Monoclonal lupus autoantibody secretion by human-human hybridomas. Selection of hybrids by conventional and novel techniques

Lupus-derived human monoclonal IgM anti-DNA antibody displays monospecificity, high affinity and private idiotype specificity

A human monoclonal IgM k anti-DNA antibody, designated 2F7, was prepared by somatic hybridization of peripheral blood lymphocytes from a lupus patient with a human-mouse heterohybridoma cell line, K6H6/B5. 2F7 was tested for its antigen binding and idiotypic specificity by direct binding and inhibition enzyme-linked immunosorbent assays. 2F7 had a high binding activity to single-stranded DNA (ssDNA) but not to double-stranded DNA. It cross-reacted with single-stranded homopolymers with pyrimidine bases and double-stranded polynucleotides containing those homopolymers, suggesting that 2F7 recognizes a conformational determinant made up of both deoxyribose-phosphate backbone and specific nucleotide base. 2F7 did not cross-react with eight structurally unrelated self-antigens. Dissociation constant (Kd) of 2F7 for sonicated ssDNA was approximately 4.5 x 10(-9) M, indicating its relatively high affinity. Idiotypic characterization with rabbit anti-idiotype raised against 2F7 suggested that 2F7 expressed an idiotype at or near its antigen-binding sites that was not detected in sera from 20 unrelated lupus patients, 10 lupus family members and 10 normal individuals. These results suggest that certain IgM class anti-DNA antibodies in human systemic lupus erythematosus may arise by antigen stimulation and not simply by polyclonal B-cell activation.

Production of a polyspecific human monoclonal antibody reacting with an epidermal antigen

A clone of cells secreting an antibody to an epidermal antigen was generated from a patient with a blistering skin lesion. Although produced by fusion of human lymphocytes to a HAT-sensitive myeloma, this clone of cells did not have characteristics of a hybridoma. A true hybridoma was produced by fusion of this clone to a HATr/ouabain(r) myeloma line. The IgM antibody secreted by this clone reacted with the intercellular region of the epidermis of normal human skin in a manner similar to pemphigus autoantibodies. In addition, in normal human kidney the antibody bound to glomeruli and tubules. It also reacted with an antigen present in the cytoplasm of a wide variety of cell lines including epithelial, lymphoid and myeloid types. No reaction was found with the surface of any of the cell lines, nor with DNA or phospholipid antigens. This monoclonal antibody may define an autoantibody specificity which mediates some autoimmune skin lesions. Its polyspecificity is reminiscent of some other human hybridoma autoantibodies, and its reaction with components of the kidney suggests an alternative pathology for renal disease in such patients.

Description and partial characterization of a nucleolar RNA-associated autoantigen defined by a human monoclonal antibody

B lymphocytes from a patient with systemic lupus erythematosus (SLE) and several circulating autoantibodies (including antinucleolar antibodies) were immortalized by fusion with a hypoxanthine/guanine phosphoribosyl transferase (HGPRT)-deficient human B cell line. Multiple human monoclonal antibodies (mAb) were obtained which, in solid-phase enzyme immunoassay, were reactive with DNA. One mAb was of special interest because it reacted strongly with both single-stranded DNA and an extractable nuclear antigen found in rabbit thymus extract (RTE). In an immunofluorescent assay using fixed human cells, the latter mAb also bound predominantly to cell nucleoli. A combination of enzyme digestion and metabolic inhibitor studies of the target cells in this immunofluorescent assay suggested that the antigen(s) bound by the mAb was an RNA-associated protein or a ribonucleoprotein that is distinct from intact RNA polymerase I and not associated with the transcriptional units of the nucleolus. In other experiments, using fractions of RTE isolated by ion-exchange chromatography, the antigens bound by the mAb were shown to be highly negatively charged molecules. Immunoprecipitation and SDS-PAGE analyses of labeled cell extracts bound by the mAb revealed a doublet of 17 and 18 kD. Since the original patient's serum autoantibodies also bound to both an RNase-sensitive, acidic, extractable nuclear antigen and to nucleoli, and immunoprecipitated proteins of similar molecular masses in SDS-PAGE, it appears that the described mAb is a product of an immortalized autoantibody-producing B cell clone from the SLE patient's peripheral blood. This mAb probably defines a novel RNA-associated autoantigen residing predominantly in the nucleolus or, less likely, a variant of either RNA polymerase I or the ribosomal autoantigens (P proteins).

A study of human-human hybridomas from patients with autoimmune thyroid disease

Human-human B-cell hybridomas were established using peripheral blood lymphocytes from patients with autoimmune thyroiditis and Graves' disease. Peripheral mononuclear cells (PMC), with or without mitogen prestimulation, were fused with HGPRT-negative human myeloma cell lines (Gm4672 and GM0462) using 44% polyethylene glycol. Developing hybridomas were screened by enzyme-linked immunosorbent assays (ELISAs) for human IgG and IgM and antibodies to human thyroglobulin (hTg) and microsomal antigen (M-Ag). A 125I-TSH binding inhibition assay was utilized for detecting antibodies to TSH receptor (TSH-R) protein. Hybridoma formation was observed only after prior mitogen stimulation of PMC. The amount of antibody secreted by the human-human hybridomas was highly variable (10 ng-100 micrograms/ml IgG/IgM). Nine and six-tenths percent of the hybrids secreted anti-hTg and 8.4% secreted anti-M-Ag. A 5% cloning efficiency was achieved, with detection of specific thyroid autoantibody secretion in one-third of the clones derived from positive hybridomas. Immunoglobulin secretion decreased with time and long-term stable clones were not achieved. Thyroid monoclonal autoantibodies to hTg, M-Ag, and TSH-R (IgG and IgM) detected during these studies were of a low affinity. In addition, antibodies were identified which exhibited marked specificity crossover between hTg, M-Ag, and nonthyroid antigens, suggesting the presence of recurrent epitopes. Such observations may help explain the multiplicity of thyroid autoantibodies in human thyroid disease and indicate a common defect in immunoregulation. We suggest that cross-reacting epitopes may be important in the derivation of thyroid-specific B-cell clones.

A method for the isolation of autoreactive B cells

A technique was developed to isolate a population of autoreactive B cells from both normal and autoimmune-prone mice. Modifications of the procedure of Haas and Layton (1975) permitted coupling the nucleoside guanosine (GU) to gelatin and subsequently coating this matrix onto tissue culture dishes. After incubation on GU-gelatin, B lymphocytes specific for GU could be isolated. Specificity was demonstrated by rosetting techniques as well as by inhibition of binding to GU-gelatin by GU-containing conjugates. Isolated GU+ B cells were triggerable with GU-Brucella abortus antigen as well as LPS, to secrete anti-GU antibody in a direct plaque assay. The DNA-binding activity of the antibody was assessed using hapten inhibition of anti-GU PFC. Both native (N) DNA as well as denatured (D) DNA inhibited plaque formation. DNA-binding ability of secreted anti-GU antibody was also demonstrated by plaque formation using D-DNA-coated erythrocytes as target cells. Isolated GU+ B cells that are triggerable with antigen will be important in investigating growth, triggering and tolerance defects in a specific population of autoreactive B cells. In addition autoreactive B cells can now be compared to nonautoreactive hapten-specific lymphocytes. These properties as well as others can now be studied in controlled systems free from the regulatory effects of murine T or accessory cells.

Optimal strategies for developing human-human monoclonal antibodies

Human monoclonal antibodies are desirable, especially as therapeutic agents, but the best means of producing them is still a matter of investigation. It is clear that human antibodies of predicted specificity from patients with autoimmune disease can be derived, and this may help unlock some of the mysteries of these illnesses. Human monoclonal antibodies against tumor-specific antigens for use in in vivo diagnosis and therapy remain desirable goals. Problems involved in their routine development include the lack of available, adequately immunized, and differentiated lymphocytes and the nature and paucity of the available human "myeloma" cell lines. These lines have been compared now by a number of authors who have reached similar conclusions. Our study directly compared the greatest number of cell lines and found UC729-6 and HF2 to be the best; on the other hand, our success in developing IgG-secreting hybridomas from U-266, using hyperimmunized lymphocytes, suggests that this line may only be capable of secretion with the more differentiated cell, the human equivalent of those hyperimmunized murine spleens. Hence both sides of the fusion equation must be made optimal. Two new approaches to circumvent this problem involve the use of either a human-murine myeloma chimera as the parental myeloma line or, more recently, genetic engineering techniques to substitute human constant regions for the murine while retaining the murine hypervariable region, preserving the binding specificity of the murine antibody.

Antibodies to DNA

Antibodies that recognize specific conformational variations of DNA structure provide sensitive reagents for testing the extent to which such conformational heterogeneity occurs in nature. A most dramatic recent example has been the development and application of antibodies to left-handed Z-DNA. They provided the first identification of Z-DNA in fixed nuclei and chromosomes, and of DNA sequences that form Z-DNA under the influence of supercoiling. Antibodies have also been induced by chemically modified DNA and by synthetic polydeoxyribonucleotides that differ from the average B-DNA structure. These antibodies recognize only the features that differ from native DNA. In most experiments, native DNA itself is not immunogenic. Antibodies that do react with native DNA occur in sera of patients with autoimmune disease, but even monoclonal anti-DNA autoantibodies usually react with other polynucleotides as well. Anti-DNA antibodies, especially those of monoclonal origin, provide a model for the study of protein-nucleic acid recognition.

Monoclonal human anti-DNA antibodies from EB virus-transformed lymphocytes of systemic lupus erythematosus (SLE) patients

Sixteen monoclonal human anti-DNA antibodies were obtained from Epstein-Barr virus-transformed lymphoblastoid cells of patients with systemic lupus erythematosus (SLE) and were studied in terms of antigenic specificity. All of the antibodies showed polyspecificity to polynucleotides. Among them, some antibodies had a specificity to single-stranded (ss) DNA. Especially, O-8 antibodies showed a preference for polynucleotides with pyrimidine bases. The binding specificity of the antibody was also studied using different sizes of dT oligomers in order to assess the size of the epitope. It was revealed that oligonucleotides with a size of more than 25-30 nucleotides are required for inhibition of the antibody to ss-DNA. Other studies also demonstrated that anti-ss-DNA (O-8) antibody and anti-double-stranded (ds) DNA (NE-28) antibody bound to different combining sites in the same polynucleotides, poly(dT). These results suggest that some anti-ss-DNA antibodies are directed to the conformational structure related to the base sequence and that nucleic acids, therefore, might be responsible for the possible immunogenic stimulus causing the anti-DNA immune response. We also indicate that this type of antibody would be popular among serum anti-DNA antibodies in SLE.