Humanisation and characterisation of PR1A3, a monoclonal antibody specific for cell-bound carcinoembryonic antigen

Carcinoembryonic antigen (CEA) is highly expressed by most tumours of gastrointestinal origin, but its use as a target for tumour therapy is complicated by the high levels of soluble CEA that are found circulating in the blood of cancer patients. A monoclonal antibody PR1A3 has been prepared, which binds preferentially to cell-surface rather than soluble CEA, this cell selectivity should make PR1A3 an ideal candidate for antibody-targeted tumour therapy. PR1A3 has been humanised and shown to retain its cell-surface specificity and affinity. Stable expression of the humanised antibody from chinese hamster ovary (CHO) cells has been achieved after transfection and amplification. Since PR1A3 binds preferentially to cell-associated CEA, a cell-free enzyme-linked immunosorbent assay (ELISA) has been developed to allow characterisation and routine assay of the antibody. This assay was developed using a recombinant chimeric protein constructed by cloning the domain of CEA that is bound by PR1A3 (the B3 domain) into a hybrid gene containing the Fc portion of IgG and three domains of biliary glycoprotein. Stable expression of this hybrid protein has been achieved from CHO cells. In ELISA both humanised and murine PR1A3 bound strongly to this antigen but only at a minimal level to soluble CEA. Two binding sites for the antibody were found on the gastric carcinoma cell line MKN45, one of higher affinity (1 nM) and the other at lower affinity (60 nM). Similar affinities were found for both murine and humanised antibodies. The data presented make it unlikely that the differential binding to cell-surface as distinct from soluble CEA can be accounted for by low affinity of PR1A3 for CEA, and provides further support for the hypothesis that some conformational change takes place on CEA release from cells and that it is this change that blocks PR1A3 binding to its epitope. Received: 5 October 1998 / Accepted: 19 November 1998     

Amelioration of delayed-type hypersensitivity responses by IL-27 administration

Interleukin (IL-) 27 is a member of the IL-12 cytokine family. Although recent analyses of WSX-1 (IL-27 receptor α chain)-deficient mice as well as in vitro studies using recombinant IL-27 revealed the immunosuppressive function of IL-27, in vivo role and therapeutic potential of IL-27 remain poorly elucidated. Here we investigated the effect of IL-27 administration on delayed-type hypersensitivity (DTH). While WSX-1-deficient mice showed higher DTH responses as shown by the degree of footpad swelling, administration of IL-27 significantly ameliorated the footpad swelling. Since the activation status of the draining lymph node cells were not affected by IL-27 deficiency, it was suggested that IL-27 affected the effector phase of the response. These results collectively indicate that IL-27 has a suppressive effect on activated T cells in the experimental model and also has a therapeutic potential for some diseases caused by immune disorder.     

Modification of delayed-type hypersensitivity reactions by muramyldipeptide in guinea pigs

Abstract N -Acetylmuramyl- l -alanyl- d -isoglutamine (muramyldipeptide, MDP) modulated delayed-type hypersensitivity (DTH) reactions and induced severe inflammatory lesions in guinea pigs. The animals immunized with heat-killed Mycobacterium tuberculosis were challenged with the purified protein derivative (PPD) at the flanks and the corneas to prepare DTH reactions at 2 weeks after the immunization, thereafter 24 h the animals received subcutaneous injections of MDP at the flanks of the opposite side. At the skin with the DTH reaction, increase of swelling and redness accompanied with hemorrhage and necrosis were observed. As corneal reactions in the animals that had received MDP, increase of cornea thickness, opaque and grayish-white and the projection of eyes accompanied with severe iritis were observed. Modification of the skin reaction occurred from 2 h after the MDP injection, rapidly increased to the maximum level around 10 h, maintained the level until 24 h, then slowly decreased. The polymorphonuclear leukocyte infiltration was observed from 15 min after the MDP injection, and tumor necrosis factor alpha, interleukin (IL)-1, and IL-6 levels in the serum and skin lesions increased after the MDP injection. Synthetic muramyltripeptide ( N -acetylmuramyl- l -alanyl- d -isoglutaminyl- l -lysine) also provoked definite skin reactions, while the larger peptidoglycan fragments and various inflammatory agents including cytokines so far examined were inactive in this respect. Cortisone and heparin inhibited definitely and slightly the reaction, respectively. A comparison was made with the modified DTH reaction and the necrotic reactions which we reported previously.     

Affinity purification of novel bispecific antibodies recognising carcinoembryonic antigen and doxorubicin

We have developed a method which combines Protein A affinity chromatography and HPLC analytical and semi-preparative hydroxyapatite affinity chromatography to purify bispecific antibodies (BsMabs) from hybrid-hybridomas secreting antibodies recognising carcinoembryonic antigen (CEA) and the chemotherapeutic drug doxorubicin (Dox). Elution of the HPLC hydroxyapatite columns with a 60–360 mM phosphate buffer gradient was found to give better separation than elution with a 60–180 mM phosphate buffer gradient. Careful monitoring of HPLC fractions by enzyme linked immunosorbent assays for anti-CEA, anti-Dox and dual anti-CEA/anti-Dox activity, and pooling of fractions on the basis of these results, enabled the purification of novel BsMabs for use in in vitro and preclinical in vivo experiments.     

Induction of cytotoxic T cells and their antitumor activity in mice transgenic for carcinoembryonic antigen

In order to develop immunotherapy strategies that are based on eliciting immune responsiveness to the self-antigen, human carcinoembryonic antigen (CEA), we examined whether cytotoxic T lymphocyte (CTL) activity against CEA could be elicited in CEA-transgenic and nontransgenic mice. CEA-transgenic [C57BL/6-TGN(CEAGe)18FJP] and nontransgenic mice were primed with CEA-transfected syngeneic fibroblasts in combination with Corynebacterium parvum. Spleen cells from immunized mice were cultured with irradiated syngeneic MC-38 colon carcinoma cells transfected with CEA (MC-38.CEA) as stimulators prior to the measurement of CTL activity. Primed nontransgenic spleen cells showed augmented CTL activity against MC-38.CEA cells as compared with control parental MC-38 cells, nontransfected or transfected with vector only. Moreover, primed CEA transgenic spleen cells showed augmented CTL activity against MC-38.CEA cells that was similar to that observed in nontransgenic mice. All CTL clones derived from either transgenic or nontransgenic mice showed cross-reactivity with MC-38 cells expressing the CEA-related antigen, nonspecific cross-reacting antigen, but not biliary glycoprotein. CEA-specific CTL clones were not identified. Adoptive transfer of cloned CTL resulted in inhibition of MC-38.CEA but not MC-38.BGP tumor growth. Tumor cures were elicited in mice treated with a combination of cloned CTL and cyclophosphamide. Histopathological examination of CEA-expressing colons from either immunized mice or recipients of cloned CTL did not reveal any autoimmune reactions. These studies demonstrate that CTL recognizing cross-reactive class I epitopes on the CEA molecule can be induced in transgenic mice. The expression of these epitopes on tumor cells creates effective targets for CTL in vivo without inducing adverse reactions in CEA-expressing normal tissues. Since anti-CEA CTL have been generated in humans, CEA-transgenic mice may be a useful model to study vaccines that are based on CTL effector mechanisms. Received: 7 January 2000 / Accepted: 8 March 2000     

Glycomic profiling of carcinoembryonic antigen isolated from human tumor tissue

Background

Carcinoembryonic antigen (CEA) is a protein commonly found in human serum, with elevated CEA levels being linked to the progression of a wide range of tumors. It is currently used as a biomarker for malign tumors such as lung cancer and colorectal cancer [Urol Oncol: Semin Orig Invest 352: 644–648, 2013 and Lung Cancer 80: 45-49, 2013]. However, due to its low specificity in clinical applications, CEA can be used for monitoring only, rather than tumor diagnosis. The function of many glycoproteins is critically dependent on their glycosylation pattern, which in turn has the potential to serve in tumor detection. However, little is known about the detailed glycan patterns of CEA.

Methods

To determine these patterns, we isolated and purified CEA proteins from human tumor tissues using immunoaffinity chromatography. The glycan patterns of CEA were then analyzed using a Matrix-Assisted Laser Desorption/Ionization-Time of Flight-Mass Spectrometry³ (MALDI-TOF-MS³) approach.

Results

We identified 61 glycoforms in tumor tissue, where CEA is upregulated. These glycosylation entities were identified as bi-antennary, tri-antennary and tetra-antennary structures carrying sialic acid and fucose residues, and include a multitude of glycans previously not reported for CEA.

Conclusion

Our findings should facilitate a more precise tumor prediction than currently possible, ultimately resulting in improved tumor diagnosis and treatment.

Electronic supplementary material

The online version of this article (doi:10.1186/s12014-015-9088-3) contains supplementary material, which is available to authorized users.     

Novel tumor-associated antigen of hepatocellular carcinoma defined by monoclonal antibody E4-65

A monoclonal antibody, E4-65, produced by immunizing mice with SMMC-7721 cells, a human hepatocellular carcinoma (HCC) cell line, was used to identify and characterize an unreported HCC-associated antigen. Indirect immunofluorescence studies showed that E4-65 antibody reacted with five out of eight HCC cell lines, but not with 10 non-HCC tumor cell lines or a normal liver cell line. Using immunohistochemical examination, E4-65 antigen was detected on the cell membranes and in the cytoplasm of human liver tumor tissues, but was not found in most other tumors, or normal adult or fetal tissues, except for a weakly positive reaction in tissues of the digestive system. Western blot analysis showed that E4-65 antibody bound to a 45 kDa protein in the human HCC cell line and tissue lysates. Enzyme treatment and lectin blotting did not detect the carbohydrate chain in E4-65 antigen. This HCC-associated protein represents a potentially useful target for diagnoses and immunotherapy of human HCC.     

Complement-dependent lysis of tumor cells by a baboon IgM antibody to a tumor-associated antigen

Summary We developed a high-titer polyclonal antiserum to a glycoprotein tumor-associated antigen (TAA) by immunization of a baboon with the purified glycoprotein antigen. The baboon serum was fractionated into IgG and IgM components by DEAE Affi-Gel blue chromatography. The ability of the baboon IgM anti-TAA antibody to effect tumor cell lysis in the presence of complement was tested using a chromium-release assay. The baboon antibody was able to lyse melanoma target cells (20.8%–71.4% cytolysis), breast carcinoma cells (36.5%–38.9% cytolysis), and a neuroblastoma cell line (35.5% cytolysis) in the presence of complement but did not effect significant lysis of autologous lymphoblastoid cell lines (4.9% cytolysis) or peripheral blood lymphocytes from healthy volunteers (12.6% cytolysis). Cytolysis of melanoma target cells was completely inhibited by preabsorption of the IgM anti-TAA antibody with UCLA-SO-M14 (M14) cells and partially inhibited by preabsorption with several other melanoma cell lines. There was no significant inhibition of tumor cell lysis after preabsorption of the antibody with lymphoblastoid cell lines. Complement-dependent lysis of M14 targets could be blocked by addition of the purified antigen to the antibody prior to incubation with the tumor cells. Our results suggest that the glycoprotein TAA resides on the tumor cell surface and that the baboon IgM anti-TAA antibody recognizes the antigen on the cell surface and is able to fix complement and effect the lysis of the tumor cells.     

Induction of tumor-specific T-cell responses by vaccination with tumor lysate-loaded dendritic cells in colorectal cancer patients with carcinoembryonic-antigen positive tumors

Background Dendritic cells (DCs) are the most effective antigen-presenting cells. In the last decade, the use of DCs for immunotherapy of cancer patients has been vastly increased. High endocytic capacity together with a unique capability of initiating primary T-cell responses have made DCs the most potent candidates for this purpose. Although DC vaccination occasionally leads to tumor regression, clinical efficacy, and immunogenicity of DCs in clinical trials has not been yet clarified. The present study evaluated the safety and effectiveness of tumor-lysate loaded DC vaccines in advanced colorectal cancer (CRC) patients with carcinoembryonic antigen (CEA) positive tumors. Results Six patients HLA-A*0201-positive were vaccinated with autologous DCs loaded with tumor lysates (TL) together with tetanus toxoid antigen, hepatitis B, and influenza matrix peptides. Two additional patients were injected with DCs that were generated from their sibling or parent with one haplotype mismatch. All patients received the vaccines every 2 weeks, with a total of three intra-nodal injections per patient. The results indicated that DC vaccination was safe and well tolerated by the patients. Specific immune responses were detected and in some patients, transient stabilization or even reduction of CEA levels were observed. The injection of haplotype mismatched HLA-A*0201-positive DCs resulted in some enhancement of the anti-tumor response in vitro and led to stabilization/reduction of CEA levels in the serum, compared to the use of autologous DCs. Conclusion Altogether, these results suggest that TL-pulsed DCs may be an effective vaccine method in CRC patients. Elimination of regulatory mechanisms as well as adjustment of the vaccination protocol may improve the efficacy of DC vaccination. An erratum to this article can be found at     

抗丙肝病毒核心抗原单克隆抗体的研制与初步鉴定

用基因工程重组技术获得的丙肝病毒（ＨＣＶ）核心蛋白抗原与鼠血清白蛋白交联后免疫Ｂａｌｂ／ｃ小鼠,用杂交瘤技术成功地建立了４株稳定分泌抗核心抗原单克隆抗体的杂交瘤细胞,试验结果表明,该４株ＭｃＡｂｓ与免疫抗原及核心区Ｃ３３肽、ＣＰ９、ＣＰ１０抗原有较强的抗原－抗体反应,与ＨＣＶ ＮＳ３、ＮＳ４、ＮＳ５无反应,在竞争ＥＬＩＳＡ中,对ＨＣＶ－ＩｇＧ阳性血清有较好的抑制作用。４株ＭｃＡｂｓ中３株为ＩｇＧ２     

Complementation of expression of carcinoembryonic antigen and tumor associated glycoprotein-72 (TAG-72) in human colon adenocarcinomas.

Enzyme-labeled monoclonal antibodies (MAbs) were used in an immunohistochemical, dual-staining study of 10 colon adenocarcinomas. MAbs B72.3 and COL-4, reactive with the high molecular weight tumor-associated glycoprotein-72 (TAG-72) antigen and carcinoembryonic antigen (CEA), respectively, were labeled with horseradish peroxidase or alkaline phosphatase. Dual staining using the two MAbs on a single tissue section (formalin-fixed, paraffin-embedded) showed that greater numbers of carcinoma cells could be detected by using the combination of the two MAbs than could be detected by use of either MAb alone. In many tumors, some carcinoma cells reacted with MAb B72.3, some reacted with MAb COL-4, and some cells reacted with both MAbs. Only 1 of 10 carcinomas showed greater than 75% reactive cells when stained with each MAb individually. In 9 of 10 cases, however, greater than 75% of cells reacted when the combination of MAbs was used. Cell surface and cytoplasmic patterns of reactivity were observed with both MAbs while some pools of extracellular mucin were composed of both TAG-72 and CEA. This study supports the rationale for the use of a combination of anti-TAG-72 and anti-CEA MAbs for in vitro immunologic detection and potential in vivo immunodiagnostic and immunotherapeutic applications for these MAbs in colon adenocarcinoma patients.     

Identification of a 220-kDa membrane tumor-associated antigen by human anti-UK114 monoclonal antibodies selected from the immunoglobulin repertoire of a cancer patient

Human monoclonal antibodies (HuMAb) specific for a 14-kDa perchloric acid-soluble protein (defined as UK114) were produced by somatic fusion of the human-mouse myeloma K6H6/B5 with Epstein-Barr virus-transformed peripheral B lymphocytes from a cancer patient previously treated with UK101 preparations, containing the UK114 protein. Three IgM-secreting clones were selected on the criteria of specificity for the purified UK114 protein immobilized onto plastic and adapted to grow in a serum-free medium. The reactivity of these antibodies showed a broad distribution pattern restricted to fresh tumor tissues and tumor cell lines, mainly of the adenocarcinoma type. None of the normal cells, nonmalignant cell lines, and normal tissues surrounding the neoplastic lesions were reactive. The immunochemical analysis of the target antigens showed that the HuMAb recognize a molecule of 220 kDa selectively expressed by the surface of tumor cells, as well as a cytoplasmic 14-kDa protein. The 220-kDa antigen was different from other tumor-associated antigens with similar molecular mass and, so far, unique. In the presence of human complement, two of three HuMAb are cytotoxic for tumor cells expressing the 220-kDa surface antigen. The tumor specificity and the lytic ability attributed to these HuMAb are promising features for the exploration of future clinical applications.     

Increased carcinoembryonic antigen expression on the surface of lung cancer cells using gold nanoparticles during radiotherapy

PurposeTumor-associated antigens are a promising target of immunotherapy approaches for cancer treatments but rely on sufficient expression of the target antigen. This study investigates the expression of the carcinoembryonic antigen (CEA) on the surface of irradiated lung cancer cells in vitro using gold nanoparticles as radio-enhancer.MethodsHuman lung carcinoma cells A549 were irradiated and expression of CEA on the cell surface measured by flow cytometry 3 h, 24 h, and 72 h after irradiation to doses of 2 Gy, 6 Gy, 10 Gy, and 20 Gy in the presence or absence of 0.1 mg/ml or 0.5 mg/ml gold nanoparticles. CEA expression was measured as median fluorescent intensity and percentage of CEA-positive cells.ResultsAn increase in CEA expression was observed with both increasing radiation dose and time. There was doubling in median fluorescent intensity 24 h after 20 Gy irradiation and 72 h after 6 Gy irradiation. Use of gold nanoparticles resulted in additional significant increase in CEA expression. Change in cell morphology included swelling of cells and increased internal complexity in accordance with change in CEA expression.ConclusionsThis study showed an increase in CEA expression on human lung carcinoma cells following irradiation. Increase in expression was observed with increasing radiation dose and in a time dependent manner up to 72 h post irradiation. The results further showed that gold nanoparticles can significantly increase CEA expression following radiotherapy.     

Detection of carcinoembryonic antigen using single-domain or full-size antibodies stained with quantum dot conjugates

Compact single-domain antibodies (sdAbs) are nearly 13 times smaller than full-size monoclonal antibodies (mAbs) and have a number of advantages for biotechnological applications, such as small size, high specificity, solubility, stability, and great refolding capacity. Carcinoembryonic antigen (CEA) is a tumor-associated glycoprotein expressed in a variety of cancers. Detection of CEA on the tumor cell surface may be carried out using anti-CEA antibodies and conventional fluorescent dyes. Semiconductor quantum dots (QDs) are brighter and more photostable than organic dyes; they provide the possibility for labeling of different recognition molecules with QDs of different colors but excitable with the same wavelength of excitation. In this study, the abilities for specific detection of CEA expressed by tumor cells with anti-CEA sdAbs biotinylated in vitro and in vivo, as well as with anti-CEA mAbs biotinylated in vitro, were compared using flow cytometry and the conjugates of streptavidin with QDs (SA-QDs). The results demonstrated that either in vitro or in vivo biotinylated anti-CEA sdAbs are more sensitive for cell staining compared to biotinylated anti-CEA mAbs. The data also show that simultaneous use of biotinylated sdAbs with highly fluorescent SA-QDs can considerably improve the sensitivity of detection of CEA on tumor cell surfaces.     

CpG oligonucleotides enhance the tumor antigen-specific immune response of an anti-idiotype antibody-based vaccine strategy in CEA transgenic mice

A murine monoclonal anti-idiotype (Id) antibody, 3H1 has been developed and characterized previously. Anti-Id 3H1 mimics a specific epitope of carcinoembryonic antigen (CEA) and can be used as a surrogate antigen for CEA. 3H1 induced anti-CEA immunity in different species of animals as well as humans and showed promise as a potential vaccine candidate in phase I/II clinical trials for colon cancer patients. One area of interest to us has been the development of new immune adjuvants that may augment the potency of 3H1 as a tumor vaccine. Oligodeoxynucleotides containing unmethylated CpG motifs (CpG ODN) are potent immunostimulatory agents capable of enhancing the Ag-specific Th1 response when used as immune adjuvants. In this study, we have evaluated the efficacy of 3H1 as a tumor vaccine when admixed with a select CpG ODN 1826 in transgenic mice that express human CEA. The vaccine potential of 3H1 was also assessed in the presence of another widely used adjuvant, QS-21. 3H1 coupled to keyhole limpet hemocyanin (KLH) and mixed with Freund’s adjuvant (FA) was used as a gold standard in this system. 3H1 vaccination with different adjuvants induced both humoral and cellular anti-3H1, as well as anti-CEA immunity in CEA transgenic mice. The immune sera could lyse CEA-transfected murine colon carcinoma cells, C15 effectively in an antibody-dependent cellular cytotoxicity assay. The anti-CEA antibody responses were somewhat comparable in each adjuvant-treated group of mice, whereas cellular immune responses were significantly greater when CpG was used as an adjuvant. Splenocytes obtained from 3H1–CpG-immunized mice showed an increased proliferative CD4⁺ Th1-type T-cell response when stimulated in vitro with 3H1 or CEA and secreted elevated levels of Th1 cytokines (IL-2, IFN-γ). This vaccine also induced MHC class I antigen-restricted CD8⁺ T-cell responses. In a solid tumor model, C15 tumor growth was significantly inhibited by 3H1 vaccinations. In 3H1–CpG-vaccinated mice, the duration of survival was, however, longer compared to the 3H1–QS21-vaccinated mice. These findings suggest that 3H1-CpG vaccinations can break peripheral tolerance to CEA and induce protective antitumor immunity in this murine model transgenic for human CEA.     

Induction of allergen-specific IgE and IgG responses by anti-idiotypic antibodies

In order to explore idiotypic, anti-idiotypic, and anti-anti-idiotypic responses to allergens, BALB/c mice were immunized with affinity-purified human idiotypic antibodies directed against a highly purified shrimp allergen. This resulted in the production of anti-idiotypic antibodies which were quantitated by using rabbit idiotypic antibodies raised against the same purified allergen. The mouse anti-idiotypic antibodies recognized shrimp-specific human idiotypic antibodies of the IgE isotype from 18 of 20 individuals, and IgG antibodies from 14 of 20 shrimp-sensitive patients. Immunization of BALB/c mice with affinity-purified, allergen-specific anti-idiotypic antibodies induced anti-allergen IgE and IgG responses in the absence of the allergen. This paper thus presents evidence that anti-idiotypic antibodies raised against allergen-specific idiotypic antibodies may substitute for the original allergen in the induction of allergen-specific idiotypic antibodies. The demonstration of shared idiotopes on IgG and IgE antibodies in the sera of shrimp-sensitive patients supports the use of allergen-specific anti-idiotypic antibodies as surrogate allergens.     

Significant accumulations of cathepsin B and prolylendopeptidase in inflammatory focus of delayed-type hypersensitivity induced by Mycobacterium tuberculosis in mice

To clarify what kinds of proteinases are secreted into the foci of allergic-inflammation involving delayed-type hypersensitivity reaction, we examined the characteristic releases of various proteinases into the foci of Mycobacterium tuberculosis (M. tuber.)-induced delayed-type allergic-inflammation in mice. The significant activities of cathepsin B and prolylendopeptidase were observed in the washing-fluids of subcutaneous inflammatory foci of M. tuber.-induced delayed-type allergic-inflammation, but not M. tuber.-induced acute-inflammation. The SDS-resistant complex of cathepsin B and a protein substrate with apparent molecular mass of 74 kDa was observed by Western blot analysis. On the other hand, no significant accumulations of other proteinases, such as matrix metalloproteinases, cathepsin D, and serine proteinases, were determined. CA-074, a specific inhibitor of cathepsin B, suppressed both swelling and cathepsin B activity in the footpad having M. tuber.-induced delayed-type allergic-inflammation in vivo. These results suggest that cathepsin B may play an important role in the formation of M. tuber.-induced delayed-type allergic-inflammation.     

针对炭疽保护性抗原不同结构域的中和性单克隆抗体的筛选和鉴定

炭疽保护性抗原（PA）是炭疽毒素的重要组分,同时也是现有炭疽疫苗的主要有效成分,在炭疽杆菌的致病与免疫中发挥关键作用。以重组PA为免疫原,采用B淋巴细胞杂交瘤技术,结合炭疽毒素敏感细胞的毒性中和试验,大量筛选抗PA单克隆抗体,获得了9株炭疽毒素中和性单抗。进一步分析表明这些单抗以IgG1亚类为主,分别识别PA 3个结构域的4个不同中和表位区。针对结构域2的4株单抗识别同一表位区,其中3株单抗的中和活性强于抗PA多抗;针对结构域4的4株单抗识别两个不同表位区;另有1株单抗识别位于结构域3的表位。实验结果提示PA具有多个中和表位,分别位于其不同结构域,其中结构域2、4包含主要中和表位。实验中获得的针对不同表位的中和性单抗为深入研究PA的免疫保护机理提供了工具,也为研制针对炭疽毒素的被动免疫制剂和治疗药物打下基础。     

Utilization of leucine methyl ester for the generation of hybridomas producing monoclonal antibodies specific to tumor-associated antigens

In an attempt to obtain monoclonal antibodies specific to tumor-associated antigens. C3H/He mice were immunized with syngeneic MM2 tumor cells, and the primed spleen cells were fused with P3-X63-Ag8.653 myeloma cells. The outgrowth of hybridomas, however, was extremely low and monoclonal antibodies were not obtained. The reason for the low hybridoma growth was studied. It was found that MM2 cells used as the immunogen, the fusion partner myeloma cells and the resulting hybridomas shared at least one tumor-associated antigen, namely Q5 antigen. Because of this common antigen, cytotoxic cells, presumably cytotoxic T lymphocytes, which were lytic to the hybridomas, were induced during the culture for generation of the hybridomas. Removal of lysosome-rich cells, including cytotoxic T lymphocytes, from the primed spleen cells before the fusion by treatment with leucine methyl ester, a lysosomotropic agent, drastically improved the outgrowth of hybridomas. By this method, seven stable hybridoma clones producing monoclonal antibodies specific to tumor-associated antigens were obtained. Two of the seven clones were found to secrete monoclonal IgM species, which reacted with the extra-cellular region of the Q5 antigen. This procedure will be an option when production of monoclonal antibodies specific to cell-surface antigens is intended and outgrowth of hybridomas is unexpectedly low.