The Complement System: Friend and Foe

Dick Wells, Odette Cancer Centre

Disclosures

I have received honoraria and research funding from

Alexion

Overview

Complement function and regulation

Implications of chronic uncontrolled complement

activation

PNH, aHUS diagnosis and management

Design of complement

Now known to be at least 27 proteins

Inactive state

(serum)

Activation and

amplification (3 pathways)

Localization on membrane

surfaces Function: LYSIS

Regulation

Figueroa JE, Densen P. Clin Microbiol Rev. 1991;4:359-395; Ross GD. Introduction and history of complement research. In Ross GD, ed.

Immunobiology of the Complement System. Orlando, FL: Academic Press, Inc; 1986:1-20; Walport MJ. N Engl J Med. 2001;344:1058-1066.

Initiation Infection Surgery Autoimmune disease Pregnancy

The Complement Cascade

Pro

xim

al

Term

inal

C3 + H2O - ALWAYS ACTIVE (chronic)

Amplification

Regulation of Complement

Regulation gives specificity

Activated complement

Self Non-self

Complement attacks both self and non-self

Host cells are protected by complement regulatory proteins

Control of complement

Direct inhibition of enzyme

activity

Disruption of enzyme

complexes

Degradation of C3b and C4b

Prevention of MAC assembly

C1 inhibitor

CD55

Factor I and cofactors

(Factor H, C4 binding

protein, MCP, TM)

CD59

MCP = membrane cofactor protein; TM = thrombomodulin; TCC = terminal complement complex.

Factor I and co-factors: Soluble and Membrane Bound Complement Regulators

Confidential – For Internal Use Only 9

CD55 and CD59:

Membrane Bound Complement Regulators

C3b

C3b

C3b

Bb

BC3b

Bb

C3b

C5convertase

RBCMembrane

C5b

C5

C5a

Anaphylotoxins

Platelets

Neutrophils

C3convertase

Classical

Alternave

Lecn

MAC

Bb

C3b

CD59CD55

Chronic Uncontrolled Complement Activation

Leads to Devastating Consequences P

roxim

al

Term

inal

-

C3 + H2O - ALWAYS ACTIVE (chronic)

Amplification

Anaphylaxis

Inflammation

Thrombosis

Consequences

Cell Destruction

Inflammation

Thrombosis

Consequences

-

Consequences of deregulation

Diseases of disordered complement

regulation

PNH aHUS

Aetiology Acquired PIGA mutation,

resulting in deficiency of

CD55 and CD59

Inherited mutation or

acquired inhibitor of

Factor I or co-factors

Tissue affected Haematopoietic Endothelial

Age at

presentation

Any Any

Pathogenetic

event

Chronic attack on vulnerable tissue by activated

complement

Clinical effects Intravascular haemolysis,

thrombosis, renal failure,

pulmonary HT, fatigue,

smooth muscle spasm, pain

Thrombotic

microangiopathy, renal

failure, neurological

abnormalities

Loss of Factor I and co-factors:

Chronic Uncontrolled Complement Activation

Simple triggers, including common infections and stressors further accelerate complement over-activity

Keir L, Coward RJ. Pediatr Nephrol. 2011;26(4):523-33.

14

Atypical HUS

Very rare (about the same as PNH)

Inherited deficiency or acquired inhibitor of I, H, TM, etc

May present from infancy to old age

Presents like TTP: microangiopathic haemolytic anaemia with thrombocytopenia, RBC fragmentation, renal failure

But ADAMTS13 >10%

Transient response to PLEX

Progresses to ESRD; recurs in transplant kidneys

Platelets

Neutrophils

C3b C5 convertase

C5b

C5

C5a

Anaphylotoxins

C3

convertase

MAC

No CD55/CD59

Unrestrained activation of terminal complement…

In PNH Chronic Uncontrolled Complement

Activation Leads to Vasoconstriction and Thrombosis

Adapted from: Gladwin MT et al. Free Rad Biol & Med. 2004;36(6):707-717; Rother RP et al. JAMA. 2005;293:1653-1662.

Chronic hemolysis

Platelet activation

Local vasoconstriction

CLOT Platelet

Activation

Leukocyte

Activation

Chronic

Uncontrolled

Complement

Activation

C5a C5b-9

C5b-9

[NO]

Inflammation

Platelet

Aggregation

Chronic Hemolysis

Inflammation

Endothelial cell injury

Systemic thrombosis

Summary: Disorders of Complement

Regulation

Complement

is always on

CD55/59 Factor I Erythrocytes Endothelium

TMA Intravascular

haemolysis

Diagnosis

PNH

Bone marrow failure

Weird thrombosis

Intravascular haemolysis

Haemoglobinuria

aHUS

MAHA (like TTP)

ADAMTS13>10%

Not responding to PLEX

HIGH-SENSITIVITY FLOW GENETIC TESTING*

Treatment of complement

regulation disorders

C5

Pro

xim

al

Te

rmin

al

1. Soliris® (eculizumab) Product Monograph, 2013.; 2. Rother RP et al., 2007.; 3. Walport MJ, 2001.; 4. Figueroa JE and Densen P, 1991.

C5a

ECULIZUMAB

• Binds with high affinity to C51,2

• Terminal complement: C5a and C5b-9

formation blocked1,2

• Proximal functions of complement

remain intact1,2:

• Weak anaphylatoxin2,4

• Immune complex clearance2

• Microbial opsonization2

Complement cascade2,3

C5b-9 C5b

C3 C3a

C3b

Eculizumab blocks terminal complement

Eculizumab blocks haemolysis in PNH

1. Hillmen P et al., Blood 2007; 110:4123-4128; 2. Hillmen P et al., Br J Hematol 2013; 162:62-73; 3. Soliris® (eculizumab) Product Monograph, Alexion

Pharma Canada, February 2013.

Crossover

• 87.6% serum LDH reduction 1 month after treatment initiation1

• 86.9% decrease in hemolysis maintained for 36 months1

Copyright © 2007 American Society of Hematology.

Reprinted with permission.

Impact on survival in PNH

.

1. Hillmen P et al., 1995.; 2. Hill A et al., 2012.; 3. Soliris® (eculizumab) Product Monograph, 2013.

100

80

60

40

20

0

0 5 10 15 20 25

Years after diagnosis

Pa

tie

nts

su

rviv

ing

(%

)

Pre-eculizumab from time of

diagnosis in 80 patients with PNH1

Age- and gender-

matched controls

Patients with PNH

• Despite best supportive care, 5-year

mortality rate was 35%1

PNH patients on eculizumab compared with

age- and gender-matched controls2*

Time (years)

• Hazard ratio = 2.24 (p = 0.013)

20

40

60

80

100

2 4 6 8 10 0 0

Age- and gender-matched

normal population

Soliris®-treated PNH population

*Survival after 10 years is slightly inferior to controls with causes of

death related to bone marrow failure and not hemolysis or thrombosis.

Copyright © 2012 American Society of

Hematology. Reprinted with

permission.

Petra Muus et al. Blood 2013;122:2186

©2013 by American Society of Hematology

aHUS: Improvement in GFR with eculizumab treatment

Wrap-up

Complement: friend and Foe

Complement is an important part of the innate immune system

Always ‘on’, ramped up when needed

Multiple complement defense proteins protect host tissues

Acquired or congenital deficiencies in complement defense proteins

CD55/59 PNH

Factor I and friends aHUS

Complement inhibition with eculizumab is effective treatment