Immunology of Transplantation Transplantation Tolerance Nov 27, 2006

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Immunology of Transplantation Transplantation
ToleranceNov 27, 2006
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(No Transcript)
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Immunosuppression-Tolerance
Aim permanent graft survival without affecting
the immune response to other Ags In rodents
permanent graft (both allo and xeno) survival has
been achieved In Human and NHP major problems
remain
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The Non-Human Primate as model
Increased complexity of the immune system of
human transplant recipients leads to barriers to
tolerance that do not exist in murine models.
The progression from rodent to NHP models is
extremely important to the eventual tolerance
induction in human transplantation. NHP models
have a number of important attributes that allow
them to serve as a bridge between what we know
from mice and the application to human graft
survival
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Tolerance vs Immunosuppression
Tolerance is long-lasting and antigen-specific
and non-toxic. Once established it does not
require further intervention Immunosuppression
is short-lived, lasts only as long as the
treatment continues, is toxic and Ag non-specific
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Strategies

• Chemical immunosuppression
• Immunological intervention
• Genetic manipulations
• A combined approach

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Chemotherapy

• Cyclosporine A
• FK506 (Tacrolimus)
• Rapamycin (Sirolimus)
• Mycophenolate-Mofetil

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Cyclosporine A (CsA)
CsA is an immunosuppressive drug widely used to
reduce the activity of the patient's immune
system. It has been extensively used in
transplants of skin, heart, kidney, lung,
pancreas, bone marrow and small intestine. CsA
is a cyclic peptide antibiotic of 11 amino acids
produced by the fungus Tolypocladium inflatum,
initially isolated from a Norwegian soil
sample. Adverse reactions convulsions, gastric
ulcer, pancreatitis, fever, vomiting, diarrhea,
confusion, pruritus, numbness, hypertension,
kidney and liver dysfunction, increased
susceptibility to opportunistic fungal and viral
infections and to malignancies, mainly lymphomas.

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CsA Mode of action Fig 14.5
CsA enters the cell and binds to an immunophilin
called Cyclophilin (CyP). The CsA-CyP complex
bind to Calcineurin preventing its activation.
Failure to activate calcineurin prevents
dephosphorylation of NFAT and thus blocks its
translocation to the nucleus. FK506 also
inhibits calcineurin activation but initial
binding is with another immunophilin called
FK-Binding protein (FKBP)
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FK 506 -Tacrolimus
First described in 1987 at Fujisawa Co. Like CsA
it is a derivative of a soil fungus, It has very
similar immunosupprressive properties to
cyclosporine, but is 10 to 100 times more potent
on a weight basis. See Fig 14.5 ADRs include
kidney damage, seizures, high blood pressure,
diabetes, high blood potassium, headache,
insomnia, confusion, neuropathy, and gout, in
addition to susceptibility to infections and
malignancies
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Rapamycin (Sirolimus) (Rapa)
Macrolide antibiotic first discovered as a
product of the bacterium Streptomyces
hygroscopicus. It is a protein kinase inhibitor.
It binds to FKBP but has no effect on
calcineurin. Instead it blocks the signal
transduction pathway that originates with the
receptors for growth factors (IL-2). The target
is mTOR (mammalian Target of Rapamycin) a protein
conserved from Drosophila which functions in a
signaling pathway that promotes tumor growth.
Rapa allows T cell activation by TCR-peptide MHC
and CD28-B7 engagement but blocks the later
stages of activation by inhibiting proliferation.
The cell cycle is arrested in the G1 phase and
the T cells die by apoptosis. Advantage Less
toxicity (no nephrotoxicity)
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Mycophenolate Mofetil (MMF)
Newer drug than the other 3. Derived from
Mycophenolic Acid. Inhibits lymphocyte
proliferation and antibody production by
interfering with guanosine nucleotide
synthesis. Better tolerated and fewer side
effects than other immunosuppressive agents. The
most common ADR are g.i. symptoms such as nausea,
vomiting and diarrhea, and slightly increased
risk of viral infections Herpes simplex and
Herpes zoster (shingles). These seem to be more
common in patients with MMF as part of
combination immunosuppressive regimens.
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Immunological Intervention

• Several approaches that have proven successful in
  murine models of transplant tolerance
• T-cell depletion
• (2) T-cell costimulation blockade
• (3) Mixed chimerism,
• (4) Regulatory T-cells.

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T cell depletion by Abs
Anti-Lymphocyte globulin (ALG) among the first to
be used. Drawbacks Horse anti-Human Lymphocyte
Ab that induces serum sickness (immune-complex
disease) after parenteral administration
Humanized mAb Mouse CDRs grafted onto human
Framework Fc segments Two types of mAbs
Depleting i.e. kill their targets by
ADCC. Non-depleting Do not kill but inactivate
the T cell
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Anti-CD4 mAb therapy Fig 14.6
Anti-CD4 non-depleting mAb. Induces graft
tolerance in mice but ineffective in NHP
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Costimulatory blockade
Anti-CD28/B7 (CD80/86) Anti CD40/CD40Ligand
(CD154) Combined CD28/B7 CD40/CD40L was most
effective. Use of CTLA4-Ig to block the CD28/B7
pathway was successful in mice but not in NHP. A
new generation of CTLA4-Ig called Belatacept with
higher avidity for B7 was much more effective and
showed promise in NHP either as monotherapy but
especially in association with Rapa and anti-IL2
leading to both T and B cell downregulation and
increased beta islets and renal allograft
survival.
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Mixed Chimerism
The grafting of bone marrow from two different
donors (A and B) into a recipient A after
immunoablative therapy (destruction of its immune
system), results in either macro- or
micro-chimerism in which both A and B
immunocompetent cells (and other blood elements)
coexist. While in mice micro-chimerism is
long-lasting, in NHP its only temporary.
Micro-chimerism lt1-2 of bone marrow cells
are of donor B origin. B allograft ?A(AxB)
chimera survives over 100 days Tolerance
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Mixed chimerism (slide 17)
A
A
B
B
B
A
B
gt 100 days
?why graft both A and B bone marrow into B??
B
Ildstand S and Sachs D Nature 1984
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In NHP, both micro- and macro-chimerism are of
short duration. However there was long term
survival of solid organ allografts. This could be
due to anergy and/or Treg cells for T cell
tolerance, and to accomodation for B cells.
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mAb to CD45RB
CD45 is a phosphatase involved in the activation
of the tyrosine kinase lck. Treatment with mAb
against CD45RB (an activation marker on both T
and B cells) ? switch from CD45RBhi to CD45 RBlow
T cells. The CD45RBlo T cells are considered a
subpopulation of Treg cells
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CD45 isoform expression (slide 20)
O
A B C
Exon B usage IL-2 production Effector cells in
IBD, rejection
Exon O usage IL-4 production CTLA-4
expression Regulatory cells
CD45RB high
CD45RB low
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Benefit of anti CD45RB mAb in kidney transplants
NHP (slide 21)
Lazarovits and Zhong et al, Nature 1996380
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Tolerance strategies (slide 23)
Therapy Rodents
Primates Humans
m CD4 CD8 ?
? ? mAb CD40L
? X
? mAb CD3
? ?
? CTLA-4-Ig ?
X ? mAb CD25
?
? ? mAb LFA-1
? ?
? mAb CD45RB
? X
? DSG/LF ?
X ?
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Donor Specific Transfusion (DST
Transfusion of allogeneic donor cells may induce
tolerance to a specific allograft. Transfusion
of donor splenic leukocytes at the time of
transplantation synergizes with B7/CD154
co-stimulatory blockade in promoting long-term
allograft survival, inducing tolerance, and
preventing chronic allograft rejection in some
models. Recent evidence suggests that indirect
presentation of the DST cells induces graft
tolerance via Treg cells
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Graft Accomodation
The process whereby the graft acquires resistance
to Ab (C)-mediated damage. It is observed
usually after depletion of anti-allograft Abs
from the recipient by absorption or
plasmapheresis. Although depletion is
short-lived, the graft survives even when Abs
return. Accomodated vascularized grafts express
anti-apoptotic genes in endothelial and smooth
muscles
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Genetic manipulations
Complement Regulatory Proteins Pigs made to
express human CRP genes Human Decay Accelerating
Factor (hDAF)
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hDAF Tg Pigs (slide 27)
hDAF
hDAF
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Genetic Manipulations contd.
Galactosyl alpha 1,3 Galactose (alpha-Gal)
deficient pigs or alpha-Gal knock-out (ko)
pigs. The grafting of pig alph-Gal -/- kidneys
or hearts to NHP failed to prolong graft survival
due to Ab against other (non-Gal) antigens
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Cloning of ?-Gal Knock out Pigs (slide 29)
Jan 3, 2002
Jan 2, 2002
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The present approaches to clinical
immunosuppression have contributed to significant
improvements in allograft survival in human and
NH primates but without full-fledged tolerance
induction (except for rodents) There still is
high toxicity, risk of infections, and failure
to prevent Ab and C-mediated rejection. The
final goal of graft- (or MHC)-specific tolerance
has not yet been achieved. It is hoped however
that combined use of immunosuppressive drugs with
monoclonal Ab therapy to T and B cell markers and
with genetically-modified donor organs would
require much smaller and therefore less toxic
dosages to achieve long term organ survival.
Most tolerance-inducing protocols discussed here
are
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