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