The observation that B cell-targeting with anti-CD19 (aCD19) also limits MS relapsing disease activity (62) makes it unlikely that the removal of CD20-expressing T cells provides the full explanation for the therapeutic mode of action of aCD20 in patients with relapsing MS, although it is possible that aCD19 therapy could indirectly reduce CD20dim T cells for example by preventing B cell-T cell contact with potential trogocytosis of CD20 molecules from B cells to the T cells (31, 63). This evidence concerns the gene CD19 and myeloid sarcoma.