Xenohybridization of Epstein-Barr virus-transformed cells for the production of human monoclonal antibodies

Quantitative analysis of IgA-subclass antibodies against tetanus toxoid

Sera were analysed for levels of IgA- and IgG-class and IgA-subclass antibodies against tetanus toxoid and synthesized, tetanus-toxoid, beta-chain peptides. Forty-five peptides, deduced from the amino-acid sequence of the tetanus-toxoid beta-chain, were synthesized, in order to analyse epitope-binding of antibodies. Monoclonal, human, anti-tetanus antibodies were used to evaluate the synthesized peptides. Five synthesized peptides, bound by high, medium or low levels of IgA antibodies, were selected for the quantification of IgA1 and IgA2 antibodies. A set of chimeric, IgA-subclass antibodies with NP-specificity were used to quantify the antigen-specific IgA-subclass antibodies in a novel assay. Antibodies against the synthesized peptides were predominantly of IgA1 subclass.

ELISA procedures for the measurement of IgG subclass antibodies to bacterial antigens

We have developed enzyme-linked immunosorbent assays (ELISA) of IgG subclass antibodies against whole bacteria and bacterial antigens using enzyme-labelled mouse monoclonal antibodies. The properties of different anti-subclass antibodies were compared. In sera from 18 healthy adults we measured the IgG subclass distribution of specific antibodies against Staphylococcus aureus and Haemophilus influenzae b and against distinct bacterial components: pneumococcal capsular polysaccharides, dextran and tetanus toxoid. We found that antibodies against protein (tetanus toxoid) were mainly IgG1, with some contribution of IgG4 and IgG2. Antibodies against polysaccharides (pneumococcal PS and dextran) and whole bacteria were restricted mainly to IgG1 and IgG2.

Productive ascites growth of heterohybridomas between Epstein-Barr virus-transformed human B cells and murine P3X63Ag8.653 myeloma cells

Heterohybridomas between Epstein-Barr virus-transformed human B cells and murine myeloma P3X63Ag8.653 cells were found to produce sizable quantities of human monoclonal antibodies in nude mouse ascites. Mice injected intraperitoneally with two of such heterohybridomas yielded several milliters of ascites fluid which contained nearly 100-fold higher anti-platelet activities than those in routine culture supernatants.

Stability of specific immunoglobulin secretion by EBV-transformed lymphoblastoid cells and human-murine heterohybridomas

We have examined variables leading to the generation of stable, antigen-specific, human immunoglobulin-secreting cell lines. Peripheral blood B lymphocytes enriched for Thomsen-Friedenreich antigen (T antigen)-specific cells were transformed with Epstein-Barr virus. Lymphoblastoid cells (LC) reactive with T antigen were either expanded without cloning or cloned at limiting dilution and then fused with murine 653 cells. Uncloned LCs from three transformations secreting polyclonal anti-T antibody (7-18 micrograms/ml/10(6) cells/24 hr total immunoglobulin) were subcultured at 100 cells/well, and T antigen-reactive cultures pooled. These cultures quickly lost specific antibody secretion, presumably due to overgrowth by clones of unknown specificity. T antigen-reactive LCs that were cloned three times at limiting dilution secreted 0.2 - 6.1 micrograms/ml/10(6) cells/24 hr but died or stopped secreting specific immunoglobulin after 77 to 155 days in culture. Pooling T antigen-reactive clones after each cloning step did not increase the long term stability compared to unpooled clones (p = 0.2). Fusions between cloned LCs and 653 cells failed to yield viable hybrids in nine of ten attempts with seven different LC lines. In contrast, fusion of uncloned LCs and 653 cells resulted in the generation of viable immunoglobulin-secreting heterohybrids in 22 of 24 fusions. The heterohybridomas produced from fusion of uncloned T antigen-reactive cultures with 653 cells secreted significantly more antibody (frequency of cell lines secreting greater than 2 micrograms/ml/10(6) cells/24 hr, p less than 0.01) and higher titers of antibody (frequency of cell lines secreting greater than four hemagglutination units of T antigen-specific antibody, p less than 0.03) than cloned lymphoblastoid cells. The hybrids maintained specific immunoglobulin secretion for longer in culture than either cloned or uncloned lymphoblastoid cell lines (p less than 0.001).

The Fc valency of an immune complex is the decisive factor for binding to low-affinity Fc gamma receptors

Tetanus toxoid (TT) was complexed with two human monoclonal antibodies. The antibodies recognized different, nonrepeating epitopes. The complexes formed were characterized by gel filtration and isokinetic sucrose density gradient centrifugation. It was found that in antigenic excess the separate antibodies formed a complex of one antibody molecule and two TT molecules [IgG1-(TT)2 and IgG3-(TT)2]. In cases where equal amounts of TT and both antibodies were mixed, a dimeric complex [IgG1-(TT)2-IgG3] was formed. The binding of these immune complexes to human neutrophils and eosinophils was studied. Whereas the immune complexes containing one antibody did not bind to either cell type, the two-antibody complex bound to both. This indicates that not the sterical change in the Fc part of an antibody molecule after binding an antigen, but the Fc valency of an immune complex is the decisive factor in Fc receptor interaction with neutrophilic and eosinophilic granulocytes.

Inhibition, by vinca alkaloids and colchicine, of antigenic modulation induced by anti-CD19 monoclonal antibodies

Several clinical trials have been reported in which monoclonal antibodies (McAb) were used for therapy of lymphoid malignancies. Such trials have shown that infusion of McAb recognizing lymphoid antigens, is well-tolerated, and leads to the coating of tumor cells and tumor regression in some patients. However, the tumoricidal capacity of a McAb is hampered by the presence of circulating free antigen, antigenic modulation, development of human anti-mouse antibodies, emergence of antigen-negative variants of tumor cells and the inadequacy of host-effector cell mechanisms. We have studied the antigenic modulation induced by immunoglobulin (Ig) heavy chain switch variants of anti-CD19 McAb. Modulation of CD19 molecules was not related to the IgG subclass of the McAb. Immunofluorescence studies on the Burkitt tumor cell line Daudi showed that CD19 molecules are internalized after incubation by anti-CD19 McAb. Next, the effect of cytoskeleton inhibitors on antigenic modulation was studied. We found that antigenic modulation on Daudi cells and on an Epstein-Barr virus-transformed B-cell line was completely inhibited by vinca alkaloids (VA) or by colchicine. Interestingly, antigenic modulation of tumor cells from a VA-resistant patient, was not inhibited by VA or colchicine. These findings provide information for the rational design of more effective clinical trials with McAb.

Production of mouse monoclonal antibodies for the analysis of idiotypes in serum of patients with chronic lymphatic leukaemia

In this report a simple procedure for the production of murine monoclonal antibodies (MoAb) against the idiotype of malignant B cells is described. Mice were immunized with lymphoid cells from patients with B-cell chronic lymphocytic leukaemia (B-CLL). After fusion of the spleen cells, hybridoma supernatants were screened for anti-idiotypic MoAb in ELISA with immunoglobulins obtained from tumour-cell lysates, xenohybridomas and patients' sera. The anti-idiotypic MoAb were used to study tumour cells and serum immunoglobulins (Ig) from four different patients with B-CLL. It was found that the serum IgM and IgD in one patient shared the same idiotype. Evidence is presented that IgG-secreting cell populations are not restricted to lambda-Ig-light chain-expressing B-CLL cells. With the help of anti-idiotype MoAb accurate measurements of total and idiotype-positive serum immunoglobulin levels during chemotherapy were possible.

Subclass restriction pattern of antigen-specific antibodies in donors with defective expression of IgG or IgA subclass heavy chain constant region genes

We have developed a method for the measurement of the IgG and IgA subclass distribution of antigen-specific human antibodies. The controls for the specificity of the assay include the use of a number of monoclonal human antibodies and sera from individuals with deletions of particular immunoglobulin heavy chain constant region genes. The system was used to determine the shift in immunoglobulin subclass patterns of specific antibodies against a variety of protein and polysaccharide antigens in individuals with a regulatory deficiency of a given IgG or IgA subclass. Normally, the pattern is quite distinct and antibodies against protein antigens are mainly of the IgG1 subclass, whereas antibodies against polysaccharide antigens are mainly of the IgG2 subclass. The results on serum from an IgG1 deficient donor suggested that IgG3 and IgG4 appear to compensate for a lack of IgG1, whereas isolated deficiencies of IgG3, IgG4, or IgA2 do not markedly influence the expected distribution of specific antibodies. In IgG2-deficient individuals a more complex pattern was observed where antibodies against protein antigens were retained, whereas levels of antibodies against polysaccharide antigens could vary markedly between donors, which appeared to be dependent on whether the IgG2 deficiency was an isolated defect or combined with IgG4/IgA deficiency. However, all the IgG2-deficient donors had a skewed pattern of anti-polysaccharide antibodies with a shift to IgG1 to IgG3.

Requirements for the establishment of heterohybridomas secreting monoclonal human antibody to rhesus (D) blood group antigen

Stable cell lines producing monoclonal human antibodies can be derived by fusion of Epstein-Barr virus-transformed peripheral blood B lymphocytes (LCL) with the mouse myeloma line X63-Ag8.653. One major limitation to this approach is the establishment of LCL cultures with sufficient cells secreting the specific antibody. In this study on the production of anti-D(Rh) antibodies, the kinetics of the appearance of specific EBV-transformable precursors in the circulation was followed after secondary immunization, and the optimum time for obtaining B cells for the establishment of suitable LCLs was found to be during the period 2-4 weeks post boost. During this period the probability of obtaining LCLs suitable for fusion is significantly higher than from blood samples collected randomly. From these high-titre LCLs the success rate for the fusion process was high. The specific EBV target cells are presumably memory cells produced after the peak of the antibody response and having only a transient appearance in the circulation.

The efficient production of stable, human monoclonal antibody-secreting hybridomas from EBV-transformed lymphocytes using the mouse myeloma X63-Ag8.653 as a fusion partner

The mouse myeloma X63-Ag8.653 was fused to peripheral blood lymphocytes (PBL) from apparently healthy individuals, autoimmune patients and volunteers immunised with Rhesus (D) positive erythrocytes. Fusions were performed with or without prior transformation of PBL with Epstein-Barr virus (EBV). Using untransformed PBL, under the best conditions a mean fusion frequency of 8.4 X 10(-6) was obtained, with 22% of the resulting hybridomas secreting human immunoglobulin. Fusions with EBV-transformed cells gave fusion frequencies of 1.0 X 10(-4), with 85-90% of hybridomas secreting human immunoglobulin. The heterohybridomas formed in both cases cloned efficiently and had doubling times of 24-30 h. The heterohybridomas secreted human IgM, IgG and IgA of both kappa and lambda isotypes and culture supernatants contained up to 50 micrograms ml-1 of human immunoglobulin. Mouse immunoglobulin was not detected in the culture supernatants. 28 hybrids were selected for vigorous growth and antibody production by repeated cloning. Immunoglobulin synthesis was stabilised in 26 of these hybridomas after two or three cloning steps. The heterohybridomas have been successfully grown in large volumes for periods up to 15 months. It is concluded that the mouse myeloma X63-Ag8.653 is a suitable fusion partner with EBV-transformed B cells in the efficient production of human monoclonal antibodies.