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Antibody-Modified Conduits for Extracorporeal Selective Cytokine Filtration in Sepsis by Morgan K. Moroi Submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Bachelor of Science in Engineering as Recommended by the Department of Mechanical Engineering at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY June 2016 @ Massachusetts Institute of Technology 2016. All rights reserved. Author .... Signature redacted 6' Department of Mechanical Engineering May 6, 2016 Cetfidby.Signature redacted Certified by... ....... ....... Robert S. Langer David H. Koch Institute Professor Thesis Supervisor Accepted bySignature redacted by... - -- - tu r -- e - c e d ............. Anette Hosoi MASSACHUSETTS INSTITUTE Professor of Mechanical Engineering OF TECHNOLOGY Undergraduate Officer JUL 08 2016 LIBRARIES

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Page 1: Signature redacted redacted

Antibody-Modified Conduits for Extracorporeal

Selective Cytokine Filtration in Sepsis

by

Morgan K. Moroi

Submitted to the Department of Mechanical Engineeringin partial fulfillment of the requirements for the degree of

Bachelor of Science in Engineering as Recommended by theDepartment of Mechanical Engineering

at the

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

June 2016

@ Massachusetts Institute of Technology 2016. All rights reserved.

Author ....Signature redacted

6' Department of Mechanical EngineeringMay 6, 2016

Cetfidby.Signature redactedCertified by... ....... .......

Robert S. LangerDavid H. Koch Institute Professor

Thesis Supervisor

Accepted bySignature redactedby... - -- - tu r -- e - c e d .............Anette Hosoi

MASSACHUSETTS INSTITUTE Professor of Mechanical EngineeringOF TECHNOLOGY Undergraduate Officer

JUL 08 2016

LIBRARIES

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2

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Antibody-Modified Conduits for Extracorporeal Selective

Cytokine Filtration in Sepsis

by

Morgan K. Moroi

Submitted to the Department of Mechanical Engineeringon May 6, 2016, in partial fulfillment of the

requirements for the degree ofBachelor of Science in Engineering as Recommended by the Department of

Mechanical Engineering

Abstract

Sepsis kills millions of people worldwide each year and occurs when microorganismsenter the bloodstream of an infected host. The presence of microorganisms in thebloodstream triggers the body to produce many inflammatory proteins, known ascytokines, that cause damage to blood vessels and vital organs. This leads to cap-illary leak, failing organs, and often death. We have developed a novel approach tomodulate the inflammatory response, using antibody-modified conduits (AMCs) tofilter harmful cytokines selectively from the circulation and in a time-specific manner.Here, we characterize variables that affect AMC performance to determine optimalAMC conditions for later use downstream.

Thesis Supervisor: Robert S. LangerTitle: David H. Koch Institute Professor

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Acknowledgments

The author gratefully acknowledges Dr. J. Brian McAlvin, Dr. Daniel S. Kohane,

and Dr. Robert S. Langer for their guidance throughout the completion of this work.

The author would also like to thank all family and friends for their continual support.

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Contents

1 Introduction 13

2 Materials and Methods 17

2.1 M aterials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

2.2 Preparation of Antibody-Modified Conduits . . . . . . . . . . . . . . 18

2.2.1 Synthesis and Dialysis of Furan-Functionalized Antibody . . . 18

2.2.2 Formation of Antibody-Modified Conduits . . . . . . . . . . . 18

2.3 In Vitro Demonstration of Selective Cytokine Filtration . . . . . . . . 21

2.4 Influence of Flow Rate on Elimination Kinetics . . . . . . . . . . . . 22

2.5 Influence of Antibody Surface Packing Density on Elimination Kinetics 23

2.6 Influence of Surface Area to Volume Relationships on Elimination Ki-

netics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2.7 Influence of PEG Spacer Length on Elimination Kinetics . . . . . . . 23

2.8 Determination of Cytokine Binding Capacity . . . . . . . . . . . . . . 24

2.9 Statistics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3 Results 25

3.1 In Vitro Demonstration of Selective Cytokine Filtration . . . . . . . . 25

3.2 Influence of Flow Rate on Elimination Kinetics . . . . . . . . . . . . 26

3.3 Influence of Antibody Surface Packing Density on Elimination Kinetics 27

3.4 Influence of Surface Area to Volume Relationships on Elimination Ki-

netics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.5 Influence of PEG Spacer Length on Elimination Kinetics . . . . . . . 29

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3.6 Determination of Cytokine Binding Capacity . . . . . . . . . . . . . . 30

4 Discussion 31

5 Conclusion 35

6 References 37

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List of Figures

1-1 Pathophysiology of the systemic inflammatory response in sepsis . . . 14

2-1 Schema of formation of an antibody-modified conduit . . . . . . . . . 20

2-2 Experimental setup for testing selective TNF-a filtration with infliximab-

m odified conduits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3-1 Type of cytokine filtered was determined by the selection of AMC

surface antibody . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

3-2 TNF-a filtration by infliximab-modified conduits, where the BSA TNF-

a solution was circulated through AMCs at varying flow rates . . . . 27

3-3 TNF-a filtration by infliximab-modified conduits prepared with vary-

ing infliximab concentrations . . . . . . . . . . . . . . . . . . . . . . . 28

3-4 TNF-a filtration by infliximab-modified conduits with varying surface

area to volume ratios . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

3-5 TNF-a filtration by infliximab-modified conduits with varying PEG

spacer lengths......... ............................... 30

3-6 TNF-a filtration by ideal infliximab-modified conduits (2.50 surface

area to volume ratio, NHS-PEGIO-Maleimide, 1 mg/mL infliximab so-

lution) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

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List of Tables

2.1 PDMS tube specifications used to prepare antibody-modified conduits. 19

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Chapter 1

Introduction

Septic shock affects millions of people worldwide every year and remains the lead-

ing cause of death in critically ill patients in the United States [1-4]. Sepsis occurs

when microorganisms (most commonly bacteria) enter the bloodstream and cause a

dynamic, unregulated systemic inflammatory response [2] (Figure 1-1). The early

stage of sepsis is dominated by a surge of pro-inflammatory cytokines, such as tumor

necrosis factor alpha (TNF-a) [5], interleukin 1 beta (IL-1#) [5,6], interleukin 6 (IL-6)

[5], and vascular endothelial growth factor (VEGF) [7]. As sepsis persists, a decrease

in pro-inflammatory cytokines and an increase in anti-inflammatory cytokines occurs,

resulting in immunoparalysis [2,5]. Recovery from this immunosuppressive state may

be associated with positive clinical outcomes [8].

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Pro-in ammato Burst

Septic shock/SIRS/MODS

DICMyocardialdepression

Vascular permeabilityEarly death

Involvement of:

Complement

IL-68 CoagulatIon

IL-12IL-12 ellularVEGF activation

0toE

0

0to

EEto

F Death

Figure 1-1: Pathophysiology of the systemic inflammatory response in sepsis.

Investigators have tried for decades to modulate the immune response during

sepsis in an effort to restore homeostasis [5]. Unfortunately, most attempts, including

corticosteroids [5,9], antiendotoxin antibodies [5,10], tumor necrosis factor antagonists

[5,11], interleukin-1-receptor antagonists [5,6], and ibuprofen [12], have largely proven

unsuccessful. Additionally, efforts to non-specifically remove both pro-inflammatory

and anti-inflammatory cytokines, by dialysis [13] or therapeutic plasma exchange

(TPE) [14], have also failed to improved survival. One reason for these failures may

be because the complex pathophysiology of sepsis changes over time. For example,

many targeted immune therapies that are beneficial during the pro-inflammatory

surge exacerbate the immunosuppression that is present in the later phase of sepsis.

We presume that previous attempts to modulate the immune system have been

unsuccessful due to prolonged inimunosuppression (via anti-inflammatory therapies)

or non-s)ecific removal of cytokines that would have been better left in the circu-

lation (via dialysis or TPE). Furthermore, we hypothesize that successful immune

14

Immuno oral sisCARS

Immune and cellulardysfunction

Secondary infectionLate death

Involvement of:IL-10

TGF-P

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modulating therapies for sepsis must remove deleterious cytokines selectively and in

a time-specific manner. Pro-inflammatory cytokines should only be removed during

the pro-inflammatory burst to prevent long-lasting immune suppression. Similarly,

anti-inflammatory cytokines should only be removed during immunoparalysis to aid

in the restoration of homeostasis.

To accomplish this, silicone tubes were individually surface modified with antibod-

ies against a particular cytokine. Known as an antibody-modified conduit (AMC),

each tube is capable of removing one type of cytokine from blood that extracorpo-

really circulates through it. If installed in parallel and for patient-specific durations

of time, AMCs may prevent multi-organ injury and mortality by allowing for spe-

cific temporally controlled manipulations of the cytokine cascade in sepsis. Here,

we specifically focus on the characterization of variables that affect AMC filtration

performance.

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Chapter 2

Materials and Methods

2.1 Materials

Polydimethylsiloxane (PDMS) tubing was purchased from Cole-Parmer Instrument

Company (Vernon Hills, IL). (3-Aminopropyl)trimethoxy-silane (APTMS) was pur-

chased from Sigma-Aldrich (St. Louis, MO). Heterobifunctional poly(ethylene glycol)

with N-hydroxysuccinimide ester and maleimide moieties (NHS-PEGa-Maleimide,

where n is the molecular weight of the PEG spacer) was purchased from Rapp

Polymere (Tuebingen, Germany). 2-Furoic acid, N-(3-Dimethylaminopropyl)-N '-

ethylcarbodiimide hydrochloride (EDC), and N-Hydroxysuccinimide (NHS) were pur-

chased from Sigma-Aldrich (St. Louis, MO). Infliximab (Janssen Biotech, Inc., Hor-

sham, PA) in distilled water (10 mg/mL) was donated by Boston Childrens Hospital

(Boston, MA). Bevacizumab (Genentech, Inc., San Francisco, CA) in distilled water

(25 mg/mL) was donated by Boston Childrens Hospital (Boston, MA). Vascular en-

dothelial growth factor A (VEGF-A) and tumor necrosis factor alpha (TNF-a) were

purchased from R&D Systems Inc. (Minneapolis, MN).

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2.2 Preparation of Antibody-Modified Conduits

2.2.1 Synthesis and Dialysis of Furan-Functionalized Anti-

body

Furan with N-hydroxysuccinimide ester (NHS-furan) was synthesized by dissolving 1

molar equivalent of furoic acid, 3 molar equivalents of EDC, and 3 molar equivalents

of NHS in dichloromethane (DCM). The aqueous solution was continuously stirred for

13 hours at room temperature and purified using a CombiFlash@ Rf 150 purification

system (Teledyne Isco, Inc., Lincoln, NE) with a 40-gram high performance silica

column (Teledyne Isco, Inc., Lincoln, NE). Elution fractions containing the product

were combined and the liquid was evaporated using a Rotavapor@ (Buchi Corpora-

tion, New Castle, DE) set to rotate at 45 'C. The final product was lyophilized (SP

Scientific VirTis Lyophilizer, Warminster, PA) for 16 hours.

NHS-furan was dissolved in dimethyl sulfoxide (DMSO) (45 mg/mL) and added to

an aqueous antibody solution (10 - 25 mg/mL) to form a 10:1 molar mixture of NHS-

furan to antibody. The mixture was rotated (VWR@ Tube Rotator, Radnor, PA)

for 2 hours at room temperature to encourage the formation of furan-functionalized

antibody.

The resulting solution was placed into the lumen of a Slide-A-LyzerT M dialysis

cassette with a 10 kDa molecular weight cutoff (Thermo Scientific, Rockford, IL).

The dialysis bag was placed into 4L 1X phosphate buffered saline (PBS) (pH 7.4)

and incubated at 2 - 8 'C with continuous stirring. The PBS buffer was exchanged

every 8 hours for 24 hours, and the final dialyzed solution was stored at 2 - 8 *C until

use.

2.2.2 Formation of Antibody-Modified Conduits

PDMS tubes were cut to length based on the desired surface area to volume ratio and

plasma oxidized (Harrick Plasma Cleaner, PDC-001, Ithaca, NY) at 1.5 mbar for the

corresponding duration (Table 2.1) (Figure 2-1). Tubes with the largest surface area

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to volume ratio (i.e. long length, small diameter) were plasma oxidized for a longer

duration of time to ensure complete diffusion of plasma throughout the tube.

Table 2.1: PDMS tube specifications used to prepare antibody-modified conduits.Surface Area to Inner Surface Plasma

. .Length Srae VolumeVolume Ratio Diameter Area Oxidation

(mm- 1 ) (mm) (mm) (mm 2 ) (mm Duration (min)

2.50 1.6 875 4400 1760 201.25 3.2 219 2200 1760 2

0.834 4.8 97 1467 1760 20.625 6.4 55 1100 1760 20.416 9.6 24 733 1760 2

Oxidized PDMS tubes were connected in series and 5% (v/v) APTMS in acetone

was circulated through the tubes at room temperature for 1 hour using a peristaltic

pump (Watson-Marlow, Inc., 120U/DV, Wilmington, MA) set at 40.0 rpm (Figure 2-

1). The resulting aminopropyl silane coated tubes were flushed with ethanol followed

by forced air to remove any residual solution. NHS-PEG,-Maleimide in 1X PBS (pH

8.5) (2 mg/mL) was then circulated at room temperature for 1 hour at 160.0 rpm

to produce Maleimide-PEG, modified tubes (Figure 2-1). Tubes were then flushed

with 10 mM 2-(N-morpholino)ethanesulfonic acid (MES) (pH 5.5) followed by forced

air. To quench residual amines, 200 mM acetic anhydride in methanol (MeOH) was

circulated at room temperature for 2 hours at 160.0 rpm (Figure 2-1). Tubes were then

flushed with 10 mM MES (pH 5.5) followed by forced air. The furan-functionalized

antibody solution was diluted with 10 mM MES (pH 5.5) to an antibody concentration

of 0.5 mg/mL and circulated at 37 'C for 13 hours at 160.0 rpm (Figure 2-1). Before

use, antibody-modified conduits were flushed with sterile IX PBS (pH 7.4).

Antibody-modified conduits were stored in sterile IX PBS (pH 7.4) at 2 - 8 'C

until use for a maximum of 2 weeks.

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CH 3 CH 3 CH 3I I I

H3Cnmo' P'CH

Unmodified PDMS

0 NH 0 NH

0 0

O 0

0 0HN HN

0 0

NH NH NHF

S ' Si 'I I |

Antibody Modified Conduit(AMC)

Air Plasma

LINH

F-uran- FuncticAntibody in

pH 5.5

OH OH OHI I I

HO' I 1 0 'OH

Oxidized PDMS

0 N 0 N7 0

0 0

0 0HN HN

0 0

NH NH NHn lzed2)MES. 2

i' ' Si Si

0100

Maleinide-PEG , Modified Surf,(Residual amines blocked by acyl

with acetic anhydride)

H 3COH 3CO-Si NH2

H 3CO

5%' (v/v) APTMSin acetone

NH 2 NH 2 NH 2

HO' I 10 OH

Aminopropyl SilaneCoated Surface

0 0HN

0 ONHS-PEG,-Maleimidein PBS (pH 8.5)

Acetic Anhydride in MeOH0 0

aceation

Figure 2-1: Schema of formation of an antibody-modified conduit. Conjugation ofantibodies onto the inner surface of silicone tubes was accomplished through foursequential reactions. The first step was to activate the silicone surface by oxygenplasma oxidation to create reactive silanol species (Si-OH). The anchoring molecule(APTMS) was then covalently grafted to the Si-OH moieties. Next, a spacer molecule(NHS-PEG,-Maleimiide) was attached to the primary amine of the APTMS anchor.In the final step, the terminal naleimide on the PEG spacer was reacted with thefuran moieties that were added to the antibodies.

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2.3 In Vitro Demonstration of Selective Cytokine

Filtration

Antibody-modified conduits with a surface area to volume ratio of 0.834 (Table 2.1)

were prepared with NHS-PEG10-Maleimide and a 0.5 mg/mL infiiximab solution and

tested to determine if selective TNF-a filtration could be achieved (PEG10 , 10 kDa

molecular weight PEG) (infiiximab is a monoclonal antibody that binds TNF-a).

Solutions of 53 (w/v) BSA in sterile lX PBS (pH 7.4) were enriched with 2000

pg/mL TNF-a and 2000 pg/mL VEGF-A and circulated through infiiximab-modified

conduits using the experimental setup in Figure 2-2. The cytokine concentrations

were chosen to be an order of magnitude greater than what would be encountered

clinically during an episode of sepsis to sufficiently challenge AMCs.

Unm>dified Pump-Compa111>le -----4"'- ·.ll

Tube

Unm>dified --­Tube Antibody-Modified

Conduit

Figure 2-2: Experimental setup for testing selective TNF-a filtration with infiiximab­modified conduits. An infiiximab-modified conduit was connected in series with two other tubes: (1) an unmodified tube (Cole-Parmer Instrument Company, PVC, ID 3/16, OD 7 /16 , Vernon Hills, IL) compatible with the gear pump system (Cole­Parmer Instrument Company, Vernon Hills, IL) , and (2) an unmodified tube (Sigma­Aldrich , PVC, ID 3/16, OD 1/8, St. Louis , MO) to return solution to the reservoir. The unmodified pump-compatible tube was clamped within the pump head, and the free ends of the modified conduit and unmodified tube were placed in a reservoir. Reservoirs were made from 50 mL conical tubes, placed on a 37 °C hot plate (IKA@ Works, Inc. , RCT basic , Wilmington, NC), and covered with Parafilm@ M (Brand GMBH, Wertheim, Germany) to avoid evaporation.

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Reservoirs were filled with 20 mL of BSA cytokine solution and a 0.5 mL sample

was taken at time zero. The cytokine solution was circulated at 20 mL/min and addi-

tional 0.5 mL samples were obtained at 0.5, 1, 2, 3, and 4 hours. The reservoir volume

and circulation rate were chosen in anticipation of in vivo experiments (rat model of

sepsis), where the rat circulating blood volume is 20-25 mL and the extracorporeal

circulation rate will be 20 mL/min. Samples were stored at -20 'C until analysis.

VEGF-A and TNF-a concentrations in the samples were determined using VEGF-A

and TNF-a enzyme-linked immunosorbent assay (ELISA) kits (R&D Systems, Inc.,

Minneapolis, MN).

This experiment was repeated with bevacizumab-functionalized AMCs with a sur-

face area to volume ratio of 0.834, using a 0.5 mg/mL bevacizumab solution (beva-

cizumab is a monoclonal antibody that binds VEGF-A).

2.4 Influence of Flow Rate on Elimination Kinetics

Infliximab-modified conduits with a surface area to volume ratio of 0.834 (Table 2.1)

were prepared with NHS-PEGiO-Maleimide and tested to characterize how flow rate

affects cytokine filtration. Solutions of 5% (w/v) BSA in sterile 1X PBS (pH 7.4)

were enriched with 2000 pg/mL TNF-a and circulated through infliximab-modified

conduits using the experimental setup in Figure 2-2. Experiments were performed

with flow rates of 10, 20, 30 and 40 mL/min to determine the influence of flow rate

on cytokine elimination kinetics. TNF-a concentration was measured by ELISA at

0, 0.5, 1, 2, 3, and 4 hours.

The rate constant, k (min-1 ), was determined for each flow rate as a measure

of how fast cytokines were cleared from the solution. Assuming a one phase decay

model, each rate constant was determined using a nonlinear curve fit.

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2.5 Influence of Antibody Surface Packing Density

on Elimination Kinetics

Antibody-modified conduits with a surface area to volume ratio of 0.834 (Table 2.1)

were prepared with NHS-PEGIO-Maleimide, followed by the addition of infliximab us-

ing circulating antibody concentrations of 0.05, 0.5, 1.0, 1.5 and 2.0 mg/mL. Solutions

of 5% (w/v) BSA in sterile 1X PBS (pH 7.4) were enriched with 2000 pg/mL TNF-a

and circulated through infliximab-modified conduits at a flow rate of 20 mL/min, us-

ing the experimental setup in Figure 2-2. Samples were obtained at 0, 0.5, 1, 2, 3 and

4 hours, and TNF-a concentrations were determined by ELISA. The rate constant,

k, was determined for each antibody concentration used.

2.6 Influence of Surface Area to Volume Relation-

ships on Elimination Kinetics

Infliximab-modified conduits with various surface area to volume relationships were

prepared with NHS-PEGIO-Maleimide (Table 2.1). Solutions of 5% (w/v) BSA in

sterile IX PBS (pH 7.4) were enriched with 3000 pg/mL TNF-a and circulated at 20

mL/min through infliximab-modified conduits, using the experimental setup in Figure

2-2. Samples were obtained at 0, 0.5, 1, 2, 3 and 4 hours, and TNF-a concentrations

were measured by ELISA. The rate constant, k, was determined for each surface area

to volume ratio.

2.7 Influence of PEG Spacer Length on Elimina-

tion Kinetics

Infliximab-modified conduits with a surface area to volume ratio of 2.50 (Table 2.1)

were prepared with either NHS-PEGiO-Maleimide or NHS-PEG 3-Maleimide. Solu-

tions of 5% (w/v) BSA in sterile IX PBS (pH 7.4) were enriched with 80,000 pg/mL

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TNF-a and circulated through infliximab-modified conduits at a flow rate of 20

mL/min, using the experimental setup in Figure 2-2. Samples were obtained at

0, 0.5, 1, 2, 3, and 4 hours, and TNF-a concentrations were measured by ELISA. The

rate constant, k, was determined for each PEG spacer length.

2.8 Determination of Cytokine Binding Capacity

Infliximab-modified conduits were prepared with the highest performing characteris-

tics (2.50 surface area to volume ratio, NHS-PEGiO-Maleimide, 1 mg/mL infliximab

solution) to determine the maximum cytokine binding capacity for AMCs. Solutions

of 5% (w/v) BSA in sterile 1X PBS (pH 7.4) were enriched with 80,000 pg/mL TNF-

a to saturate AMCs and circulated through infliximab-modified conduits, using the

experimental setup in Figure 2-2. Samples were obtained at 0, 0.5, 1, 2, 3, 4, 5, 6, 7,

and 8 hours, and TNF-a concentrations were measured by ELISA.

Cytokine binding capacity was calculated using the following equation:

Capacity = ([Cytokine]initiai - [Cytokine]saturation) x Volumecirculating fluid (2.1)

2.9 Statistics

Statistical analyses were performed with Prism (Graph-Pad Software Inc., San Diego,

CA). All data were presented as mean SD. In Sections 3.2 - 3.4, one-way analysis

of variance (ANOVA) was performed to evaluate the significance of the data and

calculate the P value. In Section 3.5, unpaired Student t-tests were performed to

evaluate the significance of the data and calculate the P value.

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Chapter 3

Results

3.1 In Vitro Demonstration of Selective Cytokine

Filtration

AMCs performed selective cytokine filtration by only clearing the cytokine they were

designed to filter. AMCs modified with infliximab removed 82% of the TNF-a present

at the starting concentration after 4 hours, while VEGF-A levels remained unaffected

(Figure 3-1). AMCs modified with bevacizumab removed 78% of the VEGF-A present

at the starting concentration after 4 hours, while TNF-a levels remained unaffected

(Figure 3-1).

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E 3000

CL 2500

C

2000 '.

............m 1000e'-h..s

S 0 1 2 34Time (hours)

TNF-a (infliximab conduit)

TNF-a (bevacizumab conduit)

VEGF-A (infliximab conduit)

VEGF-A (bevacizumab conduit)

Figure 3-1: Type of cytokine filtered was determined by the selection of AMC surfaceantibody. Conduits modified with infliximab (monoclonal antibody against TNF-o)removed TNF-o from the circulation. Conduits modified with bevacizumab (mono-clonal antibody against VEGF-A) removed VEGF-A. Data were presented as mean

SD.

9

3.2 Influence of Flow Rate on Elimination Kinetics

Rate of TNF-a elimination was directly proportional to flow rate (Figure 3-2). Curve

fitting analysis revealed that, TNF-a elimination followed a single phase, exponential

decay with strong correlation (R 2 > 0.90 for all groups) (Figure 3-2A). The differ-

ences in k values were determined to be statistically significant (P = 0.0004, one-way

ANOVA) (Figure 3-2B). Higher flow rates were correlated with higher k values, sug-

gesting that faster and more favorable kinetics were achieved at higher flow rates

(Figure 3-2B).

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A -25 _ BE - 40 mL/min 1

i20 30 mUmin 0.8-- -.. ** 20 mUmin

0

150--- -- 10 mUmin .50.6-

1000- -0.4-

L 5 0.2

z ~.. II0.0-

0 1 2 3 4 0 10 20 30 40Time (hours) Flow Rate (mUmin)

Figure 3-2: TNF-n filtration by infliximab-modified conduits, where the BSA TNF-a solution was circulated through AMCs at varying flow rates. All conduits had asurface area to volume ratio of 0.834 (Table 2.1) and were prepared with NHS-PEGio-Maleimide and a 0.5 ing/mL infliximab solution. (A) TNF-a elimination profiles foreach group. (B) Exponential decay rate constants (k) for each group. Data were

presented as mean SD.

3.3 Influence of Antibody Surface Packing Density

on Elimination Kinetics

Rate of TNF-a elimination was affected by antibody surface packing density (Figure

3-3). Curve fitting analysis revealed that TNF-a elimination followed a single phase,

exponential decay (R2 = 0.64, 0.77, 0.44, 0.93, 0.89, 0.94 for 2.0 ng/mL, 1.5 ng/mL,

1.0 mg/mL, 0.5 mg/mL, 0.1 mg/mL, 0.05 mg/mL, respectively) (Figure 3-3A). The

differences in k values were determined to be statistically significant (P = 0.0104,

one-way ANOVA) (Figure 3-3B). AMC performance (i.e. rate of TNF-a elimina-

tion) was directly proportional to infliximab concentration used to prepare AMCs

for concentrations up to 1.0 mg/mL (Figure 3-3B). AMCs prepared with infliximab

concentrations of 1.0 ing/mL or higher had similar k values (Figure 3-3B).

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A B-J -- 2.0 mg/mL

30- 1.5 mg/mL'-'250 0 1.0 mg/mL= 200 0.5 mg/mL r

C 150 -- * 0.1mg/mL1 0.05 mg/mL .V

0 100500 *

0 1 2 3 4 0.0 0.5 1.0 1.5 2.0Time (hours) Infliximab Concentration (mg/mL)

Figure 3-3: TNF-o filtration by infliximab-modified conduits with a surface area tovolume ratio of 0.834 (Table 2.1). AMCs were prepared with NHS-PEGio-Maleimnide.Surface antibody addition was performed with solutions of varying infliximab con-centration. (A) TNF-o elimination profiles for each group. (B) Exponential decayrate constants (k) for each group. Data were presented as mean SD.

3.4 Influence of Surface Area to Volume Relation-

ships on Elimination Kinetics

Rate of TNF-o elimination was directly proportional to the ratio of AMC surface

area to volume (Figure 3-4). Curve fitting analysis revealed that TNF-a elimination

followed a single phase, exponential decay with strong correlation (R' > 0.93 for all

groups) (Figure 3-4A). The differences in k values were determined to be statistically

significant (P < 0.0001, one-way ANOVA) (Figure 3-4B). Higher surface area to

volume ratios were correlated with higher k values., suggesting that faster and more

favorable kinetics were achieved by AMCs with higher surface area to volume ratios

(Figure 3-4B).

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-- +*-- 2.50 mm- 1. -~1

- 0.4-..

---- 0.--- + -- I-7.' --- I.

A -4000

.

S30000

r 2000-

0 1000-

ILL0 0

B25 mm834 mm-1625 mm-1416 mm-1

4.

3-

1. *

0.0 0.5 1.0 1.5 2.0 2.5 3.0Surface Area to Volume Ratio (1/mm)

Figure 3-4: TNF-i filtration by infliximab-modified conduits with varying surfacearea to volume ratios. All conduits were prepared with NHS-PEG1 0 -Maleimide and a0.5 mig/niL infliximab solution. (A) TNF-o elimination profiles for each group. (B)Exponential decay rate constants (k) for each group. Data were presented as mean

SD.

3.5 Influence of PEG Spacer Length on Elimina-

tion Kinetics

AMC perfornanice was enhanced by increasing PEG spacer length (Figure 3-5). Curve

fitting analysis revealed that TNF-a elimination followed a single phase. exponential

decay with strong correlation (B2 = 0.73, 0.99 for 3 kDa PEG. 10 kDa PEG. respec-

tively) (Figure 3-5A). The difference in k values was determined to be statistically

significant (P = 0.0422, unpaired Student t-test) (Figure 3-5B). AMCs prepared with

NHS-PEG1 O-Maleimide (PEGio, 10 kDa PEG) had higher k values, suggesting that

faster and more favorable kinetics were achieved by AMCs with a longer PEG spacer

length (Figure 3-5B).

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I

1 2 3 4Time (hours)

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A- BE10000 - 3 kDa PEG 2.

.- e- 10 kDa PEGC 8000 . 1.0

6000 --.

.... . ...... .....4000- \ %

20000

0 1 2 3 4 0 5 10Time (hours) PEG Spacer Length (kDa)

Figure 3-5: TNF-o filtration by inflixinab-iodified conduits. Conduits with a surfacearea to volune ratio of 2.50 were prepared with varying PEG spacer lengths and a0.5 nig/mL inflixiinab solution. (A) TNF-i elimination profiles for each group. (B)Exponential decay rate constants (k) for each group. Data were presented as mean

SD.

3.6 Determination of Cytokine Binding Capacity

Ideal AICs (NHS-PEG o-Maleimide. 1.0 mg/nL antibody loading concentration,

2.50 surface area to voluie ratio) performed selective cytokine filtration until satu-

ration (Figure 3-6). Using Equation 2.1, the binding capacity for an ideal AMC was

found to be 394 47 pg/nun 2.

2'1000000.

C 800000 .1

0* 60000C

40000,0

20000-

0'*0 1 2 3 4 5 6 7 8

Time (hours)

Figure 3-6: TNF-o, filtration by ideal infliximab-modified conduits (2.50 surface areato volume ratio, NHS-PEGIO-Maleinide, 1 ng/niL infliximab solution). Cytokinebinding capacity for this ideal type of AMC was determined to be 394 47 pg/1i11112.Data were presented as mean SD.

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Chapter 4

Discussion

The purpose of this thesis was to demonstrate the concept of selective blood filtra-

tion, using cytokines as the model target. Ultimately, these data will be used to

develop a novel therapeutic approach to the treatment of sepsis, where circulating

blood is purified by selective removal of the signaling molecules that drive systemic

inflammation. Here, we successfully characterized the variables that influence AMC

performance.

Ideally, AMCs must fulfill the following criteria: they must (1) only bind the

targeted cytokine, and (2) be able to reduce clinically relevant cytokine levels in a

timely manner and maintain them at zero. Objective (1) was fulfilled by circulating

two types of cytokines through an AMC and observing only the removal of the type

of cytokine targeted by the antibody (Section 3.1). Objective (2) was fulfilled by

characterizing AMC variables and designing an ideal AMC to have quick elimination

kinetics and a large cytokine binding capacity (Sections 3.2 - 3.6).

AMCs were determined to be capable of selective cytokine filtration. Conduits

cleared targeted cytokines, whereas non-targeted cytokines remained unaffected and

in the circulating fluid. This proof of concept provides confidence that conjugating

any type of antibody to the inner surface of silicone circuits will allow for the rapid

removal of specific cytokines. By applying this concept and expanding this technology

to target other key cytokines involved in sepsis, we hope to be able to successfully

create a platform for immune modulation via selective cytokine filtration.

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Before moving forward with expansion and further testing, it was important to

characterize variables that affected AMC performance so that the highest performing

AMCs could be used for future experimentation. These variables included: fluid flow

rate, antibody loading concentration, tubing dimension, and PEG spacer length.

In varying flow rates, we observed that higher flow rates were correlated with

faster elimination kinetics. By analogy, solute clearance with traditional hemodialysis

is enhanced by increasing the flow rate of blood [16]. Given that the highest flow rate

tested (40 mL/min) achieved the best kinetics, a flow rate of 40 mL/min will be

used in future tests. 40 mL/min is equivalent to 100 mL/kg/min for a 400 gram rat,

and this normalized flow rate is in range with those achieved during extracorporeal

membrane oxygenation (ECMO) in children and infants (75 - 150 mL/kg/min) [17].

In varying antibody loading concentration, we discovered that AMC performance

was enhanced up to an antibody loading concentration of 1.0 mg/mL. Above 1.0

mg/mL, the kinetics remained the same. We hypothesize that this occurred because

either: (1) the AMCs became saturated with antibodies when circulated with con-

centrations of 1.0 mg/mL or higher, or (2) the AMCs became oversaturated with an-

tibodies when circulated with concentrations greater than 1.0 mg/mL, increasing the

extent of steric hindrance and preventing antibodies from favorably binding cytokines

[18]. In the future, AMCs will be prepared with an antibody loading concentration

of 1.0 mg/mL.

In varying AMC dimensions, we observed that AMCs with higher surface area to

volume ratios had faster elimination kinetics. This is most likely because AMCs with

a large surface area to volume ratio possess a large blood-circuit interface, allowing

their surface antibodies to be exposed to a greater proportion of the circulating fluid.

Given this information, future AMCs will be prepared with silicone tubing with a

surface area to volume ratio of 2.50. It is important to note, however, that changing

the surface area to volume ratio will also change the fluid dynamics of the system.

The resistance to blood flow is directly proportional to the length and inversely pro-

portional to the radius to the fourth power. This could possibly cause hemolysis due

to increased shear forces, as increased resistance has been shown to cause hemolysis in

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extracorporeal circuits [19]. Future in vitro studies will need to be conducted, using

blood as the circulating fluid, to determine whether AMCs with an aspect ratio of

2.50 cause hemolysis.

In varying PEG spacer length, we found that AMCs prepared with a 10 kDa PEG

spacer outperformed those prepared with a 3 kDa PEG spacer. The use of spacers to

distance immobilized antibodies from a surface has been shown to introduce greater

freedom of antibody motion [20], reduce steric interference [20,21], and improve sur-

face antibody orientation [21]. Additionally, it is known that the use of PEG spacers

increases antibody-antigen interactions by up to 90% and is dependent upon spacer

length [21]. Thus, it is not surprising that the longer spacer displayed faster elimina-

tion kinetics. Moving forward, AMCs will be prepared with NHS-PEGiO-Maleimide

(PEG10 , 10 kDa PEG).

Given these findings, ideal tubes (NHS-PEGio-Maleimide, 1.0 mg/mL antibody

loading concentration, 2.50 surface area to volume ratio, 40 mL/min flow rate) were

tested, and the total cytokine binding capacity was calculated. The total binding

capacity was determined to be 394 47 pg/mm 2 . This capacity will be helpful in

estimating the number of AMCs needed for use in various in vivo models.

We now know that selective cytokine filtration with AMCs yields rapid elimination

of a specific cytokine with the capacity to sustain elimination for prolonged periods.

Moving forward, we plan to modulate cytokine concentrations in vivo. While we

have demonstrated proof of concept, a crucial test of this technology will be to use

AMCs, singly or in combination, to regulate cytokine levels in rats rendered septic.

In testing our device in vivo, we hope to validate that customized AMC combinations

can provide precise temporal control over circulating cytokine concentrations, thereby

preventing organ failures and death.

Also, it is important to note that while we chose sepsis as the model disease for this

technology, the underlying mechanism being addressed is the systemic inflammatory

response syndrome (SIRS), which is a common mechanism for a variety of critical

illnesses (i.e. sepsis [2], ARDS [22], pancreatitis [23], trauma [23], burns [23]). Thus,

this device, by modulating single or multiple cytokines in a temporally controlled

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manner, has the potential to aid in the critical dissection of the impact of events in the

systemic inflammatory response and become a useful tool for scientific investigation

as well as therapeutic intervention.

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Chapter 5

Conclusion

In summary, antibody-modified conduits (AMCs) were capable of selective and timely

cytokine filtration. By characterizing variables that affect AMC performance, ideal

AMC conditions (NHS-PEGio-Maleimide, 1.0 mg/mL antibody loading concentra-

tion, 2.50 surface area to volume ratio, 40 mL/min flow rate) were determined for

later use downstream. Next steps include in vivo testing to demonstrate that AMCs

can modulate cytokine levels, singly or in combination, in a temporally controlled

manner in animals rendered septic.

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Chapter 6

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