MHC Genetics and Transplantation

1. MHC Genetics and Transplantation Dr. Prakash Nagarkatti Associate Dean for Basic Science 733-3180 pnagark@uscmed.sc.edu

2. Transplantation • Graft or Transplant: Transfer of living cells, tissues and organs from one part of the body to another or from one individual to another.

3. Autogeneic (survive) Types of grafts H-2k Syngeneic (survive) Allogeneic (rejected) H-2b H-2b Xenogeneic (rejected) Xenogeneic (rejected)

4. Is allograft rejection immunological? Graft rejected in 14 days Strain B graft Strain A Graft B rejected in 7 days Graft C rejected in 14 days Strain B Strain C Thus, allograft rejection meets two important properties of immune system----specificity and memory.

5. MHC • Each species has several histocompatibility (H) loci. • In mice there are over 40 loci, called H-1, H-2,H-3,.............H-40. • If mice differ in any other loci except H-2, (such as H-1), graft rejection is slow. • Thus, H-2 was called MHC and all other loci were called minor histocomp. loci

6. Human and mouse MHC loci Human DP DQ DR B C A Complement Class I MHC D Region(Class II MHC) Mouse Complement I-Region K I-A I-E D Class I MHC

7. MHC Class I MHC Any nucleated cell Class I MHC Class II MHC B cell Macrophage Dendritic

8. Polymorphism of MHC antigens (based on phenotype)

9. MHC is highly polymorphic • MHC is highly polymorphic--->there are 100s of alleles at class I and class II MHC. • Thus in mouse species the MHC diversity can be as high as 1012. • Thus it is almost impossible to find 2 individuals having identical MHC. K IA IA IE IE D 100 X100 X100 X100X100 X100= 1012

10. Why is MHC polymorphic? • Let’s consider 2 scenarios: • All individuals have the same MHC. • Each individual has a different MHC.

11. Consider that all individuals had same MHC Virus MHC

12. All individuals had same MHC Died from grave consequences of a viral infection Died from grave consequences of a viral infection Died from grave consequences of a viral infection Died 1997 due to a viral infection Virus MHC

13. All individuals have different MHC Virus MHC

14. All individuals have different MHC Died in 1997 due to unique MHC Virus MHC

15. All individuals have different MHC Died in 1997 due to unique MHC Virus MHC

16. All individuals have different MHC Died in 1997 due to unique MHC Virus MHC

17. MHC polymorphism ensures that all individuals in a species are not equally susceptible to an infection

18. How does MHC influence allograft rejection? • Any difference in K, I or D subregion is enough to induce graft rejection. • KbIbDb---->KpIpDp--->Rejected in 7 days. • KbIbDb---->KpIpDb--->Rejected in 15 days. • KbIbDb---->KpIbDb--->Rejected in 30 days.

19. Differences in Class II MHC is also sufficient to induce graft rejection. • Example: KbIbDb---->KbIpDb--->Rejected.

20. Even within an inbred strain, graft can be rejected mouse Accepted mouse mouse Accepted mouse mouse Accepted mouse mouse mouse Rejected

21. Y chromosome in males encodes for a minor Ag called H-Y. Female mice recognize this as foreign and reject the graft.

22. Genetics of MHC Ag expression in inbred strains of mice X C3H(H-2k) DBA/2 (H-2d) Accept Accept Reject Reject X F 1(H-2 k/d) F 2 H-2k H-2d H-2 k/d H-2 k/d

23. The inheritance of MHC genes

24. Genetics of Human MHC Q/R M/N M/Q M/R N/Q N/R

25. There is one-in-four chance that HLA is compatible between siblings. • Thus HLA matched siblings are the best donors.

26. Who is the best donor? HLA matched sibling 100 % graft survival HLA matched unrelated 50 >2HLA mismatched unrelated 0 1 2 3 4 5 Survival Time Blood group ABO matching is very important!

27. Death of transplant recipient due to blood type mix-up continues to resonate in transplant community, mediaThe death of Jesica Santillan due to a blood type mismatch at Duke University Medical Center CBS "60 Minutes" aired a segment entitled "Anatomy of a Mistake”Jesica was type O, the donor was type A

28. Tissue Typing(or HLA-typing) Used to identify HLA molecules on cells Ab against HLA1 + complement Recipient Donor Cells die, appear blue

29. Uses of Tissue Typing: • Disputed paternity testing. A/B C/D E/F A/C, A/D, B/C, B/D

30. Uses of Tissue Typing: • Identifying lost babies! A/B C/D E/F G/H A/C, A/D, B/C, B/D E/G, E/H, F/G, F/H

31. Uses of Tissue Typing: • Exchange of babies in Toronto: A/B C/D E/F G/H A/C, A/D, B/C, B/D E/G, E/H, F/G, F/H

32. Uses of Tissue Typing: • Exchange of babies in Toronto: A/B C/D E/F G/H A/C, A/D, B/C, B/D E/G, E/H, F/G, F/H A/C, A/D, B/C, B/D

33. Mixed Lymphocyte Reaction: Recipient Donor • Strong Proliferation--->High incompatibility • Weak proliferation--->Low incompatibility • No proliferation---> 100% compatibility • Helps to identify any antigenic differences between donor and recipient Cell Proliferation + (Irradiate)

34. Allogeneic Hematopoietic Stem Cell Transplantation (HSCT) Used to treat certain types of cancers, diseases of blood and bone marrow. Bone marrow is used as a source of stem cells. This allows high dose of chemo- and radiation therapy to treat cancer that destroys BM stem cells. Uses BM from HLA-matched sibling/relative If mismatched, can trigger graft-vs-host disease Some times the graft-versus leukemia can help the cancer patient.

35. Graft versus Host Reaction (GVHR) • When grafted tissue has mature T cells, they will attack host tissue leading to GVHR. • Major problem for bone marrow transplant. • Methods to overcome GVHR: • Treat bone marrow to deplete T cells. • Use autologous bone marrow. • Use umbilical cord blood.

36. GVH disease in humans

37. Graft-versus-Leukemia effect Allogeneic BM cells MHC Normal cell T cells Cancer MHC Graft vs Host effect Graft vs Leukemia effect

38. Immunologically Privileged Sites • Sites where incompatible grafts survive • Ex: Hamster’s cheek pouch • Anterior chamber of eye • Brain • Lack good lymphatic system • Cells express FasL

39. Immunologically privileged tissue • Corneal or cartilage grafts---covered with Sialomucin which masks the MHC • Testes: express Fas ligand

40. Role of FasL in graft rejection: Fas Fas L T cell Testes

41. Mechanisms of allograft rejection: CD4+ IL-2, IFN-g, TNF Th1 CTL CD8+ Class II Class I Macrophage Graft cell ADCC Almost 10% of our lymphocytes can react against foreign MHC

42. agent mode of action application(s) organ transplant, hypersensitivity, autoimmunity organ transplant, corticosteroids, prednisone cyclosporine, ticrolimus anti-inflammatory, altering T-cell and PMN traffic inhibition of IL-2 production by T cells Inhibition of T cell activation by IL-2 organ transplant rapamycin Immunosuppresseive agents

43. agent mode of action application(s) purine metabolism organ transplant azathioprine, 6-MP organ transplant methotrexate folate metabolism autoimmune diseases, organ transplant cyclophosphamide, melphalan alkylation of DNA, RNA and proteins x-irradiation Lymphopenia malignancy/marrow transplantation Immunosuppresseive agents

44. Why is fetus not rejected by the mother? C/D A/B A/C, A/D, B/C, B/D

45. Fetus as an allograft Strain A Strain B mate Immunize with father’s Ags Skin graft rejected fetus survives

46. Why is fetus not rejected? • Placenta acts as a barrier or filter. • It filters anti-MHC Abs. • Trophoblast---outermost layer of fetal tissue---is in direct contact with maternal blood. • Trophoblast expresses weak or no MHC.

47. Why is fetus not rejected? • progesterone---hormone---immunosuppressive. • Placenta expresses FasL. • Spontaneous abortions are some times triggered by maternal immune response against fetus.

48. Ethical aspects: • Baby Fae---> Baboon heart in 1984---> survived for 35 days. • Cloning Human embryos. • In U.S. each year 3000 patients die and 43,000 patients are denied heart transplants. • Declaring patients dead before they are completely dead?

49. Ethical aspects Organs for sale !

50. Ethical aspects: • Thanks to mother nature ---MHC is polymorphic.