Transcript Document

Why transplant?
“Cure for organ specific disease”
(or islets since 2000)
Adapted from “Immunology” by
Goldsby, Kindt, Osborne, Kuby
ISOGRAFT
AUTOGRAFT
ALLOGRAFT
XENOGRAFT
(Experimental)
ISOGRAFT
AUTOGRAFT
ALLOGRAFT
POTENT IMMUNE RESPONSE
XENOGRAFT
(Experimental)
Immune rejection of organ transplants
is a major barrier to success
3 manifestations defined by when and how occur
-Hyperacute
-Acute
-Chronic
Hyperacute rejection - within hours
- Ab mediated
Adapted from “Immunology” by Goldsby, Kindt, Osborne, Kuby
Problematic pre-existing antibodies and how
to deal with these
Allotransplants
-natural antibodies to ABO blood group antigens
-anti-HLA antibodies raised during previous
transfusion, transplant or pregnancy
Solution: test recipient serum for ABO compatibility and
negative crossmatch
Xenotransplants
-natural antibodies to Gala1-3Gal epitope present in
lower mammals
Solution: agalactosyl transferase knockout pig
Acute rejection - within weeks
Adapted from “Immunology” by Goldsby, Kindt, Osborne, Kuby
T cells play a central role in acute rejection
Adapted from “Immunology” by Goldsby, Kindt, Osborne, Kuby
Induction in draining lymph node
T cells are activated by 2 pathways
Host
T
cell
Host
DC
Indirect (classical antigen presentation by host DC)
Transplant-derived peptide on host MHC/HLA interacts with
host T cell receptor
Response is weak for allografts but strong for xenografts
Transplant
Host
T
cell
Direct (antigen presentation by passenger donor DC)
Donor
DC
Transplant-derived peptide on donor MHC/HLA or donor
MHC/HLA alone interacts with host T cell receptor
Response is strong for allografts but weak for xenografts
Destruction by various effectors at graft site
DC
allo
xeno
Adapted from “Immunology” by Goldsby et al
Solutions to acute rejection
MHC match

Serologic methods

Cellular assays

Molecular biological methods
Critical for bone marrow and helpful for kidney, but limited organ
availability and highly polymorphic MHC means often not practical.
No MHC match for xenografts
Immunosuppress recipient

Cocktail of drugs with 3 distinct modes of action
Actions of immunosuppressive drugs
1. Inhibit T cell signaling e.g. CyclosporinA or FK-506 block
calcineurin activity and thereby IL2 synthesis.
2. Anti-proliferative e.g. Azathioprine or mycophenolic acid
inhibit synthesis of purines required for cell division. Inhibit
B and T cell proliferation.
3. Anti-inflammatory e.g. Corticosteroids bind to intracellular
steroid receptors and thereby regulate transcription of a
number of genes including cytokines, adhesion molecules and
class II molecules.
Chronic rejection
- months or years after grafting
Poorly understood combination
of immunological + other factors
Damage at time of grafting
+ acute rejection episodes
+ ongoing indirect response
Pascual et al, N. Engl. J. Med. 346:580 (2002)
result in low grade damage to
graft vascular endothelium,
smooth muscle proliferation and
migration leading to vascular
occlusion
Solution: No effective immunosuppressive regimen to date, but predict better
control of the immune response will decrease incidence of chronic rejection.
Organ transplantation is a life
saving procedure, but there are
major problems……
Problem 1
Systemic immunosuppression facilitates graft
survival at a price
- drug targets are not limited to the immune system
resulting in toxicity for other organs
-systemic immunosuppression increases
susceptibility to cancer and infection
Possible solutions under investigation
-more specific drugs? (several in clinical trials)
-induce graft tolerance? (“Holy Grail”)
-local immunosuppression? (Our approach)
Graft tolerance by chance and deduction
Transplant girl's blood change a 'miracle'
The Sydney Morning Herald. January 25, 2008
N ENGL J MED 358: 369-374 (2008).
Case history
•Hepatitis/liver failure
•Profound lymphopenia
O-
9 Y.O.
liver
graft
O+
12 Y.O.
Immunosuppression
O+
No immunosuppression
•Predominantly donor
white cells but
approx. 2%host B
cells
•IgG on RBC
progressing to active
hemolysis
O+
•Donor liver survival
•Loss of pre-existing
immunity/successful
reimmunization
•TCR excision circles
How was tolerance
established ?
Presumed events resulting in graft tolerance
•Hepatitis/liver failure
•Profound lymphopenia Donor leukocytes/stem cells not rejected + space for expansion
O-
9 Y.O.
liver
graft
O+
12 Y.O.
Immunosuppression
O+
No immunosuppression
•Predominantly donor
white cells but
approx. 2%host B
cells
•IgG on RBC
progressing to active
hemolysis
O+
•Donor liver survival
•Loss of pre-existing
immunity/successful
reimmunization
•TCR excision circles
Presumed events contributing to graft tolerance
•Hepatitis/liver failure
•Profound lymphopenia
O-
9 Y.O.
liver
graft
O+
12 Y.O.
Donor leukocytes/stem cells not rejected + space for expansion
Immunosuppression
O+
No immunosuppression
•Predominantly donor
white cells but
approx. 2%host B
cells
•IgG on RBC
progressing to active
hemolysis
Donor leukocytes outgrow host leukocytes
but residual host B cells make antibody to
donor red blood cells
O+
•Donor liver survival
•Loss of pre-existing
immunity/successful
reimmunization
•TCR excision circles
Aggressive host B cells
rejected by donor T
cells upon withdrawal
of immunosuppression
Presumed events contributing to graft tolerance
•Hepatitis/liver failure
•Profound lymphopenia
O-
9 Y.O.
Immunosuppression
Active thymus
liver
graft
O+
12 Y.O.
Stem cells
O+
No immunosuppression
•Predominantly donor
white cells but
approx. 2%host B
cells
•IgG on RBC
progressing to active
hemolysis
O+
•Donor liver survival
•Loss of pre-existing
immunity/successful
reimmunization
•TCR excision circles
Thymic engraftment
Donor cells educated to
be tolerant to host and
donor but responsive to
foreign antigen
Thymic education
T cell precursor
T cell receptor gene
rearrangement
TCR+
Immature thymocyte
TCR+
TCR+
Positive selection of cells whose
T cell receptor bind MHC Epithelial
cell
TCR+
TCR+
Death of cells that
do not interact with MHC
TCR+
TCR+
TCR+
Mature T cells
tolerant of self
into circulation
TCR+
DC
Negative selection
and death of high affinity
self reactive cells
TCR+
Thymic education in mixed chimera
T cell precursor
T cell receptor gene
rearrangement
TCR+
TCR+
TCR+
TCR+
Positive selection of cells whose
T cell receptor bind MHC Epithelial
cell
Immature thymocyte
TCR+ TCR+
TCR+
TCR+
Death of cells that
do not interact with MHC
TCR+
TCR+
TCR+
TCR+
TCR+
TCR+
TCR+
Mature T cells
Tolerant of host and donor
into circulation
TCR+
DC
DC
TCR+
TCR+
TCR+
TCR+
Negative selection and death of high affinity
host-reactive and donor-reactive cells
Tolerance is ideal, but for most
patients the risks are too great.
What else can we do…..
Local immunosuppression
Engineer graft to produce its own
immunomodulatory molecules thus
concentrating immunosuppression in
the graft microenvironment
“Helping the graft help itself”
Type 1 diabetes
Autoimmune destruction of insulin producing beta cells
Usually strikes in childhood or early adulthood
Affects over 140,000 Australians
Up to 6 insulin injections each day for rest of life
Parenteral insulin is not good enough
Quic kT ime™ and a
Photo - J PEG dec ompres sor
are needed to s ee this pi cture.
Adapted from
Pancreatic islet transplantation is a cure for
Type 1 Diabetes
Somatostatin
( cell)
Pancreatic
polypeptide
(PP cell)
Insulin
 cell
Glucagon
a cell
Adapted from seungkimlab.stanford.edu/ islet.html
Islet transplantation
www.jdrf-hms-islets.org
Westmead Hospital
Sydney
portal vein infusion of
islets into the liver
Generating local immunosuppression at the
graft site
systemic
Local
Methods of expressing immunomodulatory
molecules in primary tissues
Viral
Transient eg. adeno or
stable eg. lenti
Transgenic
Stable
Reproducible
Reproducible
Control expression
level
Select expression level
xenotransplants
Allo/xenotransplants
Immunohistolgy from seungkimlab.stanford.edu/ islet.html
Problem 2
Shortage of donor organs
Number of Deceased Donors Solid Organ Transplants
and Patients on the Waiting List 2002 - 2007
3000
Deceased Donors
Transplants
Waiting List
2500
2000
1788
1824
Australia
3000
2500
1663
1716
1757
1690
1500
2000
1500
1000
721
634
500
179
206
789
218
736
1000
740
668
500
204
202
198
0
0
2002
2003
2004
2005
2006
2007
Source:ANZOD Registry (www.anzdata.org.au)
Donor organ shortage and Type 1 diabetes
>140,000 Australians with Type 1 diabetes
198 organ donors in 2007
Xenotransplantation may provide the
solution
Why pigs?
•Reproduce quickly and have large litters
•Organs of similar size to humans
•Beta cells regulate blood glucose appropriately in
humans & pig insulin used for many years in
humans
•Relatively easy to rear in conditions free of
particular pathogens
•Can be genetically modified to reduce the risk of
immune rejection
Why not pigs?
•Ethical objections
•Religious objections
•Risk of xenozoonosis (transmission of infection
between species)
•Breed free of known pathogens
•Breed free of potential pathogens (PERVS)
•Long-term monitoring of recipients
•Current moratorium in Australia, but
experience in approx. 150 people worldwide
show no evidence of pig derived infection
Pigs can be modified to remove detrimental
and add beneficial molecules
Remove target epitopes
Add modulators of host pathways
eg. Gala(1,3)Gal
eg. complement modulators
eg. anticoagulant molecules
Add pro-survival
molecules
Add local
immunosuppression
eg. costimulation
blockade
eg. depleting antibodies