Human Leukocyte Antigens and donor selection

Transcription

1 Human Leukocyte Antigens and donor selection Duangtawan Thammanichanond, MD. PhD. Histocompatibility and Immunogenetics Laboratory, Faculty of Medicine Ramathibodi Hospital, Mahidol University

2 Outline HLA gene complex Nomenclature HLA typing resolution definitions and impact on matching status Role of DSA in HSCT HLA-Ab testing

3 Immune system The physiologic function of immune system is defense against infectious microbes. Mechanisms that normally protect individuals from infection and eliminate foreign substances also are capable of causing tissue injury and disease in some situations.

4 Alloimmune response Innate immunity Macrophages, neutrophils, NK cells, cytokines, several cellular receptors, complement, TLRs Found in simplest eukaryotes and more complex animals Adaptive immunity Appeared some 450 million years ago Found in vertebrates Principal cell of adaptive immunity: lymphocytes

5 Adaptive immune response is initiated by recognition of foreign antigens by specific lymphocytes

6 CD4+ and CD8+ T cells recognize peptide-mhc complexes displayed by APCs (signal 1) MHC molecules are required to present antigens to T lymphocytes

7 Pathophysiology of Graft versus Host disease

8 The HLA system Human Leukocyte Antigen = HLA Contribute to the recognition of self antigen and foreign antigen Major histocompatibility complex (MHC)

9 The HLA complex on the short arm of chromosome 6

10 Clustering of immune system genes in MHC HLA is a cluster of more than 200 genes.

11 HLA genes are inherited en bloc Father Mother The linked a b c d genes on A2 A3 A1 A24 each chromosome B46 DR14 B7 DR11 B8 DR17 B60 DR7 constitute a haplotype Child 1 Child 2 a c a d A2 A1 A2 A24 Child 3 b c A3 A1 Child 4 b d A3 A24 B46 B8 B46 B60 B7 B8 B7 B60 DR14 DR17 DR14 DR7 DR11 DR17 DR11 DR7

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14 One very important characteristic of the HLA genes is that they are highly polymorphic (Hypermorphic) Most polymorphic human proteins known to date

15 Number of HLA alleles HLA Polymorphism (HLA allele updated on July 2018 from HLA-A HLA-B HLA-C DRA1 DRB1 DQA1 DQB1 DPA1 DPB1 One very important characteristic of the HLA genes is that they are highly polymorphic (Hypermorphic) and several alleles exist at each locus.

16 Nomenclature Historically, HLA are defined by serological method. After technical development, HLA alleles are defined by DNA typing Serological defined HLA-A DNA typing defined Serological defined HLA-DR DNA typing defined A1 A* DR1 DRB1* A2 A* DR3 DRB1* A3 A* DR4 DRB1* A11 A* DR12 DRB1*

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19 What are P group and G group?

20 P group Alleles with nucleotide sequences encoding the same protein sequence for the antigen binding site A*02:07P contains A*02:07:01/A*02:07:02/A*02:07:03/A*02:07:04/A*02:07:05/ A*02:07:06/A*02:07:07/A*02:07:08/A*02:07:09/A*02:07:10/ A*02:07:11/A*02:265/A*02:426/A*02:452

21 G group Alleles that have identical nucleotide sequences across the exons encoding the peptide binding domains (exon 2 and 3 for HLA class I and exon 2 only for HLA class II alleles) DRB1*14:01:01G contains 14:01:01/14:54:01:01/14:54:01:02/14:54:06 Example Patient DRB1*14:54:01 Donor DRB1*14:01:01 Match at high resolution Mismatch at allele resolution

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23 Multiple allele code/nmdp code

24 What does the blank indicate? An individual may test positive for only one antigen at a given locus Ex. A*01,-, B*08, -, DRB1*03,DRB1*15 Most molecular and certainly all serological typing can NOT distinguish between a single versus a double presence of any particular allele Ans: High possibility is homozygous. Much less likely possibility is that the individual is carrying an allele that cannot be detected by the technique employed.

25 DRB3/4/5 HLA class II paralogues Divergent evolution from a common ancestor DRB4 locus was apparently duplicated from an ancestor of DRB1-DRB4 common locus around 5 million years ago.

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27 Role of HLA in allogeneic HSCT

28 A genotypically identical sibling donor is the best choice. (Matched sibling donor) Only 25-30% of the patients have this option available.

29 British Society of Histocompatibility and Immunogenetics (BSHI) Guideline Patients and selected related donors should be typed for HLA-A, -B, -C, -DRB1 and -DQB1 ( DPB1). (Grade 1A)

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32 HLA matched sibling donors are the gold standard source of stem cell for allogeneic HSCT. 70% of patients do not have available HLA identical sibling. The use of unrelated donors is increasing more rapidly than that of HLA matched-sibling donors in the US.

33 CIBMTR Summary Slides, Available at:

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35 Search for unrelated donor in Thailand Thai National Stem Cell Donor Registry (TSCDR), Thai Redcross Society จ ดต งป พ.ศ Donors ใน registry 170,000 คน, ส วนใหญ low/intermediate res typed 50% ของคนไข ท ข นทะเบ ยนรอ ไม พบ MUD Bone Marrow Donor Worldwide (BMDW) 29 million donors

36 Point to consider The definition of HLA matching is relative to the level of resolution used for the search.

37 Patient Donor Compatibility high resolution Compatibility allele level A*02:01P A*02:01P match Potential match A*02:01 A*02:06 mismatch mismatch A*02:06 A*02:126 match mismatch A*02:01 A*02:09 match mismatch DRB1*04:04 DRB1*04:VN (04:01/04:13/0 4:16/04:21) mismatch mismatch DRB1*14:01:01 DRB1*14:54:01 match mismatch

38 BSHI Guideline A 10/10 high resolution HLA-A, -B, -C, -DRB1 and - DQB1 matched unrelated PBSC or BM donor should be used where possible. (Grade 1A) Where a 10/10 matched PBSC or BM donor is not available, a single mismatch at HLA-A, -B, -C, -DRB1 or -DQB1 is acceptable. (Grade 1A)

39 Impact of single mismatches It is now a general consensus that single HLA mismatches for any single locus have a clinical impact on the HSCT outcome. Evidence for the role of HLA-DPB1 mismatches is now well documented. DPB1 mismatching has been associated with higher risks of agvhd and TRM but alos lower risks of relapse after HSCT, resulting in no difference in OS.

40 In 10/10 matched HSCT, DRB3/4/5 mismatched are associated with increased risk of agvhd.

41 HLA-C mismatch Depend on immunogenicity of certain HLA-C alleles. Residue 116 in the F pocket of the peptide binding groove has been identified as having a high frequency of mismatches that are responsible for adverse clinical outcome. Depend on expression level of certain HLA-C alleles. HLA-C mismatches involving alleles that have higher expression levels was more poorly tolerated than mismatches involving alleles that have lower expression levels.

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44 Haploidentical tx

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47 Making a decision No one source of stem cells is clearly superior to another. No randomized trials comparing alternative donor stem cell sources. Fully matched unrelated donor remain a preferable choice. If time and cost are major concerns, haploidentical tx have the advantage over MUD. Haploidentical donors allow selection from multiple donor possibilities, which in many cases allow selection of a potential donor to whom there is no DSA.

48 Role of donor-specific anti-hla antibodies (DSA) in HSCT

49 Alloimmunization -> HLA Ab Pregnancy Blood transfusion Transplantation Prior sensitization caused by blood transfusion, pregnancy, and organ transplantation can lead to production of alloantibodies.

50 HLA antibody testing Solid phase assays

51 Luminex technology Tells the instrument how much antibody is bound to the bead Laser 2 Tells the instrument which bead is being examined Laser 1

52 Different Luminex assays for HLA-Ab testing 3 Types of assay used for HLA Ab testing: 1. HLA Ab screening screening only (2,000 Baht) 2. PRA class I, II, I&II assess degree of sensitization (class I 4,000 class II 3,400 Baht) 3. HLA antibody-single Antigen class I, II specificity testing (class I 13,000 class II 11,500 Baht)

53 LABScreen Mix = screening test HLA class I: 12 beads HLA class II: 5 beads

54 PRA bead Single Antigen Bead

55 Luminex technology data Single Antigen Beads (SAB) MFI Single antigens present on each bead

56 Role of DSA in human allogeneic HSCT The correlation of pre-transplant with primary graft failure has been confirmed in numerous studies.

57 DSA is associated with primary graft failure in different settings

58 Case Betathal-E ผ ป วยเป นล กคนเด ยว, hepatosplenomegaly พ อแม ย นด เป น haploidentical donor ให

59 Mother (MM A, B, C) Vs. Father (MM B, DRB1, DRB3/4/5)

60 Haploidentical donors All haploidentical donors will be at least a 5/10 match to the patient. Additional matching alleles do not display beneficial impact in a retrospective study. Selection of maternal over paternal donor has been shown to result in better survival in T-cell depleted grafts. In T-cell replete grafts, benefit of maternal vs paternal donor is not clear.

61 DSA to father DSA to Mother

62 MFI ranges from QAP submitting laboratories

63 Evaluation of BMT candidates for desensitization

64 Conclusion Recognition of HLA incompatibilities by the immune system represents a major barrier to allohsct. HLA identical sibling donors are the gold standard. Alternative donor sources are matched unrelated donors, haploidentical donor or a cord blood unit. 10/10 matched unrelated donor remains as a preferable choice.

65 Conclusion (cont.) Haploidentical donors are increasingly used as an alternative source. Haploidentical donors offer advantages- ready availability, decrease cost of graft acquisition and often multiple donor possibilities (allow selection of donor to whom there is no DSA). The presence of DSA is associated with increased risk of graft failure.

66 Conclusion (cont.) For types of HSCT that entail several mismatches, screening for DSA is strongly recommended. No international standard for cutoff value of DSA-MFI. An MFI < 500 is commonly considered negative. Desensitization can extend opportunity for BMT to patients who harbor DSA to their only potential donors.

67 Thank you