Biological therapies in the acute respiratory distress syndrome

1. Introduction

2. Anti-cytokine therapy

3. Endothelial targets

4. Coagulation factors

5. Growth factors

6. Gene therapy

7. Mesenchymal stem cells

8. Expert review

Review

Biological therapies in the acuterespiratory distress syndromeAndrew James Boyle, James Joseph McNamee & Daniel Francis McAuley†

†Queen’s University Belfast, Centre for Infection and Immunity, Belfast, UK

Introduction: The acute respiratory distress syndrome (ARDS) is characterised

by life-threatening respiratory failure requiring mechanical ventilation, and

multiple organ failure. It has a mortality of up to 30 -- 45% and causes a

long-term reduction in quality of life for survivors, with only approximately

50% of survivors able to return to work 12 months after hospital discharge.

Areas covered: In this review we discuss the complex pathophysiology of

ARDS, describe the mechanistic pathways implicated in the development of

ARDS and how these are currently being targeted with novel biological

therapies. These include therapies targeted against inflammatory cytokines,

mechanisms mediating increased alveolar permeability and disordered

coagulation, as well as the potential of growth factors, gene therapy and

mesenchymal stem cells.

Expert opinion: Although understanding of the pathophysiology of ARDS has

improved, to date there are no effective pharmacological interventions that

target a specific mechanism, with the only potentially effective therapies to

date aiming to limit ventilator-associated lung injury. However, we believe

that through this improved mechanistic insight and better clinical trial design,

there is cautious optimism for the future of biological therapies in ARDS, and

expect current and future biological compounds to provide treatment options

to clinicians managing this devastating condition.

Keywords: acute hypoxaemic respiratory failure, acute lung injury, acute respiratory distress

syndrome, biological therapies

Expert Opin. Biol. Ther. [Early Online]

1. Introduction

Despite recognition nearly 50 years ago [1], the acute respiratory distress syndrome(ARDS) has yet to lend itself to an effective pharmacological treatment [2]. Thedefinition of ARDS has recently been updated [3], with the term acute lung injuryno longer recognised, and instead ARDS is now divided into three categories basedon severity. ARDS causes significant mortality and morbidity, and is associated witha major health care burden. The long-term morbidity to patients is significant, withsurvivors experiencing significantly reduced exercise tolerance 5 years after intensivecare unit discharge as well as other physical and psychological sequelae [4]. There arelimited treatment options available; the mainstay of care is lung-protective mechan-ical ventilation [5] with other strategies aimed at limiting ventilation-associated lunginjury [6,7]. Despite improved compliance with lung-protective ventilation [8],mortality from ARDS has remained stable since 1994 [9], highlighting the needfor new therapies for ARDS.

ARDS is an inflammatory condition characterised by neutrophil [10] andmacrophage-mediated [11] injury, with excessive pro-inflammatory cytokine andprotease activity in the alveolar space, which is associated with alveolar epithelialand capillary endothelial injury. During this inflammatory process, the coagulationcascade is activated, producing micro-thrombi and promoting fibrin deposition thatfurther exacerbates the disordered alveolar structure [2]. Protein-rich inflammatory

10.1517/14712598.2014.905536 © 2014 Informa UK, Ltd. ISSN 1471-2598, e-ISSN 1744-7682 1All rights reserved: reproduction in whole or in part not permitted

Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.

http://informahealthcare.com/journal/EBT

infiltrate accumulates within the alveolar space causingnon-cardiogenic pulmonary oedema, which impairs gaseousexchange.There is temporal overlap between this acute inflammatory

phase and the subsequent alveolar repair phase and how theacute inflammatory response interacts with the repair stageis largely unknown. As one example, temporal changes inMMPs, a group of proteases upregulated in ARDS, can pre-dict resolution of pulmonary oedema suggesting that proteaseactivity in the lung at some time points could contribute toalveolar-capillary repair [12,13]. As a result, biological therapiesthat can limit the severity of the initial inflammatory insultcould modify the process of cellular repair at a later timepoint.To date, the majority of pharmacological treatment

strategies that have been investigated have aimed to attenuatethe inflammatory response or improve the resolution ofpulmonary oedema without specific reference to timing [14].However, as ARDS is characterised by these overlapping acuteinflammatory and alveolar reparative phases, timing oftreatment may be more important than has been previouslyidentified, to permit targeting of the appropriate pathogenicprocess. This may, in part, explain the failure to establish aneffective therapy.As scientific understanding of the mechanisms underpin-

ning ARDS develops, a stratified medicine approach may bemore appropriate with biological therapies targeting processesexpressed either at a particular point in the course of theillness or in specific subgroups and this is increasingly possi-ble. Subsequent interest in biological therapies has led tonumerous potential therapies, and in the following review,the evidence to support a role for these biological agents is

presented. For the purpose of this review, a biological therapyis defined as a therapy of biological origin, that is, notchemically synthetic. We provide a summary of the biologicaltherapies discussed in Table 1.

2. Anti-cytokine therapy

2.1 IL-8IL-8 is a pro-inflammatory cytokine that plays a major role inthe recruitment, activation and influx of neutrophils to thealveolar space [15]. Neutrophil accumulation within the lungis an early pathogenic process in ARDS [10], and IL-8 is foundin significantly higher levels in broncho-alveolar lavage (BAL)fluid of at-risk patients who develop ARDS compared withthose who do not [16]. The importance of IL-8 to ARDS issupported by data showing higher BAL concentration ofIL-8 correlates with increased mortality [17,18].

In ARDS, a large proportion of IL-8 is bound to ananti-IL-8 IgG autoantibody [19], and this complex can interactwith the FcgRIIa receptor expressed by neutrophils to delayapoptosis [20] and prolong the inflammatory process. In addi-tion, IL-8:anti-IL-8 complexes have been shown to depositwithin the lung tissue itself in ARDS [21], which may act asa pro-inflammatory mediator to further the pathological pro-cess [22]. Indeed, signalling through the FcgRIIa receptor, andto a lesser extent the IL-8 receptor, has been shown to increaseneutrophil chemotaxis in ARDS [23]. The scientific rationalefor IL-8 as a key mediator in ARDS is supported clinicallywith evidence of higher levels of complexed IL-8 in patientswho die from ARDS [22].

The potential role for monoclonal antibodies that block theaction of IL-8 has been investigated in animal models ofARDS. Intravenous humanised anti-IL-8 monoclonalantibody was shown in a lipopolysaccharide (LPS) model ofARDS to reduce alveolar neutrophil infiltration, an effect inpart explained by reduced levels of BAL IL-1b and TNF-a.Histological scoring (evaluating neutrophil infiltration,capillary congestion, fibrin clot deposition, epithelial celldesquamation and alveolar septum width) was improved inthe anti-IL-8 treatment group [24]. This data suggest theremay be a role for anti-IL-8 therapy in ARDS; however,human studies are awaited and currently it is difficult to assesshow effective a therapy may be for human intervention.

2.2 TNFTNF is present in two forms, a and b, and both have an earlypathogenic role in ARDS, with their presence in plasmaassociated with the onset of ARDS during sepsis [25]. TNF-ais secreted by activated tissue macrophages and mediates theattraction and activation of neutrophils within the alveolarspace [26]. TNF-a mediates its effect through two cell-surfacereceptors, TNF-receptor (TNFR)-1 and TNFR-2, withTNFR-1 thought to primarily mediate pro-inflammatoryeffects. In the setting of murine models of ARDS, TNFR-1signalling has been shown to promote ventilator-induced

Article highlights.

. Acute respiratory distress syndrome (ARDS) causessignificant morbidity and mortality; the pathophysiologyis complex and to date, there is no effectivetherapeutic intervention.

. Many pharmacological interventions have beeninvestigated without success; biological therapies areincreasingly recognised as potential future therapies.

. Encouraging pre-clinical data has often been followedby disappointing results in clinical trials; this likelyreflects both the limitations of pre-clinical models andthe complex pathophysiology underlying ARDS andpossibly a need for improved clinical trial designin ARDS.

. Timing of therapies is of increasing importance, withtreatment targets often expressed at different periods ofillness in ARDS. Biological therapies may have anadvantage in this regard as they can actmore specifically.

. There is cautious optimism for the role of biologicaltherapies in ARDS, and in particular stem cell therapy, inthe management of this complex disorder.

This box summarizes the key points contained in the article.

A. J. Boyle et al.

2 Expert Opin. Biol. Ther. (2014) 14(7)

Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.


Table

1.Summary

ofbiologicaltherapiesin

ARDS.

Biological

substrate

Mech

anismsin

ARDS

Therapeuticagent

Phase

ofclinical

development

Resu

lts

IL-8

Neutrophilrecruitmentto

thealveolar

space

Humanisedanti-IL-8monoclonal

antibody

Pre-clinical[24]

Reducedhistologicalevidence

ofARDS

TNF-a

Secretedbymacrophagesto

attract

neutrophils

toinjuredalveolus

Actionmediatedviapro-inflammatory

TNF-receptor1

Inhaledhumanisedanti-TNFR1

monoclonalantibodies

Phase

I(NCT01587807)

Resultsawaited

CD14

Cellsurface

receptorforLPSon

macrophagesandneutrophils

Inducespro-inflammatory

cytokinerelease

(e.g.,TNF-a)

Anti-CD14monoclonalantibodies

Pre-clinical[38]

Reductionsin

pulm

onary

oedema,

neutrophilmigrationandTNF-a

production

Phase

I(NCT00233207)

Term

inateddueto

poorrecruitment

CD73

Rate-lim

itingglycoprotein

inadenosine

synthesis.

Adenosineisprotectivein

hypoxia,stim

ulatinganinnate

response

toinhibitadaptive

immunecells

IFN-b

(increasesCD73synthesisin

lungendothelialcells)

Phase

I/II[55]

Reducedmortality

ACE2

Promotesbreakdownofinjurious

AngiotensinII

RecombinantACE-2

Phase

I/II

(NCT01597635)

Resultsawaited

Adrenomedullin

Reducesvascularperm

eability

RecombinanthumanAdrenomedullin

Pre-clinical[67,68]

Reducedlunginjury

severity

TissueFactor

Initiatesextrinsiccoagulationcascade,

inducingpro-coagulantstate.Thiscan

propagate

fibrindeposition

Recombinantantibodyto

tissuefactoror

tissuefactor--factorVIIIcomplex

Phase

II(NCT00879606)

Resultsawaited

Activated

Protein

CReducedlevelsin

ARDS

Whenactivatedisapotentanti-coagulant

Syntheticactivatedprotein

CPhase

II[77]

Nosignificanteffect

upon

ventilator-freedays

Keratinocyte

growth

factor

PromotesalveolartypeIIepithelialcell

repair

Augments

AFC

RecombinanthumanKGF(paliferm

in)

Phase

II[85]

Resultsawaited

VEGF

Increasesperm

eability

ofalveolar-capillary

membrane

Bevacizumab(humanisedanti-VEGF

monoclonalantibody)

Phase

II(NCT01314066)

Term

inateddueto

poorenrolm

ent

GM-CSF

Augments

neutrophillifespanand

phagocytosis

Reducesalveolarepithelialcellapoptosis

RecombinanthumanGM-CSF

Phase

II[96]

Nobenefitin

ventilator-freedays

or

28-daymortality

GeneTherapy

Multiple

potentialtargets

Currenttherapieshave

targetedAFC

improvements

viaNa+,K

+-ATPase

andthe

b2-adrenergic

receptor

Vector-carriedgeneticmaterial

Pre-clinical

Improvements

inAFC

Stem

Cell

Cellcontact-dependentandindependent

mechanismsSecrete

soluble

mediators

(e.g.,antimicrobialpeptidesandgrowth

factors)Im

provedcellbioenergetics

Mesenchym

alstem

cells

Phase

I(NCT01775774,

NCT01902082)

Resultsawaited

AFC

:Alveolarfluid

clearance;LPS:lipopolysaccharide;KGF:

Keratinocyte

growth

factor;TNFR1:TNF-receptor1.

Biological therapies in the acute respiratory distress syndrome

Expert Opin. Biol. Ther. (2014) 14 (7) 3

Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.


lung injury, with increases in pulmonary oedema, whileTNFR-2 signalling induces a protective effect [27]. Plasmalevels of both TNFR-1 and TNFR-2 act as biomarkers forthe activity for TNF-a during ARDS, and higher plasma levelsof both receptors are independently associated with anincreased mortality from ARDS [28].These data led to investigation of anti-TNF-a agents as a

therapeutic intervention for ARDS. Animal data showedthat pre-treatment with anti-TNF-a monoclonal antibodiesattenuated the development of ARDS with reductions inneutrophil migration across the endothelial border into thealveolar space [29]. Further animal studies using polyclonalanti-TNF-a antibodies highlighted benefits to gas exchangeand lung compliance [30]. Investigation of anti-TNF agentsin humans has been less effective, with two large human trialsshowing no benefit of anti-TNF therapy in the setting ofsepsis, a common cause of ARDS [31,32]. No clinical trialsspecifically investigating anti-TNF therapy in patients withARDS have been undertaken to date.However, more recent research has focussed on the differen-

tial effect of blocking TNFR1, aiming to reduce the pro-injurious impact of TNF-a, while simultaneously maximisingthe protective effects of signalling via TNFR2. Treatment withanti-TNFR1 monoclonal antibodies in an animal model ofARDS reduced deterioration in respiratory function andreduced alveolar-epithelial permeability [33]. An early-phaseclinical trial in a model of ARDS induced by LPS in healthyvolunteers, investigating inhaled antibodies against TNFR1,has recently concluded (NCT01587807) and results areawaited. If successful further investigation will need to focusearly in the course of ARDS, as the characteristics of TNFR1suggest that it is important in the early stages of ARDS butmay not have as much impact in later stages of illness.

2.3 CD14LPS is a major component of the cell wall of gram-negativebacteria, and it is recognised by host macrophages and neutro-phils through the cell surface receptor CD14 [34]. This processrequires a soluble protein, LPS-binding protein, before LPScan interact with CD14 [35]. Once activated, CD14 inducesintra-cellular signalling for the production of pro-inflammatorycytokines, including TNF-a, IL-1 and IL-6 [36], driving thepro-inflammatory response.In patients with ARDS, soluble CD14 is related to BAL total

protein (a measure of alveolar capillary permeability) andneutrophil count, but not clinical outcome [37]. Investigationof CD14 as a therapeutic target has utilised monoclonalantibodies antagonising the cell surface receptor. The use ofanti-CD14 monoclonal antibodies in murine LPS-models ofARDS reduced pulmonary oedema, neutrophil migration andTNF-a production by macrophages, supporting a potentialtherapeutic role in ARDS [38]. A human trial investigating therole of monoclonal antibodies against CD14 was terminatedin 2007 due to poor patient recruitment (NCT00233207).While these data suggest that CD14-dependant mechanisms

contribute to LPS-induced inflammation in ARDS, given therelatively weak scientific data and that this only targets ARDSwhere LPS is implicated in the development, we do not expectfurther investigation of CD14 as a therapeutic option in theforeseeable future.

2.4 Additional cytokine targetsARDS develops as a result of a complex immune reactioninvolving many cytokines, often in combination. Inflamma-somes are intracellular molecules that can act as activators ofmultiple cytokines and propagate the immune response. InARDS, inflammasome gene expression of IL-18 is increased,while IL-18 itself correlates with disease severity and mortalityin critically ill patients [39]. Developing the ability to inactivatethe inflammasome may permit new therapeutic targets, and weexpect developments in this field as scientific understanding ofinflammasomes in ARDS improves.

IL-1b is produced by activated macrophages and epithelialcells and is a potent recruiter of neutrophils. It is elevated inBAL and plasma of ARDS patients [40], and increasesalveolar-capillary permeability; therefore, contributing to thedevelopment of inflammatory alveolar oedema [41]. Inaddition, IL-1b-dependant IL-6 induction has been shownto initiate fibroblast activity and is thought to contribute tothe fibrotic re-modelling stage of ARDS [42]. The mechanismsthrough which IL-1b is produced have been identified toinvolve the nucleotide-binding domain and leucine-richrepeat PYD-containing protein 3 (NLRP3) inflammasome,which is activated in hyperoxia [43,44]. In NLRP3-deficientmice, ARDS development was attenuated with reductions ininflammatory cell recruitment and TNF-a production [45],suggesting that strategies to target the NLRP3 inflammasomecould have many beneficial therapeutic effects.

As previously discussed, the activation and recruitment ofneutrophils to the site of lung injury is a key process in thepathophysiology of ARDS. IL-17 is primarily produced bylymphocytes and has been shown to attract neutrophils tothe lungs in a murine LPS-model of ARDS [46]. To affectthe recruitment of neutrophils, IL-17 acts in synergy withTNF-a to increase endothelial selectin expression; therefore,increasing the adhesion and transmigration of neutrophilsacross the endothelium [47]. Given the importance of thisprocess to the development of ARDS, IL-17 could become afuture biological target and may prove to be an effectivesynergistic target alongside TNFR-1 blockade.

IL-27 is produced by macrophages and dendritic cells, andis thought to have a predominantly anti-inflammatory role,although this has yet to be definitively clarified [48]. BALfrom ARDS patients contains significantly greater quantitiesof IL-27 compared to healthy controls, and correlates withseverity of disease [49]. In addition, murine models of ARDSsuggest that neutralising IL-27 may provide a protective effectto inflammation [49], and therefore, although its precise roleawaits clarification, IL-27 is showing promise as a potentialtreatment option for ARDS.

A. J. Boyle et al.


Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.


3. Endothelial targets

3.1 CD73CD73 is a membrane-bound glycoprotein that is rate limitingfor the production of extracellular adenosine during hyp-oxia [50]. CD73 is activated by stretching of epithelial cells [51],and it hydrolyzes extracellular nucleoside monophosphatesinto bioactive adenosine. Adenosine is thought to be protec-tive in tissue hypoxia, forming part of an innate responsethat inhibits adaptive inflammatory responses. It reduces neu-trophil adhesion and TNF-a production, while macrophagesexhibit increased secretion of the anti-inflammatory cytokineIL-10, and reductions in the production of pro-inflammatoryIL-12 [52,53].

The depletion of CD73 reduces adenosine production, andthis has been shown to increase alveolar capillary leakage [51],suggesting that CD73-mediated adenosine release is protec-tive in ARDS. Additionally, CD73-deficient mice are unableto recover from ARDS [54] implicating adenosine in theresolution and recovery phase of ARDS.

IFN-b increases synthesis of CD73 in lung endothelialcells. In a Phase I study, intravenous administration ofIFN-b in ARDS (when compared with a contemporaneousbut non-randomised control group) was associated with amarked reduction in mortality [55]; however, larger clinicaltrials are required to confirm this therapeutic benefit.

3.2 ACE 2The renin--angiotensin system is best known for its role in theregulation of blood pressure homeostasis. ACE converts angio-tensin 1 to angiotensin 2 (Ang 2), a powerful endogenous vaso-pressor that also promotes inflammation and increasedvascular permeability. ACE2 is a homologue of ACE [56] andfunctions to break down Ang 2 [57], therefore, opposing theeffects of Ang 2 [58].

Natural variations in ACE activity occur between individu-als according to genetic phenotype. The ACE DD phenotypecauses greater ACE activity, and is associated with increasedmortality in ARDS [59]. To support the hypothesis that ACEis damaging in ARDS, and ACE2 may therefore be protective,animal models have found that both ACE deficiency andadministration of IV recombinant human ACE2 improvelung function and pulmonary oedema [60]. Recombinanthuman ACE2 has also been shown in animal models toreduce serum TNF-a levels and attenuate hypoxia [61]. Onthe basis of this data, a human Phase I/II clinical trial is cur-rently recruiting to investigate recombinant human ACE2 inpatients with early ARDS who are haemodynamically stable(NCT01597635).

3.3 AdrenomedullinAdrenomedullin (AM) is a multifunctional regulatory peptidethat has been implicated in a number of biological func-tions [62]. AM is produced by vascular smooth muscle,

vascular endothelial cells and macrophages in response toLPS, TNF-a and IL-1 [63-65]. AM signals through cAMP,preventing increased pulmonary vascular permeability [66]

and therefore reducing alveolar oedema.This ability to attenuate alveolar endothelial permeability

led to investigation of AM as a therapeutic interventionin ARDS. In a rodent model of ARDS induced by LPSintravenous infusion of recombinant-human AM reduced theseverity of lung injury [67], and similar findings were replicatedin a murine model of ventilator-induced lung injury [68]. TheEuropean Medicines Agency granted approval for thedevelopment of AM as a medicinal product for ARDS in2010 and the use of AM in clinical trials is awaited.

The concept of targeting endothelial dysfunction, as acommon pathophysiological pathway seen in the majority ofpatients with ARDS, is a promising strategy.

4. Coagulation factors

4.1 Tissue factorIn addition to a pro-inflammatory state, there is also apro-coagulant state evident in the alveolar space of ARDSpatients, with tissue factor (TF) identified as a key moleculein this process [69]. TF is a potent initiator of the extrinsiccoagulation cascade and in ARDS alveolar epithelial cellscan express TF to stimulate the pro-coagulant state [70]; factorVIIa binds to TF to form a Factor X-binding complex, acti-vating the latter compound that cleaves prothrombin tothrombin and ultimately leads to fibrin formation. This isdamaging because fibrin can deposit within the alveolar space,increasing alveolar-capillary permeability and providing amatrix for disordered fibroblast repair. In addition to alveolarcell expression, TF can be produced in the alveolar space byneutrophils under TNF-a stimulation [71] and helps explainwhy BAL from ARDS patients has a greater concentrationof TF than that from patients with hydrostatic pulmonaryoedema [70].

On the basis of these data, attempts have been made todisrupt the coagulation cascade in ARDS. In primate modelsof sepsis, it has been shown that administration of inactivatedactivated Factor VII (FVIIa), which has higher affinity for TF,attenuated ARDS through a reduction in alveolar fibrindeposition, reduced neutrophil infiltration and alveolaroedema [72]. Two clinical trials have since taken place toestablish the impact of targeting TF as a treatment for ARDS.A Phase II study investigating inactivated recombinant FVIIain mechanically ventilated patients with ARDS for < 48 h wasdiscontinued prematurely because of excessive 28-day mortalityin one of the four treatment cohorts. A trend to increasedbleeding complications was seen with increasing doses oftreatment [73].

More recently, following a small Phase I trial of ALT-836(a recombinant antibody that binds to TF or TF--FactorVIII complex) to evaluate its pharmacokinetics and safety [74],a Phase II investigation (NCT00879606) in septic patients



Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.


with ARDS is ongoing. The primary outcome is duration ofventilation, and results of this trial are awaited.

4.2 Activated protein COnce activated, protein C is a natural anticoagulant thatpromotes fibrinolysis and inhibits thrombosis. In the settingof sepsis there are decreased levels of protein C, while levelsof thrombomodulin (one of the endothelial cell surface recep-tors that activates protein C) are increased, reflecting a reducedbinding capacity and therefore promoting a pro-coagulantstate. In a similar manner to sepsis, ARDS is a pro-coagulantenvironment and plasma protein C in ARDS patients issignificantly reduced compared to normal controls, and thesereductions are associated with a higher mortality [75].Activated protein C (APC) is an anticoagulant therapy that

has been extensively investigated in sepsis with largely negativeresults [76]. In ARDS, a Phase II randomised, double-blindclinical trial of intravenous APC found no significant effecton ventilator-free days. There were however physiologicalimprovements in the treatment group, including improve-ments to the pulmonary dead-space fraction, suggesting thatAPC may restore the lung microcirculation and improveventilation-perfusion matching [77]. In contrast to these nega-tive findings, a recent small randomised placebo-controlledtrial of 27 patients has shown that APC in the setting ofnon-sepsis may attenuate lung injury, decreasing lung injuryscore and showing anti-coagulant properties without haemor-rhagic complications [78]. This suggests that there may yet berole for APC in a sub-group of non-septic ARDS patients.The role of APC is likely to remain limited because of the

negative results observed in large clinical trials investigatingits role as a treatment for sepsis [76], where no benefit wasfound in 28-day mortality. This has led to withdrawal ofAPC as a treatment, and therefore further investigation ofAPC in the setting of ARDS is unlikely to progress. Whiletargeting the coagulation cascade remains a potential strategy,the experience to date with APC is likely to reduce enthusiasmfor large clinical trials in this area.

5. Growth factors

5.1 Keratinocyte growth factorThere is interest in augmenting the resolution of inflamma-tory pulmonary oedema in ARDS. Disordered cellular repairmechanisms and impaired alveolar epithelial cell functionare characteristic of ARDS [79], and resolution of pulmonaryoedema and outcome in ARDS are determined by alveolarepithelial fluid transport.Keratinocyte growth factor (KGF) is an epithelial-derived

fibroblast growth factor produced exclusively by mesenchymalcells. The receptor is highly expressed on epithelial cells,although has recently been reported to also be present onmacrophages, augmenting phagocytosis [80,81]. Within thelung itself KGF has a variety of beneficial effects, including

stimulation of type II alveolar cell proliferation, which isfollowed by cell migration to repair the injured alveoli [82,83].

Following pre-clinical studies suggesting benefits ofKGF [82], an ex-vivo lung perfusion (EVLP) model of ARDSshowed that KGF treatment improved lung endothelial andepithelial function, and augmented alveolar fluid clearance(AFC) [84]. This promising pre-clinical data prompted aPhase II randomised, double-blind placebo-controlled clinicaltrial investigating the effect of recombinant human KGF(palifermin) in ARDS patients [85]. Patients will receive IVpalifermin for up to 6 days and the primary outcome is oxy-genation index at day 7, a marker of ARDS severity. This trialis ongoing, with results likely to have major significance bothin relation to KGF and stem cell therapy in ARDS. Onepotential limitation of KGF as a therapy for ARDS is thatthe majority of pre-clinical data have only found it to beeffective when used prior to injury, which would limit its util-ity as a treatment for ARDS. However, it might be potentiallyuseful as a preventative therapy in patients known to be athigh risk of developing ARDS.

5.2 VEGFVEGF is a cytokine produced by a range of inflammatory andepithelial cells that significantly increases vascular permeabil-ity [86]. ARDS is characterised by increased permeability ofthe alveolar-capillary membrane, and VEGF is significantlyelevated in plasma of ARDS patients [87]. This led to thehypothesis that VEGF increases vascular permeability inARDS. However, BAL VEGF levels are significantly lowerin ARDS patients initially, and lower levels correlate withincreasing severity of lung injury, while recovery of BALVEGF levels after day 4 is associated with a recovery fromARDS [88]. It has been proposed that this apparent paradoxwith elevated plasma VEGF levels is due to BAL VEGF caus-ing increased permeability of the alveolar-capillary membraneand therefore allowing leakage of VEGF into the plasma. Thelow levels of VEGF in the alveolar space can also be explainedby other mechanisms. VEGF levels are similar betweenpatients with non-cardiogenic pulmonary oedema as seen inARDS, and those with hydrostatic pulmonary oedema [89],suggesting that changes in VEGF in the alveolar space repre-sent the severity of alveolar oedema rather than the severityof ARDS itself. In addition, an antagonist to VEGF, solubleVEGFR-1, has been identified as a naturally occurring antag-onist to VEGF in the BAL of patients with ARDS. It is foundin higher levels in BAL compared to plasma, and may explainwhy measurable VEGF levels are lower in the alveolarcompartment [90].

The potential significance of VEGF in the development ofARDS led to a Phase II clinical trial investigating IV Bevacizu-mab (humanised anti-VEGF monoclonal antibody) as a treat-ment for ARDS (NCT01314066). This trial was stoppedearly due to poor enrolment, and further trials evaluatingthe therapeutic role of anti-VEGF therapies are awaited.

A. J. Boyle et al.


Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.


5.3 GM-CSFGM-CSF is a growth factor for haematopoietic cells andpromotes type 2 epithelial cell hyperplasia [91]. Additionally,GM-CSF has an important role in regulating alveolar macro-phage functioning and surfactant homeostasis, helping tomaintain innate immune defence mechanisms [92].

Higher concentration of BAL GM-CSF in ARDS isassociated with reduced mortality [93], and mechanisms toachieve this include augmenting type II epithelial cell andmacrophage proliferation [94]. In addition, murine models ofhyperoxic lung injury show that overexpression of GM-CSFpreserves alveolar permeability and reduces alveolar epithelialcell apoptosis, therefore maintaining structural integrity [95].

Based on this experimental data, a randomised, placebo-controlled Phase II clinical trial investigating recombinanthuman GM-CSF as a treatment for ARDS was undertaken.It showed no reduction in ventilator-free days, although thestudy was underpowered as it did not recruit the plannedsample size. However, there was a non-significant trendtowards reduction in 28-day mortality and an increase inorgan failure-free days. [96]. Given this unsuccessful Phase IItrial, we do not anticipate further investigation of GM-CSFas a treatment for ARDS.

6. Gene therapy

Gene therapy is the manipulation of genetic components(genes or nucleic acid sequences) into cells to replace adisordered gene. This can occur pre-fertilisation or througha somatic approach to manipulate mature cells. By manipulat-ing messenger RNA, specific therapies can be introducedwithout wider effects [97].

There are a number of considerations with regard to genetherapy. To overcome cell defence mechanisms a carrier, orvector, is required to transport the genes into the cell. Giventhe ease with which viruses can infiltrate epithelium, viral vec-tors have been investigated to deliver gene therapy in ARDSbecause of the efficiency they offer. The viral genome is editedto prevent replication and coupled with the gene of interest topermit insertion within the host cell [98]. A number of virusesincluding adenovirus have been investigated, although successhas been limited because of innate immune activation [99].

Non-viral vectors are less efficient in entering epithelialcells, but are thought to be less immunogenic [98]. These vec-tors involve the manipulation of DNA or RNA compoundsthat are complexed with plasmids or lipids to prevent degra-dation and allow entry of the gene into the cell. Non-viraldelivery mechanisms are generally better tolerated by theinnate immune system, producing a lower immunologicalresponse, but the high degradation rate is restricting [100].

An emerging theme in many biological therapies is themost effective way to deliver the treatment to the injuredairways. Given the systemic effects many therapies couldhave upon the immune system, local delivery is an

increasingly popular option. Aerosolised delivery of genetherapy has been investigated in cystic fibrosis, a conditionwhere genetic defects lead to disordered cell membrane trans-port mechanisms, without clinical benefit [101]. Intravasculardelivery direct to the pulmonary vasculature has beenemployed successfully in pre-clinical studies using non-viralvectors [102], but has not yet faced the scrutiny of human trials.

The challenge of gene therapy in ARDS is not limited tothe delivery of genes, but crucially which genes to target.Several genes have been identified that predispose patients todeveloping ARDS, and their functions range from endothelialbarrier regulation to cytokine response and many more [103].All of these are potential therapeutic targets, but to dateprimary interest has related to genes that may impact AFCand those that can limit the development of ARDS from com-mon insults [100]. The most promising pre-clinical data relatesto Na+,K+-ATPase, a cell surface compound that regulatesfluid transport across the cell membrane. Plasmid delivery ofgenetic sequences coding Na+,K+-ATPase were delivered in amouse model of ARDS and showed protection for the devel-opment of ARDS. Of further relevance, however, was thefinding that the same treatment improved lung injury onceit was established, suggesting that genetic transfer of Na+,K+-ATPase may improve AFC [104].

Although gene therapy shows promise, current interventionis limited to animal models. The use of nanoparticles todeliver b2-adrenergic receptors showed reduction in ARDSseverity and improved AFC in mice with establishedARDS [105], while viral vector delivery of genes coding forextracellular superoxide dismutase (superoxide is producedby neutrophils in response to inflammation) reduced severityof ARDS [106]. These therapies remain experimental however,and it remains unclear the role that gene therapy will havein ARDS.

7. Mesenchymal stem cells

Stem cells are cells that have an infinite ability to self-renewand can differentiate into several cell types (pluripotent),effectively providing a repair mechanism for cells withinthe body. The bone marrow is a rich source of mesenchymalstem cells (MSCs), alongside adipose and neonatal tissues(e.g., placenta, umbilical cord), and these cells can beextracted for therapeutic use.

There are several mechanisms of action that make MSCs anappealing therapeutic concept in ARDS. MSCs are thought tobe anti-inflammatory, secreting multiple mediators thatdown-regulate the inflammatory process [107], and can alsosecrete growth factors, including KGF, that offer the benefitspreviously described. In addition, it has been suggested MSCsmay have the ability to repair the injured alveolar epithelium,differentiating into alveolar cells and replacing injured cells,although evidence to support this mechanism is limited [108].

Initial studies in animal models of sepsis showed that MSCtreatment increased IL-10 and improved organ function and



Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.


survival [109]. In addition, in an Escherichia coli model ofpneumonia several anti-microbial compounds, includingLL-37 and lipocalin 2, were found to mediate the actions ofMSCs, inhibiting bacterial growth and augmenting microbialclearance [110,111]. In a murine model of gram-negative perito-neal sepsis treated with human MSCs, survival was improvedin the treatment group with improvements noted in plateletcount and augmentation of monocyte phagocytosis [112].MSCs have also been investigated specifically in ARDS.

A rodent model of ventilator-induced lung injury showedthat MSCs can reduce lung inflammation and enhance cellu-lar repair, reducing levels of the pro-inflammatory cytokineTNF-a, mediated at least in part through KGF secretion [113].An additional mechanism of action of MSCs has been

demonstrated in an animal ARDS model, where direct cell-dependant contact allowed MSCs to mediate their protectiveeffect by adhering to alveoli and transferring their mitochon-dria to improve cell bioenergetics [114]. In a human EVLPmodel of ARDS induced by E coli, treatment with humanMSCs improved AFC, an effect that was mediated in partby secreted KGF [81], further highlighting the therapeuticpotential of MSCs and their secreted products.In addition to EVLP models of ARDS induced by LPS and

E. coli [81,84], a recent EVLP model using natively injuredhuman lungs rejected for transplant suggests that MSCs canrestore AFC in the setting of in vivo lung injury [115]. In a sim-ilar manner to E. coli injured models, this effect was mediatedin part by KGF, and provides further evidence that MSCsmay prove an effective therapy in ARDS.Given these pre-clinical data [116], research has progressed

and currently there are two early-phase studies recruiting toassess the impact of MSCs in ARDS (NCT01775774,NCT01902082). It is anticipated that there will be manyfurther developments in this field.

8. Expert review

Despite half a century of research investigating therapies forARDS [1], specific treatments remain limited to supportivecare involving protective mechanical ventilation strategiesand conservative fluid management. The development of bio-logical therapies is viewed as a potential option for improvingoutcomes in ARDS.ARDS can be caused by a wide variety of insults, including

pneumonia and non-pulmonary sepsis, aspiration, pancreati-tis and trauma [117]. The incidence of, and mortality from,ARDS varies with the associated risk factor. For example,sepsis is associated with the highest incidence and mortality,while in contrast, trauma has the lowest incidence and mortal-ity. Inflammatory cytokines and biomarkers of cell injury areknown to differ by the clinical risk for ARDS, suggesting thatthe pathophysiology may differ by clinical risk factor [117-120].To date, most trials have recruited a heterogeneous cohort ofpatients with ARDS regardless of the aetiology, rather thantesting a specific therapy for a specific cause. It is possible

that this may also help explain why pharmacological interven-tions tested to date have been unsuccessful if the mechanismbeing targeted by a therapy is not actually expressed in all ofthe population recruited. Therefore, it may be appropriateto target a given biological therapy only to patients wherethe target is expressed, for example, in patients associatedwith a specific risk factor.

As we develop our understanding of the mechanismsunderlying ARDS we identify new challenges, including iden-tifying the correct target and timing of intervention. ARDS isa complex illness characterised by an initial inflammatoryphase, followed by a resolution and repair phase, althoughthese phases overlap. Many of the failed pharmacologicaltherapies investigated in ARDS have been used early in thecourse of ARDS, without targeting a specific mechanism. Itmay be more appropriate for a therapy to be used accordingto when its target is expressed during the course of ARDS.For example, blocking the action of pro-inflammatory cyto-kines is likely to be more effective in the early course of illnesswhere limiting the initial insult is the aim of therapy, whereasthe use of growth factors may prove most beneficial at a laterstage, to promote the resolution and repair phase. Currently,interventions are usually investigated at the earliest possibleonset of injury, which may not be suitable if the intendedtarget is expressed at different time points of injury.

There remain a number of challenges to implementing astrategy of delivering novel biological therapeutics accordingto when a specific target is expressed. Defining a therapy bya single biological target could have limitations. Given theredundancy that exists in the complex mechanisms causingARDS, targeting a single pathway may not be beneficial andin fact agents with pleiotropic effects may be more advanta-geous. For example, KGF and MSCs have anti-inflammatoryproperties that are beneficial in the acute inflammatory phase,while their ability to support cellular repair is likely to bebeneficial in the later stages of ARDS. Another challenge isdefining the phase of illness. The inflammatory and reparativephases of ARDS can have significant overlap and it is there-fore not possible to be specific with regard to the stage ofillness. Unlike myocardial infarction, for example, there areno clear biomarkers to guide clinicians as to the stage ofillness, when specific targets are expressed and therefore it isnot yet possible to confidently indicate when an interventionwould be appropriate. However, recognising that a treatmentintervention has a specific target should drive us in the futureto define when that target is expressed and clarify both howand when we can manipulate it. Biological therapies maylend themselves well to this treatment strategy.

Pre-clinical research currently informs whether newtherapies are progressed to human trials. Animal models ofARDS may fail to fully replicate the complex nature of thehuman syndrome [121]. The use of more clinically relevantmodels of ARDS such as the human EVLP models as wellas models of pulmonary inflammation induced by inhaledLPS in healthy volunteers is an attempt to improve the

A. J. Boyle et al.


Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.


translation of pre-clinical findings; however these models stillhave limitations. Recognising that the translation from benchto bedside has many hurdles is important when interpretingpre-clinical research in the setting of ARDS.

There are many promising biological therapies currentlyunder investigation, and of these MSC therapy may providethe most potential for an effective treatment. MSCs havenumerous effects, including limiting the acute injury throughan anti-inflammatory action, promoting resolution of injuryand augmenting repair. This ability of MSCs to act through-out the course of ARDS provides the rationale explaining whyMSCs may overcome the challenges of appropriate timing oftreatment that could explain previous failed therapies. Cur-rently, there are two Phase I clinical trials recruiting withmore planned, and we expect significant progress in thisarea. Aligned with stem cell therapy is the use of growthfactors that are also being tested in Phase II studies [85].With over-lapping properties, it is anticipated that thesemay become effective therapies in the management ofARDS and we expect to see more clinical trials in the future.

In summary, although there have been many failed thera-pies to date [14], new biological therapies based on improvedunderstanding of the mechanisms implicated in the develop-ment of ARDS are emerging and are at various stages of

development, which could provide an effective interventionfor patients with ARDS. It is possible that the future ofARDS treatment may involve a stratified medicine approachwhere specific targets expressed in different populations or atdifferent time points are targeted with a range of biologicaltherapies.

Declaration of interest

D McAuley has performed paid consultancy work and hasbeen a member of advisory boards on ARDS for Glaxo-SmithKline. This author’s institution has been paid for theauthor to undertake bronchoscopy as part of a clinical trialfunded by GlaxoSmithKline. He has also received fees for lec-turing for AstraZenica, and has a patent submitted for a noveltreatment for ARDS (unrelated to the work described in thisreview). D McAuley has received funding from the NorthernIreland Public Health Agency Research and DevelopmentDivision Translational Research Group for Critical Care.The authors have no other relevant affiliations or financialinvolvement with any organisation or entity with a financialinterest in or financial conflict with the subject matter ofmaterials discussed in the manuscript apart from thosedisclosed.

BibliographyPapers of special note have been highlighted as

either of interest (�) or of considerable interest(��) to readers.

1. Ashbaugh D, Boyd Bigelow D, Petty T,

Levine B. Acute respiratory distress in

Adults. Lancet 1967;290:319-23

2. Ware LB, Matthay MA. The acute

respiratory distress syndrome. N Engl

J Med 2000;342:1334-49

.. Comprehensive review of ARDS.

3. The ARDS Definition Task Force. Acute

respiratory distress syndrome: the Berlin

definition. JAMA 2012;307:2526-33

4. Herridge MS, Tansey CM, Matte A,

et al. Functional disability 5 Years after

acute respiratory distress syndrome.

N Engl J Med 2011;364:1293-304

5. Ventilation with lower tidal volumes as

compared with traditional tidal volumes

for acute lung injury and the acute

respiratory distress syndrome. The Acute

Respiratory Distress Syndrome Network.

N Engl J Med 2000;342:1301-8

.. Landmark clinical trial which found a

lung protective ventilator strategy in

patients with ARDS was associated

with a 10% absolute reduction

in mortality.

6. Papazian L, Forel J-M, Gacouin A, et al.

Neuromuscular blockers in early acute


J Med 2010;363:1107-16

7. Guerin C, Reignier J, Richard J-C, et al.

Prone positioning in severe acute


J Med 2013;368:2159-68

8. Esteban A, Ferguson ND, Meade MO,

et al. Evolution of mechanical ventilation

in response to clinical research. Am J

Respir Crit Care Med 2008;177:170-7

9. Phua J, Badia JR, Adhikari NKJ, et al.

Has mortality from acute respiratory

distress syndrome decreased over time?

A systematic review. Am J Respir Crit

Care Med 2009;179:220-7

10. Abraham E. Neutrophils and acute lung

injury. Crit Care Med 2003;31:S195-9

11. Frank JA, Wray CM, McAuley DF,

et al. Alveolar macrophages contribute to

alveolar barrier dysfunction in ventilator-

induced lung injury. Am J Physiol Lung

Cell Mol Physiol 2006;291:L1191-8

12. O’Kane CM, McKeown SW,

Perkins GD, et al. Salbutamol

up-regulates matrix metalloproteinase-9

in the alveolar space in the acute

respiratory distress syndrome.

Crit Care Med 2009;37:2242-9

13. Lanchou J, Corbel M, Tanguy M, et al.

Imbalance between matrix

metalloproteinases (MMP-9 and MMP-2)

and tissue inhibitors of metalloproteinases

(TIMP-1 and TIMP-2) in acute

respiratory distress syndrome patients.

Crit Care Med 2003;31:536-42

14. Boyle AJ, Sweeney RM, McAuley DF.

Pharmacological treatments in ARDS; a

state-of-the-art update. BMC Med

2013;11:166

15. Allen TC, Kurdowska A. Interleukin

8 and acute lung injury. Arch Pathol

Lab Med 2013;138:266-9

16. Donnelly SC, Haslett C, Strieter RM,

et al. Interleukin-8 and development of

adult respiratory distress syndrome in

at-risk patient groups. Lancet

1993;341:643-7

17. Miller EJ, Cohen AB, Nagao S, et al.

Elevated levels of NAP-1/interleukin-8 are

present in the airspaces of patients with

the adult respiratory distress syndrome

and are associated with increased

mortality. Am Rev Respir Dis

1992;146:427-32

18. Agrawal A, Zhuo H, Brady S, et al.

Pathogenetic and predictive value of

biomarkers in patients with ALI and

lower severity of illness: results from two



Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.

www.ncbi.nlm.nih.gov/pubmed/4143721?dopt=Abstract





















































clinical trials. Am J Physiol Lung Cell

Mol Physiol 2012;303:L634-9

19. Kurdowska A, Miller EJ, Noble JM,

et al. Anti-IL-8 autoantibodies in alveolar

fluid from patients with the adult

respiratory distress syndrome. J Immunol

1996;157:2699-706

20. Fudala R, Krupa A, Matthay MA, et al.

Anti-IL-8 autoantibody:IL-8 immune

complexes suppress spontaneous

apoptosis of neutrophils. Am J Physiol

Lung Cell Mol Physiol

2007;293:L364-74

21. Allen TC, Fudala R, Nash SE,

Kurdowska A. Anti--interleukin

8 Autoantibody:interleukin 8 immune

complexes visualized by laser confocal

microscopy in injured lung. Arch Pathol

Lab Med 2009;131:452-6

22. Fudala R, Krupa A, Stankowska D, et al.

Anti-interleukin-8 autoantibody:

interleukin-8 immune complexes in acute

lung injury/acute respiratory distress

syndrome. Clin Sci 2008;114:403

23. Krupa A, Kato H, Matthay MA,

Kurdowska AK. Proinflammatory activity

of anti-IL-8 autoantibody:IL-8 complexes

in alveolar edema fluid from patients with

acute lung injury. Am J Physiol Lung Cell

Mol Physiol 2004;286:L1105-13

24. Bao Z, Ye Q, Gong W, et al.

Humanized monoclonal antibody against

the chemokine CXCL-8 (IL-8) effectively

prevents acute lung injury.

Int Immunopharmacol 2010;10:259-63

25. Leeper-Woodford SK, Carey PD, Byrne K,

et al. Tumor necrosis factor alpha and beta

subtypes appear in circulation during onset

of sepsis-induced lung injury. Am Rev

Respir Dis 1991;143:1076-82

26. Goncalves de Moraes VL,

Boris Vargaftig B, Lefort J, et al. Effect

of cyclo-oxygenase inhibitors and

modulators of cyclic AMP formation on

lipopolysaccharide-induced neutrophil

infiltration in mouse lung.

Br J Pharmacol 1996;117:1792-6

27. Wilson MR, Goddard ME, O’Dea KP,

et al. Differential roles of p55 and

p75 tumor necrosis factor receptors on

stretch-induced pulmonary edema in

mice. Am J Physiol Lung Cell


28. Parsons PE, Matthay MA, Ware LB,

Eisner MD. Elevated plasma levels of

soluble TNF receptors are associated with

morbidity and mortality in patients with

acute lung injury. Am J Physiol Lung


29. Windsor AC, Walsh CJ, Mullen PG, et al.

Tumor necrosis factor-alpha blockade

prevents neutrophil CD18 receptor

upregulation and attenuates acute lung

injury in porcine sepsis without inhibition

of neutrophil oxygen radical generation.

J Clin Invest 1993;91:1459-68

30. Imai Y, Kawano T, Iwamoto S, et al.

Intratracheal anti-tumor necrosis

factor-alpha antibody attenuates

ventilator-induced lung injury in rabbits.

J Appl Physiol 1999;87:510-15

31. Abraham E, Anzueto A, Gutierrez G,

et al. Double-blind randomised controlled

trial of monoclonal antibody to human

tumour necrosis factor in treatment of

septic shock. Lancet 1998;351:929-33

32. Cohen J, Carlet J. INTERSEPT:

an international, multicenter, placebo-

controlled trial of monoclonal antibody

to human tumor necrosis factor-alpha in

patients with sepsis. International Sepsis

Trial Study Group. Crit Care Med

1996;24:1431-40

33. Bertok S, Wilson MR, Morley PJ, et al.

Selective inhibition of intra-alveolar

p55 TNF receptor attenuates ventilator-

induced lung injury. Thorax

2012;67:244-51

34. Wright SD, Ramos RA, Tobias PS, et al.

CD14, a receptor for complexes of

lipopolysaccharide (LPS) and LPS

binding protein. Science 1990;249:1431

35. Schumann RR. Function of

lipopolysaccharide (LPS)-binding protein

(LBP) and CD14, the receptor for LPS/

LBP complexes: a short review.

Res Immunol 1992;143:11-15

36. Haziot A, Tsuberi BZ, Goyert SM.

Neutrophil CD14: biochemical

properties and role in the secretion of

tumor necrosis factor-alpha in response

to lipopolysaccharide. J Immunol

1993;150:5556-65

37. Martin TR, Rubenfeld GD, Ruzinski JT,

et al. Relationship between soluble

CD14, lipopolysaccharide binding

protein, and the alveolar inflammatory

response in patients with acute

respiratory distress syndrome. Am J

Respir Crit Care Med 1997;155:937-44

38. Tasaka S, Ishizaka A, Yamada W, et al.

Effect of CD14 blockade on endotoxin-

induced acute lung injury in mice. Am J

Respir Cell Mol Biol 2003;29:252-8

39. Dolinay T, Kim YS, Howrylak J, et al.

Inflammasome-regulated cytokines are

critical mediators of acute lung injury.

Am J Respir Crit Care Med

2012;185:1225-34

40. Pugin J, Ricou B, Steinberg KP, et al.

Proinflammatory activity in

bronchoalveolar lavage fluids from

patients with ARDS, a prominent role

for interleukin-1. Am J Respir Crit

Care Med 1996;153:1850-6

41. Ganter MT, Roux J, Miyazawa B, et al.

Interleukin-1beta causes acute lung injury

via alphavbeta5 and alphavbeta6

integrin--dependent mechanisms. Circ Res

2008;102:804-12

42. Olman MA, White KE, Ware LB, et al.

Pulmonary edema fluid from patients

with early lung injury stimulates

fibroblast proliferation through

IL-1beta-induced IL-6 expression.

J Immunol 2004;172:2668-77

43. Martinon F, Burns K, Tschopp J. The

inflammasome: a molecular platform

triggering activation of inflammatory

caspases and processing of proIL-beta.

Mol Cell 2002;10:417-26

44. Kolliputi N, Shaik RS, Waxman AB.

The inflammasome mediates hyperoxia-

induced alveolar cell permeability.

J Immunol 2010;184:5819-26

45. Fukumoto J, Fukumoto I,

Parthasarathy PT, et al. NLRP3 deletion

protects from hyperoxia-induced acute

lung injury. Am J Physiol Cell Physiol

2013;305:C182-9

46. Ferretti S, Bonneau O, Dubois GR,

et al. IL-17, Produced by lymphocytes

and neutrophils, is necessary for

lipopolysaccharide-induced airway

neutrophilia: IL-15 as a possible trigger.

J Immunol 2003;170:2106-12

47. Griffin GK, Newton G, Tarrio ML,

et al. IL-17 and TNF-alpha sustain

neutrophil recruitment during

inflammation through synergistic effects

on endothelial activation. J Immunol

2012;188:6287-99

48. Banchereau J, Pascual V, O’Garra A.

From IL-2 to IL-37: the expanding

spectrum of anti-inflammatory cytokines.

Nat Immunol 2012;13:925-31

49. Xu F, Liu Q, Lin S, et al. IL-27 is

elevated in acute lung injury and

mediates inflammation. J Clin Immunol

2013;33:1257-68

A. J. Boyle et al.


Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.















































































































50. Thompson LF, Eltzschig HK, Ibla JC,

et al. Crucial role for ecto-5¢-nucleotidase(CD73) in vascular leakage during

hypoxia. J Exp Med 2004;200:1395-405

51. Eckle T, Fullbier L, Wehrmann M, et al.

Identification of ectonucleotidases

CD39 and CD73 in innate protection

during acute lung injury. J Immunol

2007;178:8127-37

52. Sitkovsky MV, Lukashev D, Apasov S,

et al. Physiological control of immune

response and inflammatory tissue damage

by hypoxia-inducible factors and

adenosine A2A receptors.

Annu Rev Immunol 2004;22:657-82

53. Ohta A, Sitkovsky M. Role of

G-protein-coupled adenosine receptors in

downregulation of inflammation and

protection from tissue damage. Nature

2001;414:916-20

54. Ehrentraut H, Clambey ET,

McNamee EN, et al. CD73+ regulatory

T cells contribute to adenosine-mediated

resolution of acute lung injury. FASEB J

2013;27:2207-19

55. Bellingan G, Maksimow M, Howell DC,

et al. The effect of intravenous

interferon-beta-1a (FP-1201) on lung

CD73 expression and on acute

respiratory distress syndrome mortality:

an open-label study. Lancet Respir Med

2014;2:98-107

56. Donoghue M, Hsieh F, Baronas E, et al.

A novel angiotensin-converting

enzyme--related carboxypeptidase (ACE2)

converts angiotensin 1 to angiotensin

1-9. Circ Res 2000;87:e1-9

57. Crackower MA, Sarao R, Oudit GY,

et al. Angiotensin-converting enzyme 2 is

an essential regulator of heart function.

Nature 2002;417:822-8

58. Imai Y, Kuba K, Penninger JM.

Angiotensin-converting enzyme 2 in


Cell Mol Life Sci 2007;64:2006-12

59. Adamzik M, Frey U, Sixt S, et al. ACE

I/D but not AGT (-6)A/G polymorphism

is a risk factor for mortality in ARDS.

Eur Respir J 2007;29:482-8

60. Imai Y, Kuba K, Rao S, et al.

Angiotensin-converting enzyme

2 protects from severe acute lung failure.

Nature 2005;436:112-16

61. Treml B, Neu N, Kleinsasser A, et al.

Recombinant angiotensin-converting

enzyme 2 improves pulmonary blood

flow and oxygenation in

lipopolysaccharide-induced lung injury in

piglets. Crit Care Med 2010;38:596-601

62. Lopez J, Martınez A. Cell and molecular

biology of the multifunctional peptide,

adrenomedullin. Int Rev Cytol

2002;221:1-92

63. Kangawa K, Kitamura K, Minamino N,

et al. Adrenomedullin: a new hypotensive

peptide. J Hypertens Suppl

1996;14:S105-10

64. Kubo A, Minamino N, Isumi Y, et al.

Production of adrenomedullin in

macrophage cell line and peritoneal

macrophage. J Biol Chem

1998;273:16730-8

65. Ishizaka Y, Ishizaka Y, Tanaka M, et al.

Adrenomedullin stimulates cyclic AMP

formation in rat vascular smooth muscle

cells. Biochem Biophys Res Commun

1994;200:642-6

66. Hippenstiel S, Witzenrath M,

Schmeck B, et al. Adrenomedullin

reduces endothelial hyperpermeability.

Circ Res 2002;91:618-25

67. Itoh T, Obata H, Murakami S, et al.

Adrenomedullin ameliorates

lipopolysaccharide-induced acute lung

injury in rats. Am J Physiol Lung Cell

Mol Physiol 2007;293:L446-52

68. Muller HC, Witzenrath M, Tschernig T,

et al. Adrenomedullin attenuates

ventilator-induced lung injury in mice.

Thorax 2010;65:1077-84

69. Idell S, Koenig KB, Fair DS, et al. Serial

abnormalities of fibrin turnover in

evolving adult respiratory distress

syndrome. Am J Physiol Lung Cell


70. Bastarache JA, Wang L, Geiser T, et al.

The alveolar epithelium can initiate the

extrinsic coagulation cascade through

expression of tissue factor. Thorax

2007;62:608-16

71. Kambas K, Markiewski MM,

Pneumatikos IA, et al. C5a and TNF-

alpha up-regulate the expression of tissue

factor in intra-alveolar neutrophils of

patients with the acute respiratory distress

syndrome. J Immunol 2008;180:7368-75

72. Welty-Wolf KE, Carraway MS,

Miller DL, et al. Coagulation blockade

prevents sepsis-induced respiratory and

renal failure in baboons. Am J Respir

Crit Care Med 2001;164:1988-96

73. Vincent J-L, Artigas A, Petersen LC,

Meyer C. A multicenter, randomized,

double-blind, placebo-controlled,

dose-escalation trial assessing safety and

efficacy of active site inactivated

recombinant factor VIIa in subjects with

acute lung injury or acute respiratory

distress syndrome. Crit Care Med

2009;37:1874-80

74. Morris PE, Steingrub JS, Huang BY,

et al. A phase I study evaluating the

pharmacokinetics, safety and tolerability

of an antibody-based tissue factor

antagonist in subjects with acute lung

injury or acute respiratory distress

syndrome. BMC Pulm Med 2012;12:5

75. Ware LB, Fang X, Matthay MA. Protein

C and thrombomodulin in human acute

lung injury. Am J Physiol Lung Cell

Mol Physiol 2003;285:L514-21

76. Ranieri VM, Thompson BT, Barie PS,

et al. Drotrecogin alfa (activated) in

adults with septic shock. N Engl J Med

2012;366:2055-64

77. Liu KD, Levitt J, Zhuo H, et al.

Randomized clinical trial of activated

protein C for the treatment of acute lung

injury. Am J Respir Crit Care Med

2008;178:618-23

78. Cornet AD, Hofstra JJ, Vlaar AP, et al.

Activated protein C attenuates

pulmonary coagulopathy in patients with


J Thromb Haemost 2013;11:894-901

79. Matthay MA, Ware LB,

Zimmerman GA. The acute respiratory

distress syndrome. J Clin Invest

2012;122:2731-40

80. Finch PW, Mark Cross LJ, McAuley DF,

Farrell CL. Palifermin for the protection

and regeneration of epithelial tissues

following injury: new findings in basic

research and pre-clinical models. J Cell

Mol Med 2013;17:1065-87

81. Lee JW, Krasnodembskaya A,

McKenna DH, et al. Therapeutic effects

of human mesenchymal stem cells in

ex vivo human lungs injured with live

bacteria. Am J Respir Crit Care Med

2013;187:751-60

82. Ware LB, Matthay MA. Keratinocyte and

hepatocyte growth factors in the lung:

roles in lung development, inflammation,

and repair. Am J Physiol Lung Cell

Mol Physiol 2002;282:L924-40

83. Panos RJ, Rubin JS, Csaky KG, et al.

Keratinocyte growth factor and

hepatocyte growth factor/scatter factor

are heparin-binding growth factors for

alveolar type II cells in fibroblast-



Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.























































































































conditioned medium. J Clin Invest

1993;92:969-77

84. Lee JW, Fang X, Gupta N, et al.

Allogeneic human mesenchymal stem

cells for treatment of E. coli endotoxin-

induced acute lung injury in the ex vivo

perfused human lung. Proc Natl Acad

Sci USA 2009;106:16357-62

.. Paper describing potential role of

MSCs in a clinically relevant human

EVLP model of ARDS.

85. Cross LJ, O’Kane CM, McDowell C,

et al. Keratinocyte growth factor in acute

lung injury to reduce pulmonary

dysfunction -- a randomised placebo-

controlled trial (KARE): study protocol.

Trials 2013;14:51

86. Dvorak HF, Brown LF, Detmar M,

Dvorak AM. Vascular permeability factor/

vascular endothelial growth factor,

microvascular hyperpermeability, and

angiogenesis. Am J Pathol

1995;146:1029-39

87. Thickett DR, Armstrong L, Christie SJ,

Millar AB. Vascular endothelial growth

factor may contribute to increased

vascular permeability in acute respiratory

distress syndrome. Am J Respir Crit

Care Med 2001;164:1601-5

88. Thickett DR, Armstrong L, Millar AB.

A role for vascular endothelial growth

factor in acute and resolving lung injury.

Am J Respir Crit Care Med

2002;166:1332-7

89. Ware LB, Kaner RJ, Crystal RG, et al.

VEGF levels in the alveolar compartment

do not distinguish between ARDS and

hydrostatic pulmonary oedema.

Eur Respir J 2005;26:101-5

90. Perkins GD, Roberts J, McAuley DF,

et al. Regulation of vascular endothelial

growth factor bioactivity in patients with

acute lung injury. Thorax 2005;60:153-8

91. Huffman Reed JA, Rice WR,

Zsengeller ZK, et al. GM-CSF enhances

lung growth and causes alveolar type II

epithelial cell hyperplasia in transgenic

mice. Am J Physiol 1997;273:L715-25

92. Trapnell BC, Whitsett JA. GM-CSF

regulates pulmonary surfactant

homeostasis and alveolar macrophage-

mediated innate host defense.

Annu Rev Physiol 2002;64:775

93. Matute-Bello G, Liles WC, Radella FI,

et al. Modulation of neutrophil apoptosis

by granulocyte colony-stimulating factor

and granulocyte/macrophage colony-

stimulating factor during the course of


Crit Care Med 2000;28:1-7

94. Reed JAH, Rice WR, Zsengeller ZK,

et al. GM-CSF enhances lung growth

and causes alveolar type II epithelial cell

hyperplasia in transgenic mice. Am J

Physiol Lung Cell Mol Physiol

1997;273:L715-25

95. Paine R, Wilcoxen SE, Morris SB, et al.

Transgenic overexpression of granulocyte

macrophage-colony stimulating factor in

the lung prevents hyperoxic lung injury.

Am J Pathol 2003;163:2397-406

96. Paine R, Standiford TJ, Dechert RE,

et al. A randomized trial of recombinant

human granulocyte-macrophage colony

stimulating factor for patients with acute

lung injury. Crit Care Med 2012;40:90-7

97. Kim DH, Rossi JJ. Strategies for silencing

human disease using RNA interference.

Nat Rev Genet 2007;8:173-84

98. Devaney J, Contreras M, Laffey JG.

Clinical review: gene-based therapies for

ALI/ARDS: where are we now? Crit Care

2011;15:224

99. Sakurai H, Kawabata K, Sakurai F, et al.

Innate immune response induced by gene

delivery vectors. Int J Pharm

2008;354:9-15

100. Lin X, Dean DA. Gene therapy for ALI/

ARDS. Crit Care Clin 2011;27:705-18

101. Moss RB, Milla C, Colombo J, et al.

Repeated aerosolized AAV-CFTR for

treatment of cystic fibrosis: a randomized

placebo-controlled phase 2B trial.

Hum Gene Ther 2007;18:726-32

102. McCarter SD, Mei SHJ, Lai PFH, et al.

Cell-based angiopoietin-1 gene therapy

for acute lung injury. Am J Respir Crit

Care Med 2007;175:1014-26

103. Gao L, Barnes KC. Recent advances in

genetic predisposition to clinical acute

lung injury. Am J Physiol Lung Cell

Mol Physiol 2009;296:L713-25

104. Mutlu GM, Machado-Aranda D,

Norton JE, et al. Electroporation-

mediated gene transfer of the Na +, K + -

ATPase rescues endotoxin-induced lung

injury. Am J Respir Crit Care Med

2007;176:582-90

105. Lin E-H, Chang H-Y, Yeh S-D, et al.

Polyethyleneimine and DNA

nanoparticles-based gene therapy for acute

lung injury. Nanomedicine

2013;9(8):1293-303

106. Hassett P, Curley GF, Contreras M, et al.

Overexpression of pulmonary extracellular

superoxide dismutase attenuates

endotoxin-induced acute lung injury.

Intensive Care Med 2011;37:1680-7

107. Ghannam S, Bouffi C, Djouad F, et al.

Immunosuppression by mesenchymal stem

cells: mechanisms and clinical applications.

Stem Cell Res Ther 2010;1:2

108. Hayes M, Curley G, Ansari B, Laffey JG.

Clinical review: stem cell therapies for

acute lung injury/acute respiratory

distress syndrome - hope or hype?

Crit Care 2012;16:205

109. Nemeth K, Leelahavanichkul A,

Yuen PST, et al. Bone marrow stromal

cells attenuate sepsis via prostaglandin

E2--dependent reprogramming of host

macrophages to increase their interleukin-

10 production. Nat Med 2008;15:42-9

. Paper describing potential role of

MSCs in sepsis.

110. Krasnodembskaya A, Song Y, Fang X,

et al. Antibacterial effect of human

mesenchymal stem cells is mediated in part

from secretion of the antimicrobial peptide

LL-37. Stem Cells 2010;28:2229-38

111. Gupta N, Krasnodembskaya A,

Kapetanaki M, et al. Mesenchymal stem

cells enhance survival and bacterial

clearance in murine Escherichia coli

pneumonia. Thorax 2012;67:533-9

112. Krasnodembskaya A, Samarani G,

Song Y, et al. Human mesenchymal stem

cells reduce mortality and bacteremia in

gram-negative sepsis in mice in part by

enhancing the phagocytic activity of

blood monocytes. Am J Physiol Lung


113. Curley GF, Hayes M, Ansari B, et al.

Mesenchymal stem cells enhance recovery

and repair following ventilator-induced

lung injury in the rat. Thorax

2012;67:496-501

114. Islam MN, Das SR, Emin MT, et al.

Mitochondrial transfer from

bone-marrow-derived stromal cells to

pulmonary alveoli protects against acute

lung injury. Nat Med 2012;18:759-65

115. McAuley DF, Curley GF, Hamid UI,

et al. Clinical grade allogeneic human

mesenchymal stem cells restore alveolar

fluid clearance in human lungs rejected

for transplantation. Am J Physiol Lung

Cell Mol Physiol 2014; In press

116. Sweeney RM, McAuley DF.

Mesenchymal stem cell therapy in acute

A. J. Boyle et al.


Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.



















































































































lung injury: is it time for a clinical trial?

Thorax 2012;67:475-6

117. Rubenfeld GD, Caldwell E, Peabody E,

et al. Incidence and outcomes of acute

lung injury. N Engl J Med

2005;353:1685-93

. Paper describing epidemiology

of ARDS.

118. Sheu C-C, Gong MN, Zhai R, et al.

Clinical characteristics and outcomes of

sepsis-related vs non-sepsis-related ARDS.

Chest 2010;138:559-67

119. Eisner MD, Thompson T, Hudson LD,

et al. Efficacy of low tidal volume

ventilation in patients with different

clinical risk factors for acute lung injury

and the acute respiratory distress

syndrome. Am J Respir Crit Care Med

2001;164:231-6

120. Calfee CS, Eisner MD, Ware LB, et al.

Trauma-associated lung injury differs

clinically and biologically from acute

lung injury due to other clinical

disorders. Crit Care Med

2007;35:2243-50

121. Proudfoot AG, McAuley DF,

Griffiths MJD, Hind M. Human models

of acute lung injury. Dis Model Mech

2011;4:145-53

AffiliationAndrew James Boyle1,2,

James Joseph McNamee2 &

Daniel Francis McAuley†1,2

†Author for correspondence1Queen’s University Belfast, Centre for Infection

and Immunity, Belfast, UK

E-mail: [email protected] Victoria Hospital,

Regional Intensive Care Unit,

274 Grosvenor Road, Belfast BT12 6BA, UK



Exp

ert O

pin.

Bio

l. T

her.

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Uni

vers

ity o

f So

uthe

rn C

alif

orni

a on

04/

09/1

4Fo

r pe

rson

al u

se o

nly.

















mailto:[email protected]


Documents

Biological therapies in the acute respiratory distress syndrome