Usefulness of monitoring of B cell depletion in rituximab‐treated rheumatoid arthritis patients in order to predict clinical relapse: a prospective observational study

Summary Our objective was to evaluate the contribution of monitoring B cell subset depletion after rituximab in patients with rheumatoid arthritis ( RA ) in order to guide reintroduction to forestall relapse. This prospective, monocentre study included all RA patients receiving two 1‐g rituximab infusions at a 15‐day interval. The patients were followed clinically and biologically every 2 months until rituximab reintroduction. The physician was blinded to lymphocyte‐typing results to diagnose relapse and, hence, retreatment. Among the 39 patients included between M arch 2010 and D ecember 2011 and followed until A pril 2013, seven received two rituximab cycles, yielding a total of 46 cycles for analysis. After the two rituximab cycles, the total number of CD 19 + B cells decreased significantly (0·155 versus 0·0002 G/l, P  < 0·0001), with complete depletions in all patients of CD 19 + CD 38 ++ CD 24 ++ (transitional) ( P  < 0·0001) and CD 19 + CD 27 + (memory) B lymphocytes. A significant majority of patients relapsed within the 4 months following repopulation of total B ( P  = 0·036), B transitional ( P  = 0·007) and B memory ( P  = 0·01) lymphocytes. CD 19 + B lymphocyte repopulation preceded clinical RA relapse and enabled its prediction 4 months in advance. Hence, monitoring of CD 19 + B lymphocytes could serve as a tool to predict those relapses.