SF3B1 mutations in the hematopoietic hierarchy of MDS-RS. Cartoon illustration of normal (A) and SF3B1-mutant (B) MDS-RS hematopoietic hierarchy. SF3B1 mutations are detected in HSC, myeloid progenitors, mature myeloid types, and pro-B cells of MDS-RS patients (B). HSCs, but not progenitors, propagate the disease. B, B-cell; CLP, common lymphoid progenitor; CMP, common myeloid progenitor; Er, erythrocyte; ETP, early T-cell progenitor; GMP, granulocyte-monocyte progenitor; Gr, granulocyte; MEP, megakaryocyte-erythrocyte progenitor; Mk, mature megakaryocyte; Mo, monocyte; MPP, multipotent progenitor; proB, pro-B cell; T, T cell.