Abatacept (hCTLA4-Ig)For the Treatment of Rheumatoid Arthritis:

Product Attributes and Mechanism of Action

Joy Williams, Ph.D.

Arthritis Advisory CommitteeSeptember 6, 2005

Continuous Marketing Application (Rolling submission of BLA)

Unit: Date ofsubmission:

Pharmacology and Toxicology reviewable unit 11/15/04

Clinical pharmacology and biopharmaceuticsFull clinical reviewable unit 12/20/04

Chemistry, Manufacturing and Controls (CMC)reviewable unit 3/31/05

Abatacept BLA

PDUFA action date for BLA 125118 (Abatacept): 12/31/05

Review teamRegulatory Project manager:Erik Laughner

Product reviewers:Joy Williams, chairElizabeth ShoresSusan KirshnerEnnan GuanEdward MaxBarbara Rellahan

Clinical reviewers:Keith Hull – Chair, clinical reviewerJeffrey Siegel –Team leaderMark Walton-Director

Pharm/Tox:Anita O'Connor-toxicology reviewerAnil Rajpal-Pharm reviewerHannan Guan

Statisticians:Kyung Lee-stat reviewerBoguang Zhen-stat team leader

Facilities reviewer:Ann deMarco

DSI/BiMo: Dianne Tesch

DDMAC:Catherine Gray

DDRE:Hyon Kwon

Abatacept (CTLA4-Ig) homodimer

CTLA-4 domain:Extracellular sequence of human CTLA-4

IgG1 Fc domain:Hinge, CH2 and CH3 regionsof human IgG1 Fc sequence

Final formulationAbatacept for Injection, 250 mg/vial

sterile, non-pyrogenic lyophile for intravenous administration following reconstitution with Sterile Water for Injection; supplied with non-siliconized syringe

Excipients: maltose monohydrate, sodium phosphate monobasic,Sodium chloride, hydrochloric acid, sodium hydroxide

Abatacept manufacturing process

Abatacept is produced as a secreted protein inlarge scale culture of Chinese hamster ovary cell line

Series of purification/viral clearance steps

activated T cell Antigen presenting cell

TCR

B7

MHC + peptide

CD28

T cell activation requires signals from TCRand costimulatory molecules

T cell Antigen presenting cell

CTLA4 – a CD28 homologue thatbinds to B7 with higher affinity than CD28

TCR

B7

MHC + peptide

CD28

CTLA4

CTLA4 extracellular domain (B7-binding domain) is fused to IgG1 Fc

to create soluble CTLA4-Ig

CTLA4-Ig

CTLA4

IgG1 Fc

B7

CTLA4 extracellular dom

ain

T cell Antigen presenting cell

TCR

B7

MHC + peptide

CD28

CTLA4-Ig binds to B7 molecules and inhibitsCD28-B7 interactions; suppresses T cell response

Additional possible mechanisms of action to consider:

B7IDO

IDOIDO

tryptophan

kynurenine

T cell proliferation is inhibited

B7 engaged by CTLA4-Ig directly signals to dendritic cells

Suppresses T cell response

INF-

Grohmann et al. Nat Immunol. 3:1097-101Mellor et al. JI 171:1652-5Boasso et al. Blood 105: 1574-81Munn et al. JI 172: 4100-10

?

Additional possible mechanisms of action to consider:Potential functions of the IgG1 Fc portion of abatacept

CTLA4

IgG1 Fc

Binding toFc receptors

Antibody-dependentCellular cytoxicity (ADCC)

Phagocytosis/clearanceof opsonized cells?

Resulting in elimination of B7-expressing cellsand suppression of T cell response

B7 expressingcell

The paradox: CTLA4-Ig may disrupt critical pathwaysrequired for maintenance of immune tolerance

T regulatory cell

Antigen presenting cell

Effector T cell

B7-CTLA4

T regulatory cells are critical components in the maintenance of peripheral tolerance

to tissue-specific self-antigens

In both humans and mice, absence of T regulatory cells is associated with aggressive autoimmunity

Self-antigen

CD28-B7 interactions are essential for both thymic development of Tregs and for their peripheral homeostasis

Decrease in Tregs (CD4+CD25+) cells

in lymph nodes of wildtype mice treatedwith CTLA4Ig for 10 days

Tang et al. JI 171: 3348-52

0

1

2

3

4

% C

D4

+C

D2

5+

th

ym

oc

yte

s

wildtype B7 knockout

Decreased development of TregsIn the thymus in B7 knockout mice

In certain inbred mouse strains, autoimmune disease is exacerbatedin the absence of B7 or CD28 due to loss of Tregs

Williams et al. (not published)

Implications for development of fetal immune system during gestation?

T cell Antigen presenting cell

Activated T cells express CTLA4:CTLA4 transduces a negative signal to T cells andfunctions to attenuate the immune response

TCR

B7

MHC + peptide

CD28

CTLA4

T cell Antigen presenting cell

TCR

B7

MHC + peptide

CD28

CTLA4

Activated T cells express CTLA4:CTLA4 transduces a negative signal to T cells andfunctions to attenuate the immune response; CTLA4-Ig may interfere with this process

Mechanisms of action that may function to ameliorate RA:

Blocking CD28 costimulation Induction of suppressor antigen-presenting cells (via IDO)Depletion of B7-expressing cells

Mechanisms of action that may exacerbate autoimmunity:

Inhibition of T regulatory (CD4+CD25+) cell maintenance/developmentInhibition of endogenous CTLA4 signals

Abatacept (CTLA4-Ig) Mechanism of Action Summary