Grading and Treatment of Acute Graft-Versus-Host Disease

  • Anar MikailovEmail author
  • Molly Plovanich
  • Arturo P. Saavedra


Acute graft-versus-host disease (aGVHD) remains a major complication and is the leading cause of nonrelapse mortality after allogeneic hematopoietic stem cell transplantation (HSCT). The most commonly involved organ is the skin, providing an opportunity for clinicians to recognize and intervene in this potentially fatal process. Appropriate grading of severity is critical to determine treatment. Therapy for advanced aGVHD is challenging. This chapter reviews the evidence for commonly studied and novel approaches that hold promise.


Graft versus Host Disease Acute Graft versus Host Disease GVHD Acute GVHD Acute Cutaneous Graft versus Host Disease Staging Graft versus Host Disease Management Graft versus Host Disease 


  1. 1.
    Ferrara JL, Deeg HJ. Graft-versus-host disease. N Engl J Med. 1991;324(10):667–74.PubMedCrossRefGoogle Scholar
  2. 2.
    Ferrara JL, Levine JE, Reddy P, Holler E. Graft-versus-host disease. Lancet. 2009;373(9674):1550–61.PubMedPubMedCentralCrossRefGoogle Scholar
  3. 3.
    Jagasia MH, Greinix HT, Arora M, Williams KM, Wolff D, Cowen EW, et al. National institutes of health consensus development project on criteria for clinical trials in chronic graft-versus-host disease: I. The 2014 diagnosis and staging working group report. Biol Blood Marrow Transplant. 2015;21(3):389–401. e1PubMedCrossRefGoogle Scholar
  4. 4.
    Hymes SR, Alousi AM, Cowen EW. Graft-versus-host disease: part I. Pathogenesis and clinical manifestations of graft-versus-host disease. J Am Acad Dermatol 2012;66(4):515 e1–515 18; quiz 533–4.Google Scholar
  5. 5.
    Glucksberg H, Storb R, Fefer A, Buckner CD, Neiman PE, Clift RA, et al. Clinical manifestations of graft-versus-host disease in human recipients of marrow from HL-A-matched sibling donors. Transplantation. 1974;18(4):295–304.PubMedCrossRefGoogle Scholar
  6. 6.
    Filipovich AH, Weisdorf D, Pavletic S, Socie G, Wingard JR, Lee SJ, et al. National institutes of health consensus development project on criteria for clinical trials in chronic graft-versus-host disease: I. Diagnosis and staging working group report. Biol Blood Marrow Transplant. 2005;11(12):945–56.PubMedCrossRefGoogle Scholar
  7. 7.
    Przepiorka D, Weisdorf D, Martin P, HG K, Beatty P, Hows J, et al. 1994 consensus conference on acute GVHD grading. Bone Marrow Transplant. 1995;15(6):825–8.PubMedGoogle Scholar
  8. 8.
    Dignan FL, Clark A, Amrolia P, Cornish J, Jackson G, Mahendra P, et al. Diagnosis and management of acute graft-versus-host disease. Br J Haematol. 2012;158(1):30–45.PubMedCrossRefGoogle Scholar
  9. 9.
    SW H, Cotliar J. Acute graft-versus-host disease following hematopoietic stem-cell transplantation. Dermatol Ther. 2011;24(4):411–23.CrossRefGoogle Scholar
  10. 10.
    Harris AC, Young R, Devine S, Hogan WJ, Ayuk F, Bunworasate U, et al. International, multicenter standardization of acute graft-versus-host disease clinical data collection: a report from the Mount Sinai acute GVHD international consortium. Biol Blood Marrow Transplant. 2016;22(1):4–10.PubMedCrossRefGoogle Scholar
  11. 11.
    Ion D, Stevenson K, Woo SB, Ho VT, Soiffer R, Antin JH, et al. Characterization of oral involvement in acute graft-versus-host disease. Biol Blood Marrow Transplant. 2014;20(11):1717–21.PubMedCrossRefGoogle Scholar
  12. 12.
    Byun HJ, Yang JI, Kim BK, Cho KH. Clinical differentiation of acute cutaneous graft-versus-host disease from drug hypersensitivity reactions. J Am Acad Dermatol. 2011;65(4):726–32.PubMedCrossRefGoogle Scholar
  13. 13.
    Bolognia JL, Cooper DL, Glusac EJ. Toxic erythema of chemotherapy: a useful clinical term. J Am Acad Dermatol. 2008;59(3):524–9.PubMedCrossRefGoogle Scholar
  14. 14.
    Maiolino A, Biasoli I, Lima J, Portugal AC, Pulcheri W, Nucci M. Engraftment syndrome following autologous hematopoietic stem cell transplantation: definition of diagnostic criteria. Bone Marrow Transplant. 2003;31(5):393–7.PubMedCrossRefGoogle Scholar
  15. 15.
    Carreras E, Fernández-Avilés F, Silva L, Guerrero M, Fernández de Larrea C, Martínez C, et al. Engraftment syndrome after auto-SCT: analysis of diagnostic criteria and risk factors in a large series from a single center. Bone Marrow Transplant. 2010;45(9):1417–22.PubMedCrossRefGoogle Scholar
  16. 16.
    Gorak E, Geller N, Srinivasan R, Espinoza-Delgado I, Donohue T, Barrett AJ, et al. Engraftment syndrome after nonmyeloablative allogeneic hematopoietic stem cell transplantation: incidence and effects on survival. Biol Blood Marrow Transplant. 2005;11:542–50.PubMedCrossRefGoogle Scholar
  17. 17.
    Sale GE, Lerner KG, Barker EA, Shulman HM, Thomas ED, et al. The skin biopsy in the diagnosis of acute graft-versus-host disease in man. Am J Pathol. 1977;89(3):621–36.PubMedPubMedCentralGoogle Scholar
  18. 18.
    Zhou Y, Barnett MJ, Rivers JK. Clinical significance of skin biopsies in the diagnosis and management of graft-vs-host disease in early postallogeneic bone marrow transplantation. Arch Dermatol. 2000;136(6):717–21.PubMedCrossRefGoogle Scholar
  19. 19.
    Kuykendall TD, Smoller BR. Lack of specificity in skin biopsy specimens to assess for acute graft-versus-host disease in initial 3 weeks after bone-marrow transplantation. J Am Acad Dermatol. 2003;49(6):1081–5.PubMedCrossRefGoogle Scholar
  20. 20.
    Firoz BF, Lee SJ, Nghiem P, Qureshi AA. Role of skin biopsy to confirm suspected acute graft-vs-host disease: results of decision analysis. Arch Dermatol. 2006;142(2):175–82.PubMedCrossRefGoogle Scholar
  21. 21.
    Barksdale SK, Oberlender SA, Barnhill RL. “Rush” skin biopsy specimens in a tertiary medical center: diagnostic yield and clinical utility. J Am Acad Dermatol. 1998;38(4):548–54.PubMedCrossRefGoogle Scholar
  22. 22.
    Gratwohl A, Hermans J, Apperley J, Arcese W, Bacigalupo A, Bandini G, et al. Acute graft-versus-host disease: grade and outcome in patients with chronic myelogenous leukemia. Working party chronic leukemia of the European group for blood and marrow Transplantation. Blood. 1995;86(2):813–8.PubMedGoogle Scholar
  23. 23.
    Levine JE, Braun TM, Harris AC, Holler E, Taylor A, Miller H, et al. A prognostic score for acute graft-versus-host disease based on biomarkers: a multicentre study. Lancet Haematol. 2015;2(1):e21–9.PubMedPubMedCentralCrossRefGoogle Scholar
  24. 24.
    Martin PJ, Rizzo JD, Wingard JR, Ballen K, Curtin PT, Cutler C, et al. First- and second-line systemic treatment of acute graft-versus-host disease: recommendations of the American Society of Blood and Marrow Transplantation. Biol Blood Marrow Transplant. 2012;18(8):1150–63.PubMedPubMedCentralCrossRefGoogle Scholar
  25. 25.
    Hoffmann P, Ermann J, Edinger M, Fathman CG, Strober S, et al. Donor-type CD4(+)CD25(+) regulatory T cells suppress lethal acute graft-versus-host disease after allogeneic bone marrow transplantation. J Exp Med. 2002;196(3):389–99.PubMedPubMedCentralCrossRefGoogle Scholar
  26. 26.
    Satake A, Schmidt AM, Nomura S, Kambayashi T, et al. Inhibition of calcineurin abrogates while inhibition of mTOR promotes regulatory T cell expansion and graft-versus-host disease protection by IL-2 in allogeneic bone marrow transplantation. PLoS One. 2014;9(3):e92888.PubMedPubMedCentralCrossRefGoogle Scholar
  27. 27.
    Peccatori J, Forcina A, Clerici D, Crocchiolo R, Vago L, Stanghellini MT, et al. Sirolimus-based graft-versus-host disease prophylaxis promotes the in vivo expansion of regulatory T cells and permits peripheral blood stem cell transplantation from haploidentical donors. Leukemia. 2015;29(2):396–405.PubMedCrossRefGoogle Scholar
  28. 28.
    Penas PF, Fernandez-Herrera J, Garcia-Diez A. Dermatologic treatment of cutaneous graft versus host disease. Am J Clin Dermatol. 2004;5(6):403–16.PubMedCrossRefGoogle Scholar
  29. 29.
    Frankel HC, Qureshi AA. Comparative effectiveness of topical calcineurin inhibitors in adult patients with atopic dermatitis. Am J Clin Dermatol. 2012;13(2):113–23.PubMedCrossRefGoogle Scholar
  30. 30.
    Van Lint MT, Uderzo C, Locasciulli A, Majolino I, Scimé R, Locatelli F, et al. Early treatment of acute graft-versus-host disease with high- or low-dose 6-methylprednisolone: a multicenter randomized trial from the Italian group for bone marrow transplantation. Blood. 1998;92(7):2288–93.PubMedGoogle Scholar
  31. 31.
    MacMillan ML, DeFor TE, Weisdorf DJ. The best endpoint for acute GVHD treatment trials. Blood. 2010;115(26):5412–7.PubMedCrossRefGoogle Scholar
  32. 32.
    Holtan SG, Pasquini M, Weisdorf DJ. Acute graft-versus-host disease: a bench-to-bedside update. Blood. 2014;124(3):363–73.PubMedPubMedCentralCrossRefGoogle Scholar
  33. 33.
    Greinix HT, Volc-Platzer B, Knobler RM. Extracorporeal photochemotherapy in the treatment of severe graft-versus-host disease. Leuk Lymphoma. 2000;36(5–6):425–34.PubMedCrossRefGoogle Scholar
  34. 34.
    Knobler R, Berlin G, Calzavara-Pinton P, Greinix H, Jaksch P, Laroche L et al. Guidelines on the use of extracorporeal photopheresis. J Eur Acad Dermatol Venereol 2014;28 Suppl 1:1–37.Google Scholar
  35. 35.
    Zhang H, Chen R, Cheng J, Jin N, Chen B. Systematic review and meta-analysis of prospective studies for ECP treatment in patients with steroid-refractory acute GVHD. Patient Prefer Adherence. 2015;9:105–11.PubMedPubMedCentralGoogle Scholar
  36. 36.
    Perfetti P, Carlier P, Strada P, Gualandi F, Occhini D, Van Lint MT, et al. Extracorporeal photopheresis for the treatment of steroid refractory acute GVHD. Bone Marrow Transplant. 2008;42(9):609–17.PubMedCrossRefGoogle Scholar
  37. 37.
    Budde H, Kolb S, Salinas Tejedor L, Wulf G, Reichardt HM, Riggert J, et al. Modified extracorporeal photopheresis with cells from a healthy donor for acute graft-versus-host disease in a mouse model. PLoS One. 2014;9(8):e105896.PubMedPubMedCentralCrossRefGoogle Scholar
  38. 38.
    Taylor PA, Lees CJ, Blazar BR. The infusion of ex vivo activated and expanded CD4(+)CD25(+) immune regulatory cells inhibits graft-versus-host disease lethality. Blood. 2002;99(10):3493–9.PubMedCrossRefGoogle Scholar
  39. 39.
    Trzonkowski P, Bieniaszewska M, Juścińska J, Dobyszuk A, Krzystyniak A, Marek N, et al. First-in-man clinical results of the treatment of patients with graft versus host disease with human ex vivo expanded CD4+CD25+CD127- T regulatory cells. Clin Immunol. 2009;133(1):22–6.PubMedCrossRefGoogle Scholar
  40. 40.
    Brunstein CG, Miller JS, Cao Q, McKenna DH, Hippen KL, Curtsinger J, et al. Infusion of ex vivo expanded T regulatory cells in adults transplanted with umbilical cord blood: safety profile and detection kinetics. Blood. 2011;117(3):1061–70.PubMedPubMedCentralCrossRefGoogle Scholar
  41. 41.
    Ohnuma K, Ishii T, Iwata S, Hosono O, Kawasaki H, Uchiyama M, et al. G1/S cell cycle arrest provoked in human T cells by antibody to CD26. Immunology. 2002;107(3):325–33.PubMedPubMedCentralCrossRefGoogle Scholar
  42. 42.
    Bacigalupo A, Corte G, Ramarli D, van Lint MT, Frassoni F, Marmont A. Intravenous monoclonal antibody (BT 5/9) for the treatment of acute graft-versus-host disease. Acta Haematol. 1985;73(3):185–6.PubMedCrossRefGoogle Scholar
  43. 43.
    Dominietto A. CD26, ANTI-CD26 and GVHD 1. Lecture presented at XII Congresso Nazionale SIES 2012 Simposio GITMO, 2012, Rome.Google Scholar
  44. 44.
    Arai S, Margolis J, Zahurak M, Anders V, Vogelsang GB. Poor outcome in steroid-refractory graft-versus-host disease with antithymocyte globulin treatment. Biol Blood Marrow Transplant. 2002;8(3):155–60.PubMedCrossRefGoogle Scholar
  45. 45.
    Nishimoto M, Nakamae H, Koh H, Nakamae M, Hirose A, Hayashi Y, et al. Response-guided therapy for steroid-refractory acute GVHD starting with very-low-dose antithymocyte globulin. Exp Hematol. 2015;43(3):177–9.PubMedCrossRefGoogle Scholar
  46. 46.
    Martin PJ, Schoch G, Fisher L, Byers V, Anasetti C, Appelbaum FR, et al. A retrospective analysis of therapy for acute graft-versus-host disease: initial treatment. Blood. 1990;76(8):1464–72.PubMedGoogle Scholar
  47. 47.
    Kitajima T, Imamura S. Graft-versus-host reaction enhanced by ultraviolet radiation. Arch Dermatol Res. 1993;285(8):499–501.PubMedCrossRefGoogle Scholar
  48. 48.
    Weisdorf D, Haake R, Blazar B, Miller W, McGlave P, Ramsay N, et al. Treatment of moderate/severe acute graft-versus-host disease after allogeneic bone marrow transplantation: an analysis of clinical risk features and outcome. Blood. 1990;75(4):1024–30.PubMedGoogle Scholar
  49. 49.
    MacMillan ML, Weisdorf DJ, Wagner JE, DeFor TE, Burns LJ, Ramsay NK, et al. Response of 443 patients to steroids as primary therapy for acute graft-versus-host disease: comparison of grading systems. Biol Blood Marrow Transplant. 2002;8(7):387–94.PubMedCrossRefGoogle Scholar
  50. 50.
    Mielcarek M, Storer BE, Boeckh M, Carpenter PA, McDonald GB, Deeg HJ, et al. Initial therapy of acute graft-versus-host disease with low-dose prednisone does not compromise patient outcomes. Blood. 2009;113(13):2888–94.PubMedPubMedCentralCrossRefGoogle Scholar
  51. 51.
    Benito AI, Storer BE, Boeckh M, Carpenter PA, McDonald GB, Deeg HJ, Nash RA, et al. Sirolimus (rapamycin) for the treatment of steroid-refractory acute graft-versus-host disease. Transplantation. 2001;72(12):1924–9.PubMedCrossRefGoogle Scholar
  52. 52.
    Hoda D, Pidala J, Salgado-Vila N, Kim J, Perkins J, Bookout R, Field T, et al. Sirolimus for treatment of steroid-refractory acute graft-versus-host disease. Bone Marrow Transplant. 2010;45(8):1347–51.PubMedCrossRefGoogle Scholar
  53. 53.
    Pidala J, Kim J, Anasetti C. Sirolimus as primary treatment of acute graft-versus-host disease following allogeneic hematopoietic cell transplantation. Biol Blood Marrow Transplant. 2009;15(7):881–5.PubMedPubMedCentralCrossRefGoogle Scholar
  54. 54.
    Ghez D, Rubio MT, Maillard N, Suarez F, Chandesris MO, Delarue R, et al. Rapamycin for refractory acute graft-versus-host disease. Transplantation. 2009;88(9):1081–7.PubMedCrossRefGoogle Scholar
  55. 55.
    MacMillan ML et al. Early antithymocyte globulin therapy improves survival in patients with steroid-resistant acute graft-versus-host disease. Biol Blood Marrow Transplant. 2002;8(1):40–6.PubMedCrossRefGoogle Scholar
  56. 56.
    Khoury H, Weisdorf DJ, Davies SM, DeFor TE, Burns LJ, Ramsay NK, et al. Treatment of steroid-resistant acute graft-versus-host disease with anti-thymocyte globulin. Bone Marrow Transplant. 2001;27(10):1059–64.PubMedCrossRefGoogle Scholar
  57. 57.
    Cragg L, Blazar BR, Defor T, Kolatker N, Miller W, Kersey J, et al. A randomized trial comparing prednisone with antithymocyte globulin/prednisone as an initial systemic therapy for moderately severe acute graft-versus-host disease. Biol Blood Marrow Transplant. 2000;6(4A):441–7.PubMedCrossRefGoogle Scholar
  58. 58.
    Basara N, Blau WI, Römer E, Rudolphi M, Bischoff M, Kirsten D, et al. Mycophenolate mofetil for the treatment of acute and chronic GVHD in bone marrow transplant patients. Bone Marrow Transplant. 1998;22(1):61–5.PubMedCrossRefGoogle Scholar
  59. 59.
    Furlong T, Martin P, Flowers ME, Carnevale-Schianca F, Yatscoff R, Chauncey T, et al. Therapy with mycophenolate mofetil for refractory acute and chronic GVHD. Bone Marrow Transplant. 2009;44(11):739–48.PubMedPubMedCentralCrossRefGoogle Scholar
  60. 60.
    Krejci M, Doubek M, Buchler T, Brychtova Y, Vorlicek J, Mayer J, et al. Mycophenolate mofetil for the treatment of acute and chronic steroid-refractory graft-versus-host disease. Ann Hematol. 2005;84(10):681–5.PubMedCrossRefGoogle Scholar
  61. 61.
    Alousi AM, Weisdorf DJ, Logan BR, Bolaños-Meade J, Carter S, Difronzo N, et al. Etanercept, mycophenolate, denileukin, or pentostatin plus corticosteroids for acute graft-versus-host disease: a randomized phase 2 trial from the blood and marrow transplant clinical trials network. Blood. 2009;114(3):511–7.PubMedPubMedCentralCrossRefGoogle Scholar
  62. 62.
    Pidala J, Kim J, Perkins J, Field T, Fernandez H, Perez L, et al. Mycophenolate mofetil for the management of steroid-refractory acute graft vs host disease. Bone Marrow Transplant. 2010;45(5):919–24.PubMedCrossRefGoogle Scholar
  63. 63.
    Bolanos-Meade J, Logan BR, Alousi AM, Antin JH, Barowski K, Carter SL, et al. Phase 3 clinical trial of steroids/mycophenolate mofetil vs steroids/placebo as therapy for acute GVHD: BMT CTN 0802. Blood 2014;124(22):3221–3227; quiz 3335.Google Scholar
  64. 64.
    de Lavallade H, Mohty M, Faucher C, Fürst S, El-Cheikh J, Blaise D, et al. Low-dose methotrexate as salvage therapy for refractory graft-versus-host disease after reduced-intensity conditioning allogeneic stem cell transplantation. Haematologica. 2006;91(10):1438–40.PubMedGoogle Scholar
  65. 65.
    Huang XJ, Jiang Q, Chen H, Xu L, Liu D, Chen Y, et al. Low-dose methotrexate for the treatment of graft-versus-host disease after allogeneic hematopoietic stem cell transplantation. Bone Marrow Transplant. 2005;36(4):343–8.PubMedCrossRefGoogle Scholar
  66. 66.
    Wang Y, LP X, Liu KY, Liu DH, Wang J, Chen H, et al. Low-dose MTX combined with low-dose methylprednisolone as a first-line therapy for the treatment of acute GVHD: safety and feasibility. Bone Marrow Transplant. 2011;46(6):892–8.PubMedCrossRefGoogle Scholar
  67. 67.
    Inagaki J, Nagatoshi Y, Hatano M, Isomura N, Sakiyama M, Okamura J, Low-dose MTX. for the treatment of acute and chronic graft-versus-host disease in children. Bone Marrow Transplant. 2008;41(6):571–7.PubMedCrossRefGoogle Scholar
  68. 68.
    Couriel DR, Saliba R, de Lima M, Giralt S, Andersson B, Khouri I, Hosing C, et al. A phase III study of infliximab and corticosteroids for the initial treatment of acute graft-versus-host disease. Biol Blood Marrow Transplant. 2009;15(12):1555–62.PubMedPubMedCentralCrossRefGoogle Scholar
  69. 69.
    Gomez-Almaguer D, Ruiz-Argüelles GJ, del Carmen Tarín-Arzaga L, González-Llano O, Gutiérrez-Aguirre H, Cantú-Rodríguez O, et al. Alemtuzumab for the treatment of steroid-refractory acute graft-versus-host disease. Biol Blood Marrow Transplant. 2008;14(1):10–5.PubMedCrossRefGoogle Scholar
  70. 70.
    Schub N, Günther A, Schrauder A, Claviez A, Ehlert C, Gramatzki M, et al. Therapy of steroid-refractory acute GVHD with CD52 antibody alemtuzumab is effective. Bone Marrow Transplant. 2011;46(1):143–7.PubMedCrossRefGoogle Scholar
  71. 71.
    Schnitzler M, Hasskarl J, Egger M, Bertz H, Finke J. Successful treatment of severe acute intestinal graft-versus-host resistant to systemic and topical steroids with alemtuzumab. Biol Blood Marrow Transplant. 2009;15(8):910–8.PubMedCrossRefGoogle Scholar
  72. 72.
    Ho VT, Zahrieh D, Hochberg E, Micale E, Levin J, Reynolds C, et al. Safety and efficacy of denileukin diftitox in patients with steroid-refractory acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation. Blood. 2004;104(4):1224–6.PubMedCrossRefGoogle Scholar
  73. 73.
    Shaughnessy PJ, Bachier C, Grimley M, Freytes CO, Callander NS, Essell JH, et al. Denileukin diftitox for the treatment of steroid-resistant acute graft-versus-host disease. Biol Blood Marrow Transplant. 2005;11(3):188–93.PubMedCrossRefGoogle Scholar
  74. 74.
    Massenkeil G, Rackwitz S, Genvresse I, Rosen O, Dörken B, Arnold R. Basiliximab is well tolerated and effective in the treatment of steroid-refractory acute graft-versus-host disease after allogeneic stem cell transplantation. Bone Marrow Transplant. 2002;30(12):899–903.PubMedCrossRefGoogle Scholar
  75. 75.
    Schmidt-Hieber M, Fietz T, Knauf W, Uharek L, Hopfenmüller W, Thiel E, et al. Efficacy of the interleukin-2 receptor antagonist basiliximab in steroid-refractory acute graft-versus-host disease. Br J Haematol. 2005;130(4):568–74.PubMedCrossRefGoogle Scholar
  76. 76.
    Wang JZ, Liu KY, LP X, Liu DH, Han W, Chen H, et al. Basiliximab for the treatment of steroid-refractory acute graft-versus-host disease after unmanipulated HLA-mismatched/haploidentical hematopoietic stem cell transplantation. Transplant Proc. 2011;43(5):1928–33.PubMedCrossRefGoogle Scholar
  77. 77.
    Levine JE, Paczesny S, Mineishi S, Braun T, Choi SW, Hutchinson RJ, et al. Etanercept plus methylprednisolone as initial therapy for acute graft-versus-host disease. Blood. 2008;111(4):2470–5.PubMedPubMedCentralCrossRefGoogle Scholar

Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  • Anar Mikailov
    • 1
    Email author
  • Molly Plovanich
    • 1
  • Arturo P. Saavedra
    • 2
  1. 1.Department of DermatologyBrigham and Women’s Hospital and Harvard Medical SchoolBostonUSA
  2. 2.Department of DermatologyMassachusetts General Hospital and Harvard Medical SchoolBostonUSA

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