T Yamamura

Keio University, Tokyo, Tokyo-to, Japan

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Publications (15)60.63 Total impact

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    ABSTRACT: To target high-affinity interleukin (IL)-2 receptors involved in lymphocyte proliferation processes such as allograft rejection, autoimmune disorders, and certain haematological malignancies, using a minimally immunogenic mammalian-derived enzyme, bovine RNaseA, which becomes cytotoxic on entering cytoplasm. Laboratory study. Teaching hospital, Japan. Human lymphocytes isolated from healthy histoincompatible donors in mixed lymphocyte cultures or stimulated with phytohemagglutinin (PHA) to promote IL-2Ralpha expression. MJ, an HTLV-1-infected malignant T-cell line that overexpresses IL-2Ralpha, and the IL-2Ralpha-negative cell lines MOLT-4F and MT-1, were used as controls. Bovine RNaseA was chemically conjugated to 7G7B6, a monoclonal antibody to the alpha-chain of human IL-2 receptors, and several concentrations of the conjugates were added to the lymphocyte cultures. Inhibition of cell proliferation as a percentage of 3H-thymidine incorporation in 24 hours. 7G7B6-RNaseA dose-dependently inhibited cell proliferation in PHA-stimulated human lymphocytes at a 50% inhibitory concentration (IC50) of 2 x 10(-7) M. whereas RNase alone and RNase plus antibody had no inhibitory effect. 7G7B6-RNaseA also dose-dependently inhibited the human mixed lymphocyte reaction at an IC50 of 2 x 10(-6) M, whereas RNase alone did not. The conjugate also inhibited cell proliferation in MJ cells, a cell line that is infected with HTLV-I and overexpresses the high-affinity IL-2 receptor, at an IC50 of 5 x 10(-7) M. However the conjugate had no inhibitory effect on the IL-2 receptor non-expressing human T-cell lymphoblastic leukaemia cell lines MOLT-4F or MT-1. 7G7B6-RNaseA can inhibit cell proliferation in antigen- or mitogen-stimulated lymphocytes that overexpress high-affinity IL-2 receptors, and it may be safer than conventional chemotherapy or immunotoxins in the treatment of transplant rejection, certain lymphocytic malignancies, and other IL-2R-associated diseases, because it contains a mammalian cytotoxic enzyme.
    The European Journal of Surgery 02/2002; 168(1):49-54.
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    ABSTRACT: Although Na+/H+ exchange (NHE) has been implicated in myocardial reperfusion injury, participation of coronary microvascular endothelial cells (CMECs) in this pathogenesis has been poorly understood. NHE-induced intracellular Ca2+ concentration ([Ca2+]i) overload in CMECs may increase the synthesis of intercellular adhesion molecules (ICAM), which is potentially involved in myocardial reperfusion injury. The present study tested the hypothesis that NHE plays a crucial role in [Ca2+]i overload and ICAM-1 synthesis in CMECs. Primary cultures of CMECs isolated from adult rat hearts were subjected to acidic hypoxia for 30 min followed by reoxygenation. Two structurally distinct NHE inhibitors, cariporide and 5-(N-N-dimethyl)-amiloride (DMA), had no significant effect on the acidic hypoxia-induced decrease in intracellular pH (pH(i)) of CMECs but significantly retarded pH(i) recovery after reoxygenation. These NHE inhibitors abolished the hypoxia- and reoxygenation-induced increase in [Ca2+]i. Expression of ICAM-1 mRNA was markedly increased in the vehicle-treated CMECs 3 h after reoxygenation, and this was significantly inhibited by treatment with cariporide, DMA, or Ca2+-free buffer. In addition, enhanced ICAM-I protein expression on the cell surface of CMECs 8 h after reoxygenation was attenuated by treatment with cariporide, DMA, or Ca2+-free buffer. These results suggest that NHE plays a crucial role in the rise of [Ca2+]i and ICAM-1 expression during acidic hypoxia/reoxygenation in CMECs. We propose that inhibition of ICAM-1 expression in CMECs may represent a novel mechanism of action of NHE inhibitors against ischemia-reperfusion injury.
    AJP Heart and Circulatory Physiology 07/2001; 280(6):H2796-803. · 3.63 Impact Factor
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    ABSTRACT: Insulin-like growth factor 1 has been shown to be cytoprotective against ischemia-reperfusion injury in various organs. However, spinal cord protection by insulin-like growth factor 1 has not been tested. We have therefore examined the effect of insulin-like growth factor 1 on neuronal cell death and motor function after spinal cord ischemia. Japanese white rabbits were subjected to spinal cord ischemia by clamping the abdominal aorta for 15 minutes. Insulin-like growth factor 1 (0.3 mg/kg) at a dose equipotent to insulin (0.3 IU/kg) in lowering blood glucose level or the control (phosphate-buffered saline solution as a vehicle) was administered intravenously 30 minutes before the aortic clamp. Hind-limb motor function had recovered normally 48 hours after the operation in all the rabbits (n = 8) treated with insulin-like growth factor 1. In contrast, all the control-treated (n = 8) and all but one of the insulin-treated (n = 6) rabbits had deteriorated to paraplegia by 48 hours after the operation. Histopathologic sections in the involved spinal cord segment showed that a significantly (P <.0001) greater number of motor neuron cells were preserved in the rabbits treated with insulin-like growth factor 1 (17.9 +/- 4.8 per section) than in those treated with the control (8.0 +/- 2.1). Although insulin was equipotent to insulin-like growth factor 1 in preserving the number of motor neuron cells (18.5 +/- 2.7), the percentage of motor neuron cells positive for terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate-biotin nick-end labeling were significantly (P <.01) smaller in the rabbits treated with insulin-like growth factor 1 (6.0 +/- 4.6) compared with those treated with the control (54.6 +/- 33.8) and insulin (26.2 +/- 11.7). Immunohistochemical studies revealed that insulin-like growth factor 1 increased expression of the antiapoptotic Bcl-xL protein and inhibited expression of the proapoptotic Bax protein in motor neuron cells 24 and 48 hours after the operation. In contrast, expression of only Bax was increased after the operation in other groups of rabbits subjected to spinal cord ischemia. These results suggest that insulin-like growth factor 1, but not insulin with a conventional dose, protects motor neuron cells from ischemic spinal cord injury associated with differential regulation of Bcl-xL and Bax protein.
    Journal of Thoracic and Cardiovascular Surgery 07/2001; 122(1):136-43. · 3.53 Impact Factor
  • Transplantation Proceedings 07/2001; 33(4):2566-70. · 0.95 Impact Factor
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    ABSTRACT: Bcl-2 family proteins play a crucial role in the cytoprotective action of insulin-like growth factor-I (IGF-I) by regulating cell death signaling at the mitochondrial level. The present study examined the effect of IGF-I on the expression of Bcl-2 family proteins in the rat heart mitochondria in relation to myocardial protection against ischemia-reperfusion injury. Systemic IGF-I (1 mg) treatment in the rat increased Bcl-xL and attenuated Bax 12-24 h later in the heart mitochondria fraction. Permeability transition and cytochrome c release occurred in a Ca(2+) concentration-dependent manner in the vehicle-treated mitochondria. This was significantly inhibited by the IGF-I-pretreatment. Moreover, ATP synthesis was significantly greater in the IGF-I-pretreated mitochondria. IGF-I pretreatment 24 h before 25 min of global ischemia in the isolated rat heart model significantly improved recovery of isovolumic left ventricular function and inhibited creatine kinase release during reperfusion. This was associated with a significantly less number of terminal transferase labeling-positive myocytes and nonmyocytes 2 h after reperfusion. These results suggest that IGF-1 differentially regulates Bcl-xL and Bax in heart mitochondria, which may be causally related to myocardial protection against ischemia-reperfusion injury.
    AJP Heart and Circulatory Physiology 04/2001; 280(3):H1191-200. · 3.63 Impact Factor
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    ABSTRACT: Coenzyme Q10 (CoQ) has long been utilized as a cardioprotective agent in various heart diseases. One of the most important mechanisms by which CoQ exerts cardioprotection is aerobic ATP production as a mobile electron carrier in the mitochondrial electron transfer chain. The ability of CoQ to afford myocardial protection is also attributed to its antioxidant property. However, CoQ may also act as a pro-oxidant through the generation of reactive oxygen species. Although excess oxidative stress is known to induce death signaling via cytochrome c release from mitochondria, it is now apparent that a brief exposure to oxidative stress stimulates redox signaling for acquisition of tolerance to oxidative stress. Therefore, we have investigated dual involvement of CoQ in redox signaling generation through enhanced production of reactive oxygen species and death signaling inhibition through antioxidation. Mitochondria were isolated from the rat heart and incubated with CoQ (10 or 100 microM) or its vehicle HCO 60 for 1 h. H2O2 and cytochrome c release from respiring mitochondria were increased by antimycin A (2 microM), an inhibitor of complex III respiratory chain, or by high Ca2+ (10 microM). This enhanced release of H2O2 was associated with an increase in lipid peroxidation as measured with 4-hydroxy-2-nonenal-modified proteins and with large amplitude swelling of mitochondria. CoQ potentiated H2O2 release from antimycin A- or high Ca(2+)-treated mitochondria, but was capable of inhibiting lipid peroxidation and large amplitude swelling, and attenuated cytochrome c release from the mitochondria. In addition, CoQ increased ATP synthesis by mitochondria. These results suggest that CoQ plays dual roles in mitochondrial generation of intracellular signaling. CoQ acts as a pro-oxidant that participates in redox signaling. CoQ also acts as an antioxidant that inhibits permeability transition and cytochrome c release, and increases ATP synthesis, thereby attenuating death signaling toward apoptosis and necrosis.
    Antioxidants and Redox Signaling 03/2001; 3(1):103-12. · 7.19 Impact Factor
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    ABSTRACT: Ischemic preconditioning combined with potassium cardioplegia does not always confer additive myocardial protection. This study tested the hypothesis that the efficacy of ischemic preconditioning under potassium cardioplegia is dependent on protein kinase C isoform. Isolated and crystalloid-perfused rat hearts underwent 5 cycles of 1 minute of ischemia and 5 minutes of reperfusion (low-grade ischemic preconditioning) or 3 cycles of 5 minutes of ischemia and 5 minutes of reperfusion (high-grade ischemic preconditioning) or time-matched continuous perfusion. These hearts received a further 5 minutes of infusion of normal buffer or oxygenated potassium cardioplegic solution. The isoform nonselective protein kinase C inhibitor chelerythrine (5 micromol/L) was administered throughout the preischemic period. All hearts underwent 35 minutes of normothermic global ischemia followed by 30 minutes of reperfusion. Isovolumic left ventricular function and creatine kinase release were measured as the end points of myocardial protection. Distribution of protein kinase C alpha, delta, and epsilon in the cytosol and the membrane fractions were analyzed by Western blotting and quantified by a densitometric assay. Low-grade ischemic preconditioning was almost as beneficial as potassium cardioplegia in improving functional recovery; left ventricular developed pressure 30 minutes after reperfusion was 70 +/- 15 mm Hg (P <.01) in low-grade ischemic preconditioning and 77 +/- 14 mm Hg (P <.001) in potassium cardioplegia compared with values found in unprotected control hearts (39 +/- 12 mm Hg). Creatine kinase release during reperfusion was also equally inhibited by low-grade ischemic preconditioning (18.2 +/- 10.6 IU/g dry weight, P <.05) and potassium cardioplegia (17.6 +/- 6.7 IU/g, P <.01) compared with control values. However, low-grade ischemic preconditioning in combination with potassium cardioplegia conferred no significant additional myocardial protection; left ventricular developed pressure was 80 +/- 17 mm Hg, and creatine kinase release was 14.8 +/- 11.0 IU/g. In contrast, high-grade ischemic preconditioning with potassium cardioplegia conferred better myocardial protection than potassium cardioplegia alone; left ventricular developed pressure was 121 +/- 16 mm Hg (P <.001), and creatine kinase release was 8.3 +/- 5.8 IU/g (P <.05). Chelerythrine itself had no significant effect on functional recovery and creatine kinase release in the control hearts, but it did inhibit the salutary effects not only of low-grade and high-grade ischemic preconditioning but also those of potassium cardioplegia. Low-grade ischemic preconditioning and potassium cardioplegia enhanced translocation of protein kinase C alpha to the membrane, whereas high-grade ischemic preconditioning also enhanced translocation of protein kinase C delta and epsilon. Chelerythrine inhibited translocation of all 3 protein kinase C isoforms. These results suggest that myocardial protection by low-grade ischemic preconditioning and potassium cardioplegia are mediated through enhanced translocation of protein kinase C alpha to the membrane. It is therefore suggested that activation of the novel protein kinase C isoforms is necessary to potentiate myocardial protection under potassium cardioplegia.
    Journal of Thoracic and Cardiovascular Surgery 02/2001; 121(1):137-48. · 3.53 Impact Factor
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    ABSTRACT: Cryopreserved valve allografts have proven satisfactory in aortic and pulmonary positions but not mitrally because of the difficulty in properly aligning the mitral valve allograft due to the complex subvalvular apparatus. To make the surgical procedure easier, we developed a freehand cryopreserved mitral valve allograft with a flexible ring. Whole cryopreserved mitral valve allografts with the papillary muscle, chordae, and leaflets from donor pigs were implanted mitrally in recipient pigs under cardiopulmonary bypass divided into 2 experimental groups; control allografts without the ring (n = 6) (CA group) and allografts with a flexible ring (n = 7) (RA group). Postimplantation hemodynamics and valvular function were evaluated by measuring arterial pressure, left ventricular end diastolic pressure, and left atrial pressure and by evaluating 2-dimensional echocardiography. Allografts were evaluated pathohistologically after cryopreservation and surgery by light microscopy. Hemodynamics did not differ significantly between groups. Aortic cross-clamping and Cardiopulmonary bypass times were significantly shorter in the RA group than the CA group (p < 0.05). Pigs requiring optional procedures with sutured annuloplasty and valvuloplasty numbered more in the CA group than the RA group. Postoperative echocardiography showed satisfactory mitral valve opening in diastole and good leaflet coaptation in systole in both groups. Light microscopic examination of cryopreserved allografts after surgery showed almost normal structures. Acute hemodynamic function and morphology of freehand cryopreserved valve allografts implanted mitrally in pigs proved acceptable. Adaptation of the flexible ring to allografts might be useful for technical benefit to facilitate accurate positioning of mitral subvalvular apparatus at implantation.
    The Japanese Journal of Thoracic and Cardiovascular Surgery 01/2001; 48(12):775-81.
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    ABSTRACT: Although fibrin sealant (Beriplast, Aventis Behring, Marburg, Germany) has been widely used as a supplementary measure for hemostasis during cardiac surgery in Europe and is becoming popular in the United States, the pharmocokinetics of fibrin sealant applied in pericardial space has not been elucidated. A small incision was made on the epicardial surface of the left ventricle of a rat, and the incision was sutured. Total 0.2 ml of fibrin sealant containing iodine 125 (125I)-labeled fibrinogen, aprotinin, blood coagulation factor XIII and thrombin was applied to the area around the suture line. Distributions of 125I-labeled fibrinogen in the heart on postoperative days 1, 3, 7, and 14 were 48.2% +/- 1.8%, 20.7% +/- 2.2%, 0.15% +/- 0.02%, and 0.01% +/- 0.02%, respectively. The radioactivity was negligible in the blood, liver, spleen, and kidney except for the thyroid in which the radioactivity increased to 7.9% +/- 0.7% and 4.3% +/- 0.4%, respectively, on postoperative days 7 and 14. Iodine 125-labeled fibrinogen concentrations of the heart and other organs showed a similar change in the time course of distribution. Dense and thick fibrin network, observed on postoperative day 1, had dissipated and was thinner with collagen formation by postoperative day 7. Fibrin sealant applied to the pericardial cavity regresses rapidly and plays an important role in wound healing.
    The Annals of Thoracic Surgery 01/2001; 70(6):2132-6. · 3.45 Impact Factor
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    ABSTRACT: 1. Na+/H+ exchange has been implicated in the mechanism of reperfusion injury. We examined the effects of the cardiac-specific Na+/H+ exchange inhibitor cariporide (HOE 642) on postischaemic recovery of cardiac function and cardiomyocyte cell death (i.e. necrosis and apoptosis). 2. Rat isolated and buffer-perfused hearts were subjected to 25 min normothermic global ischaemia followed by 120 min reperfusion. Cariporide (10 micromol/L) or its vehicle (0.01% dimethylsulphoxide) was administered for 15 min before ischaemia and for the first 30 min after reperfusion. 3. Cariporide significantly improved the recovery of isovolumic left ventricular function (heart rate, left ventricular developed pressure and left ventricular end-diastolic pressure) and coronary flow throughout reperfusion. Creatine kinase release during reperfusion was significantly less in the cariporide-treated heart. In situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL)-positive cardiomyocytes were also significantly less in the cariporide-treated heart after 120 min reperfusion. Electron microscopy showed necrotic changes without typical apoptotic features in cardiomyocytes after reperfusion. Such necrotic changes were mitigated by cariporide. Simultaneous detection of necrotic and apoptotic cardiomyocytes using propidium iodide (PI) and Annexin V revealed that cardiomyocytes in the infarct area were stained with only PI or both PI and Annexin V. Cariporide did not alter the pattern of cardiomyocyte staining with PI and Annexin V, although the number of cardiomyocytes stained with PI or PI plus Annexin V was less than that in vehicle-treated hearts. 4. These results suggest that apoptosis is not a major manifestation of cardiomyocyte cell death in the ischaemic-reperfused myocardium and a cariporide-sensitive mechanism of reperfusion injury promotes both necrotic and apoptotic processes of cell death.
    Clinical and Experimental Pharmacology and Physiology 01/2001; 27(5-6):387-93. · 2.16 Impact Factor
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    ABSTRACT: The molecular mechanism of neointimal hyperplasia after vein graft surgery remains elusive. Vacuolar H(+)-ATPase (V-ATPase) is involved in intracellular trafficking and may play a crucial role in neointimal cell growth. Cultured human saphenous vein segments developed neointimal formation within 10 days. Neointimal cells were positive for vimentin and alpha-smooth muscle actin but negative for desmin, which is indicative of myofibroblasts. Those myofibroblasts were found to have originated from periadventitial fibroblasts, which upregulated the expression of 16-kDa proteolipid of V-ATPase before proliferation and phenotypic modulation. Neointimal myofibroblast growth and survival were highly sensitive to inhibition of V-ATPase by bafilomycin A(1) (BA(1)), because the incorporation of [(3)H]thymidine into the myofibroblasts was significantly inhibited by nanomolar concentrations of BA(1) and apoptotic cell death was induced by a similar concentration range of BA(1). In contrast, endothelial cells and differentiated smooth muscle cells were resistant to apoptosis by BA(1). These results suggest that V-ATPase plays a crucial role in growth and phenotypic modulation of myofibroblasts that contributes to neointimal formation in cultured human saphenous vein.
    Circulation 12/2000; 102(19 Suppl 3):III269-74. · 15.20 Impact Factor
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    ABSTRACT: SUMMARY1. Na+/H+ exchange has been implicated in the mechanism of reperfusion injury. We examined the effects of the cardiac-specific Na+/H+ exchange inhibitor cariporide (HOE 642) on postischaemic recovery of cardiac function and cardiomyocyte cell death (i.e. necrosis and apoptosis).2. Rat isolated and buffer-perfused hearts were subjected to 25 min normothermic global ischaemia followed by 120 min reperfusion. Cariporide (10 μmol/L) or its vehicle (0.01% dimethylsulphoxide) was administered for 15 min before ischaemia and for the first 30 min after reperfusion.3. Cariporide significantly improved the recovery of isovolumic left ventricular function (heart rate, left ventricular developed pressure and left ventricular end-diastolic pressure) and coronary flow throughout reperfusion. Creatine kinase release during reperfusion was significantly less in the cariporide-treated heart. In situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling (TUNEL)- positive cardiomyocytes were also significantly less in the cariporide-treated heart after 120 min reperfusion. Electron microscopy showed necrotic changes without typical apoptotic features in cardiomyocytes after reperfusion. Such necrotic changes were mitigated by cariporide. Simultaneous detection of necrotic and apoptotic cardiomyocytes using propidium iodide (PI) and Annexin V revealed that cardiomyocytes in the infarct area were stained with only PI or both PI and Annexin V. Cariporide did not alter the pattern of cardiomyocyte staining with PI and Annexin V, although the number of cardiomyocytes stained with PI or PI plus Annexin V was less than that in vehicle-treated hearts.4. These results suggest that apoptosis is not a major manifestation of cardiomyocyte cell death in the ischaemic– reperfused myocardium and a cariporide-sensitive mechanism of reperfusion injury promotes both necrotic and apoptotic processes of cell death.
    Clinical and Experimental Pharmacology and Physiology 04/2000; 27(5‐6):387 - 393. · 2.16 Impact Factor
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    ABSTRACT: Insulin-like growth factor-I (IGF-I) has been shown to produce a short-term positive inotropic effect (PIE) in the myocardium under nonischemic conditions. IGF-I also conferred cytoprotection against ischemia and reperfusion injury in various organs. IGF-I may, therefore, facilitate the recovery of postischemic cardiac function. Isolated and crystalloid-perfused rat heart was subjected to 25 min of normothermic ischemia followed by 30 min of reperfusion. IGF-I produced PIE in a dose-dependent manner at concentrations ranging between 1 and 100 nM under nonischemic conditions. Although 1 nM isoproterenol produced much greater PIE and myocardial energy conversion efficiency (MECE) than did 65 nM IGF-I in this condition, the same concentration of IGF-I administered during reperfusion conferred better recovery of left ventricular function and MECE compared with isoproterenol. The improved cardiac performance by IGF-I was associated with lower release of creatine kinase (CK). Wortmannin (100 nM), a specific inhibitor of phosphatidylinositol kinase (PI-3 kinase), abrogated IGF-I-induced improvement of contractile function and inhibition of CK release in the postischemic heart. We conclude that IGF-I administered during reperfusion accelerates recovery of cardiac performance and mitigates myocardial injury through a wortmannin-sensitive mechanism.
    Journal of Cardiovascular Pharmacology 03/2000; 35(2):275-81. · 2.38 Impact Factor
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    ABSTRACT: The gene encoding human pancreatic ribonuclease 1 (hpRNasel) was fused with a gene encoding human epidermal growth factor (hEGF). The hybrid human protein was isolated from Escherichia coli inclusion bodies, refolded and purified to homogeneity. The fusion protein competed with 125I-hEGF for binding to hEGF receptors (EGFR) and had ribonucleolytic activities approaching those of hpRNase1. Several conformations having different enzymatic activities could be detected after reversed-phase high-performance liquid chromatographic analysis, the less hydrophobic molecules being the most active. The hybrid protein was specifically cytotoxic to A431, an EGFR overexpressing squamous carcinoma cell line, with an IC50 of approximately 10(-7) M. In contrast, recombinant hpRNase1 had an IC50 higher than 10(-4) M. A mixture of free hEGF and free hpRNasel was not more cytotoxic than hpRNasel alone and no cytotoxicity was detected in EGFR-deficient control cells. Taken together, these data suggest that this construct might be useful for targeted therapy of esophageal, lung and other squamous cell carcinomas and also breast cancers overexpressing EGFR, which correlate with a poor prognosis and cannot be cured by surgery alone. Engineering hybrid molecules with endogenous human proteins for targeted therapy may alleviate the dose-limiting immunogenicity and toxicity of conventional immunotoxins.
    Protein engineering 01/1999; 11(12):1285-92.
  • Gastroenterology 01/1998; 114. · 12.82 Impact Factor