A patient with relapsed diffuse large B cell lymphoma who relapsed rapidly after a previous autologous hematopoietic stem cell transplant has recently been diagnosed with progressive multifocal leukoencephalopathy months after lymphodepleting chemotherapy with fludarabine/cyclophosphamide and anti-CD19-directed CAR T therapy [165]. This evidence concerns the gene CD19 and diffuse large B-cell lymphoma.