Preliminary results from an ongoing phase III trial (ClinicalTrials.gov Identifier: NCT02980042), evaluating tolerability and safety of switching from rituximab to ocrelizumab in adult patients with relapsing forms of MS (97), reported a similar incidence of IRRs between patients continuing rituximab and those switched to ocrelizumab and suggested a correlation between levels of CD19/CD20 B cells and risk of IRR (with a decrease by 74% of the risk when CD19 and/or CD20 were ≤1%). The gene discussed is CD19; the disease is myeloid sarcoma.