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Human parvovirus B19 infection associated with idiopathic thrombocytopenic purpura in a child following liver transplantation
Journal of Hepaiology 1991; 27: 934-936 Printed in Denmark . AN rights reserved Munksgaard
.
Copyright 0 European Association for the Study of the Liver 1997
Copenhagen
Journalof Hepatology ISSN 0168-8278
Case Report
Human parvovirusB19 infection associated with idiopathic thrombocytopenicpurpurain a child following liver transplantation Nimer Assy 1,4, Eldad Rosentha12, Anna Hazani3, Amos Etzioni2s5 and Yaacov Baruch1,4,5 ‘Liver Unit, ‘Department of Pediatrics A, ‘Hematology Clinic, and 4Department of Medicine B, Rambam Medical Center, and ‘The Bruce Rappaport Faculty of Medicine, Technion-Institute of Technology, Haifa, Israel
Background/Aims: Idiopathic (autoimmune) thromhocytopenic purpura has been previously reported as a rare complication in children following parvovirus B19 infection. In the immunocompromised host who is unable to produce neutralizing antibody, an infection with parvovirus B19 can persist and cause chronic bone marrow failure. Methods: We describe a child who had undergone liver transplantation and who had idiopathic thrombocytopenic purpura, whose history and laboratory findings suggested parvovirus B19 infection. The infection disappeared without persistent viremia, and the thrombo-
cytopenia responded completely to the administration of gamma globulin while the patient was undergoing chronic immunosuppression therapy. Results/Conclusion: Transplant physicians need to be aware of this complication, and parvovirus B19 infection should be included in the differential diagnosis of liver recipients presenting with severe thrombocytopenia.
ROMBOCYTOPENIA is a well-recognized complication following liver transplantation and may occur at any time postoperatively (1). It may be related to allograft dysfunction (primary non-function), drug toxicity (immunosuppression), graft-versus-host disease, and common viral infections (2,3). Idiopathic thrombocytopenic purpura (ITP) has already been associated with several viral infections such as measles, Epstein-Barr virus, and human immunodeficiency virus (4,5). Recently, ITP was also reported as a rare complication in children following parvovirus B19 infection (6). However, there has been no previous report of an association between ITP and parvovirus B19 infection in a liver transplant patient while under immunosuppresive therapy. This observation has several important clinical implications for transplantation hepatologists and surgeons. First, an infection with parvovirus B19 in the immunocompromised liver recipient can persist and cause chronic bone marrow fail-
ure (7,s). Second, because antiparvovirus antibodies are most commonly acquired between 5 and 15 years of age, young children who have undergone liver transplantation seem likely to experience infection with parvovirus while receiving immunosuppression therapy. Moreover, a seronegative transplant recipient may be at relatively high risk of developing this complication.
T
Received 18 March; revised 26 May; accepted 4 June 1997
Correspondence: Dr. Yaacov Baruch, Liver Unit, Rambarn Medical Center, P0.B. 9602, 31096 Haifa, Israel. Tel: 972-4-851-6408. Fax: 972-4-854-2477.
934
Key words: FK 506; Idiopathic thrombocytopenic purpura; Immunosuppression; Liver transplantation; Parvovirus B19.
Case Report A 12-year-old boy had received a liver transplant 2 years earlier because of decompensated liver cirrhosis due to Wilson’s disease. During the early postoperative period, he had mild primary graft dysfunction. The patient was on prednisone (5 mg per day) and FK 506 (10 mg per day), with whole blood levels between 5 and 15 &ml. During follow-up, he developed mild hypertension, hyperglycemia, and mild renal failure (creatinine 160 pmolll). Two years after transplantation, the patient was admitted to the hospital with large ecchymoses and conjunctival bleeding. At physical examination, the boy was generally well. Blood pressure was 120180 mmHg, temperature 37”C, and pulse 82 beats/min. He weighed 42 kg. Examination of the lungs and heart was within normal limits.
Parvovirus and ITP after liver transplant
The abdomen was soft, and the spleen enlarged and palpable 4 cm below the left costal margin. The liver was not tender and not palpable. There was no ascites and no peripheral edema. Laboratory studies revealed platelet count of 5000/ mm3 (normal: ~150 000) and white blood cell count of 1400/mm3 (normal: >4800), with 40% lymphocytes, 34% neutrophils, 22% monocytes, 3% eosinophils, and 1% atypical lymphocytes (Fig 1). Hemoglobin was 108 g/l (normal: >12). The liver enzymes had been disturbed since the operation: alanine aminotransferase (ALT) 336 U/l (normal: <30), aspartate aminotransferase (AST) 230 U/l (normal: <30), alkaline phosphatase 134 U/l (normal:
,000w 9omo
3
Fig. 1. Clinical course of the patient. cells/mm3.
WBC, white blood
potential bone marrow toxicity and the suspected effect on the host response of production of antibodies against viruses. Because there was no change in platelet count within 1 week, treatment with intravenous immunoglobulins (1 g/kg body weight ) was given. Six days after discontinuing the FK 506, cyclosporine (200 mg/day) was given, aiming at trough levels of 250 ngl ml. A few days later, the platelet count increased to 40 000/mm3, and subsequently to 70 000/mm3. A moderate rejection appeared thereafter, but was well controlled with steroid recycling. One year after the episode, the patient is doing well, the splenomegaly has resolved completely, and the platelet count is 161 000/mm3. His IgM antiparvovirus is negative (~1 dOD, the normal value of parvovirus B19 antibodies being < 1 for IgM and IgG antibodies).
Discussion Parvovirus B19 is the etiologic agent of fifth disease, a common childhood exanthem and a polyarthralgia syndrome in adults (9,lO). B19 causes a transient aplastic crisis and chronic bone marrow failure in patients with underlying hemolysis and in those taking immunosuppressive drugs, respectively (7,ll). Although severe anemia is the most striking feature of the transient aplastic crisis, leukopenia and thrombocytopenia can also occur (12). Recently, parvovirus B 19 infection associated with ITP was reported in a group of children with evidence of B19 DNA genome in the peripheral blood and in bone marrow. However, none of these patients was immunodeficient or undergoing chronic immunosuppressive therapy (6). In the immunocompromised host who is unable to produce neutralizing antibodies, an infection with parvovirus B19 can persist and cause chronic bone marrow failure, which may lead to excessive bleeding in the postoperative period (7-8,13). In our patient, the early infusion of gamma globulin preparation may have helped to neutralize the virus and eradicate the infection (14). The therapeutic mechanism of high-dose immunoglobulin (IVIG) therapy in ITP has been the subject of speculation; hypotheses have included blockade of the Fc receptors and the neutralization of host antibodies with IVIG (15,16). In our patient, we did not test the B19 DNA by polymerase chain reaction or by dot blot hybridization to see whether immunoglobulin therapy was clearly associated with the disappearance of the virus from the circulation. Although a more rapid increase in platelets is usually seen after IVIG treatment, a gradual increase has also been observed. This may be due to a specific effect on parvovirus antibodies and not a (Fc) blockade. Several scenarios of how parvovirus B19 infections
935
N. Assy et al.
are involved in autoimmunity or in ITP can be postulated. First, if the B19 virus and the infected host share antigenic determinants, virus infection may induce autoimmunity, as the virus-specific T and B cells are cross-reactive to self-antigen - a phenomenon called molecular mimicry (17). Second, during unbalanced antiviral immunity (as under immunosuppression), B19 infection may cause chronic inflammation, the virus being eliminated only very slowly and the infected tissue or blood components being destroyed by the replicating virus itself or by cytotoxic Tlymphocyte-mediated immunopathology. As a consequence, self-reactive B cells may be induced to secrete autoantibodies, and autoreactive T cells that mediate and maintain the immune process may be activated (17). Moreover, recent studies have shown that the cytotoxic effect of B19 is due to viral non-structural proteins to megakaryocytes, which may account for the thrombocytopenia induced by B19 infection (18). The role of the discontinuation of FK 506 in the process of ITP resolution and whether this somehow facilitated the disappearance of B19 viremia remains unclear. However, FK 506 may act as a pharmacologic inhibitor of reticuloendothelial function and lead to decreased clearance of IgG-coated platelets (19). The cause of leukopenia was likely related to parvovirus B19 infection, as has been previously described (12). The number of leukocytes improved and returned to normal after resolution of the viral infection. The cause of graft dysfunction in our child may be multifactorial. Rapid changes in immunosuppression (from FK-506 to cyclosporin) and/or the parvovirus B19 infection itself were the likely causes of acute graft rejection. Clinical and biochemical improvement were noted after the resolution of the viral infection. This observation raises several questions regarding the pathophysiologic aspect of immune thrombocytopenia associated with parvovirus B19 infection in liver recipients and the effect of gamma globulin administration and FK 506 discontinuation on this disorder. We suggest that parvovirus infection be included in the differential diagnosis of solid-organ transplant patients presenting with severe thrombocytopenia. Further studies on parvovirus prevalence, spectrum of disease, and role of treatment with intravenous immunoglobulin in this population
of children
are warranted.
References 1. Plevak DJ, Halma GA, Forstrom LA, Dewanjee MK, O’Connor MK, Moore SB, et al. Thrombocytopenia after liver transplantation. Transplant Proc 1988; 20 Suppl 1: 6303.
936
2. Randoux 0, Gambiez L, Navarro F, Declerck N, Labalette M, Dessaint JP et al. Post-liver transplantation thrombocytopenia: a persistent immunologic sequestration. Transplant Proc 1995; 27: 1710-l. 3. Arnold JC, Heilig B, Otto G, Kommerell B, Theilmann L. Cytomegalovirus-induced severe thrombocytopenia after liver transplantation. Transplantation 1993; 56: 1286-8. 4. McMillan R. Chronic idiopathic thrombocytopenic purpura. N Engl J Med 1981; 304: 113547. 5. Louache F, Bettaieb A, Henri A, Oksenhendler E, Far& JE Bierling P et al. Infection of megakaryocytes by human immunodeficency virus in seropositive patients with immune thrombocytopenic purpura. Blood 1991; 78: 1697-705. 6. Murray JC, Kelley PK, Hogrefe WR, McClain KL. Childhood idiopathic thrombocytopenic purpura: association with human parvovirus B19 infection. Am J Pediatr Hematol Onco1 1994; 16: 314-9. 7. Kurtzman GJ, Ozawa K, Cohen B, Hanson G, Oseas R, Young NS. Chronic bone marrow failure due to persistent B19 parvovirus infection. N Engl J Med 1987; 317: 287-94. 8. Kurtzman GJ, Cohen BJ, Meyers P Amunullah A, Young NS. Persistent B19 parvovirus infection as a cause of severe chronic anaemia in children with acute lymphocytic leukaemia. Lancet 1988; ii: 1159-62. 9. Pattison JR. Diseases caused by the human parvovirus B19. Arch Dis Child 1988; 63: 14267. 10. Harris JW. Parvovirus B19 for the hematologist. Am J Hematol 1992 ; 39: 119-30. 11. Van Horn DK, Mortimer PP Young N, Hanson GR. Human parvovirus-associated red cell aplasia in the absence of underlying hemolytic anemia. Am J Pediatr Hematol Oncol 1986; 8: 235-9. 12. Yoto Y, Kudoh T, Suzuki N, Katoh S, Matsunaga Y, Chiba S. Thrombocytopenia induced by human parvovirus B19 infections. Eur J Haematol 1993; 50: 255-7. 13. Carton EG, Plevak DJ, O’Connor MK, Forstom LA. Splenic deposition of platelets after liver transplantation. Transplant Proc 1991; 23: 1938. 14. Azzizi A, Fanci R, Ciappi S, Zakrzewska K, Bosi A. Human parvovirus B 19 infection in bone marrow transplantation patients. Am J Hematol 1993; 44: 207-9. 15. Fehr J, Hofmann V, Kappeler U. Transient reversal of thrombocytopenia in idiopathic thrombocytopenic purpura by high-dose intravenous gamma globulin. N Engl J Med 1982; 306: 1254-8. 16. McGuire WA, Yang HH, Bruno E, Brandt J, Briddell R, Coates TD, et al. Treatment of antibody-mediated pure redcell aplasia with high-dose intravenous gamma globulin. N Engl J Med 1987; 317: 1004-8. 17. Aichele P, Bachmann MF, Hengartner H, Zinkernagel RM. Immunopathology or organ-specific autoimmunity as a consequence of virus infection. Immunol Rev 1996; 152: 2145. 18. Srivastava A, Bruno E, Briddell R, Cooper R, Srivastava C, van Besien K, et al. Parvovirus B19-induced perturbation of human megakaryocytopoiesis in vitro. Blood 1990; 76: 19972004. 19. Kelly PA, Burckart GJ, Venkataramanan R. Tacrolimus: a new immunosuppressive agent. Am J Health Syst Pharm 1995; 52: 1521-35.
.
Copyright 0 European Association for the Study of the Liver 1997
Copenhagen
Journalof Hepatology ISSN 0168-8278
Case Report
Human parvovirusB19 infection associated with idiopathic thrombocytopenicpurpurain a child following liver transplantation Nimer Assy 1,4, Eldad Rosentha12, Anna Hazani3, Amos Etzioni2s5 and Yaacov Baruch1,4,5 ‘Liver Unit, ‘Department of Pediatrics A, ‘Hematology Clinic, and 4Department of Medicine B, Rambam Medical Center, and ‘The Bruce Rappaport Faculty of Medicine, Technion-Institute of Technology, Haifa, Israel
Background/Aims: Idiopathic (autoimmune) thromhocytopenic purpura has been previously reported as a rare complication in children following parvovirus B19 infection. In the immunocompromised host who is unable to produce neutralizing antibody, an infection with parvovirus B19 can persist and cause chronic bone marrow failure. Methods: We describe a child who had undergone liver transplantation and who had idiopathic thrombocytopenic purpura, whose history and laboratory findings suggested parvovirus B19 infection. The infection disappeared without persistent viremia, and the thrombo-
cytopenia responded completely to the administration of gamma globulin while the patient was undergoing chronic immunosuppression therapy. Results/Conclusion: Transplant physicians need to be aware of this complication, and parvovirus B19 infection should be included in the differential diagnosis of liver recipients presenting with severe thrombocytopenia.
ROMBOCYTOPENIA is a well-recognized complication following liver transplantation and may occur at any time postoperatively (1). It may be related to allograft dysfunction (primary non-function), drug toxicity (immunosuppression), graft-versus-host disease, and common viral infections (2,3). Idiopathic thrombocytopenic purpura (ITP) has already been associated with several viral infections such as measles, Epstein-Barr virus, and human immunodeficiency virus (4,5). Recently, ITP was also reported as a rare complication in children following parvovirus B19 infection (6). However, there has been no previous report of an association between ITP and parvovirus B19 infection in a liver transplant patient while under immunosuppresive therapy. This observation has several important clinical implications for transplantation hepatologists and surgeons. First, an infection with parvovirus B19 in the immunocompromised liver recipient can persist and cause chronic bone marrow fail-
ure (7,s). Second, because antiparvovirus antibodies are most commonly acquired between 5 and 15 years of age, young children who have undergone liver transplantation seem likely to experience infection with parvovirus while receiving immunosuppression therapy. Moreover, a seronegative transplant recipient may be at relatively high risk of developing this complication.
T
Received 18 March; revised 26 May; accepted 4 June 1997
Correspondence: Dr. Yaacov Baruch, Liver Unit, Rambarn Medical Center, P0.B. 9602, 31096 Haifa, Israel. Tel: 972-4-851-6408. Fax: 972-4-854-2477.
934
Key words: FK 506; Idiopathic thrombocytopenic purpura; Immunosuppression; Liver transplantation; Parvovirus B19.
Case Report A 12-year-old boy had received a liver transplant 2 years earlier because of decompensated liver cirrhosis due to Wilson’s disease. During the early postoperative period, he had mild primary graft dysfunction. The patient was on prednisone (5 mg per day) and FK 506 (10 mg per day), with whole blood levels between 5 and 15 &ml. During follow-up, he developed mild hypertension, hyperglycemia, and mild renal failure (creatinine 160 pmolll). Two years after transplantation, the patient was admitted to the hospital with large ecchymoses and conjunctival bleeding. At physical examination, the boy was generally well. Blood pressure was 120180 mmHg, temperature 37”C, and pulse 82 beats/min. He weighed 42 kg. Examination of the lungs and heart was within normal limits.
Parvovirus and ITP after liver transplant
The abdomen was soft, and the spleen enlarged and palpable 4 cm below the left costal margin. The liver was not tender and not palpable. There was no ascites and no peripheral edema. Laboratory studies revealed platelet count of 5000/ mm3 (normal: ~150 000) and white blood cell count of 1400/mm3 (normal: >4800), with 40% lymphocytes, 34% neutrophils, 22% monocytes, 3% eosinophils, and 1% atypical lymphocytes (Fig 1). Hemoglobin was 108 g/l (normal: >12). The liver enzymes had been disturbed since the operation: alanine aminotransferase (ALT) 336 U/l (normal: <30), aspartate aminotransferase (AST) 230 U/l (normal: <30), alkaline phosphatase 134 U/l (normal:
,000w 9omo
3
Fig. 1. Clinical course of the patient. cells/mm3.
WBC, white blood
potential bone marrow toxicity and the suspected effect on the host response of production of antibodies against viruses. Because there was no change in platelet count within 1 week, treatment with intravenous immunoglobulins (1 g/kg body weight ) was given. Six days after discontinuing the FK 506, cyclosporine (200 mg/day) was given, aiming at trough levels of 250 ngl ml. A few days later, the platelet count increased to 40 000/mm3, and subsequently to 70 000/mm3. A moderate rejection appeared thereafter, but was well controlled with steroid recycling. One year after the episode, the patient is doing well, the splenomegaly has resolved completely, and the platelet count is 161 000/mm3. His IgM antiparvovirus is negative (~1 dOD, the normal value of parvovirus B19 antibodies being < 1 for IgM and IgG antibodies).
Discussion Parvovirus B19 is the etiologic agent of fifth disease, a common childhood exanthem and a polyarthralgia syndrome in adults (9,lO). B19 causes a transient aplastic crisis and chronic bone marrow failure in patients with underlying hemolysis and in those taking immunosuppressive drugs, respectively (7,ll). Although severe anemia is the most striking feature of the transient aplastic crisis, leukopenia and thrombocytopenia can also occur (12). Recently, parvovirus B 19 infection associated with ITP was reported in a group of children with evidence of B19 DNA genome in the peripheral blood and in bone marrow. However, none of these patients was immunodeficient or undergoing chronic immunosuppressive therapy (6). In the immunocompromised host who is unable to produce neutralizing antibodies, an infection with parvovirus B19 can persist and cause chronic bone marrow failure, which may lead to excessive bleeding in the postoperative period (7-8,13). In our patient, the early infusion of gamma globulin preparation may have helped to neutralize the virus and eradicate the infection (14). The therapeutic mechanism of high-dose immunoglobulin (IVIG) therapy in ITP has been the subject of speculation; hypotheses have included blockade of the Fc receptors and the neutralization of host antibodies with IVIG (15,16). In our patient, we did not test the B19 DNA by polymerase chain reaction or by dot blot hybridization to see whether immunoglobulin therapy was clearly associated with the disappearance of the virus from the circulation. Although a more rapid increase in platelets is usually seen after IVIG treatment, a gradual increase has also been observed. This may be due to a specific effect on parvovirus antibodies and not a (Fc) blockade. Several scenarios of how parvovirus B19 infections
935
N. Assy et al.
are involved in autoimmunity or in ITP can be postulated. First, if the B19 virus and the infected host share antigenic determinants, virus infection may induce autoimmunity, as the virus-specific T and B cells are cross-reactive to self-antigen - a phenomenon called molecular mimicry (17). Second, during unbalanced antiviral immunity (as under immunosuppression), B19 infection may cause chronic inflammation, the virus being eliminated only very slowly and the infected tissue or blood components being destroyed by the replicating virus itself or by cytotoxic Tlymphocyte-mediated immunopathology. As a consequence, self-reactive B cells may be induced to secrete autoantibodies, and autoreactive T cells that mediate and maintain the immune process may be activated (17). Moreover, recent studies have shown that the cytotoxic effect of B19 is due to viral non-structural proteins to megakaryocytes, which may account for the thrombocytopenia induced by B19 infection (18). The role of the discontinuation of FK 506 in the process of ITP resolution and whether this somehow facilitated the disappearance of B19 viremia remains unclear. However, FK 506 may act as a pharmacologic inhibitor of reticuloendothelial function and lead to decreased clearance of IgG-coated platelets (19). The cause of leukopenia was likely related to parvovirus B19 infection, as has been previously described (12). The number of leukocytes improved and returned to normal after resolution of the viral infection. The cause of graft dysfunction in our child may be multifactorial. Rapid changes in immunosuppression (from FK-506 to cyclosporin) and/or the parvovirus B19 infection itself were the likely causes of acute graft rejection. Clinical and biochemical improvement were noted after the resolution of the viral infection. This observation raises several questions regarding the pathophysiologic aspect of immune thrombocytopenia associated with parvovirus B19 infection in liver recipients and the effect of gamma globulin administration and FK 506 discontinuation on this disorder. We suggest that parvovirus infection be included in the differential diagnosis of solid-organ transplant patients presenting with severe thrombocytopenia. Further studies on parvovirus prevalence, spectrum of disease, and role of treatment with intravenous immunoglobulin in this population
of children
are warranted.
References 1. Plevak DJ, Halma GA, Forstrom LA, Dewanjee MK, O’Connor MK, Moore SB, et al. Thrombocytopenia after liver transplantation. Transplant Proc 1988; 20 Suppl 1: 6303.
936
2. Randoux 0, Gambiez L, Navarro F, Declerck N, Labalette M, Dessaint JP et al. Post-liver transplantation thrombocytopenia: a persistent immunologic sequestration. Transplant Proc 1995; 27: 1710-l. 3. Arnold JC, Heilig B, Otto G, Kommerell B, Theilmann L. Cytomegalovirus-induced severe thrombocytopenia after liver transplantation. Transplantation 1993; 56: 1286-8. 4. McMillan R. Chronic idiopathic thrombocytopenic purpura. N Engl J Med 1981; 304: 113547. 5. Louache F, Bettaieb A, Henri A, Oksenhendler E, Far& JE Bierling P et al. Infection of megakaryocytes by human immunodeficency virus in seropositive patients with immune thrombocytopenic purpura. Blood 1991; 78: 1697-705. 6. Murray JC, Kelley PK, Hogrefe WR, McClain KL. Childhood idiopathic thrombocytopenic purpura: association with human parvovirus B19 infection. Am J Pediatr Hematol Onco1 1994; 16: 314-9. 7. Kurtzman GJ, Ozawa K, Cohen B, Hanson G, Oseas R, Young NS. Chronic bone marrow failure due to persistent B19 parvovirus infection. N Engl J Med 1987; 317: 287-94. 8. Kurtzman GJ, Cohen BJ, Meyers P Amunullah A, Young NS. Persistent B19 parvovirus infection as a cause of severe chronic anaemia in children with acute lymphocytic leukaemia. Lancet 1988; ii: 1159-62. 9. Pattison JR. Diseases caused by the human parvovirus B19. Arch Dis Child 1988; 63: 14267. 10. Harris JW. Parvovirus B19 for the hematologist. Am J Hematol 1992 ; 39: 119-30. 11. Van Horn DK, Mortimer PP Young N, Hanson GR. Human parvovirus-associated red cell aplasia in the absence of underlying hemolytic anemia. Am J Pediatr Hematol Oncol 1986; 8: 235-9. 12. Yoto Y, Kudoh T, Suzuki N, Katoh S, Matsunaga Y, Chiba S. Thrombocytopenia induced by human parvovirus B19 infections. Eur J Haematol 1993; 50: 255-7. 13. Carton EG, Plevak DJ, O’Connor MK, Forstom LA. Splenic deposition of platelets after liver transplantation. Transplant Proc 1991; 23: 1938. 14. Azzizi A, Fanci R, Ciappi S, Zakrzewska K, Bosi A. Human parvovirus B 19 infection in bone marrow transplantation patients. Am J Hematol 1993; 44: 207-9. 15. Fehr J, Hofmann V, Kappeler U. Transient reversal of thrombocytopenia in idiopathic thrombocytopenic purpura by high-dose intravenous gamma globulin. N Engl J Med 1982; 306: 1254-8. 16. McGuire WA, Yang HH, Bruno E, Brandt J, Briddell R, Coates TD, et al. Treatment of antibody-mediated pure redcell aplasia with high-dose intravenous gamma globulin. N Engl J Med 1987; 317: 1004-8. 17. Aichele P, Bachmann MF, Hengartner H, Zinkernagel RM. Immunopathology or organ-specific autoimmunity as a consequence of virus infection. Immunol Rev 1996; 152: 2145. 18. Srivastava A, Bruno E, Briddell R, Cooper R, Srivastava C, van Besien K, et al. Parvovirus B19-induced perturbation of human megakaryocytopoiesis in vitro. Blood 1990; 76: 19972004. 19. Kelly PA, Burckart GJ, Venkataramanan R. Tacrolimus: a new immunosuppressive agent. Am J Health Syst Pharm 1995; 52: 1521-35.