Interference by human antibodies with tumor marker assays

Transient human anti-mouse antibodies (HAMA) interference in CA 125 measurements during monitoring of ovarian cancer patients treated with murine monoclonal antibody

OBJECTIVE

To investigate the influence of human anti-mouse antibodies (HAMA) on serial CA 125 measurements in serum of patients with epithelial ovarian cancer following single intraperitoneal (IP) therapy with Yttrium-90-labeled human milk fat globule 1 murine monoclonal antibody ((90)Y-muHMFG1) as part of a large international randomized phase III trial.

METHODS

We monitored CA 125 concentrations in longitudinally collected serum samples from 224 patients after IP (90)Y-muHMFG1 (study group) and from 223 patients who received standard treatment (control group). Serum samples of 22 study patients with increased CA 125 concentrations were selected and subjected to affinity chromatography to study HAMA interference in CA 125 measurements.

RESULTS

CA 125 serum concentrations at weeks 1, 4 and 8 were significantly higher in the study group than in the control group. In the first 8 weeks after IP (90)Y-muHMFG1 administration significantly more patients of the study group (144/224) demonstrated CA 125 concentrations above the upper limit of normal of 23 U/mL, as compared to those of the control group (37/223). Affinity chromatography of serum with high CA 125 values in the first 8 weeks confirmed HAMA interference in CA 125 measurements while after 24 weeks this HAMA interference could no longer be detected.

CONCLUSIONS

This is the first study to demonstrate that clinical trials applying murine monoclonal antibodies may be flawed by a transient HAMA effect, which should be considered when monitoring ovarian cancer patients with CA 125 measurements.

Immunometric Assay Interference

Background: The primary aim of the study was to reduce interference in an in-house two-site, two-step immunometric assay.

Methods: In the running laboratory routine, 11 261 samples were tested with a carcinoembryonic antigen (CEA) assay with bovine immunoglobulin but no murine immunoglobulins in the buffer, in parallel to our routine CEA assay, using 15 mg/L heat-treated nonspecific murine immunoglobulin (MAK33) in the buffer and with the Fc fragments removed from the capture antibody.

Results: The frequency of interference was estimated to be 4.0% (95% confidence interval, 3.3–4.7%). The addition of 15 mg/L native MAK33 had little effect (frequency, 3.9%; 95% confidence interval, 3.2–4.6%), whereas adding 15 mg/L heat-treated MAK33 reduced interference to 0.86% (0.61–1.12%), and adding 50 mg/L reduced it further to 0.06% (0–0.13%). Removing the Fc fragments by itself reduced interference to 0.10% (0.02–0.19%). There were no statistically significant differences for age (P <0.23) or gender (P <0.40) between patients with interference (n = 210) and a randomly selected interference-negative control group (n = 186). Interference was not constant in patients: 15 of 25 individuals positive for interference and with four or more samples screened for interference had an interference-negative sample either before or after the peak of interference.

Conclusions: In a two-site, two-step immunometric assay using mouse monoclonal antibodies, use of heat-treated nonspecific murine immunoglobulin in the buffer or removal of the Fc fragment from the capture antibody could improve performance.

Human anti-mouse antibodies

Human anti-mouse antibodies (HAMA) are human immunoglobulins with specificity for mouse immunoglobulins. This topic currently is of interest because of the increased use of monoclonal mouse antibodies as diagnostic reagents both for in vitro laboratory measurements and for in vivo imaging studies. Monoclonal mouse antibodies also are being used therapeutically. This short article reviews the production of HAMA in patients receiving monoclonal antibodies and illustrates the potential ways that HAMA can interfere with immunoassay measurements. Methods for measuring and neutralizing HAMA also are discussed.

Performance of the enhanced Abbott AxSYM cardiac troponin I reagent in patients with heterophilic antibodies

The presence of heterophilic antibodies in the serum of a small subpopulation of individuals continues to cause false results for modern-day immunoassays. In order to determine the frequency of heterophilic antibody (HA)-related false positives within our population of positive cardiac troponin I (cTnI) patients, we assayed 200 samples using the original in-house cTnI assay (Abbott AxSYM) and the Bayer ACS:180 cTnI, which we had previously observed to be more effective at blocking HA interference. Four samples were identified as false positives based on discordant results between the two assays, as well as the correction of the false positives by treatment of the samples with heterophilic antibody blocking reagent (HBR). An 'enhanced' version of the AxSYM cTnI reagent was designed to greatly reduce or eliminate HA interference, and has now replaced the original reagents. The present study shows that the enhanced reagent significantly reduced or eliminated much of the HA interference. Comparative studies between the enhanced cTnI reagent and the original Abbott AxSYM cTnI reagent showed excellent correlation and equivalent diagnostic concordance, when HA samples were excluded from the analysis.

Prostate-specific antigen in acute hepatitis and hepatocellular carcinoma

BACKGROUND

Prostate-specific antigen (PSA) is the most important tumor marker in prostate cancer diagnosis and follow-up. Its catabolism by the liver has not influenced its use as a prostate marker until the recent report of a significant increase in a man and a woman with acute hepatitis. In addition, PSA was detected in liver tumor extracts, which warranted its evaluation in liver cytolysis and hepatocellular carcinoma. In this study, PSA was evaluated in a cohort of both sexes presenting either acute hepatitis or hepatocellular carcinoima.

METHODS

Forty-two patients with acute hepatitis (21 male patients, 21 female patients) and 54 patients with hepatocellular carcinoma (31 male patients, 23 female patients) were tested for PSA by equimolar immunoassay (Abbott AxSYM Total PSA, Abbott Diagnostics, Rungis, France) and for relevant liver biological parameters (alpha-fetoprotein, alanine aminotransferase, aspartate aminotransferase, total bilirubin, and prothrombin rate).

RESULTS

PSA was undetectable in all the female patients and was consistent with age in the males (PSA median and range in acute hepatitis, 0.36 microg/l (range, 0.05-1.3); in hepatocellular carcinoma, 0.36 microg/l (range, 0.02-3.9)). It did not correlate with alpha-fetoprotein and aminotransferases.

CONCLUSIONS

Our results confirm the well-established reliability of PSA, and show that PSA remains a valid prostate marker in patients with acute hepatitis and hepatocellular carcinoma.

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.

Anti-TAG-72 antibody B72.3--immunological and clinical effects in ovarian carcinoma

Based on the network theory, anti-tumor antibodies (Ab1) can trigger the immune system of the host into a response against tumor cells. Through an immunological cascade, anti-idiotypic antibodies bearing the internal image of epitopes of the nominal antigen (Ab2 beta) are produced that themselves can induce cellular and humoral cytotoxic effects against the antigen-expressing tumor cell. Formation of such antibodies has been shown to be associated with prolonged survival of melanoma, colorectal, and ovarian carcinoma patients. We studied anti-idiotypic antibody (Ab2) responses and clinical outcome of 31 ovarian cancer patients receiving the monoclonal antibody (MAb) B72.3, which targets the ovarian carcinoma associated antigen TAG-72. All patients were treated by surgery and polychemotherapy, which was followed by repeated (mean of 4) injections of 1 mg of the MAb B72.3. A remarkable anti-idiotypic anti-B72.3 response arose in 19 patients, with 9 of them showing a major response with Ab2 serum concentrations greater than 1,000 U/ml ("high-responders"). The median disease-free survival time, as well as the median survival time of these high-responders, was increased as compared to the low- or no responders. Evaluating our data, we conclude that monoclonal antibody treatment with the MAb B72.3 may induce humoral immunological responses in about two-thirds of our study group, although a positive clinical effect may only be expected in patients with excessive anti-idiotypic antibody formation.

Different efficacy of various blocking reagents to eliminate interferences by human antimouse antibodies with a two-site immunoassay

OBJECTIVE

The efficacy of three reagents to eliminate interferences with the cancer antigen 125 (CA-125) assay Enzymun CA-125 II by human antimouse antibodies (HAMA) formed by patients after injection of the murine anti-CA-125 antibody OC125 is compared.

METHODS

Apparent CA-125 concentrations of 14 serum samples obtained from 6 patients after multiple injections of 1 mg radiolabeled OC125 F(ab')2 fragments were measured with the Enzymun CA-125 II before and after preincubation, either with nonspecific mouse IgG, with the polymerized mouse IgG MAK-33, or with the commercially available HAMA-blocking reagent IIR.

RESULTS

In all samples with HAMA concentrations ranging from 341 to 46900 microg/L, false-positive CA-125 values were measured with the Enzymun CA-125 II, which could be reduced by preincubation with the HAMA-blocking reagents. However, although after preincubation with 2 g/L IIR for all samples the CA-125 concentrations measured were reduced to values within the normal range, after preincubation with 0.7 g/L of polyclonal mouse IgG for five samples and after preincubation with 0.7 g/L of MAK-33 for all samples also the reduced values were considerably elevated. Larger amounts of mouse IgG or MAK-33 led only to a slight reduction of the remaining false-positive CA-125 values.

CONCLUSION

The present results demonstrate that the polymerized mouse IgG MAK-33 and also the normal murine IgG are not suitable for completely eliminating interferences by HAMAs formed after OC125 treatment. Only the HAMA-blocking reagent IIR seems to be an effective agent to eliminate these interferences. Thus, further studies of this material as a blocking reagent seem to be warranted.