Establishment of human Ig producing heterohybridomas by fusion of mouse myeloma cells with human lymphocytes derived from peripheral blood, bone marrow, spleen, lymph node, and synovial fluid. Effect of polyclonal prestimulation and cryopreservation

Advancement in the development of single chain antibodies using phage display technology

Phage display technology has become an important research tool in biological research, fundamentally changing the traditional monoclonal antibody preparation process, and has been widely used in the establishment of antigen-antibody libraries, drug design, vaccine research, pathogen detection, gene therapy, antigenic epitope research, and cellular signal transduction research.The phage display is a powerful platform for technology development. Using phage display technology, single chain fragment variable (scFv) can be screened, replacing the disadvantage of the large size of traditional antibodies. Phage display single chain antibody libraries have significant biological implications. Here we describe the types of antibodies, including chimeric antibodies, bispecific antibodies, and scFvs. In addition, we describe the phage display system, phage display single chain antibody libraries, screening of specific antibodies by phage libraries and the application of phage libraries.

Electrofusion of single cells in picoliter droplets

We present a microfluidic chip that enables electrofusion of cells in microdroplets, with exchange of nuclear components. It is shown, to our knowledge for the first time, electrofusion of two HL60 cells, inside a microdroplet. This is the crucial intermediate step for controlled hybridoma formation where a B cell is electrofused with a myeloma cell. We use a microfluidic device consisting of a microchannel structure in PDMS bonded to a glass substrate through which droplets with two differently stained HL60 cells are transported. An array of six recessed platinum electrode pairs is used for electrofusion. When applying six voltage pulses of 2–3 V, the membrane electrical field is about 1 MV/cm for 1 ms. This results in electrofusion of these cells with a fusion yield of around 5%. The operation with individual cell pairs, the appreciable efficiency and the potential to operate in high-throughput (up to 500 cells sec⁻¹) makes the microdroplet fusion technology a promising platform for cell electrofusion, which has the potential to compete with the conventional methods. Besides, this platform is not restricted to cell fusion but is also applicable to various other cell-based assays such as single cell analysis and differentiation assays.

Relationship between antibody productivity by activated human lymph node lymphocytes from lung cancer patients and lymphocyte subsets

Regional lymph node lymphocytes from five patients with primary lung cancer were analyzed for subset composition, and exposed in vitro to the polyclonal human B cell mitogen Staphylococcus aureus Cowan I (SACI) or the murine B cell mitogen lipopolysaccharide (LPS) and then fused with mouse myeloma cells for investigation at the clonal level of their antibody (Ab) production and its statistical relation to the original subset composition. No correlation was found between the proportion of CD19+, CD23+, or CD3+ cells in the lymphocyte sample prior to its exposure to either SACI or LPS, and the Ab production efficiency, defined as the ratio of the number of Ab producing wells to the total number of proliferating wells. For lymphocytes exposed to LPS, however, a strong correlation (r = 0.931, p = 0.02) was observed between the Ab production efficiency and the ratio of CD8+ to CD3+ cells (CD8/CD3) in the original sample at least within the ranges studied (CD8/CD3 = 0.216-0.288). For those exposed to SACI, no correlation was found between the Ab production efficiency and the CD8/CD3 ratio (r = 0.881, p = 0.12) or the proportion of CD8+ cells (r = 0.808, p = 0.19) in the original sample. These results suggest that the repertoire of B cells responsive to LPS is different at least in part from the repertoire responsive to SACI and that the ratio CD8/CD3 could serve as a practical predictor for Ab production by human lymphocytes stimulated with LPS.

Cryopreserved Human B Cells as an Alternative Source for Single Cell mRNA Analysis

Reverse transcription-polymerase chain reaction (RT-PCR) of individual B-lymphocytes has been shown to be a powerful tool for the simultaneous analysis of different mRNA specificities in both malignant and non-malignant B cell subpopulations. However, especially for longitudinal studies, this may also require analyses of cryopreserved cells. Therefore, the current study assessed whether cryopreserved (liquid nitrogen, dimethyl sulfoxide [DMSO]-stored) viable B cells are an alternative source for single cell RT-PCR analysis. Fresh (non-frozen) and post-thawed human peripheral blood B cells were analyzed by fluorescence-activated cell sorting (FACS). As a result, different B cell subpopulations could be reliably stained and separated from both fresh and post-thawed cells by four-color flow cytometry, although slightly diminished fluorescence intensities of some subpopulation markers were observed when analyzing cryopreserved cells. Subsequently, viable individual CD19+CD27+ memory B cells were sorted into single wells and analyzed for the expression of mRNA transcripts of the 'house-keeping gene' glyceraldehyde phosphate dehydrogenase (GAPD), the constitutive B cell homing receptor CXCR4, and immunoglobulin heavy chain variable region (IgVH) genes by nested RT-PCR protocols. Comparing both B cell sources, RT-PCR analysis revealed comparable yields of cells expressing transcripts for the three mRNA specificities tested (GAPD, CXCR4, IgVH) indicating the integrity of the respective mRNAs in cryopreserved B cells. In conclusion, these data indicate that optimally cryopreserved B cells may be an alternative source for single-cell RT-PCR analysis, especially in longitudinal B cell studies. However, the settings for both FACS analysis and RT-PCR should be re-evaluated for each distinct subpopulation and target mRNA of interest when analyzing post-thawed cells.

Development of Mouse Hybridomas by Fusion of Myeloma Cells with Lymphocytes Derived from Spleen, Lymph Node, and Bone Marrow

Since its discovery by Kohler and Milstein in 1975, hybridoma technology has found a wide use in almost every field of biology and medicine. A general and simple approach for developing monoclonal antibodies is to use splenocytes from immunized mice. In the present study, 10 fusion experiments were carried out to analyze the hybridization efficiencies of mouse myeloma cells with lymphocytes derived from spleen, lymph node, and bone marrow and we found a higher yield of antigen specific antibody producing hybridoma lines when the lymph nodes were used.

Efficient production of IgG human monoclonal antibodies by lymphocytes stimulated by lipopolysaccharide, pokeweed mitogen, and interleukin 4

Extensive screening of the mitogens lipopolysaccharide (LPS), pokeweed mitogen (PWM), and Staphylococcus aureus Cowan I (SAC I), alone and in combination and with and without interleukin (IL) was performed for in vitro activation of regional lymph node lymphocytes from lung cancer patients for the production of human IgG, IgM, and IgA. As assessed by electrofusion of the lymphocytes following their exposure to these agents with mouse myeloma cells and incubation of the fused hybridoma, a remarkable stimulatory effect was shown by LPS and particularly by LPS plus IL-4, which was substantially greater than that of either SAC I or PWM with or without various IL. Optimization studies indicated that the addition of PWM to LPS and IL-4 in the culture medium further stimulated the human antibody (Ab) production, and that the optimal formulation for stimulation of human IgG production was a culture medium containing 20 micrograms/ml of LPS, 1/500 of PWM, and 100 u/ml of IL-4.

Cell cluster formation during up-scaling of a human-mouse heterohybridoma producing a polyspecific human IgM antibody

Up- and downstream processing of human monoclonal IgM is known to bring about problems with respect to clone stability and quantity of antibodies produced. A human B cell hybridoma producing a natural polyreactive IgM antibody (CB03) was adapted to growth in serum-free medium and scaled-up using a hollow fiber bioreactor system. The process of fermentation has been carried out continuously over a period of 4 months. In comparison to stationary culture conditions in the presence of 10% fetal calf serum, antibody concentrations in hollow fiber bioreactor supernatants were found to be significantly increased. Semicontinuously harvested supernatants contained up to 400 mg/liter immunoreactive IgM antibody. During the last weeks of fermentation, a markedly reduced number of viable cells was observed, whereas antibody production seemed to remain stable. Furthermore, we detected formation of cell clusters in the fermentor system. These clusters carried IgM on the surface and secreted immunoreactive IgM antibodies. Clusters were found to represent fusions of hybridoma cells using electron microscopy. Cluster formation was accompanied by decreased glucose consumption and lactate accumulation and was not seen during growth of other human hybridomas. We discuss these results in the content of the polyreactive binding properties of this particular antibody.

Real-time biospecific interaction analysis of a natural human polyreactive monoclonal IgM antibody and its Fab and scFv fragments with several antigens

Surface plasmon resonance (SPR) was used to investigate the kinetics of interactions between the human monoclonal polyreactive IgM antibody CB03, its Fab as well as its single-chain variable fragment (scFv) and different antigens. From these experiments apparent binding constants were determined and compared with binding constants obtained by ELISA experiments. In SPR studies with the complete antibody, the polyreactivity of the CB03 antibody as derived from ELISA experiments was confirmed. Interaction of scFv with kappa casein and human myoglobin is strong evidence for the location of polyreactivity within the variable domains of the antibody. Apparent binding constants of the complete antibody to immobilized kappa casein (9.2 x 10(7) M-1) and to human myoglobin (1.6 x 10(7) M-1) are up to 83 times higher than those of Fab. The binding constants of the scFv to the above mentioned antigens are again about 10 times lower when compared with Fab, which is mainly due to the lower association rates of the complexes formed by the scFv.

Purification and immunochemical characterization of a natural human polyreactive monoclonal IgM antibody

In vitro and in vivo experiments to explain the function of natural polyreactive antibodies, usually of the IgM isotype, require large amounts of purified antibodies. We have developed a two-step purification procedure using a human natural polyreactive monoclonal IgM antibody (CB03). This combines hydrophobic interaction chromatography on phenyl-Superose and gel filtration over Superose 12 and readily permits scaling-up to isolate mg to g amounts of antibody. Retention of the CB03 antibody during gel filtration by precipitation and interaction with the gel matrix was overcome by the addition of 10 mM 3-[(3-cholamidopropyl)-dimethylammonio]-1-propanesulfonate. The yield of purified antibody was 34% and Fab fragments were obtained from the purified CB03 antibody by hot tryptic digestion (yield, 68% of theoretical amount). In an enzyme-linked immunosorbent assay, Fab and complete antibody had similar reaction patterns with different antigens.

Production of stable human-mouse hybridomas secreting monoclonal antibodies against Rh D and c antigens

Peripheral blood lymphocytes from donors immunized against Rh antigens were fused with mouse myelomas and heteromyelomas in order to obtain human-mouse hybridomas secreting antibodies specific for these antigens. Three cell lines secreting anti-D IgG and two secreting anti-c IgM were stabilized and produced immunoglobulins for several months. These human monoclonal antibodies were evaluated as reagents for Rh phenotyping. Their complementary activity towards weak D and partial D antigens is examined.

In vitro stimulation of human fetal lymphocytes by mitogens and interleukins

Human lymphocytes derived from fetal spleen and liver were studied for their capacity to respond to mitogens and interleukins using different in vitro models (cell volume increase, [3H]thymidine incorporation, Ig secretion). Although the number of mature B and T cells in the fetal liver preparations remained nearly constant [Settmacher et al. (1991) Immunobiol. 182, 256], only lymphocytes obtained from fetal organisms before the 25th week of gestation could respond to some of the polyclonal stimulators (PWM, anti-CD3 + IL-2, SAC + IL-2, SAC + IL-4) tested, whereas cells obtained after that period failed. In the fetal spleen, however, with increasing percentages of mature B and T cells during fetal development, a growing ability to respond to mitogens was registered, which, however, did not achieve the values found for the adult spleen material.

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.

Influence of somatic cell hybridization and human serum on the generation and stability of human hybridomas

We describe an approach that allows the generation of stable hybridomas secreting antigen specific human IgG antibodies with an efficiency comparable to that of the generation of IgM and IgA secreting hybridomas. This was achieved by evaluating means to increase the frequency of human hybridoma formation and the stability of the generated hybridoma cells when subjected to conditions for large scale growth. To this end, we generated new fusion lines with an increased human DNA content and modified the culture system. However, the application of these new fusion lines primarily resulted in unstable giant cells. As a consequence, we evaluated whether the viability of newly formed hybrids between existing fusion lines and lymphoblastoid cell lines might be improved. In an attempt to provide as many components necessary for the growth of antibody secreting hybridomas as possible, we propagated fused cells in medium supplemented with human serum. Our results show that with this approach the frequency of initially growing hybrids was significantly increased. Furthermore, only in culture medium supplemented with human serum was it possible to obtain stable IgG secreting clones.

In vitro immunization of human tonsilar lymphocytes: effects of PWM and rIL-6

We previously described a system for the in vitro immunization of human tonsilar lymphocytes under serum-free conditions in the presence of muramyl dipeptide and rIL-2 (1). Further studies with this system reveal possible roles for PWM and rIL-6 in the immunization process. The addition of these factors led to an increase in the levels of antibody produced in lymphocyte cultures. The time of addition of these factors was found to be important in determining the extent of their effects on the overall yields of antigen-reactive cells.

Polyclonal stimulation of human B lymphocytes derived from fetal liver and spleen cells at different stages of ontogeny

The functional capacity of human lymphocytes derived from fetal liver and spleen at different stages of ontogeny (16-34 weeks of gestation) was studied using in vitro models (increase in cell volume, [3H]thymidine incorporation, Ig secretion) reflecting various stages of activation induced by mitogens (LPS, PWM) in vitro. Lymphocytes differed in their reactivity to LPS depending on the period of intrauterine development: cells from the early liver could respond with enhanced IgM production whereas lymphocytes derived from this organ after more than 25 weeks failed. The opposite was found to apply to spleen cells: only lymphocytes derived from the organ after more than 25 weeks showed significant LPS-induced in vitro differentiation. These data were in correlation with the proliferative response to LPS. It was clear that the number of CD20-positive mature B cells in the lymphocyte preparations was not responsible for these results, since comparable yields were found throughout the period of fetal development of the liver studied, whereas in the spleen increasing numbers of B cells were seen.

Construction of a bovine-murine heteromyeloma cell line; production of bovine monoclonal antibodies against rotavirus and pregnant mare serum gonadotrophin

Bovine-murine heteromyeloma cell lines were prepared by fusing lymphoid cells from a bovine leukemia virus (BLV)-infected cow with mouse myeloma cells. Selection of hybrid cell colonies was based on the ratio of bovine and murine chromosomes, the presence of cell-surface immunoglobulins and growth characteristics. First-generation fusion partners were compared for fusion efficiency and the number of antigen-specific antibody-producing clones generated. Hybrid cell colonies that initially secreted antibodies were selected from first-generation heteromyelomas to function as second-generation fusion partners. Although fusion efficiencies for both generations did not differ, the second-generation heteromyelomas yielded a higher number of specific antibody-producing clones. Fusion of hteromyelomas with either lymph node cells or splenocytes indicated that fusion with lymph node cells results in a higher number of specific antibody-producing clones, whereas fusion efficiency was found to be higher with splenocytes. The optimal time intervals between the final booster injection and fusion were found to be 4 days for splenocytes and 7 days for lymph node cells. Finally, the characterization of bovine monoclonal antibodies against bovine rotavirus and pregnant mare serum gonadotrophin and their neutralizing capacities in vitro are described.

Development of specific IgG-producing human hybridomas by fusions of lymphocytes from actively immunized persons

More than 13,500 initial hybridoma lines derived from fusions of lymphocytes from non-boosted persons were tested for IgG production against Tetanus Toxoid. However, only 2 were found to produce IgG monoclonal antibodies of the desired specificity. Peripheral blood lymphocytes were then taken from actively immunized donors 3, 7, 14 or 60 days after boosting and fused to the HAT-sensitive heteromyeloma cell line CB-F7. A strong enhancement of both IgG-producing hybridomas and specific IgG-producers was detected in fusions of lymphocyte material derived 7 days after booster injection (239 of 731 IgG-producing lines showed anti-TT-specificity). Two months after boosting no more specific IgG-producing hybridomas could be established from the peripheral blood of the donors. Data were discussed regarding an optimized human monoclonal antibody production against bacterial antigens.