Granulocyte colony-stimulating factor enhances the in vitro cytotoxicity of gemtuzumab ozogamicin against acute myeloid leukemia cell lines and primary blast cells.

OBJECTIVE: To evaluate the effects of granulocyte colony-stimulating factor (G-CSF) on the in vitro sensitivity of acute myeloid leukemia (AML) cell lines and primary AML blast cells to gemtuzumab ozogamicin (GO). MATERIALS AND METHODS: AML cell lines and primary blasts from 10 patients with AML were first incubated for 72 hours in the presence of G-CSF (5 or 100 ng/mL) and then exposed to increasing concentrations of GO (1-1,000 ng/mL) for an additional 72 hours. RESULTS: Pretreatment with G-CSF translated into significant enhancement of GO-induced cytotoxicity in the GO-sensitive HL-60 and NB-4 cells. Conversely, the response of GO-insensitive KG-1a, TF-1, and K562 cells was unaffected by in vitro priming with G-CSF. In vitro exposure to G-CSF augmented GO-induced apoptosis in 7 of 10 primary AML samples and rendered blast cells from three refractory patients sensitive to killing effect of GO. The G-CSF-induced increase of the cytocidal activity of GO was independent of effects on the cell cycle and on the expression levels of CD33 antigen. Of potential interest, G-CSF induced dose-dependent inhibition of P-glycoprotein (P-gp/ABCB1) function in the GO-sensitive HL-60 and NB-4 cells and in blasts from three patients with AML that we tested. CONCLUSION: Collectively, our findings point to G-CSF as a potential sensitizing agent that can be exploited therapeutically to improve the clinical efficacy of GO.

Endogenous G-CSF and CD34+ cell mobilization after acute myocardial infarction.

BACKGROUND: Several reports showed an increase of CD34(+) stem/progenitor cell count early after an acute myocardial infarction (AMI), suggesting a contribution of bone marrow cells in myocardial regeneration after the acute event. Nevertheless, at present plasma mediators of CD34(+) cell mobilization from bone marrow to peripheral blood in patients with AMI are poorly understood. Aim of our study was to establish the impact of different well-known mobilizing cytokines on spontaneous stem cell mobilization in patients with different ischemic heart syndromes, such as the AMI and the chronic stable angina (CSA), compared to healthy controls. METHODS: In 16 patients with AMI, 18 with CSA and 22 healthy blood donors the concentration of CD34(+) cells, and mobilizing cyokines (G-CSF, SCF, VEGF, SDF1-alpha) were assessed. RESULTS: The peak number of circulating CD34(+) cells in AMI patients (8.58+/-2.08 cells/microl) was higher than that observed in patients with CSA (3.41+/-0.56 cells/microl, p=0.0061) or in healthy controls (2.18+/-0.35 cells/microl, p<0.001). However endogenous G-CSF was significantly higher in the serum of patients with AMI compared to CSA patients and to controls and in CSA patients compared to controls. Interestingly, as regards VEGF, while this cytokine was increased in AMI with respect to control and CSA group, the latter showed a significantly lower concentration with respect to controls. Finally SDF-1 alpha was higher in AMI patients with respect to controls. CD34(+) cells were significantly correlated to G-CSF (directly) and to SCF (inversely) in patients with AMI. CONCLUSION: In the present study, we have demonstrated for the first time that the spontaneous mobilization of CD34(+) cells into the peripheral blood of patients with AMI is significantly correlated to endogenous G-CSF. Considering recent data suggesting a potential favourable effect of circulating CD34(+) cells on left ventricular function, the present evidence of a correlation between endogenous G-CSF and CD34(+) cell levels supports the pharmacological administration of G-CSF as a non-invasive option for regeneration of myocardial tissue after AMI.

Mobilization of bone marrow-derived stem cells after myocardial infarction and left ventricular function.

AIMS: Recent data suggest that the administration of bone marrow-derived stem cells (BMSC) might improve myocardial perfusion and left ventricular (LV) function after acute myocardial infarction (AMI). The aim of this study was to assess spontaneous mobilization of BMSC expressing the haematopoietic and endothelial progenitor cell-associated antigen CD34+ after AMI and its relation to post-infarction remodelling. METHODS AND RESULTS: Peripheral blood concentration of CD34+ BMSC was measured by flow cytometry in 54 patients with AMI, 26 patients with chronic stable angina (CSA), and 43 normal healthy subjects. In patients with AMI, LV function was measured by 2D-echocardiography. Eighteen AMI patients were reassessed at 1 year. BMSC concentration was higher in patients with AMI (mean peak value: 7.04+/-6.27 cells/microL), than in patients with CSA (3.80+/-2.12 cells/microL, P=0.036) and in healthy controls (1.87+/-1.52 cells/microL, P<0.001). At multivariable analysis statin use (P<0.001), primary percutaneous intervention (P=0.048) and anterior AMI (P=0.05) were the only independent predictors of increased BMSC mobilization after AMI. In the 28 patients without subsequent acute coronary events reassessed at 1 year follow-up, CD34+ cell concentration was an independent predictor of global and regional improvement of LV function (r=0.52, P=0.004 and r=-0.41, P=0.03, respectively). CONCLUSION: AMI is followed by enhanced spontaneous mobilization of BMSC, in particular, in patients on statin therapy and following a primary percutaneous intervention. More importantly persistent spontaneous mobilization of BMSC might contribute to determine a more favourable post-AMI remodelling.

Granulocyte colony-stimulating factor promotes the generation of regulatory DC through induction of IL-10 and IFN-alpha.

We have recently demonstrated that G-CSF promotes the generation of human T regulatory (T(REG)) type 1 cells. In this study, we investigated whether the immunomodulatory effects of G-CSF might be mediated by DC. CD14(+) monocytes were cultured with serum collected after clinical administration of G-CSF (post-G), which contained high amounts of IL-10 and IFN-alpha. Similar to incompletely matured DC, monocytes nurtured with post-G serum acquired a DC-like morphology, expressed high levels of costimulatory molecules and HLA-DR, and exhibited diminished IL-12p70 release and poor allostimulatory capacity. Importantly, post-G DC-like cells were insensitive to maturation stimuli. As shown by neutralization studies, IFN-alpha and, even more pronounced, IL-10 contained in post-G serum inhibited IL-12p70 release by post-G DC-like cells. Furthermore, phenotypic and functional features of post-G DC-like cells were replicated by culturing post-G monocytes with exogenous IL-10 and IFN-alpha. Post-G DC-like cells promoted Ag-specific hyporesponsiveness in naive allogeneic CD4(+) T cells and orchestrated a T(REG) response that was dependent on secreted TGF-beta 1 and IL-10. Finally, neutralization of IL-10 and IFN-alpha contained in post-G serum translated into abrogation of the regulatory features of post-G DC-like cells. This novel mechanism of immune regulation effected by G-CSF might be therapeutically exploited for tolerance induction in autoimmune disorders.