Semin Thromb Hemost 2005; 31(6): 659-672
DOI: 10.1055/s-2005-925472
Copyright © 2005 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA.

Molecular Biology of ADAMTS13 and Diagnostic Utility of ADAMTS13 Proteolytic Activity and Inhibitor Assays

Suresh G. Shelat1 , 3 , Jihui Ai1 , X. Long Zheng1 , 2 , 3
  • 1Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia
  • 2Assistant Professor, Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia
  • 3The University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania
Weitere Informationen

Publikationsverlauf

Publikationsdatum:
30. Dezember 2005 (online)

ABSTRACT

ADAMTS13, a reprolysin-like metalloprotease, limits platelet-rich thrombus formation in the small arteries by cleaving von Willebrand factor (vWF) at the Tyr1605-Met1606 peptide bond. Deficiency of plasma ADAMTS13 activity, due to either an inherited or an acquired etiology, may lead to a potentially lethal syndrome, thrombotic thrombocytopenic purpura (TTP). Molecular cloning and characterization of the ADAMTS13 gene have provided further insight into the structure-function relationships, biosynthesis, and regulation of the ADAMTS13 protease, in addition to understanding the pathogenesis of TTP and perhaps other thrombotic disorders. ADAMTS13 consists of a short propeptide, a typical reprolysin-like metalloprotease domain, followed by a disintegrin-like domain, first thrombospondin type 1 (TSP1) repeat, Cys-rich domain, and spacer domain. The carboxyl terminus of ADAMTS13 has seven more TSP1 repeats and two CUB domains. ADAMTS13 is synthesized mainly in hepatic stellate cells, but also in vascular endothelial cells. Recognition and cleavage of vWF require the proximal carboxyl terminal domains, but not the middle and distal carboxyl terminal domains. Cleavage of vWF appears to be modulated by shear force, binding to platelet or platelet glycoprotein-1bα, heparin, inflammatory cytokine (interleukin-6), and chloride ion. At the site of thrombus formation, the ADAMTS13 may be inactivated by thrombin, plasmin, and factor Xa. Having a sensitive and specific assay for ADAMTS13 activity is not only critical to understand the basic biology of ADAMTS13 protease, but also to facilitate a more timely and accurate clinical diagnosis of TTP, and to initiate potentially life-saving plasma exchange therapy. Although many assays have been developed and tested for clinical applications, the fluorescent resonance energy transfer-vWF73 assay appears to be the simplest and most promising assay to date.

REFERENCES

  • 1 Fujikawa K, Suzuki H, McMullen B, Chung D. Purification of human von Willebrand factor-cleaving protease and its identification as a new member of the metalloproteinase family.  Blood. 2001;  98 1662-1666
  • 2 Gerritsen H E, Robles R, Lämmle B, Furlan M. Partial amino acid sequence of purified von Willebrand factor-cleaving protease.  Blood. 2001;  98 1654-1661
  • 3 Soejima K, Mimura N, Hirashima M et al.. A novel human metalloprotease synthesized in the liver and secreted into the blood: possibly, the von Willebrand factor-cleaving protease?.  J Biochem (Tokyo). 2001;  130 475-480
  • 4 Zheng X, Chung D, Takayama T K et al.. Structure of von Willebrand factor-cleaving protease (ADAMTS13), a metalloprotease involved in thrombotic thrombocytopenic purpura.  J Biol Chem. 2001;  276 41059-41063
  • 5 Levy G G, Nichols W C, Lian E C et al.. Mutations in a member of the ADAMTS gene family cause thrombotic thrombocytopenic purpura.  Nature. 2001;  413 488-494
  • 6 Cal S, Obaya A J, Llamazares M et al.. Cloning, expression analysis, and structural characterization of seven novel human ADAMTSs, a family of metalloproteinases with disintegrin and thrombospondin-1 domains.  Gene. 2002;  283 49-62
  • 7 Plaimauer B, Zimmermann K, Volkel D et al.. Cloning, expression, and functional characterization of the von Willebrand factor-cleaving protease (ADAMTS13).  Blood. 2002;  100 3626-3632
  • 8 Furlan M, Robles R, Lämmle B. Partial purification and characterization of a protease from human plasma cleaving von Willebrand factor to fragments produced by in vivo proteolysis.  Blood. 1996;  87 4223-4234
  • 9 Tsai H M. Physiologic cleavage of von Willebrand factor by a plasma protease is dependent on its conformation and requires calcium ion.  Blood. 1996;  87 4235-4244
  • 10 Tsai H M, Lian E C. Antibodies to von Willebrand factor-cleaving protease in acute thrombotic thrombocytopenic purpura.  N Engl J Med. 1998;  339 1585-1594
  • 11 Moake J L. Thrombotic microangiopathies.  N Engl J Med. 2002;  347 589-600
  • 12 Furlan M. von Willebrand factor-cleaving protease in thrombotic thrombocytopenic purpura and hemolytic-uremic syndrome.  Adv Nephrol Necker Hosp. 2000;  30 71-81
  • 13 Zheng X, Majerus E M, Sadler J E. ADAMTS13 and TTP.  Curr Opin Hematol. 2002;  9 389-394
  • 14 Veyradier A, Obert B, Houllier A et al.. Specific von Willebrand factor-cleaving protease in thrombotic microangiopathies: a study of 111 cases.  Blood. 2001;  98 1765-1772
  • 15 Veyradier A, Obert B, Haddad E et al.. Severe deficiency of the specific von Willebrand factor-cleaving protease (ADAMTS 13) activity in a subgroup of children with atypical hemolytic uremic syndrome.  J Pediatr. 2003;  142 310-317
  • 16 Vesely S K, George J N, Lämmle B et al.. ADAMTS13 activity in thrombotic thrombocytopenic purpura-hemolytic uremic syndrome: relation to presenting features and clinical outcomes in a prospective cohort of 142 patients.  Blood. 2003;  102 60-68
  • 17 Zheng X L, Richard K M, Goodnough L T, Sadler J E. Effect of plasma exchange on plasma ADAMTS13 metalloprotease activity, inhibitor level, and clinical outcome in patients with idiopathic and non-idiopathic thrombotic thrombocytopenic purpura.  Blood. 2004;  103 4043-4049
  • 18 Hosler G A, Cusumano A M, Hutchins G M. Thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are distinct pathologic entities. A review of 56 autopsy cases.  Arch Pathol Lab Med. 2003;  127 834-839
  • 19 Shepard K V, Bukowski R M. The treatment of thrombotic thrombocytopenic purpura with exchange transfusions, plasma infusions, and plasma exchange.  Semin Hematol. 1987;  24 178-193
  • 20 Rock G A, Shumak K H, Buskard N A et al.. Comparison of plasma exchange with plasma infusion in the treatment of thrombotic thrombocytopenic purpura. Canadian Apheresis Study Group.  N Engl J Med. 1991;  325 393-397
  • 21 Bell W R, Braine H G, Ness P M, Kickler T S. Improved survival in thrombotic thrombocytopenic purpura-hemolytic uremic syndrome. Clinical experience in 108 patients.  N Engl J Med. 1991;  325 398-403
  • 22 Plaimauer B, Scheiflinger F. Expression and characterization of recombinant human ADAMTS-13.  Semin Hematol. 2004;  41 24-33
  • 23 Kremer Hovinga J A, Studt J D, Lämmle B. The von Willebrand factor-cleaving protease (ADAMTS-13) and the diagnosis of thrombotic thrombocytopenic purpura (TTP).  Pathophysiol Haemost Thromb. 2003;  33 417-421
  • 24 Tsai H M. Molecular mechanisms in thrombotic thrombocytopenic purpura.  Semin Thromb Hemost. 2004;  30 549-557
  • 25 Moake J L. von Willebrand factor, ADAMTS-13, and thrombotic thrombocytopenic purpura.  Semin Hematol. 2004;  41 4-14
  • 26 Sadler J E, Moake J L, Miyata T, George J N. Recent advances in thrombotic thrombocytopenic purpura.  Hematology (Am Soc Hematol Educ Program). 2004;  1 407-423
  • 27 George J N, Sadler J E, Lämmle B. Platelets: thrombotic thrombocytopenic purpura.  Hematology (Am Soc Hematol Educ Program). 2002;  1 315-334
  • 28 Kokame K, Miyata T. Genetic defects leading to hereditary thrombotic thrombocytopenic purpura.  Semin Hematol. 2004;  41 34-40
  • 29 Veyradier A, Girma J P. Assays of ADAMTS-13 activity.  Semin Hematol. 2004;  41 41-47
  • 30 Furlan M. Deficient activity of von Willebrand factor-cleaving protease in thrombotic thrombocytopenic purpura.  Expert Rev Cardiovasc Ther. 2003;  1 243-255
  • 31 Bork P, Beckmann G. The CUB domain. A widespread module in developmentally regulated proteins.  J Mol Biol. 1993;  231 539-545
  • 32 Bruno K, Volkel D, Plaimauer B et al.. Cloning, expression and functional characterization of the full-length murine ADAMTS13.  J Thromb Haemost. 2005;  3 1064-1073
  • 33 Banno F, Kaminaka K, Soejima K et al.. Identification of strain-specific variants of mouse Adamts13 gene encoding von Willebrand factor-cleaving protease.  J Biol Chem. 2004;  279 30896-30903
  • 34 Uemura M, Tatsumi K, Matsumoto M et al.. Localization of ADAMTS13 to the stellate cells of human liver.  Blood. 2005;  106 922-924
  • 35 Zhou W, Inada M, Lee T P et al.. ADAMTS13 is expressed in hepatic stellate cells.  Lab Invest. 2005;  85 780-788
  • 36 Blomhoff R, Wake K. Perisinusoidal stellate cells of the liver: important roles in retinol metabolism and fibrosis.  FASEB J. 1991;  5 271-277
  • 37 Benyon R C, Arthur M J. Extracellular matrix degradation and the role of hepatic stellate cells.  Semin Liver Dis. 2001;  21 373-384
  • 38 Okazaki I, Watanabe T, Hozawa S et al.. Molecular mechanism of the reversibility of hepatic fibrosis: with special reference to the role of matrix metalloproteinases.  J Gastroenterol Hepatol. 2000;  15(suppl) D26-D32
  • 39 Majerus E M, Zheng X, Tuley E A, Sadler J E. Cleavage of the ADAMTS13 propeptide is not required for protease activity.  J Biol Chem. 2003;  278 46643-46648
  • 40 Zheng X, Nishio K, Majerus E M, Sadler J E. Cleavage of von Willebrand factor requires the spacer domain of the metalloprotease ADAMTS13.  J Biol Chem. 2003;  278 30136-30141
  • 41 Soejima K, Matsumoto M, Kokame K et al.. ADAMTS-13 cysteine-rich/spacer domains are functionally essential for von Willebrand factor cleavage.  Blood. 2003;  102 3232-3237
  • 42 Kokame K, Matsumoto M, Soejima K et al.. Mutations and common polymorphisms in ADAMTS13 gene responsible for von Willebrand factor-cleaving protease activity.  Proc Natl Acad Sci USA. 2002;  99 11902-11907
  • 43 Kuno K, Matsushima K. ADAMTS-1 protein anchors at the extracellular matrix through the thrombospondin type I motifs and its spacing region.  J Biol Chem. 1998;  273 13912-13917
  • 44 Kuno K, Terashima Y, Matsushima K. ADAMTS-1 is an active metalloproteinase associated with the extracellular matrix.  J Biol Chem. 1999;  274 18821-18826
  • 45 Loechel F, Gilpin B J, Engvall E et al.. Human ADAM 12 (meltrin alpha) is an active metalloprotease.  J Biol Chem. 1998;  273 16993-16997
  • 46 Milla M E, Leesnitzer M A, Moss M L et al.. Specific sequence elements are required for the expression of functional tumor necrosis factor-alpha-converting enzyme (TACE).  J Biol Chem. 1999;  274 30563-30570
  • 47 Cao J, Hymowitz M, Conner C et al.. The propeptide domain of membrane type 1-matrix metalloproteinase acts as an intramolecular chaperone when expressed in trans with the mature sequence in COS-1 cells.  J Biol Chem. 2000;  275 29648-29653
  • 48 Nishio K, Anderson P J, Zheng X L, Sadler J E. Binding of platelet glycoprotein Ib alpha to von Willebrand factor domain A1 stimulates the cleavage of the adjacent domain A2 by ADAMTS13.  Proc Natl Acad Sci USA. 2004;  101 10578-10583
  • 49 Ai J, Smith P, Wang S et al.. The proximal carboxyl terminal domains of ADAMTS13 determine substrate specificity and are all required for cleavage of von Willebrand factor.  J Biol Chem. 2005;  280 29428-29434
  • 50 Kokame K, Matsumoto M, Fujimura Y, Miyata T. VWF73, a region from D1596 to R1668 of von Willebrand factor, provides a minimal substrate for ADAMTS-13.  Blood. 2003;  103 607-612
  • 51 Tsai H M. Shear stress and von Willebrand factor in health and disease.  Semin Thromb Hemost. 2003;  29 479-488
  • 52 De Cristofaro R, Peyvandi F, Palla R et al.. Role of chloride ions in the modulation of the interaction between von Willebrand factor and ADAMTS-3.  J Biol Chem. 2005;  280 23295-23302
  • 53 Bernardo A, Ball C, Nolasco L et al.. Effects of inflammatory cytokines on the release and cleavage of the endothelial cell-derived ultralarge von Willebrand factor multimers under flow.  Blood. 2004;  104 100-106
  • 54 Jenkins P V, Pasi K J, Perkins S J. Molecular modeling of ligand and mutation sites of the type A domains of human von Willebrand factor and their relevance to von Willebrand's disease.  Blood. 1998;  91 2032-2044
  • 55 Studt J D, Hovinga J A, Antoine G et al.. Fatal congenital thrombotic thrombocytopenic purpura with apparent ADAMTS13 inhibitor: in vitro inhibition of ADAMTS13 activity by hemoglobin.  Blood. 2005;  105 542-544
  • 56 Crawley J T, Lam J K, Rance J B et al.. Proteolytic inactivation of ADAMTS13 by thrombin and plasmin.  Blood. 2005;  105 1085-1093
  • 57 Antoine G, Zimmermann K, Plaimauer B et al.. ADAMTS13 gene defects in two brothers with constitutional thrombotic thrombocytopenic purpura and normalization of von Willebrand factor-cleaving protease activity by recombinant human ADAMTS13.  Br J Haematol. 2003;  120 821-824
  • 58 Assink K, Schiphorst R, Allford S et al.. Mutation analysis and clinical implications of von Willebrand factor-cleaving protease deficiency.  Kidney Int. 2003;  63 1995-1999
  • 59 Matsumoto M, Kokame K, Soejima K et al.. Molecular characterization of ADAMTS13 gene mutations in Japanese patients with Upshaw-Schulman syndrome.  Blood. 2003;  103 1305-1310
  • 60 Pimanda J E, Maekawa A, Wind T et al.. Congenital thrombotic thrombocytopenic purpura in association with a mutation in the second CUB domain of ADAMTS13.  Blood. 2004;  103 627-629
  • 61 Soejima K, Nakagaki T. Interplay between ADAMTS13 and von Willebrand factor in inherited and acquired thrombotic microangiopathies.  Semin Hematol. 2005;  42 56-62
  • 62 Furlan M, Lämmle B. Aetiology and pathogenesis of thrombotic thrombocytopenic purpura and haemolytic uraemic syndrome: the role of von Willebrand factor-cleaving protease.  Best Pract Res Clin Haematol. 2001;  14 437-454
  • 63 Uchida T, Wada H, Mizutani M et al.. Identification of novel mutations in ADAMTS13 in an adult patient with congenital thrombotic thrombocytopenic purpura.  Blood. 2004;  104 2081-2083
  • 64 Bongers T N, De Maat M P, Dippel D W et al.. Absence of Pro475Ser polymorphism in ADAMTS-13 in Caucasians.  J Thromb Haemost. 2005;  3 805 , (comment)
  • 65 Ruan C, Dai L, Su J, Wang Z. The frequency of P475S polymorphism in von Willebrand factor-cleaving protease in the Chinese population and its relevance to arterial thrombotic disorders.  Thromb Haemost. 2004;  91 1257-1258
  • 66 Majerus E M, Anderson P J, Sadler J E. Binding of ADAMTS13 to von Willebrand factor.  J Biol Chem. 2005;  280 21773-21778
  • 67 Yoo G, Blomback M, Schenck-Gustafsson K, He S. Decreased levels of von Willebrand factor-cleaving protease in coronary heart disease and thrombotic thrombocytopenic purpura: study of a simplified method for assaying the enzyme activity based on ristocetin-induced platelet aggregation.  Br J Haematol. 2003;  121 123-129
  • 68 Matsumoto M, Kokame K, Soejima K et al.. Molecular characterization of ADAMTS13 gene mutations in Japanese patients with Upshaw-Schulman syndrome.  Blood. 2004;  103 1305-1310
  • 69 Kinoshita S, Yoshioka A, Park Y D et al.. Upshaw-Schulman syndrome revisited: a concept of congenital thrombotic thrombocytopenic purpura.  Int J Hematol. 2001;  74 101-108
  • 70 Schneppenheim R, Budde U, Oyen F et al.. von Willebrand factor cleaving protease and ADAMTS13 mutations in childhood TTP.  Blood. 2003;  101 1845-1850
  • 71 Savasan S, Lee S K, Ginsburg D, Tsai H M. ADAMTS13 gene mutation in congenital thrombotic thrombocytopenic purpura with previously reported normal VWF cleaving protease activity.  Blood. 2003;  101 4449-4451
  • 72 Furlan M, Robles R, Galbusera M et al.. von Willebrand factor-cleaving protease in thrombotic thrombocytopenic purpura and the hemolytic-uremic syndrome.  N Engl J Med. 1998;  339 1578-1584
  • 73 Furlan M, Robles R, Solenthaler M, Lämmle B. Acquired deficiency of von Willebrand factor-cleaving protease in a patient with thrombotic thrombocytopenic purpura.  Blood. 1998;  91 2839-2846
  • 74 Mannucci P M, Canciani M T, Forza I et al.. Changes in health and disease of the metalloprotease that cleaves von Willebrand factor.  Blood. 2001;  98 2730-2735
  • 75 Loof A H, van Vliet H H, Kappers-Klunne M C. Low activity of von Willebrand factor-cleaving protease is not restricted to patients suffering from thrombotic thrombocytopenic purpura.  Br J Haematol. 2001;  112 1087-1088
  • 76 Bianchi V, Robles R, Alberio L et al.. Von Willebrand factor-cleaving protease (ADAMTS13) in thrombocytopenic disorders: a severely deficient activity is specific for thrombotic thrombocytopenic purpura.  Blood. 2002;  100 710-713
  • 77 Remuzzi G. Is ADAMTS-13 deficiency specific for thrombotic thrombocytopenic purpura? No.  J Thromb Haemost. 2003;  1 632-634
  • 78 Tsai H M. Is severe deficiency of ADAMTS-13 specific for thrombotic thrombocytopenic purpura? Yes.  J Thromb Haemost. 2003;  1 625-631
  • 79 Mannucci P M. Consistency of ADAMTS-13 activity assays: a moderately optimistic view.  J Thromb Haemost. 2003;  1 1880-1881
  • 80 Furlan M, Robles R, Solenthaler M et al.. Deficient activity of von Willebrand factor-cleaving protease in chronic relapsing thrombotic thrombocytopenic purpura.  Blood. 1997;  89 3097-3103
  • 81 Furlan M, Robles R, Morselli B et al.. Recovery and half-life of von Willebrand factor-cleaving protease after plasma therapy in patients with thrombotic thrombocytopenic purpura.  Thromb Haemost. 1999;  81 8-13
  • 82 Fujimura Y, Matsumoto M, Yagi H et al.. Von Willebrand factor-cleaving protease and Upshaw-Schulman syndrome.  Int J Hematol. 2002;  75 25-34
  • 83 Tsai H M, Sussman I I, Ginsburg D et al.. Proteolytic cleavage of recombinant type 2A von Willebrand factor mutants R834W and R834Q: inhibition by doxycycline and by monoclonal antibody VP-1.  Blood. 1997;  89 1954-1962
  • 84 Whitelock J L, Nolasco L, Bernardo A et al.. ADAMTS-13 activity in plasma is rapidly measured by a new ELISA method that uses recombinant VWF-A2 domain as substrate.  J Thromb Haemost. 2004;  2 485-491
  • 85 Kokame K, Nobe Y, Kokubo Y et al.. FRETS-VWF73, a first fluorogenic substrate for ADAMTS13 assay.  Br J Haematol. 2005;  129 93-100
  • 86 Furlan M, Lammle B. Deficiency of von Willebrand factor-cleaving protease in familial and acquired thrombotic thrombocytopenic purpura.  Baillieres Clin Haematol. 1998;  11 509-514
  • 87 Zheng X, Pallera A M, Goodnough L T et al.. Remission of chronic thrombotic thrombocytopenic purpura after treatment with cyclophosphamide and rituximab.  Ann Intern Med. 2003;  138 105-108
  • 88 Gerritsen H E, Turecek P L, Schwarz H P et al.. Assay of von Willebrand factor (vWF)-cleaving protease based on decreased collagen binding affinity of degraded vWF: a tool for the diagnosis of thrombotic thrombocytopenic purpura (TTP).  Thromb Haemost. 1999;  82 1386-1389
  • 89 Rick M E, Moll S, Taylor M A et al.. Clinical use of a rapid collagen binding assay for von Willebrand factor cleaving protease in patients with thrombotic thrombocytopenic purpura.  Thromb Haemost. 2002;  88 598-604
  • 90 Owen J. Inappropriate use of positive predictive value in describing the rapid collagen binding assay for von Willebrand factor cleaving protease.  Thromb Haemost. 2003;  89 768-769
  • 91 Tripodi A, Chantarangkul V, Bohm M et al.. Measurement of von Willebrand factor cleaving protease (ADAMTS-13): results of an international collaborative study involving 11 methods testing the same set of coded plasmas.  J Thromb Haemost. 2004;  2 1601-1609
  • 92 Bohm M, Vigh T, Scharrer I. Evaluation and clinical application of a new method for measuring activity of von Willebrand factor-cleaving metalloprotease (ADAMTS13).  Ann Hematol. 2002;  81 430-435
  • 93 Shenkman B, Inbal A, Tamarin I et al.. Diagnosis of thrombotic thrombocytopenic purpura based on modulation by patient plasma of normal platelet adhesion under flow condition.  Br J Haematol. 2003;  120 597-604
  • 94 Dong J F, Moake J L, Nolasco L et al.. ADAMTS-13 rapidly cleaves newly secreted ultralarge von Willebrand factor multimers on the endothelial surface under flowing conditions.  Blood. 2002;  100 4033-4039
  • 95 Zhou W, Tsai H M. An enzyme immunoassay of ADAMTS13 distinguishes patients with thrombotic thrombocytopenic purpura from normal individuals and carriers of ADAMTS13 mutations.  Thromb Haemost. 2004;  91 806-811
  • 96 Klaus C, Plaimauer B, Studt J D et al.. Epitope mapping of ADAMTS13 autoantibodies in acquired thrombotic thrombocytopenic purpura.  Blood. 2004;  103 4514-4519
  • 97 Rieger M, Mannucce P, Kremer Hovinga J A et al.. ADAMTS13 autoantibodies in patients with thrombotic microangiopathies and other immunomediated diseases.  Blood. 2005;  106 1262-1267
  • 98 Fakhouri F, Vernant J P, Veyradier A et al.. Efficiency of curative and prophylactic treatment with rituximab in ADAMTS13 deficient-thrombotic thrombocytopenic purpura: a study of 11 cases.  Blood. 2005;  106 1932-1937
  • 99 Fakhouri F, Teixeira L, Delarue R et al.. Responsiveness of thrombotic thrombocytopenic purpura to rituximab and cyclophosphamide.  Ann Intern Med. 2004;  140 314-315
  • 100 Veyradier A, Lavergne J M, Ribba A S et al.. Ten candidate ADAMTS13 mutations in six French families with congenital thrombotic thrombocytopenic purpura (Upshaw-Schulman syndrome).  J Thromb Haemost. 2004;  2 424-429
  • 101 Licht C, Stapenhorst L, Simon T et al.. Two novel ADAMTS13 gene mutations in thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome (TTP/HUS).  Kidney Int. 2004;  66 955-958

X. Long ZhengM.D. Ph.D. 

Assistant Professor, Department of Pathology and Laboratory Medicine, The Children's Hospital of Philadelphia and The University of Pennsylvania

34th St. and Civic Center Blvd, Abramson Research Center 816G, Philadelphia, PA 19104

eMail: zheng@email.chop.edu