Limiting dilution analysis of Epstein-Barr virus-induced immunoglobulin production

Exploring the native human antibody repertoire to create antiviral therapeutics

Native human antibodies are defined as those that arise naturally as the result of the functioning of an intact human immune system. The utility of native antibodies for the treatment of human viral diseases has been established through experience with hyperimmune human globulins. Native antibodies, as a class, differ in some respects from those obtained by recombinant library methods (phage or transgenic mouse) and possess distinct properties that may make them ideal therapeutics for human viral diseases. Methods for cloning native human antibodies have been beset by technical problems, yet many antibodies specific for viral antigens have been cloned. In the present review, we discuss native human antibodies and ongoing improvements in cloning methods that should facilitate the creation of novel, potent antiviral therapeutics obtained from the native human antibody repertoire.

Genetic and functional characterization of human pemphigus vulgaris monoclonal autoantibodies isolated by phage display

Pemphigus is a life-threatening blistering disorder of the skin and mucous membranes caused by pathogenic autoantibodies to desmosomal adhesion proteins desmoglein 3 (Dsg3) and Dsg1. Mechanisms of antibody pathogenicity are difficult to characterize using polyclonal patient sera. Using antibody phage display, we have isolated repertoires of human anti-Dsg mAbs as single-chain variable-region fragments (scFvs) from a patient with active mucocutaneous pemphigus vulgaris. ScFv mAbs demonstrated binding to Dsg3 or Dsg1 alone, or both Dsg3 and Dsg1. Inhibition ELISA showed that the epitopes defined by these scFvs are blocked by autoantibodies from multiple pemphigus patients. Injection of scFvs into neonatal mice identified 2 pathogenic scFvs that caused blisters histologically similar to those observed in pemphigus patients. Similarly, these 2 scFvs, but not others, induced cell sheet dissociation of cultured human keratinocytes, indicating that both pathogenic and nonpathogenic antibodies were isolated. Genetic analysis of these mAbs showed restricted patterns of heavy and light chain gene usage, which were distinct for scFvs with different desmoglein-binding specificities. Detailed characterization of these pemphigus mAbs should lead to a better understanding of the immunopathogenesis of disease and to more specifically targeted therapeutic approaches.

Generation of human Fab monoclonal antibodies against preS1 of hepatitis B virus using repertoire cloning

Human monoclonal antibodies (MAbs) have considerable potential in the prevention and treatment of many viral diseases. A combinatorial antibody library of heavy (Fd)- and light-chain genes derived from peripheral blood lymphocytes of a volunteer with high antibody titer to preS1 of HBV was constructed and expressed on the surface of filamentous phages. The library contained 7 x 10(9) independent clones. A phage antibody population from the third panning against preS1 was converted to one expressing soluble Fabs by removal of the g3 sequences from the pComb3 phagemid vector and subsequent transformation into E. coli TG1 cells. Screening of the library led to the identification of two clones, 3DW and 8GW, showing high reactivity toward preS1. The authenticity of the Fabs was confirmed by immunoblot analysis which yielded approximately 60 and approximately 30 kDa bands under nonreducing and reducing conditions, respectively. The soluble Fabs of 3DW and 8GW exhibited relative affinities of 6 x 10(5) and 8 x 10(6) M(-1), respectively. The sequencing results demonstrate that all Fd sequences belong to subgroup II and all light chain sequences belong to subgroup I. There are differences in CDR length and composition, especially in the FW3 and CDR3 regions of the heavy- and light-chain genes. These human Fab MAbs specific to preS1, generated from a combinatorial library, represent prototypes of passive immunotherapy candidates for viral hepatitis B.

Genetic and Immunological Properties of Phage-Displayed Human Anti-Rh(D) Antibodies: Implications for Rh(D) Epitope Topology

Understanding anti-Rh(D) antibodies on a molecular level would facilitate the genetic analysis of the human immune response to Rh(D), lead to the design of therapeutically useful reagents that modulate antibody binding, and provide relevant information regarding the structural organization of Rh(D) epitopes. Previously, we described a Fab/phage display-based method for producing a large array of anti-Rh(D) antibodies from the peripheral blood lymphocytes of a single alloimmunized donor. In the current study, we present a detailed analysis of 83 randomly selected clones. Sequence analysis showed the presence of 28 unique γ1 heavy chain and 41 unique light chain gene segments. These paired to produce 53 unique Fabs that had specificity for at least half of the major Rh(D) epitopes. Surprisingly, despite this diversity, only 4 closely related heavy chain germline genes were used (VH3-30, VH3-30.3, VH3-33, and VH3-21). Similarly, nearly all Vκ light chains (15/18) were derived from one germline gene (DPK9). λ light chains showed a more diverse VL gene usage, but all (23/23) used the identical Jλ2 gene. Several Fabs that differed in epitope specificity used identical heavy chains but different light chains. In particular, 2 such clones differed by only 3 residues, which resulted in a change from epD2 to epD3 specificity. These results suggest a model in which footprints of anti-Rh(D) antibodies are essentially identical to one another, and Rh(D) epitopes, as classically defined by panels of Rh(D) variant cells, are not discrete entities. Furthermore, these data imply that the epitope specificity of an anti-Rh(D) antibody can change during the course of somatic mutation. From a clinical perspective, this process, which we term epitope migration, has significance for the design of agents that modulate antibody production and for the creation of mimetics that block antibody binding in the settings of transfusion reactions and hemolytic disease of the newborn.

The human immune response to red blood cell antigens as revealed by repertoire cloning

A major goal of current immunologic research is to develop specific therapeutic strategies by which the enormous diversity in immune response can be enhanced, attenuated, or eliminated, depending on the particular disease process. For nearly a century, the human immune response to red blood cell antigens has served as a paradigm for understanding the pathophysiology of autoimmune disorders and alloimmune reactions to foreign cells and tissues. Recent developments in molecular biology have facilitated the expression of immune repertoires in the form of immunoglobulin Fab fragments on the surface of filamentous bacteriophage. Such approaches have provided powerful means for producing monoclonal antibodies for research, clinical, and therapeutic applications. Our laboratory has combined these techniques with novel cell-surface selection methods to isolate extraordinarily large arrays of human antibodies to the clinically relevant red blood cell Rh(D) antigen. Our results have provided a comprehensive genetic and serologic analysis of anit-Rh(D) antibodies within single alloimmunized individuals thereby offering new insights into the development of human immune repertoires.

Characterization of anti-sperm antibodies and their coding cDNA sequences by Epstein-Barr virus transformed B cell lines from lymphocytes of infertile women possessing anti-sperm antibodies

Epstein-Barr virus (EBV)-transformed B cell lines that produce human antisperm antibodies were established using peripheral blood lymphocytes (PBLs) from infertile women with sperm immobilizing antibodies in their sera. We obtained three stable cell populations (designated B1, B2, D5) of transformed PBLs originating from three different patients. They produced IgM sperm-reacting antibodies directed against the tail of live, methanol-fixed and NaIO4-treated human spermatozoa. The established antisperm antibodies recognized noncarbohydrate sperm membrane antigens with different specificity and distribution in the male reproductive system. Antisperm antibody-B2 corresponding antigen appears to be specific for the male reproductive system. This antigen is excreted from the epithelial cells of the ductus epididymidis and bound to the spermatozoa in the lumen of the ductus. Antisperm antibodies B1 and D5 corresponding antigens were expressed on the spermatozoa in the seminiferous tubules and were common to the secretions of the ductus epididymidis, prostate and some other somatic organs. The cDNA of the immunoglobulin heavy chain genes were analyzed by reverse transcription polymerase chain reaction (RT-PCR) using RNA extracted from these clones. The immunoglobulin heavy chain cDNA sequences of these antisperm antibodies showed extremely high homology to previously reported immunoglobulin germline DNA sequences, implying that these antisperm antibodies might be natural autoantibodies rather than antibodies stimulated by external antigen.

Factor(s) required by EBV transformed lymphocytes to grow under limiting dilution conditions

IL-6 was demonstrated to promote growth of EBV transformed lymphocytes. However IL-6 was ineffective at promoting growth of EBV transformed lymphocytes cultured at the single cell level under limiting dilution conditions. On the contrary, HECS, which is known to contain IL-6, supported very efficiently the growth of 1-2 EBV transformed cells. When IL-6 was removed from HECS, by using specific antibodies, no reduction in HECS activity was observed, indicating that probably more than one growth factor is required to support the growth of EBV transformed cells cultured at very low cell numbers in the absence of feeder cells.

Effect of cytokines on proliferation of Epstein Barr virus-transformed B lymphocytes

Plating efficiencies of EBV transformed human B cells seeded in single cell cultures are far lower (less than 1%) than observed in T cell cloning experiments. This report describes the stimulatory effect of several crude as well as recombinant growth factors on proliferation of EBV transformed B cells measured by [3H]thymidine uptake. Supernatant of LPS activated monocytes (HSF) and recombinant interleukin 4 (rIL-4), but not recombinant IL-1 beta, IL-2, IL-6, TNF alpha, GM-CSF, and interferon gamma increased [3H]thymidine incorporation. The combination of HSF and rIL-4 was found to be synergistic on B cell proliferation. Plating efficiency of EBV transformed B cells at limiting dilution was improved by HSF, but not by the combination of HSF and rIL-4.

Human monoclonal antibodies that protect mice against challenge with Pseudomonas aeruginosa

Lymphocytes from healthy volunteers and from cystic fibrosis patients were transformed with Epstein-Barr virus and cultured at a limiting dilution to generate lymphoblastoid cell lines that secreted human monoclonal antibodies specific for lipopolysaccharide (LPS) from Pseudomonas aeruginosa. Three cell lines (RM5, FDD7, and 11F9) produced immunoglobulin M (IgM) antibody species that reacted specifically with P. aeruginosa Fisher immunotypes 2, 4, and 5, respectively, and with LPS extracted from these immunotypes. A fourth cell line (9H10) produced a single IgM antibody species that recognized P. aeruginosa immunotypes 3, 6, and 7 and LPS extracted from them. Monoclonal antibodies secreted by cell lines RM5, FDD7, and 11F9 protected neutropenic mice prophylactically against challenge with P. aeruginosa immunotypes 2, 4, and 5, and those secreted by 9H10 protected against P. aeruginosa immunotypes 3 and 6 but did not protect against immunotype 7. In vivo experiments indicated that antibodies protected mice against infection by increasing the rate of bacterial clearance.

EBV transformation and microfusion as the potential source of human monoclonal antisperm antibodies

Peripheral blood lymphocytes were obtained from vasectomized men with high serum titers of antisperm antibodies. An Epstein-Barr virus (EBV) transformation was performed either with B cells or mononuclear leukocytes. The effect of feeder cells (irradiated umbilical cord blood lymphocytes), cyclosporin A, and in vitro stimulation of lymphocytes with sperm extract on EBV transformation was evaluated. Antibody-producing cells were screened for specificity against human sperm by an enzyme-linked immunosorption assay (ELISA) one to six weeks after transformation. Using B cells or leukocyte mononuclear cells, we found that the percentage of wells containing antibody reactive against human sperm was greatest two weeks after transformation (range 3% to 7.5% positive wells). To increase and maintain antibody synthesis by these transformed cells, microfusions were performed in those wells positive for antisperm antibody using the UC 729-6 lymphoblastoid cell partner. Then resultant hybridomas were expanded, subcloned, and preliminarily characterized.

Epstein-Barr virus-induced IgE production in limiting dilution cultures of normal human B cells

The induction of in vitro IgE production in human B cells from normal, nonatopic donors has been difficult and somewhat controversial. We report that IgE production is consistently observed in limiting dilution cultures of in vitro Epstein-Barr virus (EBV)-infected normal human B lymphocytes. The frequency of IgE-committed, EBV-responsive cells ranged from 1/810 to 1/10 000 B lymphocytes, and it was similar in peripheral (blood, tonsil) and central (bone marrow) tissue sites. Poisson distribution analysis of these limiting dilution cultures suggested that IgE-committed B cells comprise 0.1-1% of all EBV-responsive B lymphocytes.

Senescence of a human lymphoblastoid clone producing anti-Rhesus(D)

The exploitation of Epstein-Barr virus transformation to generate human lymphoblastoid clones (LCL) producing antibody of predefined specificity has proved highly inefficient. Observations reported here on a cloned LCL producing anti-Rhesus(D) may provide an explanation for the low success rate. Over a few months this clone manifested a progressive loss of capacity to maintain growth in culture. Evidence consistent with terminal differentiation to a cell with the properties of a nonproliferating plasma cell was obtained. These late cells differed from those in the earlier actively cycling phase in that they were no longer able to respond to autostimulatory growth factors although they continued to produce them. This irreversible senescence leading to the death of the clone may be a common feature of virally transformed B cells and this would explain many of the difficulties encountered on this route to the production of human monoclonal antibodies.