CD22 and rheumatoid arthritis: Epratuzumab, derived from IgG2 monoclonal antibody (LL2, also called HPB-2), is a humanized IgG1 antibody against CD22 that contributes to BCR signaling by phosphorylating CD22 and induces ADCC.381 Epratuzumab has clinical activity and safety, with a 43% objective response rate in follicular NHL patients.147,381 SM03, another anti-CD22 recombinant IgG1 mAb, is currently being developed to treat rheumatoid arthritis in a phase III clinical trial.382