mechanisms of action of ivig: what do we really know? · •there are too many theories to explain...
TRANSCRIPT
Mechanisms of action of IVIg: What do we really know?
Alan H. Lazarus, PhD
Canadian Blood Services St. Michael’s Hospital University of Toronto
Plasma Protein Biotechnology Meeting 2013, Lanzarote, Spain May 15, 2013
Outline •How does IVIg work in autoimmunity? •There are too many theories to explain how IVIg works!
•Present evidence against: •FcRn •Fc³ RIIB •IgG sialylation
•Evidence for immune complexed IgG acting on Dendritic cells via activating Fc³ R œ DC-SIGN
IVIg is IgG
Fc
F(ab’)2
Intravenous Immunoglobulin
Mechanisms of IVIg
•How does IVIg work in autoimmunity?
• ITP (murine passive ITP) • Inflammatory arthritis (murine krn serum transfer) • EAE (Murine model of MS)
IVIg Beneficial-Yes/likely
• CIDP
• ITP and HIV-ITP
• Hypogammaglobulinemia
• Guillain-Barré syndrome
• Kawasaki disease
• Kidney transplantation: HLA sensitization
• Toxic epidermal necrolysis, Stevens-Johnson syndrome
• Dermatomyositis, polymysitis
• Autoimmune uveitis
• Stiff-person syndrome
• Fetal/neonatal alloimmune thrombocytopenia
• Post transfusion purpura
• Autoimmune neutropenia
• Multifocal Motor Neuropathy
• Demyelinating Polyneuropathies associated with IgG or IgA monoclonal gammopathies
• Acute exacerbations in Myasthenia Gravis
• Lambert-Eaton Myasthenic syndrome
Source: Immunoglobulin Therapy Lazarus AH, Semple JW, eds. Bethesda, MD: AABB Press, 2010
0
50
100
150
200
250
Pla
tele
t co
un
t
1 2 3 24 48 72 96 hours
Time post serum injection
Most mechanistic studies in murine ITP
Harrington-1951
Yippee!
Good idea? IVIg?
Immune thrombocytopenia (ITP)
Platelet
The first demonstration that IVIg has ameliorative effects in an autoimmune disease
How does IVIg work?
We don’t know how IVIg works and the IVIg puzzle has been difficult to solve with results
that often seem to be in conflict with each other
Block Fc receptors (RES blockade)
Anti-idiotypic antibodies
complement
Immune complex
Dendritic cells
T regulatory cells
Fc sialylation
DC-SIGN
Fc³ RIIB (Inhibitory)
Fc³ RIII (Activating)
The players
Neonatal Fc receptor
Block Fc receptors (RES blockade)
Anti-idiotypic antibodies
complement
Immune complex
Dendritic cells
T regulatory cells
Fc sialylation
DC-SIGN
Fc³ RIIB (Inhibitory)
Fc³ RIII (Activating)
The players: There are too many
Neonatal Fc receptor
?
? ?
What is the FcRn and how does it work?
FcRn protects IgG from degradation in adults
From, Roopenian et al, Nature Reviews Immunology 7, 715-725
Hypothesis
IVIg works (at least in part) by saturating FcRn, thereby increasing catabolism of all IgG antibodies, including
pathogenic IgG.
FcRn deficient mice are protected from ITP to the same extent as wild-type mice.
0
200
400
600
800
1000
1200
NilIV
Ig
anti-P
LT NilIV
Ig
Wild-type FcRn KOan
ti-PLT
Pla
tele
t co
unt
x 10
9 /L
FcRn: Conclusion
IVIg can ameliorate murine ITP in the absence of FcRn or ² 2M (required for functional FcRn expression).
Immune complex
Dendritic cells
T regulatory cells
Fc sialylation
DC-SIGN
Fc³ RIIB (Inhibitory)
Fc³ RIII (Activating)
The players: There are too many
Neonatal Fc receptor
?
? ?
What is the major signaling pathway involved in FcγRIIB inhibitory function?
SHP-1
Not SHIP, SHP-1, or Btk Crow et al. Blood 102:558, 2003
IVIg ameliorated murine ITP in Fc³ RIIB deficient mice on the BALB/C background
IVIg ameliorated murine ITP in Fc³ RIIB deficient mice only on a mixed (B6;129) genetic background
BALB/c C57BL/6 B6.129
Fc³ RIIB+/+
Fc³ RIIB-/-
yes
yes yes yes
yes no
SLE Prone mice
(NZW x BXSB) F1 male mice
“There were no significant differences in the percentages or numbers of CD14+CD32B+ monocytes, or in the percentage of CD14+CD32B+ monocytes present in (20) children with ITP before and after IVIG therapy.”
Immune complex
Dendritic cells
T regulatory cells
Fc sialylation
DC-SIGN
Fc³ RIIB (Inhibitory)
Fc³ RIII (Activating)
The players: There are too many
?
?
DC-SIGN Fc³ RIIB (M¦ ) IL-4 Baso IL-33
DC-SIGN Fc³ RIIB (M¦ ) IL-4 Baso IL-33
Immune complex
Dendritic cells
T regulatory cells
Fc sialylation
DC-SIGN
Fc³ RIII (Activating)
The players: There are too many
?
Immune complex
Dendritic cells
T regulatory cells
DC-SIGN
Fc³ RIII (Activating)
The players: There are too many
Block Fc receptors (RES blockade)
Cell-associated (anti-D like effect)
RBC
OVA
OVA
Soluble
OV
A
or
Endogenous soluble antigens
0 1 2 3 40
200
400
600
800
1000
***
***
**
***
**
IVIG
anti-albumin
anti-transferrin
non-immune IgG
anti-platelet antibody
Tre
atm
ent
Pla
tele
t cou
nt x
109/
L
2006
Proposed model of IVIg action in murine ITP
Siragam et al, J Clin Invest 2005
Siragam et al, Nat Med 2006 Huang et al, Blood 2010 ITP
DC-SIGN
Fc³ RIII
Aloulou et al, Blood 2012
Proposed model of IVIg action in ITP
Tha-In et al, Blood 2007
Ephrem et al, Blood 2008
Aubin et al, Blood 2010
ITP
Conclusions (IVIg) • IVIg has beneficial effects in a large number of seemingly
unrelated autoimmune diseases and inflammatory states
• Evidence against the concept that IVIg requires the neonatal Fc receptor (FcRn) for its function
• Evidence against the concept that IVIg interacts or requires the inhibitory Fc receptor (Fc³ RIIB) for its function
• Evidence against a simple role of Fc sialic acids in mediating IVIg effects
• IVIg may interact with activating FcRs on dendritic cells in the initiation of its effects
Acknowledgements
Funding:
CBS CIHR Health Canada
Collaborators: Derry Ropenian John Semple Steve Mckenzie Mike Reilly
A. IVIg; standard single dose
C. IVIg; single dose with decay
D. IVIg; low cont. Infusion
E. IVIg; 2/week
B. IVIg; maximal continuous dosing
IVIg effectiveness and pharmacology in a model autoimmune disease