Modeling how methotrexate reduces anti-drug antibodies to adalimumab in axial spondyloarthritis

# What the study asked Axial spondyloarthritis (AxSpA) patients sometimes stop adalimumab treatment because anti-drug antibodies lower its effectiveness. Methotrexate (MTX) is sometimes combined with adalimumab and seems to reduce formation of those antibodies, but how MTX modifies the immune response is unclear. The study tests mechanistic hypotheses with a mathematical model to identify which cellular actions of MTX best explain observed clinical and laboratory data.

# How the researchers approached it

Clinical measurements used for calibration included adalimumab concentrations, lymphocyte counts, and anti-adalimumab antibody titres collected across five visits during treatment. After parameter fitting, the team generated virtual patient cohorts that reflected the observed data distributions and used those cohorts to test mechanistic scenarios.

# What they tested They implemented 31 candidate mechanisms for MTX action on immune cell subsets. These scenarios included effects such as reduced activation rates, increased apoptosis of different cell types, altered proliferation, or changes in differentiation and antigen presentation that could impact B cell production of anti-drug antibodies.

# Main result Across simulated virtual cohorts and the 31 scenarios, the model predictions converged: methotrexate most plausibly reduces immunogenicity by increasing apoptosis or otherwise suppressing activated T cells. Scenarios that targeted other cell types or mechanisms fit the combined in vitro and clinical data less consistently.

# Why that matters Activated T cells provide help to B cells for antibody production. If MTX reduces the survival or activity of these T cells, B cell-mediated generation of anti-adalimumab antibodies can fall, which preserves circulating drug concentrations and therapeutic effect. The finding provides a focused hypothesis about MTX's cellular target that can be tested experimentally.

# Data and reproducibility The authors report that individual-level clinical data are held by the CHRU de Tours and subject to data transfer agreements, but they provide the model source code and mean-value data used for the paper's analyses on GitHub: https://github.com/prashkov-lab/ENOTTA_STSM.

# Practical takeaways for clinicians and researchers

• Combining MTX with adalimumab may lower the risk of anti-drug antibody formation by reducing activated T cell survival. This offers a mechanistic rationale for combination therapy when immunogenicity is a concern.
• The model yields a clear, testable prediction: experimental or clinical measures that document reduced activated T cell counts or increased T cell apoptosis with MTX would support the proposed mechanism.
• The computational framework can be reused or extended to test alternative dosing, timing, or to include other immune-modulating drugs.

# Next steps suggested by the study Design targeted experiments that measure MTX effects on activated T cell apoptosis in patients receiving adalimumab. Apply the model to other clinical datasets and other biologics to assess generalizability.