Assays for Infliximab Drug Levels and Antibodies: A Matter of Scales and Categories

Abstract

Immunogenicity is a frequent cause of secondary non-response to tumour necrosis factor (TNF) inhibitors. Drug level measurement and detection of antidrug antibodies have been shown to be cost effective and clinically relevant, and a large number of assays are available for these purposes. It is, however, difficult to compare assays and translate results into clinical meaningful information due to different methodological approaches and a lack of assay standardization. We have analysed infliximab drug levels and antidrug antibodies in 107 patient samples using enzyme-linked immunoassays (ELISA), immunofluorometric assays (IFMA) and reporter-gene assays (RGA). The RGA gave the lowest results for drug levels, whereas the IFMA detected the highest number of antidrug antibody positive sera. Applying individualized therapeutic ranges to each assay resulted in agreement among all three assays in 74% of samples for drug levels and 98% of samples for antidrug antibodies. We found that TNF inhibitor monitoring assays measure on different scales and that the agreement between quantitative results is limited. However, interassay differences can partially be overcome by assay-individualized translations of quantities into categories, which also is necessary for a meaningful clinical application. Our data demonstrate that assays should not be used interchangeably and that direct comparison of quantitative drug levels obtained with different assays should be avoided.

Review article: consensus statements on therapeutic drug monitoring of anti‐tumour necrosis factor therapy in inflammatory bowel diseases

“…Although drug levels measured by different assays correlate and generally lead to the same therapeutic decision, there are systematic differences between measured levels . These may be overcome to a degree with better calibration against a universal standard, known concentrations of the tested drug.…”

“…Assay standardisation is required of registered pathology laboratories, while this may not necessarily be the case in the research setting. Testing drug levels in the same laboratory will minimise inter‐laboratory variability of results …”

Phosphorylation of intracellular signalling molecules in peripheral blood cells from patients with psoriasis on originator or biosimilar infliximab

“…Cells were divided and either stimulated for 15 min with TNF‐α (50 ng mL −1 ; Immunotools, Friesoythe, Germany) or left unstimulated. Next, samples were fixed with 1·5% paraformaldehyde (37 °C) incubated for 10 min at room temperature and permeabilized with ice cold 100% methanol for 30 min on ice, as described previously . The cells were washed with phosphate‐buffered saline (PBS), then stained according to a 4 × 2 fluorescence cell barcoding (FCB) grid (three time points and one internal control with two stimulation conditions) with different concentrations of Pacific Blue (100, 25, 6·3 and 0 ng mL −1 ) and Pacific Orange (70 and 0 ng mL −1 ; both Life Technologies, Grand Island, NY, U.S.A.), then incubated in the dark at 4 °C.…”

Utilidad de la monitorización terapéutica de infliximab en el manejo de la enfermedad inflamatoria intestinal

“…Varios ensayos han sido utilizados para evaluar la concentración de IFX y la presencia de anticuerpos, destacando el enzimo inmunoanálisis de absorción (ELISA), ensayo por movilidad homogénea (HMSA) y el inmunoensayo electroquimioluminicencia (ECLIA). Hasta ahora, ninguno de ellos ha sido considerado el gold estándar, sugiriéndose que estos métodos de medición no deben ser intercambiables y que la comparación entre niveles obtenidos de diferentes ensayos debe ser evitado 43 . En nuestro estudio, utilizamos un método de ELISA con la capacidad de medir la presencia de anticuerpos totales, es decir anticuerpos circulantes y unidos al fármaco.…”