ITP Conference 2002

1
ITP Conference 2002 The Cellular Immunology of
Immune Thrombocytopenic Purpura New Insights on
an Old Problem. John W. Semple, PhD Toronto
Platelet Immunobiology Group (TPIG), St.
Michaels Hospital, University of
Toronto, Canadian Blood Services, Toronto,
Ontario, Canada.
2
Outline of talk

• The Immune response
• Autoimmunity - general concepts.
• Chronic AITP.
• Update on immune abnormalities in chronic AITP.

3
Immunity
Innate Immunity
Adaptive Immunity
Barriers (skin) Secretions (lysozyme) Complement I
nflammation Granulocytes NK cells Macrophages Phag
ocytosis
B cells-- Antibody production T cells-- Cell
mediated immunity Immunoregulation
4
The Antibody Response
Secondary Response
IgG, IgA, IgE
Primary Response
T Cell Dependent
IgD/IgM
t
Ag
Ag
5
(No Transcript)
6

7
The Immune Response
Ag
APC
Ag Processing
B
Ab
CD8
1.
2.
Help
Help
cytokines
CD4
8
The T cell-APC Synapse
B7
CD28
APC
T cell
CD4 or 8
MHC
TcR
CD40
CD40L
9
Ag
APC
Ag Processing
B
Ab
CD8
1.
2.
Help
Help
cytokines
CD4
10
CD4 T cell cytokine effects
CMI DTH C-fix. Ab
IL2,IFN?
Th1
IL12
Th0
IL4
IgE C-nonfix Ab
IL2,IL4,IL12, IL13, IFN?
IL4,IL13
Th2
11
Self (Immunologically)
MHC Class II
MHC Class I
Antigen Presenting Cell (APC)
12
MHC Class II peptide
MHC Class I peptide
Antigen Presenting Cell (APC)
13
CD8 T cell
CD4 T cell
T cell receptor (TcR)
TcR
Class II
Class I
Antigen Presenting Cell (APC)
14
Autoimmunity

• Immune reactivity against self.
• Generally classed into systemic (e.g. SLE,
  RA,GVHD) and organ-specific (e.g. MS, IDDM, IBD,
  AITP etc.).
• Affect 5-7 of the population often with
  debilitating symtoms

15
Organ specific Autoimmunity

• Deficiency of central and/or peripheral tolerance
  induction mechanisms
• failure to eliminate or deactivate self
  reactive lymphocytes.

16
Thymus
Abnormal release of autoreactive T cells
Selected T cells
T cell precursors
Central Tolerance
Peripheral Tolerance
-anergy/deletion/ suppression
Molecular mimicry T helper 1/T helper 2
imbalance Cytokine Milieu Costimulation/activation
faults
Bone marrow
17
Etiological Theories

• Molecular mimicry.
• - determinant spreading.
• T helper 1/T helper 2 balance.
• Cytokine Milieu.
• Co-stimulation/activation faults.

18
Molecular Mimicry
VZV
Platelet
19
Acute AITP

• Good example of molecular mimicry.
• Cross reactivity of anti-viral antibodies
  with normal platelet epitopes.
• Wright et al, 1996

20
Th1/Th2 Balance

• Organ-specific autoimmunity is generally
  Th1-associated.
• Th1 promotes pathogenesis
• Th2 protective.
• Cytokines (e.g. TNF, GM-CSF) which support Th1
  responses are also present.

21
Costimulation/Activation faults Antigen
processing and presentation defects
22
MHCII
Macrophage (APC)
23
1.
Phagocytosis
MHCII
Macrophage (APC)
24
Destruction
2.
1.
Phagocytosis
MHCII
Macrophage (APC)
25
Infection, Cytokines (e.g. TNF, IFN)
APC Activation
Destruction
2.
1.
Phagocytosis
MHCII
Macrophage (APC)
26
Infection, Cytokines (e.g. TNF, IFN)
APC Activation
Destruction
2.
Altered processing
1.
Phagocytosis
MHCII
Macrophage (APC)
27
Infection, Cytokines (e.g. TNF, IFN)
APC Activation
Destruction
2.
Altered processing
1.
Phagocytosis
MHCII
Peptides
3.
Macrophage (APC)
28
Infection, Cytokines (e.g. TNF, IFN)
APC Activation
Destruction
2.
Altered processing
1.
Phagocytosis
MHCII
Peptides
3.
4.
Macrophage (APC)
Abnormal Presentation
29
Infection, Cytokines (e.g. TNF, IFN)
APC Activation
Destruction
2.
Altered processing
1.
CD4 T cell Activation
Phagocytosis
MHCII
TcR
Peptides
3.
4.
Macrophage (APC)
Abnormal Presentation of a platelet autoantigen
30
Immunotherapy Goals

• Antigen-specific therapy
• - peptideMHC.
• T cell receptor based immunoregulation.
• Co-stimulation.
• Oral Tolerance.

31
Immunotherapy Goals
B7
CD28
APC
T cell
CD4 or 8
MHC
TcR
CD40
CD40L
32
Oral Tolerance
Antigen
GALT
T cell Tolerance
33
Autoimmune Thrombocytopenia
Platelet count lt150x109/L

• Acute
• Childhood disorder.
• Abrupt onset.
• Usually follows infectious illness.
• Spontaneous remission.

• Chronic
• gt 6 month duration.
• Organ specific autoimmune disease.
• Autoantibodies enhance platelet destruction.
• Presence of GPIIIa-reactive T cells.
• Th0/Th1 bias.
• Cytokine abnormalities.

34
AITP Research
First demonstration of autoantibody mediated
disease (Harrington, 1951). Approximately
200 papers published since 1951 on AITP research
(not including clinical trials).
35
Funding for AITP Research
Abysmal
Its just not the major player in the field of
autoimmunity research. Call your
MP/congressman!
It seems that theres a better chance of Toronto
winning the Stanley Cup than getting monies to
study AITP.
36
Nomenclature difficulties?
ITP Idiopathic Thrombocytopenic Purpura Immune
Thrombocytopenic Purpura ATP Autoimmune
Thrombocytopenic Purpura - (adenosine
triphosphate - oops) AITP AutoImmune
Thrombocytopenic Purpura
37
Autoimmune Thrombocytopenia
38
Alloantibodies
- Transfusion - Maternal/Fetal Incompat.
Platelet
Autoantibodies
- AITP
Increased RES Destruction
39
Although the immuopathogenesis of chronic
autoimmune thrombocytopenic pupura is
autoantibody mediated, it is a primarily a T
cell-initiated disorder.
40
The Immune Response
Cytokines
CD4 T cell
Help
Help
B cell
CD8 T cell
APC
Antigen Presenation
Plt.
IgG
41
AITP T cell Related Abnormalities
PHA/ConA-induced Platelet Abs (1970s)
Fas/FasL (2000- )
Plt-induced PBMC proliferation (IL2)
(1970s- )
Chronic
T cell lines/clones (1993- )
In vitro/In vivo cytokines. (1980s- )
Defective MLR (1982)
HLA-DR Platelets (1992- )
Activated T cell phenotype (e.g. HLA DR) (1987-
)
42
AITP T cell reactivity
T cell cloning possible (1993)
GPIIIa peptide Mapping (2001)
?/? T cells (1994)
Chronic
GPIIIa processing required (1998)
GPIIIa reactive T cell line reactivity (1996-
)
Adherent APC dependent (1998)
GPIIIa chymotryptic fragment reactivity. (1998)
HLA-DR Assoc. (1998) (Japanese population)
43
T Cell Characteristics

• CD4 T cells gt CD8 T cells.
• Trend toward Th1 activation.
• Lines primarily react with GPIIbIIIa.
• Adherent cell (APC) dependent.

44
T cell reactivities in chronic AITP
Children
Adults
t
Consistent
Inconsistent
Appears to be a more heterogeneous disorder
More focused immune response.
45
AITP Cytokines
MIF
IL15
M-CSF
GM-CSF
sIL2R
Chronic
IL2
TGF-?
IL1?
IL10
TNF-?
IFN-?
IL4
IL6
46
AITP Therapy
Steroids (1950s- )
-Antigen- specific therapy
Vinca Alk., Danazol Cyclophosphamide (1970s)
-Oral Tolerance
Chronic
Cyclosporin IFN, VitC etc. (1980s- )
Anti-CD40L (1998- )
Gammaglobulins (1981- )
Rituxan (1998- )
Anti-D (1984- )
47
New immune therapies

• Anti-CD40L
• Anti-CD20
• Anti-FcR
• H. pylori chemotherapy

48
Potential antigen-specific therapies
autoantibody
Anti-id

• Anti-idiotypic antibodies
• Oral tolerance
• T cell epitopes in platelet glycoproteins

GPIIbIIIa
49
Inflammatory stimuli
CD40L
A.
GPIIbIIIa
M-CSF
CD40
Platelet Autoantigens
sIg
Activated Macrophage (APC)
CD20
Autoreactive B cell
IL1ß, IL1a
TGF-ß
D.
CD68
CD40
B7.1/7.2
IL2, IL4, IL15 IFN-?, TNF-a, GM-CSF
Autoantigen processing
B.
CD40
CD40L
CTLA-4
peptides
Autoantibody Production
MHC class II
CD28
C.
CD40L
Autoreactive Th cell
TcR
CD68/Class II microparticle
sIL2R
IL2
IFN-?, TNF-a
sIL2R-IL2
50
Conclusions

• Chronic AITP is associated with T cell activation
  patterns which resemble a pro-inflammatory
  Th0/Th1gtgtgtTh0/Th2 cytokine phenotype.
• Platelet-reactive T cell lines from chronic AITP
  patients primarily react with GPIIIa.
• Modulating T cells via cytokines or altered
  autoantigen is a potential for therapy.

51
Acknowledgements

• Youli Milev,
• Donna Cosgrave,
• Thomas Kuhne,
• Fraser Wright,
• Malini Coopamah,
• Alan Lazarus,
• Ed Speck,
• Michael Kim,
• Bernadette Garvey,
• John Freedman,
• Victor Blanchette