Helen North

HLA Selected Platelets

Dr Helen North PhDClinical Scientist

Department of Histocompatibility & ImmunogeneticsNHS Blood and Transplant Colindale

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Poor increment (<10 x 109/L or CCI <7.5 ) after at least two consecutive transfusions of random donor platelets

Platelet count taken from one hour to 24hours post transfusion.2011 NHSBT recognised count could be taken after 10 minutes

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Platelet Refractoriness

Causes:

immunological and non-immunological

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Old/poorly stored platelets, small doseSplenomegaly, hepatomegalyDIC (infection, septicaemia, malignancy)Infection (CMV)FeverAntibiotics, amphotericin B, ambisome, vancomycin, ciprofloxacin,

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Immunological causesPreformed antibodies in recipient to antigens on

platelets:

HLA - class I specific antibodies (HLA-A,-B)Most common cause of immune refractoriness

Rarely HLA -C

HPA antibodies (HPA-1a, -2b etc)Incompatibility for HPA is uncommon

ABO - antibodiesIncompatible platelets transfused into patients with high titre anti-A or anti-B have a decreased survival

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removal from circulation

phagocytosis

SPLEENpatient antibodies

transfused platelets

Y

Y

Y

YYYY

Y YY

complement and Immunoglobulin Fc Receptors

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Transfusion with non leucodepleted bloodHistory of pregnancy Multiple transfusions

Seftel et al 2004; Blood 103(1) : 333-339

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Role of H&I laboratoryInvestigate for immune refractoriness

Identify the HLA and HPA antibody specificity HLA (HPA) typing of patients

Maintain a panel of HLA and HPA typed donors Select and issue HLA compatible platelets for immune refractory patientsEssential to evaluate post-transfusion incrementsAdvice on patient management

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Laboratory tests prior to provision of HLA selected platelets

HLA class I typing 1x 6ml EDTA anti-coagulated sample

HLA-A, B,C type (HLA class I type)

using PCR-SSP or luminex SSO technology

Antigen level of typing

HLA antibody identification1x 6ml clotted serum sample

Luminex technology to identify antibody specificity

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Provision of HLA Selected Platelets (HSP)

The provision of HSP is based on the patient s:-

HLA typeHLA class I antibody specificity.

If present, HPA and ABO antibody specificity

If requested, CMV and RhD status is taken into consideration.

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Alleles Antigens

HLA-A 1,729 28

HLA-B 2,329 61

HLA-C 1,291 10

Jan 2012

To provide the best matched unit:- Require at least 24 hours notice for routine orders of HLA selected platelets

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HLA selected plateletsApheresis collection from a single donor

Platelet count >240x109/doseLeucocyte depleted Leucocyte count <5x106/doseIrradiated

Known HLA and HPA genotype

In a stable patient the expected increment after 1 dose = 30-40 x 109/L

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The donor and patient are matched at the antigen level of the HLA-A and B loci.

Patient A*01,A*02; B*08,B*44

Donor 1 A*01,A*02; B*08,B*44

Donor 2* A*01,A*01; B*08,B*08

*homozygous donor

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B match grades (B1 B2 B3 B4)Anywhere from one to four mismatched HLA antigens (HLA-A and/or B loci) are transfused into the patient.

Avoid mismatched antigen(s) to which the patient has antibodies againstideally the mismatched antigen(s) will be similar to the patient s HLA antigens (reduces risk of further sensitisation).

Patient s type: HLA-A1,A2;B8,B44Donor s type: HLA-A1,A68*;B8,B44 (B1 match)* = cross-reactive with HLA-A2

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Availability of HLA selected platelets

14,000 typed platelet apheresis donors Currently ~80% of platelet stock are from apheresis donors Patients with common HLA types

a good chance of finding a well matched platelet from the daily platelet stock

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2013 - HLA selected platelet units

In 2013:15,783 HLA selected platelets issued by NHSBT 8,773 issued to London and SE region (55.6%)

Tooting and Colindale H&I lab

75% A and B1 match grade units (Colindale 2013)

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Value of increments to NHSBTTo ensure that NHSBT is providing selected platelets that are beneficialPatients are reviewed weeklyIf post transfusion increments are poor (<10x109):

Investigate further cause of poor increments

presence of anti-HPA or ABO antibodies.Patients actively being transfused:

Monitor their antibody profile monthlyEnsure no further sensitisation

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For difficult to match patients:Not all HLA antibodies cause refractorinessIdentify acceptable mismatches

Currently only receive 50% of increments from hospitals

Varies greatly between hospitals

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Current clinical trial:Epitope matched HLA selected platelets

Currently HSP are matched based on antigens However, antibodies bind to epitopesHLAMatchmaker (Duquesnoy) identifies epletswithin antigens thought to represent epitopes

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3rd choice

2nd choice

1st choice

G052514302071N (19 Eplet)

G072414175858* B2 Grade (1 Eplet)

G072414175973U (17 Eplet)

G072414175973U A Grade (17 Eplet)

G072414175858*(1 Eplet)

G052514302071N A Grade (19 Eplet)

Eplet match and priorityCurrent match grade and priority

Data from Collette Pigden

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Increase the number of acceptable mismatched units

Without further sensitisation

Possibly increase our knowledge of acceptable mismatchingStill recruiting patients to enrol in the trial

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Case 1: Platelet refractoriness due to HLA antibodies

Patient:: 54 yr old male, diagnosis: MyelodysplasiaReferred to H&I Colindale:

Poor response to ABO compatible pooled and single donor platelets

HLA type HLA-A*30, A*32; B*18, B*35HLA antibodies detected:

All HLA-A locus antigens except A30 and A32B7 CREG antigens (B7,27,40,42,48,54,55,56,73,81)Also B8,B44,B45,B57,B58

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Case 1Due to the patient's antibody profile:

predicted not to increment with over 90% of random plateletsPre transfusion count: 13 x 109/LPost transfusion count on random platelets: 18 x 109/L

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Case 1: Increments following HLA selected platelets

Patient's HLA type is A30,A32;B18,B35A match grade HLA selected platelets

incremented from 16 to 43 x109/LHowever, only 5 A matched donors available in the UK

B2 match grade HLA selected plateletsA32,X;B14,B52 incremented from 24 to 43 x109/L

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Patient management

Patient with MDS requires lifelong platelet supportAs an outpatient, requires two HLA selected platelet units/week

to maintain an adequate platelet count. As only a small selection of donors are suitable

Search for suitably matched donors (A, B1,B2 match) and arrange for them to be bled to meet expected requests.Difficult to manage this patient at short notice