In vitro immunization for the production of antigen-specific lymphocyte hybridomas

Hybridoma technology for the generation of rodent mAbs via classical fusion

Monoclonal antibodies (mAbs) have proven to be instrumental in the advancement of research, diagnostic, industrial vaccine, and therapeutic applications. The use of mAbs in laboratory protocols has been growing in an exponential fashion for the last four decades. Described herein are methods for the development of highly specific mAbs through traditional hybridoma fusion. For ultimate success, a series of simultaneously initiated protocols are to be undertaken with careful attention to cell health of both the myeloma fusion partner and immune splenocytes. Coordination and attention to detail will enable a researcher with basic tissue culture skills to generate mAbs from immunized rodents to a variety of antigens (including proteins, carbohydrates, DNA, and haptens) (see Note 1). Furthermore, in vivo and in vitro methods used for antigen sensitization of splenocytes prior to somatic fusion are described herein.

Cooperation of dendritic cells with naïve lymphocyte populations to induce the generation of antigen-specific antibodies in vitro

The production of monoclonal antibodies by hybridoma technology is dependent on lymphocytes taken from vertebrates which have to be immunized against the corresponding antigen. We present here our first experiments which should allow the replacement of this in vivo immunization step by an in vitro immunization procedure. This work provides new possibilities for the specific activation of immune cells in order to use them for the generation of antibodies which are not of murine origin. Bone marrow-derived dendritic cells were loaded with antigen and co-cultured with naïve T and B lymphocytes of non-immunized mice. The interaction and activation of the different cell types were investigated by measuring the expression of specific cell surface markers, the release of activation-dependent interleukins and the secretion of antigen-specific antibodies. We could demonstrate that dendritic cells process and present antigen fragments and activate T cells, that T cells proliferate and release activation-induced interleukins, and that B cells maturate under the influence of activated T cells and secrete antigen-specific antibodies.

Antibodies induced by Plasmodium falciparum merozoite surface antigen-2-designed pseudopeptides possess neutralizing properties of the in vitro malarial infection

Pseudopeptide chemistry is gaining ground in the field of synthetic vaccine development. We have previously demonstrated the potential scope of introducing reduced amide peptide bond isosters in a site-directed design for obtaining structurally modified probes able to induce malaria infection-neutralizing antibodies derived from the MSP-1 antigen. This work reports the functional properties of polyclonal and monoclonal antibodies induced by site-directed designed MSP-2 N-terminus pseudopeptides and their capacity for antibody isotype switching in in vitro immunization. Structural properties of the native peptide and its pseudopeptide analogs are discussed within the context of these novel pseudopeptides' induced monoclonal antibody functional and physical-chemical properties.

Characterization of Human Tissue Factor (TF)–Specific Monoclonal Antibodies Prepared Using a Rapid Immunization Protocol

Tissue factor (TF) plays an important, physiological role in hemostasis. Recent studies have demonstrated the over-expression of TF in a number of solid tumor types and its pathological roles in angiogenesis and tumor metastasis. In this study, we report the development and characterization of a panel of murine MAbs that are specific for human TF, but do not inhibit TF-mediated blood coagulation. By using a modified repetitive immunizations at multiple sites (RIMMS) protocol in conjunction with an efficient hybridoma cloning procedure, anti-TF MAbs were generated within a relatively short time frame of 5-6 weeks. Following primary screening by ELISA, the binding of the MAbs to the native form of human TF was demonstrated in flow cytometry using a stable cell line expressing human TF. Several of these TF-specific MAbs did not inhibit blood coagulation in a blood coagulation assay and bound with high affinity (0.5-2 nM) to human TF in BIAcore analyses. Importantly, this study represents an independent evaluation of the RIMMS strategy for MAb generation and demonstrates that class-switched, high-affinity MAbs can be generated rapidly and reliably using RIMMS.

Identification of tyrosine phosphorylated adhesion proteins in human cancer cells

Tyrosine phosphorylation is a form of signal transduction that regulates cell growth, differentiation, migration, and survival. This knowledge has promoted much interest in the role of tyrosine kinases and phosphatases in regulating cell behavior during development and tumorigenesis. However, it is generally less well appreciated that tyrosine phosphorylated proteins are enriched within sites of cell adhesion, particularly in transformed cells. To identify these, we developed a panel of monoclonal antibodies specific for tyrosine phosphorylated proteins in breast cancer cells, using extensive modifications of existing technologies for immunization, somatic fusion, and antibody screening. Mice were immunized with a complex mixture of phosphotyrosine containing proteins using the newly developed RIMMS method. By increasing the sensitivity of antigen recognition, we isolated reagents specific for a wide diversity of tyrosine phosphorylated adhesion proteins in breast cancer cells.

Rapid development of affinity matured monoclonal antibodies using RIMMS

Affinity matured murine monoclonal antibody producing cell lines can now be rapidly generated using a novel repetitive, multiple site immunization strategy designated RIMMS. RIMMS capitalizes on rapid hypermutation and affinity maturation events which occur in B cell populations localized within secondary lymphatic tissue early in response to antigenic challenges. A murine myeloma cell line, P3XBcl-2-13, stably transfected with Bcl-2, enhances the outgrowth of hybridomas following somatic fusion with immune lymphocytes isolated from pooled peripheral lymph nodes (PLN) 8-14 days after the initial immunization. Immunizations somatic fusion, screening and isolation of affinity matured IgG secreting monoclonal antibody cell lines occur within a one month time period. By using RIMMS, we have been able to expedite the isolation of affinity matured monoclonal antibodies to numerous antigens, including a drug hapten.

Influence of antigen presentation and exogenous cytokine activity during in vitro primary immunizations employed for the generation of monoclonal antibodies

Hybridomas secreting monoclonal antibodies (MAbs) against African horse sickness virus (AHSV) were generated using different AHSV antigen preparations (inactivated AHSV, semi-purified virus, and a preparation of nonstructural viral proteins) in one of three different in vitro primary immunization systems: (i) the Cel-prime kit, a method using immunization of splenocytes aided by antigen-primed support cells; (ii) a system based on a cytokine soup derived from a mixed lymphocyte reaction plus stimulated EL4-IL-2 cells; (iii) a system based on a cytokine soup derived from splenocytes stimulated by pokeweed mitogen in order to obtain a mixture of cytokines enriched for Th2 lymphokines. The viability of immunized BALB/c mouse splenocytes, immunoglobulin production by the subsequently generated hybridomas, and the specificity of the MAbs were compared. The most efficient in vitro primary immunization system was the Cel-prime system employing semi-purified antigen. This efficiency was manifest in terms of a greater viability of the splenocytes in the immunization, as well as a higher number of specific antibody-secreting hybridomas. It seems probable that the support cells of the Cel-prime system have an accessory function such as that attributed to antigen-presenting cells. Such a function would result in impairment of apoptosis, and thus increase the viability of the splenocytes in the in vitro primary immunization system, as well as enhancing stimulation of the immune response against the antigen used. The presence of cytokines at the beginning of the in vitro primary immunization did have an influence, but this was secondary to what appeared to be the major event of cellular interaction associated with the accessory cell function of the support cells.

Stimulation of human peripheral lymphocytes via CD3 and soluble antigen abrogates specific antibody production by reducing memory B cell numbers

Human B cells are polyclonally activated in vitro by T cells stimulated with immobilized anti-CD3 monoclonal antibodies. We have analysed the effect of CD3 ligation on the production of antigen-specific antibodies, using peripheral blood lymphocytes from tetanus toxoid vaccinated blood donors. High levels of antigen-specific antibodies were obtained after stimulation with anti-CD3 antibodies for 7 days. Addition of soluble recall antigen did not affect the total amount of Ig produced, but dramatically decreased the antigen-specific response. The addition of IL-2, IL-4, and anti-CD40 or anti-CD28 antibodies or the removal of antigen did not restore the B cell response. Analysis using limiting dilution of B cells showed that the frequency of antigen-specific memory B cells decreased significantly in cultures stimulated with antigen. The antigen-specific B cell response could be completely restored only if the soluble antigen was cross-linked on the surface of the B cells. These results suggested that peripheral memory B cells were eliminated or anergized in the presence of soluble antigen.

Antigen-specific activation of B cells in vitro after recruitment of T cell help with superantigen

BACKGROUND

Human B cells can proliferate in vitro after stimulation with anti-Ig and via the CD40 molecule. Superantigens like SEA which bind to MHC class II antigens on, e.g. B cells can polyclonally activate T cells via interaction with their TcR. The activated T cell subsequently activates the B cells to proliferation and Ig-production.

OBJECTIVES

To investigate whether superantigen could be used to direct polyclonal T cell help to human B cells stimulated by antigen in a restricted manner resulting in production of antigen-specific antibodies in vitro.

STUDY DESIGN

Purified B cells were preincubated with the antigen in manners allowing crosslinking of surface-Ig. The antigen exposed B cells were then cultured together with autologous CD4+ helper T cells and in the presence of various concentrations of SEA. Antibody production was measured by ELISA after 7-12 days of culture.

RESULTS

Antigen-specific activation of B cells could be obtained after stimulating the B cells with antigen or anti-surface-Ig antibodies in the presence of T helper cells and SEA. The degree of B cell activation (proliferation as well as antibody production) depended on the dose of antigen as well as on the dose of SEA used. Increased crosslinking of surface-Ig on antigen-specific B cells enhanced Ig production. Specific antibody production to a secondary recall antigen (tetanus toxoid) and to primary antigens (DNP and GM2) were obtained. The specific B cell response was dependent on contact between T and B cells.

CONCLUSION

the results obtained demonstrate that the superantigen SEA can recruit T cell help to human B cells specifically stimulated by antigens, resulting in production of antigen reactive antibodies in vitro.

Characterization of a monoclonal antibody to the capsule of Haemophilus influenzae type b, generated by in vitro immunization

Monoclonal antibodies to polyribosylribitolphosphate (PRP), the capsular polysaccharide of Haemophilus influenzae type b (Hib), are useful tools in the investigation of the molecular and cellular mechanisms causing Hib meningitis. A better understanding of these mechanisms may lead to improved therapeutic strategies. A number of different in vivo immunization techniques in BALB/c mice were used, which did not however reveal detectable serum levels of antibodies to PRP. Therefore a modified in vitro immunization technique, originally established for in vitro immunization of human B lymphocytes, was used for this weak immunogen in mice. After 5 days of in vitro stimulation with purified PRP the splenic lymphocytes of BALB/c mice were fused with the mouse myeloma line P3-X63-Ag8.653. One hybridoma produced an IgM antibody (12E7) which recognized the capsular polysaccharide in ELISA and specifically labelled all tested Hib strains in immune fluorescent microscopy. The blotted polysaccharide PRP was immunostained with monoclonal antibody 12E7. Preincubation of Hib with this antibody enhanced the oxygen radical metabolism of polymorphnuclear leucocytes in a chemiluminescence assay. There was no cross-reactivity with the supernatants of other Haemophilus influenzae serotypes and other bacterial species, as shown by counterimmunoelectrophoresis.

A cell surface antigen (BAL) defined by a mouse monoclonal antibody inducing apoptosis in a human lymphocytic leukemia cell line

The lack of apoptosis or programmed cell death in human tumor cells has been suggested to be one factor allowing uncontrolled growth of neoplasms. We have developed a mouse monoclonal antibody (MAb) that induces programmed cell death in a human acute leukemia cell line (KM-3) of the pre B-cell type. Stable, antibody-producing hybridomas were produced by fusing mouse myeloma cells to spleen cells from mice immunized with viable KM-3 cells. Incubation of KM-3 cells with the MAb (designated anti-BAL) resulted in growth inhibition and subsequent cell death within 2-3 days. Anti-BAL required cross-linking with a rabbit anti-mouse antibody to induce DNA fragmentation typical of apoptosis. Immunoblotting experiments with anti-BAL identified a 37-kDa protein, apparently different from any previously described apoptosis-related surface antigen. Strongest expression of the antigen was generally found on cells of lymphoid or myeloid origin. However, several other cell types such as fibroblasts and endothelial cells were also stained by anti-BAL in flow cytometry but less intensively. Despite the apparent presence of this cell surface-bound 37-kDa antigen on several normal and malignant cell types, anti-BAL induced cell death only in human malignant cell lines expressing a more immature phenotype.

Rapid generation of monoclonal antibody-secreting hybridomas against African horse sickness virus by in vitro immunization and the fusion/cloning technique

Splenocytes from non-immune mice were stimulated in vitro using an equimolar mixture of factors from mixed lymphocyte reaction (MLR) and from phorbol-12-myristate 13-acetate (PMA) stimulated EL-4 cells, and concomitantly immunized with inactivated African horse sickness virus (AHSV) antigen serotype 4 or viral proteins 2 and 5 from AHSV serotype 9. Fusion with NSO myeloma cells was performed five days after primary or secondary stimulation/immunization. The record of hybridoma growth after a standard method of fusion, expansion of cells and subsequent cloning was compared with a fusion/cloning method in which cells were cloned within 2 to 3 days of the fusion event. Detection of antigen specific antibodies in the hybridoma culture supernatants was successful only with cells derived from primary stimulation/immunizations. Antibodies were detected using an indirect ELISA with the immunizing antigen coated on to the surface of the plates. Monoclonal hybridomas were isolated within 2 to 3 weeks using the fusion/cloning method, compared with the standard method, where it took 4 to 5 weeks. Although the total number of clones isolated from the fusion/cloning method was less than that obtained through the standard method, the yield of specific antibody-producing hybridomas as a percentage of the total picked was often more efficient with the fusion/cloning method. With respect to the immunoglobulin isotype produced, not all of the antibodies could be classified by the ELISA system used; 14% of anti-AHSV positive clones were identified as IgG-secreting cells, 25% as IgM-secreting, 18% were cross-reacting with IgG and IgM, and 43% could not be classified. Similar results in all aspects of the work were obtained whether a crude infected cell extract or purified outer capsid polypeptides VP2/5, from serotype 4 and serotype 9 respectively, were used.

Epitope mapping and binding kinetics of monoclonal antibodies studied by real time biospecific interaction analysis using surface plasmon resonance

The interaction between human heart myoglobin and ten specific monoclonal antibodies was investigated with a new biosensor technology, real time biospecific interaction analysis (RT BIA), using surface plasmon resonance. Analysis of association and dissociation kinetics was monitored in real time, with unlabelled reactants. Antibody isotyping was rapid and simple. Epitope mapping with RT BIA confirmed, with substantial time saving, the sum of results obtained in conventional labelled systems. Monoclonal antibodies with four different epitope specificities and optimal binding function were selected for a myoglobin sandwich assay with enhanced sensitivity. BIAcore can be used directly as a diagnostic tool, or as an analytical tool in immunoassay development.

In vitro immunization with antigen directly blotted from SDS-polyacrylamide gels to polyvinylidene difluoride membranes

A new immunization method has been developed for the production of monoclonal antibodies. This technique uses small amounts of partially purified and weak immunogenic antigen, bound to membranes after blotting from SDS-PAGE. For this purpose two different membranes have been tested. Immobilon-P polyvinylidene difluoride (PVDF) membranes were less mitogenic than nitrocellulose membranes, and were therefore selected for the in vitro immunization using 6-pyruvoyl tetrahydropterin synthase as antigen. The in vitro immunization method was then used for the production of monoclonal antibodies against 6-pyruvoyl tetrahydropterin synthase, one of the key enzymes on the biosynthetic pathway of tetrahydrobiopterin, the natural cofactor of the mammalian aromatic amino acid hydroxylases. The antibodies obtained were mainly of the IgM type.

Improved sensitivity in the antibody-forming cell assay for Japanese encephalitis virus in mice by optimal fixation of cells and avidin-biotin complex (ABC) immunocytochemistry

A sensitive modified method for the detection in vitro of antibody-forming cells (AFCs) in Japanese encephalitis (JE) virus infected mice is described. The procedure involves the selection of the most appropriate incubation period, after the infection of monolayer cells, for expression of viral antigens to be recognized by AFCs. Adequate preservation of the expressed antigens was achieved after fixation with paraformaldehyde-lysine-periodate buffer (PLP). The development of spots which corresponded to AFCs was successfully obtained with the use of the avidin-biotin complex (ABC) amplification reaction. The number of the spots developing after completion of the assay was greater after PLP fixation compared with other fixation solutions such as methanol, formalin and acetone-water. Optimum antigen expression on the infected cells for recognition by lymphoid cells was reached after 24 h of infection. However, it was possible to detect viral antigens on the infected cells 8 h after infection. The ABC reaction was shown to be the best procedure for developing spots compared with other immunocytochemical methods. A linear increment was observed in the number of spots that developed at different spleen cell densities. This assay is simple to perform and could detect virus-specific Ig producing cells from the spleens of mice infected with JE virus. It also makes it possible to enumerate accurately the kinetics of the AFC response in different lymphoid organs during infection or after vaccination.

Analyses of the primary in vitro responsiveness of non-immune porcine peripheral blood mononuclear cells with reference to immunization by African swine fever virus antigen and treatment with leucine methyl ester

Peripheral blood mononuclear cells (PBMC) from non-immune pigs were immunized in vitro using African swine fever (ASF) virus antigen with concomitant mitogenic stimulations known to have varying effects on B and T lymphocyte activity. None of these conditions, including those previously reported as being successful for the in vitro immunization of non-immune porcine PBMC with ASF virus antigen, supported the induction of specific antibody. Due to the reports on in vitro immunization of human PBMC, attempts were made to control suppressor cell activity in the porcine PBMC from non-immune pigs through L-leucine methyl ester (Leu-OMe) treatment. Upon immunization of the Leu-OMe treated PBMC with ASF virus antigen, concomitant with mitogen or cytokine stimulations, no specific antibody production was detected. Nevertheless, aspecific porcine immunoglobulin secretion was observed. Further analysis of the PBMC responsiveness demonstrated that 2.5 mM Leu-OMe (the dose recommended for use with human PBMC) suppressed mitogen-induced porcine lymphocyte proliferation, but in the absence of any detectable cytotoxicity. In fact, both anti-ASF virus antigen specific immunization and stimulation with "T-lymphocyte" mitogens were suppressed, whereas pokeweed mitogen stimulation of B lymphocyte aspecific immunoglobulin secretion was unaffected. Consequently, it was not possible to immunize in vitro non-immune porcine PBMC with ASF virus antigen as had been previously reported, nor was it possible to transfer the technology successfully used with non-immune human PBMC to the in vitro stimulation/immunization of non-immune porcine PBMC. The furtherance of this work will require greater insight into the immunobiological parameters and dynamics of the stimulation of non-immune porcine peripheral blood leukocytes, which are not as simple as previously reported, nor the same as identified with human PBMC.

Production of monoclonal antibodies specific for African swine fever virus following in vitro primary immunization of mouse splenocytes in the presence of stimulated T lymphocyte supernatants

Splenocytes from non-immune mice were stimulated in vitro using a kit of cytokine preparations (obtained from murine MLR and EL-4 cell cultures), and concomitantly immunized with African swine fever (ASF) virus antigen. In addition, fusions were performed at 5 days after primary or secondary stimulation/immunization. The detection of specific antibodies in the culture supernatants was not successful. In contrast, specific antibody-producing hybridomas could be generated, and this was at least comparable to a standard in vivo immunization regime, even though the optimum fusion ratio employed with these in vitro immunized splenocytes was one which is not optimum when in vivo immunized lymphocytes are used. Consequently, it would appear that hybridoma generation is a more sensitive method than the direct measurement of antibody at detecting in vitro primary immune responses. After primary in vitro immunization, the majority of immunoglobulins produced were apparently of the IgG isotype, with only 8-17% clearly IgM. These antibodies were mainly against VP73 (the major viral envelope protein) as expressed on viral antigen extracted from infected cells, although other specificities were also found. This demonstrated, by in vitro means, that the VP73 carried dominant immunogenic epitopes on ASF virus. Such observations show that the in vitro responses were closely related to those which have been detected in vivo.

Affinity repertoire of monoclonal antibodies obtained by primary or secondary in vitro immunization

The effect of the antigenic dose (1 ng-10 micrograms DNP-KLH/ml) on affinity constants of monoclonal antibodies produced by in vitro immunization was investigated. A statistically significant (p = 0.0000) trend could be demonstrated since the higher antigen concentration that was used during the five day culture the lower was the obtained Kass value. The range of affinities of the IgM monoclonal antibodies was similar to what was obtained from IgM antibodies produced by in vivo immunizations. However, the combination of a primary in vivo immunization followed by a secondary in vitro stimulation schedule resulted in an antigen dependent generation of high affinity isotype switch variants, exhibiting even higher affinities compared to monoclonal antibodies produced from only in vivo immunized animals. These results demonstrate that it is possible to elicit both an antigen-driven primary or secondary response in vitro.

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.

Rapid isolation of K88+ Escherichia coli by using immunomagnetic particles

Superparamagnetic polymer particles precoated with sheep anti-mouse immunoglobulin G were coated with immunoglobulin G2 monoclonal antibodies to the K88 antigen of Escherichia coli (MAb-K88). These immunomagnetic particles (IMP) were used for isolation and identification of K88 antigen-positive (K88+) E. coli. The bacteria presenting the K88 antigen were easily isolated in almost pure culture from a mixed culture of five different O serogroups of E. coli. Nonspecific binding of K88 antigen-negative (K88-) E. coli to the IMP was not observed. The sensitivity of the test to detect K88+ E. coli was found to be 4,000 CFU/ml with fluorescence microscopy. When bacteria attached to the MAb-K88 IMP were grown on blood agar, about 20% of the initial number of CFU was recovered. The test is promising as a rapid method for isolation and identification of K88+ E. coli from a mixed culture.

Production of monoclonal antibody against electrophoretically purified RNA polymerase II subunits using in vitro immunization

A procedure has been developed for the production of MAb against weakly immunogenic subunits of a multisubunit enzyme. This procedure takes into account the problems of insufficient antigen, single epitope immunodominance and the difficulty of mapping non-sequential determinants. Small quantities of mammalian RNA polymerase II subunits were purified by SDS-polyacrylamide gel electrophoresis and were used to immunize splenocytes in vitro. After fusion with plasmacytoma cells, the hybrid cells were cloned and screened by ELISA utilizing native RNA polymerase II. This procedure is biased towards the production of MAb directed against sequential epitopes accessible on the native enzyme. Monoclonal antibodies, produced by in vitro immunization, were shown to be useful in protein transblot analyses, to inhibit enzyme activity in vitro and to have binding affinities comparable with MAbs produced by in vivo immunization.

Human monoclonal antibodies produced by primary in vitro immunization of peripheral blood lymphocytes

A general procedure is described for the production of human monoclonal antibodies from peripheral blood lymphocytes immunized in vitro against T-cell-dependent antigens. These lymphocytes immunized in culture were used to produce human-human or human-mouse hybridomas secreting monoclonal antibodies specific for digoxin, hemocyanin, a recombinant fragment of the gp120 envelope glycoprotein of human immunodeficiency virus (PB1), or a melanoma-associated antigen (p97). Depletion of a lysosome-rich cell population, containing large granular lymphocytes, monocytes, cytotoxic T cells, and a subset of CD8-positive T cells, was shown to be crucial before the cells could be immunized in vitro. This depletion was accomplished by treating the peripheral blood lymphocytes with the lysosomotropic agent L-leucine methyl ester. In addition, the in vitro immunization had to be supported by interleukin 2, gamma-interferon, and B-cell growth and differentiation factors, derived from irradiated, pokeweed-mitogen-stimulated human T cells. The production of human monoclonal antibodies from primary, antigen-specifically activated peripheral lymphocytes might obviate the need to immunize volunteers or patients.

Positive selection of antigen-specific B lymphocytes by means of immunomagnetic particles

This paper presents a method for the isolation of highly enriched antigen-specific B lymphocytes from peripheral blood mononuclear cells (PBMC) by means of an immunomagnetic procedure. The method is illustrated by the isolation of B cells positive for rheumatoid factors (RF) from patients with rheumatoid arthritis and healthy blood donors. After Epstein-Barr virus transformation of isolated cells, more than 90% of the generated immunoglobulin-secreting cells produced RF in several experiments. Compared to the low frequency of B cells positive for RF in PBMC, this represents a 10(3)- to 10(4)-fold enrichment of antigen-specific B cells.

Biological effects of a rat monoclonal anti-mouse IFN-gamma antibody produced by in vitro immunization

This paper describes the biological effect of monoclonal antibodies to murine IFN-gamma produced by in vitro immunization with only several nanograms of rIFN-gamma. Four mAbs binding to rIFN-gamma were selected. mAb U7 was characterized in detail and shown to bind specifically to rIFN-gamma in a Western blot and to specifically inhibit the antiviral effect of rIFN-gamma and natural IFN-gamma. The activities of IFN-alpha, beta and IL2 were not affected. The M phi activating effect of both rIFN-gamma and natural IFN-gamma was also inhibited by mAb U7. Thus, we showed that it is possible to produce specific mAbs with very small amounts of cytokines by in vitro immunization.

Human monoclonal antibodies produced from L-leucine methyl ester-treated and in vitro immunized peripheral blood lymphocytes

Primary in vitro immunization of peripheral blood lymphocytes has been studied for the production of human monoclonal antibodies. Depletion of a lysosome-rich cell population, containing large granular lymphocytes, monocytes, and a subset of T suppressor cells, was shown to be crucial before the cells could be immunized in vitro. The in vitro immunized lymphocytes were used to produce human x human and human x mouse hybridomas secreting monoclonal antibodies specific for digoxin, hemocyanin, or a recombinant fragment of gp120 of human immunodeficiency virus.

A monoclonal-based, two-site enzyme immunoassay of human insulin

A procedure is described for the efficient production of insulin-specific monoclonal antibodies, which involves primary and secondary immunization of BALB/c mice in the hind footpads with bovine or porcine insulin and fusion of lymphocytes from popliteal lymph nodes with a P3x63 murine myeloma line. With this protocol, over 200 positive hybrids were obtained from four separate fusions. Dissociation constants of 31 purified monoclonals, cross-reacting with human insulin, were determined by two different methods and ranged between 4 X 10(-10) and 2 X 10(-6) mol/l. 24 monoclonals were biotinylated, paired in all possible combinations and tested by ELISA for their capacity to simultaneously bind to human insulin in a two-site assay. More than 40 monoclonal pairs were found which formed a sandwich with the hormone. The development of a simple and rapid one-step enzyme immunoassay is described, which involves a first monoclonal bound to the wells of a microtiter plate and a second monoclonal conjugated to alkaline phosphatase. With this assay, insulin can be determined in a range between 0.08 and 7.5 ng/ml in 3-4 h.

Partial purification of lymphoblasts after in vitro immunization increases the yield in Ig-producing hybridomas

Using in vitro immunization with a human plasma protein (apolipoprotein-A1) as antigen, we have shown that it is possible to prepare more monoclonal antibodies using a ten-fold lower concentration of antigen compared to in vivo immunization procedures (Weech et al., 1985). In addition, we can increase the number of Ig-producing hybridomas after in vitro immunization by a simple one-step separation of the lymphoblasts on a Percoll gradient before the fusion procedure. In order to apply this procedure to in vivo immunization techniques, it is necessary to expand the B-blast/plasma cell population by culturing the spleen cells for 4-6 days before fusion. Only antibodies of the IgM class were produced with the in vitro technique. However, by combining in vivo priming with in vitro immunization, it is possible to produce specific antibodies to both IgG and IgM classes.

In vitro B-lymphocyte antigen priming against both non-immunogenic and immunogenic molecules requiring low amounts of antigen and applicable in hybridoma technology

A method to efficiently antigen-prime B-lymphocytes with low amounts (less than 1 microgram/10(8) cells) of either immunogenic or non-immunogenic molecules is described. Keyhole limpet hemocyanin (KLH) and histone were used as prototypes for strongly immunogenic and for phylogenetically conserved non-immunogenic epitopes, respectively. Several modifications of previously reported methods were applied to the system and resulted in the requirement of antigen amounts sufficiently low to be obtainable by elution of proteins from electrophoretic gels. Antigen priming against highly purified antigen preparations is thereby feasible even when purified material cannot be obtained by conventional biochemical procedures. The amount of T- and B-lymphocytes and interleukin-2 production was estimated under various conditions during the priming procedure, and those optimal for generation of a high number of antigen-specific B-lymphocytes determined. In vitro antigen-primed B-lymphocytes were immortalized by conventional hybridoma technology. By fusion of lymphoid cells with myeloma cells at each day during the antigen-priming period, the optimal day of fusion to generate antigen-specific hybridomas was determined. Further, in 12 experiments with different antigens, 11 monoclonal antibodies to histones H3 and H4, two to the murine glucose transporter, 17 to trinitrophenyl-sheep red blood cells, and 20 to KLH were obtained. All specific hybridomas produced IgMs, as the antigen-priming period could not be extended for more than 9-10 days, whereafter a rapid decay in B-lymphocytes occurred.

Development of in vitro immunization in murine and human hybridoma technology

The development of in vitro immunization in murine and human hybridoma technology is reviewed. Special consideration is given to: technical aspects of in vitro immunization of mouse B cells; quality of antibodies produced by in vitro immunization; advantages of murine in vitro immunization; technical aspects of in vitro immunization of human B cells; and the advantages of human in vitro immunization and human monoclonal antibodies. Future developments likely to be made in this area of immunotechnology are outlined.

In vitro sensitization using thymocyte conditioned medium prepared from fetal calf, horse and rabbit sera

Thymocyte conditioned medium (TCM) was prepared using 2 lots of fetal calf, and 1 lot each of horse and rabbit sera. The 4 TCM and the respective sera alone were compared in their ability to support primary in vitro sensitization to sheep red blood cells (SRBC) as assayed by direct plaque formation. As would be expected, only the fetal calf sera (FCS) supported the primary in vitro sensitization to SRBC, while the use of the TCM prepared from the FCS resulted in a doubling of direct plaque formation. TCM prepared from either the rabbit or horse sera did not provide adequate support for this primary antibody response to SRBC. These data indicate that only sera able to support primary in vitro sensitization is useful for the preparation of active TCM ultimately used in B cell sensitization for hybridoma formation.

A filter immuno-plaque assay for the detection of antibody-secreting cells in vitro

A plaque assay has been developed that is based on enzyme immunoassay principles and capable of screening several hundred samples in one day. Single cell suspensions of in vivo or in vitro immunized mouse splenocytes are incubated on antigen-coated nitrocellulose membranes in microfilter plates or in petri dishes. The antibody production of individual cells is detected using a horse radish peroxidase-labeled second antibody, and the insoluble products of the enzymatic reaction are visualized as blue plaques on the membranes. The nitrocellulose membrane of the microfilter plates, which readily absorb a variety of antigens, and the filtration unit used for the washing steps greatly facilitates the plaque assay. Furthermore, this procedure only needs small amounts of antigen for the enumeration of isotype-specific antibody-secreting cells in a defined medium containing low protein levels or in a completely serum-free medium. The plaque assay may be used to evaluate the optimal conditions required for in vitro immunizations.

Optimization of conditions for in vitro antigenic stimulation of dissociated mouse spleen cells for the production of monoclonal antibodies against peptide hormones

Factors affecting hybridoma yield following in vitro immunization have been investigated. Of critical importance for optimum yield was the batch of young calf serum used both in immunization cultures and in post-fusion cultures. Only 1 batch of serum was found to be suitable for the immunization step. The addition of horse serum to deficient young calf serum in pre-fusion cultures did not reconstitute the essential component(s). Addition of T cell, macrophage and bovine endothelial cell conditioned medium to the supportive batch of young calf serum in pre-fusion cultures did not increase the yield of hybridomas. For one antigen (insulin) the yield of hybrid cells was dependent on the concentration of antigen in immunization cultures. This was not the case, however, with the second antigen (ACTH) within the concentration range examined. The optimum spleen cells density was 1 X 10(7) cells/ml and the optimum culture period before fusion was 5-6 days. Although in vivo priming followed by in vitro boosting decreased the yield of hybrids the relative percentage of positive hybrids was slightly increased. The results suggest that in vivo priming is not essential since primary in vitro stimulation alone produced significant numbers of hybrids secreting specific antibody.

Enzyme immunoassay of benzo[a]pyrene conjugated to DNA, RNA and microsomal proteins using a monoclonal antibody

An enzyme immunoassay for the detection of benzo[a]pyrene covalently conjugated to macromolecules has been developed. The monoclonal antibody, raised through in vitro immunization reacted with benzo[a]pyrene metabolites bound to DNA, RNA and proteins. The lower detection limit for the assay was 1 pmol for benzo[a]pyrene bound to DNA or RNA, and 5 pmol when bound to protein.