Human monoclonal antibodies derived from lymph nodes of a patient with breast carcinoma react with MuMTV polypeptides

Differential effects of anti-beta2-glycoprotein I antibodies on endothelial cells and on the manifestations of experimental antiphospholipid syndrome

BACKGROUND

The antiphospholipid syndrome (APS) entails a prothrombotic state associated with the presence of anticardiolipin antibodies (aCL). aCL were shown to promote endothelial cell and platelet activation and to induce an APS-like syndrome in mice when administered intravenously. Recent data suggest that aCL target the plasma cofactor beta2-glycoprotein I (beta2GPI) rather than negatively charged phospholipids. However, it has not been determined whether different epitope-specific anti-beta2GPI antibodies obtained from one patient possess pathogenic properties.

METHODS AND RESULTS

Three beta2GPI-binding IgM monoclonal antibodies (mAbs) (ILA-1, ILA-3, and ILA-4) were cloned from a patient with APS. The three antibodies were shown to bind beta2GPI immobilized on irradiated plates, yet only ILA-1 bound beta2GPI coated onto nonirradiated plates. Furthermore, when using the anti-beta2GPI enzyme-linked immunosorbent assay, ILA-1 was the only mAb inhibited by fluid phase beta2GPI. ILA-1 and ILA-3, but not ILA-4, induced adherence of U937 cells to endothelial cells in vitro (reflecting activation of endothelial cells). mAbs ILA-1 and ILA-3 as opposed to ILA-4 induced significant expression of adhesion molecules when preincubated with human umbilical vein endothelial cells. Passive administration of ILA-1 and ILA-3 to pregnant BALB/c mice induced clinical findings consistent with APS (increased fetal resorptions, reduced platelet counts, and prolonged activated partial thromboplastin time), whereas both ILA-4 and the control human IgM did not produce similar effects.

CONCLUSIONS

The results of the study demonstrate the differential effects of various populations of anti-beta2GPI antibodies on endothelial cell activation and on experimental APS.

Tumour cell binding by a human monoclonal IgM antibody from the spleen of a non-tumour-associated patient is due to somatic mutations in the VH gene

Recently we described the occurrence of B cells producing polyspecific natural IgM with anti-tumour specificity in the spleen of non-tumour-bearing individuals as well as in fetal organisms. Immunoprecipitation and 2-D electrophoresis showed the binding of such antibodies to a 55-kD (pI 6.0) membrane surface glycoprotein. In vitro cultivation of human cancer cell lines in the presence of the purified IgM antibodies resulted in growth inhibition and complement-mediated cell lysis. Furthermore, the antibodies were shown to be able to induce MHC class I molecule expression on tumour cells. Because of this, a role for naturally occurring antibodies with anti-tumour specificity in preventing neoplasias had been suggested. We have constructed and expressed in Escherichia coli single-chain fragments (scFv: VH-linker-VL) derived from a polyspecific human monoclonal IgM autoantibody produced by a human x mouse heterohybridoma which was obtained from the spleen of an autoimmune patient. The mutated complementarity determining region (CDR) gene segments were replaced by the equivalent germ-line sequences and the CDR3 region was swapped for that from another polyspecific human natural antibody with no binding to tumours. Using these four scFv constructs for binding analyses and in vitro cultivation experiments we found: (i) scFv containing the mutated VH region of the original antibody were able to bind to tumour cells, to induce MHC class I molecule expression, and to inhibit tumour growth in a way similar to what had been described for the complete antibody; (ii) replacement of the mutated by the germ-line VH gene independently of the CDR3 to which it had been recombined, resulted in failure to bind to tumour cells. Nevertheless, other antigens (ssDNA, tetanus toxin) were still recognized, although with lower affinity. We discuss the significance of the replacement mutations in the VH gene CDRs, selected probably by B cell contact to an (auto)antigen, for generating a tumour binding capacity, not encoded by the germ-line gene.

Production of a human monoclonal antibody to normal basal and squamous cell carcinoma-associated antigen

A human monoclonal antibody, BM2, was produced by a hybridoma line generated by fusion of lymph node cells from a patient with squamous cell carcinoma (SCC) of the tongue with human B-lymphoblastoid cell line HO-323. BM2, an IgM class antibody, was reactive with all of the SCC cell lines tested. Frozen sections of normal and malignant tumor specimens were investigated to examine the reactivity of BM2 towards them. All 35 oral SCC specimens reacted with BM2. Normal stratified squamous epithelium showed positive staining in basal cells, but no staining was seen in other layers of the stratified epithelium, simple epithelium, and tissues of nonepithelial origin. Ductal basal cells of normal salivary gland also showed positive staining. Western blotting and immunoprecipitation analysis revealed that BM2 recognized 52 kDa membrane-associated protein. BM2 may therefore be a useful tool for biological and clinical studies of SCC.

Human monoclonal IgM antibodies from foetal B-cell hybridomas directed against a surface antigen on human tumour cells

In order to assess the existence of B lymphocytes capable of producing anti-tumour antibodies in non-tumour-bearing individuals, human lymphocytes derived from foetuses and adults were fused with the heteromyeloma cell line CB-F7. By indirect immunofluorescence, 29 out of 4,472 IgM-producing hybridomas (from 8 foetuses and 8 adults) were shown to produce antibodies which bind to colon carcinoma lines Colo205 and SW620, Raji lymphoma cells and small cell carcinoma of the lung. In vitro growth of tumour cells recognized by these antibodies was inhibited. The antibodies also mediated complement-dependent cytotoxicity. All antibodies tested recognized a cell surface molecule of 55 kDa. Southern blot hybridization analysis of hybridoma DNA with a human JH probe showed that the hybridomas were derived from clonally unrelated B cells. These results demonstrate that human foetal and adult B cells from non-tumour-bearing individuals are able to produce IgM antibodies recognizing defined cell surface molecules expressed on some tumour cells.

The production of human monoclonal anti-MMTV antibodies by in vitro immunization with anti-idiotypic antibodies

We have previously reported the production of a series of human monoclonal antibodies reacting with mouse mammary tumor viral antigens as well as the human counterpart HuMTV antigen. Against two of these antibodies (B11 and 4.6/6), anti-idiotypic antibodies were generated, which appeared to be the internal image of viral antigen. Vaccination with the anti-idiotypic antibodies induced in mice humoral and cellular immunity against both MMTV and HuMTV. The current study describes a novel method to produce human anti-MMTV antibodies derived monoclonal antibodies. Normal peripheral blood lymphocytes (PBLs) were immunized in vitro in the presence of IL-2, with rabbit anti-B11 antibodies bound to silica beads. Following in vitro immunization, the lymphocytes were fused with the UC-792-6 human lymphoblastoid cell line. Four human hybridomas were found to secrete human monoclonal antibodies which bound to MMTV and HuMTV. Three of the secreted antibodies were of the IgG class and one of the IgM class. The specificity of binding was confirmed by direct and competitive ELISA assays and by radioimmunoprecipitation. Our study demonstrates the ability to generate human monoclonal anti-viral antibodies by in vitro immunization, employing "internal image" anti-idiotypic antibodies. The method can be used to generate human antibodies, especially against pathogenic agents or ill-defined antigens.

Growth inhibition of murine mammary carcinoma by monoclonal IgE antibodies specific for the mammary tumor virus

Two IgE-producing hybridomas were established from spleen cells of Balb/c mice, which had been immunized with mouse mammary tumor virus (MMTV). These IgE monoclonal antibodies (mAbs) reacted specifically with the major envelope glycoprotein (gp36) of MMTV, as established by the immunoblot assay and by passive cutaneous anaphylaxis. The effect of the IgE mAbs (produced by clone A8) on the growth of the MMTV-secreting mammary adenocarcinoma H2712 was investigated in syngeneic C3H/HeJ mice. The mice were inoculated s.c. with either 10(5) (approximately 100 x LD50) or 10(6) (approximately 1000 x LD50) tumor cells and received repeated i.p. injections of 25 micrograms anti-gp36 IgE mAbs at 4-day intervals for 8 weeks. This treatment prevented the development of subcutaneous tumors in 50% of the animals. Similar protection was observed when the tumor cells (10(5)/animal) were injected i.p. 4 days prior to the beginning of the i.p. treatment consisting of injections of 25 micrograms mAbs at 4-day intervals for 6 weeks. However, these mAbs did not protect C3H/HeJ mice against the MMTV-negative MA16/c carcinoma cells. Hence, these results support the view that IgE-mediated cytotoxic mechanisms may play an immunologically specific antitumor surveillance role and that laboratory-induced antitumor IgE mAbs have the potential of specific therapeutic agents for in vivo destruction of tumor cells.

Towards an idiotype vaccine against mammary tumors. Induction of an immune response to breast cancer-associated antigens by anti-idiotypic antibodies

Previously we have reported on the production of two sets of human monoclonal antibodies reacting with mouse mammary tumor virus (MMTV) and human mammary tumor virus (HuMTV) cross-reacting antigens. B11 is a monoclonal IgG generated by the human-human hybridoma technique using axillary lymph node of breast cancer patients. 4.6/6 is a monoclonal IgG established by the mouse-human hybridoma procedure using peripheral blood lymphocytes of a healthy investigator working with the breast cancer cell line T47D which secretes HuMTV antigens. Two anti-idiotypic (Id) antibodies were produced by immunizing rabbits with B11 or 4.6/6. Following exhaustive adsorption on unrelated human-Ig, fetal calf serum and purification on B11 or 4.6/6 affinity columns, the anti-Id antibodies were shown to react specifically with their respective Id. The binding of these anti-Id antibodies to the respective Id was specifically inhibited by prior incubation of the Id with MMTV and/or HuMTV antigens. Rabbit anti-B11 and rabbit anti-4.6/6 anti-Id antibodies were employed to immunize female C3Heb mice. Following immunizations, humoral and cellular immune responses to MMTV-related antigens could be demonstrated. The sera of the mice contained anti-MMTV antibodies and delayed-type hypersensitivity was specifically expressed when irradiated cells of the Mm5MT line (which carry surface MMTV antigens) were injected. Our results support the notion that anti-Id antibodies harboring the internal image can immunize animals against tumor cells bearing on their surface viral-associated antigens.

The significance of HLA studies in human-human hybridomas

The technique of human-human (H + H) hybridoma is employed to generate human monoclonal antibodies. However, in contrast to mouse hybridomas, the human counterpart is very difficult to establish. It is still unclear what the precise reasons are for the failure to establish the human-human hybridoma technique as a routine. Analyses of HLA antigens of seven lymphocyte donors and 22 human cell lines generated by the H + H hybridoma technique have demonstrated the importance of the compatibility between human lymphocytes and the lymphoblastoid cell lines. Furthermore, there is a preferential expression of several HLA on human hybridomas (e.g. B51; B15; B18; B35). Screening several unrelated human lymphoblastoid cell lines available demonstrated preferred HLA antigens (A2, A3; A30/31; B5; B18; B15; B35), despite the fact that these lines were derived from subjects of different ethnic origins. It seems that HLA typing of donor lymphocytes and lymphoblastoid cell lines may help to increase the yield of H + H hybridomas.

The construction and use of a human-mouse myeloma analogue suitable for the routine production of hybridomas secreting human monoclonal antibodies

A human-mouse myeloma analogue termed HMMA2.11TG/O was constructed by fusion of the mouse myeloma cell line P3x63Ag8.653, a mutant derivative of MOPC21, with bone marrow mononuclear cells from a patients with IgA myeloma. The HMMA2.11TG/O cell line is resistant to 6-thioguanine and ouabain and sensitive to HAT. The cell line secretes no detectable immunoglobulin and has a hybrid karyotype and cell surface phenotype. An average fusion efficiency for growth of hybridomas of 1/17,000 fused cells was obtained in fusions with human peripheral blood mononuclear cells (PBM), Pokeweed Mitogen (PWM) stimulated PBM, and Epstein-Barr Virus (EBV) transformed polyclonal B cell lines. Over 75% of hybrids secrete detectable immunoglobulin and the cloning efficiency of the hybrids at 1 cell/well averages 25%. Antibody secreting cloned hybridoma cell lines were obtained by fusion directly with PBM from an immunized volunteer and by fusion with in vitro, secondarily immunized, EBV transformed polyclonal cell lines. Five hybridomas secreting human monoclonal IgM anti-tetanus antibodies and 2 secreting human monoclonal IgG anti-tetanus antibodies were selected and cloned from 6 fusions performed specifically for anti-tetanus antibody. Immunoglobulin and antibody secretion by cloned hybrids has been stable for 5-10 months at present. Immunoglobulin and antibody secretion in routine cultures passaged every 3-4 days has been 8-42 micrograms/ml. This human-mouse myeloma analogue should prove useful for the routine production of human monoclonal antibodies.