1. 1 Donald M. Arnold MDCM, FRCPC Assist professor, McMaster University McMaster Platelet immunology Laboratory CBS Hamilton 1

2. 2  “Difficulties with Platelet Transfusion, HLA Serology & Management of NAIT & PTT”  Nomenclature  Limited evidence  Variability in practice  Serious illnesses  Costly, potentially dangerous treatments 2

3. 3 1.Understand the mechanism of platelet antigen sensitization 2.Explore pathophysiology of:  platelet refractoriness  fetal or neonatal alloimmune thrombocytopenia  post-transfusion purpura 3.Discuss management of PLT refractoriness, FNAT and PTP

4. 4 4

5. 5 5

6. 6 6

7. 7  Blood group antigens (ABO)  Common tissue antigens (HLA)  Platelet specific antigens (HPA) 7

8. 8  Chosen name, or name related to individual with antigen (Pl A1, Zav, Gov).  Currently all antigens are designated as human platelet antigen (HPA).  Antigens numbered in order of discovery. Higher frequency allele is “a”. e.g. PLA1 = HPA-1a, PLA2 = HPA-1b 8 Nomenclature

9. 9  To date, more than 22 platelet specific alloantigens identified, with 6 diallelic system (HPA-1, 2, 3, 4, 5, 15). Almost all are associated with a single amino acid substitution (SNP).  Antibodies against HPA-1a are most commonly implicated in NAT, PTP. 9

10. 10 Platelet Transfusion Refractoriness

11. 11 Definition  1h corrected count incr < 5 – 10 x10 9 /L  Percent PLT recovery <20%  1h CCI < 5 x10 9 /L x2 using ABO-identical fresh platelets  A post-transfusion platelet count that is less than expected 11

12. 12  Immune  Anti-HLA, anti-ABO, anti-HPA  Non-immune  Fever  Sepsis  Splenomegaly  DIC  Bleeding  VOD  GVHD 12

13. 13  Alloimmunization occurs after transfusion, pregnancy, transplantation.  Alloimmunization does not mean refractory  Strategies to reduce refractoriness: 1. Leukoreduction 2. Platelet dose? 3. Apheresis vs. whole blood derived platelets 13

14. 14

15. 15

16. 16

17. 17 Decline in PLT responsiveness A: In all patients (n=6334 transfusions; 533 patients) B: In HLA-antibody-negative patients (n= 5484 transfusions; 477 patients) Slichter Blood 2005

18. 18 Heddle, Transfusion 2008 Apheresis vs. Whole blood PLTs

19. 19

20. 20 Hod BMJ 2008

21. 21

22. 22

23. 23

24. 24 Low platelets and bleeding in a fetus or neonate caused by maternal antibodies directed against fetal platelet antigens inherited from the father. 24 Definition:

25. 25 Incidence: 1 in 1,000 to 1 in 2,000 births NIncidence Burrows and Kelton, 1993 15,9321 in 1,700 Uhrynowska, 2000 24,1011 in 2,400 Turner, 2005 26,0001 in 5,000 Kjeldsen-Kragh, 2007100,4481 in 1,700 FNAT

26. 26  Most common cause of severe TCP in infant  Most common cause of ICH in term newborns  First pregnancies, without warning  Otherwise healthy babies 26

27. 27  Fetal platelet antigen: Inherited from father  Sensitization: Transplacental  Immunization: Mother forms IgG allo-antibodies  Maternal antibodies: React with fetal platelets  Fetal platelet destruction: Spleen and RES 27

28. 28 Arnold et al, Trans Med Rev 2008

29. 29  <150,000 - 1 in 100  < 50,000 - 1 in 400  Infection  Immune mediated  Chromosomal abnormalities  <20,000 - NAT 29 Burrows, Kelton 1993

30. 30 NATHDN Affected cellsPlateletsRed blood cells Most common antigenHPA-1aRh-D Affected pregnancyFirstSecond + Timing of sensitization16 weeks onwardsAt birth, or during a procedure Affected InfantTCP, bleedingHemolysis, jaundice, kernicterus Affected fetusICHHydrops fetalis Main risk factorPreviously affected infantRh-negative mothers TreatmentSupportive PreventionIVIGRhIg (anti-D) Efficacy of prevention?99% 30 Arnold et al, Trans Med Rev 2008

31. 31  Present without warning  Require prompt recognition and treatment  IVIg (2g/kg)  Effective in 75% of affected neonates Mueller-Eckhardt C, Blut 1989  Platelet transfusions:  Antigen-negative (maternal) platelets Allen, Blood 2007  Random-donor platelets Kiefel et al Blood 2006 31

32. 32  IVIg 1g/kg/wk (2g/kg/wk for refractory)  IVIg + corticosteroids  Intrauterine platelet transfusions  Fetal blood sampling (FBS) 32

33. 33 High Risk (n= 40) Standard Risk (n= 39) (previous ICH or PLT<20) (neither) IVIg vs. IVIg + pred IVIg vs. pred (1g/kg/wk) (1mg/kg) (1g/kg/wk) (0.5mg/kg) PUBS (20 wks, repeat 3-8 wks) Outcome: increase in fetal platelet count Berkowitz, Bussel, 2006

34. 34 HIGH RISK Mothers (platelet count) Pre2-8 wksBirth IVIg alone*7,00017,00067,000 IVIg + pred 8,00067,00099,000 * One ICH 34 Berkowitz, Bussel, 2006

35. 35 STANDARD RISK Mothers* (platelet count) Pre3-8 wks IVIg alone>20,000 31,000 Pred alone >20,000 26,000 * 2 fetal deaths, 2 ICH 35 Berkowitz, Bussel, 2006

36. 36  11 SERIOUS COMPLICATIONS OF 175 PUBS (6%) - 1 Fetal Death - 9 Emergency C-Sections (14%) 36

37. 37  IVIG Cochrane collaboration 2006  Corticosteroids Berkowitz, Bussel, 2006  Invasive vs. non-invasive approach? 37 Fetal blood sampling FBS + intrauterine PLT transfusions Cesarean section No FBS Empiric treatment Vaginal delivery

38. 38  N= 100,448 pregnancies screened (for HPA-1a)  Offered early c/s with compatible platelets.  3 of 161 (6%) screen-positive infants died or had ICH; versus 10 of 51 (20%) unscreened infants. Kjeldsen-Kragh J, Blood, 2007 38

39. 39

40. 40  Frequency: uncertain  1 per 2 million RBCs (2008, SHOT)  Adults (~50 years); females (5x)  PLT <15 x10 9 /L, Bleeding ++  Onset: 9 days post blood transfusion  Recovery: 7 – 48 days after onset  Mortality ~10% (intracerebral hemorrhage)

41. 41  Sensitization by previous transfusions, pregnancy  Usually HPA-1bb recipients  Other at risk HPA genotypes

42. 42

43. 43  Transfusion of incompatible PLTs  Typically, anti-HPA-1a Abs  Destroy transfused and autologous PLTs  Theories: 1. Immune complexes 2. Adsorbed PLT antigens 3. Concomitant auto-Abs  Further research needed

44. 44  Supportive: Ag-negative platelet transfusions  IVIG  Plasma exchange  Corticosteroids

45. 45  Platelet sensitization  HLA antibodies are ubiquitous, transient  Example: PLT refractoriness  HPA antibodies are rare, persistent  Examples: FNAT, PTP

46. 46  PLT refractoriness:  Consider HLA matched, XM compatible PLTs  FNAT:  Newborn PLT <20; FNAT until proven otherwise  PTP:  Severe thrombocytopenia (PLT <15) and bleeding