NK cell development in bone marrow and liver: site matters.

The NKp46 protein is found on resting and activated natural killer (NK) cells and is involved in the recognition of malignant and infected cells. The expression of NKp46 is believed to precede that of DX5 in early NK cell development. We show that this is not the case in the bone marrow (BM). Here, NKp46 is predominantly expressed after DX5, whereas the liver harbors a subpopulation that expresses NKp46 but not DX5. NK cell precursors in the liver show much lower levels of Eomesodermin than NK cell precursors in the BM, although they express higher levels of granzymes and unlike the NK cell precursors in the BM are fully able to degranulate and produce interferon gamma (IFN-γ). The development of NK cells thus differs between the two organs. This needs to be considered when using NKp46 and DX5 as NK cell markers and when performing NK cell-specific gene deletion in Ncr1 transgenic mice.

PAK-dependent STAT5 serine phosphorylation is required for BCR-ABL-induced leukemogenesis.

The transcription factor STAT5 (signal transducer and activator of transcription 5) is frequently activated in hematological malignancies and represents an essential signaling node downstream of the BCR-ABL oncogene. STAT5 can be phosphorylated at three positions, on a tyrosine and on the two serines S725 and S779. We have investigated the importance of STAT5 serine phosphorylation for BCR-ABL-induced leukemogenesis. In cultured bone marrow cells, expression of a STAT5 mutant lacking the S725 and S779 phosphorylation sites (STAT5(SASA)) prohibits transformation and induces apoptosis. Accordingly, STAT5(SASA) BCR-ABL(+) cells display a strongly reduced leukemic potential in vivo, predominantly caused by loss of S779 phosphorylation that prevents the nuclear translocation of STAT5. Three distinct lines of evidence indicate that S779 is phosphorylated by group I p21-activated kinase (PAK). We show further that PAK-dependent serine phosphorylation of STAT5 is unaffected by BCR-ABL tyrosine kinase inhibitor treatment. Interfering with STAT5 phosphorylation could thus be a novel therapeutic approach to target BCR-ABL-induced malignancies.

Comparison of three different experimental methods for the assessment of peripheral compartment pharmacokinetics in humans.

In many cases the concentration reached in a peripheral effect compartment rather than in plasma determines the clinical outcome of therapy. Therefore, several experimental approaches have been developed for direct assessment of drug kinetics in peripheral compartments. Particularly saliva sampling, skin blister fluid sampling, and in vivo microdialysis are frequently employed for measuring peripheral drug concentrations. However, data derived from these techniques have never been directly compared. In the present study, the tissue kinetics of theophylline were measured following single dose administration simultaneously in cantharides induced skin blisters, saliva and microdialysates of subcutaneous- and skeletal muscle- tissue and compared to plasma concentrations. Theophylline was administered to 9 healthy volunteers as an i.v. infusion of 240 mg. Mean ratio (AUCsaliva/AUCplasma) was 0.63 +/- 0.05, mean ratio (AUCblister/AUCplasma) was 0.69 +/- 0.12, mean ratio (AUCmuscle/AUCplasma) was 0.41 +/- 0.10, mean ratio (AUCsubcutaneous/AUCplasma) was 0.34 +/- 0.07. The time course of the concentration(peripheral)/concentration(plasma)-ratios showed that tissue concentrations obtained by microdialysis were closely correlated to free plasma levels, whereas saliva- and cantharides blister data overestimated the corresponding free plasma concentrations. It is concluded that microdialysis represents a reliable technique for the measurement of unbound peripheral compartment concentrations and is superior to saliva- and skin blister concentration measurements.