P1254413712GdARx

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Transplantation Immunology
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• Lecture objectives
• Students are expected to understand
• Types of rejection (hyperacute, accelerated
  acute, acute and chronic)
• Immunological mechanisms of transplantation
  rejection
• ABO and other Blood types
• GVHD
• Immunosuppressive drugs

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22. Transplantation immunology
CORE

• a. Definitions of autografts, syngrafts,
  allografts, and xenografts
• b. The role of MHC antigens (alloantigens),
  minor histocompatibility antigens and ABO blood
  type in graft acceptance and rejection
• c. Mechanisms of graft rejection
• (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.
• (2) Accelerated Acute occurs within a few
  days mediated by sensitized T cells (CMI)
• (3) Acute occurs within the second week T
  cells (CMI) become sensitized to alloantigens
  (HLA antigens)
• (4) Chronic occurs months to years after the
  transplant multiple immunologic mechanisms
  chronic inflammation, pro-inflammatory cytokines,
  and increased adhesion molecules on endothelium
  important

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Transplantation immunology
CORE

• d. Graft-versus-host reaction (acute and
  chronic)
• (1) Immunologic mechanisms and types of
  transplants involved
• e. Tissue typing, preventing rejection, and
  inducing recipient unresponsiveness
• (1) ABO compatibility
• (2) Crossmatching
• (3) HLA typing
• (4) Immunosuppressive drugs
• (a) Azathioprine
• (b) Cyclosporin
• (c) Corticosteroids
• (d) Anti-lymphocyte antibodies (polyclonal
  anti-T, monoclonal anti-CD3, 4, 8)

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f. Clinical transplantation
CORE

• (1) Kidney
• (2) Liver
• (3) Pancreas
• (4) Heart
• (5) Lung
• (6) Bone marrow

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Tests before transplantation
Tests for compatibility HLA (HLA-A, HLA-B and
HLA-DR ) and ABO
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
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Terminologies

• Autograft transplantation of self tissues to a
  different site of the body (e.g. skin graft in
  burn patients)
• Syngeneic transplant between genetically
  identical individuals
• (Between identical twins)
• Allogeneic transplant between genetically
  different individuals
• (This is most common)
• Xenograft transplantation between different
  species
• (e.g. Pig to Human)

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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
MHC-b
MHC-a
TCR-a
TCR-b
APC
T
APC
T
Organ
A-RBC
Ab to A-RBC
Recipient (B type blood)
Donor (A type blood)
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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
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21. Human Blood Group Antigens
CORE

• a. ABO blood groups (structure, inheritance, and
  naturally occurring antibodies)
• b. Rh blood groups (e.g. erythroblastosis
  fetalis)

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In blood transfusion and organ transplantation,
donors and recipients should be matched for the
A/B/O blood antigens
RBCs dont 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.
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ABO Blood Group System
Blood Type Genotypes ABO EnzymesPresent RBC AntigensPresent Serum Antibodies
A AA, AO "H", "A" A, O anti-B
B BB, BO "H", "B" B, O anti-A
AB AB "H", "A", "B" A, B, O none
O OO "H" O anti-A, anti-B

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How Blood Types Are Inherited
X
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ABO match for blood transfusion
A RhD-
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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.
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Coombs test for blood typing
For blood typing, serums and red blood cells are
mixed and incubated. What is the blood type of
the recipient?
Serum from individuals of type Red blood cells of the potential recipient
O Agglutination
A Agglutination
B No agglutination
AB No agglutination
RhD No agglutination
Red blood cells from individuals of type Serum from the potential recipient
O No agglutination
A Agglutination
B No agglutination
AB Agglutination
RhD Agglutination
O A B AB
RhD ?
-
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• Jesicas story
• (http//www.usnews.com/usnews/health/articles/0307
  28/28jesica.timeline.htm)
• 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.
• Feb. 6, 2003, eveningThe 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.
• Feb. 7, early morningCDS 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.
• 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.
• 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.
• 450 p.m.The heart and lungs are transplanted
  into Jesica.
• 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.
• Feb. 19, 1130 p.m.CDS tells Jaggers a type O
  heart and lungs are available.
• Feb. 20, 1230 a.m.The Santilláns are told that
  replacement organs are on the way.
• 515 a.m.Jaggers begins the second transplant at
  6 a.m.
• Feb. 21, 2 a.m.Jesica's brain function rapidly
  declines.
• 3 a.m.A CT scan indicates significant brain
  swelling and bleeding.
• 9 a.m.Neurological tests show no brain activity.
• Feb. 22, 125 p.m.Jesica is pronounced brain
  dead.
• 507 p.m.Jesica's heart stops.

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Acute rejection
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 by previous grafts or
exposure.
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Cross-reactive recognition for alloreactivityDiff
erences in MHC molecule expression between a
donor and a recipient are said to be allogenic,
provoking alloreactions that cause graft
rejection..
Immune response to foreign antigens
Acute response to the graft expressing allogeneic
MHC
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After transplantation, donor-derived dendritic
cells migrate to the recipient spleen and
activate recipient T cells, which mediate graft
rejection
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MLR (mixed lymphocyte reaction test)Co-culture
of blood cells from donor and recipientMore
proliferation More mismatch
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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
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HLA matching improves the survival of
transplanted kidneys
Matching in HLA A, B, and DR is particularly
important
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2 types of alloreactions
Also, there is GVL (Leukemia) effect against
recipients leukemic or tumor cells
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Diseases for which bone marrow transplantation is
a therapy (BMT)

1. The graft must contain immunocompetent cells (T
   cells)
2. MHC mismatch
3. The recipient must be incapable of rejecting the
   graft

For GVHD to occur
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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
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Stages of GVHD
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• Xenotransplantation
• Pigs donors of choice
• Of similar size, farmed and consumed
• Problems
• Hyperacute rejection
• Humans have antibodies to pig endothelial
  carbohydrates
• Pigs cells are attacked by human complements
• Potential solutions
• Transgenic pigs expressing human DAF, which
  prevents complement reaction
• Transgenic pigs that dont express the reactive
  antigens.
• Advantage
• 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.

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• Immunosuppressive drugs made allogeneic
  transplantation possible.
• They also treat autoimmune diseases.
• Corticosteroids
• Cytotoxic drugs that kill proliferating
  lymphocytes
• Microbial immunosuppressive products
• Immunosuppressive antibodies
• These drugs limit the normal immune response to
  pathogens. Patients are susceptible to infection.
• 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
• These drugs are used in combination to reduce
  toxic or side-effects.
• A long-term side effect is a higher incidence of
  cancer.
• Suppress acute rejection mediated by T cells.

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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.
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Effects of corticosteroids
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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
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Cyclosporine A and FK506 inactivate calcineurin
(a calcium binding protein), which is required
for T, B and granulocyte activation
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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?
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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.
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• Summary
• Transplantation rejections
• Hyperacute
• Factors preexisting antibodies to ABO and other
  antigens.
• Accelerated Acute preexisting memory T cells
• Acute
• Factors MHC compatibility, T cells
• GVHD vs. graft rejection.
• Chronic
• Blood vessel wall thickening.
• Immunosuppressive drugs suppress the acute (and
  also slow down chronic) rejection processes.