Platelet Alloimmunization

1
Platelet Alloimmunization

• Joshua Field
• June 23, 2005

2
Case

• 24 year-old woman G0P0 with a history of AML with
  normal cytogenetics, day 20 of 73.
• She initially presented with pancytopenia,
  including a platelet count of 6,000.
• Prior to the initiation of her induction
  chemotherapy, she received her first platelet
  transfusion. Her platelet increment was 18,000.
• Throughout her induction, she has received
  CMV-negative, leukoreduced, irradiated blood
  products. Platelets are single donor.

3
Case

• On day 20, she is to receive platelet
  transfusion 9.
• Now her platelet increment at 24 hours is 2,000.
• Transfused another unit of single donor platelets
  and checked a 1-hour increment 3,000.
• What to do?

4
Definition

• Platelet refractoriness Inappropriately low
  increment in platelet count following a
  transfusion.
• Platelet alloimmunization Formation of
  antibodies directed to foreign antigens on the
  surface of platelets.
• Formula to determine platelet response
• 1 hour Increment lt 5,000-7,500.
• Corrected Count Increment
• (Platelet increment X BSA)/Platelet dose
• Expected gt 7500 at 10-60 minutes or gt4500 at
  18-24 hours.
• Less than predicted platelet increment on 2
  occasions
• Fresh platelets lt 72 hours.
• ABO compatible.

5
Why is this a big deal?

• Blood Rev, 1998 pp. 234-8 Recommend platelet
  transfusion threshold of 10X10(9). Blanket
  recommendation.
• NEJM, 1997 pp. 1870-5 Newly diagnosed AML.
  Compared threshold of 10K vs. 20K. Found a
  similar bleeding risk.

6
Pathophysiology
Ibalpha
IbB
IX
IIIa
V
IIb
Ia
Platelet
ABH
IIa
CD109
B2 microglobulin
HLA I
7
Pathophysiology

• Immune
• HLA class I A,B. Primary trigger WBCs in
  platelet and RBC transfusions.
• Human platelet antigens Minor role.
• ABH
• Blood, 1979 HLA-matched platelets with
  incompatible ABO resulted in 23 lower increment.
• Enormous variability in expression of ABO on
  platelets.
• Non-immune Sepsis, DIC, drugs, splenomegaly,
  etc.

8
Pathophysiology
Transfused Blood product
WBC
Anti-HLA antibodies
HLA I
Transfused Platelet
9
Prevalence and Incidence

• Kiefel, et al, Transfusion, 2001 766-70.
• 252 patients with solid tumor and hematological
  malignancies, heavily transfused, platelet
  refractory.
• 42 anti-HLA antibodies.
• 8 anti-HPA antibodies.
• TRAP trial 27 developed LCT antibodies.

10
Risk

• High number of transfusions?
• Dutcher, et al, Blood, 1981 1007-11.
• 114 patients, no transfusion history.
• Received random donor platelets.
• Lymphocytotoxic HLA antibody screen.
• 42 developed a positive screen at 8 weeks.
• About 10 at one week.
• Antibody lost in 20.
• Suggests early event.

11
Risk

• Patients received pooled platelets.
• Exposed lt20 donors 22 LCT antibody-positive.
• Exposed 20-60 41 LCT antibody-positive.
• Same conclusion with single donor platelets?

12
Risk

• Does disease matter?
• Hematological malignancies Blood, 1987 pp.
  1727-9 incidence of LCT in AML 44 vs. ALL 18.
  Contribution of steroids?
• Blood, 1981 pp. 122-8 Heavily transfused
  patients, examine for LCT.
• Acute leukemia 20/65.
• Lymphoma 5/19.
• Sarcoma 2/16.
• Aplastic anemia 7/8.

13
Platelet refractoriness
What is etiology?
Check 1 hour and 24 hour increment
Fever, sepsis, splenomegaly, drugs, etc.
Poor increment
ABO compatible platelets
Poor increment
LAT
Positive
HLA matched/mismatched platelets/antigen negative
Poor increment
Check platelet-specific antibodies
IVIG or pray or quit transfusing platelets
14
Diagnosis and Management

• Lymphocytotoxic antibodies
• Patient serum and complement added to lymphocytes
  with known human leukocyte antigens.
• Antibodies attach to HLA, activate complement,
  lyse cells.
• Dye is added, which colors the wells of lysed
  cells.
• Reported as a percentage reactive (what is a
  positive result?)
• May be able to determine the target antigen.

15
Diagnosis and Management

• American Journal of Hematology, 1983 363-70
  Screened heavily transfused patients for LCT,
  then measured platelet response.
• Sensitivity 63.
• Specificity 94.

16
Diagnosis and Management

• Alloimmunized patient
• HLA-matched platelets
• Mismatched platelets (CREGS)
• Antigen-negative platelets
• HPA-negative platelets
• Platelet crossmatch (not at Barnes)
• IVIG

17
Diagnosis and Management

• HLA-matched platelets
• BJH, 1987 115-21 90 refractory patients may
  benefit.
• American Journal of Hematology, 1977 219-26 60
  refractory patients benefit.
• BIG PROBLEM Donor pool around 10,000.
• Of note Barnes donor pool is about 1500. Huh?

18
Diagnosis and Management

• Public epitope versus private epitope

HLA-A1
HLA-A3
HLA-A10
19
Diagnosis and Management

• American Journal of Hematology, 1977 pp. 219-26.
• Cross-reactive groups (CREGS)
• Platelets mismatched at 1 or 2 cross-reactive HLA
  antigens produced increments similar to perfect
  matches.
• Provides 10 times as many prospective donors.

20
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21
Diagnosis and Management

• HLA-B12 Found in 25 of population.
• Szatkowski, et al. Tissue Antigens 1980 361-8
  HLA-B12 positive patients may have 35-fold
  differences in expression of the antigen between
  platelets.
• Schiffer, et al. Blood 1989 1172-6 Selectively
  mismatched at B12 69 transfusion were
  successful.

22
Diagnosis and Management

• HLA antigen negative platelets
• If identify specificity of anti-HLA antibody
• Antigen-negative platelets.

23
Diagnosis and Management

• Platelet crossmatch Transfusion, 1990 314-7.
• Perform an ELISA with stored platelets and
  patients serum.
• 14/34 transfusions into heavily alloimmunized
  patients produced CCI gt 7500.

24
Diagnosis and Management

• Alloimmunization to Platelet-Specific Antigens
  Not common.
• Blood, 85 (7), 1995 pp 1736-41
• 229 heavily transfused patients.
• 5 patients with anti-HPA antibodies.
• European Journal of Hematology, 56(4) 248-51
• Anti-HPA 9.6.

25
Diagnosis and Management

• IVIG
• Blood, 1990 313-16 400 mg/kg for 5 days.
  Incompatible platelet donor before and after
  treatment. Improved 1-6 hour, not 24 hour.
• American Journal of Hematology, 1991 15-23 Post
  transfusion increment increased. Best in
  patients with PRAlt85.

26
Prevention of alloimmunization

• TRAP Study Group NEJM, 1997 1861-9
• 530 newly diagnosed AML, no alloantibodies,
  undergoing induction chemotherapy.
• Received
• Random donor platelets.
• Filtered, random donor platelets.
• UVB, random donor platelets.
• Filtered, single donor platelets.
• all received filtered, leukoreduced RBCs.

27
Prevention of alloimmunization

• Results LCT positive and refractory.
• Random donor platelets 13
• Filtered, random donor platelets 3
• UVB, random donor platelets 5
• Filtered, single donor platelets 4
• all received filtered, leukoreduced RBCs.
• Concluded leukoreduced, UVB beneficial. Single
  donor platelets not helpful.

28
Case

• Transfused ABO compatible platelets 1 hour
  increment 4,000 24 hour increment 2,000.
• Lymphocytotoxic antibody screen was performed
  PRA 90.
• HLA-matched platelets 1 hour increment 5,000
  24 hour increment 3,000.
• She received 2 more HLA-matched platelet
  transfusions with poor increment.

29
Case

• Transfuse as needed for bleeding.
• Random donor platelets anyone?
• She has no siblings and will undergo
  consolidation chemotherapy with high-dose
  cytosine arabinoside.