Adalimumab (ADM) is a fully human antibody that targets the pro-inflammatory cytokine TNF-alpha. The introduction of therapeutic antibodies has revolutionized the treatment of chronic inflammatory diseases like inflammatory bowel disease (IBD), rheumatoid arthritis (RA), spondyloarthritis and plaque psoriasis. It has been shown that adalimumab can induce deep remission and improve the patient’s quality of life. Some patients do not respond to adalimumab therapy upon induction (primary non-responders), while others lose response over time (secondary nonresponders).
Secondary loss of response is often due to the development of anti-adalimumab antibodies (ATA), because of the immunogenic character of the drug. ATA can develop in any patient undergoing adalimumab therapy and are primarily neutralizing the activity of adalimumab through immunocomplex formation.
In addition, these immunocomplexes are rapidly cleared from the system. Analytically, they are responsible for subtherapeutic adalimumab concentrations. Therefore, in the case of very low trough concentrations of adalimumab (< 1 μg/mL), subsequent measurement of ATA may be helpful to determine the optimal treatment strategy.
Diagnostic Value
The diagnostic value of the Anti-Adalimumab ELISA lies in its ability to stratify patients with subtherapeutic adalimumab concentrations (< 1 μg/mL) in patients who need dose intensification or a drug (class) switch. Patients with low adalimumab concentrations (< 1 μg/mL) and low ATA titers can benefit from adalimumab dose intensification, as shown in several studies.
However, the ATA titers of patients with low ATA titers undergoing a dose intensified treatment regimen must be adequately monitored. Patients that have high ATA titers are preferably switched to another drug, both within class or out of class.
Note. The Anti-Adalimumab ELISA is not capable of measuring ATA in the presence of high concentrations of adalimumab. It should only be used when < 1 μg/mL adalimumab is quantified in the sample using the apDia Adalimumab ELISA.
Principle of the ATA ELISA
The apDia Anti-Adalimumab ELISA uses a highly specific monoclonal antibody – clone 6A10, developed at the KU Leuven – that only bridges adalimumab.
Microtiter strips coated with adalimumab (Humira®) are incubated with calibrators, controls and diluted patient samples. During this incubation step ATA binds specifically to the adalimumab on the solid phase. After removal of the unbound serum proteins by a washing procedure, the strips are incubated with biotin conjugated adalimumab (Humira®), binding directly to the antigen-antibody complex. After removal of the unbound biotin conjugate, the strips are incubated with peroxidase conjugated streptavidin. After removal of the unbound peroxidase conjugate, the strips are incubated with a chromogenic solution containing tetramethylbenzidin and hydrogen peroxide: a blue colour develops in proportion to the amount of immunocomplex bound to the wells of the strips. The enzymatic reaction is stopped by the addition of 0.5M H2SO4 and the absorbance values at 450 nm are determined.

A standard curve is obtained by plotting the absorbance values versus the corresponding calibrator values. The concentration of ATA in patient samples is determined by interpolation from the calibration curve.