Characterization of AB154, a Humanized, Non-Depleting α-TIGIT Antibody Undergoing Clinical Evaluation in Subjects with Advanced Solid Tumors
Anderson AE, Lopez A, Udyavar A, Narasappa N, Lee S, DiRenzo D, Zhang K, Singh H, Zhao S, Gerrick K, Park A, Seitz L, Walker N, Walters MJ and Tan JBL.
Arcus Biosciences, Inc., Hayward, CA, USASITC 2019
Poster P260
Introduction
AB154 is a humanized antibody that blocks human TIGIT (T-cell
immunoreceptor with Ig and ITIM domains), an inhibitory receptor expressed on
natural killer (NK) cells, CD8+ T cells, CD4+ T cells and regulatory T cells (Treg).
CD226 (or DNAX Accessory Molecule-1, DNAM-1) is an activating receptor that
competes with TIGIT for shared ligands CD155 (PVR) and CD112 (Nectin-2),
expressed by cancer and antigen-presenting cells. AB154 blocks TIGIT with
sub-nanomolar affinity, thus prevents binding to its ligands and shifts the
immune balance towards a more favorable CD226 interaction. Because AB154
is engineered without FcγR binding function, the immune suppressive TIGIT-
CD155 interaction is blocked with minimal risk of depleting intra-tumoral
antigen-experienced CD8+ T cells. AB154 has the potential to promote
sustained immune activation and tumor clearance, particularly in combination
with other immunotherapies such as AB122 (anti-PD1).
Methods
Results
Gene Expression: Expression of TIGIT, PD-1 (PDCD1), and CD226 on select
tumor types were derived from RNASeq in The Cancer Genome Atlas (TCGA)
database.
Immunohistochemistry (IHC): Anti-CD155 antibody (Cell Signaling
Technology, D8A5G) was used to stain FFPE human tissues. Samples were
deparaffinized according to standard methods and heat-induced epitope
retrieval was performed using sodium citrate. Anti-rabbit HRP and DAB
chromogen were used for detection.
ADCC Assay: AB154 and versions of AB154 modified to restore wild-type (WT)
IgG1 effector function or to display enhanced FcγR binding via Fc mutations
(EEF) were used in antibody-dependent cell cytotoxicity (ADCC) studies.
Identification of Intra-tumoral Antigen-Experienced T cells: Dissociated
tumor samples from head and neck cancer patients were purchased from
Discovery Life Sciences (n = 5). Cells were assessed for viability, surface and
intracellular markers related to T cell lineage, exhaustion, and activation by flow
cytometry.
AB154 Potency in Healthy Volunteers vs. Lung Cancer Patients: Whole
blood was obtained from healthy volunteers (n = 3) and non-small cell lung
carcinoma (NSCLC) patients (n = 3) and assessed by flow cytometry. TIGIT
receptor occupancy was determined using saturating levels of a commercially-
available human α-TIGIT antibody that binds competitively with AB154.
Clinical PK/PD: A Phase 1 dose-escalation study is underway to evaluate
AB154 as a monotherapy and in combination with AB122 (anti-PD1) in subjects
with advanced solid malignancies. Whole blood was assessed by flow
cytometry using saturating levels of a competing anti-TIGIT antibody to
determine receptor occupancy (RO) as well as changes in Ki67 expression.
Conclusions
• TIGIT, PD-1, and CD226 expression are correlated in many tumor types and
are often co-expressed on tumor infiltrating lymphocytes (TILs). CD155 is
also highly expressed by cancer types of interest.
• CD8+ T cells make up the majority of antigen-experienced T cells in
advanced head and neck tumor samples. Antigen experience occurs
alongside markers of immune exhaustion and loss of CD226 expression.
• Antibodies engineered with enhanced effector function (EEF) can facilitate
ADCC on intra-tumoral antigen-specific CD8+ T cells.
• TIGIT receptor density is often comparable or higher on intra-tumoral
antigen-experienced CD8+ T cells than on Treg, highlighting the danger of
targeting these cells with depleting antibodies.
• AB154 potently binds TIGIT in peripheral blood from both healthy volunteers
and NSCLC patients.
• AB154-dosed patients have had complete receptor coverage on all TIGIT-
expressing peripheral leukocytes in this Phase 1 trial (NCT03628677).
Proliferative bursts in CD8+ T cells demonstrate immune engagement.
• A Phase 2 study including the combination of AB154 and AB122 is planned.
TIGIT, PD-1, and CD226 Are Co-Expressed on
Human Tumors
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Figure 1. TIGIT binds to CD155 and results in decreased activation of the
TIGIT-expressing immune cells. AB154 blockade of TIGIT allows CD155 to bind
CD226, favoring T cell and NK cell activation.
Figure 2. RNASeq data from TCGA reveals high levels of TIGIT and PD-1
(PDCD1) co-expression across many tumor types. CD226 is often expressed in
TIGIThi PD-1hi tumor types.
November 7-10, 2019. National Harbor, Maryland
Figure 6. Patients and healthy donors had similar TIGIT expression in
peripheral blood lymphocytes, including CD8+ and CD8- T cells, NK cells and
NKT cells, as measured using saturating levels of a commercially available α-
TIGIT antibody. Fluorophore-conjugated AB154 was used to directly determine
binding affinity in whole blood, with equipotency observed on lymphocytes
isolated from healthy donors and cancer patients. In human whole blood, ex
vivo addition of AB154 achieved complete inhibition of TIGIT.
Figure 4. In T cells isolated from advanced head and neck tumor samples (n =
5), markers of antigen experience are predominantly found on the CD8+ subset.
CD8+ antigen-experienced T cells (CD103+CD39+) express higher levels of PD-
1 and TIGIT that are consistent with an “activated” or “exhausted” phenotype.
CD226 is progressively lost from the inexperienced CD103-CD39- population to
the experienced CD103+CD39+ CD8 T cell population. TIGIT receptor density is
often comparable or higher on antigen-experienced CD8 T cells than on Treg.
PD-1 is consistently highest on intra-tumoral CD103+CD39+ CD8 T cells.
Similar AB154 Potency on Peripheral Blood
Lymphocytes Isolated from Healthy Volunteers
and NSCLC Patients
TIGIT and PD-1 Are Highly Expressed by
Intra-tumoral Antigen-Experienced CD8+ T Cells
FSC-A
SS
C-A
FSC-A
FS
C-H
CD56
CD
3
CD56
CD
3
CD4
CD
8
CD4
Fo
xP
3
TregCD8+ T
cells
CD4+
T cellsNK
NKT
T
AB154:
Receptor
Occupancy: 0%
CD3
TIG
IT
100%
AB154α-TIGIT
(saturating)
Pre-dose Low dose
AB154
High dose
TIGIT-
expressing
cell
1) As of the DCO of 16-Sep-2019, 10 participants have been dosed with
AB154 monotherapy (0.5, 1, and 3 mg/kg) and 6 participants with
AB122/AB154 combination therapy (1 and 3 mg/kg).
2) No DLTs have been observed with either regimen. DLT evaluation of the
fully enrolled AB154 10 mg/kg + AB122 combination cohort is ongoing.
3) No subject has experienced any AB154-related SAEs or ≥Gr3 AEs.
Total Receptor Coverage Achieved in AB154
Monotherapy and Combination Cohorts
NSCLC (Adeno)
HNSCC (Squam)
TNBC NSCLC (Squam)
Cervical
0
10
20
30
40
50
60
70
80
90
100
CD
15
5
Ex
pre
ss
ion
(% P
osit
ive P
ixel)
Figure 7. Complete receptor coverage has been observed in all TIGIT-
expressing peripheral lymphocytes after initial dosing at every trough timepoint
for all enrolled subjects. PK data for the second monotherapy cohort (AB154 at
1 mg/kg Q2W) is shown. Spikes in Ki67 expression occur between Day 3 and
Day 29 in CD8+ T cells for both monotherapy and combination subjects. Where
present in this small number of subjects, the magnitude of this proliferative burst
appears to increase in a AB154 dose-dependent manner, which may also be
enhanced by combination with AB122 (anti-PD-1).
Safety and Tolerability of AB154
Demonstrated in Ongoing Phase 1 Study
Enhanced Effector Function Results in NK-
Mediated Killing of Activated TIGIT+ CD8+ T Cells
Strong CD155 Staining in Tumors of Interest
Figure 5. Activated CD8+ T cells expressing high levels of TIGIT are particularly
susceptible to antibody-dependent cell-mediated cytotoxicity (ADCC) when
targeted by an antibody with enhanced effector function (EEF). Data from four
combinations of T cell donors (n = 2) and NK cell donors (n = 2) are shown.
*p ≤ 0.05. **p ≤ 0.01. ***p ≤ 0.001. ****p ≤ 0.0001.
Pre-d
ose
C1D
1 1h
r
C1D
3
C1D
8
C1D
15
C2D
29
C2D
31
C2D
36
C3D
57
C4D
85
0
20
40
60
80
100
AB154 (0.5 mg/kg Q2W)
TIG
IT R
ecepto
r
Occupancy %
Trough Drug Levels
AB154 infusion
Complete Target CoverageAfter First Dose of AB154
AB154
TIGIT
0.5 mg/kg 1 mg/kg 3 mg/kg 1 mg/kg 3 mg/kg1
2
3
4
5
Proliferation in CD8+ T cells
Pe
ak F
old
Ch
an
ge
(Ki6
7+
%,
Da
y 3
- 2
9)
AB154(Monotherapy)
AB154 +AB122 (240 mg)
0 7 14 21 28 35 42
1
10
100AB154 (1 mg/kg Q2W)
Time from First Dose (Days)
AB
15
4 (
g/m
L)
Figure 3. CD155 immunohistochemistry (IHC) shows membrane and
cytoplasmic localization on cancerous cells, blood vessels, and tertiary
lymphoid structures (TLS) in NSCLC and other tumors of interest. Arrows
indicate positive staining. CD155 protein levels were quantified from IHC.
No
Ab
hIgG
1.Fc
Sile
nt
AB15
4
hIgG
1.W
T
AB15
4-W
T
AB15
4-EEF
0
10
20
30
40
% D
ea
d (T
ce
lls)
****
********
ns
ns
**
Activated
CD8+ T cell
NK cell
4 h
37 °CT
IGIT
DNAM-1
Pre-activation Post-activation
Resting
CD8+ T cell
α-CD3/CD28
beads
ADCC
0
20
40
60
80
100
TIG
IT+
%
Healthy
NSCLC
CD8+
T cellsCD8
-
T cellsNKT NKTotal
LymphocytesT cells
0.01 0.1 1 10 100
0
10
20
30
40
AB154-AF647 (nM)
EC50 = 0.13 nM
0.01 0.1 1 10 100
0
10
20
30
40
AB154-AF647 (nM)
TIG
IT+
%
(To
tal L
ym
ph
ocyte
s)
EC50 = 0.14 nM
CD226
TIGIT CD155
AB154
GzmBIFNg
GzmBIFNg
Cytotoxic Granules
CD226
TIGITCD155
SuppressedImmune Cell
ActivatedImmune Cell
Tumor Cell T Cell/NK CellT Cell/NK Cell
* Data collected as of 8-Oct-2019
TGCT: Testicular Germ Cell Tumors; LUAD: Lung Adenocarcinoma; HNSC: Head and Neck Squamous Cell
Carcinoma; CESC: Cervical Squamous Cell Carcinoma; LUSC: Lung Squamous Cell Carcinoma
Tumor
Stroma
vessels
Tumor
TLS
NSCLC
HNSCC CervicalTNBC
NSCLCNSCLC
C1D15 C2D29
Predose Predose
1 0.5 mg/kg 99.7 ± 0.3 100 ± 0
2 1 mg/kg 100 ± 0 100 ± 0.12
3 3 mg/kg 100 ± 0 100 ± 0
1 1 mg/kg 100 ± 0 99.6 ± 0.75
2 3 mg/kg 100 ± 0 100 ± 0
3 10 mg/kg 100 TBD
AB154
Monotherapy
AB154 + AB122
(240 mg)
Combination
Receptor Occupancy
(Mean+SD%)Study Arm Cohort
AB154
Dosing
(Q2W)
TIGIT PD-1 CD226
TIGIT
CD
22
6
CD45
Via
bili
ty
FSC-A
CD
3
CD8
FoxP
3
CD103
CD
39
TregCD4+
CD8+
Treg
CD8+
CD4+
CD103
CD103
CD8+
Treg CD4+
0
50
100
% o
f C
D3
+
TIGIT PD-1 CD226
0
5×103
1×104
1.5×10 4
Ge
oM
ea
n o
f
CD
8+ T
ce
lls
0
20
40
60
80
100
% o
f C
D8
+ T
ce
lls
CD226-
TIGIT+
CD226+
TIGIT+
CD226-
TIGIT-
CD226+
TIGIT-
CD103-CD39
-
CD103+
CD39-
CD103+
CD39+
A B C D E
0
3000
6000
9000
12000
15000
PD
-1 M
FI
CD103+ CD39+
CD8+ T cells
Treg
A B C D E
0
3000
6000
9000
12000
TIG
IT M
FI
Subject Subject
CD103+ CD39+
CD103- CD39-
CD103+ CD39-
CD8+ T Cells
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