Purification and immunochemical characterization of ascitic fluid glycoproteins containing certain tumor-associated and blood group antigen markers

Overcoming soluble target interference in an anti-therapeutic antibody screening assay for an antibody-drug conjugate therapeutic

BACKGROUND

The standard safety evaluation of biotherapeutics includes assessment of immunogenicity. Anti-therapeutic antibodies (ATA) can be detected in serum using immunoassays with a bridging format. However, these assays can be subject to interference.

RESULTS

In the bridging ATA assay for 3A5 TDC, an antibody-drug conjugate that binds to the multimeric extracellular domain of MUC16 (CA125), soluble CA125 in the serum caused false-positive results by binding to the ATA assay reagents. This interaction was blocked by wheat germ agglutinin lectin as it binds to the glycans in CA125; thus, the specificity of the assay improved.

CONCLUSION

The assay development and validation results showed that the addition of wheat germ agglutinin eliminates the interference from circulating CA125 without impacting the ability to detect ATA.

False positive carbohydrate antigen 19-9 (CA19-9) results due to a low-molecular weight interference in an apparently healthy male

BACKGROUND

We investigated the presence of interference in a patient who had an elevated CA19-9 concentration using the ADVIA Centaur but results within reference limits with ROCHE Modular Analytics E170 and Brahms KRYPTOR analysers.

METHODS

We performed repeat analyses using the same (ADVIA Centaur) and alternate immunossays (Roche Modular Analytics E170 and Brahms KRYPTOR) on the patient's sample and investigated for known interferences. To determine the nature of the interference, we measured CA19-9 on the ADVIA Centaur after dilution experiments and after incubation with non-immune animal sera and in heterophilic blocking tubes (HBT). We also undertook polyethylene glycol precipitation, lectin inhibition experiments and gel filtration chromatography.

RESULTS

A curvilinear response to dilution was observed with the ADVIA Centaur. Other known interferences were excluded. Treatment with HBT or non-immune animal sera did not give clinically different results from untreated samples. There was only 0.59% recovery after PEG precipitation in the sample from the case patient. Lectin reduced the assay signal in four patient samples (recovery=1.9-14.1%) but not in the case patient (recovery=106.2%). Gel filtration studies suggested the presence of a low molecular weight (approximately 100 kDa) interference in the case patient's serum.

CONCLUSIONS

We report a novel mode of interference and show a non-CA19-9, low molecular-weight interference affecting the ADVIA Centaur CA19-9 immunoassay.

An improved ELISA for the determination of sialyl Lewis(x) structures on purified glycoconjugates

The membrane carbohydrate antigen, sialyl Lewis x (sLe(x)), is involved in cellular adhesive interactions in many diseases, such as cancer, inflammation and thrombosis. This antigen is also found on soluble macromolecules, such as serum glycoproteins, but the precise role of soluble sLe(x) in modifying disease processes, or reflecting the pathological changes is still unclear. Although methods were previously reported for the measurement of soluble sLe(x), many of these were not well characterised, measurements were mainly made on mixtures of molecules, and the anti-sLe(x) antibodies were used at concentrations that made the assay expensive. In this study an ELISA has been devised that detects sLe(x) in purified soluble glycoconjugates using the anti-sLe(x) antibody, CSLEX I. Commercially-available haptoglobin (Hp) and synthetic complexes of Lewis antigens with polyacrylamide were used as model substances in developing the procedure. Key steps were washing the antibody/antigen complex with ten times diluted salt solution to prevent dissociation of the complex and the use of bovine serum albumin for blocking non-specific interactions. The assay was shown to be very specific, its precision was in the range 6-12%, and it could detect less than a pmol of sLe(x). It could also distinguish between different densities of sLe(x) on the same amount of glycoconjugate. Determination of sLe(x) in Hp isolated from small groups of healthy individuals, cancer patients, and rheumatoid arthritis sufferers suggested that the antigen expression is increased in disease. This method, which is an improvement on those previously described will be useful for determining sLe(x) in many different types of soluble glycoconjugate, and used in combination with synthetic carbohydrate polyacrylamide complexes, will help to standardize measurements of soluble sLe(x) in the future.

Binding of type 1-piliated Escherichia coli to vaginal mucus

To better understand the interactions involved in bacterial adherence and the role of mucus in the pathogenesis of urinary tract infections, we developed a system to study the binding of a recombinant Escherichia coli strain, HB101/pWRS1-17, expressing type 1 pili, to vaginal mucus collected from 28 women. Bacteria bound to differing extents to all specimens examined, and preincubation of bacteria with mannose inhibited binding by 50 to 89%. Additionally, all mucus samples showed reactivity with anti-mannose antibody, and the levels of reactivity correlated with the levels of bacterial binding, suggesting that the mannose-terminal saccharides present on these glycoproteins are the receptors for the binding of type 1-piliated bacteria. Mucus specimens collected over periods of 5 days and 12 weeks exhibited significant variation in bacterial binding, indicating temporal differences in the ability of vaginal mucus to act as a receptor for type 1-piliated E. coli. The results show that vaginal mucus can bind bacteria and may thus influence the initial attachment and subsequent colonization of the vaginal and urinary tract epithelium by E. coli.

Blood group antigen expression on vaginal and buccal epithelial cells and mucus in secretor and nonsecretor women

Blood group antigens on epithelial cells may influence bacterial adherence to mucosal surfaces. In the urinary tract the presence of these genetically determined carbohydrate structures may affect bacterial colonization of the vaginal mucosa and subsequent urinary tract infection. In previous studies the detection of ABH and Lewis antigen expression and distribution in tissues have made use of semiquantitative immunohistochemical staining techniques. To determine the pattern and intensity of blood group antigens on epithelial cells and in the mucus overlying them, we developed quantitative immunoassays that use monoclonal antibodies to detect changes in the expression and intensity of ABH and Lewis antigens on cells and in mucus. Vaginal and buccal cell specimens from 23 healthy women (15 secretors and 8 nonsecretors) with no history of urinary tract infections and known blood group types were analyzed for the expression of these antigenic determinants. The profile of ABH antigen expression was generally consistent with the ABO phenotype of the individual and appeared to be influenced by the secretor status; the levels of A, B and H determinants were higher for secretors than nonsecretors. Lewis antigens were detected on vaginal and buccal cells, and mucus. Le(a) and Le(x) antigen expression was greater on cells and mucus from nonsecretors, whereas the expression of Le(b) and Le(y) was greater on cells and mucus from secretors. Variability in antigen expression was observed among individuals with the same blood type and secretor status. The patterns of antigen expression were similar for the vaginal and buccal cell, and mucus samples of an individual but the amount of antigen generally differed for the various samples. These findings document the variation of blood group antigen expression on vaginal epithelial cells and mucus, which may have a significant role in susceptibility to urinary tract infections in women.