Gene

therapy

for

arthritis

Arthritis

is

among

the

leading

causes

of

disability

in

the

developed

world

There

remains

no

cure

for

this

disease

and

the

current

treatments

are

only

modestly

effective

at

slowing

the

disease

's

progression

and

providing

symptomatic

relief

The

clinical

effectiveness

of

current

treatment

regimens

has

been

limited

by

short

half-lives

of

the

drugs

and

the

requirement

for

repeated

systemic

administration

Utilizing

gene

transfer

approaches

for

the

treatment

of

arthritis

may

overcome

some

of

the

obstacles

associated

with

current

treatment

strategies

The

present

review

examines

recent

developments

in

gene

therapy

for

arthritis

Delivery

strategies

gene

transfer

vectors

candidate

genes

and

safety

are

also

discussed

Introduction

Rheumatoid

arthritis

-LRB-

RA

-RRB-

is

the

most

common

inflammatory

disorder

affecting

approximately

of

the

North

American

adult

population

It

causes

significant

pathology

and

functional

impairment

in

affected

individuals

RA

is

a

multifactorial

disease

whose

main

risk

factors

include

genetic

susceptibility

sex

and

age

smoking

infectious

agents

hormones

diet

and

socioeconomic

and

ethnic

factors

-LSB-

-RSB-

Those

afflicted

by

RA

report

a

decrease

in

quality

of

life

measures

such

as

persistent

pain

functional

disability

fatigue

depression

and

an

inability

to

perform

daily

tasks

-LSB-

-RSB-

RA

is

also

a

significant

burden

on

the

health

care

system

averaging

between

per

patient

per

year

for

direct

and

indirect

costs

in

developed

countries

-LSB-

-RSB-

Although

the

pathogenesis

of

RA

is

not

completely

understood

specific

HLA-DR

genes

autoantibody

and

immune

complex

production

T

cell

antigen-specific

responses

networks

of

cytokine

production

and

a

hyperplastic

synovium

have

all

been

shown

to

play

a

role

RA

primarily

affects

diarthrodial

joints

of

the

hands

and

feet

These

joints

are

normally

lined

by

a

thin

cell

layer

-LRB-

cells

-RRB-

of

both

type

I

-LRB-

macrophage-like

-RRB-

and

type

II

-LRB-

fibroblast-like

-RRB-

synoviocytes

In

RA

the

joint

is

inflamed

and

the

synovium

becomes

hyperplastic

creating

a

pannus

of

synovial

tissue

comprised

of

T

cells

B

cells

mast

cells

dendritic

cells

macrophages

and

synoviocytes

that

invade

and

destroy

nearby

cartilage

and

bone

Neutrophils

accumulate

in

the

synovial

fluid

and

also

contribute

to

the

destructive

processes

-LSB-

-RSB-

Macrophages

and

fibroblast-like

synoviocytes

-LRB-

FLS

-RRB-

secrete

inflammatory

cytokines

such

as

TNFα

and

all

of

which

contribute

to

cartilage

and

bone

destruction

They

have

been

implicated

as

major

contributors

to

many

aspects

of

RA

including

inflammatory

cell

infiltration

fibrosis

and

T

cell

proliferative

responses

-LSB-

-RSB-

These

cytokines

are

thought

to

act

primarily

through

MAP

kinase

and

nuclear

factor

κB

-LRB-

NFκB

-RRB-

signaling

pathways

to

activate

transcription

factors

that

turn

on

genes

for

chemokines

and

cell

adhesion

molecules

along

with

extracellular

matrix

degrading

enzymes

like

matrix

metalloproteinases

-LRB-

MMPs

-RRB-

Chemokines

and

chemokine

receptors

have

also

been

linked

to

RA

-LSB-

-RSB-

Initial

treatment

strategies

for

RA

include

drugs

such

as

non-steroidal

anti-inflammatory

drugs

-LRB-

NSAIDs

-RRB-

and

glucocorticoids

While

providing

pain

relief

and

decreased

joint

swelling

these

drugs

are

unable

to

stop

the

progression

of

RA

-LSB-

-RSB-

This

led

to

the

use

of

small

molecules

like

methotrexate

that

were

demonstrated

to

slow

disease

progression

For

many

decades

these

disease-modifying

agents

of

rheumatic

disease

-LRB-

DMARDs

-RRB-

were

the

best

treatment

option

for

RA

In

recent

years

a

further

understanding

of

the

disease

process

has

led

to

the

development

of

biologic

DMARDs

primarily

aimed

at

neutralizing

the

effects

of

pro-inflammatory

cytokines

The

most

successful

agents

in

this

class

are

anti-TNF-α

molecules

and

blocking

agents

Based

on

improvement

criteria

set

forth

by

the

American

College

of

Rheumatology

-LRB-

ACR

-RRB-

these

drugs

are

more

effective

than

treatment

with

methotrexate

alone

Even

so

less

than

half

of

the

patients

show

improvement

of

at

least

in

their

ACR

scores

In

addition

the

half-life

of

these

drugs

is

relatively

short

and

they

require

frequent

systemic

administration

in

order

to

be

effective

-LSB-

-RSB-

Gene

transfer

strategies

have

the

potential

to

overcome

some

of

these

limitations

potentially

leading

to

increased

efficacy

and

decreased

frequency

of

administration

Gene

delivery

strategies

Although

the

majority

of

inflammation

in

RA

is

localized

to

the

joints

there

are

systemic

components

to

the

disease

Therefore

when

developing

treatment

strategies

one

must

consider

whether

the

therapy

should

be

delivered

locally

or

systemically

Local

administration

is

attractive

because

it

has

less

potential

for

side

effects

and

the

treatment

is

delivered

directly

to

the

joint

the

main

site

of

inflammation

However

systemic

features

of

the

disease

would

seem

to

be

left

untreated

Interestingly

several

researchers

have

observed

a

contralateral

effect

in

animal

models

of

local

gene

delivery

where

the

delivered

transgene

is

protective

not

only

to

the

injected

joint

but

also

to

distal

untreated

joints

-LSB-

-RSB-

This

effect

appears

to

be

independent

of

trafficking

of

modified

immune

cells

to

distal

joints

because

ex

vivo

modified

fibroblasts

alone

are

still

able

to

confer

a

contralateral

effect

-LSB-

-RSB-

It

is

also

independent

of

systemic

circulating

levels

of

transgene

and

non-specific

immunosuppression

and

instead

was

found

to

depend

on

a

complex

antigen-specific

mechanism

-LSB-

-RSB-

Systemic

delivery

typically

by

intravenous

administration

would

be

expected

to

have

a

broader

therapeutic

effect

but

is

also

associated

with

an

increase

in

side

effects

and

toxicity

Another

consideration

for

gene

transfer

is

whether

to

employ

in

vivo

or

ex

vivo

delivery

strategies

In

vivo

strategies

have

the

advantage

of

being

relatively

easy

and

less

expensive

In

addition

many

more

studies

have

been

performed

in

animal

models

looking

at

in

vivo

gene

delivery

Ex

vivo

strategies

although

expensive

and

time-consuming

have

the

advantage

of

being

able

to

treat

and

select

very

specific

cells

avoiding

the

possibility

that

the

gene

transfer

vector

could

genetically

modify

a

stem

cell

population

and

result

in

oncogene

activation

A

phase

I

clinical

trial

has

been

performed

using

a

retroviral

vector

to

deliver

receptor

antagonist

-LRB-

-RRB-

to

cultured

autologous

synovial

fibroblasts

-LSB-

-RSB-

The

cells

were

then

injected

into

the

RA

patients

joints

After

a

scheduled

arthroplasty

week

later

significant

expression

of

the

transgene

was

seen

in

the

injected

joints

No

adverse

events

were

reported

This

trial

was

initiated

following

previous

experiments

where

antagonists

of

both

and

TNF-α

were

delivered

to

autologous

cultured

rabbit

fibroblasts

ex

vivo

and

injected

into

arthritic

rabbit

knee

joints

with

significant

therapeutic

benefit

-LSB-

-RSB-

Most

ex

vivo

studies

use

fibroblast-like

synoviocytes

-LRB-

FLS

-RRB-

as

the

target

cell

These

cells

have

been

targeted

specifically

because

they

are

thought

to

be

directly

responsible

for

cartilage

destruction

and

drive

and

perpetuate

the

inflammatory

response

and

autoimmunity

-LSB-

-RSB-

The

disadvantages

of

using

this

cell

type

are

that

FLS

have

a

low

proliferation

rate

lack

highly

specific

surface

markers

and

are

a

non-homogenous

population

Future

studies

may

examine

other

strategies

including

gene

delivery

to

T

cells

dendritic

cells

muscle

cells

or

mesenchymal

stem

cells

-LSB-

-RSB-

Gene

transfer

vectors

Gene

transfer

vectors

can

be

broadly

categorized

into

two

groups

viral

and

non-viral

vectors

In

general

viral

vectors

tend

to

provide

for

longer-term

gene

expression

but

often

come

with

additional

safety

concerns

ranging

from

fears

of

generating

replication

competent

virus

during

vector

production

random

insertion

of

the

transgene

into

the

genome

following

treatment

or

development

of

a

harmful

immune

response

Plasmid

DNA

The

most

common

non-viral

vector

used

in

arthritis

studies

is

plasmid

DNA

Plasmid

DNA

can

be

delivered

by

liposomes

gene

gun

or

direct

injection

of

the

plasmid

The

use

of

plasmid

DNA

tends

to

be

less

toxic

and

less

immunogenic

than

the

use

of

viral

vectors

and

is

also

easy

and

relatively

inexpensive

to

produce

However

plasmid

DNA

often

leads

to

low

transfection

efficiency

and

short-term

expression

of

the

transgene

lasting

only

weeks

-LSB-

-RSB-

These

limitations

make

it

unlikely

that

local

delivery

of

plasmid

DNA

in

the

joint

will

be

successful

The

most

success

with

the

use

of

plasmid

DNA

in

gene

transfer

for

arthritis

has

been

garnered

through

delivery

of

transgenes

to

skeletal

muscle

Electrotransfer

of

soluble

TNF-α

receptor

I

variants

to

the

tibial-cranial

muscle

at

the

onset

of

collagen-induced

arthritis

-LRB-

CIA

-RRB-

led

to

a

decrease

in

the

clinical

and

histological

signs

of

disease

for

up

to

weeks

-LSB-

-RSB-

Similarly

plasmids

encoding

cDNA

for

other

anti-inflammatory

molecules

such

as

and

a

soluble

TNFR-Fc

fusion

protein

have

been

demonstrated

to

improve

both

macroscopic

and

microscopic

scores

of

CIA

when

delivered

intramuscularly

-LSB-

-RSB-

Plasmid

encoding

TGF-β

delivered

to

skeletal

muscle

delayed

progression

of

streptococcal

cell

wall

induced

arthritis

when

administered

at

the

peak

of

the

acute

phase

and

virtually

eliminated

subsequent

inflammation

and

arthritis

when

given

at

the

beginning

of

the

chronic

phase

of

the

disease

-LSB-

-RSB-

Intramuscular

injections

of

plasmids

encoding

immuno-modulatory

molecules

such

as

viral

and

soluble

complement

receptor

type

I

have

given

similar

results

-LSB-

-RSB-

Intramuscular

delivery

of

a

plasmid

encoding

and

inhibitor

of

matrix

metalloproteinases

completely

abolished

the

development

of

arthritis

in

a

rat

adjuvant-induced

arthritis

model

-LSB-

-RSB-

Intravenous

delivery

of

a

plasmid

encoding

the

heparin-binding

domain

of

fibronectin

inhibited

leukocyte

recruitment

and

decreased

inflammation

in

CIA

-LSB-

-RSB-

Intra-dermal

injection

of

plasmid

encoding

and

intra-peritoneal

injection

of

plasmid

liposome

complexes

have

also

been

demonstrated

to

delay

onset

and

progression

of

CIA

-LSB-

-RSB-

The

liposome

delivered

DNA

was

able

to

maintain

expression

for

only

days

after

injection

significantly

less

than

the

intramuscular

studies

mentioned

above

Recently

the

use

of

chitosan

a

polycationic

polysaccharide

derived

from

crustacean

shells

has

been

shown

to

act

as

an

efficient

gene

carrier

to

rabbit

knee

joints

both

in

vitro

and

in

vivo

-LSB-

-RSB-

Other

non-viral

vectors

Other

non-viral

gene

delivery

systems

that

have

potential

in

the

treatment

of

RA

are

the

artificial

chromosome

expression

-LRB-

ACE

-RRB-

system

and

the

sleeping

beauty

-LRB-

SB

-RRB-

transposon

system

The

ACE

system

is

attractive

because

it

is

non-integrating

and

can

provide

stable

and

long-term

gene

expression

of

one

or

multiple

genes

A

feasibility

study

was

recently

performed

in

a

Mycobacterium

tuberculosis

rat

arthritis

model

which

demonstrated

that

rat

skin

fibroblasts

could

be

modified

ex

vivo

to

express

a

reporter

gene

from

an

artificial

chromosome

These

cells

when

subsequently

injected

into

rat

joints

demonstrated

engraftment

into

the

synovial

tissue

microarchitecture

and

detectable

transgene

expression

The

ACE

system

did

not

induce

local

inflammation

at

the

injection

site

that

is

often

associated

with

viral

vector

administration

-LSB-

-RSB-

The

sleeping

beauty

transposon

system

melds

the

advantages

of

both

viral

and

non-viral

vectors

allowing

for

both

integration

into

the

genome

and

long

term

expression

No

studies

have

yet

been

performed

in

arthritis

models

using

the

sleeping

beauty

transposon

system

but

success

has

been

found

in

both

cancer

and

hemophilia

models

suggesting

that

it

might

be

have

potential

to

successfully

treat

arthritis

as

well

-LSB-

-RSB-

Viral

vectors

are

by

far

the

most

widely

used

vectors

for

delivering

transgenes

in

arthritic

animal

models

-LSB-

-RSB-

There

are

several

different

viral

vectors

that

have

been

examined

for

use

in

gene

transfer

for

arthritis

including

adenovirus

retrovirus

adeno-associated

virus

-LRB-

AAV

-RRB-

and

lentivirus

each

with

their

respective

advantages

and

disadvantages

Adenovirus

Adenovirus

is

a

non-encapsidated

double-stranded

DNA

virus

that

can

infect

non-dividing

cells

and

can

be

produced

at

high

titers

Many

gene-therapy

studies

have

been

performed

with

this

vector

but

it

has

several

limitations

that

may

prevent

it

from

being

successful

in

the

clinic

The

high

prevalence

of

neutralizing

antibodies

may

prevent

successful

administration

or

re-administration

Injected

adenovirus

also

causes

a

significant

inflammatory

immune

response

which

is

a

safety

concern

In

addition

adenovirus

vectors

typically

only

allow

for

weeks

of

transgene

expression

which

would

limit

its

long-term

efficacy

Some

improvements

to

adenoviral

vectors

have

recently

been

made

in

an

effort

to

improve

delivery

of

transgenes

to

the

synovium

FLS

lack

the

coxsackie-adenovirus

receptor

-LRB-

CAR

-RRB-

and

are

not

efficiently

transduced

by

adenovirus

By

modifying

the

fiber

knobs

on

the

virus

adenoviral

transgene

delivery

to

synoviocytes

and

synovium

was

improved

dramatically

-LSB-

-RSB-

Other

recent

improvements

include

the

development

of

an

adenoviral

vector

with

an

inflammation

inducible

promoter

-LSB-

-RSB-

This

would

allow

expression

of

the

transgene

during

active

disease

but

expression

would

turn

off

once

inflammation

was

brought

under

control

Retrovirus

Retroviruses

mostly

derived

from

the

Moloney

murine

leukemia

virus

have

a

relatively

simple

genome

and

structure

They

are

enveloped

viruses

and

contain

two

identical

copies

of

their

RNA

genome

The

key

feature

of

the

retroviral

life

cycle

is

the

ability

of

the

RNA

genome

to

be

reverse

transcribed

into

double-stranded

DNA

which

can

then

randomly

integrate

into

the

genome

They

have

been

mostly

used

in

ex

vivo

studies

and

are

desirable

vectors

for

several

reasons

They

can

provide

for

long-term

stable

expression

and

their

integration

into

the

genome

makes

it

possible

to

permanently

correct

a

genetic

defect

-LSB-

-RSB-

For

arthritis

in

particular

the

inflamed

synovium

appears

to

be

more

susceptible

to

uptake

of

the

virus

-LSB-

-RSB-

The

drawbacks

to

retroviral

vectors

are

that

they

only

infect

non-dividing

cells

and

are

produced

at

low

titers

The

fact

that

these

vectors

integrate

into

the

genome

randomly

is

also

a

concern

In

fact

in

a

recent

clinical

trial

in

France

using

a

retrovirus

to

correct

an

X-linked

SCID

disorder

out

of

children

developed

leukemia

after

the

vector

inserted

in

or

near

a

known

oncogene

As

a

result

similar

trials

in

the

U.S.

for

this

disorder

have

been

halted

until

more

information

can

be

gathered

-LSB-

-RSB-

Future

improvements

to

these

vectors

including

the

development

of

self-inactivating

vectors

which

contain

no

retroviral

promoter

or

enhancer

elements

and

use

of

vectors

from

non-oncogenic

retroviruses

will

hopefully

make

them

safer

for

clinical

use

-LSB-

-RSB-

Lentivirus

Lentivirus

vectors

are

derived

from

retroviral

vectors

but

have

the

advantage

of

infecting

non-dividing

cells

The

most

commonly

studied

lentiviral

vectors

are

derived

from

either

human

immunodeficiency

virus

-LRB-

HIV

-RRB-

or

feline

immunodeficiency

virus

-LRB-

FIV

-RRB-

although

equine

anemia

infectious

virus

and

visna

virus

have

also

been

examined

-LSB-

-RSB-

The

primary

concern

with

HIV

vectors

is

safety

In

contrast

FIV

is

non-pathogenic

in

humans

and

does

not

cause

serologic

conversion

-LSB-

-RSB-

Using

an

FIV

vector

TNF-α

was

transduced

into

primary

human

FLS

with

high

efficiency

When

injected

into

knees

of

SCID

mice

these

cells

induced

cell

proliferation

and

caused

bone

and

joint

destruction

-LSB-

-RSB-

A

replication-defective

HIV

vector

encoding

endostatin

was

injected

into

joints

of

TNF-α

transgenic

mice

and

was

shown

to

decrease

synovial

blood

vessel

density

and

decrease

the

overall

arthritis

index

-LSB-

-RSB-

Similarly

intra-articular

expression

of

angiostatin

inhibited

the

progression

of

CIA

in

mice

-LSB-

-RSB-

A

study

examining

a

VSV-G

pseudo-typed

HIV

vector

which

has

increased

host

range

and

stability

demonstrated

that

a

transgene

could

be

efficiently

delivered

to

the

synovium

of

rat

knee

joints

with

transgene

expression

lasting

up

to

weeks

in

immunocompromised

animals

-LSB-

-RSB-

AAV

One

of

the

most

promising

gene

transfer

vectors

is

AAV

which

is

a

small

non-enveloped

single-stranded

DNA

virus

with

broad

tissue

tropism

It

belongs

to

the

Parvoviridae

family

and

has

a

kb

genome

AAV

normally

requires

adenovirus

or

herpesvirus

to

produce

active

infection

Several

serotypes

have

been

identified

in

primates

with

being

the

prototype

for

most

gene

transfer

studies

Heparan

sulfate

proteoglycan

has

been

identified

as

the

primary

attachment

receptor

for

AAV

with

fibroblast

growth

factor

receptor

and

integrin

αvβ5

acting

as

co-receptors

-LSB-

-RSB-

Although

little

is

known

about

the

details

of

AAV

infection

some

of

the

basic

mechanisms

have

been

described

The

virus

enters

the

cell

by

receptor-mediated

endocytosis

Acidification

of

late

endosomes

leads

to

AAV

release

into

the

cytosol

with

subsequent

translocation

of

the

virus

to

a

perinuclear

region

-LSB-

-RSB-

The

virus

then

enters

the

nucleus

by

an

unknown

mechanism

that

is

independent

of

the

nuclear

pore

complex

-LSB-

-RSB-

Following

uncoating

the

single-stranded

genome

is

converted

to

a

double

strand

and

the

viral

DNA

integrates

into

chromosome

-LRB-

locus

-RRB-

in

a

site-specific

manner

-LSB-

-RSB-

AAV

is

an

attractive

vector

for

gene

transfer

studies

for

several

reasons

It

has

been

shown

to

deliver

transgenes

to

a

wide

variety

of

tissues

has

low

immunogenicity

and

mediates

long-term

gene

expression

-LSB-

-RSB-

Recombinant

replication

incompetent

AAV

vectors

have

been

designed

that

lack

the

Rep

genes

which

are

required

for

integration

so

long-term

expression

with

these

vectors

is

thought

to

be

mediated

by

episomal

viral

DNA

-LSB-

-RSB-

In

addition

AAV

vectors

have

been

designed

that

are

able

to

package

double-stranded

viral

genomes

bypassing

a

rate-limiting

step

of

viral

transduction

-LRB-

second-strand

synthesis

-RRB-

and

allowing

rapid

and

highly

efficient

transduction

both

in

vitro

and

in

vivo

-LSB-

-RSB-

Several

studies

have

demonstrated

the

efficacy

of

AAV

vectors

in

arthritis

models

Primary

and

recurrent

arthritis

were

suppressed

following

a

single

injection

of

AAV

encoding

into

knee

joints

of

rats

with

LPS-induced

arthritis

Surprisingly

disease-regulated

expression

of

the

transgene

was

observed

-LSB-

-RSB-

Our

laboratory

has

recently

observed

a

similar

phenomenon

in

in

vitro

cultured

FLS

infected

with

AAV

in

which

inflammatory

cytokines

can

increase

transgene

expression

in

these

cells

in

a

regulatable

manner

Protesosome

inhibition

has

also

been

shown

to

enhance

AAV

transduction

of

human

synoviocytes

both

in

vitro

and

in

vivo

-LSB-

-RSB-

AAV

encoding

soluble

TNF-α

receptor

type

I

decreased

synovial

cell

hyperplasia

and

cartilage

and

bone

destruction

in

human

TNF-α

transgenic

mice

injected

intra-articularly

with

the

virus

-LSB-

-RSB-

Intra-articular

or

peri-articular

delivery

of

AAV

encoding

in

CIA

mice

was

also

shown

to

decrease

paw

swelling

protect

from

cartilage

destruction

and

delay

the

onset

of

CIA

-LSB-

-RSB-

A

transgene

delivered

by

AAV

under

control

of

a

tetracycline

inducible

promoter

decreased

the

incidence

and

severity

of

CIA

on

a

macroscopic

radiologic

and

histologic

level

-LSB-

-RSB-

More

recently

angiostatin

an

anti-angiogenic

molecule

was

demonstrated

to

efficiently

decrease

development

of

CIA

in

the

treated

joint

when

delivered

by

AAV

-LSB-

-RSB-

AAV

vectors

are

in

clinical

trials

for

the

treatment

of

cystic

fibrosis

and

hemophilia

B

and

preliminary

results

are

promising

-LSB-

-RSB-

Targeted

Genetics

Corporation

-LRB-

Seattle

WA

-RRB-

is

currently

conducting

a

phase

I

clinical

trial

-LRB-

identifier

-RRB-

to

assess

the

safety

of

using

an

vector

to

deliver

a

soluble

TNF

receptor-Fc

fusion

gene

in

RA

Gene

transfer

strategies

inhibition

Several

gene

transfer

strategies

have

been

aimed

at

neutralizing

the

effects

of

communicates

with

many

different

cell

types

in

the

joint

Its

action

on

these

cells

leads

to

emigration

of

blood

cells

to

the

synovium

increased

cartilage

destruction

and

increased

production

of

other

chemokines

and

pro-inflammatory

mediators

by

macrophages

B

cells

and

T

cells

-LSB-

-RSB-

Neutralization

of

this

key

cytokine

has

proven

beneficial

in

the

treatment

of

RA

Several

animal

models

support

using

gene

transfer

to

block

the

effects

of

this

cytokine

Primary

and

recurrent

arthritis

were

suppressed

following

a

single

injection

of

AAV

encoding

into

knee

joints

of

rats

with

LPS-induced

arthritis

-LSB-

-RSB-

Adenoviral

vectors

encoding

proved

more

effective

than

soluble

type

I

TNF

receptor-IgG

fusion

protein

at

reducing

cartilage

matrix

degradation

and

decreasing

leukocyte

infiltration

into

the

joint

space

of

rabbits

with

antigen-induced

arthritis

-LSB-

-RSB-

Rabbit

synovial

fibroblasts

modified

ex

vivo

using

a

retrovirus

encoding

demonstrated

a

chondroprotective

and

mild

anti-inflammatory

effect

when

injected

back

into

the

joint

after

onset

of

antigen-induced

arthritis

-LSB-

-RSB-

This

led

to

a

phase

I

clinical

trial

using

a

retroviral

vector

to

deliver

to

cultured

human

autologous

synovial

fibroblasts

The

cells

were

then

injected

into

RA

patient

joints

After

a

scheduled

arthroplasty

week

later

significant

expression

of

the

transgene

was

seen

in

the

injected

joints

and

no

adverse

events

were

reported

-LSB-

-RSB-

Intramuscular

injection

of

plasmid

DNA

encoding

has

also

been

shown

to

decrease

paw

swelling

and

arthritis

incidence

in

a

CIA

mouse

model

Reduced

synovitis

and

cartilage

erosion

were

also

seen

-LSB-

-RSB-

In

a

rat

model

of

bacterial

cell

wall-induced

arthritis

rat

synoviocytes

were

modified

ex

vivo

using

a

retroviral

vector

to

express

When

injected

into

ankle

joints

prior

to

reactivation

of

arthritis

a

decreased

severity

of

arthritis

and

attenuated

destruction

of

cartilage

and

bone

was

observed

-LSB-

-RSB-

In

a

SCID

mouse

model

human

RA

FLS

transduced

with

retrovirus

encoding

co-implanted

with

normal

human

cartilage

was

able

prevent

progressive

cartilage

degradation

compared

to

controls

-LSB-

-RSB-

mouse

fibroblasts

transfected

with

plasmid

encoding

were

able

to

prevent

the

onset

of

CIA

and

cartilage

destruction

when

injected

into

knee

joints

of

CIA

mice

-LSB-

-RSB-

Similar

effects

on

arthritis

were

seen

in

a

rabbit

model

of

antigen-induced

arthritis

in

which

a

retroviral

vector

carrying

the

gene

was

used

to

transduce

rabbit

fibroblasts

ex

vivo

with

subsequent

injection

of

the

cells

into

the

knee

joint

-LSB-

-RSB-

More

recently

the

soluble

form

of

receptor

accessory

protein

-LRB-

-RRB-

was

delivered

to

CIA

mice

either

using

an

adenoviral

vector

or

by

injection

of

plasmid

transfected

cells

In

both

instances

a

profound

prophylactic

effect

on

the

development

of

CIA

was

observed

-LSB-

-RSB-

TNF-α

inhibition

TNF-α

is

another

pro-inflammatory

cytokine

that

plays

a

key

role

in

the

pathogenesis

of

RA

Many

of

its

effects

overlap

those

of

listed

above

Currently

therapies

aimed

at

neutralizing

this

cytokine

represent

the

most

successful

treatment

strategies

for

RA

Current

regimens

involve

receiving

injections

-LRB-

etanercept

-RRB-

or

infusions

-LRB-

infliximab

-RRB-

every

or

weeks

respectively

Gene

transfer

strategies

have

the

potential

to

provide

longer-term

control

and

may

also

be

delivered

locally

rather

than

systemically

potentially

minimizing

treatment

side

effects

Several

studies

in

animal

models

have

been

performed

After

one

injection

at

onset

of

CIA

intramuscular

electrotransfer

of

plasmids

encoding

soluble

TNF

receptor

I

variants

led

to

a

decrease

in

clinical

and

histological

signs

of

CIA

-LSB-

-RSB-

Expression

lasted

up

to

weeks

and

was

as

least

as

efficient

as

repeated

injections

of

the

recombinant

protein

etanercept

in

controlling

the

disease

A

similar

study

using

a

retroviral

vector

to

deliver

the

transgene

peri-articularly

saw

similar

results

and

also

observed

a

decrease

in

systemic

levels

of

antibodies

to

collagen

type

II

-LSB-

-RSB-

Electrotransfer

of

a

plasmid

encoding

a

soluble

TNF

receptor

Fc

fusion

protein

was

also

beneficial

in

a

CIA

model

and

was

associated

with

a

decrease

in

the

levels

of

and

in

the

paw

-LSB-

-RSB-

Other

studies

using

electrotransfer

or

intramuscular

injection

of

a

plasmid

with

a

doxycycline-regulated

promoter

to

control

expression

of

a

dimeric

soluble

TNF

receptor

II

molecule

saw

a

therapeutic

effect

on

CIA

only

when

doxycycline

was

administered

-LSB-

-RSB-

In

TNF-α

transgenic

mice

intra-articular

delivery

of

soluble

TNF

receptor

I

by

adeno-associated

virus

led

to

a

decrease

in

synovial

cell

hyperplasia

and

cartilage

and

bone

destruction

-LSB-

-RSB-

Similarly

encoding

sTNFRI-Ig

was

also

able

to

decrease

paw

swelling

in

a

rat

AIA

model

when

expression

was

under

control

of

an

inflammation

responsive

promoter

but

interestingly

not

if

expression

was

under

control

of

the

CMV

promoter

-LSB-

-RSB-

Splenocytes

from

arthritic

mice

can

passively

transfer

collagen

type

II-induced

arthritis

when

injected

into

SCID

recipients

If

these

splenocytes

were

first

modified

ex

vivo

using

retroviral

vectors

to

express

soluble

tumor

necrosis

factor

receptor

the

SCID

recipients

did

not

develop

arthritis

bone

erosion

or

joint

inflammation

-LSB-

-RSB-

Delivery

of

a

rat

TNF

receptor

Fc

fusion

protein

in

a

streptococcal

cell

wall-induced

arthritis

model

by

either

plasmid

or

local

or

systemic

administration

of

AAV

vectors

encoding

the

molecule

led

to

decreased

inflammation

pannus

formation

bone

and

joint

destruction

and

mRNA

expression

of

joint

pro-inflammatory

cytokines

-LSB-

-RSB-

Adenoviral

delivery

of

a

soluble

TNF

receptor

type

I-IgG

fusion

protein

directly

to

rabbit

knees

with

antigen-induced

arthritis

reduced-cartilage

matrix

degradation

and

decreased

leukocyte

infiltration

into

the

joint

space

especially

when

administered

in

conjunction

with

a

soluble

type

I

receptor-IgG

fusion

protein

-LSB-

-RSB-

The

above

animal

model

data

has

led

to

the

initiation

of

a

phase

I

clinical

trial

using

AAV

vectors

to

deliver

soluble

TNF

Receptor

Fc

fusion

protein

-LRB-

Targeted

Genetics

Corporation

-RRB-

inhibition

is

a

pro-inflammatory

cytokine

that

is

overexpressed

in

the

synovium

of

RA

patients

and

correlates

with

inflammation

Elevated

levels

of

this

cytokine

are

also

observed

in

serum

and

synovial

fluid

Overexpression

of

an

protein

using

an

adenoviral

vector

was

able

to

ameliorate

arthritis

in

a

CIA

model

indicating

neutralization

of

may

be

an

effective

target

in

the

future

treatment

of

RA

-LSB-

-RSB-

Immune

deviation

Previously

an

imbalance

between

and

cytokines

was

thought

to

play

a

role

in

the

pathogenesis

of

several

inflammatory

diseases

including

RA

cells

secrete

cytokines

like

IFN-γ

that

promote

a

pro-inflammatory

environment

while

cytokines

secrete

cytokines

like

and

that

down-regulate

activity

It

was

previously

felt

that

overproduction

of

cytokines

contributed

significantly

to

the

pathogenesis

of

RA

More

recently

a

new

subset

of

T

cells

termed

cells

have

been

identified

-LSB-

-RSB-

These

cells

produce

among

other

cytokines

a

pro-inflammatory

cytokine

previously

implicated

in

the

pathogenesis

of

CIA

-LSB-

-RSB-

Dysregulation

of

cells

and

overproduction

has

been

implicated

in

the

pathogenesis

of

inflammatory

diseases

and

the

development

of

severe

autoimmunity

In

fact

the

pathogenesis

of

RA

may

be

more

directly

related

to

an

imbalance

between

cells

and

regulatory

T

cells

than

an

imbalance

between

and

cells

-LSB-

-RSB-

Regardless

of

the

exact

mechanism

several

strategies

aimed

at

immune

deviation

have

been

successful

in

animal

models

of

arthritis

and

are

outlined

below

inhibits

activated

monocytes/macrophages

from

secreting

a

variety

of

pro-inflammatory

molecules

A

possible

role

for

this

cytokine

in

the

pathogenesis

of

RA

was

observed

when

adenoviral

delivery

of

to

RA

synovial

tissues

explants

led

to

a

decrease

in

TNF-α

and

when

compared

to

controls

-LSB-

-RSB-

Subsequent

studies

demonstrated

that

adenoviral

delivery

of

directly

to

ankle

joints

in

a

rat

antigen-induced

arthritis

model

significantly

decreased

paw

size

bony

destruction

vascularization

inflammatory

cell

infiltration

and

inflammatory

cytokine

production

-LSB-

-RSB-

overexpression

during

immune-complex-mediated

arthritis

significantly

decreased

chondrocyte

death

and

MMP

mediated

cartilage

destruction

despite

the

presence

of

enhanced

inflammation

-LSB-

-RSB-

Using

to

skew

the

cytokine

profile

towards

or

perhaps

by

inhibiting

cell

production

has

also

proven

successful

Adenoviral

delivery

of

to

RA

synovial

tissue

explants

demonstrated

decrease

TNF-α

and

in

the

cultured

medium

-LSB-

-RSB-

Intra-articular

delivery

of

adenoviral

vectors

encoding

to

CIA

mice

led

to

an

enhanced

onset

of

inflammation

but

less

chondrocyte

death

and

cartilage

and

bone

erosion

Proteoglycan

synthesis

was

enhanced

and

there

was

decreased

MMP

activity

-LSB-

-RSB-

cathepsin

K

and

osteoprotegrin

ligand

mRNA

levels

were

also

reduced

-LSB-

-RSB-

Kim

et

al.

observed

similar

effects

on

CIA

upon

local

and

systemic

administration

of

adenoviral

vectors

encoding

-LSB-

-RSB-

AAV-mediated

delivery

of

has

also

prove

beneficial

in

CIA

models

-LSB-

-RSB-

Electrotransfer

of

an

encoding

plasmid

prior

to

CIA

onset

decreased

synovitis

and

cartilage

destruction

with

an

associated

decrease

in

in

the

paw

and

an

increased

ratio

-LSB-

-RSB-

Similar

results

were

also

seen

using

either

gene

gun

delivery

or

intra-dermal

administration

of

plasmid

encoding

-LSB-

-RSB-

Both

retroviral

and

adenoviral

delivery

of

in

a

rat

antigen-induced

arthritis

model

had

beneficial

effects

-LSB-

-RSB-

Cell-based

therapies

that

deliver

in

arthritis

models

have

also

been

successful

Injection

of

fibroblast

transfected

with

plasmid

encoding

decreased

histologic

evidence

of

joint

inflammation

and

destruction

in

a

CIA

model

-LSB-

-RSB-

Likewise

collagen

type

II

pulsed

antigen

presenting

cells

engineered

to

secret

down-regulated

CIA

-LSB-

-RSB-

is

an

anti-inflammatory

cytokine

that

has

demonstrated

benefit

in

several

animal

models

of

RA

Either

intramuscular

administration

via

electrotransfer

or

intra-dermal

injection

of

plasmid

encoding

had

beneficial

effects

on

CIA

-LSB-

-RSB-

Similarly

systemic

administration

of

a

plasmid

liposome

mixture

decreased

signs

of

CIA

after

a

single

intra-peritoneal

injection

-LSB-

-RSB-

Viral

-LRB-

-RRB-

is

homologous

to

human

and

mouse

but

while

retaining

its

immunosuppressive

function

it

lacks

many

of

the

immunostimulatory

properties

of

and

therefore

may

be

a

superior

treatment

option

An

adenoviral

vector

encoding

was

able

to

decrease

CIA

when

delivered

locally

or

systemically

-LSB-

-RSB-

Electrotransfer

of

viral

decreased

histologic

evidence

of

arthritis

in

an

arthrogen

collagen-induced

arthritis

model

and

was

associated

with

decreased

TNF-α

and

transcripts

in

the

joint

-LSB-

-RSB-

A

tet-inducible

transgene

delivered

by

AAV

was

able

to

decrease

macroscopic

radiology

and

histologic

signs

of

CIA

only

when

doxycycline

was

administered

-LSB-

-RSB-

TGF-β

is

a

pleiotropic

cytokine

with

many

different

effects

on

many

different

cell

types

and

has

been

suggested

of

playing

a

role

in

RA

While

some

of

its

effects

like

immunosuppression

would

appear

to

be

beneficial

for

RA

it

has

also

been

associated

with

pro-inflammatory

activity

Not

surprisingly

data

from

animal

models

using

gene

transfer

support

both

possibilities

making

its

true

role

in

RA

difficult

to

decipher

Splenocytes

from

CIA

mice

were

isolated

and

infected

ex

vivo

with

a

retroviral

vector

encoding

TGF-β

These

cells

were

then

injected

in

the

intra-peritoneal

cavity

days

after

arthritis

onset

Without

TGF-β

expression

an

exacerbation

of

arthritis

is

normally

observed

However

TGF-β

expressing

splenocytes

were

able

to

inhibit

this

exacerbation

and

also

resulted

in

a

decrease

in

activity

and

a

transient

reduction

in

anti-collagen

type

II

antibodies

-LSB-

-RSB-

In

a

rat

streptococcal

cell

wall-induced

arthritis

model

intramuscular

delivery

of

plasmid

encoding

TGF-β

showed

significant

decreases

in

inflammatory

cell

infiltration

pannus

formation

bone

and

joint

destruction

and

inflammatory

cytokine

production

-LSB-

-RSB-

In

contrast

to

the

above

reports

another

study

found

that

injection

of

adenovirus

encoding

TGF-β

into

the

knees

of

rabbits

with

antigen-induced

arthritis

resulted

in

significant

pathology

in

the

knee

joint

and

surrounding

tissue

suggesting

that

TGF-β

therapy

may

not

be

suitable

for

treating

arthritis

in

some

models

-LSB-

-RSB-

fusion

protein

binds

to

the

co-stimulatory

molecules

and

present

on

antigen-presenting

cells

and

blocks

interactions

resulting

in

decreased

T

cell

activation

It

has

been

shown

to

ameliorate

several

experimental

autoimmune

diseases

including

CIA

A

single

intravenous

injection

of

an

adenovirus

encoding

fusion

protein

suppressed

established

CIA

as

least

as

efficiently

as

repeated

injections

of

monoclonal

antibody

to

Pathogenic

cellular

and

humoral

responses

were

also

diminished

in

adenoviral

vector

treated

group

as

compared

to

antibody

treated

and

control

groups

-LSB-

-RSB-

CIA

could

also

be

inhibited

both

histologically

and

clinically

by

intra-articular

administration

of

a

low

dose

of

adenovirus

encoding

fusion

protein

-LSB-

-RSB-

Promoting

apoptosis

One

of

the

key

features

of

RA

is

the

increased

cellularity

of

the

synovial

lining

leading

to

pannus

formation

which

has

been

shown

to

contribute

to

cartilage

invasiveness

and

bone

destruction

Promoting

synovial

apoptosis

has

been

suggested

as

a

treatment

strategy

for

RA

In

a

rabbit

model

of

arthritis

intra-articular

adenoviral

delivery

of

TNF-related

apoptosis-inducing

ligand

-LRB-

TRAIL

-RRB-

was

able

to

increase

apoptosis

in

the

synovial

cell

lining

decrease

inflammatory

cell

infiltration

and

promote

new

matrix

deposition

-LSB-

-RSB-

Mice

injected

with

collagen

type

II-pulsed

antigen

presenting

cells

engineered

to

express

TRAIL

under

control

of

a

doxycycline

inducible

promoter

decreased

the

incidence

of

CIA

and

infiltration

of

T

cells

in

the

joint

in

the

presence

of

doxycycline

In

situ

TUNEL

staining

demonstrated

TRAIL-induced

apoptosis

of

activated

T

cells

in

the

spleen

-LSB-

-RSB-

Modulation

of

TRAIL

receptor

expression

on

RA

synoviocytes

has

also

been

suggested

as

a

gene

therapy

strategy

for

the

treatment

of

RA

-LSB-

-RSB-

Injection

of

adenovirus-expressing

Fas

ligand

-LRB-

FasL

-RRB-

into

joints

of

CIA

mice

induced

apoptosis

and

ameliorated

CIA

IFN-γ

production

by

collagen-specific

T

cells

was

also

reduced

-LSB-

-RSB-

Ex

vivo

modified

T

cells

engineered

to

express

FasL

were

injected

into

human

RA

synovial

tissue

that

had

been

implanted

in

SCID

mice

Analysis

of

the

tissue

following

treatment

demonstrated

that

synoviocytes

and

mononuclear

cells

present

in

the

tissue

had

been

eliminated

by

apoptosis

through

a

Fas/FasL

interaction

-LSB-

-RSB-

Similar

results

were

observed

when

adenovirus

encoding

FasL

was

injected

directly

into

the

implanted

tissue

-LSB-

-RSB-

Dendritic

cells

modified

by

adenoviral

vectors

to

express

FasL

were

able

to

suppress

CIA

when

systemically

injected

and

also

demonstrated

decreased

IFN-γ

production

from

spleen-derived

lymphocytes

and

decreased

T-cell

proliferation

in

response

to

collagen

stimulation

-LSB-

-RSB-

Fas-associated

death

domain

protein

-LRB-

FADD

-RRB-

also

plays

a

key

role

in

Fas-mediated

apoptosis

of

synovial

cells

It

was

found

that

adenoviral

vectors

expressing

FADD

could

induce

apoptosis

in

synoviocytes

both

in

vitro

and

in

vivo

suggesting

that

this

strategy

may

be

effective

in

the

treatment

of

RA

-LSB-

-RSB-

Anti-angiogenesis

Increased

cellularity

of

the

synovial

lining

is

also

associated

with

neo-vascularization

in

the

local

environment

of

the

joint

This

angiogenesis

is

necessary

for

the

development

and

maintenance

of

the

pannus

and

also

provides

nutrients

required

for

the

survival

and

proliferation

of

infiltrating

inflammatory

cells

-LSB-

-RSB-

A

peptide

targeted

to

the

integrins

present

in

the

inflamed

synovium

and

associated

with

angiogenesis

was

fused

to

an

anti-apoptotic

peptide

Systemic

administration

of

this

fusion

peptide

in

a

CIA

model

resulted

in

decreased

clinical

arthritis

and

increased

apoptosis

of

synovial

blood

vessels

-LSB-

-RSB-

fibroblasts

modified

with

retroviral

vectors

to

express

angiostatin

were

able

to

decrease

pannus

formation

and

cartilage

erosion

when

injected

into

knee

joints

of

mice

with

CIA

Arthritis-associated

angiogenesis

was

also

inhibited

-LSB-

-RSB-

AAV

and

HIV

vector-mediated

delivery

of

angiostatin

to

CIA

knee

joints

were

similarly

beneficial

-LSB-

-RSB-

The

potent

anti-angiogenic

factor

endostatin

was

able

to

decrease

arthritis

and

reduce

blood

vessel

density

in

a

human

TNF-transgenic

mouse

model

of

arthritis

when

delivered

to

knee

joints

using

a

lentiviral

vector

-LSB-

-RSB-

has

also

been

demonstrated

to

play

a

role

in

angiogenesis

in

arthritis

Adenoviral

delivery

of

a

soluble

receptor

for

resulted

in

a

decreased

incidence

and

severity

of

CIA

inhibition

of

angiogenesis

and

was

associated

with

decreased

bone

destruction

that

appeared

to

result

from

a

decrease

in

RANKL

-LSB-

-RSB-

VEGF

is

another

angiogenic

factor

that

promotes

synovitis

and

bone

destruction

in

arthritis

When

soluble

VEGF

receptor

I

was

administered

via

adenoviral

vectors

to

CIA

mice

disease

activity

was

suppressed

significantly

-LSB-

-RSB-

Thrombospondins

-LRB-

and

-RRB-

have

also

been

shown

to

inhibit

angiogenesis

and

also

decrease

pro-inflammatory

cytokine

production

in

animal

models

of

arthritis

-LSB-

-RSB-

In

addition

adenoviral

gene

transfer

of

a

urokinase

plasminogen

inhibitor

was

also

able

to

inhibit

angiogenesis

in

a

CIA

model

-LSB-

-RSB-

Targeting

matrix

degradation

enzymes

Matrix

metalloproteinases

-LRB-

MMPs

-RRB-

degrade

extracellular

matrix

components

and

have

been

demonstrated

to

contribute

to

cartilage

degradation

in

RA

Ribozymes

and

an

antisense

construct

targeting

the

destruction

of

delivered

to

RA

synovial

fibroblasts

via

retroviral

vectors

decreased

production

and

reduced

the

invasiveness

of

RA

synovial

fibroblasts

in

a

SCID

mouse

model

of

RA

suggesting

that

this

may

be

an

effective

approach

to

inhibiting

cartilage

destruction

in

RA

-LSB-

-RSB-

Another

strategy

that

has

proven

successful

is

to

increase

the

ratio

of

tissue

inhibitors

of

matrix

metalloproteinases

-LRB-

TIMPs

-RRB-

to

MMPs

In

a

rat

antigen-induced

arthritis

model

intramuscular

injection

of

naked

DNA

encoding

completely

abolished

the

development

of

the

disease

-LSB-

-RSB-

Likewise

adenoviral

delivery

of

and

to

RA

synovial

fibroblasts

significantly

decreased

their

invasiveness

both

in

vitro

and

in

an

in

vivo

SCID

mouse

model

of

RA

These

molecules

were

found

to

act

by

both

decreasing

MMP

production

and

reducing

cell

proliferation

-LSB-

-RSB-

Targeting

NFκB

The

transcription

factor

NFκB

plays

a

significant

role

in

the

activation

of

many

cytokines

that

contribute

to

the

pathogenesis

of

RA

Inhibition

of

this

factor

could

lead

to

therapeutic

benefit

in

RA

Injection

of

decoy

oligodeoxynucleotides

with

high

affinity

for

NFkB

into

ankle

joints

of

CIA

rats

significantly

decreased

joint

swelling

and

joint

destruction

The

levels

of

the

pro-inflammatory

cytokines

TNF-α

and

were

also

decreased

in

the

treated

joints

-LSB-

-RSB-

Another

group

found

that

inhibiting

NFκB

in

RA

synovial

fibroblasts

using

an

adenovirus

to

deliver

a

dominant

negative

inhibitor

of

NFκB

led

to

an

increase

in

apoptosis

upon

stimulation

with

TNF-α

These

cells

are

normally

resistant

to

apoptosis

when

stimulated

with

TNF-α

suggesting

that

this

strategy

may

be

beneficial

in

the

treatment

of

RA

-LSB-

-RSB-

In

adjuvant

arthritis

in

rats

a

dominant

negative

IkB

kinase

β

-LRB-

IKKβ

-RRB-

was

used

to

inhibit

the

NFκB

pathway

Delivering

the

molecule

intra-articularly

using

an

vector

resulted

in

significantly

reduced

paw

swelling

and

decreased

levels

of

and

TNF-α

Bone

and

cartilage

destruction

as

well

as

and

levels

were

unaffected

The

same

vector

was

also

able

to

efficiently

transduce

ex

vivo-cultured

biopsies

from

joints

of

human

RA

patients

TNF-α-induced

production

was

significantly

decreased

in

the

ex

vivo

cultures

receiving

the

vector

encoding

IKKβ

-LSB-

-RSB-

Other

strategies

Other

molecules

that

have

been

demonstrated

to

play

a

role

in

arthritis

using

gene

transfer

in

various

in

vitro

or

animal

models

are

Csk

cathepsin

L

fibronectin

soluble

superoxide

dismutase

and

catalase

Ras

and

prothymosin

α

-LSB-

-RSB-

Vectors

and

genes

used

to

successfully

treat

animal

models

of

arthritis

are

summarized

in

Table

Table

of

vectors

and

genes

used

in

animal

models

of

arthritis

AdenovirusAAVRetrovirusLentivirusPlasmid

DNAGenes

demonstrated

to

successfully

treat

arthritis

in

various

animal

sTNFRI-Ig

fusion

protein

protein

TRAIL

Csk

IFN-β

prothymosin-α

VEGF

receptor

I

soluble

receptor

FADD

FasL

urokinase

plasminogen

inhibitor

dominant

negative

NFκB

sTNFR-Ig

sTNFRI

sTNFR

Fc

fusion

protein

angiostatin

sTNFRI

variants

TGF-β

angiostatin

soluble

complement

receptor

I

superoxide

dismutase

catalaseAngiostatin

sTNFRI

receptor

variants

sTNFR

Fc

fusion

protein

sTNFRII

TGF-β

soluble

complement

receptor

I

fibronectin

peptide

Safety

concerns

As

with

most

investigative

therapies

one

of

the

most

important

concerns

with

regards

to

gene

transfer

technologies

is

the

issue

of

safety

While

the

FDA

has

outlined

specific

strict

standards

for

clinical

trial

protocols

for

gene

transfer

studies

there

have

been

several

instances

where

the

therapy

has

resulted

in

serious

adverse

events

in

patients

enrolled

in

the

studies

The

most

widely

known

is

probably

the

September

death

of

Jesse

Gelsinger

who

had

a

fatal

systemic

inflammatory

response

to

adenoviral

vector

gene

transfer

-LSB-

-RSB-

Retroviral

vectors

have

also

resulted

in

insertional

mutagenesis

leading

to

a

secondary

malignancy

-LSB-

-RSB-

Lentiviral

vectors

may

have

this

potential

as

well

as

sharing

a

similar

mechanism

although

this

has

never

been

demonstrated

in

clinical

studies

More

recently

in

July

of

Jolee

Mohr

a

patient

enrolled

in

Targeted

Genetics

clinical

trial

for

rheumatoid

arthritis

using

AAV

vectors

died

several

weeks

following

her

second

injection

of

the

experimental

treatment

The

trial

is

currently

suspended

and

although

the

investigation

into

her

death

is

still

ongoing

initial

results

suggest

she

died

of

a

systemic

fungal

infection

that

may

be

unrelated

to

the

injected

virus

This

case

and

the

final

results

of

the

investigation

are

likely

to

have

a

large

impact

on

the

future

of

gene

therapy

trials

in

the

United

States

as

AAV

has

been

heralded

as

one

of

the

most

promising

vectors

in

the

field

precisely

because

it

has

until

now

failed

to

reveal

significant

safety

concerns

in

previous

studies

Future

of

gene

therapy

for

arthritis

Much

progress

has

been

made

in

the

past

several

years

in

the

use

of

gene

therapy

for

the

treatment

of

arthritis

However

there

are

many

obstacles

that

must

be

overcome

in

order

for

it

to

become

a

viable

treatment

option

Future

studies

will

need

to

address

improving

targeted

delivery

of

vectors

regulating

transgene

expression

obtaining

long-term

transgene

expression

and

improving

the

safety

and

efficacy

of

the

vectors

already

in

use

before

gene

therapy

becomes

a

viable

clinical

therapy

for

arthritis

Even

in

light

of

the

recent

setback

in

clinical

trials

utilizing

AAV

vectors

the

authors

believe

that

the

future

of

gene

transfer

for

arthritis

will

rely

heavily

upon

this

vector

Once

the

safety

issues

have

been

clarified

these

trials

can

hopefully

move

forward

Presently

AAV

would

seem

to

be

the

viral

vector

that

has

the

best

profile

in

terms

of

safety

efficacy

and

level

and

length

of

transgene

expression

Alternatively

strategies

using

siRNA

technology

or

preventing

the

dysregulation

of

cells

would

appear

to

be

emerging

as

treatment

strategies

that

may

one

day

outperform

the

current

standards

of

care

for

rheumatoid

arthritis

B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O B I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O 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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O

rheumatoid arthritis
gene therapy
gene transfer
inflammation
cytokines