[Demonstration of circulating CEA or CEA-like antigens and immunoglobulin G containing immune complexes in colorectal carcinoma]

Novel isoelectric target depletion (ITaD) protocol reduces the need for specific reagents for immunogenicity testing

Background: The development of immunogenicity assays for clinical drug candidates targeting soluble proteins is challenging when the soluble target might produce either false-positive or false-negative signals in bridging anti-drug antibody screening assays. A generic soluble target removal protocol that uses a pH-dependent depletion was evaluated. Results: An anti-drug antibody bridging assay with a pH-dependent soluble target depletion step was successfully developed. Endogenous target levels of ∼600 nM could be depleted below 8 pM. The assay was highly drug tolerant and met regulatory requirements. Conclusion: A reagent-independent target depletion protocol can be used for immunogenicity testing in the presence of a soluble target. The generic protocol circumvents common depletion or masking protocols.

Chemotherapy of a patient because of spuriously elevated alpha-fetoprotein levels. Identification of the responsible factor

Because of spuriously elevated alpha-fetoprotein levels, a course of polychemotherapy was given to a patient. We purified and identified the serum factor responsible for falsely high AFP levels as an IgG directed against mouse IgG. On gel filtration it behaves differently from true AFP, exhibiting a molecular weight of around 150,000. Chromatography on 'Protein A-Sepharose' revealed properties indistinguishable from those of IgG. The patient had never been treated with mouse antibodies, neither for diagnostic nor therapeutic purposes and he had had no contact with animals professionally.

Carcinoembryonic antigen: a rat model

It has been shown that a TAA termed rat CEA had the tissue distribution and physico-chemical properties similar to those of human CEA. In addition, it has been demonstrated that these two antigens shared antigenic determinants. These findings supported our contention that rat CEA and human CEA are analogous moieties. The production of CEA-specific autoantibodies and the induction of resistance to CEA-positive rat tumors after immunization of rats with extracts containing rat CEA raises the possibility that human CEA may be immunogenic in man. Treatment with heat, proteolytic enzymes and periodate oxidation revealed that rat CEA, similar to human CEA contained both carbohydrate and protein epitopes. The epitopes shared by rat and human CEA that were detectable by the monkey anti-human CEA serum appeared to be carbohydrate, whereas the epitopes on rat CEA with which the rat mAb combined appeared to be protein, and those detected by the rabbit anti-rat CEA serum appeared to be carbohydrate, as well as protein. These studies also indicated that, although the rat, rabbit and monkey produced antibodies specific for rat CEA, the epitopes detectable by antibodies from one species appeared to be distinct from those detectable by antibodies from the other two species. These observations have important implications in studies on human CEA. Its use as a reliable diagnostic marker for malignancy hinges on the detection of tumor-specific epitopes on the molecule. Such epitopes have not yet been clearly identified by antibodies produced in foreign species. Indeed, our finding that the rat mAb to rat CEA bound only to tumor extracts and not to extracts of normal tissues, including intestinal tissues, suggests that human beings would be the most likely source of a tumor-specific antibody to human CEA. In future studies, the role antibodies play in immunity against CEA-positive tumors will be explored and attempts will be made to determine whether all of the serologically detectable epitopes on rat CEA can induce tumor resistance, or whether this activity is limited to epitopes detectable only by rat antibodies. This information could have important implications in the use of human CEA in the immunotherapy of malignancies.

CEA-containing immune complexes in sera of patients with colorectal and breast cancer--analysis of complexed immunoglobulin classes

A sandwich enzyme immunoassay was developed to detect circulating immune complexes containing carcinoembryonic antigen (CEA) and immunoglobulin (Ig) G, IgA, or IgM using a nitrocellulose-bound anti-CEA antibody as the solid phase reagent. Elevated levels of CEA-containing circulating immune complexes (CEA-IC) were found in 15.4% of 117 sera from patients with colorectal cancer in a postsurgery follow-up study. Also in 24.5% of 102 sera from patients with breast cancer in different states of disease CEA-IC were found. The predominant Ig determined in CEA-IC of colorectal cancer patients was IgA, followed by IgG and IgM, whereas IgG and IgM were the most frequent Igs in CEA-IC of breast cancer patients. Elevated CEA levels were found in 12.0% of the colorectal cancer patients and in 25.4% of sera from breast cancer patients. No significance for the coincidence of elevated CEA levels and CEA-IC was recorded in all patients sera tested. In sera of patients with disease recurrence, however, both parameters were shown to be elevated (CEA 80.7% and CEA-IC 42.3%). The data presented indicate the detection of CEA-IC as an additional parameter for the identification of patients at increased risk for disease recurrence.

Detection of circulating Yersinia-immunoglobulin complexes by enzyme immunoassay (EIA)

An enzyme immunoassay (EIA) was developed for the detection of Yersinia-immunoglobulin complexes of known Ig class. Immune complexes (ICs) were attached to polystyrene microtiter plates by rabbit anti-human immunoglobulins, and the existence of Yersinia enterocolitica O:3 antigens was demonstrated using Fab fragments of alkaline phosphatase (AP)-conjugated antibody against the same serotype. Simultaneous binding of Yersinia antigens and immunoglobulins was a prerequisite for the detection of ICs. The method will be valuable for research into the immunopathogenetic mechanisms leading to reactive arthritis after Yersinia infection.