Background/Purpose:  Tumor necrosis factor inhibitor (TNFi) biologics are a mainstay of therapy for rheumatoid arthritis (RA) patients with disease-modifying antirheumatic drug failure. However, RA patients receiving TNFi biologics can develop anti-drug antibodies that neutralize drug action, decrease drug exposure, and lead to a loss of efficacy. Therefore, an assay that can monitor TNFi biologic immunogenicity and plasma concentrations can indicate when anti-drug antibodies diminish TNFi effectiveness and require drug substitutions. Our aim is to use a novel assay that simultaneously monitors anti-adalimumab (anti-ADA) IgG levels and plasma adalimumab (ADA) concentrations to determine the frequency of anti-ADA antibodies among patients enrolled on the Rheumatoid Arthritis Comparative and Effectiveness Research (RACER) study at University of Pittsburgh Medical Center.

Methods:  Our cytometric assay uses streptavidin beads, biotinylated ADA F(ab’)2 antibody fragment, biotinylated TNF-α, and anti-Fc antibody for measuring anti-ADA and ADA. A total of 168 normal human plasma samples (negative controls) and 207 RACER patient samples were evaluated using our cytometric assay and an anti-ADA bridging ELISA (116 from patients with no previous ADA exposure and 91 from patients receiving ADA for ≥ 6 months).

Results:  Among patients receiving ADA, 49% tested positive for anti-ADA IgG. Surprisingly, 27% of ADA naïve patients were positive for anti-ADA, whereas all control human plasma samples were negative. Comparing our cytometric assay to the bridge ELISA: 78% and 66% of ADA treated and naïve patients were positive for anti-ADA antibodies, respectively. Of those samples positive by our cytometric assay, 94% were also positive by ELISA. Due to the unexpected high positive rate, we measured ADA concentrations before and after adding ADA to the following representative RACER samples: ADA naïve patient samples positive for anti-ADA, control patient samples negative for anti-ADA, and discrepant samples positive by flow cytometry but negative by ELISA. No ADA was detectable among naïve patients, whereas ADA was detectable among patients receiving ADA. Upon ADA addition, lower ADA levels were measured among discrepant samples compared to controls (P < 0.05). Furthermore, ADA decreased the anti-ADA levels of controls containing known amounts of anti-ADA IgG by 82%, whereas none of the naïve patient samples decreased anti-ADA levels, suggesting that the positive signals detected were not due to anti-ADA antibodies. Our results confirmed that samples collected from patients with no prior ADA exposure had no detectable ADA or anti-ADA IgG. In contrast, discrepant samples contained anti-ADA IgG antibodies that diminished detection of ADA.

Conclusion:  Our cytometric assay can detect anti-ADA antibodies and distinguish anti-ADA immunogenicity from interference by measuring ADA drug concentrations and neutralization. The high positive rates estimated using our cytometric assay are likely due to anti-hinge antibodies and blocking strategies are currently being evaluated. Our method can be easily modified to measure the immunogenicity and drug levels of other TNFi biologics.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/a-cytometric-assay-for-monitoring-adalimumab-immunogenicity-and-drug-concentrations-can-distinguish-anti-adalimumab-antibodies-from-interference/