Custom-tailored drug immunoconjugates in cancer therapy.

Forty-three patients with disseminated refractory malignancies each received an individually specified combination of either Adriamycin (n = 24) or mitomycin-C (n = 19) conjugated to a cocktail of murine monoclonal antibodies (mAb). Cancers were typed with both immunohistochemistry and flow cytometry using a panel of antibodies. Cocktails of up to six antibodies were selected based on total binding of greater than 80% of the malignant cells in the biopsy specimen. These mAb cocktails were then drug conjugated, safety tested, and administered intravenously. The Adriamycin immunoconjugates were well tolerated in 22/24 patients, with 17/24 having significant side effects. Fever, chills, pruritis, and skin rash were by far the most common transitory reactions. All were well controlled with premedication. A total of up to 1 g Adriamycin and 5 g mAb were administered to each patient. The limiting factor appeared to be a variable dissociation of active Adriamycin from the antibody that unpredictably caused hemopoietic depression. Similar findings were noted among 19 patients treated with mitomycin-C conjugates. Thrombocytopenia at a 60-mg dose of mitomycin-C in this schedule was dose limiting. Serological evidence suggested that the development of an immunoglobulin M antibody specific against the mouse mAb had the specificity and sensitivity to predict clinical reactions. These antibodies were quantitatively less in mitomycin-C-treated patients. Selected patients were retreated. One patient with chronic lymphocytic leukemia was treated on three occasions with regression of peripheral lymph nodes. Two patients with breast carcinoma had definite improvement in ulcerating skin lesions, and two patients with tongue carcinoma had shrinkage of their lesions. No responses were seen with mitomycin-C conjugates but binding was noted to tumors. Drug-induced colitis was seen at higher doses with some binding of these conjugates to normal colon epithelium. This study demonstrated the feasibility of preparing individually specified drug immunoconjugate cocktails for patients with refractory malignancies. Cocktail formulation and antibody delivery to the tumor in vivo was accomplished. There was limited antigenic drift among various biopsies within the same patient over time. The major technical hurdle continues to be the selection of effective drug conjugation methods to optimally bind drugs to mAbs for targeted cancer therapy.     

Adriamycin custom-tailored immunoconjugates in the treatment of human malignancies

Twenty-three patients with disseminated refractory malignancies each received a tailored combination of adriamycin-conjugated murine monoclonal antibodies. Tumors were typed using a panel of antibodies. Cocktails of up to six antibodies were selected based on binding greater than 80% of the malignant cells as tested by immunoperoxidase and flow cytometry. These monoclonal antibodies were then conjugated to Adriamycin and administered intravenously. Seventeen of 23 patients had reactions to the administration of immunoconjugates, but these were tolerable in all but two patients. Fever, chills, pruritis, and skin rash were by far the most common transitory reactions. All were well controlled with premedication. In several patients there was limited antigenic drift among various biopsies within the same patient over time. This observation confirms the necessity for the use of a cocktail of antibodies if one wishes to cover all tumor cells. Preliminary serologic evidence suggests that the development of an IgM antibody, which is specific against the mouse monoclonal antibody, has the specificity and sensitivity to predict clinical reactions. Selected patients were re-treated. One patient with chronic lymphocytic leukemia had re-treatment on three occasions and demonstrated regression of peripheral lymph nodes. Two patients with breast carcinoma had definite improvement in ulcerating skin lesions and two patients with tongue carcinoma had shrinkage of their lesions. In the course of the study free Adriamycin released from the monoclonal antibodies was discovered to be a limiting factor in the amount of antibody that could be administered. Up to 1 g of Adriamycin and up to 5 g of monoclonal antibody were administered. The limiting factor appeared to be a variable dissociation of active Adriamycin from the antibody that unpredictably caused hemopoietic depression. This study demonstrates the feasibility and reviews technical considerations in preparing immunoconjugate cocktails for patients with refractory malignancies. The major technical hurdle appears to be the selection of an effective conjugation method that can be used to optimally bind Adriamycin to monoclonal antibodies for targeted cancer therapy.     

Evaluation and clinical relevance of patient immune responses to intravenous therapy with murine monoclonal antibodies conjugated to adriamycin

A retrospective study was performed in order to examine the clinical relevance of human anti-murine antibodies (HAMA) to concurrent clinical events in 21 patients receiving intravenous therapy with cocktails of murine monoclonal antibodies conjugated to Adriamycin. In vivo tumor localization of the murine antibodies was also evaluated. Serum levels of HAMA, human-murine immune complexes (HMIC), and murine antibodies were measured using an automated fluorescence immunoassay. Immunohistochemical staining was performed on frozen sections of tumor biopsies from eight of the patients to examine the in vivo binding of the murine antibodies. The patients were divided into low, intermediate, and high antibody dose groups. The incidence of allergic symptoms (80%) and HAMA correlation (75%) were highest in the low dose group. Specific IgM HAMA was the most highly correlated with allergic reactions, being present in 61.5% of the allergic patients. Thirteen of the 21 patients studied (61.9%) developed allergic symptoms after one or more doses of the murine monoclonal antibody conjugates. The percentages of total antibody doses in the patients' sera at varying intervals post-infusion varied widely from patient to patient for any given time point and dose, suggesting complex factors in the distribution and clearance of the murine antibodies. All eight of the patients biopsied during or post-therapy exhibited tumor localization of the murine monoclonal antibodies. Six of the eight had concurrent HAMA in their sera. Thus, the presence of HAMA did not prevent in vivo localization of the murine antibodies in the target tumors.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preliminary clinical study of transferrin-adriamycin conjugate for drug delivery to acute leukemia patients

Seven patients with acute leukemia were treated intravenously with low doses of transferrin-Adriamycin conjugate. The total amount of drug given each patient was far below known toxicity levels for free Adriamycin. The number of tumor cells in peripheral blood diminished in treated patients, and bone marrow aspirates showed no evidence of disease progression. Two patients gave a febrile response and no hypersensitivity reactions were observed. Results of parallel basic research have shown that transferrin receptors on acute leukemia cells bind transferrin-Adriamycin conjugates, and kill by mechanisms at either the plasma membrane or nuclear levels, or both. Such conjugates may provide an alternative to monoclonal antibody drug targeting.     

Anti-CD22-MCC-DM1 and MC-MMAF conjugates: impact of assay format on pharmacokinetic parameters determination

CD22 represents a promising target for antibody-drug conjugate therapy in the context of B cell malignancies since it rapidly internalizes, importing specifically bound antibodies with it. To determine the pharmacokinetic parameters of anti-CD22-MCC-DM1 and MC-MMAF conjugates, various approaches to quantifying total and conjugated antibody were investigated. Although the total antibody assay formats gave similar results for both conjugates, the mouse pharmacokinetic profile for the anti-CD22-MCC-DM1 and MC-MMAF appeared significantly different depending on the conjugated antibody assay format. Since these differences significantly impacted the PK parameters determination, we investigated the effect of the drug/antibody ratio on the total and conjugated antibody quantification using multiple assay formats. Our investigations revealed the limitations of some assay formats to quantify anti-CD22-MCC-DM1 and MC-MMAF with different drug load and in the context of a heterogeneous ADC population highlight the need to carefully plan the assay strategy for the total and conjugated antibody quantification in order to accurately determine the ADC PK parameters.     

Tumour localization of monoclonal antibody against a rat mammary carcinoma and suppression of tumour growth with adriamycin-antibody conjugates

Summary Monoclonal antibody to the rat mammary carcinoma Sp4 isolated from hybridoma supernatants and labelled with ¹²⁵I showed preferential in vivo localization into subcutaneous growths of Sp4 compared with normal tissues and a range of other transplanted tumours. No specific localization was seen with ¹²⁵I-labelled normal rat immunoglobulin. Adriamycin conjugated to monoclonal antibody significantly retarded Sp4 tumour growth at 1/25th of the effective dose of the free drug, and in some cases brought about total tumour regression. Normal rat immunoglobulin-adriamycin conjugates were relatively ineffective. These studies indicate that monoclonal antibody directed against tumour cell surface antigens may be highly effective for tumour targeting of therapeutic agents.     

Toxicities associated with monoclonal antibody infusions in cancer patients

The toxicity during and following 291 infusions of 19 murine and three human monoclonal antibodies (MoAB) in 177 cancer patients with 10 different malignancies was assessed. Doses ranged from 0.5 to 500 mg administered over 0.25 to 24 hours. Various reactions in varying degrees were observed in 45 (28%) patients during their first MoAb infusion. Nine additional patients experienced toxicity following a subsequent antibody infusion. Antibodies that reacted with circulating cells were associated with toxicity in 20 of 28 (71%) of the first infusions, compared to 24 of 127 (19%) for patients receiving antibodies that did not react with circulating cells. Fevers, rigors, chills, and diaphoresis were observed in 10% to 12% of the patients and were associated with binding to circulating cells. Presumed hypersensitivity reactions, including urticaria, pruritus, bronchospasm, and anaphylaxis occurred in 20 patients (11%). There were five episodes of bronchospasm and a single episode of anaphylaxis. Liver transaminases were elevated in 14%. There was no correlation between dose or infusion rate and toxicity. Murine monoclonal antibodies that are not conjugated to cytotoxic agents can be given with an acceptable frequency of side effects and serious allergic reactions. There is a small risk of anaphylaxis, and one should avoid rapid infusion of high antibody doses in the presence of circulating target cells and/or circulating free antigen.     

3-Carboxy-6-chloro-7-hydroxycoumarin: A highly fluorescent, water-soluble violet-excitable dye for cell analysis

In our search for new violet-excitable dyes with improved photophysical and photochemical properties, we examined several halogen-substituted hydroxycoumarins and found that chlorinated derivatives are at least as bright as their fluorinated analogs. A monochlorinated hydroxycoumarin was found to have a high quantum yield (∼0.98), and human leucocyte-specific monoclonal antibodies (CD3, CD4, and CD45) conjugated with this dye exhibited reliable performance in flow cytometry assays. Additional studies were performed, with BD Horizon V450-antibody conjugates being included in eight-color cocktails aimed at subsetting lymphocytes and myeloid cells. Such cocktails can frequently be unstable due to the tendency of one or more components to lose structural integrity, photobleach, or develop unwanted affinities for another component. However, the cocktails employed in this study enabled several different applications to be run and established that multicolor reagent mixtures containing V450-antibody conjugates are functional and stable.     

Significance of antigen, drug, and tumor cell targets in the preclinical evaluation of doxorubicin, daunorubicin, methotrexate, and mitomycin-C monoclonal antibody immunoconjugates

We tested drug monoclonal antibody immunoconjugates in vitro in 72 h 3H-thymidine assays and in vivo in athymic mice bearing human tumor xenografts of the same target cells. Experimental arms included control, monoclonal antibody, drug, drug + antibody, the test immunoconjugate, and a negative control immunoconjugate with an equivalent molar amount of drug for in vitro experiments, and the amount of drug conjugated to 500 micrograms of antibody in the animal experiments. Monoclonal antibodies included T101, an IgG2a that reacts with a rapidly modulating antigen, 9.2.27, an IgG2a that reacts with a slowly modulating antigen, and ME7, an IgG1 that reacts with a slowly modulating antigen. Cells used in testing included MOLT-4 (T lymphoma), 8392 (B lymphoma), and M21 (melanoma). Drugs tested were doxorubicin, daunorubicin, methotrexate, and mitomycin-C. M21 cells were resistant to daunorubicin in vitro but were inhibited by the 9.2.27 daunorubicin immunoconjugate. T101, 9.2.27, and ME7 cis-aconitate anthracycline immunoconjugates and mitomycin-C-glutarate immunoconjugates were specifically cytotoxic only for antigen positive cells in vitro and were superior to free drug in vivo. These results confirm that antigen specific-cytotoxic drug immunoconjugates can be produced that are superior to the same dose of free drug. However, each monoclonal antibody drug target system is unique and must be well-characterized for appropriate interpretation of data.     

Phase I trial of mitomycin C immunoconjugates cocktails in human malignancies

Nineteen patients with refractory solid malignancies received individualized combinations of mitomycin C conjugated murine monoclonal antibodies selected by immunohistochemical and flow cytometric screening of tumor specimens. There were no responses in this Phase I study. Thrombocytopenia precluded escalation above a mitomycin C dose of 60 mg per treatment cycle. Preclinical, clinical, and toxicity experiences with this investigational approach to the treatment of cancer are discussed.     

Antibodies directed against receptor tyrosine kinases

Approximately 30 therapeutic monoclonal antibodies have already been approved for cancers and inflammatory diseases, and monoclonal antibodies continue to be one of the fastest growing classes of therapeutic molecules. Because aberrant signaling by receptor tyrosine kinases (RTKs) is a commonly observed factor in cancer, most of the subclasses of RTKs are being extensively studied as potential targets for treating malignancies. The first two RTKs that have been targeted by antibody therapy, with five currently marketed antibodies, are the growth factor receptors EGFR and HER2. However, due to systemic side effects, refractory patients and the development of drug resistance, these treatments are being challenged by emerging therapeutics. This review examines current monoclonal antibody therapies against RTKs. After an analysis of agents that have already been approved, we present an analysis of antibodies in clinical development that target RTKs. Finally, we highlight promising RTKs that are emerging as new oncological targets for antibody-based therapy.     

抗体药物的发展与应用

早期抗体药物是鼠源单克隆抗体,存在免疫原性强、半衰期短等问题。历经数十年的发展,抗体药物从最初的鼠源单抗,逐步发展为人鼠嵌合抗体、人源化抗体及全人源化抗体。通过片段重组、位点修饰、药物偶联等方法,科研人员研发了包括抗体融合蛋白、抗体偶联药物、双特异性抗体、小分子抗体片段等形式多样的抗体药物。抗体药物在恶性肿瘤、自身免疫病、感染性疾病的治疗上发挥重要作用。通过对抗体药物人源化历程,不同类型的抗体结构和特点,以及抗体药物在新型冠状病毒肺炎治疗中的应用进行综述,并对抗体药物的发展前景进行展望,以期为我国抗体药物的研发提供参考。     

用单克隆抗体检测微量乙醛—蛋白结合物

用乙醛和小鼠血清白蛋白的结合物免疫BALB/C小鼠.采用高效融合程序制备出只与乙醛反应的单克隆抗体.这种单克隆抗体能够检测1×10~(-3)微摩尔的乙醛,在鉴定酒精摄入量及其对人体有害程度的研究中具有一定意义.     

Rat serum antibodies binding to high-molecular-weight glycoprotein(s) on syngeneic colon carcinomas,demonstrated by competition with rat monoclonal antibody

Summary Sera from rats immunized to syngeneic 1,2-dimethylhydrazine colon carcinomas were analyzed for their ability to inhibit the binding of a syngeneic rat IgM monoclonal antibody (10B12) specific for high-molecular-weight glycoprotein(s) from rat colon carcinoma. Immunization with irradiated tumour cells or with tumour tissue extracts resulted in the appearance of a strong inhibiting activity. Sera of animals with established growing tumours and of females shortly after partus also inhibited binding of the monoclonal antibody, while unimmunized animals or animals immunized with irrelevant antigens had no inhibiting antibodies in their sera. Dimethylhydrazinetreated animals showed an increased titer of antibodies binding to the high-molecular-weight glycoprotein, but showed no inhibition of binding of the 10B12 monoclonal antibody. The syngeneic 10B12 rat antibody obviously does not reflect a rare event captured from a hyperimmune animal by the hybridoma technique but rather represents an antibody specificity frequently appearing in the immune response to tumours expressing the high-molecular-weight glycoprotein.     

The effect of bispecific monoclonal antibody recognizing both hepatoma-specific membrane glycoprotein and anthracycline drugs on the metastatic growth of hepatoma AH66

A monoclonal mouse antibody (MoHG) was produced using in vitro cultured AH66R tumor cells treated with cholesteryl hemisuccinate as an immunogen. The antibody identified a 90 kd membrane glycoprotein (HG-90) which is expressed on in vitro cultured hepatoma cell lines AH66 and AH66R. A monoclonal antibody was prepared to the anthracycline drug daunomycin, and it also reacted with adriamycin. A fusion was made of the hybridoma HG-90 with the hybridoma which recognized daunomycin/adriamycin. This bispecific hybridoma A8C recognized both determinants. We studied the therapeutic effect of the A8C bispecific antibody with adriamycin treatment and compared it to the effect of the bispecific antibody to which adriamycin had been conjugated via an albumin (Alb) bridge. The therapy model used was the tumor AH66R in Donryu rats. Tumor bearing rats had their subcutaneous tumors resected on day 10, a time when distant metastases were present. After the surgical resection of the tumor the rats were injected intravenously for two cycles with the bispecific antibodies, followed by the administration of adriamycin (ADR) or MoHG.Alb.ADR conjugates. A slight therapeutic effect occurred with either MoHG or ADR alone but treatment with the bispecific antibody followed by the administration of ADR or with the MoHG.Alb.ADR conjugates significantly prolonged survival, with 60% of the treated animals being "tumor free" when sacrificed on day 80. Lower serum concentrations of alphafetoprotein were observed with the bispecific antibody and drug treatment. This suggests that the bispecific antibody/drug treatment is potentially more beneficial in the suppression of distant metastases than the MoHG.Alb.ADR conjugate. This may be due to an increase in the local drug concentration of unmodified adriamycin.     

Specific and nonspecific macromolecule-drug conjugates for the improvement of cancer chemotherapy

Antineoplastic drugs such as daunomycin, adriamycin, methotrexate, 5-fluorouridine, cytosine arabinoside, and platinate were bound to antibodies directly or via a polymeric bridge. The drug antibody conjugates retained most of their drug and antibody activities when tested in vitro. Daunomycin–antibody conjugates were shown to penetrate tumor cells in the conjugated form. In animals, daunomycin–antibody conjugates were at least as effective chemotherapeutically as the corresponding free drugs and considerably less toxic. In some tumor systems, the daunomycin–antibody conjugates represented an improvement over the free drug. This improvement was restricted in some tumors to a particular injection route of the tumor and the treatment.     

Antiproliferative effect of a lectin- and anti-Thy-1.2 antibody-targeted HPMA copolymer-bound doxorubicin on primary and metastatic human colorectal carcinoma and on human colorectal carcinoma transfected with the mouse Thy-1.2 gene

The aim of this study was to compare the potential of two plant lectins [peanut agglutinin (PNA) and wheat germ agglutinin (WGA)], monoclonal antibody (anti-Thy-1.2), its F(ab')(2) fragments, and galactosamine as targeting moieties bound to the polymer drug carrier to deliver a xenobiotic, doxorubicin, to selected cancer cell lines. We have used primary (SW 480, HT 29) and metastatic (SW 620) human colorectal cancer cell lines and a transfectant, genetically engineered SW 620 cell line with mouse gene Thy-1.2 (SW 620/T) to test the possibility of marking human cancer with xenogeneic mouse gene and use it for effective site-specific targeting. The targeting moieties and doxorubicin were conjugated to a water-soluble copolymer based on N-(2-hydroxypropyl)methacrylamide (HPMA) acting as a carrier responsible for controlled intracellular release of the targeted drug. FACS analysis showed a strong binding of WGA-FITC to all tested cell lines. Binding of PNA-FITC was considerably weaker. The in vitro antiproliferative effect of lectin-targeted HPMA carrier-bound doxorubicin evaluated as [(3)H]TdR incorporation reflected both the intensity of the binding and the different sensitivity of the tested cancer cells lines to doxorubicin. The antiproliferative effect of conjugates targeted with WGA was comparable to that with the conjugates targeted with the anti-Thy-1.2 monoclonal antibody or their F(ab')(2) fragments. The magnitude of the cytotoxic effect of HPMA-doxorubicin targeted with PNA was lower in all tested cell lines. While the conjugates with WGA were more cytotoxic, the conjugates with PNA were more specific as their binding is limited to cancer cells and to the sites of inflammation. Noncytotoxic conjugates with a very low concentration of doxorubicin and targeted with PNA, anti-Thy-1.2, or their F(ab')(2) fragments exerted in some lines (SW 480, SW 620) low mitogenic activity. The Thy-1.2 gene-transfected SW 620 metastatic colorectal cancer cell line was sensitive to the antiproliferative effect of Thy-1.2-targeted doxorubicin as was shown for the Thy-1. 2(+) EL4 cell line and for Thy-1.2(+) concanavalin A-stimulated mouse T lymphocytes. These results represent the first indication of the suitability of transfection of human cancer cells with selected targeting genes for site-specific therapy of malignancies.     

In Vitro and In Vivo Evaluation of Cysteine and Site Specific Conjugated Herceptin Antibody-Drug Conjugates

Antibody drug conjugates (ADCs) are monoclonal antibodies designed to deliver a cytotoxic drug selectively to antigen expressing cells. Several components of an ADC including the selection of the antibody, the linker, the cytotoxic drug payload and the site of attachment used to attach the drug to the antibody are critical to the activity and development of the ADC.The cytotoxic drugs or payloads used to make ADCs are typically conjugated to the antibody through cysteine or lysine residues. This results in ADCs that have a heterogeneous number of drugs per antibody. The number of drugs per antibody commonly referred to as the drug to antibody ratio (DAR), can vary between 0 and 8 drugs for a IgG₁ antibody. Antibodies with 0 drugs are ineffective and compete with the ADC for binding to the antigen expressing cells. Antibodies with 8 drugs per antibody have reduced in vivo stability, which may contribute to non target related toxicities.In these studies we incorporated a non-natural amino acid, para acetyl phenylalanine, at two unique sites within an antibody against Her2/neu. We covalently attached a cytotoxic drug to these sites to form an ADC which contains two drugs per antibody.We report the results from the first direct preclinical comparison of a site specific non-natural amino acid anti-Her2 ADC and a cysteine conjugated anti-Her2 ADC. We report that the site specific non-natural amino acid anti-Her2 ADCs have superior in vitro serum stability and preclinical toxicology profile in rats as compared to the cysteine conjugated anti-Her2 ADCs. We also demonstrate that the site specific non-natural amino acid anti-Her2 ADCs maintain their in vitro potency and in vivo efficacy against Her2 expressing human tumor cell lines. Our data suggests that site specific non-natural amino acid ADCs may have a superior therapeutic window than cysteine conjugated ADCs.     

Antibody-nucleic acid interactions. Monoclonal antibodies define different antigenic domains in 2',5'-oligoadenylates

To define the epitopes involved in binding anti-oligonucleotide antibodies, several hybridomas producing monoclonal antibodies directed against 2',5'-oligoadenylate were established. A solid-phase enzyme-linked immunoassay that employed microtiter wells coated with Ficoll-2',5'-oligoadenylate conjugates proved useful in screening and characterizing hybridoma supernatants. Control experiments demonstrated that the conjugates were irreversibly adsorbed to polystyrene wells under the conditions employed in the assay. Reactivity of monoclonal antibodies with numerous analogues of 2',5'-oligoadenylate was measured by using a competition assay. Several monoclonal antibodies originating from different mice immunized with the same or different immunogens possessed distinctive fine specificities. At least one 2',5'-phosphodiester bond was important in forming each epitope, suggesting that the ribose phosphate backbone is a critical element in defining an antigenic domain of an oligonucleotide. The purine bases were also important, and modification of the bases had varied effects on the extent of antibody recognition. The length of the oligonucleotide and the nature of the termini were also of some importance. In several instances the modification created by linkage of 2',5'-oligoadenylate to carrier protein also contributed to the determinant. The monoclonal antibody most specific for 2',5'-oligoadenylates was relatively insensitive to ionic strength. In contrast, a monoclonal antibody with a 2',5'-oligopurine specificity appeared to bind 2',5'-oligoadenylate through one ion pair, whereas the binding of a monoclonal antibody with a low degree of base specificity appeared to bind through two ion pairs. The results demonstrated that 2',5'-linked oligoadenylate-protein complexes possess at least three distinct oligonucleotide-related antigenic surfaces that can be recognized with high apparent affinity by monoclonal antibodies. A model for the three epitopes is presented.     

Characterization of a mouse/human chimeric monoclonal antibody (17-1A) to a colon cancer tumor-associated antigen

Mouse monoclonal antibody 17-1A is specific for an antigen expressed on cells of human gastrointestinal malignancies and has been used in radioimmune imaging and therapy trials for patients with colon and pancreatic cancer. The cell line SG3/5 was generated by transfection of a nonproducing mouse myeloma line (SP2/0) with a chimeric gene construct composed of variable regions from the mouse 17-1A immunoglobulin (gamma 2a, kappa) and constant regions of human k and gamma 3 immunoglobulin genes. The secreted immunoglobulin was bound by mouse monoclonal antibodies to human IgG(Fc) and IgG3 but not by staphylococcal protein A. Gel filtration HPLC profiles of purified chimeric antibody were similar to normal human IgG3 but quite different from native 17-1A and normal human IgG1, 2, and 4. Native and chimeric 17-1A had similar patterns of reactivity with colon cancer, other adenocarcinoma, and leukemic cell lines. Competitive inhibition documented that native and chimeric 17-1A had identical capacities to inhibit radiolabeled native 17-1A binding to colon cancer cell lines. Thus, the chimeric 17-1A exhibits molecular characteristics of normal human IgG3 but retains the specificity and binding affinity of the native 17-1A murine monoclonal antibody. The native and chimeric 17-1A mediated similar modest degrees of human lymphocyte and monocyte ADCC in a 4-hr 51Cr release assay, and both failed to mediate complement lysis of colon carcinoma cell lines in the presence of human complement. This human/mouse chimeric monoclonal antibody may be a good candidate for use in clinical trials because it retains the tumor antigen specificity and human effector cell recognition of the native 17-1A, would presumably have a fivefold to 10-fold longer circulating half-life in man, and should be considerably less immunogenic as compared with native murine immunoglobulins.