Anti-drug antibody assay

Quasi-quantitative assays traditionally include measures of enzymatic or ligandbinding activity, as in flow cytometry and anti-drug antibody assays [9]. One of the common characteristics of these assays is the lack of a true reference standard, where reference standards are poorly characterized, do not completely represent native protein, or differ from native proteins in terms of potency or immunoreactivity. As stated above, if the analytical response is continuous across the range in question, the analytical results can be expressed in terms of a characteristic of known test samples. The following is one example an ELISA qualified as a quasi-quantitative assay because it could not be validated as a relative quantitative assay. 

While the procedures and the parameters evaluated during the validation for each ADA method may be different, each of them must be able to distinguish a positive from a negative response in a complex milieu. Without appropriately validated anti-drug antibody assays, the relevance of ADA on safety and efficacy in the context of nonclinical and clinical studies cannot be determined. 

Anti-drug Antibody Assays. Basically, the protein sequence of biophar-maceutical therapeutics can be nonhuman, chimeric, humanized, or fully human. Most such therapeutics elicit some level of antibody response against the product leading to... 

Cons This format can result in false-positive results if there are other factors in the serum beside anti-drug antibody that may form a bridge between the capture and detection reagents. The bridging assay is affected more by free drug interference than the sandwich or indirect assays. 

As a result of the quasi-quantitative nature of anti-drug antibody immunoassays and the lack of a reference standard a threshold value, the so-called cutoff or cutpoint is used to identify positive samples from nonspecific background noise. The assay cutoff is preferably determined by analyzing samples from healthy individuals and those affected by the disease. The data are subsequently used to... 

Binding anti-drug antibodies are ideally further examined for their capacity to neu-tralize/modulate a functionally relevant response of the drug. This often involves cell-based assays, similar in design to the ones used in potency assays. 

Stefan and Bokretsion [84] constructed lately an amperometric immuno-sensor based on diamond paste (diamond powder and paraffin oil) impregnated with anti-azidothymidine antibody for the assay of azidothy-midine (AZT, an approved and widely used antiretroviral drug for the treatment of human immunodeficiency virus infection) in its pharmaceutical formulations. The potential used for azidothymidine assay was -1-240 mV vs. Ag/AgCl electrode. 

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