Transplantation Immunology
Immunology
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Introduction
Immunology
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Conceptions
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Transplantation
Grafts
Donors
Recipients or hosts
Orthotopic transplantation
Heterotopic transplantation
Immunology
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Nobel Prize in Physiology or Medicine
1912
• Alexis Carrel (France)
• Work on vascular suture
and the transplantation of
blood vessels and organs
Great events in history
of transplantation
Immunology
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Nobel Prize in Physiology or Medicine
1960
• Peter Brian Medawar (1/2)
• Discovery of acquired
immunological tolerance
– The graft reaction is an
immunity phenomenon
– 1950s, induced immunological
tolerance to skin allografts in
mice by neonatal injection of
allogeneic cells
Great events in history
of transplantation
Immunology
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Nobel Prize in Physiology or Medicine
1990
• Joseph E. Murray (1/2)
• Discoveries concerning
organ transplantation in the
treatment of human disease
– In 1954, the first successful
human kidney transplant was
performed between twins in
Boston.
– Transplants were possible in
unrelated people if drugs
were taken to suppress the
body's immune reaction
Great events in history
of transplantation
Immunology
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Nobel Prize in Physiology or Medicine
1980
• George D. Snell (1/3), Jean Dausset (1/3)
• Discoveries concerning genetically
determined structures on the cell surface
that regulate immunological reactions
– H-genes (histocompatibility genes), H-2 gene
– Human transplantation antigens (HLA) ----MHC
Great events in history
of transplantation
Immunology
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Nobel Prize in Physiology or Medicine
1988
• Gertrude B. Elion (1/3) , George H. Hitchings (1/3)
• Discoveries of important principles for drug
treatment
– Immunosuppressant drug (The first cytotoxic drugs)
----- azathioprine
Great events in history
of transplantation
Immunology
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Today, kidney, pancreas, heart,
lung, liver, bone marrow, and cornea
transplantations are performed
among non-identical individuals with
ever increasing frequency and
success
Immunology
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Classification of grafts
• Autologous grafts (Autografts)
– Grafts transplanted from one part of the body
to another in the same individual
• Syngeneic grafts (Isografts)
– Grafts transplanted between two genetically
identical individuals of the same species
• Allogeneic grafts (Allografts)
– Grafts transplanted between two genetically
different individuals of the same species
• Xenogeneic grafts (Xenografts)
– Grafts transplanted between individuals of
different species
Immunology
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Immunology
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• Grafts rejection is a kind of specific
immune response
– Specificity
– Immune memory
• Grafts rejection
– First set rejection
– Second set rejection
Immunology
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First- and Second-set Allograft Rejection
Immunology
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Part one
Immunological Basis of
Allograft Rejection
Immunology
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I. Transplantation antigens
• Major histocompatibility antigens
(MHC molecules)
• Minor histocompatibility antigens
• Other alloantigens
Immunology
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1. Major histocompatibility antigens
• Main antigens of grafts rejection
• Cause fast and strong rejection
• Difference of HLA types is the main
cause of human grafts rejection
Immunology
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2. Minor histocompatibility antigens
• Also cause grafts rejection, but slow
and weak
• Mouse H-Y antigens encoded by Y
chromosome
• HA-1～HA-5 linked with non-Y
chromosome
Immunology
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Immunology
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3. Other alloantigens
• Human ABO blood group antigens
• Some tissue specific antigens
– Skin＞kidney＞heart＞pancreas ＞liver
– VEC antigen
– SK antigen
Immunology
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II. Mechanism of allograft
rejection
• Cell-mediated Immunity
• Humoral Immunity
• Role of NK cells
Immunology
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1. Cell-mediated Immunity
• Recipient's T cell-mediated cellular
immune response against alloantigens
on grafts
Immunology
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Molecular Mechanisms of
Allogeneic Recognition
？T cells of the recipient recognize the
allogenetic MHC molecules
？Many T cells can recognize allogenetic
MHC molecules
– 10-5-10-4 of specific T cells recognize
conventional antigens
– 1%-10% of T cells recognize allogenetic
MHC molecules
Immunology
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？The recipient’ T cells recognize
the allogenetic MHC molecules
• Direct Recognition
• Indirect Recognition
Immunology
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Direct Recognition
• Recognition of an intact allogenetic MHC
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molecule displayed by donor APC in the
graft
Cross recognition
– An allogenetic MHC molecule with a bound
peptide can mimic the determinant formed by a
self MHC molecule plus foreign peptide
– A cross-reaction of a normal TCR, which was
selected to recognize a self MHC molecules plus
foreign peptide, with an allogenetic MHC
molecule plus peptide
Immunology
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• Cross recognition
Immunology
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• Passenger leukocytes
– Donor APCs that exist in grafts, such as
DC, MΦ
– Early phase of acute rejection
– Fast and strong
Immunology
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？Many T cells can recognize
allogenetic MHC molecules
• Allogenetic MHC molecules (different residues)
• Allogenetic MHC molecules–different peptides
• All allogenetic MHC molecules on donor APC
can be epitopes recognized by TCR
Immunology
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Indirect recognition
• Uptake and presentation of allogeneic
donor MHC molecules by recipient
APC in “normal way”
• Recognition by T cells like
conventional foreign antigens
Immunology
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Immunology
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• Slow and weak
• Late phase of acute rejection and chronic
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rejection
Coordinated function with direct recognition in
early phase of acute rejection
Immunology
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Difference between Direct Recognition
and Indirect Recognition
Direct
Recognition
Indirect
Recognition
Allogeneic MHC
molecule
Intact allogeneic
MHC molecule
Peptide of allogeneic
MHC molecule
APCs
Recipient APCs are
not necessary
Recipient APCs
Activated T cells
CD4＋T cells and/or
CD8＋T cells
CD4＋T cells and/or
CD8＋T cells
Roles in rejection
Acute rejection
Chronic rejection
Degree of rejection
Vigorous
Weak
Immunology
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Role of CD4＋T cells and CD8＋T cells
• Activated CD4+T by direct and indirect
recognition
– CK secretion
– MΦ activation and recruitment
• Activated CD8+T by direct recognition
– Kill the graft cells directly
• Activated CD8+T by indirect recognition
– Can not kill the graft cells directly
Immunology
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Immunology
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2. Humoral immunity
• Important role in hyperacute rejection
(Preformed antibodies)
– Complements activation
– ADCC
– Opsonization
• Enhancing antibodies
/Blocking antibodies
Immunology
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3 .Role of NK cells
• CKs secreted by activated Th cells can
promote NK activation
Immunology
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Part two
Classification and Effector
Mechanisms of Allograft
Rejection
Immunology
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Classification of Allograft
Rejection
• Host versus graft reaction (HVGR)
– Conventional organ transplantation
• Graft versus host reaction (GVHR)
– Bone marrow transplantation
– Immune cells transplantation
Immunology
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I. Host versus graft reaction
(HVGR)
• Hyperacute rejection
• Acute rejection
• Chronic rejection
Immunology
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1. Hyperacute rejection
• Occurrence time
– Occurs within minutes to hours after host
blood vessels are anastomosed to graft
vessels
• Pathology
– Thrombotic occlusion of the graft vasculature
– Ischemia, denaturation, necrosis
Immunology
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• Mechanisms
– Preformed antibodies
• Antibody against ABO blood type antigen
• Antibody against VEC antigen
• Antibody against HLA antigen
Immunology
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– Complement activation
• Endothelial cell damage
– Platelets activation
• Thrombosis, vascular occlusion, ischemic
damage
Immunology
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2. Acute rejection
• Occurrence time
– Occurs within days to 2 weeks after
transplantation, 80-90% of cases occur
within 1 month
• Pathology
– Acute humoral rejection
• Acute vasculitis manifested mainly by
endothelial cell damage
– Acute cellular rejection
• Parenchymal cell necrosis along with
infiltration of lymphocytes and MΦ
Immunology
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Hyperacute Rejection: the early
days
• Mediated by pre-existing IgM
alloantibodies
• Antibodies come from carbohydrate
antigens expressed by bacteria in
intestinal flora
– ABO blood group antigens
• Not really a problem anymore
Hyperacute Rejection: Today
• Mediated by IgG antibodies directed
against protein alloantigens
• Antibodies generally arise from
– Past blood transfusion
– Multiple pregnancies
– Previous transplantation
• Mechanisms
– Vasculitis
• IgG antibodies against alloantigens on
endothelial cell
– Parenchymal cell damage
• Delayed hypersensitivity mediated by
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CD4+Th1
Killing of graft cells by CD8+Tc
Immunology
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Immunology
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3. Chronic rejection
• Occurrence in time
– Develops months or years after acute
rejection reactions have subsided
• Pathology
– Fibrosis and vascular abnormalities with loss
of graft function
Immunology
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• Mechanisms
– Not clear
– Extension and results of cell necrosis in
acute rejection
– Chronic inflammation mediated by CD4+T
cell/MΦ
– Organ degeneration induced by non
immune factors
Immunology
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Immunology
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Kidney Transplantation----Graft Rejection
Immunology
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Chronic rejection in a kidney allograft with arteriosclerosis
Immunology
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II.Graft versus host reaction
(GVHR)
• Graft versus host reaction (GVHR)
– Allogenetic bone marrow transplantation
– Rejection to host alloantigens
– Mediated by immune competent cells in
bone marrow
• Graft versus host disease (GVHD)
– A disease caused by GVHR, which can
damage the host
Immunology
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• Graft versus host disease
Immunology
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• Graft versus host disease
Immunology
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Conditions
• Enough immune competent cells in grafts
• Immunocompromised host
• Histocompatability differences between
host and graft
Immunology
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Bone marrow transplantation
Thymus transplantation
Spleen transplantation
Blood transfusion of neonate
In most cases the reaction is directed
against minor histocompatibility
antigens of the host
Immunology
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1. Acute GVHD
• Endothelial cell death in the skin, liver,
and gastrointestinal tract
• Rash, jaundice, diarrhea,
gastrointestinal hemorrhage
• Mediated by mature T cells in the
grafts
Immunology
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• Acute graft-versus-host reaction with
vivid palmar erythema
Immunology
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2. Chronic GVHD
• Fibrosis and atrophy of one or more of
the organs
• Eventually complete dysfunction of the
affected organ
Immunology
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Both acute and chronic GVHD are
commonly treated with intense
immunosuppresion
• Uncertain
• Fatal
Immunology
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Part three
Prevention and Therapy of
Allograft Rejection
Immunology
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• Tissue Typing
• Immunosuppressive Therapy
• Induction of Immune Tolerance
Immunology
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I. Tissue Typing
• ABO and Rh blood typing
• Crossmatching (Preformed antibodies)
• HLA typing
– HLA-A and HLA-B
– HLA-DR
Immunology
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• Laws of transplantation
Immunology
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II. Immunosuppressive Therapy
• Cyclosporine(CsA), FK506
– Inhibits NFAT transcription factor
• Azathioprine, Cyclophosphamide
– Block the proliferation of lymphocytes
• Ab against T cell surface molecules
– Anti-CD3 mAb----Deplete T cells
• Anti-inflammatory agents
– Corticosteroids----Block the synthesis and
secretion of cytokines
Immunology
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Removal
of T cells from marrow graft
Immunology
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III. Induction of Immune
Tolerance
• Inhibition of T cell activation
– Soluble MHC molecules
– CTLA4-Ig
– Anti-IL2R mAb
• Th2 cytokines
– Anti-TNF-α，Anti-IL-2，Anti-IFN-γ mAb
• Microchimerism
– The presence of a small number of cells of
donor, genetically distinct from those of the
host individual
Immunology
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Part IV
Xenotransplantation
Immunology
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• Lack of organs for transplantation
• Pig-human xenotransplantation
• Barrier
Immunology
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• Hyperacute xenograft rejection (HXR)
– Human anti-pig nature Abs reactive with
Galα1,3Gal
– Construct transgenic pigs expressing
human proteins that inhibit complement
activation
• Delayed xenograft rejection (DXR)
– Acute vascular rejection
– Incompletely understood
• T cell-mediated xenograft rejection
Immunology
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Bone Marrow Transplantation
• Rescue procedure for hemopoietic
reconstitution subsequent to cancer
chemo- or radio- therapy
Graft vs. Host Disease
• Caused by the reaction of grafted mature
T-cells in the marrow inoculum with
alloantigens of the host
• Acute GVHD
– Characterized by epithelial cell death in the
skin, GI tract, and liver
• Chronic GVHD
– Characterized by atrophy and fibrosis of one
or more of these same target organs as well
as the lungs
Heart Transplantation
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Heart transplantation is indicated for
those in end-stage heart disease with a
New York Heart Association of class III
or IV,
ejection fractions of <20%,
maximal oxygen consumption of (VO2)
<14 ml/kg/min, and
expected 1-year life expectancy of
<50%.
Introduction
• More than 4000 patients in the United States are
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registered with the United Organ Sharing
Network (UNOS) for cardiac transplantation.
There are only about 2500 heart donors yearly.
Scarcity of donors is complicated by the use of
single organs, heart injury with common braindeath injuries, difficulty with ex-vivo
preservation, heart disease among donors, and
the complexity of the operation.
Matching Donor and Recipient
• Because ischemic time during cardiac transplantation is
crucial, donor recipient matching is based primarily not
on HLA typing but on the severity of illness, ABO blood
type (match or compatible), response to PRA, donor
weight to recipient ratio (must be 75% to 125%),
geographic location relative to donor, and length of time
at current status.
• The PRA is a rapid measurement of preformed reactive
anti-HLA antibodies in the transplant recipient. In
general PRA < 10 to 20% then no cross-match is
necessary. If PRA is > 20% then a T and B-cell crossmatch should be performed.
• Patients with elevated PRA will need plasmapheresis,
immunoglobulins, or immunosuppresive agents to lower
PRA.
Heart Transplantation
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Survival is 80% at five years but at five year
50% also have coronary vascular disease
due to chronic rejection.
Immunosuppressive Agents
• Azathioprine: purine analogue that works by
nonspecific suppression of T and B-cell
lymphocyte proliferation.
• Dosage is 1 to 2 mg/kg per day.
• Side effects are bone marrow suppression (dose related),
increased incidence of skin cancer (use sunscreen),
cutaneous fungal infections, and rarely liver toxicity and
pancreatitis.
• Drug interactions: allopurinol (decrease dose by 75%) and
TMP/Sulfa (worsens thrombocytopenia).
Immunosuppressive Agents
• Cyclosporin: inhibits T-cell lymphokine production.
Highly lipophilic.
• Dosage is 8 to 10mg/kg/day in 2 divided doses. IV doses are 1/3 of
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oral doses in a continuous infusion.
Drug levels are frequently measured for dosage and toxicity, but
levels are not highly predictive of actual immunosuppressive effect.
Drug levels are reflected for 5 to 10 days because of a long half life.
Side effects: nephrotoxicity caused by afferent arteriolar
constriction and manifested by oliguria. Loop diuretics may
exacerbate this side effect. Dosage adjustments should only be
made if creatinine level is >3.0mg/dL (some renal insufficiency is
expected). Other side effects include hypertension, hypertrichosis,
tremor, hyperkalemia, hyperlipidemia, and hyperuricemia.
Multiple drug interactions.
Immunosuppressive Agents
• Corticosteroids: immunosuppressives of
uncertain mechanism. Used for maintenance of
immunosuppression and to manage acute
rejections.
• High doses used initially tapered over the 1st 6 months to 5
to 15mg/d prednisone.
• Side effects include mood and sleep disturbances, acne,
weight gain, obesity, hypertension, osteopenia, and
hyperglycemia.
Immunosuppressive Agents
• Mycophenolate mofetil: selectively inhibits
lymphocyte proliferation.
• Dosage is 2g/d po.
• Side effects include GI disturbances. Does not cause
significant bone marrow suppression.
• FK-506 (tacrolimus): Lymphophilic macrolide
that inhibits lymphokine production similar to
cyclosporine.
• More toxic than cyclosporine.
• Side effects include nephrotoxicity and neuotoxicity.
Immunosuppressive Agents
• Antilymphocyte globulin: Horse polyclonal
antibody designed to inhibit T cells by binding to
surface antigens.
• It is generally used at the time of transplantation for
induction therapy or during acute rejections.
• Dosage is 10 to 15 mg/kg qd through a central venous
catheter.
• Goal is to keep T lymphocyte count ~200cells/microL.
• Side effects include fevers, chills, urticaria, serum sickness,
and thrombocytopenia.
Immunosuppressive Agents
• Muromonab-CD3 (OKT3): a murine monoclonal antibody
to the CD3 complex on the T-cell lymphocyte designed
for selective T-cell depletion.
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Usual dose is 5mg/d IV bolus over 10 to 14 days.
CD3 cells are monitored with goal <25cells/mL.
Used in patients with renal insufficiency.
Side effects include cytokine release syndrome (fever, chills,
nausea, vomiting, mylagia, diarrhea, weakness, bronchospasm, and
hypotension), pulmonary edema.
• Rapamycin: Similar mechanism of action of FK-506
except that it antagonizes the proliferation of
nonimmune cells such as endothelial cells, fibroblasts,
and smooth muscle cells.
• Not routinely used at present.
• May have a roal in prevention of immunologically mediated
coronary allograft vasculopathy.
Basic Drug Regimen
• Immunosuppressives
• Antibiotic prophylaxis
• PCP: TMP/Sulfa or Dapsone or Pentamidine aerosols.
• CMV infection: Ganglyclovir, acyclovir.
• Fungal infections: Nystatin.
Antihypertensives
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• Diuretics as needed
• Potassium and Magnesium replacement (cyclosporin leads to
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wasting of thes electrolytes.
Lipid-lowering agents. (Avoid allograft vasculopathy).
Glucose lowering agents (DM and steroids)
Anticoagulation if transplant heterotopic.
Cyclosporin dose lowering meds (Diltiazem / Verapamil /
Theophyilline)
Complications - Rejection
• Avoidance with preoperative therapy with
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cyclosporin, corticosteroids, and azathioprine.
If rejection is suspected then workup should
include: measurement of cyclosporine level
CKMB level, echocardiography for LV function,
and endomyocardial biopsy.
Signs and symptoms of rejection only manifest
in the late stages and usually as CHF (rarely
arrhythmias). Due to close surveillance, most
rejection is picked up in asymptomatic patients.
Staging of Acute Rejection
• If acute rejection is found, histologic review of
endomyocardial biopsy is performed to determine the grade
of rejection.
• Grade 0 — no evidence of cellular rejection
• Grade 1A — focal perivascular or interstitial infiltrate without
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myocyte injury.
Grade 1B — multifocal or diffuse sparse infiltrate without myocyte
injury.
Grade 2 — single focus of dense infiltrate with myocyte injury.
Grade 3A — multifocal dense infiltrates with myocyte injury.
Grade 3B — diffuse, dense infiltrates with myocyte injury.
Grade 4 — diffuse and extensive polymorphous infiltrate with
myocyte injury; may have hemorrhage, edema, and microvascular
injury.
Treatment of Acute Rejection
• Grade 1A and Grade 1B: No treatment is necessary.
• Grade 2: Probably no treatment is necessary. Short course
of steriods (Prednisone 100mg qd x 3 days) is optional.
• Grade 3A and Grade 3B: High dose corticosteroids
(Solumedrol 1mg/kg IV). If no response then ATGAM (OTK3
also an option, but causes more intense cytokine reaction).
• Grade 3 with hemodynamic compromise or Grade 4: High
dose corticosteriods plus ATGAM or OTK3.
• It is critical that an endomyocardial biopsy be performed to
document reversal of rejection after treatment. Otherwise
additional agents will need to be added. A biopsy is obtained
1 week after initial biopsy showed rejection and then 1 week
after therapy complete. If ATGAM or OTK3 is used biopsy
should be obtained at the end of a course of therapy (usually
7 to 14 days) and then again 1 week later off therapy.
Complications - Rejection
• Allograft vasculopathy (Chronic rejection): Transplant
coronary artery disease that is the leading cause of
death in patients more than 1 year after transplantation.
• Likely a result of a proliferative response to
immunologically mediated endothelial injury (chronic
humoral rejection).
• It differs from native CAD in that it is manifested by
concentric stenoses, predominately subendocardial
location, lack of calcification, can be rapidly progressive
and lack of angina pectoris.
• Risk factors include degree of histocompatibility,
hypertension, hyperlipidemia, obesity, and CMV
infection.
Complications – Rejection
Allograft Vasculopathy
• Treatment is mainly prevention with statins, diltiazem,
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and antioxidant vitamins. Rapamycin is an agent that
has shown promise in preventing this complication.
Treatment with percutaneous interventions and CABG is
limited due to its diffuse nature and subendocardial
locations.
Retransplantation for this disorder is an option, but
retrospective analysis have shown this approach does
not improve mortality as patients do significantly worse
with a second transplant as compared with the first.
Complications - Infection
• There are two peak infection periods after
transplantation:
• The first 30 days postoperatively: nosocomial infections related
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to indwelling catheters and wound infections.
Two to six months postoperatively: opportunistic
immunosuppresive-related infections.
• There is considerable overlap, however as fungal
infections and toxoplasmosis can be seen during the
first month.
• It is important to remember that immunosuppressed
transplant patients can develop severe infections in
unusual locations and remain afebrile.
Opportunistic Infections
• CMV: most common infection transmitted donor
to recipient.
• Manifested by fever, malaise, and anorexia. Severe infection
can affect the lungs, gastrointestinal tract, and retina.
• If donor is CMV positive and the recipient is CMV negative,
prophylaxis with IV ganciclovir or foscarnet is given for 6
weeks and followed by longterm oral prophylaxis with
acyclovir.
• If the recipient is CMV positive a less potent regimen can be
used.
• Bone marrow toxicity related to treatment can occur and be
confused with that due to azathioprine treatment.
Complications - Malignancy
• Transplant recipients have a 100-fold increase in the prevalence of
malignant tumors as compared with age-matched controls.
• Most common tumor is posttransplantation lymphoproliferative
disorder (PTLD), a type of non-Hodgkin’s lymphoma believed to be
related to EBV.
• The incidence is as high as 50% in EBV-negative recipients of EBV-positive
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hearts.
Treatment involves reduction of immunosuppressive agents, administration
of acyclovir, and chemotherapy for widespread disease.
• Skin cancer is common with azathioprine use.
• Any malignant tumor present before transplantation carries the risk
for growth once immunosuppresion is initiated because of the
negative effects on the function of T-cells.
Transplantation
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Kidney 25,000 patients are waiting for
kidney transplantation
savings in three years compared to the cost
of three years of renal dialysis.
Liver One-year survival exceeds 75% and
five-year is 70%.
Pancreas Transplantation
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Graft survival is 72% at one-year and this
is further improved if a kidney is
transplanted simultaneously.
The overall goal of pancreas transplantation
is to prevent the typical diabetic secondary
complications: neuropathy, retinopathy, and
cardiovascular disease.