CBS Transfusion Medicine Resident Scientific Session
Nov 2, 2010
Recent advances in Fc receptordependent therapies
Alan H. Lazarus, PhD
Canadian Blood Services
St. Michael’s Hospital
University of Toronto
Outline
•Mechanisms of platelet destruction in ITP
•Recent advances in:
• Fc receptor blockade
• IVIg
• anti-D
• Inhibition of Fc receptor signaling
•Conclusions
Immune thrombocytopenic purpura
(ITP)
Platelet
An Fc-independent mechanism of potential immune
thrombocytopenia-ROS
GPIIbIIIa
ROS
Zang W et al, Blood 2008
Li Z et al, J Biol Chem 2008
Li Z et al, Blood 2009
Wright JF et al, Br J Haem 1996
Peterson, Blood 2008 Quinine
Fc-independent immune thrombocytopenia-GPIb
Platelet
GPIb
Nieswandt et al Blood 2000
Webster et al Blood 2006
Go et al Haematologica 2007
Carbohydrates important
for IgG function?
Fc
F(ab’)2
IgG subclass-specific effects of EndoS-mediated hydrolysis
of the IgG-associated sugar side chain.
Albert H et al. PNAS 2008;105:15005-15009
©2008 by National Academy of Sciences
A potential alternative mechanism of platelet destruction?
Cell Mediated Immunity
Olsson et al, Nature Medicine 2003
Zhang et al, Eur J Haem 2006
An alternative mechanism which may contribute to
immune thrombocytopenia?
MK in Bone Marrow
PLT
PLT
Decreased platelet production due to
antibody and/or T cells inhibiting or destroying MK
Mechanism
Fc receptors Reference
classic anti-IIbIIIa
yes
Harrington Experiment
1951
anti-IIbIIIa (49-66)
no
Zhang, 2008
Li, 2008
Li, 2009
anti-GPIb
no
Nieswandt, 2000
Webster, 2006
Go, 2007
T cells
no
Olsson, 2003
Zhang, 2006
Chow, 2010
Direct effect on MK
?
Chang 2003
McMillan 2004
Houwerzijl 2004
Outline
•Mechanisms of platelet destruction in ITP
•Recent advances in:
• Fc receptor blockade
• IVIg
• anti-D
• Inhibition of Fc receptor signaling
+other potential Fc receptors for IgG (FCRL’s)
Fc receptor blockade
•Antibody specific for FcRIIIa worked in
refractory ITP (Clarkson, 1986)
•Antibody specific for FcRI worked in ITP
(Terjanian, 2000 abstract in Blood)
•Humanized antibody for FcRIIIa (GMA161&
3G8) worked but with side effects (Bussel, 2006 &
Nakar, 2009 abstracts in Blood)
Fc receptor blockade
• Clodronate is effective in a mouse model of
passive ITP (Alves-Rosa 2000, 2002; Deng &
Balthasar 2005, 2007; Li 2006)
Taken from, www.clodronateliposomes.org
Outline
•Mechanisms of platelet destruction in ITP
•Recent advances in:
• Fc receptor blockade
• IVIg
• anti-D
• Inhibition of Fc receptor signaling
Intravenous Immunoglobulin
IVIg is IgG
Fc
F(ab’)2
How does IVIg work?
What does IVIg bind to?
•
•
•
•
•
•
•
•
Other antibodies [Schussler, 1997]
Glycolipids [Vuist, 1997]
Superantigens [Takei, 1993]
HLA antigens [Glotz, 1993]
DNA & Phospholipid [Krause, Blank, Shoenfeld. 1998]
Fas/FasL [Viard, 1998, Prasad, 1998, Altznauer, 2003]
IgE Fc receptor & Tetanus toxoid [Horn, 1999]
Galactose disaccharides [Barreau, 2000]
• Auto-antigens [reviewed in St-Amour, 2009]
• Red Blood cells [Salama, 1984]
• ……
Theories of IVIg action
•
•
•
•
•
•
•
•
•
•
Fc receptor blockade
Inhibitory FcγRIIB expression
Regulation of cytokine production
Anti-idiotypic antibodies
Inhibits complement activation
Clearance of pathogenic antibody-FcRn.
Apoptosis
IVIg possesses anti-inflammatory sugars
IVIg forms soluble immune complexes
Dendritic cells
Hypothesis
Can antibodies which form an
immune complex ameliorate ITP?
Teeling et al, Blood 2001
Experimental Design
Cell-associated:
(anti-D like effect)
Soluble:
OVA
A murine model of
Passive Immune Thrombocytopenia
Ravetch et al (NY)
Bleeker et al (Amsterdam)
24h
Balthasar & Deng (Buffalo)
Lemieux & Bazin (Quebec City)
Webster et al (Toronto)
FSC
800
600
400
Treatment
Platelet count x 109/L
1000
***
***
***
***
2
3
4
200
0
0
1
anti-platelet antibody
Inhibitory FcγRIIB
Activating FcγR
1000
800
800
Treatment
1000
600
400
600
400
200
200
0
0
0
1
2
anti-platelet antibody
3
4
0
1
Treatment
FcγRIIB-/- mice
***
2
3
anti-platelet antibody
***
4
If IVIg functions via the formation of an
immune complex, could these complexes be
reacted with cells which could then be
adoptively transferred to recipients?
Mix
Wash
Load
Inject
Amelioration of ITP?
Adoptive-transfer of IVIg effects
with leukocytes
Siragam et al, Nature Medicine 2006
Proposed model of IVIg action in murine ITP
ITP
Siragam et al, J Clin Invest 2005
Park-Min, Immunity 2007
Siragam et al, Nat Med 2006
Tha-In et al, Blood 2007
Ephrem et al, Blood 2008
Aubin et al, Blood 2010
Outline
•Mechanisms of platelet destruction in ITP
•Recent advances in:
• Fc receptor blockade
• IVIg
• anti-D
• Inhibition of Fc receptor signaling
F c  R IIIA E x p re s s io n
Anti-D-like antibodies reduce the ability to detect
activating Fcγ receptors on macrophages
200
150
100
*
*
TER119
M1/69
50
0
Nil
IVIg
30-F1
Song et al, Blood 105:1546-8, 2005
Does anti-D ameliorate ITP via the same mechanism as IVIg?
2 hr
IVIG
IL-10
Anti-D
IL-10
MCP-1
IL-6
TNFα
Cooper et al, Br J Haem 2004
Blood 2007
Of the 6 patients in the study who had failed to respond to IVIG and
anti-D given as single agents, 5 of them responded when given in combination.
Outline
•Mechanisms of platelet destruction in ITP
•Recent advances in:
• Fc receptor blockade
• IVIg
• anti-D
• Inhibition of Fc receptor signaling
•Conclusions
A new therapeutic intervention based upon the
mouse model of ITP?
Platelet phagocytosis in ITP
syk
R406
Braselmann, et al. J Pharmacol Exp Ther, 2006
Inhibition of syk ameliorates murine ITP
Platelet count x 10 9/L
1000
Unmanipulated
800
600
400
200
0
Treatment
Nil
Vehicle
R788
25 mg/kg
R788
40 mg/kg
IVIg
2 g/kg
Podolanczuk, A. et al. Blood 2009;113:3154-3160
syk inhibition in 16 adult refractory ITP patients
Podolanczuk, A. et al. Blood 2009;113:3154-3160
Copyright ©2009 American Society of Hematology. Copyright restrictions may apply.
Conclusions
•Multiple potential mechanisms of
thrombocytopenia in ITP.
•The mechanism of IVIg remains unclear but may
work via an Fc receptor-dependent cellular
pathway (DC)
•Anti-D appears to work via a mechanism distinct
from IVIg
•Inhibition of Fc receptor signaling or function
could be a potential therapy in ITP
Thank you!
Andrew R Crow
Dr. Zhong-Wei Chai
Sara Suppa
Xi Chen
Joan Legarda
Patrick Mott
Dr. John Freedman
Dr. Bernadette Garvey
Dr. John Semple
Dr. Heyu Ni
Dr. Valery Leytin
Dr. Margaret Rand
Derry Roopenian
Jim Bussel
Anna Podolanczuk