Allogeneic hematopoietic stem cell transplantation represents the most effective form of immunotherapy for chemorefractory diseases. However, animal models have been missing that allow evaluation of donor-patient–specific graft-versus-leukemia effects. Thus, we sought to establish a patient-tailored humanized mouse model that would result in long-term engraftment of various lymphocytic lineages and would serve as a donor-specific surrogate. Following transfer of donor-derived peripheral blood stem cells into NOD/SCID/IL-2Rγnull (NSG) mice with supplementation of human IL-7, we could demonstrate robust engraftment and multilineage differentiation comparable to earlier studies using cord blood stem cells. Phenotypical and functional analyses of lymphoid lineages revealed that >20 wk posthematopoietic stem cell transplantation, the majority of T lymphocytes consisted of memory-type CD4+ T cells capable of inducing specific immune functions, whereas CD8+ T cells were only present in low numbers. Analysis of NSG-derived NK cells revealed the expression of constitutively activated CD56brightCD16− killer Ig-like receptornegative NK cells that exhibited functional impairments. Thus, the data presented in this study demonstrate that humanized NSG mice can be successfully used to develop a xenotransplantation model that might allow patient-tailored treatment strategies in the future, but also highlight the need to improve this model, for example, by coadministration of differentiation-promoting cytokines and induction of human MHC molecules to complement existing deficiencies in NK and CD8+ T cell development.

No abstract

The negative influence of hypoxia on the outcome of malignant tumors may be caused by direct oxygen effects, and potentially, the selection of resistant tumor cells under repetitive hypoxia. To evaluate whether cyclic hypoxia selects for resistant cells and to analyze the underlying mechanisms, the influence of cyclic hypoxia on intracellular death pathways was determined in tumor cells. It could be demonstrated that cyclic hypoxia selects for cells with increased resistance against hypoxia-induced apoptosis. These cells exhibited a cross-resistance against paradigmatic triggers of mitochondrial apoptotic pathways (ionizing radiation/etoposide). In contrast, TRAIL-receptor mediated apoptosis remained unaffected. Thus, cyclic hypoxia selects for cells with defects of the mitochondrial rather than receptor-mediated pathways. Selection of p53-defective cells has been described as a consequence of cyclic hypoxia; therefore, we evaluated the impact of hypoxic selection on activation of p21 and downstream mediators of p53-dependent apoptosis. p53 function and protein levels of key mediators of mitochondrial apoptosis remained unaffected by hypoxic selection. However, radiation-induced conformational changes of Bax were reduced after cyclic hypoxia. In summary, it could be demonstrated that hypoxic stress confers a selection pressure on mitochondrial apoptotic pathways and, consecutively, to an increased resistance toward mitochondrial death triggers.

No abstract

Although immortalized cell lines have been extensively used to optimize treatment strategies in cancer, the usefulness of such in vitro systems to recapitulate primary disease is limited. Therefore, the design of in vivo models ideally utilizing patientderived material is of critical importance. In this regard, NOD.Cg-Prkdc scid IL2rg tmWjl /Sz (NSG) mice have been reported to provide superior engraftment rates. However, limited data exist on the validity of such a model to constitute a surrogate marker for clinical parameters. We studied primary and serial engraftment on more than 200 NSG mice with 54 primary pediatric B cell precursor acute lymphatic leukemia (B-ALL), myeloid leukemia (AML) and T cell leukemia (T-ALL) samples, characterized the leukemogenic profile and correlated engraftment kinetics with clinical outcome. Median time to engraftment was 7-10 weeks and 90% of the mice engrafted. Male recipients conferred significantly higher engraftment levels than female recipients (p 0.004). PCR-based minimal residual disease marker expression and fluorescence in situ hybridization confirmed the presence of patient-specific genetic aberrations in mice. Transcriptome cluster analysis of genes known to be important in the leukemogenesis of all three diseases revealed that well-known tumor-regulating genes were expressed to a comparable extent in mice and men. The extent of engraftment and overall survival of NSG mice highly correlated with the individual prognosis of B-ALL, AML and T-ALL patients. Thus, we propose an in vivo model that provides a valuable preclinical tool to explore the heterogeneity of leukemic disease and exploit patient-tailored leukemia-targeting strategies within multivariate analyses.Over the last decades, remarkable progress has been made in curing childhood acute leukaemia. 1,2 However, the current protocols using intensive poly-chemotherapy induce longterm remission in only 80% of the children and are often associated with significant treatment-related toxicity. Therefore, ongoing research aims to improve therapy for children who are at risk for relapse, while reducing adverse effects in patients with a more favorable prognosis. 3,4 To this end, cultured immortalized cell lines have been widely used to study the characteristics of various malignant stem cell clones or blasts and to evaluate or optimize new treatment strategies. However, the usefulness of such in vitro systems to