Different behaviour of mouse-human chimeric antibody F(ab')2 fragments of IgG1, IgG2 and IgG4 sub-class in vivo.

Mouse-human chimeric monoclonal antibodies (MAbs) of 3 different human IgG sub-classes directed against carcinoembryonic antigen (CEA) have been produced in SP-0 cells transfected with genomic chimeric DNA. F(ab')2 fragments were obtained by pepsin digestion of the purified chimeric MAbs of human IgG1, IgG2 and IgG4 sub-class and of parental mouse MAb IgG1. The 4 F(ab')2 fragments exhibit similar molecular weight by SDS-PAGE. They were labelled with 125I or 131I and high binding (80 to 87%) to purified unsolubilized CEA was observed. In vivo, double labelling experiments indicate that the longest biological half-life and the highest tumour-localization capacity is obtained with F(ab')2 from chimeric MAb of human IgG2 sub-class, whereas F(ab')2 from chimeric MAb IgG4 give very low values for these 2 parameters. F(ab')2 from chimeric MAb IgG1 and from parental mouse MAb yield intermediate results in vivo. Our findings should help to select the appropriate human IgG sub-class to produce chimeric or reshaped MAb F(ab')2 to be used for tumour detection by immunoscintigraphy and for radioimmunotherapy.     

Evaluation of L6, an anti-carcinoma murine monoclonal antibody, in tumor-bearing nude mice

L6 is a murine monoclonal antibody (MAb) binding to cells of most human carcinomas, mediating antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity, and inhibiting tumor growth in nude mice [10]. Fab and F(ab')2 fragments of L6, as well as intact MAb, have been evaluated for immunospecific localization in nude mice xenografted with a human lung carcinoma. They were compared with preparations of an isotype-matched control immunoglobulin, P1.17, after labelling with 125I or 131I. L6 Fab fragments prepared from MAb L6 and labelled with 67Ga via desferrioxamine were also tested. The data suggest that MAb L6 may be useful for in vivo detection of human carcinomas.     

Penetration and binding of radiolabeled anti-carcinoembryonic antigen monoclonal antibodies and their antigen binding fragments in human colon multicellular tumor spheroids

The binding and penetration of two 125I-labeled anti-carcinoembryonic antigen (CEA) monoclonal antibodies (MAb) and their F(ab')2 and Fab fragments were measured in multicellular spheroids of poorly (HT29) and moderately well differentiated (Co112) human colon adenocarcinomas which express different amounts of CEA. Spheroids cultured in vitro model tumor microenvironments where poor vascular supply may modulate antigen expression and accessibility. The two MAb studied, 202 and 35, were shown previously to react with different CEA epitopes and to have high affinities of 1.2 and 5.8 X 10(9) M-1, respectively. MAb 202 has also been shown to cross-react with antigens present on human granulocytes and normal epithelial cells from human lung and pancreas. Specific binding of intact MAb and fragments of both antibodies was demonstrated for both types of human colon carcinoma spheroids compared to mouse colon carcinoma (CL26) and mammary tumor (EMT6/Ro) spheroids. Total binding of MAb and fragments was greater (1.5- to 2.5-fold) after 4 h compared to 1 h of exposure; the amount of binding compared to control IgG1 was 5- to 30-fold greater after 1-h incubation and 15 to 200 times greater after 4 h. This binding was stable as demonstrated by short and long wash experiments at 37 degrees and 4 degrees C. The binding of F(ab')2 and Fab fragments of the anti-CEA MAb 35 to spheroids of human colon Co112 was almost 2-fold greater than that of the intact MAb. However, for MAb 202, the binding of intact MAb and F(ab')2 was greater than that of Fab fragments. In addition the binding of both intact and F(ab')2 fragments of MAb 202 was greater than that obtained with MAb 35. Specific binding of both antibodies to HT29 spheroids, which express less CEA, was decreased for MAb and fragments of both 202 and 35. Autoradiography and immunoperoxidase experiments were performed to determine the penetration of MAb and fragments after incubation with intact spheroids. Comparisons were made with labeled MAb directly applied to frozen sections of spheroids. F(ab')2 and Fab fragments of both antibodies were bound at the surface of intact spheroids and penetrated to eight to ten cells, but the intact MAb were localized mainly at the spheroid surface and the outer one to three cell layers. There was much less binding at the surfaces of HT29 compared to Co112 spheroids. An enzyme immunoassay using MAb 35 and 202 demonstrated that Co112 spheroids produced about 8-fold more CEA/mg of cell protein than did monolayer cultures.(ABSTRACT TRUNCATED AT 400 WORDS)     

Swine monoclonal antibodies of high affinity and specificity to carcinoembryonic antigen

To avoid the exclusive use of rodent monoclonal antibodies (MAbs) in patients for the detection of tumors by immunoscintigraphy and for radioimmunotherapy, swine MAbs were produced that are directed against carcinoembryonic antigen (CEA). Spleen cells from 2 pigs immunized with purified colon carcinoma CEA were fused with a nonsecreting mouse myeloma cell line by conventional methods, except that a particularly long immunization protocol and large amounts of spleen and myeloma cells were used. Of 1,200 growing hybrids tested, 20 were found initially to produce antibodies binding to radiolabeled CEA. Seven stable clones producing anti-CEA MAbs for more than 6 months were derived from these hybrids by repeated subcloning. The pig origin of the seven MAbs was demonstrated in a solid-phase CEA enzyme immunoassay where anti-pig immunoglobin (Ig) antibodies coupled to peroxidase gave a positive reaction while anti-mouse Ig antibodies were entirely negative. All swine MAbs were of the IgG isotype. Three anti-CEA MAbs showed no cross-reactivity with granulocytes, while four others gave various degrees of reactivity with different granulocyte glycoproteins. Competitive binding to CEA performed for two purified swine MAbs showed that they recognized two different epitopes. The affinity constants measured for these two MAbs by Scatchard plot on purified CEA were high (1.2 X 10(9) and 1.2 X 10(10) liter/mol). One of the MAbs was tested in vivo for tumor localization by injection, after radiolabeling, in nude mice bearing human colon carcinoma xenograft. High ratios of tumor to normal tissue were obtained with mean values of 10.5 for intact MAbs and of 26.8 for F(ab')2 fragments of the porcine MAb. The results showed that heterofusion with this particular protocol can be used to produce swine MAbs of high affinity and specificity for a well-defined tumor marker. These reagents may have an important clinical utility, particularly in patients who became sensitized to mouse immunoglobulins.     

Baboon anti-idiotype antibodies mimic a carcinoembryonic antigen epitope.

A baboon was immunized with NP-4, a murine monoclonal antibody (MAb) to carcinoembryonic antigen (CEA). Anti-idiotype antibodies were purified from the baboon serum by affinity chromatography on a NP-4-coupled matrix, followed by adsorption of the non-specific antibodies on an irrelevant MAb. Baboon anti-idiotype antibodies inhibited specifically the binding between NP-4 and CEA. Mice immunized with baboon anti-idiotype antibodies produced antibodies to the CEA epitope recognized by NP-4. These results indicate that baboon anti-idiotype antibodies functionally mimic a CEA epitope and that they can be suitable for idiotype therapy of human CEA-producing carcinomas.     

Polyclonal and monoclonal anti-CEA antibodies in immunolocalization of colorectal cancer

Antibodies to carcinoembryonic antigen (CEA) from sheep and monkey were immunoadsorbent purified. Mouse monoclonal antibody (MAb) anti-CEA I-38S1 and Fab fragments of this antibody were prepared from mouse ascitic fluid. The IgG preparations were labelled with 123I or 131I, the Fab fragments with 131I. The antibody reactivity was unchanged after labelling. Patients with advanced colorectal carcinomas received an intravenous injection of 50-200 MBq 123I or 30-160 MBq 131I coupled to 250-500 micrograms antibody or antibody fragment. Patient examinations were performed using emission tomography (SPECT) and/or conventional gamma camera scintigraphy. The specific localization of labelled anti-CEA to tumor was compared to known tumor localized by CAT-scan, other x-ray methods or laparotomy, 50% of known tumors were accurately localized with sheep anti-CEA. In contrast, 70-80% of known tumor sites were correctly localized with polyclonal monkey anti-CEA antibodies, with monoclonal anti-CEA antibodies or with Fab fragments of the latter. A few previously unknown tumors were detected.     

Immunohistochemical localization and molecular characteristics of three monoclonal antibody-defined epitopes detectable on carcinoembryonic antigen (CEA)

Three murine monoclonal antibodies (MAbs) reactive to different epitopes on CEA were selected according to their ability to bind to various human tissue sections. The most selective MAb, BW 431/31, bound to the majority of colon carcinomas but only faintly to normal colon mucosa. In addition to the tissues stained by MAb BW 431/31, MAb BW 250/183 reacted with granulocytes, colon mucosa and faintly with pancreatic ducts. The third MAb, BW 374/14, reacted with granulocytes, colon mucosa, strongly with pancreatic ducts and with alveolar and bronchial epithelium. The antigenic determinants recognized by the 3 MAbs in human tissue sections were resistant to formaldehyde fixation and paraffin embedding as well as to periodic acid oxidation and neuraminidase treatment. The last two treatments suggest that the epitopes are protein in nature. Using MAb affinity chromatography, 3 antigen preparations were isolated from a human colon carcinoma xenograft with an approximate molecular weight of 180 kd. These preparations were shown to bear the epitopes from each of the MAbs and from a polyclonal antiserum specific for purified CEA. Furthermore, the ability of MAb BW 431/31 to localize its antigenic determinant in vivo on a human colon carcinoma xenograft is evaluated and its possible application in the patient is suggested.     

Complementary reactivities of anti-carcinoembryonic antigen and antitumor-associated glycoprotein 72 monoclonal antibodies in lung carcinomas.

Monoclonal antibodies (MAbs) COL-4 and COL-12, to the carcinoembryonic antigen (CEA), and B72.3, CC-49, CC-83, to the tumor-associated glycoprotein 72 (TAG-72), were used to study the expression of distinct epitopes of the two molecules in 71 cases of lung carcinoma of differing histotype. These MAbs reacted with the majority of adenocarcinomas by immunoperoxidase on tissue sections, but demonstrated a more restricted reactivity with squamous carcinomas. MAb CC-49 detected the highest percentages of adenocarcinoma cells while the B72.3 epitope was expressed more in squamous carcinoma cells. No significant reactivity with any of these MAbs was observed in small cell carcinomas. The expression of the CEA and TAG-72 epitopes in non-small cell lung cancers was highly heterogeneous: a distinct epitopes in non-small cell lung cancers was highly heterogeneous: a distinct epitope could be expressed by the majority of cells, whereas another of the same antigenic molecule was either poorly or not expressed. In adenocarcinomas, mixtures of anti-CEA, anti-TAG-72, and anti-(TAG-72 plus CEA) MAbs resulted in additive reactivity with an increase of the immunopositive tumors and of the percentages of immunostained cells. This was particularly evident for the anti-(TAG-72 plus CEA) mixture. In squamous cell carcinomas the increase was modest and was mainly related to anti-TAG-72 reactivity. These studies suggest variability in the antigenic structure of tumor-associated antigens expressed by carcinomas and indicate that anti-(TAG-72 plus CEA) mixtures may represent an immunological adjunct for clinical application in adenocarcinoma patients. On the other hand, TAG-72 should be considered a better target antigen, as compared to CEA, in the detection of squamous cell carcinomas.     

Cell mediated cytotoxicity of human colon carcinoma cells by a monoclonal antibody (R4) recognizing the carcinoembryonic antigen (CEA) and CEA-related molecules

We report a novel anti-CEA monoclonal antibody (MAb) designated R4, which mediates antibody-dependent cell-mediated cytotoxicity (ADCC) of human colon carcinoma cells and displays differential reactivity for human carcinomas versus the normal counterparts. R4 (IgG1) reacted with the cell surface of 6 colon carcinoma cell lines expressing CEA. Western blot analysis and epitope mapping using native and baculovirus recombinant CEA and non specific cross-reacting antigen (NCA) demonstrated that MAb R4 recognizes a proteinic epitope located on the 3' end of the domain I shared by CEA and NCA molecules. Immunohistochemical analysis demonstrated an intense staining of MAb R4 with the majority of the neoplastic tissues tested, including colon (13/13), stomach (2/2), breast (9/10), lung (7/10) and endometrial (2/4) carcinomas, whereas no reactivity with the correspondent normal tissues was observed. Using human PBLs from healthy donors as effector cells, we have shown that MAb R4 mediated antibody dependent-cell mediated cytotoxicity (ADCC) of human carcinoma cells LS-174T, CBS and WiDr. This activity was enhanced after PBLs activation with interleukin-2 (IL-2). The specificity of MAb R4 for an epitope shared by two tumor overexpressed antigens, CEA and NCA, resulting in an intense reactivity with neoplastic cells and the peculiar property to mediate ADCC, indicate that MAb R4 might be a novel powerful reagent for diagnostic and immunotherapy of carcinoma patients.     

Protein epitopes in carcinoembryonic antigen. Report of the ISOBM TD8 workshop.

To characterize antigenic sites in carcinoembryonic antigen (CEA) further and to investigate whether there are differences between colon tumor CEA and meconium CEA (NCA-2) that can be detected by anti-CEA monoclonal antibodies (MAb), 19 new anti-CEA MAb were analyzed with respect to specificity, epitope reactivity and affinity. Their reactivities were compared with 10 anti-CEA MAb with known CEA-domain binding specificity that have previously been classified into five nonoverlapping epitope groups, GOLD 1-5. Cross-inhibition assays with antigen-coated microtiter plates and immunoradiometric assays were performed in almost all combinations of MAbs, using conventionally purified CEA (domain structure: N-A1B1-A2B2-A3B3-C) from liver metastasis of colorectal carcinomas, recombinant CEA, meconium CEA (NCA-2), truncated forms of CEA and NCA (CEACAM6) as the antigens. The affinity of the MAbs for CEA was also determined. The new MAbs were generally of high affinity and suitable for immunoassays. Three new MAbs were assigned to GOLD epitope group 5 (N-domain binding), 3 MAbs to group 4 (A1B1 domain), 1 to group 3 (A3B3 domain), 3 to group 2 (A2B2 domain) and 3 to group 1 (also the A3B3 domain). Three MAbs formed a separate group related to group 4, they were classified as GOLD 4' (A1B1 domain binding). The remaining 3 MAbs appear to represent new subspecificities with some relationship to GOLD groups 1, 2 or 4, respectively. Five MAbs, all belonging to epitope group 1 and 3, reacted strongly with tumor CEA but only weakly or not at all with meconium CEA, demonstrating that the two products of the CEA gene differ from each other, probably due to different posttranslational modifications.     

Serologic mapping and biochemical characterization of the carcinoembryonic antigen epitopes using fourteen distinct monoclonal antibodies

A series of 14 monoclonal anti-carcinoembryonic antigen (CEA, Mr 180,000) antibodies (MAbs) that show a strong degree of selective reactivity for human colon carcinomas versus normal adult tissues were used to construct a serological map of the CEA molecule. The MAbs were generated using extracts of colon carcinomas as immunogen and are thus given a COL designation. None of the 14 COL-MAbs tested were reactive with purified non-specific cross-reacting antigen (NCA, Mr 55,000) from normal lung, although some showed reactivity to human granulocytes. All the COL-MAbs tested were reactive with normal fecal antigen-2 (NFA-2, Mr 170,000); however, many of the COL-MAbs demonstrated a higher affinity constant to CEA than to NFA-2. Cross-competition radioimmunoassays classified the 14 COL-MAbs into 5 groups. The chemical nature of the COL-binding domains was tested using chemically or enzymatically treated CEA; all reacted with periodate-treated CEA and deglycosylated CEA, indicating that the COL-reactive epitopes appear to be of a proteinaceous nature. Heat treatment, reduction, alkylation, pepsin digestion or pronase treatment of CEA, however, gave differential results with respect to COL binding. Antibody titration experiments were carried out to define differential reactivities to colorectal carcinoma versus NCA-containing granulocyte extracts; these results were compared with results obtained using several anti-CEA MAbs that have been used in clinical trials. Granulocyte binding and biochemical studies showed that the COL MAbs may distinguish as many as 7 to 10 CEA epitopes.     

Effects of neocarzinostatin-chimeric Fab conjugates on the growth of human pancreatic carcinoma xenografts.

Neocarzinostatin (NCS) was bound covalently to human/mouse chimeric Fab fragments of MAb A7 (chA7Fab) directed against human pancreatic carcinoma. The anti-tumour effect of chA7Fab-NCS was tested in a nude mouse model on pancreatic carcinoma and compared with A7-NCS or NCS alone. The anti-tumour effect of chA7Fab-NCS increased in a dose-dependent manner and was significantly greater than either A7-NCS or NCS. Tumour growth was completely suppressed after the administration of chA7Fab-NCS. An enzyme-linked immunosorbent assay with rabbit anti-mouse immunoglobulin was performed to examine the antigenicity of chA7Fab. ChA7Fab had less reactivity with rabbit anti-mouse immunoglobulin than either whole antibody A7 or murine Fab fragments of A7. Thus, chA7Fab-NCS can inhibit human pancreatic cancer growth in an animal and may be useful for targeting chemotherapy to pancreatic cancer in humans.     

Epitopes of carcinoembryonic antigen defined by monoclonal antibodies prepared from mice immunized with purified carcinoembryonic antigen or HCT-8R cells

A library of 18 monoclonal antibodies (MAbs) reactive with purified carcinoembryonic antigen (CEA) has been prepared. The specificity of these MAbs was tested and they have been separated into nine subgroups, each recognizing a different region of the CEA molecule. Seven MAbs from four of the groups also react with the nonspecific cross-reacting antigen. Some of the MAbs are directed against conformational determinants: three of the MAb groups bind poorly to sodium dodecyl sulfate-treated CEA, while five of the groups are not reactive with reduced and alkylated CEA. Three of the groups react with purified CEA but not with the cell surface CEA of HCT-8R cells, while the other groups react with both forms. The MAbs were tested for binding to fragments of CEA obtained by chemical cleavage and the groups of MAbs were found to react with different subsets of such fragments.     

Therapy and Imaging of Pancreatic Carcinoma Xenografts with Radioiodine-labeled Chimeric Monoclonal Antibody A10 and Its Fab Fragment

Recombinant mouse/human chimeric monoclonal antibody A10 (ch-A10) and its Fab fragment (ch-Fab) react with carcinoembryonic antigen on various gastrointestinal carcinomas. We performed biodistribution studies with ¹²⁵I-labeled ch-Al0 and ch-Fab in an antigen-positive human pancreatic carcinoma (BxPC-3) xenograft model. We also evaluated the anti-tumor effect of ¹³¹I-labeled ch-Al0 and studied the detection of BxPC-3 xenografts with ¹²³I-labeIed ch-Fab in whole body scintigraphy. In comparative biodistribution studies, the tumor uptake of ¹²⁵I-labeled ch-Al0 was significantly greater than that of ¹²⁵I-labeIed ch-Fab 24 h post-injection. However, the tumor-to-blood ratio was 46.8 for ch-Fab at 24 h post-injection, while it was only 1.4 for ch-Al0. Microautoradiography studies showed that ch-Fab penetrated more uniformly into the tumor nodules than did ch-Al0. In mice given a therapeutic dose of ¹³¹I-labeled ch-AlO, a significant inhibition of tumor growth was seen, while control ^I31l-labeled human IgG did not affect tumor growth. Leukocyte toxicity was observed within 3 weeks after injection of ¹³¹I-labeled ch-Al0, but leukocyte counts recovered to normal levels at 8 weeks post-injection. In whole-body scintigraphy, clear and rapid tumor imaging was obtained with 200 (Ci of ¹²³I-labeled ch-Fab 24 h post-injection. These results suggest that radioiodine-labeled chimeric A10 antibodies could potentially be useful candidates for radioimmunotherapy and radio-immunodetection of pancreatic carcinomas.     

Immunohistochemical analysis of pulmonary and pleural neoplasms using a monoclonal antibody (47D10) which reacts with nonspecific cross-reacting antigen

A series of 251 human pulmonary carcinomas were analyzed immunohistochemically for the antigens recognized by a new monoclonal antibody (MAb) 47D10. These antigens are part of a complex family of substances similar to, yet distinct from carcinoembryonic antigen (CEA), and are termed 'nonspecific cross-reacting antigens' (NCAs). The NCA epitope recognized by the MAb 47D10 is expressed on the cell surface and has previously been shown to be distinct from epitopes detected by several anti-CEA MAbs, as well as by MAbs 19-9 and Du-PAN-2. The NCA epitope recognized by MAb 47D10 is well preserved in formalin-fixed and paraffin-embedded tissues. Using immunohistochemistry, this epitope has been shown to have a limited biodistribution in normal tissues, and to be expressed by adenocarcinomas arising in the pancreas, colon, breast, ovary, prostate and lung. The frequency and pattern of NCA expression in human pulmonary neoplasms was found to correlate with the known distribution of CEA: and was often present in the non-small-cell carcinomas. In addition, the expression of CEA relative to NCA was evaluated in a select group of non-small-cell carcinoma cases using several anti-CEA MAbs, to directly compare the expression of CEA to NCA. In general, the NCA reaction pattern is more intense and expressed on more cells within the tumors than that of CEA expression.     

Establishment and Characterization of Mouse-Human Chimeric Monoclonal Antibody to erbB-2 Product

A mouse-human chimeric antibody for erbB -2 product was established by a new procedure using heavy chain loss mouse mutant hybridoma and human immunoglobulin expression vector. The E401 hybridoma secreted anti- erbB -2 product monoclonal antibody (MoAb) (IgG1, k ). The gene of the mouse variable regions of heavy chain was amplified and cloned by the polymerase chain reaction technique directly from the E401 hybridoma RNA. The variable region of heavy chain was joined with the expression vector, which contains human γ1 constant gene. The expression vector was transfected into heavy chain loss mutant cells E401-12, which produced only murine immunoglobulin light chains. A chimeric monoclonal antibody CH401 retained full binding reactivity to erbB -2 product, compared with murine E401 parental antibody. Furthermore, the chimeric MoAb CH401 was much more efficient in supporting antibody dependent cell-mediated cytotoxicity activity against erbB -2-bearing human adenocarcinoma cells than murine MoAb E401. These suggest that a chimeric monoclonal antibody CH401 may be a potent reagent for therapy of human adenocarcinomas.     

Characterization of the colorectal carcinoma-associated antigen defined by monoclonal antibody D612

Monoclonal antibody (MAb) D612 recognizes an antigen expressed on the cell surface of normal and malignant gastrointestinal epithelium. It is a murine IgG2a/kappa which has been previously shown to mediate killing of human colon carcinoma cells using human effector cells (which could be enhanced in the presence of interleukin-2). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analyses of MAb D612 immunoprecipitates of extracts of L-[35S]methionine-, L-[3H]leucine-, and D-[3H]glucosamine-labeled human colon carcinoma cells showed that the D612 antigen is a Mr 48,000 glycoprotein. Similar estimates of molecular mass were obtained from SDS-PAGE analyses of MAb D612 immuno-precipitates of radioiodinated extracts of surgically resected colon carcinoma and adjacent normal colonic mucosa. D612 antigen was not detectable in immunoprecipitates of supernatant media from radiolabeled cell cultures, suggesting that the antigen is not readily shed from the surface of cultured cells. The D612 antigen was shown to be clearly distinct from previously described gastrointestinal carcinoma-associated glycoproteins: the D612 antigen shows a migration pattern of SDS-PAGE distinct from those of the antigens recognized by MAbs KS1/4 and GA733, and reciprocal immunodepletion analyses of D-[3H]glucosamine-labeled colon carcinoma cells utilizing MAbs D612 and GA733 revealed no cross-reactivity between these antibodies. Similarly, competitive binding studies between MAbs 17-1A and KS1/4 and MAb D612 revealed no similarity between the epitopes recognized by MAb D612 and MAbs 17-1A and KS1/4. MAbs D612 and 17-1A were also titered in immunoperoxidase staining assays on serial frozen sections of normal and malignant colon. MAb D612 showed a higher titer of immunostaining reactivity with both normal and malignant colon than did MAb 17-1A. MAb D612 showed roughly equivalent immunostaining titers against normal and malignant colon; whereas MAb 17-1A showed higher titer of immunostaining reactivity against the normal colon tissue than against the malignant colon. Flow cytometric analysis of phosphatidylinositol-specific phospholipase C-treated colon carcinoma cells revealed no loss of D612 antigen from the cell surface, suggesting that the mechanisms of attachment of the D612 antigen to the cell surface does not involve linkage to a phosphatidylinositol glycan.(ABSTRACT TRUNCATED AT 400 WORDS)     

188Re标记CEA嵌合人源化抗体在荷人结肠癌裸鼠的放射免疫显像研究

背景与目的：癌胚抗原（carcinoembbryonic antigen,CEA）在多种肿瘤,尤其是结肠癌中高表达,抗CEA抗体在人结肠癌的诊断治疗中具有良好的应用前景。本研究采用^188Re标记CEA嵌合抗体,研究其在荷人结肠癌裸鼠体内的生物分布及放射免疫显像。方法：用氯化亚锡还原法标记CEA嵌合抗体及其亲本鼠单抗C50,薄层层析法鉴定标记抗本的标记率、放化纯度及体外稳定性,ELISA鉴定标记后的免疫活性,研究^188Re-CEA嵌合抗体在荷人结肠癌裸鼠体内的分布及放射免疫显像效果,并与C50鼠单抗的显像效果进行比较。结果：^188Re-CEA嵌合抗体的放化纯度大于95%;比活为36MBq/mg;免疫活性为61%;薄层层析示其在体外稳定。^188Re-CEA嵌合抗体的生物学分布显示：注射后24h,肿瘤与肾脏、血液的放射性比值分别为0.75、0.99,与其余各脏器的放射性比值均大于1.78;48h,肿瘤与肾脏、血液的放射性比值分别为1.02、1.12,与其余各脏器的放射性比值均大于2.08。20h后,肿瘤显影清晰。CEA嵌合抗体的放射生物学特性及显像效果与C50鼠单抗基本相同。结论：^188Re-CEA嵌合抗体在裸鼠体内放射免疫显像显示出良好的肿瘤特异性,且显像速度较快,可显示的肿瘤最小可达0.5cm。CEA嵌合抗体降低了免疫原性,在人体内显像更优于其亲本鼠单抗C50。     

Pilot trial of murine monoclonal antibodies in patients with advanced melanoma

We have performed a pilot trial with two murine monoclonal antibodies (MAbs) directed against two surface membrane antigens, p97 (MAb 96.5) and a proteoglycan antigen (MAb 48.7) primarily expressed in human melanoma. Five patients with disseminated melanoma were studied, all of whom had multiple cutaneous metastases. Four patients received 212 mg each of antibodies 96.5 and 48.7, and one patient received 424 mg of antibody 96.5 alone. MAbs were administered in escalating doses over ten days in four patients and over six days in one patient. There was no clear treatment-related toxicity. Immunohistologic studies on biopsies taken two to 240 hours after treatment showed extensive binding of murine immunoglobulin to melanoma cells, but not to normal cells in the same section. The intensity of antibody binding was uniform across the diameter of the tumor nodules. In two patients, no murine immunoglobulin was detected in biopsies taken ten days after the last treatment. The mean initial elimination half-life (T1/2) of infused MAbs was 40.5 hours in two patients who received a combination of both antibodies and 53.0 hours in a third patient who received only antibody 96.5; none of these patients had previously been exposed to mouse immunoglobulin. The elimination T1/2 was 21 hours in a fourth patient, who three months previously had tumor imaging with 2-mg radiolabeled antigen-binding fragments (Fab) prepared from antibody 48.7. Serum from this patient appeared to contain anti-idiotypic antibodies which specifically bound Fabs of antibody 48.7. Three other patients also developed human anti-mouse antibodies. There were no objective tumor regressions, and no histologic changes were noted on biopsy.     

Chimeric anti-N-glycolyl-ganglioside and its anti-idiotypic MAbs: immunodominance of their variable regions

P3 monoclonal antibody (MAb) is a murine IgM that specifically recognizes N-glycolyl (NeuGc)-gangliosides and sulfatides. It also reacts with antigens expressed in human breast tumors and melanoma. In syngeneic model, P3 MAb is able to elicit a strong anti-idiotypic (Ab2) antibody response, even in the absence of adjuvants or carrier proteins. 1E10 MAb is an anti-idiotypic antibody specific for P3 MAb that has demonstrated anti-tumoral effects in syngeneic and allogeneic animals. Here we report the construction of the human IgG(1) chimeric P3 and 1E10 antibodies, and the evaluation of the maintenance of the main properties of the murine MAbs. Chimeric P3 antibody specifically reacted with GM3(NeuGc) and GM2(NeuGc) gangliosides, and not with their acetylated variants. Also, it strongly recognized the anti-idiotypic 1E10 MAb. Chimeric 1E10 antibody specifically reacted with P3 MAb. Upon immunization of Balb/c mice with both chimeric antibodies, we were able to demonstrate the immunodominance of their variable regions. The anti-idiotypic response induced by both antibodies was strong and in most of the mice was even significantly higher than the anti-isotypic response, despite the fact that 70% of the chimeric molecule is xenogenic with respect to the animal model.