Transplantation Immunology Lecture objectives Students are ...
<ul><li>Lecture objectives </li></ul><ul><li>Students are expected to understand: </li></ul><ul><li>Types of rejection (hyperacute, accelerated acute, acute and chronic) </li></ul><ul><li>Immunological mechanisms of transplantation rejection </li></ul><ul><li>ABO and other Blood types </li></ul><ul><li>GVHD </li></ul><ul><li>Immunosuppressive drugs </li></ul>
22. Transplantation immunology <ul><li>a. Definitions of autografts, syngrafts, allografts, and xenografts </li></ul><ul><li>b. The role of MHC antigens (alloantigens), minor histocompatibility antigens and ABO blood type in graft acceptance and rejection </li></ul><ul><li>c. Mechanisms of graft rejection </li></ul><ul><li>(1) Hyperacute rejection: recipient has pre-existing antibodies to ABO antigens or HLA antigens; occurs within minutes to hours; mechanism by Types II and III reactions. </li></ul><ul><li>(2) Accelerated Acute: occurs within a few days; mediated by sensitized T cells (CMI) </li></ul><ul><li>(3) Acute: occurs within the second week; T cells (CMI) become sensitized to alloantigens (HLA antigens) </li></ul><ul><li>(4) Chronic: occurs months to years after the transplant; multiple immunologic mechanisms; chronic inflammation, pro-inflammatory cytokines, and increased adhesion molecules on endothelium important </li></ul>CORE
f. Clinical transplantation <ul><li>(1) Kidney </li></ul><ul><li>(2) Liver </li></ul><ul><li>(3) Pancreas </li></ul><ul><li>(4) Heart </li></ul><ul><li>(5) Lung </li></ul><ul><li>(6) Bone marrow </li></ul>CORE
Tests for pathogens Human Immunodeficiency Virus (HIV-1/2), Hepatitis B (HbsAg) Hepatitis C (HCV). Also CMV, HTLV-1, syphilis, Epstein-Barr virus, and HTLV-2 Tests for compatibility: HLA (HLA-A, HLA-B and HLA-DR ) and ABO Tests before transplantation
Terminologies <ul><li>Autograft: transplantation of self tissues to a different site of the body </li></ul><ul><li>(e.g. skin graft in burn patients) </li></ul><ul><li>Syngeneic transplant: between genetically identical individuals </li></ul><ul><li>(Between identical twins) </li></ul><ul><li>Allogeneic transplant : between genetically different individuals </li></ul><ul><li>(This is most common) </li></ul><ul><li>Xenograft: transplantation between different species </li></ul><ul><li>(e.g. Pig to Human) </li></ul>
Transplantation Immunology Allogenic immune responses after transplantation are caused by genetic differences (e.g. MHC and ABO) between donors and recipients. Immune system A Immune system B Organ Recipient (B type blood) T T APC APC MHC-a MHC-b TCR-a TCR-b Ab to A-RBC A-RBC Donor (A type blood)
Hyperacute (immediate) reaction Response to ABO antigens (and/or MHC class I/II molecules) expressed by Endothelial cells 1. Preexisting antibodies to A/B antigen in recipients bind A/B antigens on endothelial cells of transplanted organs, and induce acute rejection. 2. This can be caused by pre-existing antibodies to MHC I/II molecules too, which can arise from pregnancy, blood transfusion or previous transplantation. In this case, fetal cells induce antibody formation in the mother Graft failure
21. Human Blood Group Antigens <ul><li>a. ABO blood groups (structure, inheritance, and naturally occurring antibodies) </li></ul><ul><li>b. Rh blood groups (e.g. erythroblastosis fetalis) </li></ul>CORE
In blood transfusion and organ transplantation, donors and recipients should be matched for the A/B/O blood antigens RBCs don’t express MHC molecules but express different types of carbohydrate antigens (A,B, and O). These antigens are similar to bacterial cell surface antigens. Therefore, most people possess antibodies that react against the antigens except the antigen they express themselves. O persons have antibodies to A and B. Anti-A or B antibodies cause complement fixation and rapid clearance of RBC (hemolytic reaction; renal failure) or hyperacute rejection. Similar to TYPE II hypersensitivity reaction. There is no antibody to O antigen in A, B or AB person because all express the core O antigen. Remember that self reactive B cells are deleted in the body.
ABO Blood Group System anti-A, anti-B O "H" OO O none A, B, O "H", "A", "B" AB AB anti-A B, O "H", "B" BB, BO B anti-B A, O "H", "A" AA, AO A Serum Antibodies RBC Antigens Present ABO Enzymes Present Genotypes Blood Type
How Blood Types Are Inherited X AO AB AA AB OA OB
Other blood group antigens (minor antigens) Rhesus: C, D and E RhD is most important clinically among minor antigens due to its high immunogenicity RhD+ : 85%; RhD-:15% Other minor blood group antigens such as Kell, Duffy, and MN are less immunogenic.
Coomb’s test for blood typing RhD ? O A B AB For blood typing, serums and red blood cells are mixed and incubated. What is the blood type of the recipient? - No agglutination RhD+ No agglutination AB No agglutination B Agglutination A Agglutination O Red blood cells of the potential recipient Serum from individuals of type Agglutination RhD+ Agglutination AB No agglutination B Agglutination A No agglutination O Serum from the potential recipient Red blood cells from individuals of type
<ul><li>Jesica’s story: </li></ul><ul><li>(http://www.usnews.com/usnews/health/articles/030728/28jesica.timeline.htm) </li></ul><ul><li>This is the sequence of events, as reconstructed by U.S. News , that led to the death of Jesica Santillán at Duke University Medical Center after she received a transplanted heart and lungs with the wrong blood type. </li></ul><ul><li>Feb. 6, 2003, evening The New England Organ Bank can't find a local candidate for a heart and lungs from a donor at Children's Hospital Boston with type A blood. The "match-run list" of candidates shows two possibilities, a child and an adult, at Duke University Medical Center in Durham, N.C. NEOB notifies Carolina Donor Services, Duke's link with the national transplant system. CDS phones Duke. Pediatric heart transplant surgeon James Jaggers turns the organs down for the child listed, but requests them for 17-year-old Jesica Santillán. He does not recall mentioning or discussing blood type. CDS verifies with NEOB that Jesica is not on the match-run list. </li></ul><ul><li>Feb. 7, early morning CDS calls the United Network for Organ Sharing in Richmond, Va., which has data on everyone awaiting an organ, to ask if Jesica is wait-listed for a heart and lungs. The CDS coordinator mentions that she has type A blood. She is type O. The donor is type A. A UNOS specialist says she is listed. He does not address the misstated blood type. CDS notifies NEOB that Jesica is listed, and NEOB releases the organs to Jaggers. CDS reports this back to Jaggers. </li></ul><ul><li>About 9 a.m. Duke surgeon Shu Lin and a CDS representative fly to Boston. Lin calls Jaggers with a thumbs-up on the condition and size of the donor heart and lungs. Blood type is not mentioned. </li></ul><ul><li>11 a.m. The organs are removed and packed in ice. A tag identifies the blood as type A. The organs are flown to Durham. </li></ul><ul><li>4:50 p.m. The heart and lungs are transplanted into Jesica. </li></ul><ul><li>10 p.m. As Jesica is being closed, Duke's transplant lab reports the mismatch. Antirejection drugs are administered, but the heart and lungs begin to fail. Jesica is put on a heart-lung machine. </li></ul><ul><li>Feb. 19, 11:30 p.m. CDS tells Jaggers a type O heart and lungs are available. </li></ul><ul><li>Feb. 20, 12:30 a.m. The Santilláns are told that replacement organs are on the way. </li></ul><ul><li>5:15 a.m. Jaggers begins the second transplant at 6 a.m. </li></ul><ul><li>Feb. 21, 2 a.m. Jesica's brain function rapidly declines. </li></ul><ul><li>3 a.m. A CT scan indicates significant brain swelling and bleeding. </li></ul><ul><li>9 a.m. Neurological tests show no brain activity. </li></ul><ul><li>Feb. 22, 1:25 p.m. Jesica is pronounced brain dead. </li></ul><ul><li>5:07 p.m. Jesica's heart stops . </li></ul>
Acute rejection (within weeks) is caused by effector CD4+ Th1 cells or CD8 T cells responding to HLA differences between donors and recipients (similar to TYPE IV hypersensitivity reaction); Can be prevented by immunosuppressive drugs or anti-T cell antibodies Accelerated Acute rejection ( within days) is mediated by sensitized (memory) T cells induced by previous grafts or exposure. Acute rejection:
Cross-reactive recognition for alloreactivity Differences in MHC molecule expression between a donor and a recipient are said to be allogenic, provoking alloreactions that cause graft rejection.. Acute response to the graft expressing allogeneic MHC Immune response to foreign antigens
After transplantation, donor-derived dendritic cells migrate to the recipient spleen and activate recipient T cells, which mediate graft rejection
MLR (mixed lymphocyte reaction test): Co-culture of blood cells from donor and recipient More proliferation: More mismatch
Chronic rejection: Occurs months or years after transplantation. Thickening of blood vessel walls leading to ischemia The mechanism is not entirely clear but it may be due to chronic DTH response localized tissue anemia due to obstruction of the inflow of arterial blood
HLA matching improves the survival of transplanted kidneys Matching in HLA A, B, and DR is particularly important
2 types of alloreactions Also, there is GVL (=Leukemia) effect against recipients’ leukemic or tumor cells
Diseases for which bone marrow transplantation is a therapy (BMT) <ul><li>The graft must contain immunocompetent cells (T cells) </li></ul><ul><li>MHC mismatch </li></ul><ul><li>The recipient must be incapable of rejecting the graft </li></ul><ul><li>(=immunodeficient after radiation/chemo therapy) </li></ul>For GVHD to occur:
Pros and Cons of bone marrow transplantation (BMT) Pros: Can cure a number of malignant and genetic diseases Large numbers of potential donors Simple procedure: takes 30 min to take out marrow from a donor from iliac crests of the pelvis under local anesthesia Cons: 1. In GVHD, donor-derived lymphocytes attack host tissues 2. Non-functional T cells due to MHC mismatch Alternative sources of stem cells to minimize GVHD 1. Autologous BMT: using self marrow obtained before radiation therapy 2. Umbilical cord blood cells, which are enriched with hematopoietic stem cells (CD34+ cells). These fetal cells cause less GVHD. 3. Isolated stem cells free of T cells
Stages of GVHD <ul><li> Stage 1 (mild) : a skin rash over less than 25% of the body. </li></ul><ul><li>Stage 2 (moderate) : a skin rash over a more than 25% of the body accompanied by mild liver or stomach and intestinal disorders. </li></ul><ul><li>Stage 3 (severe) : redness of the skin, similar to a severe sunburn, and moderate liver, stomach and intestinal problems . </li></ul><ul><li>Stage 4 (life-threatening) : blistering, peeling skin, and severe liver, stomach, and intestinal problems. </li></ul>
<ul><li>Xenotransplantation </li></ul><ul><li>Pigs: donors of choice </li></ul><ul><li>Of similar size, farmed and consumed </li></ul><ul><li>Problems: </li></ul><ul><li>Hyperacute rejection </li></ul><ul><li>Humans have antibodies to pig endothelial carbohydrates </li></ul><ul><li>Pig’s cells are attacked by human complements </li></ul><ul><li>Potential solutions: </li></ul><ul><li>Transgenic pigs expressing human DAF, which prevents complement reaction </li></ul><ul><li>Transgenic pigs that don’t express the reactive antigens. </li></ul><ul><li>Advantage: </li></ul><ul><li>MHC molecules of different species are so different from those of humans that human T cells can not recognize them. So T-cell mediated rejection is mild. </li></ul>
<ul><li>Immunosuppressive drugs made allogeneic transplantation possible. </li></ul><ul><li>They also treat autoimmune diseases. </li></ul><ul><li>Corticosteroids </li></ul><ul><li>Cytotoxic drugs that kill proliferating lymphocytes </li></ul><ul><li>Microbial immunosuppressive products </li></ul><ul><li>Immunosuppressive antibodies </li></ul><ul><li>These drugs limit the normal immune response to pathogens. Patients are susceptible to infection. </li></ul><ul><li>As the immune system accommodates the graft, the dose of immunosuppressive drugs is gradually reduced so that patients can have certain defense ability against pathogens </li></ul><ul><li>These drugs are used in combination to reduce toxic or side-effects. </li></ul><ul><li>A long-term side effect is a higher incidence of cancer. </li></ul><ul><li>Suppress acute rejection mediated by T cells. </li></ul>
1. Corticosteroids: Prednisolone Induces expression of many genes, one of which is IkB-alpha that inhibits NF-Kb activation. Side effects: fluid retention, weight gain, diabetes, loss of bone mineral, thinning of the skin.
Cyclosporine A, FK506 (Tacrolimus) and Rapamycin Cyclosporine: a cyclic decapeptide from a soil fungus. Targets calcineurin and blocks NFAT activation FK506: A macrolide isolated from a soil actinomycete Targets calcineurin and blocks NFAT activation Rapamycin: A macrolide isolated from a soil bacterium. Blocks signal transduction from IL-2 receptor
Cyclosporine A and FK506 inactivate calcineurin (a calcium binding protein), which is required for T, B and granulocyte activation
Cytotoxic drugs: kill dividing cells Azathioprine: inhibits DNA replication. Kills not only lymphocytes but also all dividing cells in the body: bone marrow cells, intestinal epithelial cells and hair follicle cells Cyclophosphamide: cross-link DNA. Side effect includes damage to bladder. Methotrexate: prevents DNA replication by inhibiting thymidine synthesis Specificity issue?
Antibodies specific to human T cells (e.g. anti-CD3) are used to deplete T cells or to suppress their functions : These antibodies can be made in sheep or goats that have been immunized with human lymphocytes or from mouse hybridoma cells. Limitation: These non-human antibodies can induce formation of antibodies to the anti-T cell antibodies, which reduces the effectiveness of anti-T cell antibodies after the first use .
<ul><li>Summary: </li></ul><ul><li>Transplantation rejections: </li></ul><ul><li>Hyperacute </li></ul><ul><li>Factors: preexisting antibodies to ABO and other antigens. </li></ul><ul><li>Accelerated Acute: preexisting memory T cells </li></ul><ul><li>Acute: </li></ul><ul><li>Factors: MHC compatibility, T cells </li></ul><ul><li>GVHD vs. graft rejection. </li></ul><ul><li>Chronic </li></ul><ul><li>Blood vessel wall thickening. </li></ul><ul><li>Immunosuppressive drugs suppress the acute (and also slow down chronic) rejection processes. </li></ul>