1. The Ubiquitous HLA System: applications in transfusion and transplantation Dr Mary Purna Chacko Department of Transfusion Medicine and Immunohaematology Christian Medical College and Hospital, Vellore ISBTI 2012

2. The Human Leukocyte Antigen (HLA) System Highly polymorphic cell surface molecules First identified and characterised in leukocytes

3. HLA expression Class I (HLA A, B and C)– all nucleated cells and platelets Class II (HLA DR, DQ and DP)– B cells, activated T cells, macrophages, dendritic cells

4. Function of HLA molecules – I mmune recognition Antigen presenting cell HLA peptide T cell

5. Allo-recognition Donor antigen presenting cell Recipient T cell Recipient antigen presenting cell TCR donor HLA peptide Recipient HLA donor HLA peptide Processing and presentation by recipient APC DIRECTINDIRECT

6. HLA typing Serology eg. HLA B7 Molecular –low resolution – PCR SSP, PCR SSOP eg. HLA B*07 –Subtype – High resolution PCR SSP, PCR SSOP, SBT eg.HLA B*07:01 –Non coding polymorphisms - SBT eg.HLA B*07:01:01

7. HLA related immune reactions HLA related immune reactions OF RECIPIENT AGAINST DONOR TISSUE HUMORAL IMMUNITY Febrile non- haemolytic transfusion reaction (FNHTR) Immunological platelet refractoriness (IPR) Humoral graft rejection CELLULAR IMMUNITY Cellular graft rejection

8. HLA antibody mediated immune reactions LeukocytePyrogenic cytokines FNHTR Platelets Immunological platelet refractoriness Graft Hyperacute/acute graft rejection

9. HLA antibodies HLA antibodies Induced by Pregnancy Transfusion Transplantation

10. Prevention of allo- sensitisation Leuko-reduction Prevents direct allo-recognition Inhibits indirect allo-recognition Removes antibody target in FNHTR UVB irradiation

11. The allosensitised patient - defining allosensitisation Crossmatch Mixed antigen screening assay Percentage Panel Reactive Antibody (PRA)assay Single antigen assay Does the patient have antibodies against this donor? To what percentage of the population does the patient have antibodies? What is his chance of getting a compatible donor? What are the antigens against which the patient has antibodies? Which donors should be avoided? Does the patient have anti- HLA antibodies?

12. Donor selection 1.Unmatched compatible donor Crossmatch Antigen negative approach – single antigen assay HLA matchmaker 2. Matched donor

13. HLA inheritance Father Mother Child 1Child 2Child 3Child 4 Chance of having an HLA identical sibling =1-(0.75) n Haplotype A Haplotype B Haplotype C Haplotype D Haplotype A Haplotype CHaplotype D Haplotype B Haplotype C Haplotype B Haplotype D

14. HLA related immune reactions OF DONOR AGAINST RECIPIENT Transfusion associated acute lung injury (TRALI) Transfusion associated graft versus host disease (TA GVHD)

15. TRALI Endothelial cell neutrophile Anti HLA/HNA antibody Chemotactic factors Adherence to pulmonary endothelium/epithelium Pulmonary edema

16. PREVENTION OF TRALI Antibodies most commonly found in multiparous women Avoid use of female donor plasma* *Eder et al (Transfusion 2010); Nakazawa et al (Transfusion 2009)

17. Graft versus Host Disease 1.Transfer of viable lymphocytes 2.Inability of host to mount immune response 3.Sharing of HLA haplotypes prevents recipient from recognising donor tissue as foreign A2 B7 A3 B35

18. Prevention of graft versus host disease Choosing HLA matched donors Irradiation – Inactivates viable lymphocytes

19. If we cannot end our differences, at least we can make the world safe for diversity John F. Kennedy