Production of heterohybridomas secreting autoreactive and polyreactive human monoclonal antibodies

Evidence for multiple shared antigenic determinants within Ro60 and other lupus-related ribonucleoprotein autoantigens in human autoimmune responses

Ab responses directed against several ribonucleoprotein (RNP) Ags are a characteristic feature of systemic lupus erythematosus (SLE). Previous work in our laboratory using mouse model systems had revealed that both epitope spreading and inherent cross-reactivity between ribonucleoproteins contributes to the observed multiple specificities in autoimmune sera. We have now extended these studies to human autoimmune responses. Using purified polyclonal and mAbs derived from SLE patients, cross-reactivity between Ro60 and SmD was demonstrated. The cross-reactive epitope was mapped to nonhomologous regions on Ro60(481-505) and SmD(88-102). Five mAbs specifically recognized apoptotic cells, demonstrated variable levels of cross-reactivity toward other nonhomologous ribonucleoprotein targets and bound multiple, nonoverlapping and nonhomologous epitopes on Ro60. Our study demonstrates that cross-reactivity between frequently targeted autoantigens is an important aspect of human systemic autoimmune responses. The presence of multiple cross-reactive epitopes on Ro60 might be important for the generation of anti-Ro60 Ab in SLE patients and in normal individuals displaying no evidence of clinical disease.

Molecular structure of eight human autoreactive monoclonal antibodies

The heavy (H) and light (L) chain V-region sequences of eight human autoreactive immunoglobulin M (IgM) monoclonal antibodies (mAbs: BY-4, BY-7, BY-12, IRM-3, IRM-7, IRM-8, IRM-10 and CDC-1) were determined at the cDNA level. All VH and VL families were identified. Four different VH families were represented, VH3 being the most common as five of the mAbs (BY-7, BY-12, IRM-3, IRM-8 and CDC-1) used genetic elements of this family, whereas VH1, VH2 and VH4 were only present in IRM-7, BY-4 and IRM-10, respectively. BY-4, BY-7, BY-12, IRM-7 and IRM-10 reacted with a variety of self as well as non-self antigens, thus exhibiting polyreactive behaviour. Comparison of the gene segments utilized by these mAbs with their germline counterparts revealed that the gene segments were close to germline configuration. The length of H-CDR3 was found to be relatively long (27-60 nucleotides) among the polyreactive mAbs and the presence of Tyr and Trp residues in this region seems to be of vital importance for polyreactivity. We have analysed the utilization of gene elements and the presence of amino acid residues in regions particularly important for antigen binding, such as CDR. Common molecular features relating to the function of the mAbs are discussed.

Identification of cation-independent mannose 6-phosphate receptor/insulin-like growth factor type-2 receptor as a novel target of autoantibodies

Two human monoclonal autoantibodies, B-33 and B-24, were generated from the B cells of a patient with scleroderma. Both monoclonal antibodies (mAbs) were composed of mu and lambda chains, and recognized cytoplasmic vesicular structures by indirect immunofluorescence on Hep-2 cell line slides, although mAb B-24 showed an additional diffuse cytoplasmic staining pattern. By Western blot, mAb B-24 exhibited a polyreactive-like binding pattern, whereas mAb B-33 failed to recognize any electroblotted Hep-2 antigen. The polyreactive versus monospecific behaviour of mAbs B-24 and B-33 was further confirmed by enzyme-linked immunosorbent assay (ELISA) with a variety of foreign and autoantigens. The N-terminal sequence of a protein band isolated by affinity chromatography with mAb B-33 was identical to that of cation-independent mannose 6-phosphate receptor (CI-MPR), also known as the insulin-like growth factor type-2 receptor (IGF-2R). Immunofluorescence experiments on Hep-2 cell line slides demonstrated a striking co-localization between the staining pattern exhibited by these mAbs and the pattern obtained using a goat anti-CI-MPR serum, indicating the recognition by B-24 and B-33 of a structure located predominantly in late endosomes. Sequence analysis of the V-region gene segments of B-33 and B-24 showed both to be identical, except for the existence of a point mutation in B-33 located in the H-complementarity-determining region 3 (H-CDR3) (position 100D), which produces a non-conservative replacement of Gly by Ser. This single replacement appears to be responsible for the dramatic change in reactivity of human mAb B-33. The data shown here provide new evidence of the critical role played by the H-CDR3 region in distinguishing a polyspecific from a monospecific antibody. A population study demonstrated the existence of immunoglobulin G (IgG) reactivity against CI-MPR/IGF-2R in serum specimens from five individuals with different pathological conditions, thus indicating that this molecule is a potential target for the human autoimmune response.

Lack of suppressive antibody activity in sera from patients with active-phase autoimmune diseases

To investigate the presence of a suppressive antibody activity in sera from patients with autoimmune diseases, the IgG autoreactivity in whole serum was compared to that of the IgG fraction purified by affinity chromatography on protein G-sepharose. Competitive inhibition assays on the binding to histone, dsDNA, RNP and thyroglobulin of the purified IgG fraction by the autologous IgM present in serum without IgG and depleted of <100 kD components (named IgM fraction) were also performed. The IgG reactivity to the autoantigens tested was considerably increased in the IgG fraction than in the whole serum drawn from a healthy control and from three SLE patients in an inactive-phase of disease. Addition of the IgM fraction to the autologous purified IgG resulted in a dose-dependent inhibition of IgG binding to the autoantigens tested. However, no differences were observed between the autoreactivity of the IgG in whole serum and that of the purified IgG fraction from active-phase SLE patients, or from two patients with autoimmune thyroiditis, and the autologous IgM fractions did not inhibit significantly binding to the autoantigens under study of the purified IgG fraction. Our findings support the concept that the IgG autoreactivity in physiological conditions is regulated by idiotypic interactions between IgG and IgM, and suggest that this regulation is broken in the active phase of autoimmune diseases and that clinical remission from SLE could be associated with the restoration of this control mechanism. Additionally, qualitative differences, such as polyreactivity or change of idiotype in the autoreactive IgG fraction from active-phase disease might contribute to escape of regulation.

The frequent expansion of a subpopulation of B cells that express RF-associated cross-reactive idiotypes: evidence from analysis of a panel autoreactive monoclonal antibodies

Preferential expression of VH gene segments is evident within the adult human primary B-cell repertoire. The repertoire may be influenced by genetic factors, e.g. VH gene segment polymorphisms, or in a temporal manner due to the exposure to environmental antigens. The molecular characteristics of 15 autoreactive human monoclonal antibodies (MoAbs) are reported. All antibodies were of the IgM isotype, and 12 of the 15 were polyreactive and included rheumatoid factor type specificity, i.e. reactivity with IgG. Nine of the 15 MoAbs are products of VH3 gene segments, as evidenced by staphylococcal protein A binding; four of these express the cross-reactive idiotype recognized by the mouse MoAb 3H7 and are thus products of the VH26 gene segment. One of the five remaining VH3 gene products expresses the cross-reactive idiotypes recognized by the mouse MoAbs B6 and D12. V-gene family usage, determined by polymerase chain reaction (PCR) amplification of cDNA and further hybridization with family-specific oligonucleotide probes, confirmed the cross-reactive idiotype studies and showed that only VH3-gene-encoded proteins bound staphylococcal protein A. Five of the six non-VH3 gene segment products express the cross-reactive idiotype recognized by the mouse MoAb LC1 and could be assumed to be products of the VH4.21 gene segment; however, one human MoAb is shown to be the product of a VH2 gene segment. This is interesting because it turns LC1 from being an anti-cross-reactive idiotype antibody into an anticlan reagent.

Human monoclonal antibody against colon cancer

The purpose of the study was to produce human monoclonal antibodies (hMcAb) against human colon cancer for use in radioimmunoimaging. Human-mouse heterohybridomas were developed by fusing SHM-D33 mouse-human hybrid heteromyeloma cells with human lymphocytes from colon cancer tumor-draining lymph nodes. The hybridomas capable of secreting human monoclonal antibodies were screened by using human colon cancer cell lines and pathological biopsies with ELISA and immunohistochemical methods. hMcAb clone H11 was selected for a large-scale antibody production, which was purified from mouse ascites. Biodistribution study demonstrated that specific uptake of 125I-hMcAb H11 by human colon cancer xenografts was significantly higher than by normal tissues. Radioimmunoimaging of human colon cancer xenografts exhibited distinct tumor visualization during the period of 72-96 hr after intraperitoneal injection of 125I-hMcAb H11. The development of human monoclonal antibodies such as hMcAb H11 may be useful for radioimmunodetection and therapy of colon cancer.

B-cell epitopes on the hepatitis C virus nucleocapsid protein determined by human monospecific antibodies

Four monospecific antibodies against the hepatitis C virus nucleocapsid protein, which was expressed by recombinant baculovirus, were obtained by Epstein-Barr virus transformation of B cells from three patients with chronic hepatitis C virus infection. One of these antibodies was IgG and the other three were IgM. Their specificities were characterized initially by enzyme-linked immunosorbent assay and immunoblotting against hepatitis C virus proteins expressed by six recombinant baculoviruses with different hepatitis C virus sequence insertions. These specificities were confirmed, and their epitopes were more precisely determined with a series of overlapping decapeptides made by solid-phase pin technology. Two antibodies (1F4 and 2G6) reacted with the same peptides located near the amino(N)-terminus of nucleocapsid protein (amino acids 33-50). The third antibody (3B5) recognized the peptide consisting of amino acids 133-142, and the fourth antibody (3B9) was mapped to the carboxy(C)-terminus and reacted with a peptide consisting of amino acids 165-174. This epitope has not previously been reported. Two antibodies, 1F4 and 3B9, which are specific to the N-terminus and C-terminus of nucleocapsid protein, respectively, have been stably produced for more than 6 mo and are being subcloned to establish monoclonality. These antibodies should be useful reagents for the study of hepatitis C virus.

A human monoclonal autoantibody to a nucleolar structure

Peripheral blood lymphocytes from a scleroderma patient (CDC) were isolated, transformed with Epstein-Barr virus and fused to the heteromyeloma SHM-D33. Supernatants from cultures were screened for autoantibody production against nucleoprotamine by ELISA. Positive wells were cloned by limiting dilution. After cloning, supernatants from two wells were positive for the nucleoprotamine assay. One named CDC-1 has been studied in our laboratory. CDC-1 recognized a nucleolar antigen by indirect immunofluorescence. By using an ELISA with purified recombinant antigens, CDC-1 reacted against Ro/SS-A, U1 (RNP) and Sm. By immunoblotting using a lysate of MOLT-4 cell line, CDC-1 was able to react against a structure of 60 kD. When the antigen recognized by CDC-1 was purified, SDS-PAGE under reducing conditions with purified antigen and subsequent silver staining of the gel allowed us to detect three bands at 60, 55 and 39 kD, respectively. A screening by ELISA with previously characterized antisera against our purified antigen demonstrated reactivity of the CDC-1 antigen with those antisera able to recognize Ro/SS-A.