Engineering Antibodies (1) MSc Programme University of Nottingham 14th February 2005

1
Engineering Antibodies (1)MSc Programme
University of Nottingham14th February 2005

• by
• Mike Clark, PhD
• Department of Pathology
• Division of Immunology
• Cambridge University
• UK
• www.path.cam.ac.uk/mrc7/

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Antibody based immunotherapeutics
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IgG is the preferred class
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Schematic view of IgG domains
5
Antibody fragments can also be used
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Antibodies can be derived from immunised animals
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The antibody immune response in-vivo can be
T-cell dependent or independent
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Antibody fragments can also be selected from
in-vitro systems such as phage expression
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Cycles of selection and mutation can give an
artificial in-vitro immune response based simply
on binding affinity
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The Selection of IgG Fc Regions for appropriate
effector functions The role of isotypes and
polymorphisms
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Effector functions of human IgG
IgG1
IgG2
IgG3
IgG4
Complement activation
Classical pathway



-
Alternative pathway

-
-
-
Fc receptor recognition



Fc
g
RI
-


Fc
RIIa, 131R/R
g
-
-



Fc
g
RIIa, 131H/H
-



Fc
g
RIIb
-


Fc
g
RIII
/
-
/
-
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Unlike mouse the human IgG subclasses are very
similar in sequence but they still have different
properties
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The IgG receptor FcRn
Interaction with FcRn and with Protein A through
similar region
FcRn is important for IgG half-life and transport
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Residues at key positions in mutatedconstant
regions
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Test systems antibodies with CD52 and a-RhD
specificities

• Short, GPI-anchored glycoprotein
• Found on T cells and some B cells, granulocytes
  and eosinophils
• About 45 x 104 molecules/cell
• Good target for CDC and ADCC
• Humanised variable domains of CAMPATH-1 antibody
  used
• Range of antibodies with same variable domains
  already existed

CD52
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Test systems antibodies with CD52 and a-RhD
specificities

• Protein complex on erythrocyte membrane
• 1 - 3 x 104 molecules/cell
• Provides opportunities for use of agglutination
  and rosetting assays
• Target for ADCC
• Used variable domains of Fog-1, a human IgG
  isolated from hyperimmunised, RhD- blood donor

a-RhD
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Complement-mediated lysis of mononuclear cells
45
CAMPATH-1
antibodies
40
G1
35
G1D a
30
G1D b
G1D c
25
G1D ab
specific Cr release
20
G1D ac
15
G2
G2D a
10
G4
5
G4D b
G4D c
0
-5
1
10
100
0.1
m
antibody,
g/ml
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Complement-mediated lysis withCAMPATH-1 G1(6.3
mg/ml),inhibited by CAMPATH-1 G2Da
25
20
15
10
specific Cr release
5
0
-5
1
10
100
1000
G2Da concentration,
m
g/ml
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Binding to the FcgRI-bearing cell line, B2KA,
measured by fluorescence staining
G2
G1Da
CAMPATH-1H antibodies at 100 mg/ml
G4
G1Db
G1Dc
G1
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Binding to the FcgRIa-bearing cell line, B2KA,
measured by fluorescent staining
CAMPATH-1
160
antibodies
140
G1
120
G1D a
G1D b
100
G1D c
mean fluorescence
G1D ab
80
G1D ac
60
G2
G2D a
40
G4
20
G4D b
G4D c
0
0.001
0.01
0.1
1
10
100
antibody,
m
g/ml
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Chemiluminescent response of human monocytes to
sensitised RBC
Fog-1
140
antibodies
120
G1
G1D a
100
G1D b
80
G1D c
chemiluminescence
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G1D ab
40
G1D ac
G2
20
G2D a
0
G4
-20
G4D b
0
5000
10000
15000
20000
25000
30000
G4D c
antibody molecules/cell
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Inhibition of chemiluminescent response to
clinical sera by Fog-1 G2Da
280
240
200
G1
anti-D serum A
anti-D serum B
160
anti-D serum C
chemiluminescence
anti-D serum D
120
anti-D serum E
anti-CD serum
anti-K serum
80
40
0
0
10
100
1000
G2Da concentration, mg/ml
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Binding to the cell line 3T6 FcgRIIa 131R,
measured by flow cytometry
100
Fog-1 antibodies
90
G1
G1Da
80
G1Db
70
G1Dc
G1Dab
60
mean fluorescence
G1Dac
G2
50
G2Da
40
G4
G4Db
30
G4Dc
G1Dg
20
IgA1,k
10
0.1
1
10
100
antibody concentration, mg/ml
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Activity of Fog-1 antibodies in ADCC
120
100
80
60
RBC lysis
40
20
0
-20
0.1
1
10
100
1000
10000
antibody concentration, ng/ml
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Inhibition by Fog-1 antibodies of ADCC due to
Fog-1 IgG1 (at 2ng/ml)
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40
G2
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G2
D
a
30
25
RBC lysis
20
G1D
a
15
10
G1
D
c
G1Db, G1Dab, G1Dac, G4,
G4Db, G4Dc

5
0
0.0001
0.001
0.01
0.1
1
10
100
1000
10000
inhibitor antibody concentration, ng/ml
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Summary of antibody activities
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Effect of mutations cannot always be predicted
from wildtype antibody activities

• Complement lysis
• IgG2 activity is only 3-fold lower than that of
  IgG1
• but placing IgG2 residues in IgG1 (Db, Dc)
  eliminates lysis.
• FcgRIIa 131H binding
• IgG1 and IgG2 show equal binding
• but G1Db and G1Dc activities are 30-fold lower.
• IgG1 binding may depend heavily on the mutated
  regions. Other subclasses may have additional
  sites of interaction with the effector molecules.

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Db and Dc mutants
The 3 pairs of Db and Dc mutants show reduced
activity in all functions assayed but the
residual levels of activity differ
Db slightly more active in FcgRIIa 131H and 131R
binding
Dc more active in FcgRI binding, monocyte
activation FcgRIIIb NA1and NA2 binding and ADCC
These mutants differ only by -/ G236. This must
affect the ability of the FcR to accommodate the
IgG2 lower hinge.
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What of the immunogenicity of therapeutic
antibodies?
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Bad News

• Universal tolerance to all self-antigens does not
  exist.
• Auto and allo-immunity are common observations
• Human proteins can be immunogenic in humans.
  (e.g. recombinant insulin, EPO and Factor VIII)
• Human antibodies can be immunogenic in humans
  (anti-idiotype and anti-allotype) and this
  applies to chimeric, humanised and fully human
  antibodies.

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Good News

• Auto and allo-immunity are common observations
  but these immune reponses can be modified and
  regulated.
• Human antibodies can be immunogenic in humans but
  this immunogenicity varies from antibody to
  antibody for complex reasons, and is probably
  more dependent on the mode of action, and not
  just the way they were made (i.e. chimeric,
  humanised or fully human).

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Antigenicity and Immunogenicity

• Antigenicity is simply an ability of a molecule
  to be recognised by a pre-existing T-cell
  receptor (TCR) or a B-cell receptor (antibody)
• But once an antigen is recognised by a receptor
  it can either be immunogenic or tolerogenic.
• The same antigen can sometimes induce tolerance
  and sometimes provoke an immune response
  depending upon factors such as mode of
  administration and uptake by and co-stimulation
  of antigen presenting cells (APCs).

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Immunogenicity

• Immunogenicity of T-cell dependent antigens
  relies on presentation by professional APCs (e.g.
  Dendritic cells).
• Dendritic cells (and other APCs) acquire antigen
  through use of innate receptors including
  complement receptors and Fc receptors, thus
  allowing recognition and uptake of immune
  complexes.

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Induction of tolerance to therapeutic antibodies

• Benjamin,R.J., Cobbold,S.P., Clark,M.R.,
  Waldmann,H. (1986) J. Exp. Med. 163, 1539-1552.
  Tolerance to rat monoclonal antibodies
  implications for serotherapy
• Observation
• Relatively easy to tolerise mice, with
  de-aggregated human immunoglobulin or with rat
  immunoglobulin, despite large differences in the
  constant region sequences between mouse, human
  and rat.
• However in mice which are tolerant of soluble
  rat IgG2b, administration of antibodies which
  bind to mouse cell surface antigens provokes a
  strong anti-idiotype response.
• Explanation
• Is this a function of the inherent
  immunogenicity of immune complexes?
• Aggregated antibody is more likely to activate
  complement and to bind to low affinity Fc
  receptors.

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Antibody selection and design

• The choice of antibody constant region is largely
  dictated by functional requirements of the
  antibody.But what about the V-regions ?

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The V-region Mythology
Chimaeric 65 Human ?
Humanised 95 Human ?

• This commercial marketing mythology is based on
  an assumption that mouse and human antibody
  sequences are unique.
• However a study of the Kabat database shows
  that there is high sequence homology for
  antibodies from different species.

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Kabat database variability of VH sequences
Mouse VH
Human VH
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Are chimaeric, humanised and fully human
antibodies so very different in sequence?
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Possible to select alternative V genes for
humanisation
Gorman,S.D., Clark,M.R., Routledge,E.G.,
Cobbold,S.P. Waldmann,H. P.N.A.S. 88,
4181-4185 (1991) Reshaping a therapeutic CD4
antibody. Routledge,E., Gorman,S., Clark,M.
in Protein engineering of antibody molecules for
prophylactic and therapeutic applications in man.
(Ed. Clark,M. ) Pub. Academic Titles, UK (1993)
pp. 13-44 Reshaping of antibodies for therapy.

• Gorman et al recognised that homology also
  extended through the CDR regions not just the
  framework regions
• Homology to Kol was increased from 69 to 89
  by the humanisation process.

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The same strategy can be applied to almost any
V-region
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Sequence homologies of some rodent, humanised and
human sequences
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Homologies for antibody heavy chain V
regions compared with human germline
sequences Sorted by homology
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What of the Emperors new clothes?
Appropriate selection of sequences of antibody
Constant and Variable regions is likely to be
only one factor controlling the immunogenicity of
therapeutic antibodies. However it is the final
sequence of the antibodies which matters and not
the route by which they were made. For example it
is possible to come up with alternative humanised
sequences for the same antibody. Similar
sequences can often be found for mouse, rat and
human variable regions within the
databases. Even fully human antibodies may
contain unusual motifs or structures as a result
of the somatic recombination and junctional
diversity combined with somatic hypermutation.
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What determines immunogenicity?

• Classical Self vs non-Self (Peter Medawar)
• Aquired neonatal tolerance to antigens.
• Danger Hypothesis (Polly Matzinger)
• Cell killing (inappropriate, non-apoptotic)
• Inflammation (cytokine release)
• Pattern recognition (Charles Janeway)
• Innate receptors for infectious pathogens
• Complement activation and fixation of C3 (Fearon)
• ( Fc receptors for immune complexes)

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The effect of aglycosylation on the
immunogenicity of a humanised therapeutic CD3
monoclonal antibody Routledge et al 1995
Transplantation 60, 847-853
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The effect of aglycosylation on the
immunogenicity of a humanised therapeutic CD3
monoclonal antibody Routledge et al 1995
Transplantation 60, 847-853
The human IgG1in the CD3 transgenic mice was able
to kill target cells, to activate complement, to
bind to FcR and to cause cytokine release.
Whereas the aglycosylated antibody was poor in
these functions and produced only a weak immune
response. Is this a special case or can it be
generalised to other antibodies? Is it consistent
with the Matzinger Danger Hypothesis as applied
to therapeutic administration of recombinant
antibodies?
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Elimination of the immunogenicity of therapeutic
antibodies. Gilliland et al 1999 J.Immunol 162,
3663-3671

• Took CAMPATH antibody and mutated a key residue
  in the CDR region so as to prevent cell binding
  to CD52.
• This variant could be used to tolerise CD52
  transgenic mice so that they no longer mounted an
  immune response to the wild type CAMPATH

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Factors likely to influence immunogenicity of
therapeutic antibodies
Murine constant regions V-region sequences Human
Ig allotypes Unusual glycosylation Method of
administration Frequency of administration Dosage
of antibody Patients' disease status Patients'
immune status Patients' MHC haplotype Specificity
of antibody Cell surface or soluble
antigen? Formation of immune complexes with
antigen Complement activation by antibody Fc
receptor binding by antibody Inflammation and
cytokine release
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Will the idiotype always be immunogenic?
The idiotype will obviously always be unique and
thus antigenic. However it may be possible
through mode of use to influence whether this
antigenic idiotype is immunogenic or tolerogenic!
Take home message to remember In immunological
terms antigenicity is certainly not the same as
immunogenicity!