Transplantation

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Transplantation
Autograft within the same individual
Isograft (syngeneic graft) between genetically
identical individuals
Allograft between genetically different members
of the same species
Xenograft between different species
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Immune response rejects allograft and xenograft.
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Different stages of graft rejection
Hyperacute rejection (minutes to hours)
Chronic rejection (months to years)
Acute rejection (about 10 days)
transplant
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Hyperacute Rejection
Preformed antibodies against carbohydrate or MHC
antigens on donor vascular endothelium.
cross-react with blood group antigens.
Natural antibodies (IgM) against gut
microorganisms.
cross-react with species-specific carbohydrate
antigens.
IgG antibodies against MHC. From previous blood
transfusion or transplant.
Women may develop antibodies against paternal MHC
from the fetus.
Leukocyte from transfused blood or fetus
Hyperacute rejection
Previous graft
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Hyperacute rejection
Antibodies binding to endothelial antigens
Lysis by MAC
Complement activation
Vascular endothelial cells of donor organ
No treatment
Inflammation (endema)
Loss of anti-thrombotic molecules (blood-clotting)
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Hyperacute rejection against allograft can be
avoided by ABO-matching and crossmatch.
Crossmatch determines whether the recipient has
antibodies against the MHC of the donor.
Recipient serum
Donor leukocyte
complement
Lysis of donor leukocyte?
Hyperacute rejection is a major problem in
Xenografts.
Human antibodies against cell-surface
carbohydrate antigen of other mammals. RCAs are
species-specific.
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T cells cause acute graft rejection.
Athymic mice accept tissue grafts. T cell
reconstitution restores graft rejection.
Immunosuppressants for T cell activation reduce
graft rejection.
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Both CD4 and CD8 T cells contribute to graft
rejection.
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Allogenic MHC activates T cells.
Syngeneic identical in all genetic loci.
Congenic genetically identical except at a
single loci (e.g. MHC).
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Mixed lymphocyte reaction
curve 0 no MHC II disparity
curve 1 1 MHC II disparity
curve 2 2 MHC II disparity
APC-MHC II (stimulator)
CD4 T cells (responder)
Proliferation 3H-thymidine incorporated into DNA
during DNA synthesis
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Allogenic MHC is recognized by 1-10 of T cells.
MLR
Allo self X
Physiological T cell activation
allogenic MHC
donor APC
foreign peptide (X) self MHC
Self APC
Self peptide self MHC
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MHC matching improves graft acceptance.
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MHC typing
Microcytotoxicity
Quick
A few hours
Imprecise
The antibodies do not distinguish all
the difference in HLA.
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Mixed Lymphocyte Reaction (MLR)
Takes several days
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CTL activity can be demonstrated by CML.
Cell-mediated lympholysis assay
priming
priming
Target cell incubated with Na251CrO4
51Cr binds to protein.
Cell lysis by CTLs release 51Cr (?-ray)
MHC I disparity may be sufficient. Priming and
IL2 may be needed.
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NK cells cause hybrid resistance in bone marrow
transplant.
Bone marrow
H-2a/b
H-2a
NK (Ly49 for H-2a)
rejection
NK (Ly49 for H-2b)
H-2b
H-2a/b
NK (Ly49 for H-2a)
rejection
NK (Ly49 for H-2b)
H-2a/b
H-2a/b
NK (Ly49 for H-2a)
acceptance
NK (Ly49 for H-2b)
NK cells make little contribution to rejection of
solid tissues.
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Complete matching of MHC is rare.
Twins
Sibling (1/4)
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Minor Histocompatibility Antigens
Non-MHC alloantigens capable of eliciting a T
cell mediated response
One set of minor histocompatibility antigen is
encoded on the Y chromosome (H-Y). Autosome
minor histocompatibility antigens also exist.
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Acute graft rejection
Injury induces inflammation
graft
Donor APC (direct activation)
Perforin Granzyme FasL-Fas
CTL
Recipient APC (indirect activation)
M?
TH1
IFN-?
Lytic enzymes NO
IL2
CD4 T
CD8 T
Conditioning of APC
CD40L-CD40
Lymph node
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Graft versus host disease (GVHD)
Bone marrow transplant is used to treat leukemia,
lymphoma, and immunodeficiency diseases.
recipient
Lymphocytes depleted by radiation or radiomimetic
drugs.
Donor bone marrow (contaminated by T cells)
HSC
T cell
Recipient APC
BM
Lymph node
Tissue damage, GVHD
effector T cells
Kill leukemia cells (graft versus leukemia
effect)
Depletion of T cells in donor bone
marrow. Immunosuppression drug.
thymocyte
thymus
tolerized T cells
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Immunosuppression drug
TCR/CD3
ZAP-70
Phosphorylation (kinases/phosphatases)
GEF
PLC-??
Ras
PIP2
IP3
DAG
MAP kinase cascade
PKC
Ca2
Cyclosporin A (CsA)
FK506
AP-1
NF-?B
transcription
NFAT
Expression of genes involved in proliferation and
T cell effector functions
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CsA and FK504 (tacrolimus) inhibit IL2 production.
TCR
cyclophilin
Immunophilin peptidyl-prolyl cis-trans isomerases
Cytoplasm
Ca2
FKBP
calmodulin
Ca2/calmodulin
CsA / cyclophilin
FK506 / FKBP
Calcineurin (Ser/Thr phosphatase)
NF-AT
Nuclear factor of activated T cells
NF-AT
active
inactive
IL2 gene
NF-AT
nucleus
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Rapamycin (sirolimus) blocks T cell proliferation.
APC
CD4 T cell
CsA / cyclophilin FK506 / FKBP
Activated CD4 T cell
Rapamycin / immunophilin complex inhibits a
protein kinase (mTOR mammalian target of
rapamycin). mTOR regulates translation, and is
essential for G1 to S phase transition.
Rapamycin / immunophilin
Proliferation
G1
S
Balance between graft tolerance and infection.
Toxic to many tissues (kidney)
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Corticosteroids
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Cytotoxic drugs inhibit DNA synthesis.
Lymphocytes are very sensitive to DNA synthesis
inhibitors.
Azathioprine, mycophenolate, and methotrexate
interfere with the synthesis of nucleotides.
Cyclophosphamide is metabolized to phosphoramide
mustard, which alkylates DNA.
Highly toxic. Used at lower dose in combination
with other drugs.
Radiation
Lymphocytes are very sensitive to X-rays.
Anti-T cell antibodies
Anti-CD3 antibodies, anti-CD2 antibodies,
anti-ICAMI antibodies.
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Azathioprine and corticosteroids
Cyclosporin A and corticosteroids
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Tolerance induction
Mixed chimerism
recipient
T cells depleted by anti-T cell antibodies,
radiation
Donor BM
HSCd
HSCr
HSCd
thymus
APCd
APCr
Td
Tr
Donor organ
Tolerized to both donor and recipient antigens
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Peripheral tolerance induction
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Chronic graft rejection
Arteriosclerosis of graft blood vessels,
accompanied by fibrosis and atrophy.
Chronic rejection is frequently associated with
anti-donor antibodies.
Refractory to increases in immunosuppressive
therapy.
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Major limitation availability of donor organ
Xenograft
Pig as organ donor
Non-human cells contain a disaccharide antigen
(galctosyl-1,3-?-galactose) that is not present
on human cells.
This sugar is present in microbes. Human has
preformed antibodies against it.
RCA does not work well across species.
Transgenic pig expressing human RCA.
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Relevant part in book
Transplantation p479-496 MLR, CML, GVHD
p334-336