HLA Selected Platelets

Transcription

1 HLA Selected Platelets Dr PhD Clinical Scientist Department of Histocompatibility & Immunogenetics NHS Blood and Transplant Colindale

2 Poor increment (<10 x 10 9 /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 NHSBT recognised count could be taken after 10 minutes

3 Causes: Platelet Refractoriness immunological and non-immunological

4 Old/poorly stored platelets, small dose Splenomegaly, hepatomegaly DIC (infection, septicaemia, malignancy) Infection (CMV) Fever Antibiotics, amphotericin B, ambisome, vancomycin, ciprofloxacin,

5 Immunological causes Preformed antibodies in recipient to antigens on platelets: HLA - class I specific antibodies (HLA-A,-B) HPA Most common cause of immune refractoriness Rarely HLA -C antibodies (HPA-1a, -2b etc) Incompatibility for HPA is uncommon ABO - antibodies Incompatible platelets transfused into patients with high titre anti-a or anti-b have a decreased survival

6 patient antibodies Y Y Y Y Y Y Y YY Y SPLEEN phagocytosis removal from circulation transfused platelets complement and Immunoglobulin Fc Receptors

7 Transfusion with non leucodepleted blood History of pregnancy Multiple transfusions Seftel et al 2004; Blood 103(1) :

8 Role of H&I laboratory Investigate 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 patients Essential to evaluate post-transfusion increments Advice on patient management

9 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 identification 1x 6ml clotted serum sample Luminex technology to identify antibody specificity

10 Provision of HLA Selected Platelets (HSP) The provision of HSP is based on the patient s:- HLA type HLA class I antibody specificity. If present, HPA and ABO antibody specificity If requested, CMV and RhD status is taken into consideration.

11 Alleles Antigens Jan 2012 HLA-A 1, HLA-B 2, HLA-C 1, To provide the best matched unit: - Require at least 24 hours notice for routine orders of HLA selected platelets

12 HLA selected platelets Apheresis collection from a single donor Platelet count >240x10 9/ dose Leucocyte depleted Leucocyte count <5x10 6 /dose Irradiated Known HLA and HPA genotype In a stable patient the expected increment after 1 dose = x 10 9 /L

13 The donor and patient are matched at the antigen level of the HLA-A and B loci. Patient Donor 1 Donor 2* A*01,A*02; B*08,B*44 A*01,A*02; B*08,B*44 A*01,A*01; B*08,B*08 *homozygous donor

14 B match grades (B 1 B 2 B 3 B 4 ) 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 against ideally 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,B44 Donor s type: HLA-A1,A68*;B8,B44 (B1 match) * = cross-reactive with HLA-A2

15

16 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

17 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)

18 Value of increments to NHSBT To ensure that NHSBT is providing selected platelets that are beneficial Patients are reviewed weekly If post transfusion increments are poor (<10x10 9 ): Investigate further cause of poor increments presence of anti-hpa or ABO antibodies. Patients actively being transfused: Monitor their antibody profile monthly Ensure no further sensitisation

19 For difficult to match patients: Not all HLA antibodies cause refractoriness Identify acceptable mismatches Currently only receive 50% of increments from hospitals Varies greatly between hospitals

20 Current clinical trial: Epitope matched HLA selected platelets Currently HSP are matched based on antigens However, antibodies bind to epitopes HLAMatchmaker (Duquesnoy) identifies eplets within antigens thought to represent epitopes

21 1 st choice 2 nd choice 3 rd choice Current match grade and priority G N A Grade (19 Eplet) G U A Grade (17 Eplet) G * B2 Grade (1 Eplet) Eplet match and priority G * (1 Eplet) G U (17 Eplet) G N (19 Eplet) Data from Collette Pigden

22 Increase the number of acceptable mismatched units Without further sensitisation Possibly increase our knowledge of acceptable mismatching Still recruiting patients to enrol in the trial

23 Case 1: Platelet refractoriness due to HLA antibodies Patient:: 54 yr old male, diagnosis: Myelodysplasia Referred to H&I Colindale: Poor response to ABO compatible pooled and single donor platelets HLA type HLA-A*30, A*32; B*18, B*35 HLA antibodies detected: All HLA-A locus antigens except A30 and A32 B7 CREG antigens (B7,27,40,42,48,54,55,56,73,81) Also B8,B44,B45,B57,B58

24 Case 1 Due to the patient's antibody profile: predicted not to increment with over 90% of random platelets Pre transfusion count: 13 x 10 9 /L Post transfusion count on random platelets: 18 x 10 9 /L

25 Case 1: Increments following HLA selected platelets Patient's HLA type is A30,A32;B18,B35 A match grade HLA selected platelets incremented from 16 to 43 x10 9 /L However, only 5 A matched donors available in the UK B2 match grade HLA selected platelets A32,X;B14,B52 incremented from 24 to 43 x10 9 /L

26 Patient management Patient with MDS requires lifelong platelet support As 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