Multilineage expression of haemopoietic precursors with an abnormal clone in idiopathic myelofibrosis

Summary. To clarify the lineage involvement of haemopoietic progenitor cells in idiopathic myelofibrosis (MF), simultaneous analysis of morphology and chromosomes were performed on single colonies from a 70‐year‐old Japanese woman with typical presentation of MF. The cytogenetic analysis of unstimu‐lated peripheral blood cells revealed three cell lines 47.XX, −6, +9, +der(6)t (1;6)(lqter→1q21::6p21→6qter), 46,XX, −6, +der(6) and 46.XX. Of 91 metaphases examined, the numbers of each cell line were 43, 41 and 7, respectively. Blood mononuclear cells were plated at 2 × 10³ or 1 × 10⁴/ml in methylcellulose medium containing phytohaemagglutinin‐stimulated leucocyte conditioned medium and erythropoietin. On days 10,12 and 14 of culture, 47 individual colonies were lifted and served for morphological and cytogenetic examination. Morphological examination revealed that the colonies contained neutrophils (n), macrophages (m), basophils (b), erythrocytes (E) and megakaryocytes (M). Twenty‐two of the 47 colonies had analysable metaphases, yielding totally 158 metaphases. Twelve colonies contained three or more metaphases. Eight colonies (3bE, IE, 2b, InEM, IbEM) were of the abnormal cell line 46,XX, − 6, + der(6), and four colonies (2E, IbE, ImE) were of the karyotypically normal cell line 46,XX. The other abnormal cell line 47.XX, −6, +9, +der(6) was not detected in any of the metaphases obtained from single colonies. These results provided direct evidence that the pluripotent stem cells were involved in MF.