-alpha. One humanized version (MAb78D) was indeed able to do so, whereas the other (MAb78C) was not found to exert any inhibitory activity at all concentrations tested. The antagonistic effect of MAb78D was concentration dependent and could be overcome by increasing the concentrations of chimeric or murine MAb78. Two different models of MAb78-huTNF-alpha interaction that may help explain the antagonist activity of humanized MAb78D are discussed.

Idiotope determining regions of a mouse monoclonal antibody and its humanized versions. Identification of framework residues that affect idiotype expression.

The contribution of framework regions (FRs) of antibody-variable domains to idiotype expression was studied by examining the interaction of various "humanized" versions of a mouse anti-TNF alpha monoclonal antibody (mAb78) with polyclonal and two monoclonal antibodies (mAb1G3 and mAb9F1), generated against the mAb78 idiotype. Humanized mAb78, bearing human constant domains and mouse complementarity-determining regions (CDRs) inserted with human FRs, was found to be five to sevenfold less reactive than mAb78 with polyclonal anti-idiotype antibodies and 200 to 300-fold less active in neutralizing TNF alpha. The substitution of heavy-chain FRs residues of the humanized antibody with original mouse residues 28 to 30, 48 to 49, 67 to 68, 70 to 71, 78, 80 and 82 progressively restored the immunoreactivity with polyclonal immunoglobulin Gs to the level of a version having mouse heavy chain and human light chain FRs, and increased 10 to 20-fold the TNF alpha neutralizing activity. This suggests that at least some of these residues are critical for TNF alpha binding as well as for the expression of idiotopes that are strongly immunogenic in syngeneic animals. All antibody versions with either human or mouse FRs were able to bind to various extents mAb1G3, a gamma-type anti-Id antibody that inhibits mAb78/TNF alpha interaction by paratope blockade. At variance, only the antibody versions containing mouse FRs were able to bind mAb9F1, an alpha-type anti-Id antibody unable to block the access of TNF alpha to mAb78 paratopes. Substitution of heavy chain FR residues 28 to 30 markedly decreased the binding of mAb1G3 (100 to 1000-fold). This suggests that these antibodies recognize CDR and FR idiotopes, respectively, that can be drastically modified by changes in the FRs. In conclusion, the results suggest that CDRs as well as FRs markedly contribute to antibody Id expression. Although strongly immunogenic idiotopes are probably located within the CDRs, the results also suggest that some FR residues are critically involved in shaping antibody Id diversity by affecting the structure of CDR-related idiotopes.

Cloning and expression in Escherichia coli of the cDNA encoding human cardiac troponin I.

We have cloned and sequenced the human cardiac troponin I (cTnI)-encoding cDNA with the aim of expressing the cDNA in Escherichia coli. The cDNA was successfully expressed as a fusion product with beta-galactosidase and as an unfused protein. Both polypeptides were recognised by an anti-human cTnI antibody.

Reshaping a human monoclonal antibody to inhibit human respiratory syncytial virus infection in vivo.

We transferred the complementarity determining regions from a murine monoclonal antibody that neutralizes infection by respiratory syncytial virus (RSV) to a human IgG1 monoclonal antibody. The resulting reshaped human antibody lost affinity for RSV, but an additional alteration to one of the framework regions restored binding affinity and specificity. This second generation reshaped human monoclonal antibody cross-reacted with all clinical isolates of RSV tested and both prevented disease and cured mice even when administered four days after infection. We expect the antibody will prove useful in the management of this major childhood disease.

Structure of the met protein and variation of met protein kinase activity among human tumour cell lines.

An in vitro autophosphorylation assay has been used to demonstrate that there is considerable variation in met associated protein kinase among human tumour cell lines. Of particular note was the very high level of autophosphorylation of the 140 kD met protein (p140met) in experiments with A431 human cervical carcinoma cells. In contrast in experiments with Daoy human medulloblastoma cells we failed to detect phosphorylation of p140met; instead a high level of phosphorylation of a 132 kD protein was observed. To help understand the basis for the variation in kinase activity and to learn more about the structure of the mature met protein we have analysed p140met in SDS-polyacrylamide gels under non-reducing conditions. Under these conditions the met protein had an apparent molecular weight of 165,000 indicating that the mature met protein may exist as an alpha beta complex in which p140met (designated the beta subunit) is joined by disulphide bonds to a smaller, 25 kD, alpha-chain. We have identified a potential proteolytic cleavage site with the sequence Lys-Arg-Lys-Lys-Arg-Ser at amino acids 303-308 in the human met protein that may account for cleavage of the met protein into alpha and beta subunits.

Characterization of the mouse met proto-oncogene.

The DNA sequence of cDNA clones prepared from transcripts of the mouse met proto-oncogene reveals that the mouse met gene encodes a 1380 amino acid protein with the characteristics of a growth factor receptor. This protein can be divided into several putative domains, including an intracellular protein tyrosine kinase domain, a transmembrane domain and a 929 amino acid extracellular domain, possessing a potential proteolytic cleavage site with the sequence Lys-Arg-Arg-Lys-Arg-Ser. To gain additional insights into the function of the met protein we have examined the level of met transcripts in tissues of the late-gestation mouse conceptus. Transcription of met was observed in most of the tissues analysed, but the highest levels of met mRNA were detected in the yolk sac, amnion and kidney; no transcripts were detectable in the calvaria. Chromosomal localization using a series of mouse-hamster hybrid cell lines has demonstrated that met is located on mouse chromosome 6.

tpr homologues activate met and raf.

We have previously described the primary structure of the entire met domain and part of the tpr domain present in the human tpr-met oncogene. The isolation and sequencing of an additional cDNA clone now enables us to present the complete primary sequence of the tpr domain. A computer search has unearthed a remarkable identity between tpr and a rat sequence found at the 5-prime end of the activated raf oncogene. The occurrence of tpr-like sequences in combination with two oncogenes suggests that tpr contributes a domain(s) relevant to the observed activation of met and raf.

Primary structure of the met protein tyrosine kinase domain.

The primary structure of the protein tyrosine kinase domain of the human met gene has been determined from cDNA clones prepared from transcripts of the activated human met gene. These analyses reveal that the met kinase domain (located on human chromosome 7) possesses unique features that distinguish met from other members of the src family of protein tyrosine kinases. The results also demonstrate that the product of the activated met gene is a fusion protein and that the amino terminal end of this fusion protein, which is encoded by human chromosome 1, exhibits homology to laminin B1.

The activated human met gene encodes a protein tyrosine kinase.

We have raised antibodies against a synthetic dodecapeptide corresponding to the carboxyl terminus of the predicted met gene product. Phosphorylation of 60 kDa and 65 kDa proteins on tyrosine residues was observed when immunoprecipitates of cells containing the activated human met gene were incubated with [gamma-32P]ATP. Phosphoproteins with the same molecular masses could be immunoprecipitated from cells metabolically labelled with [32P]orthophosphate. When considered together, these observations indicate that the activated human met gene encodes 60 kDa and 65 kDa proteins that can catalyse autophosphorylation on tyrosine residues.

Activation of the met oncogene in the human MNNG-HOS cell line involves a chromosomal rearrangement.

In this study it is demonstrated that the activated met gene, which was originally detected in the MNNG-HOS chemically transformed human cell line, is a chimeric gene formed by the joining together of two distinct regions of DNA. Rearrangement of cellular DNA in MNNG-HOS cells was demonstrated by Southern analyses, which showed that the MNNG-HOS cell line contained unique met-related DNA fragments that were not detected in the parental cell line, HOS. Chromosomal localization using a series of rodent-human hybrid cell lines showed that the 5' end of the activated met gene is derived from human chromosome 1, in contrast to the 3' end of met which has been previously localized to human chromosome 7. The chimeric gene is transcribed to produce a 5-kb mRNA that is encoded both by regions of the gene derived from chromosome 1 and by regions of the gene derived from chromosome 7. Karyotype analysis of HOS and MNNG-HOS cells has identified several marker chromosomes that involve translocations of chromosomes 1 and 7. The possible location of the activated met locus within these rearranged chromosomes is discussed.