Granulocyte Colony Stimulating Factor Preferentially Causes Proliferation of Pre-Existing Monosomy 7 Cells in Aplastic Anemia and Myelodysplastic Syndrome Because of Abnormal Truncated GCSF-Receptors on These Cells.

Administration of granulocyte colony stimulating factor (GCSF) has been linked to development of monosomy 7 in some patients with aplastic anemia (AA) and congenital neutropenia. We assessed the effect of GCSF on monosomy 7 to determine if this chromosomal abnormality developed de novo or if GCSF simply favored expansion of a pre-existing clone. Bone marrow mononuclear cells (BMMNC) were co-cultured for 14 days with pharmacological doses of GCSF and examined by fluorescent in situ hybridization (FISH). No karyotypically healthy control, AA, or myelodysplastic syndrome (MDS) bone marrow showed development of monosomy 7. In BMMNC cultures from thirteen patients with MDS and monosomy 7, all developed substantial increases in numbers of monosomy 7 cells after prolonged exposure to GCSF. Experiments on stored AA samples obtained six months prior to the development of abnormal karyotype showed monosomy 7 on FISH ,with expansion of that clone on co-culture with GCSF. GCSFR mRNA was increased in BM from monosomy 7 patients as measured by real time PCR, and monosomy 7 cells expressed more GCSFR on the cell surface than did normal cells. As a truncated GCSFR isoform is associated with a hyperproliferative response to G-CSF and prolonged activation of signal transducer and activator of transcription (STAT) complexes, we sequenced the GCSFR DNA of monosomy 7 cells and measured the expression of the truncated GCSFR mRNA relative to full length GCSFR in patients with monosomy 7. While genomic GCSFR DNA showed no abnormalities, mRNA demonstrated increased proportions of the truncated isoform IV in all six patients tested. We examined GCSF-mediated GCSFR signal transduction of the Jak/Stat system in monosomy 7 CD34 cells. STAT-1 was increased and the STAT 5: STAT 3 rato was increased by ten-fold in all patients with monosomy 7 compared to normals and to MDS with normal cytogenetics. In conclusion, pharmacologic doses of GCSF appear to increase the proportion of monosomy 7 cells; this heightened sensitivity to GCSFmay be related to altered amounts of the truncated form of the receptor, with changes in GCSF signal transduction resulting in expansion of the monosomy 7 clone.