The two patients with natalizumab rebound and lytic EBV infection had CD4+ and CD8+ T-cell infiltrates, with CD8+ T cells predominating.142,143 A small population of T cells express CD20, which they are thought to acquire from B cells through trogocytosis.150 Trogocytosis is when one cell physically extracts, ingests or bites off cellular material from another cell.151 In people with MS, it is thought that T cells acquire CD20 on their surface after interacting with B cells during the process of B-cell antigen presentation. Here, CD4 is linked to myeloid sarcoma.