Development of human anti-murine antibody (HAMA) response in patients

False diagnosis and needless therapy of presumed malignant disease in women with false-positive human chorionic gonadotropin concentrations

BACKGROUND

12 women were diagnosed of having postgestational choriocarcinoma on the basis of persistently positive human chorionic gonadotropin (hCG) test results in the absence of pregnancy. Most of the women had extirpative surgery or chemotherapy, or both, without significant diminution in hCG titre. Our aim was to assess whether the hCG concentrations were false-positive test results.

METHODS

Samples were tested for hCG, hCG free beta subunit, and hCG beta-core fragment. Assay kinetics were also assessed, and samples were tested independently by competitive RIA. False-positive hCG concentrations were identified by two criteria: detection of hCG in serum and lack of detection of hCG and its degradation products in urine; and wide variations in results for different hCG assays. We corroborated false-positive hCG values by the lack of parallel changes in hCG results when serum was diluted, by false detection of other antigens, and by failure to detect hCG with in-house assays.

FINDINGS

All 12 women met both criteria for false-positive hCG, and all had corroborating findings. In all 12 cases, a false diagnosis had been made, and most of the women had been subjected to needless surgery or chemotherapy. Assay kinetics indicated that heterophilic antibodies were responsible for the false-positive results. As a result of our findings all further therapy was stopped.

INTERPRETATION

Current protocols for the diagnosis and treatment of choriocarcinoma should be modified to include a compulsory test for hCG in urine.

Human Anti-Animal Antibody Interferences in Immunological Assays

Purpose: The scope and significance of human anti-animal antibody interference in immunological assays is reviewed with an emphasis on human anti-animal immunoglobulins, particularly human anti-mouse antibodies (HAMAs).

Issues: Anti-animal antibodies (IgG, IgA, IgM, IgE class, anti-isotype, and anti-idiotype specificity) arise as a result of iatrogenic and noniatrogenic causes and include human anti-mouse, -rabbit, -goat, -sheep, -cow, -pig, -rat, and -horse antibodies and antibodies with mixed specificity. Circulating antibodies can reach gram per liter concentrations and may persist for years. Prevalence estimates for anti-animal antibodies in the general population vary widely and range from <1% to 80%. Human anti-animal antibodies cause interferences in immunological assays. The most common human anti-animal antibody interferent is HAMA, which causes both positive and negative interferences in two-site mouse monoclonal antibody-based assays. Strategies to prevent the development of human anti-animal antibody responses include immunosuppressant therapy and the use of humanized, polyethylene glycolylated, or Fab fragments of antibody agents. Sample pretreatment or assay redesign can eliminate immunoassay interferences caused by anti-animal antibodies. Enzyme immunoassays, immunoradiometric assays, immunofluorescence, and HPLC assays have been designed to detect HAMA and other anti-animal antibodies, but intermethod comparability is complicated by differences in assay specificity and lack of standardization.

Conclusions: Human anti-animal antibodies often go unnoticed, to the detriment of patient care. A heightened awareness on the part of laboratory staff and clinicians of the problems caused by this type of interference in routine immunoassay tests is desirable. Efforts should be directed at improving methods for identifying and eliminating this type of analytical interference.

In vitro and in vivo behavior of radiolabeled chimeric anti-EGFRvIII monoclonal antibody: comparison with its murine parent

The mutant version of the epidermal growth factor receptor EGFRvIII has been found on gliomas and other tumors, but not on normal tissues. Radioiodinated murine (mu) L8A4 monoclonal antibody (MAb) specifically targets EGFRvIII xenografts in vivo when labeled using N-succinimidyl 5-iodo-3-pyridinecarboxylate (SIPC). A chimeric (ch) MAb consisting of the variable region of muL8A4 and the constant domains of human IgG2 has been developed that has an affinity and radioiodinated immunoreactive fraction comparable to muL8A4. In vitro, both MAbs were internalized and processed by EGFRvIII expressing cell lines (U87MG delta EGFR or NR6M) at similar rates (maximum intracellular retention, 35-40%). In paired-label tissue distribution studies in athymic mice bearing U87MG delta EGFR tumor xenografts, the ch:mu L8A4 uptake ratio in normal tissues rose to greater than 2:1, whereas in tumor, the ratio remained 1:1 throughout the experiment. These results indicate that chL8A4 exhibits similar binding and internalization properties as its murine parent, but suggest different intracellular processing and/or deposition of catabolites in normal tissues for chL8A4.

Tissue distribution and radiation dosimetry of astatine-211-labeled chimeric 81C6, an alpha-particle-emitting immunoconjugate

A paired-label study was performed in athymic mice bearing subcutaneous D-54 MG human glioma xenografts to compare the localization of human/mouse anti-tenascin chimeric antibody 81C6 labeled by reaction with N-succinimidyl 3-[211At]astatobenzoate and N-succinimidyl 3-[131I]iodobenzoate. Over the 48-h observation period, the distribution of 211At- and 131I-labeled antibody were quite similar in tumor and normal tissues except stomach. These data were used to calculate human radiation doses for both intravenously and intrathecal administered 211At-labeled chimeric 81C6 using a quality factor of 5 for alpha-emissions.

Chimeric anti-tenascin antibody 81C6: increased tumor localization compared with its murine parent

When labeled using the Iodogen method, a chimeric antibody composed of the human IgG2 constant region and the variable regions of murine anti-tenascin 81C6 exhibited superior uptake in human glioma xenografts compared with its murine parent. In the current study, three paired-label experiments were performed in athymic mice with subcutaneous D-54 MG human glioma xenografts to evaluate further the properties of radioiodinated chimeric 81C6. These studies demonstrated that (a) the enhanced tumor uptake of chimeric 81C6 is specific; (b) when labeling was performed using N-succinimidyl 3-iodobenzoate, chimeric 81C6 again showed preferential accumulation in tumor compared with murine 81C6; and (c) the tumor uptake advantage observed previously with murine 81C6 for N-succinimidyl 3-iodobenzoate compared with Iodogen labeling did not occur with chimeric 81C6.

Interference by human antibodies with tumor marker assays

Many cancer patients respond to the in vivo application of murine monoclonal antibodies with the formation of various human antibodies which can interfere with tumor marker assays. While interferences by nonspecific human anti-mouse antibodies can be eliminated by addition of nonspecific mouse IgG, special problems can occur when the antibody applied in vivo also is employed in the in vitro assay. In ovarian cancer patients treated with the anti-CA-125 antibody OC125 and with the anti-TAG-72 antibody B72.3, respectively, we measured erroneous values for the tumor associated antigens CA-125 and TAG-72 due to human antiidiotypic or antiantiidiotypic antibodies. These interferences can only be prevented by using reagent antibodies different from the antibody applied in vivo. However, because it is difficult to eliminate interferences completely, tumor marker values determined in patients treated with monoclonal antibodies should be interpreted with care.

Human antibodies from transgenic mice

We have used homologous recombination in ES cells to engineer B cell-deficient mice that are incapable of expressing endogenous immunoglobulin heavy and kappa light chain genes. We find that B cell development in these mutant mice can be rescued by the introduction of human germline-configuration heavy- and kappa light-chain minilocus transgenes. The transgenes rearrange during B cell differentiation, and subsequently undergo class switching and somatic mutation in response to antigen stimulation; thus recapitulating both stages of the humoral immune response using human, rather than mouse, sequences. The mice can be immunized; and human sequence, antigen specific, monoclonal antibodies can be obtained using conventional rodent hybridoma technology. These animals are also of interest for studying the normal processes of immunoglobulin gene expression. We discuss the example of heavy chain class switching, which has not been previously observed within an autonomous transgene.

[Monoclonal antibodies and rheumatoid polyarthritis]

Monoclonal antibodies allow to foresee selective immunotherapy in rheumatoid arthritis (RA). Several molecules implicated in the immunopathogenesis of the disease represent the targets (antigens) of monoclonal antibodies already used in man: T cell antigens, T cell activation antigens, adhesion molecules, cytokines. The first open studies gave promising results. However complementary investigations are requested to confirm the clinical efficacy and to precise the real place of these biologic agents in the strategy of treatment of RA or auto-immune diseases.