primary mechanisms of self-tolerance...cd8 + t cell exhaustion memory and exhausted cd8 + t cells...

Fellows Symposium on

Transplantation Medicine

Sunday, September 25

8:00 am - 8:30 am

Primary Mechanisms of

Self-tolerance

Maria-Luisa Alegre, MD, PhD

September 23-25, 2011

Hilton DFW Lakes Executive Conference Center

Grapevine, Texas

www.a-s-t.org

American Society of Transplantation

Fellows Symposium


Grapevine, TX


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The University of Chicago

Primary Mechanisms of Self-Tolerance

Marisa Alegre, MD, PhD

T Cell Tolerance

How Is Tolerance to Self-Antigens Normally Maintained?

Central Tolerance Peripheral Tolerance

Ignorance, Anergy, Clonal deletion, Immune deviation, Suppression

Negative selection

TCRCD28

DP Thymocyte

APC

12

B7 MHC

Very strong interaction => death

by negative selection

Intermediate interaction => positive selection (survival) => export to the periphery of self-

restricted, self-tolerant T cells

Very weak or no interaction

(TCR that does not recognize self MHC) => death by neglect

Thymic Selection of T Cells

Strong interaction => positive selection of Tregs

The Transcription Factor AIRE Allows Expression of Self-Antigens in the Thymus to Favor Negative

Selection of Autoreactive T Cells

Science 298:1395

AIRE Knockout Mice Develop AutoimmunityAire mutant people develop APS (autoimmune polyendocrinopathy syndrome)

Aire (TF) is predominantly expressed in thymic medullary epithelial cells Aire promotes ectopic expression of peripheral antigens


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nTregs and iTregs

iTregs

Peripheral AireClonal deletion

TCRCD28

T Cell

APC

Ignorance

Anergy (tolerance) Apoptosis

TCRCD28

T Cell

APC

Proliferation

Differentiation Effector function

12

1

Peripheral Mechanisms to Prevent Autoimmunity: Lack of Costimulatory Ligands on Most Tissue Cells => Anergy

TCR

CD28B7

T Cell APC TCR

CD28B7

B7CTLA4

T Cell APC

Resting T Cell Activated T Cell

Negative Regulators of T cell Activation Terminate

an Immune Response and Prevent Autoimmunity

TCR

CD28T Cell B7

MHC

APC

PDL

CTLA-4

PD1

BTLA

B7

HVEM

Cell-cycle arrest

Cell death

Peripheral Mechanisms to Prevent Autoimmunity: T Cell-Intrinsic Negative Regulators of T Cell

Proliferation

Fas FasL

Peripheral Expression of Aire and CD8 Tolerance

Nature Immunol. 8:181, 2007

Science 321:847, 2008

CD8+ T Cell Exhaustion

Memory and exhausted CD8+ T cells express many inhibitory receptors

Blackburn et al., Nature Immunol, 10:29, 2009


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Increased Viral Control after Simultaneous Blockade

of LAG-3 and PDL-1

Blackburn et al., Nature Immunol, 10:29, 2009

Different Types of Regulatory T Cells

• Treg CD4+/FoxP3+

• NKT cells

• TR1 cells (in humans)

• Th3 cells (generated after antigen encounter in a tolerogenic form; ie soluble, oral…)

• Occasional report of CD8+ cells, or CD4+/CD25-

cells with suppressor activity

Naturally occurring (innate) but not

exclusively

Foxp3 Encodes the Transcription Factor Scurfin

• Scurfin is a forkhead/winged/helix transcription factor

• The scurfy mouse strain has a Foxp3 mutation leading to deletion of forkhead domain => lethal CD4-dependent lymphoproliferation; same in Foxp3-deficient mice; lack CD4+/CD25+

• Foxp3 is selectively expressed in CD4+/CD25+ T cells (among T cells)

• Transfer of CD4+/CD25+ T cells to neonatal Foxp3-deficient mice corrects disease

• Ectopic expression (transgenic or retroviral) of Foxp3 confers suppressive function to CD4+/CD25- T cells

Sakaguchi, Science 299:1057 2003

Rudensky, Nature Immunol. 2003 Ramsdell, Nature Immunol. 2003

Naïve peripheral CD4+ T Cell

iTreg

TGF-ββββIL-10

TGFββββ+IL-2

Suppression of Tconv

nTreg

Cell-cell contact

Strong Stimulus

NF-κκκκB, IL-2

Immature thymocyte

Two Types of FoxP3+ Tregs: Natural and Induced

FoxP3

FoxP3

FoxP3-Induced Surface Molecules and Cytokines Defining Tregs

Zhang et al, Curr Opin Organ Transplant 14:40, 2009

Suppression of the Immune Response by Tregs

•Direct signals to APC (IDO)

•Inhibitory cytokines (IL-10, TGF-ββββ, IL-35)

•Immature APC

•Inhibitory cytokines (IL-10, TGF-ββββ)

•Short contact time

Treg

APC

CD40CD40L

TCRMHC

TeffTCR

CD28

B7

--

--

- ?

•Inhibitory cytokines

(IL-10, TGF-β, β, β, β, IL-35)

B7

CTLA-4


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Tang and Bluestone, Nature Immunology 9:239, 2008

Suppressive Cytokines Produced by Tregs

Bettini and Vignali, Curr Opin Immunol, 21:612, 2009

IL-12Ra (p35) +

EBI3 (IL-27)

Collison and Vignali, Immunol Rev, 226:248, 2008 Kim and Ahmed, Current Opinion in Immunology 2010, 22:223–230

T Cell Tolerance to Viral and Tumor Antigens

Anti-CD154 mAb Induces “Robust” Donor-Specific Transplantation Tolerance

Anti-CD154 (1mg d0, 7, 14)

+ DST

BALB/c (H-2d) heart into

C57BL/6 (H-2b)

allograft acceptance

Rati

o T

reg

/CD

4+

Te

ff

0.0

0.2

0.4

0.6

0.8

Spleen Heart Spleen Heart Spleen Heart

Rejecting Tolerant + CpG

*** ***

0 10 2 10 3 10 4 10 5

0

10 2

103

10 4

10 5

0 102

103

104

105

0

102

103

104

105

CD8

Th

y1

.1

No Treatment

Tolerant

0.54

0.04

Stimulators: B6 (syngeneic) Balb/c (allogeneic) C3H (3rd party)

Naïve B6 unTx

B6 + anti-CD154

Accumulation of Intragraft Tregs Deletion of Alloreactive CD8+ T Cells

Hyporesponsiveness of Alloreactive Splenic T Cells

Mechanisms of T Cell Tolerance by Anti-CD154 in Transplantation


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B Cell Tolerance

Reprinted from Cellular and Molecular Immunology, ©2007 with permission from Elsevier

B Cell Mechanisms of Tolerance

B Cell Tolerance

Clonal anergy- usually in periphery - impaired survival

a. Anergic B cells downregulate BCR and CXCR5 and are excluded from follicles, but this does not dictate survival

b. Increased dependence of anergic cells on TNF family survival factor BAFF. (BAFF signals contribute to phosphorylation and degradation of the pro-apoptotic protein Bim).

Marcus Clark, PhD, University of Chicago

3-83 BCR-Igi BALB/c recipients: ≥95% of B cells express the 3-83 BCR that recognize Class I molecule, Kb

Tracking the Fate of Alloreactive B Cells during Allograft Tolerance

Day 0:

B/6 Heart Transplant into 3-83i Recipients

DST + Anti-CD154

(Li et al. PNAS 2007, JI 2008)

Tolerance Induces Deletion of 3-83 B Cells

Tol KbDb KO

15.3 ± 0.7

29.6 ± 1.4

29.0 ± 5.2

39.3 ± 0.4

Rejecting

22.2 ± 2.0

24.0 ± 9.3

46.4 ± 3.9

38.8 ± 3.6

IgM

3-8

3 I

dio

typ

e

LN

PC

Spleen

BM

Naïve Tolerant

52.9 ± 13.0

19.1 ± 5.0

38.5 ±

1.6

1.0 ± 0.5

1.8 ± 1.3

14.8 ± 1.3

24.7 ± 6.9

67.3 ± 4.8

(Analysis at 4 wks post-Tx)

Li et al. 2007. PNAS

Potential Role for Regulatory B Cells


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Summary

• Lymphocytes adhere to rules of tolerance centrally (thymus and BM) and in the periphery

• T cells can undergo anergy, deletion, iTreg differentiation, exhaustion

• B cells can undergo anergy, follicular exclusion, deletion and present antigen in a way that can inactivate T cells

• Tolerogenic DCs can promote iTreg differentiation or induce anergy of T cells.




8:30 am - 9:00 am

How is Tolerance Induced in

the Graft?

Ronald G. Gill, PhD



Grapevine, Texas

www.a-s-t.org


Fellows Symposium


Grapevine, TX

Ronald G. Gill, PhD

www.a-s-t.org 1

How is tolerance induced in the How is tolerance induced in the

graft?graft?

Ronald G. GillRonald G. Gill

University of Colorado, DenverUniversity of Colorado, Denver

Colorado Center for Transplantation Care, Research, and EducatioColorado Center for Transplantation Care, Research, and Educationn

Allograft Tolerance:Allograft Tolerance:

An antigen (donor)-specific response that results

in preservation of the graft.

• Not immune deficiency

• Not immunesuppression

General Strategy for Facilitating ToleranceGeneral Strategy for Facilitating Tolerance

• Minimize function of graft destructive

cells

• Facilitate activation of graft-’protective’

cells

Antigen

Presenting

Cell

MHC TCR

CD40 CD40

B7 CD28

T Cell

Signal 1

Signal 2

IL-12

The ‘context’ of antigen presentation dictates the

fate of the donor-reactive T cell.

‘Plasticity’:

A hallmark feature of the immune system

Allograft

No Response Destructive

Immunity

Non-destructive

Immunity

Clonal Deletion/

Inactivation

Active

Regulation


Fellows Symposium


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Ronald G. Gill, PhD

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Potential Routes of Tolerance:Potential Routes of Tolerance:

• Clonal Deletion / Inactivation (‘Recessive’)

• Active inhibition / regulation (‘Dominant’)

Evidence of T cell depletion during toleranceEvidence of T cell depletion during tolerance

• Requirement for killing mechanisms (perforin)

• Inhibition of apoptosis inhibits tolerance

• Direct evidence of T cell elimination

0

20

40

60

80

100

% G

rafts F

unctionin

g

0 20 40 60 80 100

Days Post Transplantation

Perforin-Deficient Mice (pfp-/-) are Resistant to Tolerance Induction

B6 pfp -/- + anti-CD154 (n = 7)

B6 pfp -/- Untreated (n = 9)

B6 w.t. + anti-CD154 (n = 5)

B6 w.t. Untreated (n = 9)

From: AD Wells et al. Nat. Med. 5:1303, 1999

T cell over-expression of the anti-apoptotic molecule Bcl-xL

inhibits allograft tolerance induction

Exposure to donor antigen + anti-CD154 results in transient

depletion of donor-reactive CD8 T cells

(N.N. Iwakoshi et al. J. Immunol. 167:6623, 2001)

CD8+DES+ = donor-reactive TcR transgenic CD8 T cells

Anti-CD154 = hamster anti-mouse CD154 monoclonal

DST = donor specific transfusion (donor spleen on day -7)

Active Regulation of the AlloresponseActive Regulation of the Alloresponse

• Types of Regulatory T cells

• ‘Linked’ Suppression

• ‘Infectious’ Tolerance


Fellows Symposium


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Ronald G. Gill, PhD

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Active ToleranceActive Tolerance

•Requires Antigen Recognition

•Predominantly a CD4-dependent response

•Does not require the deletion of graft-destructive T cells

‘‘RecessiveRecessive’’ or or ‘‘DominantDominant’’ tolerance?tolerance?

ReRe--emergence of the modern concept emergence of the modern concept

of of ‘‘regulatoryregulatory’’ allograft tolerance:allograft tolerance:

S. Qin et al. ‘Infectious’ Transplantation

Tolerance. Science. 259:974, 1993

‘Linked’ Suppression:

The APC serves as the intermediary between

T effector (Teff) and T regulatory (Treg) cells

From:

R.L. Lechler et al. Nat.Rev.Immunol. 3:147, 2003

Key Relationship Between ‘Linked’ recognition and

‘Infectious’ Tolerance

From: JA Bluestone. Nat. Rev. Immunol. 5:343, 2005

Varied Phenotypes of Varied Phenotypes of ‘‘RegulatoryRegulatory’’ T cellsT cellsHow do Regulatory T cells ‘Regulate’?


Fellows Symposium


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Ronald G. Gill, PhD

www.a-s-t.org 4

Do you Do you needneed to be donor hypoto be donor hypo--responsive to responsive to

maintain allograft tolerance?maintain allograft tolerance?

00

2020

4040

6060

8080

100100

% a

llo

graft

su

rv

iva

l%

all

ograft

su

rv

iva

l

00 2020 4040 6060

Day Post Spleen TransferDay Post Spleen Transfer

naivenaive

toleranttolerant

tolerant + natolerant + naïïveve

Targeting of LFA-1 + CD154 results in

‘dominant’, transferable transplantation tolerance

(Nicolls et al. J. Immunol. 169:4831, 2002)

toleranttolerant

naivenaive

Lower Limit of Detection

00

2020

4040

6060

8080

0.00010.00010.0010.0010.010.010.10.1

% S

pec

ific

Ly

sis

‘Dominant’ Tolerance Despite Potent Anti-Donor

CTL Reactivity

Fraction of CultureFraction of Culture

backgroundbackground

(anti(anti--CD154 + antiCD154 + anti--LFALFA--1) 1)

00

2020

4040

6060

8080

cpm

cpm

x 1

0x

10

-- 33

33 44 55

Day of CultureDay of Culture

toleranttolerant

naivenaive

Tolerant spleen cells exhibit normal antiTolerant spleen cells exhibit normal anti--donor donor

backgroundbackground

100100

proliferative responses in vitro.proliferative responses in vitro.

(anti(anti--CD154 + antiCD154 + anti--LFALFA--1) 1)

‘Linked’ Suppression:

Accounts for the lack of allograft rejection despite

the presence of donor-reactive T cellsBarriers to Consistent Induction Barriers to Consistent Induction

of Toleranceof Tolerance

• Genetic variability

• Pre-existing memory cells (‘heterologous’immunity)

• Concurrent inflammation / infection

• ‘Dual’ role of immune mediators in rejection andtolerance


Fellows Symposium


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Ronald G. Gill, PhD

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From: PT Wash et al. J. Clin. Invest. 114:1398, 2004

Both elimination of effector cells and generation of regulation may occur in the generation of allograft

tolerance

Current Conundrum:Current Conundrum:

Some cells types / molecules can participate both in graft rejection and tolerance

QuestionQuestion: : : : : : : : Are the Are the ‘‘propro--inflammatoryinflammatory’’

contributions of contributions of IFNIFNγγγγγγγγ, perforin, and , perforin, and

NK cells important for immunity or NK cells important for immunity or

tolerance?tolerance?

PropositionProposition:::::::: YESYES

Opposing Roles for NK Cells in

Transplantation

Promote Inflammation

Regulate Alloreactivity

NKCell

NK

ADCC

DC licensing

Promote Th1Immunity

Enhance ReperfusionInjury

Endothelial CellInjury

Varied Contributions of NK Cells to Immunity

NK Cells Required Cardiac Allograft Rejection

in CD28-/- Mice

S. Maier et al. Nat. Med. 7:557, 2001


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Ronald G. Gill, PhD

www.a-s-t.org 6

0

20

40

60

80

100

0 20 40 60 80 100

Day Post-Transplantation

% A

llo

gra

ft S

urv

ival

B6 control (n=9)

B6 + Anti-CD154 (n=10)

B6 + Anti-NK1.1(n=6)

B6 + Anti-CD154 + Anti-

NK1.1 (PK136; n=20)

p < 0.01

Tolerance to Islet Tolerance to Islet AllograftsAllografts RequiresRequires NK CellsNK Cells

((BeilkeBeilke et al. Nat. Med. et al. Nat. Med. 11:1059, 2005)11:1059, 2005)

PerforinPerforin: : : : : : : : Role in Immunity and Role in Immunity and

ToleranceTolerance

0

20

40

60

80

100%

Gra

fts F

unctionin

g

0 20 40 60 80 100


Perforin-Deficient Mice (pfp-/-) are Resistant to

Tolerance Induction

B6 pfp -/- + anti-CD154 (n = 7)

B6 pfp -/- Untreated (n = 9)

B6 w.t. + anti-CD154 (n = 5)

B6 w.t. Untreated (n = 9)

Perforin: Perforin: How can the How can the samesame molecule be required both molecule be required both

for immunity and for tolerance?for immunity and for tolerance?

ImmunityImmunity

((redundantredundant))

T cellsT cells

RegulationRegulation

((nonnon--redundantredundant))

NK cellsNK cells

0

20

40

60

80

100

0 20 40 60 80 100


C57Bl/6 IFNγ KO (n = 8)

C57Bl/6 (n = 24)

Pe

rce

nt

Gra

fts F

un

ctio

nin

g

Anti-LFA-1 Fails to Induce Long-Term Islet Allograft

Survival in C57Bl/6 IFN γγγγ-Deficient Recipients

(BALB/c C57Bl/6)


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Ronald G. Gill, PhD

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IFNIFNγγγγγγγγ

Tissue InjuryTissue Injury

Effector T cells

ToleranceTolerance

Treg

Role for IFNRole for IFNγγ in Treg Function and Allograft in Treg Function and Allograft

ToleranceTolerance

B. Sawitzki B. Sawitzki et al. et al. J. Exp. Med. 201:1925, 2005J. Exp. Med. 201:1925, 2005

P. Thebault P. Thebault et alet al. Am. J. Transplant 7:2472, 2007. Am. J. Transplant 7:2472, 2007

Wei Wei et alet al. Am. J. Transplant. 10:69, 2010. Am. J. Transplant. 10:69, 2010

IL-2

T CellProliferation

IncreasedAICD

(Activation Induced Cell Death)

Enhance Tregs

Cytokines with ‘Split’ Personalities

Wound Healing

Fibrosis

TGFTGFββ

RegulatoryRegulatory(Treg: FoxP3)

Th-17

IL-6

ProPro--InflammatoryInflammatory

Summary

• Tolerance is an active response to the graft

• Involves both deletional and regulatory components

• Some immune pathways contribute to both rejection

and tolerance




9:00 am - 9:30 am

Clinical Strategies of Tolerance

Induction

Roslyn B. Mannon, MD



Grapevine, Texas

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Fellows Symposium


Grapevine, TX


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Roslyn B. Mannon, MD, FASNRoslyn B. Mannon, MD, FASNAST Fellows Symposium 2011

Clinical Strategies to Tolerance Induction

Roslyn B. Mannon, MDUniversity of Alabama at Birmingham

I have no financial relationships to disclose within the past 12 months relevant to my

presentationand

My presentation does not include discussion of off-label or investigational use therapies

The Contributions of Animal Models in Transplantation

• 600 BC Sushruta, autologous skin graft to face• <1000 AD, Cosmos and Damian, leg transplant• 1800’s, Hunter successfully replaced a premolar (in

man)• 1900, Landsteiner and Miller discover ABO, rH blood

groups• 1902, Alexis Carrel developed the vascular

anastomosis in a dog (forerunner).• 1905, Carrel and Guthrie, heart transplant to neck of

dog.• 1906, Jabouley transplanted kidneys from sheep,

goats, monkeys into man.• 1908, Carrel transplanted kidneys between cats.• 1920, Williamson accurately predicted tissue type in

dogs as a forerunner of typing in man.

More Animal Contributions

• 1930, George Snell identified MHC antigens in the mouse (H-2 system).

• 1943, Peter Medawar evaluated responses between homografts and autografts in rabbits.

• 1945, Medawar proposed that rejection was an immunologic response in the recipient against the donor tissue.

• 1954, Merrill and Murray performed first kidney transplant in identical twins (largest of the large animal models).

• 1955, Welch performed first liver transplant in dogs.• 1959, Merrill and Murray successful kidney transplant in

man.• 1960’s, Sir Roy Calne used azathioprine in human recipient

of kidney transplant.

The Legacy ofSir Peter Medawar

• Experimental design

– Crude cell/tissue mixture from an allogeneic adult mouse injected into 6 fetuses of a CBA female produced 5 pups

– Pups skin-grafted at 8 weeks– Experiments repeated in neonatal mice

• Results– Of 5 skin grafts

• 2 promptly destroy (likely acute rejection)• 1 with prolonged involution (likely chronic rejection)• 2 accepted at 77 and 101 days

– Implantation of LN fragments from donor antigen-immunized mice lead to prompt rejection of these two surviving grafts

– Inoculation of neonatal mice with various tissues of different strains was largely unsuccessful• Only 9 of 96 skin grafts experienced prolonged survival

Medawar Conclusions

• Medawar and colleagues– Effect of treatment was a continuum ranging from no effect on survival to indefinite survival

– Regimen ineffective in neonatal (older) mice

– Therapy consistently overcome by memory

• Misconceptions– A brief, limited intervention in most individuals can consistently produce tolerance to alloantigens


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Definition of Tolerance

• Experimental definitions of tolerance are less applicable to clinical transplantation– Long-term allograft acceptance without ongoing immunosuppression in an immunocompetent recipient

– Acceptance of subsequent donor but not 3rd party organs/tissues

• A working definition for functional or operational tolerance in humans would be continued stableallograft function in the absence of immunosuppression

– Critical role of histology

Mechanisms of Tolerance

• Clonal exhaustion• Anergy• Deletion

– Specific deletion of donor specific cells [bone marrow infusion]

– Non specific deletion of donor reactive cells [rATG, Campath]

• Regulation• Ignorance

– Absence of secondary lymphoid organs– Immune privilege

Limits to Animal Models—Ken Newell says,

• Mice aren’t men– There is an increasing realization that the guiding principles gleaned from rodent transplant models may not translate to man

• Livers aren’t kidneys– Organ specific diversity in immunogenicity implies differences in immune response mechanisms and therefore tolerance.

Man versus MouseT Cell Repertoire

Man Mouse

T Cell Number 1012 2 x 108

# Unique T Cell Clones 2 x 107 2 x 106

Clone Size 1-4 x 103 100-200

# Alloreactive T Cells 1010 1-2x106

# Alloreactive T Cell Clones

2 x 105 1-2x 104

Heirarchy of Immunogenicity

Immunogenecity

Ease of Tolerance

Liver Kidney Heart Islets Pancreas Intestine Lung

Costimulatory Blockade


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Costimulatory Paradigm

• Positive

• Negative

T Cell

APCSignal 2

Signal 1

T Cell

APCSignal 2

Signal 1

ProliferationCytokine ProductionPrevention of AnergyTH differentiation

Inhibition of proliferationInhibition of Cytokine ProductionApoptosisInduction of Tregs?

Growing Family of “Co-Stimulation”

Li et al. Transplant Rev 2009; 229: 271

Blockade of CD28/B7-1 Prolongs Cardiac Allograft Survival

0.5 mg/d CTLA4Ig x 7d

0.05 mg/d CTLA4Ig x 7d

None

IsotypeControl

Turka et al. PNAS 1992; 89: 11102

Norway (RT1n)→ Lewis (RT1l)

Combined Costimulatory Blockade Leads to Long Term Graft Survival of Heart

and Skin Grafts

Time (days)

Balb/c (H-2d)→ C3H (H-2)

CTLA4Ig 200µg d 0,2,4,6

MR1 250µg d 0,2,4CTLA4Ig alone

CTLA4Ig + MR1

Larsen et al. Nature 1996; 381: 434

LEA29Y (Belatacept) Rhesus Renal Allograft Model

• 4-fold increase in avidity to CD86 and 2-fold to CD80.

CTLA4Ig LEA29Y

MMF/CsA

Basiliximab LEA+Basiliximab

LEA+MMF/CsA

Larsen et al. AJT 2005; 5:443Great paper to show the basic development with animal models

Belatacept (Nulojix®) in the Clinic

• Not for tolerance induction

• FDA approved for prophylaxis against acute rejection in kidney recipients


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Regulation

Tolerance Promoted by Tregs

Kingsley and Wood. Transplant International 2007; 20: 828

Ex-Vivo Expanded Tregs Ameliorate Allograft Rejection In Vivo

Nadig and Wood Nat Med 2010; 16:809

++TregTreg

Regulatory T Cells After DepletionalInduction Therapy with Campath-1H

JASN 2007; 18:1007

%CD25+Sirolimus

Possible Strategies

• Ex vivo Treg expansion followed by infusion at time of transplant

• Post transplant therapy to enhance Tregfunction and/or number

Hematopoietic Chimerism


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Chimerism and Tolerance

• Ray Owen - Freemartin cattle, Science 1945

• Sir Peter Medawar – neonatal tolerance, Nature 1953

• Main and Prehn – acquired tolerance in adults induced by lethal irradiation plus full BMT = fully allogeneic chimeras J Nat Can Instit 1955

• Ildstad and Sachs – mixed allogeneicchimerism Nature 1984

Non-Myeloablative Strategies

• Anti-T cell mAbs, low does TBI (3 Gy), thymic irradiation (7 Gy) [Sharabi J Exp Med 1989]

• Mega dose BM (200 million/mouse) plus costim blockade [Wekerle J Exp Med 1998, Durham J Immunol 2000]

• Low dose BM (20 million/mouse), busulfan, costim blockade [Adams J Immunol 2001]

New Strategy: Mixed Chimerism in HumansN Engl J Med 2008; 358: 362

Case report: 10 more enrolled

N Engl J Med 2008; 358: 353

Barriers to Tolerance

• Memory

• Homeostatic proliferation

• Heterologous Immunity

Memory Cells Resist Tolerance

Valujskikh et al. AJT 2002; 2: 501


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Weeks Post-Tx

Tx

Rejection

Memory Phenotype Cells Predominate Following Alemtuzumab Depletion

Pearl et al. AJT 2005; 5: 465

Homeostatic Proliferation Impairs Tolerance

Wu and Turka Nat Med 2004; 10: 87

BALB/c↓

B6 WT or SCID+

B6 cells

B6THY1.1 CSFE↓

B6 SCID Thy 1.2

Day 5 Day 10

Preferential Memory Cell Homeostatic Proliferation Following Subtotal Lymphocyte

Depletion

Neujahr and Turka J Immunol 2006; 176: 4632

B6 mice +antiCD4 +

antiCD8 +BRDu

CD4 gate

CD8 gate

Naïve CD62LhiCD44lo

Memory CD62LloCD44hi

Virally Induced Alloreactive Memory Cells Prevent Tolerance Induction

Adams and Larsen JCI 2003; 111: 1587

Summary/Conclusion

• Tolerance to an organ may engage a number of different mechanisms

• A number of preclinical models have been utilized; the results in mice do not translate into NHP models, and also not to Man.

• However, these models provide valuable input into the mechanisms of human disease and have demonstrated the critical complicating factors between preclinical models and man.




10:00 am - 11:00 am

Literature in Transplantation:

Key Papers of 2010 - 2011 Combined Session

There are no advance slides for this session.



Grapevine, Texas

www.a-s-t.org




11:00 am - Noon

Career Development in Basic

and Translational Transplant

Investigation

Facilitator: Robert L. Fairchild, Ph.D

Panel: Maria-Luisa Alegre, MD, PhD, Mark L. Barr, MD, William M.

Baldwin, MD, PhD, Ronald G. Gill, PhD, Roslyn B. Mannon, MD and

Kenneth A. Newell, MD, PhD

There are no advance slides for this session.



Grapevine, Texas

www.a-s-t.org

primary mechanisms of self-tolerance...cd8 + t cell exhaustion memory and exhausted cd8 + t cells...

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