Specificity analysis of human monoclonal antibodies reactive with cell surface and intracellular antigens

Analysis of the Human Immune Repertoire using Human Monoclonal Antibodies

The investigations of the human immune response to cancer and other diseases have been hampered by the difficulty in determining the specificity of low-titered antibodies in serum, and the inability to define the specificity of individual lymphocytes. In order to study these issues, we developed the hybridoma technology so that human monoclonal antibodies (hMAb) could be reliably and reproducibly obtained.

Using a variety of fusion partners of both mouse and human origin, a large number of human immunoglobulin-secreting hybrids have been generated. We have found that 5 to 10% of the hybridomas produced secrete hMAb reactive with antigens (Ag) expressed by human cells. Specificity analysis and cellular localization studies of the Ag have been performed for a large number of these hMAb, and several general points have emerged from our study: (A) A significant proportion of the evaluable B-cell repertoire is directed to the production of antibodies reactive with Ags expressed by human cells. (B) The great majority of these Ags have an intracellular location, and are broadly distributed, being expressed by both normal and malignant cells. (C) Intracellular and cell surface differentiation Ags and other Ags with restricted distribution have been defined by hMAb, including a series of cell surface and intracellular Ags not detected on normal cells. (D) The relationship of these findings to cancer is unclear as hMAb showing distinctive distributions have been generated from the lymphocytes of normal individuals as well as tumor-bearing patients. (E) hMAb with distributions distinct from any known mouse monoclonal antibodies (mMAb) have been obtained. These reagents may hold great promise for antibody-directed in vivo diagnosis and therapy of cancer and other diseases due to their unique specificity and decreased immunogenicity compared with mMAb.

CXCL13 antibody for the treatment of autoimmune disorders

BACKGROUND

Homeostatic B Cell-Attracting chemokine 1 (BCA-1) otherwise known as CXCL13 is constitutively expressed in secondary lymphoid organs by follicular dendritic cells (FDC) and macrophages. It is the only known ligand for the CXCR5 receptor, which is expressed on mature B cells, follicular helper T cells (Tfh), Th17 cells and regulatory T (Treg) cells. Aberrant expression of CXCL13 within ectopic germinal centers has been linked to the development of autoimmune disorders (e.g. Rheumatoid Arthritis, Multiple Sclerosis, Systemic Lupus Erythematosis). We, therefore, hypothesized that antibody-mediated disruption of the CXCL13 signaling pathway would interfere with the formation of ectopic lymphoid follicles in the target organs and inhibit autoimmune disease progression. This work describes pre-clinical development of human anti-CXCL13 antibody MAb 5261 and includes therapeutic efficacy data of its mouse counterpart in murine models of autoimmunity.

RESULTS

We developed a human IgG1 monoclonal antibody, MAb 5261 that specifically binds to human, rodent and primate CXCL13 with an affinity of approximately 5 nM and is capable of neutralizing the activity of CXCL13 from these various species in in vitro functional assays. For in vivo studies we have engineered a chimeric antibody to contain the same human heavy and light chain variable genes along with mouse constant regions. Treatment with this antibody led to a reduction in the number of germinal centers in mice immunized with 4-Hydroxy-3-nitrophenylacetyl hapten conjugated to Keyhole Limpet Hemocyanin (NP-KLH) and, in adoptive transfer studies, interfered with the trafficking of B cells to the B cell areas of mouse spleen. Furthermore, this mouse anti-CXCL13 antibody demonstrated efficacy in a mouse model of Rheumatoid arthritis (Collagen-Induced Arthritis (CIA)) and Th17-mediated murine model of Multiple Sclerosis (passively-induced Experimental Autoimmune Encephalomyelitis (EAE)).

CONCLUSIONS

We developed a novel therapeutic antibody targeting CXCL13-mediated signaling pathway for the treatment of autoimmune disorders.

T follicular helper cells during immunity and tolerance

Helper T cells are required for the generation of a potent immune response to foreign antigens. Amongst them, T follicular helper (Tfh) cells are specialized in promoting protective, long-lived antibody responses that arise from germinal centers. Within these structures, the specificity of B cell receptors may change, due to the process of random somatic hypermutation aimed at increasing the overall affinity of the antibody response. The danger of emerging self-reactive specificities is offset by a stringent selection mechanism delegated in great part to Tfh cells. Only those B cells receiving survival signals from Tfh cells can exit the germinal centers to join the long-lived pools of memory B cells and bone marrow-homing plasma cells. Thus, a crucial immune tolerance checkpoint to prevent long-term autoantibody production lies in the ability to tolerize Tfh cells and to control positive and negative selection signals delivered by this subset. This review tackles the known mechanisms that ensure Tfh tolerance, many of them shared by other T helper subsets during thymic development and priming, but others unique to Tfh cells. Amongst the latter are checkpoints at the stages of Tfh differentiation, follicular migration, growth, longevity, and quality control of selection signals. Finally, we also discuss the consequences of a breakdown in Tfh tolerance.

Dysregulation of germinal centres in autoimmune disease

In germinal centres, somatic hypermutation and B cell selection increase antibody affinity and specificity for the immunizing antigen, but the generation of autoreactive B cells is an inevitable by-product of this process. Here, we review the evidence that aberrant selection of these autoreactive B cells can arise from abnormalities in each of the germinal centre cellular constituents--B cells, T follicular helper cells, follicular dendritic cells and tingible body macrophages--or in the supply of antigen. As the progeny of germinal centre B cells includes long-lived plasma cells, selection of autoreactive B cells can propagate long-lived autoantibody responses and cause autoimmune diseases. Elucidation of crucial molecular signals in germinal centres has led to the identification of novel therapeutic targets.

In vitro affinity maturation of human IgM antibodies reactive with tumor-associated antigens

Human lymphocytes secreting tumor cell-specific IgM antibodies were enriched in vitro following the stimulation of allogeneic human splenocytes from nontumor-bearing donors with cytostatic tumor cells or tumor cell plasma membrane fractions. The antibodies were generally of the IgM class and displayed low intrinsic affinity (K(d) > 100 nM). Nonetheless, the avidity arising from multivalent binding sites permitted the identification of multiple monoclonal antibodies (MAbs) displaying specificity for cultured tumor cells. Five antibodies were cloned from the B cells and two of these were expressed as human Fabs with IgG(1) constant regions. Although the avidity of the human IgM antibodies was sufficient to permit detection in the original screening, the monovalent Fabs displayed low binding activities, consistent with their low intrinsic affinity. Thus, in vitro affinity maturation was used to rapidly generate multiple variants of both antibodies displaying greater than 100-fold higher affinity. Two of the antibodies were characterized further and shown to have distinct specificities. One of the targets, LH11238, is associated both with the plasma membrane and with lysosomes and is rapidly internalized following incubation of the antibody with intact live cell monolayers. The second antigen, designated LH13, is a secreted antigen that has been enriched 200-fold from conditioned media and consists of two reactive bands at 42 and 45 kDa on denaturing Western blots. The stimulation and enrichment of human lymphocytes in culture coupled with rapid in vitro affinity maturation of low affinity antibodies potentially enables the discovery of human antibodies to a broader range of epitopes, including those that might be of greater therapeutic relevance.

Immune response to a differentiation antigen induced by altered antigen: a study of tumor rejection and autoimmunity

Recognition of self is emerging as a theme for the immune recognition of human cancer. One question is whether the immune system can actively respond to normal tissue autoantigens expressed by cancer cells. A second but related question is whether immune recognition of tissue autoantigens can actually induce tumor rejection. To address these issues, a mouse model was developed to investigate immune responses to a melanocyte differentiation antigen, tyrosinase-related protein 1 (or gp75), which is the product of the brown locus. In mice, immunization with purified syngeneic gp75 or syngeneic cells expressing gp75 failed to elicit antibody or cytotoxic T-cell responses to gp75, even when different immune adjuvants and cytokines were included. However, immunization with altered sources of gp75 antigen, in the form of either syngeneic gp75 expressed in insect cells or human gp75, elicited autoantibodies to gp75. Immunized mice rejected metastatic melanomas and developed patchy depigmentation in their coats. These studies support a model of tolerance maintained to a melanocyte differentiation antigen where tolerance can be broken by presenting sources of altered antigen (e.g., homologous xenogeneic protein or protein expressed in insect cells). Immune responses induced with these sources of altered antigen reacted with various processed forms of native, syngeneic protein and could induce both tumor rejection and autoimmunity.

A novel human monoclonal antibody, TONO-1, reactive with T-lymphocytic leukemia cells

Mononuclear cells from the peripheral blood of patients with systemic lupus erythematosus (SLE) were transformed with the Epstein-Barr virus (EBV) and the resultant polyclonal B-lymphoblastoid cell lines were tested for antibody activity to membrane antigens of certain T-cell lines. B lymphoblastoid cell lines secreting specific antibodies were fused with (mouse x human) heteromyeloma SHM-D33 cells. Among the large number of hybridomas generated, one which produced a human monoclonal antibody (MAb) TONO-1 (IgM, lambda) was selected. MAb TONO-1 proved to be reactive with 4 human T-cell lines, HPB-MLT, L-MAT, MOLT-3 and MOLT-4F, but not with B-leukemia, Burkitt's lymphoma, myelomonocytic leukemia, erythroleukemia or non-hematopoietic malignant cell lines. MAb TONO-1 reacted positively with fresh leukemia cells from 2 of 7 patients with acute T-lymphocytic leukemia, but no reaction was observed in non-T-cell leukemia cases. Normal lymphocytes, monocytes, granulocytes, red blood cells and platelets in the peripheral blood did not demonstrate remarkable binding. Neither thymocytes nor bone-marrow cells from healthy volunteers were reactive. The antigens defined by MAb TONO-1 were polypeptides of 57 kDa and 68 kDa. Immunohistological studies revealed no staining of thymocytes in the thymus of a 6-month-old child, but showed epithelial reticular cells and Hassall's corpuscles to stain positively. These results suggest that MAb TONO-1 is directed to T-leukemic cells and some components of thymus tissue.

Human antibodies from transgenic mice

We have used homologous recombination in ES cells to engineer B cell-deficient mice that are incapable of expressing endogenous immunoglobulin heavy and kappa light chain genes. We find that B cell development in these mutant mice can be rescued by the introduction of human germline-configuration heavy- and kappa light-chain minilocus transgenes. The transgenes rearrange during B cell differentiation, and subsequently undergo class switching and somatic mutation in response to antigen stimulation; thus recapitulating both stages of the humoral immune response using human, rather than mouse, sequences. The mice can be immunized; and human sequence, antigen specific, monoclonal antibodies can be obtained using conventional rodent hybridoma technology. These animals are also of interest for studying the normal processes of immunoglobulin gene expression. We discuss the example of heavy chain class switching, which has not been previously observed within an autonomous transgene.

Human monoclonal antibodies from stomach carcinoma patients react with Helicobacter pylori and stimulate stomach cancer cells in vitro

BACKGROUND

In recent studies, an increased incidence of gastric adenocarcinomas was observed in patients with Helicobacter pylori infection. However, the extent to which this coincidence is caused by immunologic mechanisms is unknown.

METHODS

Two human monoclonal antibodies (MoAbs) from patients with stomach carcinoma and H. pylori-associated gastritis were isolated and established by fusion of spleen cells with the heteromyeloma HAB-1. The reactivity of these human MoAbs was investigated in functional adhesion assays and on Western blots of tissue, tumor cell, and bacterial extracts. Their stimulation and proliferation were tested by the MTT test and 3-H-thymidine incorporation tests.

RESULTS

The two monoclonal immunoglobulin-M antibodies, 103/51 and 105/79, inhibited adhesion of tumor cells. On bacterial extracts antibody 103/51 identified protein bands of 55 kilodaltons (kd) and 80 kd, and in tumor cell extracts, a specific protein of approximately about 110 kd and 140 kd. Antibody 105/79 identified a 55 kd protein in bacterial extracts and a 110 kd protein in tumor extracts. In addition, in the 3-H-thymidine incorporation and MTT assay the antibodies showed a stimulatory and growth-enhancing effect on tumor cells in vitro. A similar activity was observed in sera from patients with gastric carcinoma, indicating a physiologic role of such antibodies in vivo.

CONCLUSION

The human monoclonal antibodies described here react with H. pylori and cross-react with and stimulate gastric carcinoma cells. It is possible that the production of these antibodies is primarily stimulated by bacterial antigens which cause chronic gastritis and that they might be indirectly responsible for the recently described higher incidence of gastric cancer because of the simultaneous reaction and stimulation of tumor cells they cause.

Tumor-associated antigens recognized by human monoclonal antibodies

BACKGROUND

Nonhuman monoclonal antibodies (MoAbs) of desired specificities have been studied in cancer treatment and tumor targeting with minimal success. Attempts of using humanized chimeric antibodies have not improved significantly their clinical applications. We have engaged in the development of human MoAbs by incorporating the in vitro immunization protocols to the nodal lymphocytes of cancer patients. Three human MoAbs thus generated were found to be strongly reactive with various human malignancies. The antigens recognized by the three antibodies were selected for immunochemical and biochemical characterizations.

METHODS

The antigens investigated were AgSK1, PA 1-2 and PA 3-1. The patterns of each antigen expression in various human cancer cell lines were studied by the immunocytochemical staining technique. The expression of AgSK1 in association with cellular proliferation was examined by the flow cytometry analysis. In studying the biochemical natures of these antigens, their sensitivities toward various chemical and physical treatments were determined. The antigens that were shown to be proteins were subjected to SDS-PAGE and Western blot for estimations of molecular weights.

RESULTS

The AgSK1 was detected in 10 human carcinoma cell lines but in none of the melanoma cell lines. This suggests that SK1 may be an epithelial or carcinoma marker. The phenotypic expressions of AgSK1 were shown to be associated with proliferation of carcinoma cells. Biochemically AgSK1 was a sialophycoprotein with an estimated molecular weight of 42-44 kilodaltons (kDa). HuMAb PA1-2 demonstrated a unique staining pattern at both the cytoplasmic and intercellular interface. The stained filamentlike structures extending from cell to cell indicated that Ag PA1-2 might play a role in cellular interactions. Biochemically, Ag PA1-2 appeared to be an asialocarbohydrate. The Ag PA3-1 was a cytoplasmic glycoprotein expressed by all 13 cell lines. The estimated molecular weights of PA3-1 were 164, 104, and 40 kDa.

CONCLUSIONS

Tumor-associated antigens recognized by the human MoAbs may be more relevant clinically than those recognized by the mouse immune system. Carcinoma-specific human MoAbs are desirable for cancer treatment and tumor localization.

A novel human monoclonal antibody directed to a tumor-associated antigen

Twelve human monoclonal antibodies (HuMAb) were established by the fusion of (mouse x human) heteromyeloma cells with B-lymphoblastoid cells derived from the regional lymph nodes of three patients with squamous cell carcinoma of the lung. They were tested for reactivity to two kinds of proteins (purified protein derivatives and bovine serum albumin) by ELISA, Sq-19 (squamous cell carcinoma) culture cells by indirect membrane immunofluorescence tests, and Sq-19 tumor xenograft by immunohistological study. Among them, one HuMAb 904F (IgM, lambda) was selected. In indirect membrane immunofluorescence tests, this 904F antibody reacted with various kinds of cell lines, e.g. lung cancer, esophageal cancer, endometrial cancer, and stomach cancer. It did not react with malignant hematopoietic and diploid fibroblast cell lines. Immunohistologically, it stained the tumor nests of squamous cell carcinoma, adenocarcinoma, and large cell carcinoma of the lung. It also stained those of esophagus and colon, but not those of small cell carcinoma of lung, or stomach. On frozen-section specimens of normal tissues from various organs, it showed only limited areas of positive staining. Limited positive findings were observed at a reticular zone of the adrenal gland, at the esophagus as weak staining, and at islets of the pancreas as very weak staining. Western blotting analysis demonstrated that it recognized a 54 kDa trypsin-sensitive molecule which is expressed on the surface of tumor cells. These results suggest the 904F monoclonal antibody detects a novel tumor-associated antigen which is recognized by the human immune system.

Monoclonal antibodies against a 65-kDa tumor-associated phosphoprotein: development and use in cancer detection

Five hybridoma cell lines secreting monoclonal antibodies (MAbs) to a 65-kDa tumor-associated phosphoprotein (p65) were established. Purified to homogeneity, p65 was used as an immunogen to induce immune response in C57BL/6N mice. Splenocytes were fused with mouse myeloma cells and hybridoma lines were selectively subcloned. A rapid and sensitive sandwich type ELISA, using purified MAbs was established to measure markedly elevated amounts of p65 in sera obtained from both tumor-bearing rats and from cancer patients. The p65 from rat and human sources was added quantitatively to normal sera to construct standard curves. The average level of p65 in normal rat sera was 38 ng/ml +/- 13 ng/ml (mean +/- SD), and in sera from rats bearing mammary adenocarcinomas, the average value was 1005 +/- 140 ng/ml. In normal human sera the mean level of p65 was 34 +/- 35 ng/ml (mean +/- SD) and sera of patients with variety of cancers had an average p65 value of 344 +/- 57 ng/ml. More than 80% of tested sera from adenocarcinoma-bearing rats (20/24) as well as from cancer patients (82/98) had p65 levels elevated two standard deviations above the mean. Overall the assay had a sensitivity of 80.9% and specificity of 85%. The purified IgG1 MAbs, with high titers and strong anti p65 specificities were also used to develop an immunohistochemical method to visualize the expression of p65 in rat tumor tissue sections. The HB2, HF11 and RE6 cell lines have proved to be quite stable in the ability to secrete anti-p65 MAbs.

A cancer-reactive human monoclonal antibody derived from a colonic cancer patient treated with local immunotherapy

A human monoclonal antibody, YJ-37 (IgM) was generated through the fusion of human B lymphoblastoid cell line HO-323 with the regional lymph node lymphocytes from a colonic cancer patient who was treated with a local immunotherapy. This antibody was purified and conjugated with biotin, after which direct immunohistochemical staining was performed. The results revealed that YJ-37 selectively reacted with colonic cancer (7/19), gastric cancer (3/6), endometrial cancer (1/2) and colonic adenoma (7/13), but not with normal epithelia. Membrane immunofluorescence and FACS analysis also showed that YJ-37 bound to tumor cell surfaces. Furthermore, the chemical structure of the antigen defined by YJ-37 was analyzed by means of thin-layer chromatography immunostaining and ELISA. The results indicated that YJ-37 reacted with sialylated lacto-series carbohydrate chains, which have been reported to accumulate in cancer cells.

Human antiglioma monoclonal antibodies from patients with astrocytic tumors

The current management of malignant gliomas is unsatisfactory compared to that of other solid tumors; the expected median survival period is less than 1 year with the patient undergoing conventional surgery, radiotherapy, and chemotherapy treatment. Immunological reagents could be a useful adjunct. Human monoclonal antibodies derived from patients with astrocytic tumors might recognize subtle antigenic specificities that would differ from those recognized by xenogeneic (murine) systems. Five hybridomas, designated as BT27/1A2, BT27/2A3, BT32/A6, BT34/A5, and BT54/B8, were produced from the fusion of peripheral blood lymphocytes of four patients with astrocytic tumors to the human myeloma-like cell line TM-H2-SP2. This cell line has a 46, XX karyotype and is negative for hypoxanthine guanine phosphoribosyltransferase. All five human monoclonal antibodies produced 2.4 to 44 micrograms/ml of immunoglobulin M, had a similar but not identical pattern of reactivity against a panel of human tumor cell lines, and failed to react with normal human astrocytes. Labeling of four neuroectodermal tumor explant cultures by BT27/2A3 was demonstrated by flow cytometry. Karyotyping of three of the five hybridomas demonstrated that two were pseudodiploid (2-3n) and one hypodiploid (less than 2n). The monoclonality of the hybridomas was evaluated by Southern blot analysis of JH gene rearrangements, revealing two types of rearrangements for each hybridoma, both consistent with monoclonality. Preliminary antigen characterization indicated that at least four of the five human monoclonal antibodies were directed to cell-surface glycolipids.

Immunotherapy with monoclonal antibodies in metastatic melanoma

Therapy for metastatic melanoma has been disappointing to date. Treatment with chemotherapy only uncommonly results in complete responses and rarely results in long-term survivors. The identification of human melanoma cell surface antigens has led to the development of an array of mouse monoclonal antibodies (MAb) for use in the diagnosis and therapy of patients with metastatic melanoma. Strategies utilizing MAbs based on immunologic approaches have been developed. Naked MAbs directed against glycoprotein surface antigens or conjugated to toxins or radionuclides have shown little biologic or clinical activity. However, phase I studies of MAb directed against glycolipid antigens have yielded objective tumor shrinkage with occasional complete responses. Severe toxicity has been seen infrequently. Possible anti-tumor mechanisms include complement activation and antibody-dependent cellular cytotoxicity utilizing natural killer cells or monocytes as effector cells. Strategies to enhance the anti-tumor effects of MAb, including combinations with cytotoxic agents and cytokines, have been introduced with limited success thus far. The development of a human IgG anti-mouse antibody has been seen in nearly all treated patients. A new generation of MAb engineered to overcome the immunogenicity of mouse MAb and to enhance immune effector function will soon enter clinical trials.

Tumour-associated antigens of mammary carcinomas recognized by human monoclonal antibody 1G12

We have reported the production of human monoclonal antibodies (mAb), by the fusion of lymph node lymphocytes from a primary carcinoma patient with murine myeloma cells. Seven heterohybridomas showed reactivity with class III antigens, and five hybridomas (1G12, 2D4, 4H5, 5D10 and 3B10) were reactive with class II antigens. One of these human mAbs (1G12) was intensively studied and results are presented here. 1G12 reacted strongly and specifically with five mammary carcinoma cell lines and showed no cross-reactivity with seven normal fibroblast cells. It continuously produced human mAbs (IgM) at a rate of 4.5-12.5 micrograms/ml over a period of 2 years. Human mAb 1G12 (IgM) was purified by either a combination of anion-exchange chromatography (ABx) and gel filtration (Superose 6) or affinity chromatography (agarose). Immunohistological analysis of frozen tissue sections was performed with biotinylated 1G12. All mammary carcinomas analysed (n = 26) were positive, while the connective tissue of 36 different patients was completely negative with 1G12. In normal breast, endometrium and intestine only a weak or moderate staining of the epithelial cells was observed. Normal oesophagus, small bowel, cervix, uterus, lung and skin were completely negative. Partly purified tumour antigen recognized by 1G12 had a molecular mass of 1-2 MDa and showed strong binding with Ulex europaeus lectin I and Bauhina purpurea agglutinin, indicative for the glucoprotein nature of antigens. These results show that human mAb 1G12 may be useful for the analysis of tumour-associated antigen of mammary carcinoma patients. In further studies the therapeutic and diagnostic application of 1G12 should be analysed in more detail.

Development of a cell surface reacting human monoclonal antibody recognizing ovarian and certain other malignancies

A human monoclonal antibody designated AC6C3 was developed by fusing regional lymph node lymphocytes from a patient with epithelial ovarian carcinoma with cells of the hybrid myeloma SPAZ 4. This monoclonal antibody recognized a determinant expressed on the cell surface of ovarian tumor cell lines. The AC6C3 hybridoma has been maintained for more than 24 months by repeated cloning and secretes IgM at concentrations of 2-8 micrograms/10(6) cells/24h. The AC6C3 monoclonal antibody reacted with a cell surface component of ovarian tumor cell lines, as determined by cell surface immunofluorescence staining using the fluorescent activated cell sorter (FACS). In contrast, nylon wool nonadherent peripheral blood lymphocytes or red blood cells from normal donors were negative (less than 5% of the cells were stained). Immunoperoxidase staining with the AC6C3 monoclonal antibody of nonpermeabilized cryostat sections of freshly obtained or cryopreserved ovarian carcinoma specimens and human ovarian tumor xenografts demonstrated strong reactivity of these specimens. Most normal tissues including brain, liver, heart, kidney and peritoneum demonstrated negative or weak reactions with AC6C3. Other carcinomas including breast, colon and some malignancies of neuroectodermal origin were strongly reactive with AC6C3. AC6C3 mediated complement-dependent cytotoxicity and identified a 32 Kd band in Western blotting and immunoprecipitation experiments conducted on surface labelled SKOV3 cells. The association constant for AC6C3 was determined at 2.3 x 10(10) M-1.

14C1, an antigen associated with human ovarian cancer, defined using a human IgG monoclonal antibody

We have selected a human EBV-transformed cell line from the involved lymph nodes of an ovarian cancer patient which secretes an IgG1 kappa antibody, able to recognize an antigen present on the surface of ovarian cancer cells. The antigen, termed '14Cl,' has previously been shown by immunohistological techniques to be present on the surface of the malignant cells within tumour specimens. Western blotting analysis has shown that the majority of primary ovarian cancer specimens and three continuous cell lines derived therefrom express 14Cl; other tissue types were negative. Preliminary biochemical characterization has been carried out, which shows that the 14Cl antigen has a molecular weight range of 25-32 kD and an isoelectric point from pI 6.3 to 6.8. We believe that the 14Cl antigen is immunologically relevant to ovarian cancer patients and may therefore represent a novel target for both active and passive immunotherapy.

Expression of 38-kD cell-surface glycoprotein in transformed human keratinocyte cell lines, basal cell carcinomas, and epithelial germs

In this study, we attempted to identify and characterize transformation-induced cell-surface glycoproteins of human keratinocytes. Therefore, we first searched for glycoproteins which are significantly elevated in human keratinocytes after transformation and immortalization by SV40 virus and which are also found at high levels in keratinocytic cell lines derived from squamous cell carcinomas of the skin. Out of at least 80 different cell-surface antigenic systems of human tumor cells, only three glycoproteins showed elevated expression in transformed keratinocytes. Among these, a 38-kD glycoprotein (gp 38) was highly increased in all transformed keratinocyte cell lines tested, but was not elevated in transformed fibroblasts. The expression of gp 38 was further characterized in normal epidermis and in its benign and malignant hyperproliferative disorders: gp 38 was generally not expressed in normal epidermis and in benign hyperproliferative disorders. In contrast, strong and homogeneous reactivity was found in solid and fibrosing basal cell carcinomas whereas no or low reactivity was detected in squamous cell carcinomas and in those parts of BCC revealing keratotic differentiation. Interestingly, high expression of gp 38 was also found in primary epithelial germs of fetal skin, secondary germ cells of the telogenic hair follicle and secretory tubules of sweat glands. The immunohistologic data suggest that gp 38 is preferentially expressed by epidermal cells which lack squamous and pilosebaceous differentiation.

The use of Fab' fragments in a screening method for the detection of human anti-tumor monoclonal antibodies

The use of immunoperoxidase staining methods to detect human monoclonal antibodies that react with frozen tissue sections of human tumors is limited due to endogenous immunoglobulin present in the sections. The endogenous immunoglobulin produces a significant background staining which makes the detection of a specific reaction difficult and unreliable. A method of incubating the sections with papain fragments (Fab') of goat anti-human immunoglobulin was evaluated. It was demonstrated that Fab' fragments of goat anti-human polyvalent immunoglobulin can block endogenous immunoglobulin background staining after prolonged washing of tissue sections (20h) and thus facilitating the screening of monoclonal antibodies against frozen sections of tumor tissue.

Establishment of an anti-A human monoclonal antibody from a blood group A lung cancer patient: evidence for the occurrence of autoimmune response to difucosylated type-2 chain A

A human monoclonal antibody, NCC-HAL-27, has been established by a combination of transformation by Epstein-Barr virus (EBV) and a newly devised "micro cell fusion" technique. Lymphocytes used were derived from a blood group A lung cancer patient. Cancer cells, as well as normal epithelial cells of lung, stomach and colon (including autologous tissue) from blood group A individuals, fixed in formalin, were immunohistochemically stained by the antibody. A higher concentration (greater than 140 mg/ml) of the antibody agglutinated only type-A (not B or 0) erythrocytes. The structural specificity of NCC-HAL-27 was determined by particle-concentrated fluorescence immunoassay and thin-layer chromatography immunostaining using purified, well-defined glycolipids. The antibody was found to be directed against type-2 chain A and difucosylated type-2 chain A antigens with no cross-reactivity with known A-like antigens, such as Tn and Forssman antigen, generally expressed irrespective of ABO status. Interestingly, however, the antibody detected the expression of incompatible A antigen in colon cancers of B and 0 individuals with high incidence (30%-40%). The finding that a monoclonal antibody generated from a blood group A cancer-bearing host is directed against autologous A antigen is novel because the ABO blood group antigens are the major alloantigens in man, with strictly controlled immunotolerance. The induction of anti-A in this patient could, therefore, be directly associated with the lung cancer.

A human monoclonal antibody recognizing a surface antigen on stomach cancer cells

Lymph-node lymphocytes of a patient with stomach cancer were fused with the mouse-human heterohybridoma, HM-5. A clone (2F9) was isolated that showed stable production of an IgM antibody reactive with NUGC-4 stomach cancer cell line. This antibody reacted predominantly with a cell surface antigen on cell lines originating from gastro-intestinal cancer and adenocarcinoma of lung, whereas it was not generally reactive with other types of cancers, or with normal kidney cells or fibroblasts. Biotin-labeled 2F9 antibody clearly stained cell smears and the nude mouse tumor of NUGC-4, but it did not show a positive reaction with stomach cancer tissues obtained from more than 10 patients, indicating that the antigen detected is very weakly expressed on tumor cells or on a limited number of stomach cancers. The antigen shed from NUGC-4 cell line was detected in the culture supernatant. 2F9 antibody precipitated a glycoprotein with a molecular weight of over 200 kilodaltons as well as a possible glycolipid, from NUGC-4 cells labeled with [3H]glucosamine or [35S]-H2SO4. Periodic acid treatment of the tissue section decreased reactivity with 2F9 antibody, but heat, neuraminidase or protease treatment did not. These results suggested that the epitope is present on a carbohydrate moiety not containing sialic acid, and that a part of the antigen molecule is sulfated.

Human monoclonal antibodies against cytokeratin 18 generated from patients with gastric cancer

By co-culturing regional lymph node B-cells and HAT-sensitive mutant cells obtained from RPMI-1788 cells, no less than 20,000 Epstein-Barr (EB)-transformed colonies were obtained from 32 patients with gastric cancer. From B-cell cultures generating antibodies reactive with gastric cancer tissues as well as cultured gastric cancer cells, two EB-transformed cell clones termed C418-59 and C1218-39 were isolated. Both of them produced human IgM-class antibodies, termed Mab418-59 and Mab1218-39, respectively. Both antibodies reacted with an antigen with a molecular weight of 45 kd existing in gastric cancer MKN-45, MKN-1, and Kato-III cells, and also with all of 4 adenocarcinomas of the stomach in paraffin sections. The antigen recognized by both antibodies was identified as a kind of cytoskeletal protein, cytokeratin 18. In this study, it was confirmed that B-cell clones generating autoantibodies against cytokeratin 18 were present in some patients with gastric cancer.

Rat serum antibodies binding to high-molecular-weight glycoprotein(s) on syngeneic colon carcinomas, demonstrated by competition with rat monoclonal antibody

Sera from rats immunized to syngeneic 1,2-dimethylhydrazine colon carcinomas were analyzed for their ability to inhibit the binding of a syngeneic rat IgM monoclonal antibody (10B12) specific for high-molecular-weight glycoprotein(s) from rat colon carcinoma. Immunization with irradiated tumour cells or with tumour tissue extracts resulted in the appearance of a strong inhibiting activity. Sera of animals with established growing tumours and of females shortly after partus also inhibited binding of the monoclonal antibody, while unimmunized animals or animals immunized with irrelevant antigens had no inhibiting antibodies in their sera. Dimethylhydrazine-treated animals showed an increased titer of antibodies binding to the high-molecular-weight glycoprotein, but showed no inhibition of binding of the 10B12 monoclonal antibody. The syngeneic 10B12 rat antibody obviously does not reflect a rare event captured from a hyperimmune animal by the hybridoma technique but rather represents an antibody specificity frequently appearing in the immune response to tumours expressing the high-molecular-weight glycoprotein.

B-lymphocytes from melanoma patients and normal individuals react with melanoma cells but also with irrelevant antigens

Peripheral B-lymphocytes of 13 patients with uveal melanoma and of 5 healthy individuals were transformed with Epstein-Barr virus (EBV). The reactivity of these transformed cells with autologous or allogeneic melanoma cells and lymphocytes was measured by the enzyme-linked immunosorbent assay (ELISA). Antigens which are neither self nor common environmental antigens (i.e., plant protoplasts, schistosome antigen and keyhole limpet haemocyanin) were used for controls. Lymphocyte reactivity with all types of antigen was apparent both in patients with uveal melanoma and in normal controls. The response detected by the techniques available is likely to reflect antibody multispecificity leading to mis-identification of irrelevant antigens.

Recognition of galactosylgloboside by monoclonal antibodies derived from patients with primary lung cancer

Lymph node lymphocytes from patients with primary lung cancer were immortalized with Epstein-Barr virus, and culture supernatants were screened for cell-surface reactivity against allogeneic cancer cell lines. The percentage of wells containing detectable antibodies in initial screening ranged from 1 to 17%, but the vast majority of the cultures lost antibody activity on subsequent expansion. Two antibody-secreting clones, J309 and D579, derived from separate individuals and reactive with anaplastic lung cancer cell lines, were successfully expanded and fused with the NS-1 mouse myeloma cell line. The antibodies produced by these clones exhibited identical restricted serologic reactivity against cultured cell lines and detected a carbohydrate antigen present in the neutral glycolipid fraction of MCF-7 breast cancer cells. Serologic, immunochemical, and chemical analyses revealed that the antigen recognized by antibodies J309 and D579 is galactosylgloboside [Gal(beta 1----3)GalNAc(beta 1----3)Gal(alpha 1----4)Gal(beta 1----4)- GlcCer]. Conclusions regarding the significance of these findings with respect to the biology of lung cancer await further information concerning the distribution of galactosylgloboside in normal and malignant tissues and the frequency of antibodies to this structure in normal and tumor-bearing individuals.

A transformation-associated 130-kD cell surface glycoprotein is growth controlled in normal human cells

Two characteristics of cell surface molecules involved in the regulation of cell proliferation are altered expression in relation to growth phase in normal cells and overexpression in transformed cells. Here, we describe a similar pattern of expression for a 130-kD cell surface glycoprotein (gp 130) in human cells. Synthesis and cell surface expression of gp130 were greatly increased in both virally and chemically transformed fibroblasts, fibrosarcomas, a squamous cell carcinoma of the skin, and T cell leukemia lines. Furthermore, gp130 expression was induced in serum-starved fetal fibroblasts by serum stimulation, and in fresh T cells by various activating agents. Expression in response to serum stimulation was associated primarily with the transition from a quiescent state (G0) into the cell cycle (G1).

Somatic mutations in B lymphocytes: new perspectives in tolerance research?

This paper extends the concept of clonal anergy developed in the author's laboratory. It has been shown that the primary population of B lymphocytes induced into clonal expansion and IgM antibody formation by mitogens contains many cells capable of autoantibody synthesis, but the affinity of binding to the self constituents, or indeed to foreign antigens, is low. The creation of high affinity antibody, which will still register strongly in an ELISA as an IgG molecule, demands not only the addition of lymphokines to cause isotype switching, but also intentional immunization of the donor mice to permit mutations in V region genes and selection of higher affinity B memory cells. This process appears to begin about 6 days after in vivo immunization. It is postulated that these mutational events occur primarily in germinal centres, and that there must be mechanisms to prevent escape of cells which, by chance, mutate not to higher affinity against an immunogen, but to higher affinity against a self constituent. If such mutants were allowed to enter the long-lived, recirculating pool of B lymphocytes, they might pose a graver threat of autoimmune disease than the low-affinity anti-self cells of the primary repertoire. Therefore, it is suggested that recently mutated germinal centre B cells represent a pool of 'pre-memory' cells, which are immature in the sense of displaying the same kind of sensitivity to negative signalling by antigen that immature B cells from newborn spleen or adult bone marrow display. If so, then the earliest phases of memory generation represent a second window of opportunity for tolerance induction within the B lymphocyte compartment.

Human monoclonal antibodies and monoclonal antibody multispecificity

The majority of human anti-tumour monoclonal antibodies (Mabs) isolated to date have been disappointing. Firstly, they react or cross react with intracellular cytoskeletal proteins or nuclear antigens and therefore are of limited value as blood borne agents. They are also generally of the IgM isotype and show relatively low intrinsic affinity for the primary epitope. Secondly, such Mabs can be generated from normal, non tumour bearing subjects at a frequency comparable to their production from tumour patients. This latter observation is true also for common autoantigens such as DNA and IgG since Mabs to these can also be generated from normal subjects in addition to autoimmune individuals. This article rationalises these observations in the context of the requirement for clinical use for human Mabs. It discusses the evidence that there is a potentially useful B cell response to be immortalised, and examines the consequences of the newly recognised phenomenon of monoclonal antibody multispecificity both on the methodology of their generation and on their subsequent use as imaging and therapeutic tools.