Helmut Simon

Inhibition of Allogeneic T Cell Proliferation by Indoleamine 2,3-Dioxygenase–expressing Dendritic Cells: Mediation of Suppression by Tryptophan Metabolites

Indoleamine 2,3-dioxygenase (IDO), an enzyme involved in the catabolism of tryptophan, is expressed in certain cells and tissues, particularly in antigen-presenting cells of lymphoid organs and in the placenta. It was shown that IDO prevents rejection of the fetus during pregnancy, probably by inhibiting alloreactive T cells, and it was suggested that IDO-expression in antigen-presenting cells may control autoreactive immune responses. Degradation of tryptophan, an essential amino acid required for cell proliferation, was reported to be the mechanism of IDO-induced T cell suppression. Because we wanted to study the action of IDO-expressing dendritic cells (DCs) on allogeneic T cells, the human IDO gene was inserted into an adenoviral vector and expressed in DCs. Transgenic DCs decreased the concentration of tryptophan, increased the concentration of kynurenine, the main tryptophan metabolite, and suppressed allogeneic T cell proliferation in vitro. Kynurenine, 3-hydroxykynurenine, and 3-hydroxyanthranilic acid, but no other IDO-induced tryptophan metabolites, suppressed the T cell response, the suppressive effects being additive. T cells, once stopped in their proliferation, could not be restimulated. Inhibition of proliferation was likely due to T cell death because suppressive tryptophan catabolites exerted a cytotoxic action on CD3+ cells. This action preferentially affected activated T cells and increased gradually with exposure time. In addition to T cells, B and natural killer (NK) cells were also killed, whereas DCs were not affected. Our findings shed light on suppressive mechanisms mediated by DCs and provide an explanation for important biological processes in which IDO activity apparently is increased, such as protection of the fetus from rejection during pregnancy and possibly T cell death in HIV-infected patients.

Mitomycin C-treated antigen-presenting cells as a tool for control of allograft rejection and autoimmunity: From bench to bedside

Cells have been previously used in experimental models for tolerance induction in organ transplantation and autoimmune diseases. One problem with the therapeutic use of cells is standardization of their preparation. We discuss an immunosuppressive strategy relying on cells irreversibly transformed by a chemotherapeutic drug. Dendritic cells (DCs) of transplant donors pretreated with mitomycin C (MMC) strongly prolonged rat heart allograft survival when injected into recipients before transplantation. Likewise, MMC-DCs loaded with myelin basic protein suppressed autoreactive T cells of MS patients in vitro and prevented experimental autoimmune encephalitis in mice. Comprehensive gene microarray analysis identified genes that possibly make up the suppressive phenotype, comprising glucocorticoid leucine zipper, immunoglobulin-like transcript 3, CD80, CD83, CD86, and apoptotic genes. Based on these findings, a hypothetical model of tolerance induction by MMC-treated DCs is delineated. Finally, we describe the first clinical application of MMC-treated monocyte-enriched donor cells in an attempt to control the rejection of a haploidentical stem cell transplant in a sensitized recipient and discuss the pros and cons of using MMC-treated antigen-presenting cells for tolerance induction. Although many questions remain, MMC-treated cells are a promising clinical tool for controlling allograft rejection and deleterious immune responses in autoimmune diseases.

Instabile CO2-Fixierung und Photosynthese

Algenzellen enthalten im Licht instabil gebundenes CO2. Es ließ sich zeigen, daß das labile Fixierungsprodukt beim Abtöten der Zellen mit heißem Äthanol augenblicklich zerstört wird. Auch in angesäuertem kaltem Aceton zerfällt es innerhalb weniger Min., doch läßt es sich durch Zusatz von Hydroxylamin unmittelbar vor dem Abtöten der Algen mit kalten organischen Lösungsmitteln erhalten bzw. in ein stabiles Derivat überführen. Die Verbrennung von Scenedesmus-Suspensionen nach kurzer Photosynthese in 14C-markierter Bicarbonatlösung und anschließende Radioaktivitätsmessung des entstandenen CO2 ermöglichte Aussagen über Menge und Stabilität des labilen Komplexes.

Darstellung einiger 35S-markierter Verbindungen im Mikromaßstab

Es werden Verfahren zur Darstellung von Thioharnstoff-35S, Thioglykolsäure-35S, Thioglykol-35S und Cysteamin-35S, ausgehend von Natriumsulfat-35S (trägerfrei) über Schwefelwasserstoff-35S, beschrieben.

Über die Aufnahme von 5.6-Dimethyl-benzimidazol und 5.6-Dichlorbenzimidazol durch Lactobacillus leichmannii 313

Lactobacillus leichmannii 313 nimmt bei der Züchtung in Gegenwart von 5.6-Dimethylbenzimidazol-[2-14C] oder 5.6-Dichlor-benzimidazol-[2-14C] 40 000 bis 47 000 Moleküle dieser Verbindungen pro Zelle auf, gleichgültig ob Vitamin B12 oder Thymidin als Wuchsstoff verwendet wird. - Die Synthese der radioaktiven Benzimidazole im 1/2-mMol-Maßstab wird beschrieben.