S Seifert

Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Saxony, Germany

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Publications (43)71.25 Total impact

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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 30(12).
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    ABSTRACT: The preparation and stability of a new (188)Re-S(4)-complex [S(4) = (1-aza-18-crown-6)(O)C-C(SH)-C(SH)-C(O)NH-(CH(2))(3)-NH-(CH(2))(3)-NHC(O)-C(SH)-C(SH)-C(O)(1-aza-18-crown-6] was studied at therapeutic relevant radioactive concentrations. The results were compared with (188)Re-MAG(3) (MAG(3): mercaptoacetyltriglycine) and (188)Re-DMSA preparations (DMSA: dimercaptosuccinic acid) performed with the same highly concentrated [(188)Re]perrhenate solution (12-15 GBq/ml). The (188)Re complexes were prepared by direct reduction of perrhenate ((188)Re-S(4)-complex) as well as via the (188)Re-EDTA precursor complex ((188)Re-MAG(3), (188)Re-DMSA). The preparations were stabilised with 15 mg of ascorbic acid and analysed after 1, 2, and 24 hours by TLC and HPLC. Additionally, in vitro and in vivo stability studies were performed with the purified complexes. After stabilisation with 15 mg of ascorbic acid, all of the complexes were nearly stable under nitrogen for hours, and only 2-8% of perrhenate was observed after 24 h. In contrast, only the (188)Re-S(4) complex was completely stable in vitro and in all investigated in vivo samples after separation of ligand excess and reducing agent by HPLC. The bridging amine group or free carboxylic groups of the S(4)-ligand framework make available reactive positions for coupling biomolecules to the chelate. Thus it appears that the new (188)Re-S(4) complexes offer the possibility of stable and high specific activity labelling of biomolecules for therapeutic application.
    Nuklearmedizin 02/2007; 46(5):181-4. · 1.67 Impact Factor
  • S Seifert, H-J Pietzsch
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    ABSTRACT: An easy and gentle method for the preparation of 188Re(V) complexes with bidentate and tetradentate ligands is described starting from the precursor complex 188Re(III)-EDTA. That complex is prepared at room temperature in acidic solution and reacts by a combined re-oxidation/ligand exchange reaction with appropriate ligands like DMSA or ECD (DMSA = dimercapto succinic acid, ECD = L,L-ethylene dicysteine diethyl ester) or en, tau, and cyclam (en = ethylene diamine, tau = 1,4,8,11-tetraazaundecane, cyclam = 1,4,8,11-tetraazacyclo-tetradecane) to the 188Re(V)-oxo- and dioxocomplexes, respectively. The chelates were unambiguously identified by chromatographic comparison with spectroscopically characterised samples or known 99mTc-kit reconstitutions. The reaction succeeds under mild conditions (room temperature, short time, neutral or weak basic solutions) with high yields and has potential for labelling of sensitive biomolecules with 188Re.
    Applied Radiation and Isotopes 03/2006; 64(2):223-7. · 1.18 Impact Factor
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    ABSTRACT: A new type of tetradentate S4 ligand has been synthesized by bridging two molecules of meso-2,3-dimercaptosuccinic acid for stable binding and easy conjugation of rhenium-188 to tumor targeting structures. The stereoisomeric tetrathiolato S4 ligands form very robust anionic five-coordinated oxorhenium(V) and oxotechnetium(V) complexes. Two routes for the preparation of the (188)Re(V) oxocomplexes with (iBu)2N(O)C-C(SH)C(SH)C(O)NH(CH2)3NH(CH2)3NHC(O)C(SH)C(SH)C(O)N(iBu)2 (ligand 1) and its hydrophilic crown ether derivative (ligand 2) were tested and optimized. Several isomers were separated by HPLC from the preparation solutions and characterized in vitro and in vivo. The identity of the species obtained was determined by comparison with the HPLC profiles of reference (185/187)Re analogues and (99/99m)Tc complexes which were characterized by ESI-MS. All of them were absolutely stable in rat and human plasma solutions. Challenge experiments with cysteine corroborated the high inertness of the isomers toward ligand exchange reactions. Various in vivo samples, taken off at different times from blood, intestine, and urine of rats, confirmed the high in vivo stability of the (188)Re-S4 complexes. Biodistribution studies using male Wistar rats were performed and exhibited a high uptake and fast clearance from the liver of the more lipophilic cis and trans isomers of complex I (log P(o/w) between 1.5 and 1.7), whereas the isomers of the hydrophilic complex II (log P(o/w) about -1.75) were rapidly excreted via the renal and the hepatobiliary pathway. The low level of activity in the stomach confirms good in vivo stability. Thus, these new (188)Re-S4 complexes fulfill the requirements for a stable and high specific activity labeling of biomolecules with rhenium-188.
    Bioconjugate Chemistry 01/2006; 17(6):1601-6. · 4.58 Impact Factor
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    ABSTRACT: Development of new radiopharmaceuticals based on rhenium-188 depends on finding appropriate ligands able to give complexes with high in vivo stability. Rhenium(III) mixed-ligand complexes with tetradentate/monodentate ('4 + 1') coordination of the general formula [Re(NS(3))(PRR'R' ')] (NS(3) = tris(2-mercaptoethyl)amine and derivatives thereof, PRR'R' ' = phosphorus(III) ligands) appear to be among the promising tools to achieve this goal. According to this approach, we synthesized and characterized a series of rhenium model complexes. In vitro stabilities of the corresponding rhenium-188 complexes were determined by incubating 2-3 MBq or alternatively 37 MBq of the complexes in phosphate buffer, human plasma, and rat plasma, respectively, at 22 degrees C or 37 degrees C, followed by checking the amount of (188)ReO(4)(-) formed after 1 h, 24, and 48 h by thin-layer chromatography. The rate of perrhenate formation varied over a wide range, depending primarily on the nature of the phosphorus(III) ligand. Physicochemical parameters of the corresponding nonradioactive rhenium complexes were analyzed in detail to find out the factors influencing their different stability and furthermore to design new substitution-inert '4 + 1' complexes. Tolman's cone angle of phosphorus(III) ligands and the lipophilic character of the inner coordination sphere were found to be crucial factors to build up stable rhenium '4 + 1' complexes. Additional information useful to describe electronic and steric properties of these compounds were selected from electronic spectra (wavelength of the Re-->S charge-transfer band), cyclovoltammetric measurements (E degrees of the Re(III)/Re(IV) couple), and NMR investigations ((31)P chemical shift of coordinated P(III) ligands).
    Bioconjugate Chemistry 01/2005; 16(3):634-43. · 4.58 Impact Factor
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    ABSTRACT: Mixed-ligand model complexes of general formula [(99m)Tc(O)(kappa(3)-PNX)(kappa(1)-SPh))] [X = O (1a), S (2a)] were prepared in a one-step procedure from [(99m)TcO(4)(-)] using stannous chloride as reducing agent. Stability studies and challenge experiments with glutathione showed that complex 2a presented promising features for pursuing animal studies. The activity in the brain (% dose injected/organ) at 5 min (0.14% +/- 0.03) and 120 min (0.11% +/- 0.02) pi encouraged the synthesis of several mixed-ligand "3 + 1" oxo complexes of general formula [M(O)(kappa(3)-PNS)(kappa(1)-SL))] (M = (99m)Tc, 3a-6a, Re, 3-6), in which the tridentate ligand is the heterofunctionalized phosphine 2-(diphenylphosphanyl)-N-(2-thioethyl)benzamide (PNS) and the co-ligands are different arylpiperazine derivatives (HSL1-HSL4). The (99m)Tc complexes have been characterized by comparison of their retention times in the HPLC chromatogram (gamma-detection) with the retention times of the analogous Re complexes (UV detection at 254 nm). The (99m)Tc complexes, obtained with radiochemical purity higher than 95%, after HPLC purification, are stable in saline, 0.01 M PBS (pH 7.4), rat plasma (4 h, 37 degrees C), and glutathione (10 mM solutions, 2h, 37 degrees C). Binding affinity and selectivity for 5-HT(1A) receptors (relative to the 5-HT(2A) receptor) were determined, complex 5 demonstrating the best values (IC(50) for the 5-HT(1A) 2.35 +/- 0.02 nM; competitor 5-HT(2A) 372 +/- 11 nM). Biodistribution and stability studies in mice indicated a preferred hepatobiliary excretion, a high in vivo stability, but a poor brain uptake.
    Bioconjugate Chemistry 01/2005; 16(3):660-8. · 4.58 Impact Factor
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    ABSTRACT: New oxotechnetium complexes of general formula [99mTc(O)(PNS)(S(CH2)nOSiR3)] (4-6) were synthesized by direct reduction of [99mTcO4]- with stannous chloride, in the presence of the tridentate heterofunctionalized phosphine H2PNS and of the monodentate silylated thiols [HS(CH2)nOSiR3] (n = 2, R = Ph (1); n = 3, R = Ph (2); n = 3, R = Et (3)). The mixed-ligand rhenium and technetium complexes of general formula [M(O)(PNS)(S(CH2)nOH)] (n = 2: M = 99mTc, (7), M = Re, (7a); n = 3: M = 99mTc, (8), M = Re, (8a)) were also prepared. All the 99mTc complexes were obtained with high radiochemical purity (> 95%), after purification by HPLC, and were characterized by comparison of their HPLC profiles with the ones obtained for the corresponding Re compounds. The silylated compounds 4-6 are stable in phosphate saline buffer (PBS) pH 7.4, rat plasma, human serum and whole blood, and do not bind to plasmatic proteins, and also do not challenge with glutathione. The biological behavior of [99mTc(O)(PNS)(S(CH2)nOH)] (7, 8) and [99mTc(O)(PNS)(S(CH2)nOSiR3)] (4-6) was studied. The effect of the pH on the cleavage of the O-Si bond in complexes 4-6 was also evaluated.
    Nuclear Medicine and Biology 09/2004; 31(6):785-93. · 2.52 Impact Factor
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    ABSTRACT: Technetium and rhenium tricarbonyl complexes with derivatized cyclopentadienyl ligands were prepared starting from pertechnetate and an appropriate ferrocene ligand. Furthermore, the complexes (M(CO)3cp-COOC5H9N-R, M=Tc, Re; R=Me, isopropyl) could be obtained starting from the precursor complexes [99mTc(CO)3(H2O)3]+ and [Re(CO)3Br3]2−. Their chemical identity was confirmed by chromatographic methods and electron spray mass spectrometry. The biodistribution of the 99mTc complexes (cytectrene I and cytectrene II) in Wistar rats was studied. Both compounds show high uptake in the brain and fast blood clearance. The pattern of regional distribution in the brain demonstrated in autoradiographic studies indicates binding to the 5-HT1A and α1 adrenergic receptors.
    Journal of Organometallic Chemistry 01/2004; 689(25):4739-4744. · 2.00 Impact Factor
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    ABSTRACT: Improved methods are presented for the preparation of 99mTc and 188Re mixed-ligand complexes with tetradentate and monodentate ligands of the general formula [MIII(Lm)(Ln)] (M = Tc, Re; Lm = NS3 or NS3COOH; Ln = isocyanide or phosphine). To avoid the undesired formation of reduced-hydrolyzed species of both metals, the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand 2,2',2' '-nitrilotris(ethanethiol) (NS3) or its carboxyl derivative NS3COOH (a) and the monodentate phosphine ligands (triphenylphosphine L1, dimethylphenylphosphine L2) or isocyanides (tert-butyl isonitrile L3, methoxyisobutyl isonitrile L4, 4-isocyanomethylbenzoic acid-L-arginine L5, 4-isocyanomethylbenzoic acid-L-arginyl-L-arginine L6, 4-isocyanomethylbenzoic acid-neurotensin(8-13) L7) to the so-called '4+1' complex. Copper(I) isocyanide complexes are used for preparing the '4+1' complexes. That facilitates storage stability and allows kit formulations, and, moreover, enables the formation of 188Re complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed, and that results in high specific activity labeling of interesting molecules. The lipophilicity of complexes can be controlled by introducing a carboxyl group into the tetradentate ligand and/or derivatization of the monodentate ligands. Furthermore, the carboxyl group enables the conjugation of biomolecules. As an example, the neurotensin derivative CN-NT(8-13) was prepared and labeled with 99mTc according to the '4+1' approach, and its behavior in vivo was studied.
    Bioconjugate Chemistry 01/2004; 15(4):856-63. · 4.58 Impact Factor
  • S Seifert, R Syhre, H Spies, B Johannsen
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    ABSTRACT: Starting from our previous finding that 99mTc(V) dimercaptosuccinic acid (99mTc(V)-DMSA), a useful agent for the localization of osteosarcoma and bone metastases, loses its bone affinity when one ester group is introduced into the complex we studied the impact of esterification in more detail. This paper reports on the evaluation of various ester complexes of 99mTc(V)-DMSA in rats and tumour-bearing nude mice with regard to their tumour retention and improvement of the tumour to tissue ratios. The distribution patterns of the complexes [99mTcO(DMSA)2]- (A), [99mTcO(DMSA/DMSEt)]- (B) and [99mTcO(DMSEt)2]- (C) are gradually changed with the number of ester groups in the anionic complex. However, the asymmetric diester complex [99mTcO(DMSA/DMSEt2)]- (D) is very slowly cleared, especially from the blood of nude mice. Moreover, this complex differs significantly from the symmetrical complex C in its elimination behaviour from the liver and kidneys. The tumour uptake is maintained with complexes that contain one or two non-hydrolysable ester functions. Preliminary biodistribution studies of the monoethyl and diethyl ester complexes B, C and D in comparison with A in tumour-bearing nude mice showed similar uptake into the human squamous cell carcinoma (FaDu) as well as into the human colonic cell carcinoma (HT29) of nude mice. The low bone accumulation of B, C and D results in excellent tumour-to-bone ratios, e.g., approx. 3:1 for the ester complex B compared to approx. 1:2 for complex A. Differences were observed in the accumulation and elimination behaviour of the complexes A and B in various bone structures of rats. The age-dependent uptake of A and B was compared in long bone (femur) and in cranial bone of rats. The results suggest that 99mTc(V)-DMSA complexes that contain a functional ester, and their 188Re analogues, may be superior to 99mTc(V)/188Re(V)-DMSA in diagnostic and therapeutic nuclear medicine.
    Nuclear Medicine Communications 11/2003; 24(11):1175-83. · 1.38 Impact Factor
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    ABSTRACT: A novel type of mixed-ligand Tc(III) complexes, [Tc(SCH(2)CH(2)-E-CH(2)CH(2)S)(PR(2)S)] (E = S, N(CH(3)); PR(2)S = phosphinothiolate with R = aryl, alkyl) is described. These "3+2"-coordinated complexes can be prepared in a two-step reduction/substitution procedure via the appropriate chloro-containing oxotechnetium(V) complex [TcO(SES)Cl] [E=S, N(CH(3)]. Tc(III) compounds have been fully characterized both in solid and solution states and found to adopt the trigonal-bipyramidal coordination geometry. The equatorial trigonal plane is formed by three thiolate sulfur atoms, whereas the phosphorus of the bidentate P,S ligand and the neutral donor of the tridentate chelator occupy the apical positions. The (99)Tc(III) complexes have been proven to be identical with the (99m)Tc agents prepared at the no-carrier-added level by comparison of the corresponding UV/vis and radiometric HPLC profiles. Challenge experiments with glutathione clearly indicate that this tripeptide has no effect on the stability of the (99m)Tc complexes in solutions. Biodistribution studies have been carried out in rats at 5 and 120 min postinjection. The substituents at the bidentate P,S ligand significantly influence the biodistribution pattern. Remarkable differences are observed especially in brain, blood, lungs, and liver. All the complexes are able to penetrate the blood-brain barrier of rats and showed a relatively fast washout from the brain.
    Bioconjugate Chemistry 01/2003; 14(1):136-43. · 4.58 Impact Factor
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    ABSTRACT: This paper reports the synthesis, biological evaluation, in vitro and ex vivo autoradiography of the first Tc-99m ligand with subnanomolar affinity for the 5-HT(1A) receptor and a remarkably high affinity for the alpha1-adrenergic receptor. The neutral "3+1" mixed-ligand complex combines 4-(6-mercaptohexyl)-1-(2-methoxyphenyl)piperazine as monodentate and 3-(N-methyl)azapentane-1,5-dithiol as tridentate unit with oxotechnetium(V). The analogous rhenium complex was synthesized for complete structural characterization and used in receptor binding assays. In competition experiments both complexes display subnanomolar affinity for the 5-HT(1A) receptor (IC(50)0.24 nM for Re, 0.13 nM for Tc) but also very high affinities for the alpha1-adrenergic receptor (IC(50) 0.05 nM for Re, 0.03 nM for Tc). Biodistribution studies show a brain uptake in rat of 0.22% ID five minutes post injection. In vitro autoradiographic studies in rat brain and postmortem human brain indicate accumulation of the Tc-99m complex in brain areas which are rich in 5-HT(1A) receptors or in alpha1-adrenergic receptors. This in vitro enrichment can be blocked respectively by the 5-HT(1A) receptor agonist 8-OH-DPAT or by prazosin hydrochloride, an alpha1-adrenergic receptor antagonist. Ex vivo autoradiographic studies in rats show a slight accumulation of the Tc-99m complex in 5-HT(1A) receptor-rich areas of the brain, which could not be blocked, as well as in regions rich in alpha1-adrenergic receptors, which could be blocked by prazosin hydrochloride.
    Nuclear Medicine and Biology 06/2002; 29(4):375-87. · 2.52 Impact Factor
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    ABSTRACT: Tc(III) and Re(III) complexes [M(NS(3))(CNR)] (M = Re, 99mTc, NS(3) = 2,2',2"-nitrilotris(ethanethiol), CNR = functionalized isocyanide bearing a derivative of WAY 100635) have been synthesized and characterized. Re was used as Tc surrogate for chemical characterization and in vitro receptor-binding studies. For two representatives subnanomolar affinities for the 5-HT(1A) as well as for the alpha1-adrenergic receptor were reached. Biodistribution studies in rats of the 99mTc complexes showed brain uptakes between 0.3 and 0.5% ID/organ (5 min p.i.). In vitro autoradiography of one 99mTc representative in sections of post mortem human brain indicate its accumulation in 5-HT(1A) receptor-rich brain regions. However, addition of the specific 5-HT(1A) receptor agonist 8-OH-DPAT as well as the alpha1-adrenoceptor antagonist prazosin could not substantially block this tracer accumulation. A preliminary SPET study in a monkey showed negligible brain uptake.
    Nuclear Medicine and Biology 06/2002; 29(4):389-98. · 2.52 Impact Factor
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    ABSTRACT: Technetium(I) thioether carbonyl complexes and their reaction products with histidine were prepared and characterised by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, various chromatographic and electrophoretic methods and electrospray mass spectrometry. Their behaviour in aqueous solutions was studied on the carrier-added (99Tc) and the no-carrier-added (99mTc) levels. HPLC and electrophoretic studies show the identity of reaction products at both concentration levels. Technetium(I) carbonyl complexes containing a bidentate dithioether ligand [Tc(CO)3Cl(SS)], as well as a tridentate carboxylato thioether ligand [Tc(CO)3(SSO)], undergo a ligand exchange reaction with histidine and form the complex [Tc(CO)3His]. EXAFS measurements were performed to estimate the structural parameters of the dissolved technetium(I) carbonyl complexes and their reaction products after the challenge experiments. The calculated bond lengths and coordination numbers are in agreement with the expected values and confirm the ligand exchange reactions.
    Inorganica Chimica Acta. 10/2001; 322(s 1–2):79–86.
  • Journal of Labelled Compounds 05/2001; 44(S1).
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    ABSTRACT: The reactivity of labile 3 + 1 mixed-ligand 99mTc complexes of the type [99mTcO(SES)(RS)] with SES being a tridentate dithiol ligand and glutathione or dimethylcysteamine as monodentate ligands RSH towards proteins was investigated in vitro and in vivo. It was found that the complexes undergo reversible transchelation reactions with SH group-containing components of blood such as albumin or haemoglobin. High labelling yields were obtained when 3 + 1 complexes with the tridentate SSS ligand were used. The biodistribution of blood proteins labelled by ligand-exchange reaction with the [99TcO(SSS)] or [99mTcO(SNMeS)] core was studied and compared with the in vivo distribution of the labile 3 + 1 complexes containing glutathione as monodentate ligand.
    Applied Radiation and Isotopes 05/2001; 54(4):637-44. · 1.18 Impact Factor
  • Journal of Labelled Compounds 05/2001; 44(S1).
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    ABSTRACT: Five-coordinate oxotechnetium(V) mixed-ligand complexes [TcO(SES)(S-p-C6H4-OMe)], where SES is a tridentate dithiolato fragment of the type -S(CH2)2E(CH2)2S- (E = O, 1; E = S, 2; E = NMe, 3) are converted via reduction-substitution reactions in the presence of PMe2Ph into the corresponding five-coordinate Tc(III) complexes [Tc(SES)(S-p-C6H4-OMe)(PMe2Ph)] (E = O, 4; E = S, 5; E = NMe, 6). Rearrangement of the original square pyramidal "3 + 1" oxo species to the trigonal bipyramidal "3 + 1 + 1" Tc(III) complexes occurs by placing the three thiolate donors on the basal plane, the phosphine phosphorus, and the heteroatom of the tridentate ligand at the apexes of the bipyramid. These Tc(III) complexes are diamagnetic species, thereby allowing multinuclear NMR characterization in solution, which confirm their structures to be identical to those observed in the solid state via X-ray determinations.
    Inorganic Chemistry 02/2001; 40(1):59-64. · 4.59 Impact Factor
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    ABSTRACT: Mixed — ligand model complexes, [99mTc(O)(PNX)(SPh)] (XO (1a), S (2a)), were synthesized from [99mTcO4]−. These compounds were characterized by comparing their radioactive HPLC profiles with the UV profiles of the analytically pure Re compounds 1 and 2. Based on stability studies, undertaken in aqueous solutions and in glutathione challenge experiments, 2a was chosen for biodistribution studies in rats. Using this approach, the labelling of a 5‐HT1A receptor ligand (derivatized aryl‐piperazine) with 99mTc was also performed using the PNS chelate.
    Journal of Labelled Compounds and Radiopharmaceuticals 01/2001; 44. · 1.24 Impact Factor
  • Radiochimica Acta - RADIOCHIM ACTA. 01/2001; 89.

Publication Stats

164 Citations
71.25 Total Impact Points

Institutions

  • 1995–2010
    • Helmholtz-Zentrum Dresden-Rossendorf
      • Institute of Radiopharmacy
      Dresden, Saxony, Germany
  • 2005
    • The Immune Tolerance Network
      Seattle, Washington, United States
  • 1999
    • Bundesanstalt für Materialforschung und -prüfung
      Berlín, Berlin, Germany
  • 1997
    • Technische Universität Dresden
      Dresden, Saxony, Germany