An enzyme immunofiltration assay useful for detecting human monoclonal antibody

Characterization of human IgG1 monoclonal antibody against gangliosides expressed on tumor cells

A human IgG1.k monoclonal antibody (MAb) designated GMA1 was developed by fusing pooled lymph node lymphocytes from cancer patients with the human lymphoblastoid cell line, SHFP-1. The GMA1 MAb reacted with several melanoma and neuroblastoma cell lines. Normal tissue derived from human brain and tumor-cell lines derived from colon, ovary, and breast were not reactive. FACS analysis performed using live cells demonstrated that the antibody recognizes a cell-surface antigen. Enzyme immunoassay (EIA) and thin layer chromatography (TLC) immunostaining with purified gangliosides indicated that the antibody has specificity for the major tumor associated gangliosides GD3, GM3, and GD2. GMA1 heavy and light chain genes were isolated by RT-PCR and a recombinant derivative of this human antibody was expressed in Chinese hamster ovary (CHO) cells. High-level antibody synthesis and secretion was achieved using a vector designed to maximize expression. FACS analysis and TLC immunostaining indicated recombinant GMA1 reacted with human tumor cell lines and gangliosides GD3, GM3, GD2 in a manner similar to the antibody produced by the hybridoma cell line, demonstrating that the specificity of the antibody was not altered during molecular cloning.

Isotype-directed enrichment of B cells by magnetic beads in the generation of immunoreactive human monoclonal antibodies

Pooled lymphocytes collected from cancer patients were mixed with a biotinylated murine MAb specific to human IgG4. To this were added streptavidin-conjugated magnetic beads. After magnetically separating the bead-lymphocyte complex, the B cells were washed and fused with the WIL-2 derived human fusion partner, SHFP-1. Subsequently derived human-human hybridomas were screened for IgG4 immunoreactivity to target tumor cell lines. Several hybridomas reacted with a variety of malignant cell types, including melanoma, neuroblastoma, and pancreatic tumor cells. One hybridoma in particular, designated SC-GM4, recognized an antigen by Western blot with an apparent molecular weight of 57 kDa. This facile approach of magnetically separating selected populations of lymphocytes should be relatively simple to apply to other antigens and antibodies to preselect the type, class, and properties of the desired MAb.

Human IgG and IgM monoclonal antibodies against autologous melanoma produced by Epstein-Barr-virus-transformed B lymphocytes

The serum antibody response to human melanoma has prognostic and potential physiological consequences. The specificity of the host B cell antibody response may be an important determinant of disease outcome. We have utilized Epstein-Barr virus (EBV) transformation to analyze the repertory of the host B cell response to melanoma. Production of antibody that binds selectively to autologous (eight cases) or allogeneic (four cases) short-term-cultured melanoma cells was assessed from EBV-transformed B lymphoblastoid cells. Forty-two cultures of EBV-transformed B cells that secreted IgM and 23 that secreted IgG antibodies gave patterns of differential reactivity with autologous or allogeneic melanoma. Antibody-forming B cells persisted in producing melanoma-reactive IgG and IgM for 8-21 weeks. Preselection of B cells by adsorption to tumor cell antigens before transformation enhanced the frequency of antibody secretion. The specificity of the antibody produced by the longest-producing culture appears to be restricted to a subset of melanomas. The patient from whom this tumor-restricted IgG-producing B cell was retrieved was unusual, having had a transient serum IgG of similar specificity, and having manifest a syndrome of vitiligo at the time of her development of serum antimelanoma antibody, followed by disease-free survival of resected recurrent metastatic melanoma to the present (more than 6 years). This study has given support to findings of conventional serology, revealing the production of melanoma-reactive antibody from B cells of patients who have demonstrable serological response to tumor.

Growth of human-human hybridomas in serum-free media enhances antibody secretion

Human-human hybridomas derived from fusing lymph node lymphocytes with UC 729-6 were adapted to grow in commercially available serum-free medium and were compared with serum-supplemented [10% fetal bovine serum (FBS)] cultures. Over a 6-d period, no significant changes occurred in the growth of the cells in 10% FBS or serum-free medium. In cultures supplemented with 10% FBS more total proteins were secreted than in serum-free cultures. However, there was an enhanced secretion of three- to four-fold of both immunoreactive human IgG and IgM under serum-free conditions compared to serum-supplemented conditions. Serum-free conditions may provide the appropriate milieu for the increased level of Ig secretion from human hybridomas derived from UC 729-6 in that there are no inhibitors that may be present in serum.

A semi-automated fluorescent (SAF) assay using viable, whole cells for screening hybridoma supernatants

In the production of monoclonal antibodies, a rapid, sensitive, accurate assay is needed for the critical step of screening. We report the modification of an assay using viable whole cells for screening hybridoma supernatants. The modified assay uses fluorescent second antibodies for detection and has been adapted to an instrument capable of automating a number of assay steps. The modified assay is compared to a dot radioimmunoassay developed and used in our laboratory. The fluorescence assay is highly sensitive but shows more background effect, especially in samples with high protein content, such as ascites. The automated fluorescence assay is very rapid, capable of completing an assay in less than 90 min, and can be performed with minimal operator involvement. The assay was performed successfully with several different antibodies and cell types. This screening procedure should be especially useful for laboratories with large numbers of fusions to evaluate.

Membrane filtration enzyme immunoassay, a novel, rapid method for measurement of virus-specific immunoglobulins G and M and detection of viral antigens

A novel membrane filtration enzyme immunoassay (MF EIA) is described in which virus-antibody complexes formed are trapped onto the surface of membranes with low protein-binding affinity by vacuum filtration. Class-specific immunoglobulin G (IgG) or IgM antibody was measured by adding enzyme-conjugated antiimmunoglobulin and incubating prior to the final wash and addition of enzyme substrate. Influenza A virus-specific IgG antibodies measured by MF EIA showed similar sensitivity for detecting seroconversion in volunteers administered influenza virus subunit vaccines and subtype specificity comparable to that observed by the hemagglutination inhibition technique. Cytomegalovirus-specific IgG antibodies measured by MF EIA with commercially available complement fixation antigens gave results similar to those of conventional enzyme-linked immunosorbent assay and complement fixation tests. The MF EIA method is also suitable for detection of rotavirus antigen in feces.

Genetically stable human hybridomas secreting tumor-reactive human monoclonal IgM

Human lymphocytes obtained from regional draining lymph nodes of patients with cancers of the cervix, kidney, prostate, and vulva were immortalized by polyethylene glycol-mediated somatic cell hybridization with either human UC 729-6 or murine P3-NS-1-Ag4-1. Four reactive human IgM-secreting hybridomas, termed CLNH5, MHG7, VLN1H12, and WLNA67 were isolated and characterized. Hybrids obtained by fusions with UC 729-6 have remained tetraploid for over 18 months, have doubling times from 25-35 hours, and have continuously secreted approximately 0.5-5.0 micrograms IgM/10(6) cells/ml per day. MHG7, a mouse-human hybrid, required subcloning every 4-6 months to maintain human IgM secretion. Binding of these human monoclonal antibodies (MoAbs) against a panel of cell lines was assessed by an enzyme-linked immunoassay (EIA). CLNH5 reacted with carcinomas of the cervix, lung, and vulva. MHG7 reacted with carcinomas of the prostate, stomach, and vulva. VLN1H12 reacted with carcinomas of the cervix, lung, prostate, stomach, and vulva. WLNA6 reacted strongly with a carcinoma of the lung. All four human MoAbs failed to react by EIA with hematopoietic cells or normal fibroblast cell lines. The data suggest that regional draining lymph nodes of cancer patients have been primed to produce antibodies against antigens associated with tumor cells and that UC 729-6 served as a genetically suitable vector for the capture and immortalization of these Ig-secreting B lymphocytes.

An ELISA using avidin-biotin complex for the determination of ABH group from saliva

The ABH group in a trace amount of saliva could be determined by an enzyme-linked immunosorbent assay (ELISA) using an avidin-biotin-peroxidase complex (ABC) technique. In this method ABH blood group substances as a solid phase are adsorbed to wells of a microtiter plate made of polystyrene. The primary antibody corresponding to the blood antigen adheres onto the wells, and reacts with the biotinylated secondary antibody. The previously formed ABC reagent is then added to the above wells, and finally the absorbance produced by the interaction of the peroxidase activity with a chromogenic substance is measured at 492 nm. This method proved to be clearly more sensitive for the detection of ABH blood groups in secretor-saliva than the conventional hemagglutination inhibition test. Also the ABH group of non-secretor-saliva could be easily determined by this method.

Variations in the secretion of monoclonal antibodies by human-human hybridomas

A series of human-human hybridomas derived from a single fusion of UC 729-6 with lymph node lymphocytes were examined for the type and nature of macromolecules synthesized and secreted. One hybrid, VLN3G2, secreted fourfold higher IgG than that present in the cytoplasm over 4 days of growth, while the IgM distribution was opposite to that of IgG. VLN5C7, contrary to VLN3G2, contained several-fold more cytoplasmic IgG as well as IgM than the amounts secreted over the same period of time. Of the secreted IgG and IgM by both of these hybridomas, only the IgG showed immunoreactivity against target A431 cell surface antigen(s). Another hybridoma, termed VLN1H12, secreted immunoreactive IgM against target A431 cells, but no detectable IgG. Cytoplasmic proteins prepared by repeated freeze-thaw of the hybridoma cells, membrane proteins obtained by NP-40 extraction of the cell membrane, and secreted proteins present in the supernates of the various hybridomas were assayed by an enzyme-linked immunoassay (ELISA), to understand the discrepancy observed in the immunoglobulins of the cellular and extracellular compartments. The parental UC 729-6 cell line used in these cell fusions produced only trace amounts of immunologically inactive IgM and no detectable IgG. Molecular sieving column chromatography of these hybridoma supernates suggested the presence of intact IgG and IgM molecules and the absence of free heavy chains or hybrid antibodies containing both mu and gamma heavy chains. Intrinsic labeling of VLN3G2 hybridoma cells with 35S-methionine demonstrated the presence of not only a nonimmunoglobulin protein but also a small molecular weight protein-A-binding polypeptide in the culture supernatant. 35S-methionine-incorporated IgG and IgM antibodies, isolated from spent media, cytoplasm, and cell membranes of VLN3G2, also showed binding to protein-A-bearing bacteria. In conclusion, the differences observed in the amounts of secreted MAbs by the human-human hybridomas were not due to the decreased synthesis of these molecules.

Immunodetection of cell-bound antigens using both mouse and human monoclonal antibodies

A micro enzyme-linked immunoassay (EIA) has been developed for the rapid and sensitive detection of either human or mouse monoclonal antibodies reactive with cell bound antigens. Whole intact cells are immobilized onto 96-well flat bottom microtiter plates by drying in an oven at 37 degrees C overnight prior to the start of the assay. This method of attachment was suitable for all cell types tested, regardless of origin, size and chromosomal content. The dried cells were then rehydrated, incubated with the appropriate test hybridoma supernatant, followed with subsequent analysis by EIA. The plates can be stored at 4 degrees C up to 1 month for future EIA analysis. This assay offers high sensitivity, requires only small amounts of target cells and test hybridoma supernatant, and can be completed within 3 h. This EIA is well suited for the rapid screening of large numbers of hybridoma supernatants and can also be adapted to include cells of any species, providing the appropriate antibody reagents are available.

A human monoclonal antibody reactive with human prostate

A human immunoglobulin M monoclonal antibody secreting hybridoma, termed MHG7, has been isolated and characterized for its reactivity against human prostate cells. Lymphocytes isolated from a regional draining lymph node of a patient with prostate carcinoma were fused with murine P3-NS1-Ag4-1 myeloma cells. Supernatants from the generated mouse-human somatic cell hybrids were first screened for human immunoglobulin production by an enzyme immunoassay. The identified human immunoglobulin-secreting hybridomas were expanded for further analysis and their supernatants screened by enzyme immunoassay against a panel of prostate cell lines. The human immunoglobulin M monoclonal antibody MHG7, in addition to reacting with prostate cell lines, also reacted with prostate carcinoma cells and benign prostatic hypertrophy cells on both frozen and paraffin embedded tissue sections. These data suggest that regional draining lymph nodes of prostate carcinoma patients can be used as a source of human lymphocytes for generating human immunoglobulin-secreting hybridomas reactive with human prostate cells.

UC 729-6, a human lymphoblastoid B-cell line useful for generating antibody-secreting human-human hybridomas

UC 729-6, a 6-thioguanine-resistant human lymphoblastoid B-cell line, was fused with normal and malignant human lymphocytes. Parent UC 729-6 cells were diploid with a 21p+ marker chromosome, expressed surface and cytoplasmic IgM kappa, and doubled every 17 hr. The resulting human-human hybridomas were pseudotetraploid containing the 21p+ marker, doubled every 20-30 hr, and secreted 3-9 micrograms of human Ig per ml per 10(6) hybrid cells for greater than 9 months in continuous culture. Human Ig-secreting hybridomas were generated in 88% (14/16) of the fusions carried out and were cloned by limiting dilution (one cell per three wells) without the use of feeder layers. The mean fusion frequencies (number of wells, plated at 10(5) cells per well, showing hybrid growth per 10(6) lymphocytes fused) of UC 729-6 with normal lymphocytes ranged from 0.45 to 2.9 and with malignant B lymphocytes, from 3 to 10. Analysis of the human-human hybridomas derived from lymphocytes isolated from regional draining lymph nodes of cancer patients revealed several that secreted human monoclonal antibody that reacted by an enzyme immunoassay with some carcinoma cell lines but not with normal fibroblast cell lines. These data suggest that (i) UC 729-6 can be fused with human lymphocytes to generate stable human-human hybridomas, some of which secrete antibody reactive to human cell surface antigens, and (ii) UC 729-6 can be used to rescue Ig from nonsecretory malignant B cells and thereby allow for the production of anti-idiotype antibodies.