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

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 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

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

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  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 Platelet Transfusion Refractoriness

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

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

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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 Heddle, Transfusion 2008 Apheresis vs. Whole blood PLTs

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20 Hod BMJ 2008

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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 Incidence: 1 in 1,000 to 1 in 2,000 births NIncidence Burrows and Kelton, ,9321 in 1,700 Uhrynowska, ,1011 in 2,400 Turner, ,0001 in 5,000 Kjeldsen-Kragh, ,4481 in 1,700 FNAT

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  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 Arnold et al, Trans Med Rev 2008

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

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  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

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

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

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  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,

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

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

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

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