development of a tetravalent anti-gpa33/anti-cd3 bispecific ......2018/08/04 · the presence of...

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Development of a tetravalent anti-GPA33/anti-CD3 bispecific antibody

for colorectal cancers

1Zhihao Wu, 1Hong-Fen Guo, 1Hong Xu, 1Nai-Kong V. Cheung

1 Memorial Sloan Kettering Cancer Center, New York, NY 10065

Running Title: Development of an anti-GPA33 x anti-CD3 tetravalent T-BsAb

Keywords: T cell engaging bispecific antibody, bispecific antibody, colorectal cancer, anti-CD3

bispecific antibody

Financial Support: This work was supported in part by Funds from Enid A. Haupt Endowed Chair, the

Robert Steel Foundation. Technical service provided by the MSK Animal Imaging Core Facility was

supported in part by the NCI Cancer Center Support Grant P30 CA008748.

Conflict of interest: ZW, HX and NKC were named as inventors in a patent on humanized A33 and T-

BsAb antibodies filed by Memorial Sloan Kettering Cancer Center (MSKCC).

Corresponding author: Nai-Kong V. Cheung Department of Pediatrics Memorial Sloan Kettering Cancer Center 1275 York Ave, Box 170, New York, NY 10065. Phone: +1 646-888-2313 Email: [email protected]

on August 21, 2021. © 2018 American Association for Cancer Research. mct.aacrjournals.org Downloaded from

Author manuscripts have been peer reviewed and accepted for publication but have not yet been edited. Author Manuscript Published OnlineFirst on August 6, 2018; DOI: 10.1158/1535-7163.MCT-18-0026

mailto:[email protected]

http://mct.aacrjournals.org/

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ABSTRACT

Despite progress in the treatment of colorectal cancer (CRC), curing metastatic CRC (mCRC) remains a

major unmet medical need worldwide. Here we described a T cell engaging bispecific antibody (T-BsAb)

to redirect polyclonal cytotoxic T cells to eradicate CRC. A33, a murine antibody specific for GPA33, was

humanized to huA33 and reformatted to huA33-BsAb, based on a novel IgG(L)-scFv platform by linking

the anti-CD3 huOKT3 scFv to the carboxyl end of the light chain. This T-BsAb was stably expressed in CHO

cells and purified as a stable monomer by HPLC, retaining immunoreactivity by FACS through 30 days of

incubation at 37°C. In vitro, it induced activation and expansion of unstimulated T cells and elicited potent

T-cell dependent cell-mediated cytotoxicity (TDCC) against colon and gastric cancer cells in an antigen-

specific manner. In vivo, huA33-BsAb inhibited the colon and gastric cancer xenografts, in both

subcutaneous and intraperitoneal tumor models. More importantly, both microsatellite instable (MSI)

and microsatellite stable (MSS) CRC were effectively eliminated by huA33-BsAb. These preclinical results

provide further support for the use of IgG(L)-scFv platform to build BsAb, and especially one targeting

GPA33 for CRC. These preclinical results also support further development of huA33-BsAb as a potential

immunotherapeutic.




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Introduction

Colorectal cancer (CRC) is the 3rd leading cause of death among cancers in the United States (1)

and accounted for 10% of all cancers in men and 9.2% in women worldwide (2). Although there has been

steady yearly 3% decline of incidences from 2004 to 2013, around 135,000 new cases are expected

annually in the United States alone. Although localized and regional diseases are often curable, the

prognosis of metastatic CRCs (mCRCs) is poor, with a 5-year survival rate of only 14% (1).

The standard treatment of mCRC consists of chemotherapy in combination with monoclonal

antibodies that blocked tumor signaling or angiogenesis. Currently four monoclonal antibody drugs have

been approved by FDA for CRC treatment. Bevacizumab and ramucirumab target the VEGF-VEGFR

angiogenesis pathway, whereas cetuximab and panitumumab target the EGFR pathway. However,

cetuximab and panitumumab do not provide clinical benefits in mCRC patients with RAS mutations (3),

which account for around 40% of mCRC (4, 5). Moreover, improvement in survival with these antibodies

is generally modest and can be associated with severe side effects (5-7).

Given the clinical success in melanoma, renal cell carcinoma and lung cancer, immune checkpoint

inhibitors (ICI) have revolutionized modern immunotherapy and have become the backbones of

numerous ongoing trials in a broad spectrum of adult cancers (8, 9). Unfortunately, for CRC, benefits so

far have been restricted to the subset of patients with microsatellite instability (MSI), while the majority

of mCRC are microsatellite stable (MSS) and are not expected to benefit from ICI monotherapy (10-12).

More effective strategies to take advantage of T cells to treat mCRC are needed. T cell engaging

bispecific antibodies (T-BsAbs), which function by actively redirecting polyclonal cytotoxic T cells to kill

cancer cells, are promising candidates. Their efficacy in leukemia has been proven for blinatumomab, an




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anti-CD19 T-BsAb approved by the FDA in 2014. For solid tumors, numerous preclinical studies have

documented their potent anti-tumor activities and several are in clinical trials.

We hypothesized that T-BsAbs could expand the potential of ICIs and overcome genetic barriers

in the treatment of mCRC. We now report a T-BsAb that targets the protein GPA33, an antigen expressed

in >95% of colon cancers and a subset of gastric cancers (13). This target has been extensively explored in

radioimmunodiagnosis and radioimmunotherapy, notably using a murine-derived antibody A33 against

GPA33 (14-17) and its humanized version, which have been relatively well tolerated (15, 18, 19), despite

the presence of human anti-mouse antibodies (HAMA) (18, 19), and human anti-human antibodies (HAHA)

(15, 20). Using a rehumanized version of the mouse A33, we successfully built a tetravalent T-BsAb, and

characterized its in vitro physicochemical properties and functional activities, as well as its in vivo anti-

tumor properties in multiple xenograft models. We showed that its efficacy was independent of the MSI

status of CRC tumors, a necessary attribute if this T-BsAb is meant to function against all mCRCs.




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Material and Methods

Cell lines and human white cells

Cell lines used in this study and their sources were summarized in Table S1. Luciferase expressing

cell lines were established using lentiviral transduction. All cells were authenticated by STR typing within

6 months of experiments. Cells were maintained in RPMI medium supplemented with 10% FBS (Sigma),

0.03% L-Glutamine (Gibco) and Pen/Strep (Gibco). Buffy coats from healthy donors were purchased from

New York Blood Center and human peripheral blood mononuclear cells (PBMCs) were isolated by Ficoll

gradient of Buffy coats.

SEC-HPLC analysis

Size purity of T-BsAb was analyzed using HPLC system (Shimadzu Scientific Instruments Inc.).

Monomeric species was identified using molecular weight standard (Bio-Rad) and percent monomer was

calculated based on the relative area under curve (AUC) of different non-buffer peaks.




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Humanization of murine A33 and construction of huA33-BsAb bispecific antibody

Using CDR grafting, mouse A33 was humanized as IgG1. Two different VH and VL sequences were

combined to generate 4 different humanized A33 antibodies. Binding kinetics was compared with that

of chimeric antibody chA33 using Surface Plasmon resonance (SPR) analysis. The heavy chain of selected

sequence is

EVQLVESGGGLVKPGGSLRLSCAASGFAFSTYDMSWVRQAPGKRLEWVATISSGGSYTYYLDSVKGRFTISRDNAKNSL

YLQMNSLRAEDTAVYYCAPTTVVPFAYWGQGTLVTVSS

and the light chain sequence is

DIQMTQSQSSLSTSVGDRVTITCKASQNVRTVVAWYQQKPGKSPKTLIYLASNRHTGVPSRFSGSGSGTEFTLTISNVQP

EDFADYFCLQHWSYPLTFGSGTKLEIKR.

HuA33-BsAb was constructed by fusing the humanized OKT3 scFv onto the C-terminus of the light

chain of huA33 antibody via a (G4S)3 linker as previously described (21, 22). The DNA construct was then

transfected into CHO-S cells and stable clones were selected for high levels of antibody production. For

larger-scale antibody purification, selected stable clone was expanded in shaker flasks. Bispecific antibody

was purified from supernatant using one-step protein A affinity chromatography.

SPR analysis

Human GPA33 (Novoprotein) was immobilized on CM5 chips. Five concentrations of 2-fold serially

diluted huA33 IgG1 or T-BsAbs (starting at 20 nM) were flowed over the chip using a BiacoreTM T100

system. Binding kinetics of huA33 was measured at 25°C and those of T-BsAbs at both 25°C and 37°C. The

sensorgrams were fitted with 1:1 binding model for both to derive kinetic parameters.




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Immunohistochemistry (IHC)

IHC staining of human tissue was done using ABC immunoperoxidase (Vector Laboratories,

Burlingame, CA) 5 µm thick sections were fixed in cold acetone for 30 minutes at −20°C, followed by rinsing

in phosphate buffered saline (PBS), and immersed in 0.1% hydrogen peroxide for 15 min at room

temperature (RT). All the following steps were performed at RT. Avidin and biotin solutions were added

sequentially for 20 min each. After blocking with 10% horse serum in PBS for 1 hr. Each subsequent step

was followed by washing of slides with PBS., primary huA33-BsAb or control T-BsAb was added to the

tissue sections at 1.0 μg/ml for 45 min, followed by anti-OKT3-mFc at 0.1 μg/ml for 30 min. Lastly,

biotinylated horse anti-mouse IgG (H + L) antibody at 1:500 dilution was added for 30 min, followed by

100 μl of ABC for 30 min. Peroxidase substrate was then added to each tissue section for 2 min, rinsed

with running tap water for 5 min and counterstained with Myer's hematoxylin. Stained slides were

dehydrated by dipping sequentially in 75%, 95%, and 100% ethanol, and finally in xylene. Dehydrated

slides were mounted with one drop of Cytoseal (Richard-Allan Scientific, Kalamazoo, MI) for examination.

Human CD3 IHC was performed at Molecular Cytology Core Facility of MSKCC using Discovery XT

processor (Ventana Medical Systems). Anti-CD3 antibody (DAKO, cat# A0452, 1.2 µg/ml) was applied to

deparaffinized sections and incubated for 5 hr, followed by 60 minutes incubation with biotinylated goat

anti-rabbit IgG (Vector labs, cat# PK6101) and detected with DAB detection kit (Ventana Medical Systems)

according to manufacturer’s instruction. Slides were counterstained with hematoxylin and coverslipped

with Permount (Fisher Scientific). All images were captured using Nikon ECLIPSE Ni-U microscope and

NIS-Elements 4.0 imaging software (Nikon Instruments, Inc., Japan).

T-cell dependent cytotoxicity (TDCC) assays

Cytotoxicity assays were performed using both 51Cr-release assay and LDH-release assay (Pierce).

For both assays, we used anti-CD3/anti-CD28 Dynabeads activated T cells (ATC) for 14 days as effector




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cells, except for sorted cells from PBMC, which were used for TDCC assay without prior stimulation. 51Cr

assay was done as previously described (23). LDH assay was done following manufacturer’s instructions.

EC50 values were calculated by fitting the curves to a 4-parameter nonlinear regression model using

GraphPad Prism.

Cytokines and cytolytic molecules release assay

T cells were purified from PBMC using pan T cell isolation kit (Miltenyi Biotec). Target and control

tumor cells were incubated with 2x106 cells/well at an effector to target ratio of 5:1 in 24-well plates in

triplicates, with 2ml total volume per well. Culture supernatants were collected at 24 hours, 48 hours, 72

hours and 96 hours and cytokine levels were measured with flow cytometry using LEGENDplexTM human

CD8/NK Panel (Biolegend), following manufacturer’s protocol.

T cell proliferation assay

Fresh PBMC from healthy donors were labeled with 2.5 µM CFSE (Life TechnologiesTM) for 5min

at room temperature, followed by neutralization using PBS containing 5% FBS. Target cells were then

incubated with labeled PBMC under different conditions at 37°C before analyzing expression of surface

activation markers and T cell proliferation at 24 hours and 96 hours.

In vivo tumor therapy

All experiments have been conducted in accordance with and approved by the Institutional

Animal Care and Use Committee (IACUC) in Memorial Sloan Kettering Cancer Center. For subcutaneous

(s.c.) tumor models, 5x106 LS174T, 3x106 Colo205 or 5x106 SNU16 cells were combined with fresh PBMC

at 1:1 ratio, mixed with Matrigel (volume of cell:gel=1:2), and implanted with 100 µl/mouse at the flank

of Balb/c Rag2-/-IL2Rγ-/- (DKO) mice (derived from colony of Dr. Mamoru Ito, CIEA, Kawasaki, Japan, and

now commercially available from Taconic as CIEA BRG mice). Treatment started after confirmation of




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tumor presence with a BIW schedule at 100 µg/mouse and continued for 3-4 weeks. Tumor growth was

monitored by weekly measurement of tumor volume using a caliper or a digital device Peira TM900

Scanner (Peira Scientific Instruments). When caliper was used, the tumor volume was calculated as length

x width x width/2.

For intraperitoneal (i.p.) tumor models, 3x106 or 1x106 luciferase expressing LS174T-luc or

SW1222-luc cells, respectively, were resuspended in RPMI medium and injected intraperitoneally into

DKO mice. Human effector cells were injected intravenously as 20x106 ATC per dose for LS174T-luc tumors

or 5x106 ATC per dose for SW1222-luc tumors, whereas antibody was injected at 50µg/mouse/dose for

LS174T-luc tumors or 100µg/mouse/dose for SW1222-luc tumors. Mice were treated with 2-3 weekly

cycles, with each component separated by 3-4 days. Growth of tumors was followed weekly by measuring

luminescence signals on an IVIS Spectrum in vivo imaging system (Perkin Elmer) after injection of 3

mg/mouse of luciferin. Luminescence signals were analyzed and quantified using Living Image Software

(Perkin Elmer).

Antibodies and flow cytometry

Anti-hCD25-PE, anti-CD69-PE, anti-hCD8-APC, anti-hCD45-PECy7, anti-hCD4-PE, anti-hCD4-BV421,

anti-hCD62L-PercpCy5.5, anti-hPD1-BV421 and anti-hCD45RO-PECy7, were from Biolegend. Goat anti-

human IgG-PE was from SouthernBiotech. Streptavidin-PE, anti-hCD4-APC and anti-hCD25-APC were

from BD biosciences. All FACS analyses were carried out using FACSCalibur or LSRII system (BD Biosciences)

and analyzed using FlowJo (FLOWJO).

Affinity maturation using yeast display

Parental huA33 was converted into scFv format with a 20 amino acid (G4S)4 linker and cloned into

a yeast display vector. HuA33 scFv was randomly mutated using GeneMorph II mutagenesis kit (Agilent




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Technologies). PCR product was electroporated together with linearized vector into yeast and the library

was subjected to 4 rounds of sorting using biotinylated GPA33. Individual clones from the last round were

PCR amplified and sequenced to analyze the mutation pattern. Conversion of selected scFv clones into T-

BsAb format was done using a one-step 4-fragment ligation method with 50ng linearized vector and a 1:3

vector to insert molar ratio for the other 3 components. Ligation was done with Rapid DNA ligation kit

(ThermoFisher Scientific) at room temperature for 1hour. Type II restriction enzyme SapI (NEB) was used

to ensure seamless linkage among the different components (Figure S3). Selected clones were transiently

expressed using Expi293 expression system (ThermoFisher Scientific) following manufacturer’s

instructions. Supernatant from Expi293 cells after 4-5 days of culture in shaking flasks was used to purify

antibodies using MabSelect SuRe (GE Healthcare) and dialyzed against pH8.0 citrate buffer in dialysis

membrane (SpectrumLabs.com).

Statistical analysis

Differences in tumor sizes were tested using two-tailed Student’s t-test. Kaplan Meier survival analysis

and log-rank test were used to compare survival curves. When p<0.05, the differences were considered

as significant.

Results

HuA33 retained affinity for GPA33

When compared to chimeric A33, all four newly humanized A33 antibodies have slightly improved

koff in binding to immobilized GPA33 in SPR analysis (Figure 1A). Based on the KD, stability at 37°C and T20

humanness score (24), one huA33 clone was chosen for further development.

HuA33-BsAb was highly stable and bound to antigens with high affinity and specificity




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The huA33 antibody was reformatted into the 2+2 bispecific format (25) by fusing scFv of

humanized OKT3 to the C-terminus of light chain via a flexible GS linker (Figure 1B). The DNA construct

was used to establish a CHO-S stable cell line producing 50 mg/L to 100 mg/L of protein without extensive

optimization. Slightly lower yields were observed using Expi293 transient expression system (around 33

mg/L). One-step protein A purification routinely produced protein with purity above 90%, as measured

by SEC-HPLC. After incubating the protein at 37°C for 4 weeks, there was only minimal decrease in the

percentage of monomers, as shown in Figure 1C. These data suggest that huA33-BsAb had good solubility,

purity and thermal stability, all of which are critical characteristics for further downstream development.

We measured the avidities of huA33-BsAb towards GPA33 at both 25°C and 37°C using GPA33

immobilized CM5 chips. As shown in Figure 1D, huA33-BsAb bound GPA33 with a high apparent affinity

of around 0.2 nM, which is slightly lower than 0.13 nM obtained for parental huA33. FACS analysis of a

panel of cell lines derived from different cancers showed that huA33-BsAb stained colon cancer cell lines

and one gastric cancer cell line but not GPA33(-) neuroblastoma cell line IMR32, osteosarcoma cell line

TC32 or melanoma cell line SKMEL5 (Figure 1E and Table S1), suggesting that huA33-BsAb retained the

specificity of parental antibody A33 in binding to target antigens on colon cancer cells and a subset of

gastric cancer cells. Specific expression of GPA33 on colon tissues was also confirmed by

immunohistochemistry (Figure S1). Staining of activated T cells also showed that huA33-BsAb bound to

CD3 on T cell surface (Figure 1E)

HuA33-BsAb activated and induced cell cycle entry of fresh T cells

To test the ability of huA33-BsAb to activate unstimulated T cells, CFSE-labeled PBMCs were mixed

with Colo205 cells at an effector to target ratio of 5:1 (E:T= 5:1), and cultured in the presence of huA33-

BsAb (1 µg/ml). As negative controls, we used huA33-C825 that carried an irrelevant scFv (26) instead of

the anti-CD3 scFv, as well as a control T-BsAb antibody that did not bind to Colo205 by FACS. After 24 and




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96 hours, cells were stained with different T cell activation markers to assess T cell activation status and

proliferation. As early as 24 hours, huA33-BsAb caused activation of both CD4(+) and CD8(+) T cells, as

shown by the upregulation of CD25 and CD69 markers on cell surface (Figure 2A). In contrast, huA33-C825

and control T-BsAb caused only minimal upregulation of CD25. Control T-BsAb did increase the expression

of CD69, especially in CD4(+) T cells. Similarly, PD-1 upregulation was observed after 24 hours and

persisted until 96 hours (Figure S2A). Cell division, as measured by CFSE dye dilution, was observed in both

CD4(+) and CD8(+) T cells after 96 hours (Figure 2B). CD8(+) T cells showed higher cell division cycles,

suggesting that CD8(+) T cells divided faster than CD4(+) T cells (Figure 2C). Control antibody huA33-C825

did not stimulate significant amount of cell division in either T cell subset, confirming the requirement of

CD3 activation for T cell division. A low level of cell division was induced by control T-BsAb, consistent with

the low level of activation observed above. When GPA33(-) SKMEL5 targets were used, huA33-BsAb did

not activate T cells (Figure S2B). These data suggested that activation of T cells by huA33-BsAb depended

on the presence of cognate antigens on tumor cells. We also observed that cell division was associated

with expansion of CD45RO(+) effector/memory cells (Figure 2D), suggesting the importance of this subset

in mediating T-BsAb activity which was confirmed below. These assays were repeated using a different

colon cancer cell line LS174T with similar conclusions (Figure S2C).

To see if T cells can be activated in vivo, we conducted an in vivo proliferation assay by mixing

CFSE-labeled PBMC with Colo205 cells and implanted the mixture subcutaneously onto DKO mice. HuA33-

BsAb was injected the next day and the tumors were isolated after another 4 days and analyzed by FACS.

As shown in Figure 2E, around 25% of CD4(+) and CD8(+) T cells upregulated CD25 expression while

undergoing cell division (progressive halving of CFSE fluorescence), suggesting that huA33-BsAb was able

to stimulate T cell activation and proliferation in vivo as well.

HuA33-BsAb induced secretion of inflammatory cytokines and cytolytic molecules




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We next examined the secreted cytokine profile of T cells activated by huA33-BsAb in the

presence of target tumors. Total T cells were purified from PBMC and cultured in the presence of Colo205

tumor cells at E:T= 5:1; to estimate nonspecific activation, we used SKMEL5 as a negative control. Cell

culture supernatants were collected daily over 4 days and the levels of cytokines and cytotoxic molecules

were measured using a flow cytometry based multiplex method. As shown in Figure 3, both Th1 cytokines

(IL-2, IFNγ, TNFα) and Th2 cytokines (IL-4, IL-10) were secreted by activated T cells, although IL-4 was

secreted at a much lower level than other cytokines. Similarly, significant amount of IL-6 was secreted by

activated T cells. Interestingly, Th17 cytokine IL-17α was also secreted at high levels. As expected,

cytotoxic components sFasL, Granzyme A, Granzyme B, Perforin and Granulysin were all released in the

supernatant.

HuA33-BsAb redirected T cells to specifically kill colon cancer and gastric cancer cells

We next tested if huA33-BsAb could redirect T cells to kill cancer cells. Based on the survey of

GPA33 expression on multiple human cancer cell lines (Table S1), we selected 3 colon cancer cell lines

(LS174T, SW1222 and Colo205) and one gastric cancer cell line (SNU16) for cytotoxicity studies. These cell

lines were classified as MSI (LS174T) subtype or MSS (SW1222, Colo205, SNU16) subtype based on their

microsatellite instability profile (27-29). Moreover, LS174T cells carried a KRAS G12D mutation while the

others carried p53 mutations or deletions (30-33). Cancer cells were incubated with activated T cells at

E:T=10:1 in the presence of 10-fold serial dilutions of huA33-BsAb. GPA33(-) melanoma cell line SKMEL5

and osteosarcoma cell line TC32 were used as negative controls. As shown in Figure 4A, huA33-BsAb

redirected T cells to specifically kill all GPA33-expressing cancer cells regardless of their genetic

backgrounds, while sparing SKMEL5 and TC32, confirming the antigen specificity of huA33-BsAb mediated

TDCC. Maximal level of cytotoxicity seemed to correlate with the level of FACS staining (Figure 1E and

Figure 4A). Moreover, TDCC induced by huA33-BsAb was potent, with EC50 values in the pM range. We




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also confirmed the specificity of TDCC mediated by huA33-BsAb by replacing either the huA33 arm with

control BsAb or OKT3 arm with irrelevant C825; replacement of either arm completely abolished TDCC

activity (Figure S3).

To see which subsets of T cells were mobilized by huA33-BsAb, we sorted CD45RA(+)CD62L(+) and

CD45RA(-)CD45RO(+)CD62L(-) memory subsets from both CD4(+) and CD8(+) T cells. Sorted cells were

cultured in the presence of Colo205 tumors cells at E:T=5:1 for 48 hours before measuring cytotoxicity. As

shown in Figure 4B, both CD4(+) and CD8(+) memory T cell subsets were capable of inducing cytotoxicity,

with CD8(+) memory T cells mediating more efficient killing at higher concentration. Interestingly,

CD45RA(+)CD62L(+) subsets of both CD4(+) and CD8(+) populations, with the majority being naïve T cells,

were capable of inducing cytotoxicity after 48 hours, although the potency was less compared to memory

T cells. When T cells from the TDCC assay were stained with CD45RO and CD25, it was found that CD25

expression was upregulated in the presence of huA33-BsAb, in both CD45RO+ and CD45RO- fractions

(Figure S4), confirming that both naïve and memory T cells could be activated by T-BsAb. The majority of

CD45RA(+)CD62L(+) T cells stayed CD45RO(-) after incubation, with a small but significant population

increasing their CD45RO expression, especially among the CD8(+) cells. However, this population could

have derived from either the maturation of naïve T cells or from expansion of rare CD45RO+ cells present

in the initial culture. Overall these data demonstrated that huA33-BsAb could induce potent cytotoxicity

against colon and gastric cancer cells in a GPA33 dependent manner, by mobilizing both CD4 and CD8 T

cells, especially those of the memory phenotype.

Affinity maturation of huA33-BsAb by yeast display

In an attempt to further improve the potency of huA33-BsAb, we used yeast display method to

affinity mature scFv derived from huA33. Since scFv tends to aggregate easily, we developed a method to




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rapidly reformat scFv to T-BsAb (Figure S5A), which is a more relevant format and could be readily

produced in high yield and purity.

From sequence analysis of 60 single clones, we selected 7 clones (Figure S5B) for further

characterization by SPR and TDCC assay. All 7 clones showed increased binding affinity (4.3 to 51-fold) as

compared to parental antibody (Figure S5C). Majority of improvement was contributed by slower off-rate.

When tested in TDCC assay, all clones showed slight improvement in maximal killing (Figure S5D); however,

no significant enhancement in EC50 was observed (Figure S5D).

In vivo therapy studies using huA33-BsAb

Efficacy of huA33-BsAb was tested in vivo with two xenograft models in DKO mice adoptively

transferred with human T cells: (1) s.c. tumor plus s.c. effectors and (2) i.p. tumor plus i.v. effectors.

1) HuA33-BsAb cured MSI tumor LS174T in a s.c. xenograft model and suppressed tumor growth in

an i.p. model

LS174T cells were mixed with PBMC at a 1:1 ratio and implanted subcutaneously in DKO mice. As

shown in Figure 5A, without i.v. antibody treatment, both tumor only and tumor+PBMC groups showed

rapid tumor growth. Mice from tumor+PBMC group developed tumor ulceration and had to be euthanized.

In contrast, 6 doses of i.v. huA33-BsAb over 3 weeks effectively cured the mice, which remained tumor

free for at least 120 days.

To simulate malignant ascites, a common occurrence in colon cancers, luciferase-expressing

LS174T cells were planted intraperitoneally into DKO mice. When tumor growth was confirmed by

luminescence, mice were randomized into different treatment groups: ATC only, ATC+huA33-C825,

ATC+control BsAb, and ATC+huA33-BsAb. Antibody treatment started on day 8 after tumor implantation

and consisted of 6 doses intraperitoneally over 3 weeks, whereas T cell treatment consisted of weekly




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injection of ATC through retro-orbital route over 3 weeks. . As shown in Figure 5B and Figure 5C, all three

control groups showed exponential growth of tumor in the abdomen. In contrast, i.p. huA33-BsAb

significantly suppressed metastatic growth of LS174T tumor in the abdominal areas of treated mice,

accompanied by substantial amount of T cell tumor infiltration (Figure 5D). All mice in this group remained

alive until at least 55 days without further treatment, while all mice in control groups succumbed to

tumors by Day 43 (Figure 5B, right panel). This is consistent with our previous results showing that huA33-

C825 had no direct anti-tumor effect on LS174T tumor (26, 34).

These data suggested that huA33-BsAb was effective against CRC tumors with an MSI genotype.

However, as mentioned before, MSI tumors account for only a minority of CRC cancer patients. Majority

of CRC patients are MSS. Therefore, efficacy of huA33-BsAb was tested further using MSS tumors.

2) HuA33-BsAb cured MSS tumor COLO205 in a s.c. xenograft model and suppressed tumor growth

of metastatic MSS tumor SW1222

Two MSS colon cancer cell lines Colo205 and SW1222 were tested. For Colo205 cells, tumors were

implanted subcutaneously with PBMC as effector cells. In this model, 4 doses of i.v. huA33-BsAb were

enough to completely eradicate Colo205 tumors and the mice remained tumor free for at least 4 months

after a total of 6 doses of antibody treatment (Figure 6A and 6B).

For the SW1222 cell line, tumors were planted intraperitoneally and treated with 6 doses of i.p.

antibody over 3 weeks, and i.v. T cell weekly over 2 weeks. As shown in Figure 6C and 6D, the two control

groups had tumor growth spread throughout the whole abdominal area, whereas treatment with huA33-

BsAb suppressed tumor growth and significantly prolonged mice survival.




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These results together suggested that huA33-BsAb had similar efficacy in MSS tumors as that in

MSI tumors. We expected more treatment cycles could eradicate the growth of tumors more efficiently,

as was shown in subcutaneous models.

3) HuA33-BsAb inhibited growth of gastric cancers in a s.c. xenograft model

GPA33 is expressed in a subset of gastric cancer cells (13). By FACS analysis and in vitro TDCC

assays, SNU16 expressed GPA33 and was sensitive to huA33-BsAb redirected T cell killing. SNU16 cells

were xenografted subcutaneously after mixing with human PBMC. As expected, i.v. huA33-BsAb

effectively cured the mice of s.c. tumors (Figure S6) and significantly prolonged survival.




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Discussion

Curing mCRC is an urgent unmet medical need. In this study, we demonstrated a potential

strategy using a T-BsAb, huA33-BsAb, in vitro and in vivo, to redirect polyclonal cytotoxic T cells to kill

tumors that expressed GPA33 antigen. Besides systemic spread, peritoneal carcinomatosis has also been

difficult to control. Unlike metastasis to liver and lung, it is usually unresectable and unresponsive to

chemotherapy and radiation, resulting in significant morbidity. Current treatment is mostly palliative,

consisting of cytoreductive surgery or hyperthermic chemotherapy (HIPEC), which are effective in only a

small percentage of patients with small volume disease. Development of effective immunotherapy using

i.p. T-BsAbs for malignant ascites, as demonstrated in this study, is an attractive alternative for several

reasons. First, the peritoneal cavity is an immunocompetent compartment harboring immune cells, the

majority (>40%) being T cells and monocytes/macrophage (>40%) (35). Second, intraperitoneally

administered antibodies are placed in immediate contact with cancer cells, facilitating tumor binding

through high local drug concentrations. Third, rapid uptake of antibodies by tumors reduces systemic drug

exposure, hence limiting the toxicity of T cell activating biologics commonly seen with i.v. injections. It

was not surprising that the first T-BsAb drug approved for solid tumor, the anti-EpCAM antibody

catumaxomab, was administered intraperitoneally for malignant ascites. Besides targeting the peritoneal

tumor compartment, huA33-BsAb could suppress tumor growth and prolong survival in subcutaneous

xenograft models of aggressive mCRC. Furthermore, huA33-BsAb could recruit cytotoxic T cells from the

systemic circulation into the peritoneal cavity for effective tumor kill – an important first step in T-cell

based immunotherapy. Unlike the robust response of s.c. models, i.p. tumors were not cured in all mice.

However, considering the suboptimal engraftment of human cells in Balb/c derived DKO mice without

exogenous cytokines (36, 37), the efficacy of huA33-BsAb could be underestimated. One could even

propose combining injections of i.p. huA33-BsAb with i.p. T cells or with i.p. PBMC to enhance the anti-

tumor effects.




19

T-BsAbs generally have higher tumor killing potency than ADCC-dependent IgG antibodies,

possibly because of the presence of competing IgGs present in the medium and/or the intrinsic differences

between cytotoxic T cells and NK cells. Our in vitro TDCC assay showed that huA33-BsAb killed colon

cancer cell lines with an EC50 of around 4-66 pM and 25 pM for purified CD4(+) memory T cells (Figure 4B),

which was 2-40 times lower than the apparent affinity of the molecule. This potency is comparable to

MEDI-565(38), which has an EC50 of 91 pM and higher than RG7802, which has an EC50 of 0.24 nM-6.28

nM (39). One of the most potent T-BsAbs reported so far by Xu et al (21) that targeted GD2 has EC50s in

the fM range. These differences may be attributed to the differences in the intrinsic properties of antigens

or in the particular epitopes targeted by T-BsAb. Nevertheless, it is still not clear if high potency translates

into clinical benefit since more efficient killing of tumor cells can be accompanied by more on-target off-

tumor toxicities, unless the therapeutic window is improved (21). A tradeoff between potency and toxicity

has to be carefully considered, especially for tumor antigens that are also expressed in normal tissues.

Our analyses of cytokines and cytotoxic molecules in culture supernatants provided a mechanistic

basis for the action of huA33-BsAb. Cytokines belonging to Th1, Th2 and Th17 types were all involved,

although with different kinetics. Cytokines play a major role in modifying the immunological landscape of

tumor microenvironment and may be important for the long term efficacy and toxicity of T cell based

immunotherapy. An extreme example is the uncontrolled simultaneous release of a myriad of cytokines

that results in “cytokine storm”, a potentially fatal condition, of which IL-6 is one of the main components.

Understanding how a tumoricidal cytokine pattern transitions into systematic toxicity will undoubtedly

help improve current T cell based immunotherapy.

We also tested if increasing affinity of huA33-BsAb to 3.2 pM could improve T-BsAb potency.

While the facile yeast system was efficient in identifying novel mutations to improve affinity, no significant

improvement in EC50 among these variants was observed in TDCC assay. There appears to be an affinity




20

ceiling of sub-nM, beyond which further increase in affinity will not significantly improve the potency of

T-BsAbs, as was also observed using other T cell engaging molecules (40). The molecular basis of this

phenomenon is unclear. It is also possible that antibodies with these extremely high affinity molecules

became irreversibly trapped by dead cells and no longer available during cytotoxicity assays.

Besides GPA33, both EpCAM and CEA are being tested as therapeutic targets for mCRC. EpCAM

has the advantage of being restricted to epithelial cells, which are not present in healthy peritoneal cavity

because it is of mesenchymal origin. CEA has the advantage of having a polarized expression pattern with

expression restricted to the apical surface of normal colon tissues. However, both proteins are expressed

in a wide variety of normal tissues and could potentially raise toxicity concerns. In contrast, the expression

of GPA33 is specifically restricted to colon tissues and not other organs, which could be advantageous in

limiting its toxicity. Since the huA33 antibody is not cross-reactive with mouse GPA33, it is impossible for

us to test systemic toxicity in the murine xenograft models used. However, we reasoned that healthy

normal colon cells could be shielded from the peritoneal cavity by the physical barriers of serosa and

muscular layers wrapping around colons. In addition, on the luminal side, the continuous turnover of the

gut epithelium carrying with it GPA33 could partially alleviate this cross-reactivity issue (41). It is

conceivable that removing FcR(n) affinity could further reduce antibody transport into the gut lumen (42).

More careful investigations using antibodies against this antigen in non-human primates or in humans will

be needed to address these issues. The results from ongoing Macrogenics’ phase I clinical trial of MGD007

(Clinicaltrials.gov, NCT02248805), a bivalent (1+1) T-BsAb directed at GPA33, with anti-tumor efficacy in

a Colo205 subcutaneous xenograft model, should provide valuable information on the clinical safety of

such approaches.




21

Acknowledgements

We thank Dr. Mamoru Ito of Central Institute for Experimental Animals, Kawasaki, Japan, for providing

the DKO mice. Z Wu, HF Guo, Hong Xu and NKV Cheung were partly supported by Enid A. Haupt Endowed

Chair and the Robert Steel Foundation. MSK Animal Imaging Core Facility was supported by NCI Cancer

Center Support Grant P30 CA008748.




22

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25

Figure Legends

Figure 1. Stability and binding characteristics of huA33-BsAb antibody

A. SPR analysis of 4 versions of humanized A33. All antibodies were in IgG1 format. 3A3-H1L1, 3A3-H1L2,

3A3-H2L1 and 3A3-H2L2 were 4 versions of humanized 3A3 (monospecific). 3A3-chA33 was chimeric 3A3.

B. Design and Construction of huA33-BsAb. C. Accelerated stability test of purified huA33-BsAb at 37°C

over 4 weeks; monomer% represents the percentage of monomers in SEC profile for each time point,

based on AUC analysis excluding buffer peak. D. SPR analysis of huA33-BsAb at 25°C and 37°C according

to conditions in Materials and Methods. Data were fit to a 1:1 binding model. E. FACS staining of different

tumor cell lines and activated T cells. MFI values were geometric means.

Figure 2. In vitro and in vivo activation of human PBMC by huA33-BsAb

A. Activation of CD25 and CD69 on T cells 24hours after incubation with Colo205 cells and different

antibodies. B. Quantification of dividing cells based on CFSE dye dilution 96 hours after incubation with

Colo205 cells and different antibodies. C. Representative images for B. D. Staining of CD45RO 96hours

after incubation with Colo205 cells and huA33-BsAb in an independent experiment. E. In vivo activation

and proliferation of T cells by huA33-BsAb.

Figure 3. Profile of secreted cytokines and cytotoxic components by huA33-BsAb activated T cells in the

presence of target tumor

Kinetics of production of cytokines and cytolytic molecules by T cells in the presence of huA33-BsAb and

target cell Colo205 or negative control cell SKMEL5 over 4 days. SKMEL5 itself secreted copious amount

of IL-6; therefore only supernatant from T cells incubated with Colo205 cells in the absence of antibody

was used as control. IFNg, granzyme A, granzyme B and perforin were from a second independent

experiment.




26

Figure 4. in vitro cytotoxicity induced by huA33-BsAb

A. Cytotoxicity elicited by huA33-BsAb against different target tumor cell lines and control cells. Activated

T cells were used as effector cells at an effector to target ratio of 10:1. Cells were incubated for 16hours

before reading. B. Cytotoxicity induced by huA33-BsAb against Colo205 cells. Sorted fresh T cell subsets

were used as effector cells (E:T=5:1). Cells were incubated for 48hours before reading. EC50 for CD4

memory T cells was 25 pM.

Figure 5. huA33-BsAb eliminated MSI CRC tumors in xenograft model

A. Tumor growth of s.c. LS174T tumors in treatment group and control groups. PBMCs were planted s.c.

Antibodies were injected i.v. Tumor sizes were assessed by volume. (p=0.0133 for tumor+scPBMC versus

tumor+scPBMC+huA33-BsAb; p=0.006 for tumor only versus tumor+scPBMC+huA33-BsAb) B. Left:

Growth of i.p. LS174T tumor in treatment group and control groups as assessed by bioluminescence. * p

< 0.01 determined by Student’s t test when treatment group (ATC+huA33-BsAb) was compared with the

corresponding control groups, respectively. Right: Survival of mice in treatment group and control groups.

C. Representative bioluminescent images of abdominal LS174T tumors from different groups in B were

shown. D. IHC images of CD3 staining. Representative images (200X magnifications) of IHC staining of

abdominal LS174T tumor sections collected 5 days after iv ATC were shown.

Figure 6. huA33-BsAb cured MSS CRC tumors in s.c. xenograft model (6A and 6B) and suppressed tumor

growth in i.p. metastasis model (6C and 6D)

A. Luminescence images showing growth of s.c. Colo205 tumors in different groups. ATC were injected

intravenously; antibodies were injected intraperitoneally. B. Left: quantification of signals; right:

survival of mice among different treatment groups. Mice treated with 4 doses i.v. huA33-BsAb showed

complete tumor eradication. C. Luminescence images of i.p. SW1222 tumor, where ATC were injected




27

i.v. weekly over 2 weeks, and 6 doses of huA33-BsAb intraperitoneally. On day 21, tumor growth was

significantly different between huA33-BsAb+ATC group and no treatment group (p=0.0051) or ATC only

group (p=0.0233). By day 30, tumor growth in huA33-BsAb+ATC group was still significantly suppressed

when compared to no treatment group (p=0.0037). Mouse #1 from tumor only group and mouse #3

from tumor+ATC group which did not take tumor after 21 days were excluded from imaging in later time

points and not included in tumor growth comparison nor survival analysis in. D. Survival of mice with i.p.

SW1222 tumor treated with ATC with or without huA33-BsAb.




Figure 1 Humanization of A33 and physico-biochemical characterization of huA33-BsAb

antibody

hA33

hOKT3

N297A/K322A

A B

C D

0 100 200 300

0

50

100

time (s)

Resp

on

se (

0=

baselin

e),

(100=

Sam

ple

1 s

top

)

3A3-chA33

3A3-H1L1

3A3-H1L2

3A3-H2L1

3A3-H2L2

E




Figure 2 In vitro and in vivo activation of human PBMC by huA33-BsAb

A B

C

D

0.016% 0.087% 87.5%

0% 0.085% 94.7%

NoAb huA33-BsAb huA33-C825

CD4

CD8

1.16%

6.01%

control BsAb

CFSE

NoAb huA33-BsAb

CD

45

RO

CFSE

CD4

CD8

E

NoA

b

huA33

-C82

5

huA33

-BsA

b

contr

ol BsA

b

NoA

b

huA33

-C82

5

huA33

-BsA

b

contr

ol BsA

b0

20

40

60

80

%C

D25 o

r %

CD

69

CD4

CD8

CD25 CD69

NoA

b

huA33

-C82

5

huA33

-BsA

b

contr

ol BsA

b0

20

40

60

80

100

%D

ivid

ing

cells

CD4

CD8




Figure 3 Profile of secreted cytokines and cytotoxic components by huA33-BsAb activated

T cells in the presence of target tumor




Figure 4 in vitro cytotoxicity induced by huA33-BsAb

Colo205 LS174T SNU16 SW1222 SKMEL5 TC32

EC50 4.89pM 17pM 66pM 3.96pM 2622pM 564.5pM

B

A




Figure 5 huA33BsAb eliminated MSI+ CRC tumors in xenograft model

A

C

B

0 20 40 600

50

100

Days post tumor implantation

Perc

en

t su

rviv

al

p<0.001

ATC only

ATC+huA33-C825

ATC+huA33-BsAb

ATC+contro BsAb

D

CD3

ATC+huA33-C825 ATC+control BsAb ATC+huA33-BsAb

0 5 10 15 20 25

0

2000

4000

6000

8000

Days post tumor implantation

Bio

lum

inescen

ce

(ph

oto

ns

em

itte

dx

10

7/w

ho

le m

ou

se

/s)

ATC only

ATC+huA33-C825

ATC+control BsAb

ATC+huA33-BsAb

ATC Injection

BsAb Injection

*




Figure 6 huA33-BsAb cures MSS CRC tumors in s.c. xenograft model and suppress growth of i.p.

metastasis model

A

B

C D




Published OnlineFirst August 6, 2018.Mol Cancer Ther Zhihao Wu, Hongfen Guo, Hong Xu, et al. antibody for colorectal cancersDevelopment of a tetravalent anti-GPA33/anti-CD3 bispecific

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