CD19 and rheumatoid arthritis: First, it would help predict which subsets of patients are more likely to respond to treatment or have a sustained clinical response, a concept supported by studies in RA in which patients who had higher proportions of double‐negative naïve B cells (CD19+IgD−CD27−) and lower percentages of plasmablasts (CD19+IgD+CD27++) and memory B cells (CD19+IgD+CD27+CD95−; CD19+CD27+) were more likely to have a favourable clinical response with RTX.104, 105