CD34 and plasma cell myeloma: Stx1 targets cells that express the glycolipid Gb3Cer/CD77, whose frequent occurrence on tumor cells derived from patients with hematological cancers (follicular lymphoma, multiple myeloma, chronic lymphocytic leukemia), along with its absence on human CD34+ hematopoietic stem cells, justify the ex vivo use of cytotoxic concentrations of Stx1 in purging CD77+ tumor cells from autologous stem cell transplants [10,29].