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Krüppel-like factor 5 (KLF5) has been implicated as a tumor suppressor in various solid tumors such as breast and prostate, and recent studies have demonstrated a role for this protein in neutrophil differentiation of acute promyelocytic leukemia cells in response to ATRA. Here, we show that KLF5 expression increases during primary granulocyte differentiation and that expression of KLF5 is a requirement for granulocyte differentiation of 32D cells. In AML, we show that KLF5 mRNA expression levels are reduced in multiple French-American-British subtypes compared to normal controls, and also in leukemic stem cells relative to normal hematopoietic stem cells. We demonstrate that in selected AML cases, reduced expression is associated with hypermethylation of the KLF5 locus in the proximal promoter and/or intron 1, suggesting that this may represent a Class II genetic lesion in the development of AML. Refereed/Peer-reviewed

The sensitivity to recombinant human interferon-alpha 2a (IFN) of peripheral blood granulocyte-macrophage colony-forming units (PB CFU-GM) from patients with chronic myeloid leukaemia (CML) was studied in a semi-solid clonogenic assay, and compared with normal PB CFU-GM. Like normal PB CFU-GM, the growth of CML PB CFU-GM in vitro was found to be dependent on the plating concentration used. The optimal CFU-GM growth occurred when CML PB mononuclear cells (MNC) were plated at low concentrations in the range of 0.01-0.1 x 10(5)/ml, compared to the range of 0.3-3.0 x 10(5)/ml optimal for CFU-GM growth in normal subjects. The optimal plating concentration for CML PB CFU-GM was similar to that observed in PB collected from patients with ovarian carcinoma during haematological recovery following chemotherapy-induced myelosuppression (recovery phase). The recovery phase PB was used as a source of non-leukaemic cells with a higher incidence of CFU-GM similar to that of CML. IFN produced a dose-related inhibition of CFU-GM growth in normal, recovery phase ovarian carcinoma and CML, PB MNC. The IFN concentration required to inhibit 50% of the CFU-GM in culture (LD50) was found to be significantly influenced by the plating concentration. When cells were cultured at 1.0 x 10(5) MNC/ml the mean LD50 for 7 CML patients was similar to that in normal (n = 5) or recovery phase (n = 5) peripheral blood, 273 i.u./ml, 1047 i.u./ml and 795 i.u./ml, respectively. In contrast when CML cells were cultured at 0.03 x 10(5) MNC/ml the concentration for optimal CML CFU-GM growth, the mean LD50 was significantly lower than that in normal PB and recovery phase PB, 4 i.u./ml, 251 i.u./ml and 78 i.u./ml, respectively (p less than 0.05). This is the first report of a differential sensitivity to IFN between CML and non-CML progenitors using an optimized PB CFU-GM assay system and proposes that further study of the in vitro culture of CML progenitors may increase our understanding of the clinical effects of IFN.

A study was carried out to determine whether bone marrow biopsy performed on day 6 of induction therapy for acute myeloid leukaemia (AML) can identify those patients with resistant disease who would need an intensification of the first course of induction. Bone marrow biopsies were performed on day 6 of induction chemotherapy in 44 patients with AML treated with daunorubicin, cytosine arabinoside and thioguanine. Biopsies were assessed for blast count, trephine cellularity and leukaemic index. Discrimination between patients who went on to achieve remission and those with resistant disease was best achieved using the reduction in bone marrow cellularity from pretreatment marrow to day-6 marrow. However, this discriminator identified only 50% of the patients with resistant disease and included 13% of patients who achieved remission with the first course of chemotherapy. The other parameters of response were even less effective at discriminating between chemotherapy-resistant and chemotherapy-responsive disease.