Despite the great research advances in dissecting the mechanisms underlying rheumatoid arthritis onset and development, the exact pathophysiology of this disease remains unsolved. In the past years, the introduction of biologicals, and in particular of therapeutic monoclonal antibodies (mAb), has constituted a major breakthrough in the clinical management of the disease. Although these new drugs have proven effective, in some patients, remission or low disease activity is only partially or temporally achieved. Understanding the mechanism behind this incomplete response might lead to improved therapies and in ultimately to improved quality of life for patients. This thesis describes our efforts to elucidate the mechanisms behind response to B-cell depletion therapy using rituximab in rheumatoid arthritis. We evaluated how both direct and indirect effects can influence clinical response to the treatment. To achieve this we applied AIRR sequencing or Adaptive Immune Receptor Repertoire sequencing, which allows to identify and quantify all T- and B-cell receptors within an individual. This methodology allowed us to fingerprint and monitor ongoing immune responses in cohorts of rheumatoid arthritis patients undergoing rituximab treatment
