Antigen-specific human monoclonal antibodies from mice engineered with human Ig heavy and light chain YACs

Passive immunization against dental caries and periodontal disease: development of recombinant and human monoclonal antibodies

Indigenous micro-organisms in the oral cavity can cause two major diseases, dental caries and periodontal diseases. There is neither agreement nor consensus as to the actual mechanisms of pathogenesis of the specific virulence factors of these micro-organisms. The complexity of the bacterial community in dental plaque has made it difficult for the single bacterial agent of dental caries to be determined. However, there is considerable evidence that Streptococcus mutans is implicated as the primary causative organism of dental caries, and the cell-surface protein antigen (SA I/II) as well as glucosyltransferases (GTFs) produced by S. mutans appear to be major colonization factors. Various forms of periodontal diseases are closely associated with specific subgingival bacteria. Porphyromonas gingivalis has been implicated as an important etiological agent of adult periodontitis. Adherence of bacteria to host tissues is a prerequisite for colonization and one of the important steps in the disease process. Bacterial coaggregation factors and hemagglutinins likely play major roles in colonization in the subgingival area. Emerging evidence suggests that inhibition of these virulence factors may protect the host against caries and periodontal disease. Active and passive immunization approaches have been developed for immunotherapy of these diseases. Recent advances in mucosal immunology and the introduction of novel strategies for inducing mucosal immune responses now raise the possibility that effective and safe vaccines can be constructed. In this regard, some successful results have been reported in animal experimental models. Nevertheless, since the public at large might be skeptical about the seriousness of oral diseases, immunotherapy must be carried out with absolute safety. For this goal to be achieved, the development of safe antibodies for passive immunization is significant and important. In this review, salient advances in passive immunization against caries and periodontal diseases are summarized, and the biotechnological approaches for developing recombinant and human-type antibodies are introduced. Furthermore, our own attempts to construct single-chain variable fragments (ScFv) and human-type antibodies capable of neutralizing virulence factors are discussed.

Human antiglomerular basement membrane autoantibody disease in XenoMouse II

BACKGROUND

Previous studies have identified regions within alpha3(IV) collagen in human antiglomerular basement membrane (anti-GBM) disease, however, information pertaining to the nature of the pathogenic human autoantibodies has been limited by a lack of a relevant disease model. Availability of engineered mice that produce antibodies (that is, XenoMouse II strains) provides an ideal opportunity to examine the human antibody response.

METHODS

XenoMouse II mice that produce human IgG2 (gamma2kappa) in response to antigenic challenge were immunized with various forms of alpha3(IV)NC1 GBM collagen, including native bovine alpha3(IV) NCl collagen, E. coli expressed r alpha3(IV)NCl, and mammalian fetal kidney 293 cell expressed r alpha3(IV)NC1 preparations. The mice were evaluated for autoantibody (Ab) production and nephritis.

RESULTS

All immunized XenoMouse II animals produced human anti-GBM Ab associated with proliferative glomerulonephritis, linear IgG deposits along the murine GBM and tubular basement membrane (TBM), C3 deposits (weaker). A fully human mAb (Ig gamma2kappa), produced from a mouse immunized with native bovine alpha3(IV)NCl collagen produced basement membrane deposits, nephritis and proteinuria on transfer to normal XenoMouse II. Furthermore, monoclonal antibodies (mAb) shared idiotypic properties with polyclonal autoantibodies derived from patients with anti-GBM disease, supporting a structural relationship among the antibodies.

CONCLUSIONS

The results further support the importance of alpha3(IV)NCl collagen in the pathogenesis of anti-GBM disease. Moreover, to our knowledge this is the first demonstration that experimentally induced, pathogenic human autoantibodies result in disease. This new model of anti-GBM disease, therefore, provides the means and unique reagents to both decipher the molecular basis of the human anti-GBM autoantibody response and the opportunity to test specific therapies aimed at modulation of either B cells producing human autoantibodies or the human pathogenic antibodies themselves, in vivo, prior to trial in patients with the spontaneous form of the disease.

Future of monoclonal antibodies in the treatment of hematologic malignancies

BACKGROUND

The approval of monoclonal antibodies (MAbs) as antibody-targeted therapy in the management of patients with hematologic malignancies has led to new treatment options for this group of patients. The ability to target antibodies to novel functional receptors can increase their therapeutic efficacy.

METHODS

The authors reviewed improvements in MAb design to enhance their effectiveness over the existing therapeutic MAb currently approved for treating hematologic malignancies.

RESULTS

Three classes of therapeutic MAbs showing promise in human clinical trials for treatment of hematologic malignancies include unconjugated MAb, drug conjugates in which the antibody preferentially delivers a potent cytotoxic drug to the tumor, and radioactive immunotherapy in which the antibody delivers a sterilizing dose of radiation to the tumor.

CONCLUSIONS

A better appreciation of how MAbs are metabolized in the body and localized to tumors is resulting in the development of new antibody constructs with improved biodistribution profiles.

Effects of anti-TGF-beta type II receptor antibody on experimental glomerulonephritis

BACKGROUND

Renal fibrosis, characterized by the accumulation of extracellular matrix (ECM), is a common histopathological feature of progressive renal disease of diverse etiology. Interaction between transforming growth factor-beta (TGF-beta) and TGF-beta type II receptor (TGF-betaIIR) may play an important role in the ongoing fibrotic process. TGF-betaIIR and TGF-beta have been reported to be up-regulated in human glomerulopathies. In order to block the TGF-beta system, many studies have inhibited TGF-beta itself, but not its receptors. Our study explored the effects of fully human monoclonal antibody against TGF-betaIIR (hTGF-betaIIRAb) on experimental proliferative glomerulonephritis.

METHODS

hTGF-betaIIRAb was generated from Xenomice. The expression of TGF-betaIIR was studied by immunohistochemistry in normal and anti-Thy-1 nephritis rats. hTGF-betaIIRAb or control Ab was injected intraperitoneally at day 0 and day 4 of anti-Thy-1 nephritis, and rats were sacrificed at day 7. Effects of hTGF-betaIIRAb were assessed by histological and immunopathological measurements.

RESULTS

The specificity of hTGF-betaIIRAb was confirmed by ELISA and Western blot analysis. By immunostaining, TGF-betaIIR expression was up-regulated in the proliferative lesions of anti-Thy-1 nephritis at day 7. In the hTGF-betaIIRAb-treated group, the extent of mesangial expansion was less than that in the control group. By immunohistology, alpha-smooth muscle actin, fibronectin-EDA, and type I collagen were significantly reduced in the hTGF-betaIIRAb-treated group.

CONCLUSIONS

Anti-TGF-betaIIR antibody ameliorated ECM accumulation in anti-Thy-1 nephritis. Our data suggest that TGF-betaIIR may be one of the therapeutic targets, and that fully human monoclonal antibody against TGF-betaIIR may have a new therapeutic potential for renal fibrosis.

Anti-TNF alpha therapy of rheumatoid arthritis: what have we learned?

Rheumatoid arthritis (RA), a systemic disease, is characterized by a chronic inflammatory reaction in the synovium of joints and is associated with degeneration of cartilage and erosion of juxta-articular bone. Many pro-inflammatory cytokines including TNF alpha, chemokines, and growth factors are expressed in diseased joints. The rationale that TNF alpha played a central role in regulating these molecules, and their pathophysiological potential, was initially provided by the demonstration that anti-TNF alpha antibodies added to in vitro cultures of a representative population of cells derived from diseased joints inhibited the spontaneous production of IL-1 and other pro-inflammatory cytokines. Systemic administration of anti-TNF alpha antibody or sTNFR fusion protein to mouse models of RA was shown to be anti-inflammatory and joint protective. Clinical investigations in which the activity of TNF alpha in RA patients was blocked with intravenously administered infliximab, a chimeric anti-TNF alpha monoclonal antibody (mAB), has provided evidence that TNF regulates IL-6, IL-8, MCP-1, and VEGF production, recruitment of immune and inflammatory cells into joints, angiogenesis, and reduction of blood levels of matrix metalloproteinases-1 and -3. Randomized, placebo-controlled, multi-center clinical trials of human TNF alpha inhibitors have demonstrated their consistent and remarkable efficacy in controlling signs and symptoms, with a favorable safety profile, in approximately two thirds of patients for up to 2 years, and their ability to retard joint damage. Infliximab (a mAB), and etanercept (a sTNF-R-Fc fusion protein) have been approved by regulatory authorities in the United States and Europe for treating RA, and they represent a significant new addition to available therapeutic options.

Heterosubtypic immunity to influenza A virus in mice lacking IgA, all Ig, NKT cells, or gamma delta T cells

The mechanisms of broad cross-protection to influenza viruses of different subtypes, termed heterosubtypic immunity, remain incompletely understood. We used knockout mouse strains to examine the potential for heterosubtypic immunity in mice lacking IgA, all Ig and B cells, NKT cells (CD1 knockout mice), or gamma(delta) T cells. Mice were immunized with live influenza A virus and compared with controls immunized with unrelated influenza B virus. IgA(-/-) mice survived full respiratory tract challenge with heterosubtypic virus that was lethal to controls. IgA(-/-) mice also cleared virus from the nasopharynx and lungs following heterosubtypic challenge limited to the upper respiratory tract, where IgA has been shown to play an important role. Ig(-/-) mice controlled the replication of heterosubtypic challenge virus in the lungs. Acute depletion of CD4+ or CD8+ T cell subsets abrogated this clearance of virus, thus indicating that both CD4+ and CD8+ T cells are required for protection in the absence of Ig. These results in Ig(-/-) mice indicate that CD4+ T cells can function by mechanisms other than providing help to B cells for the generation of Abs. Like wild-type mice, CD1(-/-) mice and gamma(delta) (-/-) mice survived lethal heterosubtypic challenge. Acute depletion of CD4+ and CD8+ cells abrogated heterosubtypic protection in gamma(delta) (-/-) mice, but not B6 controls, suggesting a contribution of gamma(delta) T cells. Our results demonstrate that the Ab and cellular subsets deficient in these knockout mice are not required for heterosubtypic protection, but each may play a role in a multifaceted response that as a whole is more effective than any of its parts.

Single domain camel antibodies: current status

The antigen-binding capacity of the paired variable domains of an antibody is well established. The observation that the isolated heavy chains of anti-hapten antibodies retain some antigen-binding capacity in the absence of light chains led to attempts to obtain an even smaller antigen-binding unit in a VH format. Unfortunately, the poor solubility, the reduced affinity for the antigen and the irreproducible outcome showed that additional protein engineering would be required to successfully generate single-domain antibody fragments. By serendipity, it was discovered that this engineering is already performed continuously in nature. Part of the humoral immune response of camels and llamas is based largely on heavy-chain antibodies where the light chain is totally absent. These unique antibody isotypes interact with the antigen by virtue of only one single variable domain, referred to as VHH. Despite the absence of the VH-VL combinatorial diversity, these heavy-chain antibodies exhibit a broad antigen-binding repertoire by enlarging their hypervariable regions. Methods are described to tap the VHH repertoire of an immunised dromedary or llama. These VHH libraries contain a high titre of intact antigen-specific binders that were matured in vivo. Synthetic libraries of a 'camelised' human VH, a mouse VH or a camelid VHH scaffold with a randomised CDR3 could constitute a valid alternative to immune libraries to retrieve useful single-domain antigen binders. The recombinant VHH that are selected from such libraries are well expressed, highly soluble in aqueous environments and very robust. Some in vivo matured VHH were also shown to be potent enzyme inhibitors, and the low complexity of the antigen-binding site is an asset in the design of peptide mimetics. Because of their smaller size and the above properties, the VHH clearly offer added-value over conventional antibody fragments. They are expected to open perspectives as enzyme inhibitors and intrabodies, as modular building units for multivalent or multifunctional constructs, or as immuno-adsorbents and detection units in biosensors.

Size matters: use of YACs, BACs and PACs in transgenic animals

In 1993, several groups, working independently, reported the successful generation of transgenic mice with yeast artificial chromosomes (YACs) using standard techniques. The transfer of these large fragments of cloned genomic DNA correlated with optimal expression levels of the transgenes, irrespective of their location in the host genome. Thereafter, other groups confirmed the advantages of YAC transgenesis and position-independent and copy number-dependent transgene expression were demonstrated in most cases. The transfer of YACs to the germ line of mice has become popular in many transgenic facilities to guarantee faithful expression of transgenes. This technique was rapidly exported to livestock and soon transgenic rabbits, pigs and other mammals were produced with YACs. Transgenic animals were also produced with bacterial or P1-derived artificial chromosomes (BACs/PACs) with similar success. The use of YACs, BACs and PACs in transgenesis has allowed the discovery of new genes by complementation of mutations, the identification of key regulatory sequences within genomic loci that are crucial for the proper expression of genes and the design of improved animal models of human genetic diseases. Transgenesis with artificial chromosomes has proven useful in a variety of biological, medical and biotechnological applications and is considered a major breakthrough in the generation of transgenic animals. In this report, we will review the recent history of YAC/BAC/PAC-transgenic animals indicating their benefits and the potential problems associated with them. In this new era of genomics, the generation and analysis of transgenic animals carrying artificial chromosome-type transgenes will be fundamental to functionally identify and understand the role of new genes, included within large pieces of genomes, by direct complementation of mutations or by observation of their phenotypic consequences.

Development of ABX-EGF, a fully human anti-EGF receptor monoclonal antibody, for cancer therapy

Overexpression of epidermal growth factor receptor (EGFr) has been demonstrated on many human tumors, and the increase in receptor expression levels has been linked with a poor clinical prognosis. Blocking the interaction of EGFr and the growth factors could lead to the arrest of tumor growth and possibly result in tumor cell death. To this end, using XenoMouse technology, ABX-EGF, a human IgG2 monoclonal antibody (mAb) specific to human EGFr, has been generated. ABX-EGF binds EGFr with high affinity (5x10(-11) M), blocks the binding of both EGF and transforming growth factor-alpha (TGF-alpha) to various EGFr-expressing human carcinoma cell lines, and inhibits EGF-dependent tumor cell activation, including EGFr tyrosine phosphorylation, increased extracellular acidification rate, and cell proliferation. In vivo ABX-EGF prevents completely the formation of human epidermoid carcinoma A431 xenografts in athymic mice. More importantly, administration of ABX-EGF without concomitant chemotherapy results in complete eradication of established tumors. No tumor recurrence was observed for more than 8 months following the last antibody injection, further indicating complete tumor cell elimination by the antibody. Inhibition of human pancreatic, renal, breast and prostate tumor xenografts which express different levels of EGFr by ABX-EGF was also achieved. Tumor expressing more than 17000 EGFr molecules per cell showed significant growth inhibition when treated with ABX-EGF. ABX-EGF had no effect on EGFr-negative tumors. The potency of ABX-EGF in eradicating well-established tumors without concomitant chemotherapy indicates its potential as a monotherapeutic agent for treatment of multiple EGFr-expressing human solid tumors, including those where no effective chemotherapy is available. Utilization of mAbs directed to growth factor receptors as cancer therapeutics has been validated recently by the tumor responses obtained from clinical trials with Herceptin, the humanized anti-HER2 antibody, in patients with HER2 overexpressing metastatic breast cancer. Being a fully human antibody, ABX-EGF is anticipated to exhibit a long serum half-life and minimal immunogenicity with repeated administration, even in immunocompetent patients. These results demonstrate the potent anti-tumor activity of ABX-EGF and its therapeutic potential for the treatment of multiple human solid tumors that overexpress EGFr.

Therapeutic antibody expression technology

With the technological advances made during the past decade, antibodies now represent an important and growing class of biotherapeutics. With the potential new targets resulting from genomics and with methods now in place to make fully human antibodies, the potential of antibodies as valuable therapeutics in oncology, inflammation and cardiovascular disease can be fully realised. Systems to produce these antibodies as full-length molecules and as fragments include expression in both mammalian and bacterial cells grown in bioreactors and in transgenic organisms. Factors including molecular fidelity and the cost of goods are critical in evaluating expression systems. Mammalian cell culture and transgenic organisms show the greatest promise for the expression of full-length, recombinant human antibodies, and bacterial fermentation seems most favorable for the expression of antibody fragments.

Novel control motif cluster in the IgH delta-gamma 3 interval exhibits B cell-specific enhancer function in early development

The majority of the human Ig heavy chain (IgH) constant (C) region locus has been cloned and mapped. An exception is the region between C delta and C gamma 3, which is unstable and may be a recombination hot spot. We isolated a pBAC clone (pHuIgH3'delta-gamma 3) that established a 52-kb distance between C delta and C gamma 3. Sequence analysis identified a high number of repeat elements, explaining the instability of the region, and an unusually large accumulation of transcription factor-binding motifs, for both lymphocyte-specific and ubiquitous transcription activators (IKAROS, E47, Oct-1, USF, Myc/Max), and for factors that may repress transcription (Delta EF1, Gfi-1, E4BP4, C/EBP beta). Functional analysis in reporter gene assays revealed the importance of the C delta-C gamma 3 interval in lymphocyte differentiation and identified independent regions capable of either enhancement or silencing of reporter gene expression and interaction with the IgH intron enhancer E mu. In transgenic mice, carrying a construct that links the beta-globin reporter to the novel delta-gamma 3 intron enhancer (E delta-gamma 3), transgene transcription is exclusively found in bone marrow B cells from the early stage when IgH rearrangement is initiated up to the successful completion of H and L locus recombination, resulting in Ab expression. These findings suggest that the C delta-C gamma 3 interval exerts regulatory control on Ig gene activation and expression during early lymphoid development.

The antiviral activity of antibodies in vitro and in vivo

This chapter discusses in vitro and in vivo antiviral activities of antibody. Since experimentation is far easier in vitro , researchers have been sought to develop in vitro assays that are expected to predict activity in vivo . This could be important in both vaccine design and in passive antibody administration. The proposed mechanisms of in vitro neutralization range from those requiring binding of a single antibody molecule to virus to those requiring substantially complete antibody coating of virus. In vitro, antiviral activity can be separated into activity against virions and activity against infected cells. The activity against virions most often considered is neutralization that can be defined as the loss of infectivity, which ensues when antibody molecule(s) bind to a virus particle, and occurs without the involvement of any other agency. In vivo, it is conventional to distinguish phenomenologically between two types of antibody antiviral activity. One of them is the ability of antibody to protect against infection when it is present before or immediately following infection. Evidence for a number of viruses in vitro indicates that lower antibody concentrations are required to inhibit infection propagated by free virus than are required to inhibit infection propagated by cell-to-cell spread.

A targeted DNA vaccine augments the natural immune response to self TNF-alpha and suppresses ongoing adjuvant arthritis

Depending on the mode of immunization, a single administration of CFA may result in the development of a local inflammatory process or chronic poly adjuvant-induced arthritis (AA). Administration of naked DNA encoding TNF-alpha results in the generation of immunological memory to its gene product. Upon induction of AA, this memory effectively inhibited the development of disease. Self-specific Abs developed in DNA-vaccinated animals were neutralizing in vitro and could adoptively transfer the beneficial effect of the vaccine. Administration of CFA to induce a local delayed-type hypersensitivity response rather than AA did not lead to an elicited production of Abs to the gene product of the above vaccine. Thus, elicitation of protective immunity is dependent on the development of an autoimmune condition. Most importantly, the administration of the TNF-alpha DNA construct after the onset of disease led to a rapid, long-lasting remission. This suggests a highly effective way by which a DNA vaccine encoding an autologous proinflammatory cytokine can be used to reprogram the immune system to generate protective immunity to its own potentially harmful activities.

Production of protective human antipneumococcal antibodies by transgenic mice with human immunoglobulin loci

Infections with Streptococcus pneumoniae remain a significant cause of morbidity and mortality. To gain insight into structure-function relationships for human antibodies to pneumococcal capsular polysaccharide (PPS), we studied the response of transgenic mice reconstituted with human immunoglobulin loci, XenoMouse, to PPS antigens in a pneumococcal vaccine. Enzyme-linked immunosorbent assays of sera from mice vaccinated with a 23-valent pneumococcal vaccine revealed that they produced serotype-specific human antibodies, with the greatest response being to the PPS of serotype 3 (PPS 3). Molecular sequence analysis of three monoclonal antibodies (MAbs) to PPS 3 generated from lymphoid cells from mice vaccinated with a 23-valent pneumococcal vaccine or a PPS 3-bovine serum albumin conjugate revealed that they all used heavy-chain immunoglobulin genes from the V(H)3 family, two expressed light chain genes from the human Vkappa1 family, and one expressed a mouse lambda light chain. The protective efficacy of the two MAbs was examined in mice. A 10-microgram dose of both, and a 1-microgram dose of one, significantly prolonged survival from a lethal serotype 3 infection in CBA/N mice. Our data show that XenoMouse mice produced protective, serotype-specific human antibodies to PPS 3, and they lend support to the proposal that these animals represent a useful model to study the human antibody response to PPS antigens.

High-level rearrangement and transcription of yeast artificial chromosome-based mouse Ig kappa transgenes containing distal regions of the contig

The mouse Ig kappa L chain gene locus has been extensively studied, but to date high-level expression of germline transgenes has not been achieved. Reasoning that each end of the locus may contain regulatory elements because these regions are not deleted upon V kappa-J kappa joining, we used yeast artificial chromosome-based techniques to fuse distal regions of the contig to create transgene miniloci. The largest minilocus (290 kb) possessed all members of the upstream V kappa 2 gene family including their entire 5' and 3' flanking sequences, along with one member of a downstream V kappa 21 gene family. In addition, again using yeast artificial chromosome-based technology, we created Ig kappa miniloci that contained differing lengths of sequences 5' of the most distal V kappa 2 gene family member. In transgenic mice, Ig kappa miniloci exhibited position-independent and copy number-dependent germline transcription. Ig kappa miniloci were rearranged in tissue and developmental stage-specific manners. The levels of rearrangement and transcription of the distal and proximal V kappa gene families were similar to their endogenous counterparts and appeared to be responsive to allelic exclusion, but were differentially sensitive to numerous position effects. The minilocus that contained the longest 5' region exhibited significantly greater recombination of the upstream V kappa 2 genes but not the downstream V kappa 21 gene, providing evidence for a local recombination stimulating element. These results provide evidence that our miniloci contain nearly all regulatory elements required for bona fide Ig kappa gene expression, making them useful substrates for functional analyses of cis-acting sequences in the future.

Antibody Repertoires of Four- and Five-Feature Translocus Mice Carrying Human Immunoglobulin Heavy Chain and κ and λ Light Chain Yeast Artificial Chromosomes

We have produced mice that carry the human Ig heavy (IgH) and both κ and λ light chain transloci in a background in which the endogenous IgH and κ loci have been inactivated. The B lymphocyte population in these translocus mice is restored to about one-third of normal levels, with preferential (3:1) expression of human λ over human κ. Human IgM is found in the serum at levels between 50 and 400 μg/ml and is elevated following immunization. This primary human Ab repertoire is sufficient to yield diverse Ag-specific responses as judged by analysis of mAbs. The use of DH and J segments is similar to that seen in human B cells, with an analogous pattern of N nucleotide insertion. Maturation of the response is accompanied by somatic hypermutation, which is particularly effective in the light chain transloci. These mice therefore allow the production of Ag-specific repertoires of both IgM,κ and IgM,λ Abs and should prove useful for the production of human mAbs for clinical use.

Antibody engineering via genetic engineering of the mouse: XenoMouse strains are a vehicle for the facile generation of therapeutic human monoclonal antibodies

The major impediment to the development of murine monoclonal antibodies (mAbs) for therapy in humans has been the difficulty in reducing their potential immunogenicity. XenoMouse¿trade mark omitted¿ mice obviate this problem while retaining the relative ease of generating mAbs from a mouse. XenoMouse strains include germline-configured, megabase-sized YACs carrying portions of the human IgH and Igkappa loci, including the majority of the variable region repertoire, the genes for Cmicro, Cdelta and either Cgamma1, Cgamma2, or Cgamma4, as well as the cis elements required for their function. The IgH and Igkappa transgenes were bred onto a genetic background deficient in production of murine immunoglobulin. The large and complex human variable region repertoire encoded on the Ig transgenes in XenoMouse strains support the development of large peripheral B cell compartments and the generation of a diverse primary immune repertoire similar to that from adult humans. Immunization of XenoMouse mice with human antigens routinely results in a robust secondary immune response, which can ultimately be captured as a large panel of antigen-specific fully human IgGkappa mAbs of sub-nanomolar affinities. Monoclonal antibodies from XenoMouse animals have been shown to have therapeutic potential both in vitro and in vivo, and appear to have the pharmacokinetics of normal human antibodies based on human clinical trials. The utility of XenoMouse strains for the generation of large panels of high-affinity, fully human mAbs can be made available to researchers in the academic and private sectors, and should accelerate the development and application of mAbs as therapeutics for human disease.

Dominance of intrinsic genetic factors in shaping the human immunoglobulin Vlambda repertoire

The expressed human immunoglobulin Vlambda repertoire demonstrates a strong bias in the use of individual Vlambda segments. Mechanisms that underlie such biases can be divided into two categories: intrinsic genetic processes that lead to the preferential rearrangement and/or expression of certain segments; and selection following light chain expression. Here, we have used two approaches to investigate the factors that shape the human Vlambda repertoire. Firstly, we characterised 136 Vlambda rearrangements (59 productive and 77 non-productive) amplified from the human genomic DNA of peripheral blood cells. Secondly, we analysed Vlambda segment use in a library of 2000 cDNA clones from a transgenic mouse containing a 380 kb region (including 15 functional Vlambda segments) from the human immunoglobulin lambda locus. By hybridisation and sequencing we found that the patterns of use of human Vlambda segments in the transgenic mouse were similar to those found in the expressed human peripheral blood repertoire and in productive and non-productive genomic DNA rearrangements. These data indicate the importance of intrinsic genetic factors in shaping the human Vlambda repertoire and highlight the remarkable conservation of the molecular mechanisms involved in the production of the antibody repertoire in mouse and man. Therefore, transgenic mice represent a good model for analysis of the human antibody repertoire and for the production of human antibodies.

Isolation and Characterization of Human Monoclonal Antibodies to Digoxin

Fab preparations of sheep polyclonal anti-digoxin Abs have proven useful for reversal of the toxic effects of digoxin overdoses in patients. Unfortunately, the use of foreign species proteins in humans is limited because of the potential for immunological responses that include hypersensitivity reactions and acute anaphylaxis. Immunization of recently developed transgenic mice, whose endogenous μ heavy and κ light chain Ig genes are inactivated and which carry human Ig gene segments, with a digoxin-protein conjugate has enabled us to generate and isolate eight hybridoma cell lines secreting human sequence anti-digoxin mAbs. Six of the mAbs have been partially characterized and shown to have high specificity and low nanomolar affinities for digoxin. In addition, detailed competition binding studies performed with three of these mAbs have shown them to have distinct differences in their digoxin binding, and that all three structural moieties of the drug, the primary digitoxose sugar, steroid, and five-member unsaturated lactone ring, contribute to Ab recognition.

Prevention of experimental autoimmune encephalomyelitis by MIP-1alpha and MCP-1 naked DNA vaccines

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease of the central nervous system (CNS). RT-PCR verified by Southern blotting and sequencing of PCR products of two C-C chemokines, MIP-1alpha and MCP-1, was performed on brain samples from EAE rats to evaluate mRNA transcription of these chemokines at different stages of disease. mRNA transcription in of each chemokine peaked after the onset of disease and declined during its remission. Each PCR product was then used as a construct for naked DNA vaccination. The subsequent in vivo immune response to MIP-1alpha or MCP-1 DNA vaccines prevented EAE. Immunization of CFA without the encephalitogenic epitope did not elicit an anti-C-C chemokine regulatory response in DNA- vaccinated rats. Thus, modulation of EAE with C-C chemokine DNA vaccines is dependent on targeting chemokines that are highly transcribed at the site of inflammation at the onset of disease.

Augmentation of natural immunity to a pro-inflammatory cytokine (TNF-alpha) by targeted DNA vaccine confers long-lasting resistance to experimental autoimmune encephalomyelitis

TNF-alpha is thought to be a key pro-inflammatory cytokine in T cell-mediated autoimmune diseases, particularly in rheumatoid arthritis (RA) and multiple sclerosis (MS). Experimental autoimmune encephalomyelitis (EAE) serves as an animal model for MS. The current study observes a notable TNF-alpha-specific antibody titer generated during the course of EAE, apparently not sufficient to prevent the development of disease. Administration of TNF-alpha-naked DNA vaccine enhanced the production of TNF-alpha-specific antibody titer and conferred EAE resistance. These antibodies were found to be neutralizing in vitro and capable of inhibiting the development of disease when transferred to other EAE rats. Thus, modulation of EAE with TNF-alpha DNA vaccines enhances the regulation of natural immunity to a self pro-inflammatory cytokine and provides a tool by which the immune system is encouraged to elicit anti-self protective immunity to restrain its own harmful reactivity when such a response is needed.

Transgenic animal bioreactors in biotechnology and production of blood proteins

The regulatory elements of genes used to target the tissue-specific expression of heterologous human proteins have been studied in vitro and in transgenic mice. Hybrid genes exhibiting the desired performance have been introduced into large animals. Complex proteins like protein C, factor IX, factor VIII, fibrinogen and hemoglobin, in addition to simpler proteins like alpha 1-antitrypsin, antithrombin III, albumin and tissue plasminogen activator have been produced in transgenic livestock. The amount of functional protein secreted when the transgene is expressed at high levels may be limited by the required posttranslational modifications in host tissues. This can be overcome by engineering the transgenic bioreactor to express the appropriate modifying enzymes. Genetically engineered livestock are thus rapidly becoming a choice for the production of recombinant human blood proteins.

Using monoclonal antibodies to prevent mucosal transmission of epidemic infectious diseases

Passive immunization with antibodies has been shown to prevent a wide variety of diseases. Recent advances in monoclonal antibody technology are enabling the development of new methods for passive immunization of mucosal surfaces. Human monoclonal antibodies, produced rapidly, inexpensively, and in large quantities, may help prevent respiratory, diarrheal, and sexually transmitted diseases on a public health scale.

Long-Lasting Protective Immunity to Experimental Autoimmune Encephalomyelitis Following Vaccination with Naked DNA Encoding C-C Chemokines

DNA vaccination represents a novel means of expressing Ag in vivo for the generation of both humoral and cellular immune responses. The current study uses this technology to elicit protective immunity against experimental autoimmune encephalomyelitis (EAE), a T cell-mediated autoimmune disease of the central nervous system that serves as an experimental model for multiple sclerosis. RT-PCR verified by Southern blotting and sequencing of PCR products of four different C-C chemokines, macrophage-inflammatory protein-1α (MIP-1α), monocyte-chemotactic protein-1 (MCP-1), MIP-1β, and RANTES, were performed on brain samples from EAE rats to evaluate mRNA transcription at different stages of disease. Each PCR product was then used as a construct for naked DNA vaccination. The subsequent in vivo immune response to MIP-1α or MCP-1 DNA vaccines prevented EAE, even if disease was induced 2 mo after administration of naked DNA vaccines. In contrast, administration of the MIP-1β naked DNA significantly aggravated the disease. Generation of in vivo immune response to RANTES naked DNA had no notable effect on EAE. MIP-1α, MCP-1, and MIP-1β mRNA transcription in EAE brains peaked at the onset of disease and declined during its remission, whereas RANTES transcription increased in EAE brains only following recovery. Immunization of CFA without the encephalitogenic epitope did not elicit the anti-C-C chemokine regulatory response in DNA-vaccinated rats. Thus, modulation of EAE with C-C chemokine DNA vaccines is dependent on targeting chemokines that are highly transcribed at the site of inflammation at the onset of disease.

Deposition of genetically engineered human antibodies into the egg yolk of hens

To determine if human immunoglobulins (hIg) are capable of being transported into the hen's egg, 10 microg each of purified hIgG and hIgA were intravenously injected into SC Hyline(TM) hens and their presence in egg yolk and egg white was determined by ELISA. In both cases deposition into the egg yolk was observed and in the case of hIgA, deposition was also observed in the egg white. Two stably transfected DT40 cell lines secreting recombinant human IgG3 and IgA (rhIgG3 and rhIgA) were injected into laying hens. The DT40 cells colonized the host and rhIgG3 and rhIgA were deposited in egg yolk. Deposition of rhIgA was also observed in the egg white. These data demonstrate that human immunoglobulins and other foreign proteins may be targeted to the chicken's egg. In view of the high rate of reproduction, the short generation interval, the high rates of egg production and the extensive infrastructure to fractionate egg yolk proteins, it should be possible to produce large amounts of foreign protein in the eggs of transgenic chickens.

Human monoclonal anti-HCMV neutralizing antibody from phage display libraries

Human cytomegalovirus (HCMV) infection in immunocompromised patients causes considerable morbidity and mortality. Although ganciclovir prophylaxis reduces the incidence of HCMV disease, severe side effects raise serious problems. Thus, the development of new strategies for prophylaxis are clearly needed, and human monoclonal antibodies offer a potential alternative. We describe the cloning, using the phage display system, of a recombinant human Fab fragment against HCMV. A phage display library with 4 x 10(6) clones was panned three times against lysates of HCMV-infected cells, and screened by ELISA. Of six antigen-binding clones, one monoclonal antibody reacted strongly to HCMV. In immunostaining analysis, this Fab was able to stain HCMV-infected cells from 24 h post-infection (pi) through to 96 h pi, but not at 6 h pi. In the presence of cytosine arabinoside, HCMV-infected cells were not stained, even at 24 h pi. These results indicate that an HCMV protein that was recognized by the Fab was synthesized in the late phase of infection. In addition, this Fab exhibited neutralizing activity: at 1 microg/ml it reduced HCMV plaque formation by 50%. The Fab was able to neutralize three HCMV strains, but it did not neutralize HSV-1 or -2 infection.

Regulation of B cell development by variable gene complexity in mice reconstituted with human immunoglobulin yeast artificial chromosomes

The relationship between variable (V) gene complexity and the efficiency of B cell development was studied in strains of mice deficient in mouse antibody production and engineered with yeast artificial chromosomes (YACs) containing different sized fragments of the human heavy (H) chain and kappa light (L) chain loci. Each of the two H and the two kappa chain fragments encompasses, in germline configuration, the same core variable and constant regions but contains different numbers of unique VH (5 versus 66) or Vkappa genes (3 versus 32). Although each of these YACs was able to substitute for its respective inactivated murine counterpart to induce B cell development and to support production of human immunoglobulins (Igs), major differences in the efficiency of B cell development were detected. Whereas the YACs with great V gene complexity restored efficient development throughout all the different recombination and expression stages, the YACs with limited V gene repertoire exhibited inefficient differentiation with significant blocks at critical stages of B cell development in the bone marrow and peripheral lymphoid tissues. Our analysis identified four key checkpoints regulated by VH and Vkappa gene complexity: (a) production of functional mu chains at the transition from the pre B-I to the pre B-II stage; (b) productive VkappaJkappa recombination at the small pre B-II stage; (c) formation of surface Ig molecules through pairing of mu chains with L chains; and (d) maturation of B cells. These findings demonstrate that V gene complexity is essential not only for production of a diverse repertoire of antigen-specific antibodies but also for efficient development of the B cell lineage.

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.

Bispecific antibodies for treatment of cancer in experimental animal models and man

Immunotherapy is a powerful anti-cancer treatment modality. However, despite numerous encouraging results obtained in pre-clinical studies, a definite breakthrough towards an established clinical treatment modality has as yet not occurred. Antibodies against tumor antigens have been shown to localise at the site of the tumor, but inadequate triggering of immune effector mechanisms have thwarted clinical efficacy thus far. Cellular immunotherapy has been hampered by limitations such as lack of specificity, down-regulation of major histocompatibility complex (MHC)-expression or Fas ligand up-regulation on tumor cells. This review focuses on the use of bispecific antibodies (BsAbs) for immunotherapy of cancer. Using BsAbs, it is possible to take advantage of the highly specific binding characteristics of antibodies and combine these with the powerful effector functions of cytotoxic immune effector cells. BsAbs share two different, monoclonal antibody-derived, antigen-recognizing moieties within one molecule. By dual binding, BsAbs reactive with a trigger molecule on an immune effector cell on the one hand and a surface antigen on a tumor target cell on the other are thus able to functionally focus the lytic activity of the immune effector cell towards the target cell. Over the last few years, the concept of BsAb-mediated tumor cell killing has been studied extensively both in preclinical models and in a number of phase I clinical trials. Promising pre-clinical results have been reported using tumor models in which diverse immune effector cell populations have been used. Despite this pre-clinical in vivo efficacy, the first clinical trials indicate that we are still not in a position to successfully treat human malignancies. This review discusses the production of BsAbs, the choice of trigger molecules in combination with potential effector cells and the preclinical models that have led to the current use of BsAbs in experimental clinical trials. It has become clear that appropriate immune cell activation and establishing a favourable effector-to-target cell ratio will have direct impact on the efficacy of the therapeutic approaches using BsAbs. New directions are discussed, i.e. finding appropriate dosage schemes by which immune effector cells become redirected without inducing hyporesponsiveness, defining possibilities for combining different immune effector cell populations and creating an in situ tumor environment that allows maximal tumoricidal activity

Production and selection of antigen-specific fully human monoclonal antibodies from mice engineered with human Ig loci

The ability to produce highly specific fully human monoclonal antibodies to human antigens has potential significant applications to human therapy. This review describes the creation of novel mouse strains engineered to produce a diverse repertoire of fully human antibodies in the absence of mouse antibodies. These mouse strains have been generated by introducing megabase-sized human immunoglobulin loci, containing the majority of the human antibody gene repertoire, in nearly germline configuration, into mice deficient in mouse antibody production. The mice produce high levels of human IgMkappa and IgGkappa antibodies with a diverse adult-like repertoire. Upon immunization with multiple human antigens the mice generate high affinity, antigen-specific fully human monoclonal antibodies with neutralization activity. Comparison of these mice to other strains containing limited human antibody gene repertoire underscores the importance of the large number of variable genes for faithful reproduction of functional and diverse human antibody response in mice.

Exploring gene function: use of yeast artificial chromosome transgenesis

Transgenesis is a very powerful tool in functional analysis of proteins and control of gene expression. One of the main drawbacks has been the low levels of expression, lack of tissue specificity, and inappropriate expression frequently observed for transgenes made with small plasmid-based constructs. The use of much larger DNA fragments cloned in yeast artificial clones (YACs), bacterial artificial clones, or P1-based artificial clones has been found to give much better levels of expression, generally very close to that of an endogenous gene, and tissue-specific expression matching that of the endogenous gene. In addition, the large DNA can easily be subtly modified by homologous recombination. This article describes the background and methods of YAC transgenesis.

Design, synthesis, and application of a protein A mimetic

Low-molecular-weight synthetic molecules that mimic the activity of native biological macromolecules have therapeutic potential, utility in large-scale production of biopharmaceuticals, and the capacity to act as probes to study molecular recognition events. We have developed a nonpeptidyl mimic for Staphylococcus aureus Protein A (SpA). The specific recognition and complexation elements between the B domain (Fb) of SpA and the Fc fragment of IgG were identified from the x-ray crystallographic structure. Computer-aided molecular modeling was used to design a series of biomimetic molecules around the Phe132-Tyr133 dipeptide involved in its binding to IgG. One of the ligands binds IgG competitively with SpA in solution and when immobilized on agarose beads, with an affinity constant of 10(5)-10(6) M-1. The immobilized artificial Protein A was used to purify IgG from human plasma and murine IgG from ascites fluid, and to remove bovine IgG from fetal calf serum.

Mechanism of Protective Immunity Against Influenza Virus Infection in Mice Without Antibodies

There is considerable interest in developing viral vaccines intended to induce T cell immunity, especially cytotoxic CD8+ T lymphocytes, when Abs are not protective or are too narrow in viral strain specificity. We have studied protective immunity in doubly inactivated (DI) mice devoid of Abs and mature B cells. When infected with influenza B virus, these mice cleared the virus in a process dependent upon CD8+ T lymphocytes. Cytotoxic activity was detected in lung lymphocytes of DI mice after primary or secondary infection, and was abrogated by depletion of CD8+ cells in vivo. Challenge experiments showed that DI mice could be protected by immunization against reinfection 1 mo later, and protection was virus specific. Depletion of CD4+ or CD8+ T cells in vivo during the challenge period partially abrogated, and depletion of both subsets completely abrogated, the protection. This indicates that both CD4+ and CD8+ T cells are required effectors in the optimal control of virus replication. Thus, when Abs fail to protect against varying challenge viruses, as is the case with variant strains of influenza and HIV, there is hope that T cells might be able to act alone.

Concentrations of serum interleukin-8 after successful cardiopulmonary resuscitation in patients with cardiopulmonary arrest

To assess differences in serum interleukin-8 concentrations in resuscitated and nonresuscitated patients after cardiopulmonary resuscitation (CPR), and to compare changes of interleukin-8 levels with hemodynamic variables after restoration of spontaneous circulation, 39 patients with out-of-hospital cardiopulmonary arrest who had undergone CPR were studied. Venous blood samples were taken after CPR and 1 and 2 hours after restoration of spontaneous circulation to measure serum interleukin-8 levels by the enzyme-linked immunosorbent assay method. The median serum interleukin-8 levels after CPR were significantly higher in resuscitated than in nonresuscitated patients (64.9 pg/ml; range 30.2 to 1497 vs 0 pg/ml; range 0 to 31.6 pg/ml; p < 0.001). One and 2 hours after restoration of spontaneous circulation, the median serum interleukin-8 levels were 96.2 pg/ml and 155.4 pg/ml, respectively. Mean values of systolic blood pressure immediately after and 1 and 2 hours after restoration of spontaneous circulation were 117 +/- 9 mm Hg, 130 +/- 11 mm Hg, and 136 +/- 13 mm Hg, respectively. No significant correlations were found between hemodynamic values and serum interleukin-8 levels. In conclusion, successful initial resuscitation was associated with increased serum interleukin-8 concentrations. The interleukin-8 levels remained at high values 2 hours after restoration of spontaneous circulation.

Production of human antibody repertoires in transgenic mice

Transgenic mice have been created that carry human immunoglobulin heavy and light chain genes in germline configuration and that have the corresponding endogenous genes silenced. The transgenes are either minigene constructs or large, almost authentic, transloci on yeast artificial chromosomes and undergo B-cell-specific DNA rearrangement and hypermutation in the mouse lymphoid tissue. Monoclonal antibodies with good affinities for human antigens have been obtained after immunisation. These mice may be a future source of human antibodies for therapy.

Inactivation of the mouse HPRT locus by a 203-bp retroposon insertion and a 55-kb gene-targeted deletion: establishment of new HPRT-deficient mouse embryonic stem cell lines

To obtain useful hypoxanthine phosphoribosyl-transferase (HPRT)-deficient mouse ES cell lines, two different methods were employed: (i) selection of spontaneous 6-TG-resistant mutants and (ii) gene targeting of the HPRT locus. The first approach resulted in the establishment of E14.1TG3B1, a spontaneous HPRT-deficient cell line with an insertional mutation of 203 bp in the third exon of the HPRT gene. The insert is highly homologous to the B2 mouse repetitive element and has all the expected retroposon characteristics, thus providing an example of gene inactivation by retroposon insertion. This clone exhibited stable 6-TG resistance and high germ-line transmission frequency. Thus E14.1TG3B1 is a useful ES cell line for modifying the mouse genome using the HPRT gene as a selection marker and for transmission at a high frequency into the mouse germ line. The second approach resulted in a 55-kb deletion of the mouse HPRT locus, demonstrating the feasibility of replacement-targeting vectors to generate large genomic DNA deletions.

Functional expression and germline transmission of a human chromosome fragment in chimaeric mice

Human chromosomes or chromosome fragments derived from normal fibroblasts were introduced into mouse embryonic stem (ES) cells via microcell-mediated chromosome transfer (MMCT) and viable chimaeric mice were produced from them. Transferred chromosomes were stably retained, and human genes, including immunoglobulin (Ig) kappa, heavy, lambda genes, were expressed in proper tissue-specific manner in adult chimaeric tissues. In the case of a human chromosome (hChr.) 2-derived fragment, it was found to be transmitted to the offspring through the germline. Our study demonstrates that MMCT allows for introduction of very large amounts of foreign genetic material into mice. This novel procedure will facilitate the functional analyses of human genomes in vivo.

Antibody engineering

The development of recombinant techniques for the rapid cloning, expression, and characterization of cDNAs encoding antibody (Ab) subunits has revolutionized the field of antibody engineering. By fusion to heterologous protein domains, chain shuffling, and inclusion of self-assembly motifs, novel molecules such as bispecific Abs can now be generated which possess the subset of functional properties designed to fit the intended application. Rapid technological developments in phage display of peptides and proteins have led to a plethora of applications directed towards immunology and antibody engineering. Many of the problems associated with the therapeutic use of Abs are being addressed by the application of these new techniques.

Production of transgenic mice with yeast artificial chromosomes

Techniques are now available that allow the transfer of intact yeast artificial chromosome (YAC) DNA into transgenic mice. Coupled with the ability to perform mutagenesis on YAC sequences by homologous recombination in yeast, they enable the analysis of large genes or multigenic loci in vivo. This system has been used to study the developmental regulation of the human beta-globin locus.

Functional transplant of megabase human immunoglobulin loci recapitulates human antibody response in mice

We constructed two megabase-sized YACs containing large contiguous fragments of the human heavy and kappa (kappa) light chain immunoglobulin (Ig) loci in nearly germline configuration, including approximately 66 VH and 32 V kappa genes. We introduced these YACs into Ig-inactivated mice and observed human antibody production which closely resembled that seen in humans in all respects, including gene rearrangement, assembly, and repertoire. Diverse Ig gene usage together with somatic hypermutation enables the mice to generate high affinity fully human antibodies to multiple antigens, including human proteins. Our results underscore the importance of the large Ig fragments with multiple V genes for restoration of a normal humoral immune response. These mice are likely to be a valuable tool for the generation of therapeutic antibodies.

Potential therapeutic use of antibodies directed towards HuIFN-gamma

IFN-gamma is an important regulator of immune responses and inflammation. Studies in animal models of inflammation, autoimmunity, cancer, transplant rejection and delayed-type hypersensitivity have indicated that administration of antibodies against IFN-gamma can prevent the occurrence of diseases or alleviate disease manifestations. Therefore, it is speculated that such antibodies may have therapeutical efficacy in human diseases. Since animal-derived antibodies are immunogenic in patients several strategies are being developed in order to reduce or abolish this human anti-mouse antibody (HAMA) response. In our laboratory, we have constructed a single-chain variable fragment (scFv) derived from a mouse antibody with neutralizing potential for human IFN-gamma. A scFv consists of only variable domains tethered together by a flexible linker. The scFv was demonstrated to neutralize the antiviral activity of HuIFN-gamma in vitro and therefore might be considered as a candidate for human therapy.

A method for high efficiency YAC lipofection into murine embryonic stem cells

We describe a modified protocol for introducing yeast artificial chromosomes (YACs) into murine embryonic stem (ES) cells by lipofection. With a decreased DNA:cell ratio, increased concentration of condensing agents and altered culture conditions, this protocol reduces the requirement for YAC DNA to a few micrograms, improves the recovery of neomycin-resistant ES colonies and increases the yield of clones containing both flanking vector markers and insert. These modifications enable generation of sufficient 'intact' transgenic clones for biological analysis with a single experiment.