München, Techn. Universiẗat, Diss., 2007.

Techn. Universiẗat, Diss., 2005--München. / Dateien in unterschiedlichen Formaten.

HA22 is an immunotoxin composed of an anti-CD22 variable fragment linked to a 38 kDa truncated protein derived from Pseudomonas exotoxin A. The mechanisms of cytotoxicity and resistance of HA22 against Acute Lymphoblastic Leukaemia (ALL) and Burkitt’s lymphoma were studied. Using a bone marrow mesenchymal cell culture assay to support ALL cell viability, I? investigated the in vitro cytotoxicity of HA22 against ALL blasts from newly diagnosed and relapsed patients. There was interpatient variability in sensitivity to HA22. There was no significant difference in HA22 sensitivity between diagnosis and relapse samples but peripheral blood ALL blasts were more sensitive to HA22 than those from bone marrow. The mechanisms of resistance to HA22 were studied, using cell lines as a model. The number of CD22 sites/ cell and the rates of immunotoxin internalisation did not affect HA22 cytotoxicity. HA22 mutants with resistance to lysosomal degradation and enhanced targeting to the endoplasmic reticulum had improved cytotoxicity. The role of apoptosis pathways proteins in HA22-mediated cell death was studied. Their role is complex but raised levels of the anti-apoptotic pathway protein Bcl-2 were found in the most resistant NALM6 cell line. Penetration of HA22 into Burkitt’s lymphoma masses was studied using a flow cytometric based method. HA22 rapidly penetrated into the lymphoma masses, however a barrier to further uptake is present which could not be overcome by the addition of adriamycin or taxol in the murine xenograft model. The ability of Acute Myeloid Leukaemia (AML) blasts to create an immunosuppressive niche was investigated using a cell line model and primary patient samples. AML blasts suppress T cell proliferation through altered arginine metabolism, dependent on the enzymes arginase II and iNOS. Small molecule inhibitors to arginase and iNOS restored T cell proliferation in vitro. AML further enhances its immunosuppressive niche by transforming surrounding monocytes into an M2-immunosuppressive phenotype, in an arginase dependent manner. The immunomodulatory protein Serum Amyloid A (SAA) was secreted by AML blasts, and leads to AML chemotaxis, IL-1production, and release of S100A9 protein. Finally, invariant Natural Killer T cells (iNKT) were shown to be cytotoxic to some AML blasts, in the presence of Galactosylceramide, and thus able to restore T cell proliferation. The results provide a strong rationale for the clinical testing of these novel immunotherapeutic and immunomodulatory strategies in patients with haematological malignancies.

京都大学 / 0048 / 新制・課程博士 / 博士(医学) / 甲第18157号 / 医博第3877号 / 新制||医||1003(附属図書館) / 31015 / 京都大学大学院医学研究科医学専攻 / (主査)教授 武藤 学, 教授 清水 章, 教授 生田 宏一 / 学位規則第4条第1項該当 / Doctor of Medical Science / Kyoto University / DFAM

The purpose of these experiments was to determine the effects of cholinergic depletion on spontaneous and evoked activity of neurons in the different layers of the posteromedial barrel subfield (PMBSF) of the rat somatosensory cortex. Acetylcholine neurons in nucleus basalis of Meynert (NBM) were selectively lesioned with an immunotoxin (IT), 192 IgG-saporin. Spontaneous activity was significantly lower in layers II-III, Va, and VI in IT-injected animals compared to control animals. Evoked activity was significantly lower in layers II-III, IV, Vb, and VI of IT-injected animals compared to control animals. The largest difference was observed in layer Vb. Thus, cholinergic depletion causes significant changes in the magnitude of spontaneous and evoked activity but these differences are not completely in register with one another.

Immunotoxins (ITx) represent a new, alternate class of therapeutic agent. ITx is made when the active part of a toxin is conjugated with the binding portion of an antibody that recognizes a cancer-specific antigen. The antibody component makes ITx highly specific, as it will only bind to cells displaying the correct surface antigen. This characteristic lowers the chance of nonspecific cell damage, which causes many of the severe side effects of other chemotherapeutics. The ITx we use is a conjugate of saporin toxin. Saporin is a ribosomal inhibiting protein derived from the plant Saponaria officinales, which kills the cell by inhibiting protein synthesis. ITx enters the cancer cell by binding to the cellular marker it is specific for on the cell surface. From there, it is endocytosed, compartmentalized in an endosome, and eventually escapes to the cytosol where its ribosomal target is located. Increasing the rate of escape to the cytosol is the key to increasing cell death. The mechanism by which saporin escapes the endosome and enters the cytosol is poorly understood. Two potential mechanisms involving the rupture of the endocytic vesicle were examined. Through experiments using large unilamellar vesicles as endosomal mimics, we have been able to characterize the mechanism by which saporin works to burst the endosomal membrane through RET and calcein release. Understanding this process is the key to producing more effective immunotoxin sensitizing drugs.

Yes / Expression of the transmembrane NG2 chondroitin sulphate proteoglycan (CSPG) defines a distinct population of NG2-glia. NG2-glia serve as a regenerative pool of oligodendrocyte progenitor cells in the adult central nervous system (CNS), which is important for demyelinating diseases such as multiple sclerosis, and are a major component of the glial scar that inhibits axon regeneration after CNS injury. In addition, NG2-glia form unique neuron–glial synapses with unresolved functions. However, to date it has proven difficult to study the importance of NG2-glia in any of these functions using conventional transgenic NG2 ‘knockout’ mice. To overcome this, we aimed to determine whether NG2-glia can be targeted using an immunotoxin approach. We demonstrate that incubation in primary anti-NG2 antibody in combination with secondary saporin-conjugated antibody selectively kills NG2-expressing cells in vitro. In addition, we provide evidence that the same protocol induces the loss of NG2-glia without affecting astrocyte or neuronal numbers in cerebellar brain slices from postnatal mice. This study shows that targeting the NG2 CSPG with immunotoxins is an effective and selective means for killing NG2-glia, which has important implications for studying the functions of these enigmatic cells both in the normal CNS, and in demyelination and degeneration.