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Keywords:

  • anti-HPA-1a;
  • foetal;
  • neontal;
  • thrombocytopenia

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

Thrombocytopenia is detected in around one percent of newborns. In otherwise healthy term newborns, thrombocytopenia is most often caused by alloantibodies transferred from the mother to the foetus. In the Caucasian populations human platelet antigen (HPA)-1a is the most immunogenic HPA. In Japan and China antibodies in the HPA-4 system are the most frequent cause of FNAIT. The immune response against the HPA must be understood in order to avoid immunization or prevent induction of FNAIT where mothers are already immunized.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

Thrombocytopenia is detected in around one percent of newborns (platelet count <150 × 10E9/L) [1]. The pathophysiology may be prematurity, infections, syndromes based on genetic variations and antibody induced thrombocytopenia. In most cases the thrombocytopenia is mild and asymptomatic. Foetal and neonatal alloimmune thrombocytopenia (FNAIT) is found in 1:1,100–2,000 newborns in Caucasian populations [2,3]. In otherwise healthy term newborns, severe thrombocytopenia (<50 × 10E9/L) is most often caused by maternal alloantibodies. When the platelet count is less than 50 × 10E9/L, there is risk of haemorrhage. In alloimmune thrombocytopenia, skin bleedings are most common. Intracranial haemorrhage (ICH) is the most feared complication. The frequency of FNAIT associated ICH is 1:12,500–1:25,000 newborns and around 10% of the children die, the rest may have severe life-long disabilities due to brain damage [3].

Placental transfer of IgG

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

There is an active transfer of IgG antibodies from the mother to the foetus based on FcRn receptors in throphoblasts [4]. Transplacental transport of IgG protects the foetus and the newborn from infections. The transfer is not based on the specificity of the IgG molecules. This means that maternal antibodies reacting with foetal antigens may destroy or disturb foetal cells and tissues illustrated when the mother has antibodies to thyroid receptors and the newborn has transient hyperthyroidism, and in haemolytic disease of the newborn (HDN) where haemolysis of red cells is induced, most often based on anti-D antibodies transferred from mother to the Rh(D) positive foetus. This is also the case in FNAIT where maternal antibodies to platelet antigens transverse the placenta and bind to antigen positive platelets. The sensitized platelets are in turn removed in the mononuclear phagocyte system and if platelet destruction exceeds platelet production, the foetus or newborn become thrombocytopenic and may be at risk of bleeding.

Platelet antigens

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

Platelets have many polymorphic surface molecules, the most polymorphic are the HLA class I molecules. In addition, there are polymorphisms in some of the platelet surface glycoproteins; altogether 17 biallelic systems of human platelet antigens (HPA) have been described [5]. The amino acid differences are based on single nucleotide polymorphisms. Alloimmunization may take place in connection with pregnancy or upon blood transfusions. HPA-1a is the most immunogenic platelet antigen which is found in >80% of FNAIT cases in Caucasians [6]. Since the genetic background differs among ethnic groups, the pattern of immunization differs. In China and Japan, almost all individuals carry the HPA-1a allele and alloimmunization against this antigen is thus extremely rare. On the contrary, the HPA-4b antigen which is absent in Caucasians, is more frequently found in Japan and China and antibodies in the HPA-4 system is the clinically most important platelet antibodies in East Asia [7,8].

Immunization with human platelet antigens

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

FNAIT is most often diagnosed after birth of a child with thrombocytopenia and bleeding symptoms. Prospective studies have shown that immunization against HPA-1a may take place during pregnancy (around 25%) or at the time of delivery (75%). Also, prospective studies and one retrospective study have shown a correlation between the maternal anti-HPA-1a antibody level and the severity of thrombocytopenia in the newborn [3,9,10]. Some retrospective studies do not support these data [11,12].

Follow-up and treatment of FNAIT

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

No country has introduced general screening for HPA alloimmunization during pregnancy. In most cases, clinical follow-up and treatment take place in the subsequent pregnancy after birth of a child with FNAIT. Although never documented in randomized clinical trials, many centres will treat immunized women with intravenous immunoglobulin (IVIg) and/or steroids. Intrauterine blood sampling and transfusions are no longer part of standard follow-up procedure due to reports of severe complications [13]. In many cases, delivery is performed by elective caesarean section and compatible platelet concentrates are available for immediate transfusion to the newborn if needed.

Future management of FNAIT

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

Results from prospective studies in Europe have shown that FNAIT is more similar to haemolytic disease of the newborn (HDN) than thought before [14]. It is believed that treatment with IVIg in the pregnancy and careful delivery and transfusion of platelet to the newborn will reduce morbidity and mortality of FNAIT [13]. Several reports conclude that general screening should be introduced based on the results from the implemented interventions [3,14–16]. The ultimate goal would be to prevent immunizations in women at risk of FNAIT. Experiments in a murine β3 integrin knock-out model have shown that immunization with β3 integrin positive platelets can be avoided by injection of anti-β3-integrin antibodies at the time of immunization [17]. This antibody induced immunomodulatory effect resembles the effect of anti-D given to Rh(D) negative women after birth of an Rh(D) positive child. In Europe we are planning a study where non-immunized HPA-1a negative women will be given anti-HPA-1a antibodies after delivering an HPA-1a positive child. Based on the number of immunization in primigravida, 75% of the HPA-1a immunizations could be avoided by this approach.

The presence of IgG antibodies in the mother is a consequence of activation of HPA-1a specific B- and T-cells [18]. The B-cells need T-cell help to become antibody producing plasma cells [19]. It is conceivable that T-cell tolerance can be induced by blocking the HPA 1a T-cell receptors by non-stimulating peptides [20]. Another approach could be to block anti-HPA-1a antibodies by soluble epitopes or anti-idiotypic antibodies [21].

Challenges in transfusion medicine related to FNAIT

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

HPA-1a typing can be performed by genotyping using different PCR methodologies or by phenotyping by ELISA or flow cytometry [22,23]. Detection of anti-platelet antibodies is performed by flow cytometry (including Luminex technology) or ELISA [24,25]. To determine the specificity and quantity of the antibodies, the monoclonal antibody immobilization of platelet antigen assay (MAIPA) is used at present [26]. This method is complicated and labour intensive and has been shown difficult to standardize [27].

Compatible blood products must be available immediately for severely thrombocytopenic newborn. The platelet unit should be from a donor lacking the platelet antigen that the woman’s antibodies are specific for. If the mother in addition has anti-HLA class I antibodies one should also take these antibodies in account when selecting the platelet donor. To provide compatible platelet products for newborn in need, is challenging and typing of many donors may be necessary [28]. If a newborn shows sign of petechiae and have low platelet count at birth, transfusion of random platelets may be used before diagnosis is made and compatible platelets are available [29].

Conclusion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

In the future, FNAIT due to anti-HPA-1a antibodies may be managed similar to HDN by identifying women at risk in early pregnancy and giving prophylaxis in order to prevent immunization in connection with delivery. Immunization in early pregnancy cannot be prevented by prophylaxis and detailed knowledge about the mechanism of immunization and the activity of the different cell types is necessary to prevent FNAIT in the next incompatible pregnancy of already immunized women.

Disclosures

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References

Bjørn Skogen, Mette Kjær Killie, Jens Kjeldsen-Kragh and Anne Husebekk have shares in a company trying to develope a prophylaxis against HPA-1a immunization.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Placental transfer of IgG
  5. Platelet antigens
  6. Immunization with human platelet antigens
  7. Follow-up and treatment of FNAIT
  8. Future management of FNAIT
  9. Challenges in transfusion medicine related to FNAIT
  10. Conclusion
  11. Disclosures
  12. References
  • 1
    Hohlfeld P, Forestier F, Kaplan C, Tissot JD, Daffos F: Fetal thrombocytopenia: a retrospective survey of 5,194 fetal blood samplings. Blood 1994; 84:18511856
  • 2
    Williamson LM, Hackett G, Rennie J, Palmer CR, Maciver C, Hadfield R, et al.: The natural history of fetomaternal alloimmunization to the platelet-specific antigen HPA-1a (PlA1, Zwa) as determined by antenatal screening. Blood 1998; 92:22802287
  • 3
    Kjeldsen-Kragh J, Killie MK, Tomter G, Golebiowska E, Randen I, Hauge R, et al.: A screening and intervention program aimed to reduce mortality and serious morbidity associated with severe neonatal alloimmune thrombocytopenia. Blood 2007; 110:833839
  • 4
    Firan M, Bawdon R, Radu C, Ober RJ, Eaken D, Antohe F, et al.: The MHC class I-related receptor, FcRn, plays an essential role in the maternofetal transfer of gamma-globulin in humans. Int Immunol 2001; 13:9931002
  • 5
    Landau M, Rosenberg N: Molecular insight into human platelet antigens: structural and evolutionary conservation analyses offer new perspective to immunogenic disorders. Transfusion 2010; 51:558569
  • 6
    Hadley AG: Diagnosis of alloimmune thrombocytopenia; in Hadley AG, Soothill P (eds): Alloimmune disorders of Pregnancy: Anaemia, Thrombocytopenia and Neutropenia in the Fetus and Newborn, , Cambridge University Press, 2002:219229.
  • 7
    Ohto H: Neonatal alloimmune thrombocytopenia. Nippon Rinsho 1997; 55:23102314
  • 8
    Feng ML, Liu DZ, Shen W, Wang JL, Guo ZH, Zhang X, et al.: Establishment of an HPA-1- to -16-typed platelet donor registry in China. Transfus Med 2006; 16:369374
  • 9
    Killie MK, Husebekk A, Kjeldsen-Kragh J, Skogen B: A prospective study of maternal anti-HPA 1a antibody level as a potential predictor of alloimmune thrombocytopenia in the newborn. Haematologica 2008; 93:870877
  • 10
    Killie MK, Husebekk A, Kaplan C, Taaning E, Skogen B: Maternal human platelet antigen-1a antibody level correlates with the platelet count in newborns: a retrospective study. Transfusion 2007; 47:5558
  • 11
    Ghevaert C, Campbell K, Stafford P, Metcalfe P, Casbard A, Smith G, et al.: HPA-1a antibody potency and bioactivity do not predict severity of fetomaternal alloimmune thrombocytopenia. Transfusion 2007; 47:12961305
  • 12
    Bertrand G, Drame M, Martageix C, Kaplan C: Prediction of the fetal status in noninvasive management of alloimmune thrombocytopenia. Blood 2011;117:32093213. Epub 2011 Jan 14.
  • 13
    Kamphuis M, Oepkes D: Fetal and neonatal alloimmune thrombocytopenia: prenatal interventions. Prenat Diagn 2011; 31:712719
  • 14
    Skogen B, Husebekk A, Killie MK, Kjeldsen-Kragh J: Neonatal alloimmune thrombocytopenia is not what it was: a lesson learned from a large prospective screening and intervention program. Scand J Immunol 2009; 70:531534
  • 15
    Kamphuis MM, Paridaans N, Porcelijn L, De Haas M, Van Der Schoot CE, Brand A, Bonsel GJ, Oepkes D: Screening in pregnancy for fetal or neonatal alloimmune thrombocytopenia: systematic review. BJOG 2010; 117:13351343
  • 16
    Knight M, Pierce M, Allen D, Kurinczuk JJ, Spark P, Roberts DJ, Murphy MF: The incidence and outcomes of fetomaternal alloimmune thrombocytopenia: a UK national study using three data sources. Br J Haematol 2011; 152:460468
  • 17
    Tiller H, Killie MK, Chen P, Eksteen M, Husebekk A, Skogen B, Kjeldsen-Kragh J, Ni H: Prophylactic administration of anti-β3 antibody mediated immune suppression (AMIS) and prevented complications in a murine model of fetal and neonatal alloimmune thrombocytopenia (FNAIT). Vox Sang 2010; 99(Supplement 2): 13.
  • 18
    Ahlen MT, Husebekk A, Killie MK, Skogen B, Stuge TB: T-cell responses associated with neonatal alloimmune thrombocytopenia: isolation of HPA-1a-specific, HLA-DRB3*0101-restricted CD4 +  T cells. Blood 2009; 113:38383844
  • 19
    Stuge TB, Skogen B, Ahlen MT, Husebekk A, Urbaniak SJ, Bessos H: The cellular immunobiology associated with fetal and neonatal alloimmune thrombocytopenia. Transfus Apher Sci 2011; 5359 [Epub ahead of print]
  • 20
    Anani Sarab G, Moss M, Barker RN, Urbaniak SJ: Naturally processed peptides spanning the HPA-1a polymorphism are efficiently generated and displayed from platelet glycoprotein by HLA-DRB3*0101-positive antigen-presenting cells. Blood 2009; 27:114
  • 21
    Ghevaert C, Wilcox DA, Fang J, Armour KL, Clark MR, Ouwehand WH, Williamson LM: Developing recombinant HPA-1a-specific antibodies with abrogated Fcgamma receptor binding for the treatment of fetomaternal alloimmune thrombocytopenia. J Clin Invest 2008; 118:29292938
  • 22
    Skogen B, Bellissimo D, Hessner MJ, Santoso S, Aster RH, Newman PJ, et al.: Rapid determination of platelet alloantigen genotypes by polymerase chain reaction using allele-specific primers. Transfusion 1994; 34:955960
  • 23
    Wu GG, Kaplan C, Curtis BR, Pearson HA: Report on the 14th International Society of Blood Transfusion Platelet Immunology Workshop. Vox San 2010; 99:375381
  • 24
    Killie MK, Kjeldsen-Kragh J, Randen I, Skogen B, Husebekk A: Evaluation of a new flow cytometric HPA 1a screening method: A rapid and reliable tool for HPA 1a screening of blood donors and pregnant women. Transfus Apher Sci 2004; 30:8992
  • 25
    Chong W, Metcalfe P, Mushens R, Lucas G, Ouwehand WH, Navarrete CV: Detection of human platelet antigen-1a alloantibodies in cases of fetomaternal alloimmune thrombocytopenia using recombinant β3 integrin fragments coupled to fluorescently labeled beads. Transfusion 2011; 51:12611270
  • 26
    Kiefel V, Santoso S, Weisheit M, Mueller-Eckhardt C: Monoclonal antibody-specific immobilization of platelet antigens (MAIPA): a new tool for the identification of platelet-reactive antibodies. Blood 1987; 70:17221726
  • 27
    Bertrand G, Jallu V, Gouet M, Kjaer KM, Lambin P, Husebekk A, et al.: Quantification of human platelet antigen-1a antibodies with the monoclonal antibody immobilization of platelet antigens procedure. Transfusion 2005; 45:13191323
  • 28
    Ranasinghe E, Walton JD, Hurd CM, Saul L, Smith G, Campbell K, Ouwehand WH: Provision of platelet support for fetuses and neonates affected by severe fetomaternal alloimmune thrombocytopenia. Br J Haematol 2001; 113:4042
  • 29
    Kiefel V, Bassler D, Kroll H, Paes B, Giers G, Ditomasso J, Alber H, Berns M, Wiebe B, Quenzel EM, Hoch J, Greinacher A: Antigen-positive platelet transfusion in neonatal alloimmune thrombocytopenia (NAIT). Blood 2006; 107:37613763