Sandwich enzyme immunoassay using three monoclonal antibodies against different epitopes of carcinoembryonic antigen (CEA).

Purified monoclonal antibodies (Mab) produced by 3 hybridomas and reacting with 3 different epitopes of carcinoembryonic antigen (CEA) were used in a solid phase enzyme immunoassay. Two Mabs were physically adsorbed to polystyrene balls and the third Mab was coupled to alkaline phosphatase using the bifunctional reagent N-succinimidyl-3-(2-pyridyldithio)-propionate. During a first incubation, CEA from heat-extracted serum samples was immunoadsorbed to the antibody coated balls. After washing of the balls, bound CEA was detected by a second incubation with the enzyme coupled Mab. The sensitivity of the assay was 0.6 ng per ml of serum. A total of 196 serum samples from patients with various types of carcinoma, with liver cirrhosis, or from healthy blood donors with or without smoking habits, were tested. The results obtained with the monoclonal enzyme immunoassay (M-EIA) were compared with those obtained with perchloric acid extracts of the same serum samples tested by an inhibition radioimmunoassay using conventional goat anti-CEA antiserum. There was an excellent correlation between the two assays. In particular, the new M-EIA gave good results for the detection of tumor recurrences in the follow-up of colon carcinoma patients. However, despite the use of exclusively monoclonal antibodies the new assay detected a similar percentage of slightly elevated CEA values as the conventional assay in patients with non-malignant disease, suggesting that the CEA associated with non-malignant diseases is immunologically identical to the CEA released by colon carcinoma.

Biodistribution of anti-CEA F(ab')2 fragments after intra-arterial and intravenous injection in patients with liver metastases due to colorectal carcinoma.

The biodistribution of simultaneous intra-arterial and intravenous injections of a radiolabelled anti-CEA MAb F(ab')2 fragment was studied in three patients with liver metastases from colorectal cancer. Identical MAb fragments, labelled with either 125I or 131I, were injected over a period of 30 min into the hepatic artery and into a peripheral vein. After 1 or 2 days, biodistribution was measured in the surgically removed metastases, normal tissue samples and blood. By tissue radioactivity counting, tumour uptake in the range 6.3-9.1% of injected dose per gram was found. Superimposable metastasis-to-blood and metastasis-to-normal liver ratios were obtained for both iodine isotopes in all three patients. The results indicate that the intra-arterial injection of MAb F(ab')2 fragments gives no measurable advantage over more convenient injections into a peripheral vein.

Monoclonal antibodies identify a CEA crossreacting antigen of 95 kD (NCA-95) distinct in antigenicity and tissue distribution from the previously described NCA of 55 kD.

During the selection of monoclonal antibodies (MAb) raised against purified carcinoembryonic antigen (CEA), two MAbs were identified which immunoprecipitated a glycoprotein of 95 kD present both in perchloric acid extracts of normal lung and on the surface of normal granulocytes. This antigen was distinct from the previously reported normal glycoprotein crossreacting with CEA (NCA) which had a molecular weight of 55 kD. The difference between the smaller and the larger crossreacting antigens termed NCA-55 and NCA-95, respectively, was demonstrated by SDS-polyacrylamide gel electrophoresis, by elution from Sephadex-G200 and by selective binding to a series of anti-CEA MAb. Out of six MAb which all bound CEA purified from colon carcinoma, three did not react with these two crossreacting antigens, one bound only NCA-95, one reacted only with NCA-55 and one reacted with both NCA-55 and NCA-95. Immunoadsorbent purified preparations of 125I labelled NCA-95 and NCA-55 were found useful for the screening of new anti-CEA MAb. In addition, when tested on frozen sections of colon carcinoma, normal spleen, normal lung and pancreas, each type of MAb gave a clearly different pattern of reactivity. The three anti-CEA MAb which did not bind any of the crossreacting antigens stained only the colon carcinoma cells; the MAb binding to either one of the two types of NCA gave a similar pattern of reactivity both on colon carcinoma cells and on granulocytes. However, on normal lung and pancreas, the MAb binding NCA-55 stained granulocytes as well as bronchiolar and alveolar epithelial cells in lung and inter- and intra-lobular duct epithelial cells in pancreas, whereas the MAb binding only NCA-95 stained only the granulocytes. Thus, the newly identified NCA-95 appears to differ from NCA-55 not only in terms of molecular size and antigenicity but also by the fact that in normal lung and pancreas it is found in granulocytes but not in epithelial cells.

Long-term follow-up of colorectal carcinoma patients by repeated CEA radioimmunoassay.

One of the major practical applications of carcinoembryonic antigen (CEA) assay is the monitoring of colorectal carcinoma patients after complete tumor resection. During the last 5 years, we have followed by repeated CEA assays 66 patients with histologically confirmed colon or rectum adenocarcinoma. Among 19 patients who developed a tumor recurrence, 17 had increased CEA levels preceding the clinical diagnosis by 2 to 26 months. Among the 47 patients who did not show any clinical evidence of tumor recurrence, 35 had CEA values remaining below the limit of 5 ng/ml, whereas 12 had moderate elevations of CEA level fluctuating around this limit. The majority of patients in this last group were heavy smokers or had liver enlargement, but in a few of them we did not find a satisfactory explanation for their moderately increased CEA levels. While our results confirm that repeated CEA assays can predict tumor recurrence with a lead time of several months over clinical diagnosis, they also give a word of warning concerning the interpretation of moderate elevations of CEA level. A moderate increase of CEA level can be the result of early distant metastases, local recurrence or exacerbation of an inflammatory disease. We feel that the decision of second look operations based on CEA results should be made only if increasing CEA values have been observed on three different blood samples taken within a period of 3 months and if no nonmalignant diseases known to increase CEA level are present. Ultimately only randomized clinical studies will determine if second look operations motivated by elevated CEA levels can improve the quality and length of survival of patients with colorectal carcinoma.

Low TCR avidity and lack of tumor cell recognition in CD8(+) T cells primed with the CEA-analogue CAP1-6D peptide.

The use of "altered peptide ligands" (APL), epitopes designed for exerting increased immunogenicity as compared with native determinants, represents nowadays one of the most utilized strategies for overcoming immune tolerance to self-antigens and boosting anti-tumor T cell-mediated immune responses. However, the actual ability of APL-primed T cells to cross-recognize natural epitopes expressed by tumor cells remains a crucial concern. In the present study, we show that CAP1-6D, a superagonist analogue of a carcinoembriyonic antigen (CEA)-derived HLA-A*0201-restricted epitope widely used in clinical setting, reproducibly promotes the generation of low-affinity CD8(+) T cells lacking the ability to recognized CEA-expressing colorectal carcinoma (CRC) cells. Short-term T cell cultures, obtained by priming peripheral blood mononuclear cells from HLA-A*0201(+) healthy donors or CRC patients with CAP1-6D, were indeed found to heterogeneously cross-react with saturating concentrations of the native peptide CAP1, but to fail constantly lysing or recognizing through IFN- gamma release CEA(+)CRC cells. Characterization of anti-CAP1-6D T cell avidity, gained through peptide titration, CD8-dependency assay, and staining with mutated tetramers (D227K/T228A), revealed that anti-CAP1-6D T cells exerted a differential interaction with the two CEA epitopes, i.e., displaying high affinity/CD8-independency toward the APL and low affinity/CD8-dependency toward the native CAP1 peptide. Our data demonstrate that the efficient detection of self-antigen expressed by tumors could be a feature of high avidity CD8-independent T cells, and underline the need for extensive analysis of tumor cross-recognition prior to any clinical usage of APL as anti-cancer vaccines.

Mise au point concernantl'utilisation du dosagede l'antigène carcino-embryonnaire (CEA)en clinique

The carcinoembryonic antigen (CEA) is a tumor marker defined by specific heterologous antisera. Elevated levels of circulating CEA have been detected by radioimmunoassay in 20-90 per cent of cases of colorectal carcinomas depending on the degree of tumor spread. The fact that elevation of CEA level can also be observed in other types of carcinomas and in several non malignant conditions greatly limit the value of the CEA test for the early diagnosis of colorectal carcinoma. Thus, the CEA assay should not be used as a screening test for cancer. Repeatecl CEA mesurements, however, appear to be of importance for the evaluation of tumor resection and the detection of tumor recurrence. The only localized tumors known to produce elevation of CEA above the levels observed in non malignant diseases are carcinomas of the large bowel and the pancreas. In carcinomas derived from other organs a marked increase of CEA level is always associated with the presence of distant metastasis. Therefore at the present time the clinical applications of the CEA radioimmunoassay should be limited to the differentiai diagnosis of patients with suspicion of primary colorectal or pancreatic carcinoma, to the detection of distant metastasis in other types of carcinomas and to the post operative follow up of patients who had elevated levels of CEA before surgery. Well-controlled studies are still needed to determine if therapeutic decisions based on CEA results can lead to improved survival.

Des antisérums dirigés contre l'antigène carcino-embryonnaire (CEA) peuvent induire une lyse spécifique des cellules de carcinome du côlon par des lymphocytes normaux

Antibody-dependent cell-mediated cytotoxicity (ADCC) against human colon carcinoma cells grown in vitro was demonstrated with two specific rabbit anti-carcinoembryonic antigen (cea) antisera. The same antisera did not lyse the colon carcinoma cells in the presence of complement but without lymphocytes. The normal human lymphocytes in the absence of anti-CEA antiserum had a very low cytotoxic activity during the three hours 51Cr release assay used in this study. Two colon carcinoma cell lines, HT-29 and Co-115, expressing CEA on their surface as demonstrated by immunofluorescence, were significantly lysed in the ADCC test, whereas control tumor cell lines, not expressing CEA, were not affected by the anti-CEA sera and the lymphocytes. The specificity of the reaction was further demonstrated by the inhibition of antibody-dependent cell-mediated cytotoxicity after the addition of increasing amounts of purified CEA to the antiserum. The absorption of the anti-CEA antisera was controlled by radioimmunoassay. Absorption of the antisera by normal lung extracts and red cells of different blood groups did not decrease the cytotoxicity.

Tumor targeting with newly designed biparatopic antibodies directed against two different epitopes of the carcinoembryonic antigen (CEA).

In an attempt to improve tumor targeting and tumor retention time of monoclonal antibodies (MAbs), we prepared biparatopic antibodies (BpAbs) having the capability of binding 2 different non-overlapping epitopes on the same target antigen molecule, namely, the carcinoembryonic antigen (CEA). Six BpAbs were constructed by coupling 2 different Fab' fragments from 4 different specific anti-CEA MAbs recognizing 4 CEA epitopes (Gold 1-4). Demonstration of the double paratopic binding of these antibodies for CEA was confirmed in vitro by inhibition radioimmunoassay and cross-inhibition analysis by surface plasmon resonance (SPR; BIACORE) technology. Using the latter technique, the affinity constants for CEA immobilized onto the sensor chip were found to range from 0.37 to 1.54 x 10(9) M(-1) for the 4 parental F(ab')2 fragments and from 1.88 to 10.14 x 10(9) M(-1) for the BpAbs, demonstrating the advantage of biparatopic binding over conventional F(ab')2 binding. The Ka improvement was particularly high for BpAb F6/35A7 and BpAb F6/B17 with a 9.5- and 8.1-fold increase, respectively, as compared with the parental F(ab')2. In vivo, the 6 BpAbs were compared with their 2 respective parental F(ab')2 by injection of 131I-BpAb/125I-F(ab')2 parental fragments into nude mice xenografted with the human colon carcinoma T380. Dissection 72 hr post-injection demonstrated that BpAb B17/CE25 and BpAb F6/B17 gave higher tumor uptake than that of their parental F(ab')2. This finding is particularly interesting for BpAb F6/B17, which compared favorably with the F6 F(ab')2, one of the best parental F(ab')2 fragments used in our study.

Studies of the association of the A, B and Lewis Blood group antigens with carcinoembryonic antigen (CEA).

Carcinoembryonic antigen (CEA) was purified from primary tumour or from hepatic metastases obtained from ten cases of carcinoma of the colon. In nine cases the blood group antigens A, B, Lea or Leb were detected in CEA preparations by the binding of 125I-labelled CEA by blood group antibodies. The extent of binding appeared to preclude simple contamination of CEA preparations by blood group glycoprotein. In all cases the blood group antigens detected were consistent with the patients' known blood groups. Blood group I and i activities were not detected. It is concluded that the determinants of A, B and Lewis antigens and of CEA share the same glycoprotein carrier molecules.

Direct comparison of a radioiodinated intact chimeric anti-CEA MAb with its F(ab')2 fragment in nude mice bearing different human colon cancer xenografts.

Tumour localisation and tumour to normal tissue ratios of a chimeric anti-carcinoembryonic antigen (CEA) monoclonal antibody (MAb), in intact form and as an F(ab')2 fragment labelled with 125I and 131I, were compared in groups of nude mice bearing four different colon cancer xenografts, T380, Co112 or LoVo, of human origin, or a rat colon cancer transfected with human CEA cDNA, called '3G7'. For each tumour, three to four mice per time point were analysed 6, 12, 24, 48 and 96 h after MAb injection. In the different tumours, maximal localisation of intact MAb was obtained at 24 to 48 h, and of F(ab')2 fragment 12 to 24 h after injection. Among the different tumours, localisation was highest with colon cancer T380, with 64% of the injected dose per gram (% ID/g) for the intact MAb and 57% for its F(ab')2 fragment, while in the three other tumours, maximal localisation ranged from 14 to 22% ID g-1 for the intact MAb and was about 11% for the F(ab')2. Tumour to normal tissue ratios of intact MAb increased rapidly until 24 h after injection and remained stable or showed only a minor increase thereafter. In contrast, for the F(ab')2 fragment, the tumour to normal tissue ratios increased steadily up to 4 days after injection reaching markedly higher values than those obtained with intact MAb. For the four different xenografts, tumour to blood ratios of F(ab')2 were about 2, 3 and 5 to 16 times higher than those of intact antibodies at 12, 24 and 96 h after injection, respectively.