ava i l ab l e a t www.sc i enced i r ec t . com

C l i n i ca l Immuno logy

www.e l sev i e r . com/ l o ca t e / y c l im

Clinical Immunology (2012) 142, 9–14

REVIEW

Anti-CD25 (daclizumab) monoclonal antibody therapyin relapsing–remitting multiple sclerosisRoland Martin⁎

Department of Neuroimmunology and Multiple Sclerosis Research, Neurology Clinic, University Hospital, University Zürich,Frauenklinikstrasse 26, 8091 Zürich, Switzerland

Received 13 March 2011; accepted with revision 30 October 2011Available online 9 November 2011

⁎ Fax: +0041 44 255 4507.E-mail address: roland.martin@usz

1521-6616/$ - see front matter © 2011doi:10.1016/j.clim.2011.10.008

KEYWORDSMultiple sclerosis;Immunomodulatorytherapy;Monoclonal antibodytreatment;Daclizumab;Anti-CD25

Abstract Following the recent approval of the first oral therapy for multiple sclerosis (MS),fingolimod, multiple other oral compounds, and also a number of monoclonal antibodies (mab)are currently in phase III clinical testing. One of these is daclizumab, a humanized mab againstthe interleukin-2 receptor alpha chain (IL2RA or CD25). Efficacy to block clinical and inflamma-tory activity of relapsing–remitting MS (RR-MS) has been shown for daclizumab in several smallphase IIa studies and one large phase IIb clinical trial, and phase III testing is ongoing. Differentfrom prior expectations about its mechanism of action that anticipated that daclizumab wouldblock the activation and expansion of autoreactive T cells, we and others have shown that theexpansion of regulatory natural killer (NK) cells, which express high levels of the marker CD56,

appears to be the most important biological effect of CD25 blockade. From these data CD25inhibition is one of the most promising upcoming treatments of RR-MS and possibly also otherautoimmune conditions. Clinical and mechanistic data will be summarized in this short review.© 2011 Published by Elsevier Inc.

.ch.

Published by Elsevier Inc.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102. Clinical Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103. Safety and Tolerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124. Mechanistic Insight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125. Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Conflict of Interest Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1314

10 R. Martin

1. Introduction

All available treatments for MS and most of those in mid- tolate stage clinical development are either immunosuppres-sive or immunomodulatory. These include interferon-b(IFN-b) and glatiramer-acetate (GA), which have been ap-proved over a decade ago and remain the main first-linetreatments of RR-MS, a humanized monoclonal antibodyagainst CD49d/very late antigen-4 (VLA-4), natalizumab,which is substantially more effective than IFN-β and GA,and the recently introduced fingolimod, a sphingosin-1 phos-phate receptor agonist, the first oral therapy of RR-MS.Mitoxantron, a chemotherapeutic drug, has been approvedfor both RR-MS and secondary progressive MS (SP-MS) withongoing relapse activity, and finally azathioprine, anotherimmunosuppressive compound which has been on the marketfor several decades, however for other indications than MS,has also been approved for MS in some countries. Cladribine,a potent immunosuppressive and orally available compound,has recently also been approved in a few countries, butmarketing has been stopped after approval had been deniedin North America and Europe. Besides these already ap-proved drugs, several other small molecule drugs or mono-clonal antibodies are in late stage clinical development andthese include the orally available compounds fumaricacid, teriflunomide and laquinimod [1], and finally themabs alemtuzumab (humanized anti-CD52), rituximab/ocrelizumab (chimeric- and humanized anti-CD20 respec-tively) and daclizumab (humanized anti-CD25) [2]. A chime-ric anti-CD25 mab, basiliximab, like daclizumab has longbeen approved for the prevention of allograft rejection;however, it has not been tested as a treatment of MS in aclinical trial thus far. Daclizumab (Zenapax®) has recentlybeen withdrawn from the market. While the reasons forthis withdrawal are not clear, the decision was most likelybased on strategic/marketing considerations and not relatedto the safety profile or other characteristics of daclizumab.

The latter anti-CD25 mab daclizumab, which shall bebriefly reviewed here, was originally developed by ThomasWaldmann, National Cancer Institute, National Institutes ofHealth (NIH), Bethesda, to block cell proliferation of virallytransformed T cells in human T lymphotropic virus I (HTLV-I)-induced adult T cell leukemia (ATL) [3,4]. Daclizumab isthe humanized version of the initial mouse mab, which isdirected against the interleukin-2 receptor alpha chain(IL2RA, CD25). Daclizumab is an IgG1 mab and binds tothe TAC epitope or binding site of IL-2 to CD25. Differentfrom numerous other cell-depleting mabs, e.g. rituximab/ocrelizumab and alemtuzumab, daclizumab binds to theCD25 epitope and “masks” the IL-2 binding site, but doesnot lead to complement fixation, antibody-mediated cellu-lar cytotoxicity, relevant modulation of the CD25 moleculeor the entire IL-2 receptor complex, and also does not inducesignaling events or has agonistic activities [2]. As mentionedpreviously, daclizumab had been approved under thename Zenapax® for many years as an immunomodulatory/-suppressive treatment for the prevention of allograft rejec-tion and for treating ATL.

With respect to clinical use outside of transplantationmedicine and oncology (in ATL), daclizumab has been testedsuccessfully in cases of treatment-refractory uveitis by

Nussenblatt, Waldmann and colleagues at the National EyeInstitute, NIH [5], and later also in HTLV-I-associated mye-lopathy/tropical spastical paraparesis (HAM/TSP), a HTLV-I-induced and at least in part immune-mediated chronic ence-phaloymelitis, by Jacobson, Waldmann and colleagues [6]. Inthese exploratory trials the rationale was to block the ex-pansion or virus-specific (HAM/TSP) and/or autoreactive(uveitis and possibly also in HAM/TSP) T cells after their ac-tivation and hence also the subsequent steps, which presum-ably lead to tissue damage in the central nervous system(CNS) in HAM/TSP or the eye in uveitis. Particularly in theuveitis trials, anti-CD25 treatment looked promising with re-spect to halting disease activity in patients, in whom the au-toimmune disease could not be controlled by othermedications, but there was also an indication of efficacy inHAM/TSP, and in both indications no serious safety concernsarose [5–8]. Following the positive experience and favorablesafety profile of anti-CD25 treatment in uveitis and HAM/TSP, we (the Cellular Immunology Section, NINDS, NIH; R.Martin and colleagues) and the Department of Neurology,University of Utah at Salt Lake City (J. Rose and colleagues)began to explore the use of anti-CD25/daclizumab also inRR-MS patients with active inflammation RR-MS.

2. Clinical Observations

Until now, six clinical trials have been conducted with dacli-zumab all in RR-MS and SP-MS (the manuscript from the lastphase IIa trial in treatment-naive RR-MS at NINDS is in prep-aration), and the main results of the five published trials willbe summarized briefly here (see also Table 1). The first twotrials were single center trials conducted at NINDS, NIH, as abaseline-to-treatment crossover and MRI-controlled phaseIIa study in RR-MS and SP-MS patients, who had failed IFN-βtherapy [9], and an open proof-of-concept study at the Uni-versity of Utah, Salt Lake City, by Rose and colleagues,which included both RR- and SP-MS patients, who had failedsingle or multiple treatments prior to enrollment [10]. In themeantime, three other phase IIa trials and one larger phaseIIb study with intravenous daclizumab (once monthly) havebeen conducted including two more baseline-to-treatmentcrossover studies either in IFN-β non-responders [11,12] ortreatment-naive RR-MS patients (manuscript in preparation)and the placebo-controlled, randomized multicenter phaseIIb trials (CHOICE trial), in which two doses of subcutaneous(s.c.) daclizumab were compared against placebo [13].Below, the main results of these trials will be summarizedin chronology of initiation and/or publication.

NINDS daclizumab trial 1 [9]: The target population wasRR-MS patients, who had failed IFN-β. In this baseline-to-treatment crossover, MRI-controlled study, the reductionof gadolinium (Gd) contrast-enhancing, i.e. fresh inflamma-tory lesions served as the primary outcome, and additionalclinical, MRI and laboratory parameters were followed aswell. The most important entry criteria was the requirementof continuing MRI activity (Gd+lesions) during the baselinephase and while the patients were still treated with IFN-β.When fulfilling this activity criterion, patients were enrolledafter four monthly baseline MRIs and daclizumab (1 mg/kgbody weight, every 4 weeks i.v.; first two doses given attwo weekly intervals and then monthly) was added to the

Table 1 Summary of clinical testing of daclizumab in MS.

Trialname/site

Target population Number ofpatients

Duration oftreatment

Efficacy Adverse events Reference #

Daclizumab only

Univ. Utah Ambulatory RR-MSand SP-MS

19 5–25 months Yes a Skin rashes, paresthesias 10

NIH RR-MS, SP-MS 11 6.5 months Yes b Infections 9Failing IFN-β

Univ. Utah RR-MS 9 Up to 27.5 months Yes b Transient thrombo-cytopenia, skinrashes, lymphadenopathy, infections

11Failing IFN-β

NIH RR-MS, SP-MS 15 5.5 IFN-β Yes c Mouth ulcers, skin rashes, elevationof liver enzymes, lymphadenopathy

129 months Dac

CHOICE RR-MS 153 Dac add-on toIFN-β;

Yes d Infections, infestations, skin rashes,injection site reactions

13

1 mg/4 weekly2 mg/2 weekly

a Open label trial.b Open label, baseline-to-treatment crossover trials in patients failing interferon; predefined endpoints.c Baseline-to-treatment crossover trial, in which daclizumab (Dac) was added to IFN after a monotherapy phase of IFN.d Controlled, randomized, multi-center phase IIb trial.

11Anti-CD25 (daclizumab) monoclonal antibody therapy in relapsing–remitting multiple sclerosis

IFN-β treatment. The treatment phase lasted 6 months. Theprimary outcome was met, and we observed a 78% reductionin new Gd-enhancing MRI lesions, 80% reduction in the annu-alized relapse rate as well as significant improvements in theScripps Neurological Rating Scale (SNRS) and the 9-hole pegtest and trends towards improvement in all other outcomes[9]. Due to the small patient number and short treatmentperiod the improvement in clinical parameters has to beconsidered with caution; however, the reduction of inflam-matory activity as measured by Gd-enhancing lesions wassubstantial. Since the patients had failed IFN-β treatmentand were still active while on IFN-β, we considered thesedata highly promising and initiated subsequent studies (seebelow). One of the patients, who had very active diseaseand showed up to 30 monthly Gd-enhancing lesions/month,responded incompletely, and therefore we decided to in-crease daclizumab to 2 mg/kg body weight in 2 weeks inter-vals (i.e. four times the dose than the remaining patients).Upon dose escalation the patient responded to daclizumabsimilar to the remaining patient cohort.

Salt Lake City trial 1 [10]: In parallel to the above trialRose and colleagues conducted an open-label study withdaclizumab (1 mg/kg body weight, every 4 weeks i.v.) in 19ambulatory RR- and SP-MS patients, who had failed to re-spond to single or multiple prior therapies. In 16 patientsdaclizumab was given as monotherapy. Treatment lastedfor 5–25 months (average 13.6 months), and the investiga-tors observed sustained clinical improvement in 10 and clin-ical stabilization in the remaining 9 patients. InflammatoryMRI activity was reduced significantly particularly in thosepatients responding to drug, and like in the abovementionedfirst NINDS trial daclizumab treatment was toleratedwell [10].

Salt Lake City trial 2 [11]: RR-MS patients on IFN-β thera-py with continuing relapses and contrast-enhancing lesionswere selected and given two biweekly doses of daclizumab1 mg/kg i.v. and then every 4 weeks thereafter. IFN waswithdrawn at month 5.5, and patients were then continued

on placebo or monotherapy. Patients with recurrentcontrast-enhancing lesions (CEL) were restarted on IFN-βand received a higher dose of daclizumab (1.5 mg/kg i.v.every 4 weeks). Nine patients qualified and completed thetrial, and efficacy was shown for reduction of total andnew CEL (pb0.001), relapses, timed ambulation, expandeddisability status scale (EDSS) and SNRS (pb0.05 to pb0.01)[11]. It was concluded that daclizumab reduced MRI-measured disease activity and improved clinical scores inRR-MS patients with active disease not controlled by IFN-β.No serious adverse events were observed.

NINDS trial 2 [12]: In an open-label baseline versus treat-ment phase IIa clinical trial of 15 RR-MS patients with incom-plete response to IFN-β Bielekova et al. examined thenumber of CEL during baseline on IFN-β treatment, for5.5 months on combination therapy of continuing IFN-β anddaclizumab (1 mg/kg i.v. every 4 weeks) and then, if pa-tients showed at least a 75% reduction of CEL compared tobaseline for another 10 months on daclizumab monotherapy,i.e. after withdrawing IFN-β [12]. Daclizumab monotherapywas efficacious in 9/13 patients; however, IFN-β/daclizu-mab combination treatment was necessary in the remainingfour due to incomplete disease control. 5/15 patients expe-rienced adverse events, and in two daclizumab therapy wasdiscontinued due to systemic adverse events (mouth ulcers,photosensitivity rash, transient formation of autoantibodiesrequiring steroid therapy). A 72% inhibition of new CELsand 77% inhibition of total CELs were observed with daclizu-mab therapy. The reduction in volume of CELs betweencombination- and monotherapy also reached statisticalsignificance (pb0.001), and improvements were observedin all clinical measures of disability including EDSS, SNRS,and the multiple sclerosis functional composite (MSFC). Anumber of MRI measures were also followed, but were notaffected significantly except for transient increases of T1hypointensities and brain fractional volume [12]. Data fromimmunological studies will be mentioned below.

12 R. Martin

Salt Lake City retrospective analysis of long-term daclizu-mab therapy in RR-MS [14]: In a retrospective review of sideeffects and clinical outcomes in 12 RRMS patient receivinglong-term daclizumab therapy (average 42.1 months; 0.85–1.5 mg/kg every 4 weeks) Rojas et al. report that daclizu-mab was generally well tolerated and led to a significant re-duction in relapse rate and improvement in EDSS (pb0.0001)and concluded that these data provide further evidencefor the efficacy of daclizumab in RR-MS, but that formal con-firmation is required [14].

CHOICE study [13]: In a phase IIb, randomized, double-blind, placebo-controlled study 230 patients with activeRR-MS were randomly assigned to IFN-β plus high dose ofdaclizumab (2 mg/kg s.c. every 2 weeks), IFN-β plus lowdose of daclizumab (1 mg/kg s.c. every 4 weeks) or werecontinued on IFN-β and received placebo for 24 weeks.The primary endpoint was the total number of new or en-larged Gd-enhancing lesions measured every 4 weeks be-tween weeks 8 and 24. Exploratory immunological studieswere conducted in parallel. In the high dose daclizumabarm a 72% reduction (p=0.004) of new or enlarged Gd-enhancing lesions was observed over placebo (4.75 lesions)and a 25% reduction (p=0.51) in the low dose daclizumabgroup [13]. Common adverse events were equally distributedamong the groups, and the conclusionswere that add-on dacli-zumab at the high dose significantly reduced the number ofnew or enlarging Gd-enhancing lesions compared to IFN-βalone. Inflammatory disease activity returned to baselinelevels 2–3 months after treatment discontinuation. Datafrom mechanistic studies will be mentioned below.

In summary the above clinical trials were mostly explor-atory proof-of-concept phase IIa trials with the exceptionof the CHOICE study (phase IIb) [13]. The trials employeddifferent designs (daclizumab in combination with IFN-β oras monotherapy), examined small patient numbers withhighly active RR-MS, who had often failed prior therapy, inmost cases IFN-β, and followed patients for various times.The CHOICE phase IIb trial examined larger patient cohortsin a randomized, multi-center and double blind trial andcompared IFN-β treated patients with patients receivingcombination therapy of IFN-β with either low or high doseof daclizumab [13]. The main limitation of the latter trialwas its short duration of only 6 months. Despite these limita-tions the following conclusions can be drawn from theclinical use of daclizumab in RR-MS. Probably the mostimportant point is the consistency of the various trials. Allof them showed a clear and significant reduction ofinflammatory activity as measured by the number of CEL,and stabilization or improvement of clinical measures wasalso observed across the trials [9–14]. Efficacy was showneven in very active RR-MS patients, who had failed prioranti-inflammatory therapy; however it could also be arguedthat patients failing IFN-β treatment represent a specialsubgroup of patients, who do not necessarily reflect theentire population of RR-MS patients. The overall good safetyand tolerability profile (see below) with no serious adverseevents and no deaths are a clear plus when comparing dacli-zumab with other mabs or highly effective oral therapiesof MS [2]. Finally, the various proof-of-concept trials andthe CHOICE study have identified a biologically active doserange that is between 1 and 2 mg/kg i.v. every 4 weeks orrespectively 2 mg/kg s.c. every 2 weeks [9–14].

3. Safety and Tolerability

In the reported trials Daclizumab treatment i.v. or s.c. hasbeen generally tolerated very well over treatment periodsfrom 6 to 25 months [9–14]. The observed side effects includ-ed single cases of transient elevations of liver transaminasesor bilirubin, mild leuko- and lymphopenia, transient throm-bocytopenia, autoantibodies, transient photosensitivity-like rashes, which responded well to low doses of cortico-steroids, granuloma annulare, transient headaches andconstipation, breast tenderness, lymphadenopathies, pares-thesia, iron deficiency, upper respiratory- and urinary tractinfections, and one case of exacerbation of ongoing depres-sion [9–15]. Importantly, no serious adverse events andparticularly no deaths were reported. While it has to beconsidered that the number of MS patients treated withdaclizumab is still small, the mab has been given to uveitispatients over several years and was also tolerated well[5,7,8,16]. Probably more relevant, there is well over adecade of experience with daclizumab in the transplantsetting with patients, who usually receive multiple otherimmunosuppressive- and immunomodulatory drugs such assteroids, azathioprine, cyclosporine, mycophenolate andothers. Anti-CD25 is considered well tolerated and safe.Safety concerns that arose with other mabs in MS or otherautoimmune diseases including secondary and rarely fatalautoimmune diseases (alemtuzumab) and PML (natalizu-mab, rituximab, alemtuzumab, efalizumab) have not beenobserved with daclizumab. A recent Cochrane report thatevaluated the experience with anti-CD25 mab therapy in alarge number of allotransplantation trials, which comparedstandard immunosuppression versus standard immunosup-pression plus anti-CD25, came to the conclusion that severeinfections, e.g. reactivation of cytomegalovirus infection,or secondary malignancies occurred less frequently inpatients receiving anti-CD25 therapy [17]. These datahint at effects of anti-CD25 that may lead to bettercontrol of latent/persistent viral infections and also im-proved control/elimination of malignant cells rather thancompromising immune function globally by eliminating alarger number of immune cells (alemtuzumab, rituximab)or more specific aspects of immune function such as e.g.cell migration to the CNS (natalizumab). These findingsare probably at least in part explained by the mechanismsof action of anti-CD25 treatment by expanding natural killer(NK) cells, which will be detailed below.

4. Mechanistic Insight

As mentioned above, the long-standing assumption of themechanism of action of anti-CD25 therapy in the transplantcontext was that blocking the interaction between IL-2 andthe IL-2 receptor binding site (Tac epitope) of CD25 wouldinhibit the expansion of recently activated T cells. To pro-vide some background, T cell activation requires recognitionby the T cell receptor of a complex composed of antigenicpeptide and self-HLA/MHC. Following activation CD4+and CD8+ T cells express several activation markers amongthem all three components of the heterotrimeric high-affinity IL-2 receptor complex, which is the major growthfactor receptor. The growth factor IL-2 is primarily secreted

13Anti-CD25 (daclizumab) monoclonal antibody therapy in relapsing–remitting multiple sclerosis

by CD4+ T cells subsequent to T cell activation, and hencethe IL-2/IL-2 receptor interaction represents the majorautocrine growth factor pathway that is important forexpanding effector- and regulatory T cells [18]. The IL-2 re-ceptor heterotrimer is composed of a common gamma chain(CD132; shared by the receptors for IL-4, -7, -9, -15, -21), IL-2 receptor beta chain (CD122; shared with the receptor forIL-15), and the IL-2 receptor alpha chain (CD25; private tothe IL-2 receptor) [19]. CD25 is important for high affinitybinding of IL-2, but does not contain signaling domains.Hence, only the heterotrimer binds IL-2 with high affinityand is expressed on activated T cells, for which it serves asmajor growth factor receptor. The intermediate affinity IL-2 receptor consists of beta- and gamma chains (i.e. CD122/CD132), and different from the heterotrimer is constitutive-ly expressed on certain cell types including NK cells. In dis-tinction from T cells, which cannot be activated by IL-2alone, but need TCR-mediated antigen-specific activation,NK cells can be activated and expanded by IL-2 recognitionvia the intermediate affinity receptor. That the above pointsare important for understanding the mechanism of action ofanti-CD25 treatment was only recognized during mechanisticstudies along the first NINDS daclizumab trial [9,20]. The lat-ter showed only moderate reduction of CD4+ and CD8+ T cellnumbers ex vivo and growth inhibition in vitro [20], butmarked expansion of NK cells expressing CD56 at high levels(CD56bright NK cells) [20]. The expansion of CD56bright NKcells most likely occurs via the following mechanism. Anti-CD25 blocks the binding of IL-2 that is produced by recentlyactivated T cells to their own high affinity IL-2 receptor, andin turn is available for binding to the intermediate affinityreceptor (beta-/gamma chains) on NK cells, which areactivated by this signal and subsequently expanded. Invitro studies support this scenario [20,21]. Furthermore,CD56bright NK cells, which had been directly isolated fromdaclizumab-treated patients, were shown to kill recently ac-tivated CD4+ T cells not via a perforin-mediated mechanism,but by as yet unknown receptor/ligand interactions [20].Whether this is the main immunoregulatory mechanismof CD56bright NK cells remains to be determined. Recentlypublished data suggest that anti-CD25 also interferes withearly dendritic cell-T cell interaction [22]. In addition,anti-CD25 treatment interferes with CD40L expression [23],and CD25high T regulatory (Treg) cells are slightly diminishedin frequency and possibly also in their function [24]. Howev-er, different from prior knock out experiments of e.g. IL-2,which resulted in an autoimmune condition [25], the expec-tation that blocking IL-2 binding to the IL-2 receptor onTregs would lead to the same problems in humans did notmaterialize. In contrast, blocking the IL-2 receptor alphachain in humans improves autoimmune diseases such as MSand uveitis, and we assume that the expansion of CD56bright

NK cells and their function are the most important mecha-nism of action of anti-CD25 treatment. CD56bright NK cellsare of high interest in several respects. They play immuno-regulatory roles in other contexts and are involved in pro-tecting the growing fetus from immune-mediated damageby the maternal immune system [26], and they are most like-ly also relevant for containing latent/persistent infections,e.g. by herpes viruses, and elimination of mutated-/tumorcells [27,28]. The relative expansion of CD56bright NK cellsby anti-CD25 treatment was first noted by our studies, but

has now been confirmed by other groups not only in MS,but also in anti-CD25 treatment of uveitis [29]. Although itwas not noticed the expansion of NK cells and their above-mentioned biological effects probably also occurred in thecontext of the use of anti-CD25 in the prevention of allo-transplantation. A Cochrane review of the use of daclizumabin allotransplantation notes among other findings thatthe comparison of placebo or other mabs or anti-thymocyteglobulin (ATG) versus daclizumab resulted in less secondaryreactivations of herpes viral infections and less secondaryhematologic and solid malignancies, which stronglyargues that the expansion of CD56bright NK cells probablyalso played a role, although this speculation awaits formalstudy [17]. The importance of CD56bright NK cells in thetreatment with daclizumab is further supported by a clearcorrelation of the increase of this cell population with thedecrease of CNS inflammation as measured by reduced CEL[20]. Consistent with this observation, partial responders toanti-CD25 therapy do not show the expansion of CD56bright

NK cells [12,13], and therefore the number of CD56bright NKcells represents a highly useful biomarker for further clinicaltesting.

5. Outlook

Available data, although certainly not sufficient yet, stronglysuggest that anti-CD25 therapy of RR-MS patients with dacli-zumab will be effective in pivotal clinical trials. Severalphase II trials and a phase III trial are ongoing (see http://clinicaltrials.gov) that address both mechanism of actionand efficacy with respect to a clinical endpoint. Since thepreviously marketed daclizumab formulation that was usedi.v. in allotransplantation has been withdrawn due to unclearreasons (no apparent safety concerns were reported) andcurrent large scale clinical testing is not concluded, it re-mains to be seen when and if daclizumab will be approvedin the future. Also, whether daclizumab will be comparableto currently available (natalizumab, fingolimod, mitoxan-trone) or coming (alemtuzumab, rituximab/ocrelizumab)highly active drugs is not clear in the moment; however,the longstanding experience with daclizumab in the trans-plant sector as well as in autoimmune disease suggeststhat its adverse event profile will probably be betterthan that observed with most if not all abovementioneddrugs, and life-threatening side effects such as PML areunlikely to occur. Finally, its unique mechanism of actionthat enhances a cell population, CD56bright NK cells, withimmunoregulatory-, anti-viral, and anti-tumor activity rath-er than depleting certain immune cells or blocking importantaspects of immune function will be a distinguishing charac-teristic and desirable for all patients at risk of adverseevents that are observed in depleting and immunosuppres-sive therapies.

Conflict of Interest Statement

R. Martin, B. Bielekova, H.F. McFarland and T. Waldmann areco-inventors on an NIH-held patent on the use of daclizumabin RR-MS patients.

14 R. Martin

References

[1] R. Gold, Oral therapies for multiple sclerosis: a review ofagents in phase III development or recently approved, CNSDrugs 25 (2011) 37–52.

[2] A. Lutterotti, R. Martin, Getting specific: monoclonal anti-bodies in multiple sclerosis, Lancet Neurol. 7 (2008) 538–547.

[3] T.A. Waldmann, D.L. Longo, W.J. Leonard, J.M. Depper, C.B.Thompson, M. Kronke, C.K. Goldman, S. Sharrow, K. Bongio-vanni, W.C. Greene, Interleukin 2 receptor (Tac antigen)expression in HTLV-I-associated adult T-cell leukemia, CancerRes. 45 (1985) 4559s–4562s.

[4] R.L. Kirkman, M.E. Shapiro, C.B. Carpenter, D.B. McKay, E.L. Mil-ford, E.L. Ramos, N.L. Tilney, T.A. Waldmann, C.E. Zimmerman,T.B. Strom, A randomized prospective trial of anti-Tac monoclo-nal antibody in human renal transplantation, Transplant. Proc.23 (1991) 1066–1067.

[5] R.B. Nussenblatt, E. Fortin, R. Schiffman, L. Rizzo, J. Smith, P.Van Veldhuisen, P. Sran, A. Yaffe, C.K. Goldman, T.A.Waldmann,S.M. Whitcup, Treatment of noninfectious intermediate and pos-terior uveitis with the humanized anti-Tac mAb: a phase I/II clin-ical trial, Proc. Natl. Acad. Sci. U. S. A. 96 (1999) 7462–7466.

[6] T.J. Lehky, M.C. Levin, R. Kubota, R.N. Bamford, A.N. Flerlage,S.S. Soldan, T.P. Leist, A. Xavier, J.D. White, M. Brown, T.A.Fleisher, L.E. Top, S. Light, H.F. McFarland, T.A. Waldmann,S. Jacobson, Reduction in HTLV-I proviral load and spontaneouslymphoproliferation in HTLV-I-associated myelopathy/tropicalspastic paraparesis patients treated with humanized anti-Tac,Ann. Neurol. 44 (1998) 942–947.

[7] S. Yeh, K. Wroblewski, R. Buggage, Z. Li, S.K. Kurup, H.N. Sen,S. Dahr, P. Sran, G.F. Reed, R. Robinson, J.A. Ragheb, T.A.Waldmann, R.B. Nussenblatt, High-dose humanized anti-IL-2receptor alpha antibody (daclizumab) for the treatment of ac-tive, non-infectious uveitis, J. Autoimmun. 31 (2008) 91–97.

[8] H.N. Sen, G. Levy-Clarke, L.J. Faia, Z. Li, S. Yeh, K.S. Barron, J.G.Ryan, K. Hammel, R.B. Nussenblatt, High-dose daclizumab for thetreatment of juvenile idiopathic arthritis-associated active anteri-or uveitis, Am. J. Ophthalmol. 148 (696–703) (2009) e691.

[9] B. Bielekova, N. Richert, T. Howard, G. Blevins, S. Markovic-Plese,J. McCartin, J.A. Frank, J. Wurfel, J. Ohayon, T.A. Waldmann,H.F. McFarland, R. Martin, Humanized anti-CD25 (daclizumab) in-hibits disease activity in multiple sclerosis patients failing to re-spond to interferon beta, Proc. Natl. Acad. Sci. U. S. A. 101(2004) 8705–8708.

[10] J.W. Rose, H.E. Watt, A.T. White, N.G. Carlson, Treatmentof multiple sclerosis with an anti-interleukin-2 receptor mono-clonal antibody, Ann. Neurol. 56 (2004) 864–867.

[11] J.W. Rose, J.B. Burns, J. Bjorklund, J. Klein, H.E. Watt, N.G.Carlson, Daclizumab phase II trial in relapsing and remittingmultiple sclerosis: MRI and clinical results, Neurology 69(2007) 785–789.

[12] B. Bielekova, T. Howard, A.N. Packer, N. Richert, G. Blevins, J.Ohayon, T.A. Waldmann, H.F. McFarland, R. Martin, Effect ofanti-CD25 antibody daclizumab in the inhibition of inflamma-tion and stabilization of disease progression in multiple sclero-sis, Arch. Neurol. 66 (2009) 483–489.

[13] D. Wynn, M. Kaufman, X. Montalban, T. Vollmer, J. Simon, J.Elkins, G. O'Neill, L. Neyer, J. Sheridan, C. Wang, et al., Dacli-zumab in active relapsing multiple sclerosis (CHOICE study): aphase 2, randomised, double-blind, placebo-controlled, add-on trial with interferon beta, Lancet Neurol. 9 (2010) 381–390.

[14] M.A. Rojas, N.G. Carlson, T.L. Miller, J.W. Rose, Long-termdaclizumab therapy in relapsing–remitting multiple sclerosis,Ther. Adv. Neurol. Disord. 2 (2009) 291–297.

[15] L.R. Mehta, J.W. Rose, Recurrent granuloma annulare dur-ing treatment with daclizumab, Mult. Scler. 15 (2009)527–528.

[16] R.R. Buggage, G. Levy-Clarke, H.N. Sen, R. Ursea, S.K. Srivastava,E.B. Suhler, C. Altemare, G. Velez, J. Ragheb, C.C. Chan, R.B.Nussenblatt, A.T. Bamji, P. Sran, T. Waldmann, D.J. Thompson,A double-masked, randomized study to investigate the safetyand efficacy of daclizumab to treat the ocular complicationsrelated to Behcet's disease, Ocul. Immunol. Inflamm. 15 (2007)63–70.

[17] A.C.Webster, L.P. Ruster, R. McGee, S.L. Matheson, G.Y. Higgins,N.S. Willis, J.R. Chapman, J.C. Craig, Interleukin 2 receptor an-tagonists for kidney transplant recipients, Cochrane DatabaseSyst. Rev. (2010) CD003897.

[18] H.P. Kim, J. Imbert, W.J. Leonard, Both integrated and differ-ential regulation of components of the IL-2/IL-2 receptor sys-tem, Cytokine Growth Factor Rev. 17 (2006) 349–366.

[19] W.J. Leonard, J.R. Gnarra, M. Napolitano, M. Sharon, Struc-ture, function, and regulation of the interleukin-2 receptorand identification of a novel immune activation gene, Philos.Trans. R. Soc. Lond. B Biol. Sci. 327 (1990) 187–192.

[20] B. Bielekova, M. Catalfamo, S. Reichert-Scrivner, A. Packer, M.Cerna, T.A. Waldmann, H. McFarland, P.A. Henkart, R. Martin,Regulatory CD56(bright) natural killer cells mediate immuno-modulatory effects of IL-2Ralpha-targeted therapy (daclizu-mab) in multiple sclerosis, Proc. Natl. Acad. Sci. U. S. A. 103(2006) 5941–5946.

[21] J.F. Martin, J.S. Perry, N.R. Jakhete, X. Wang, B. Bielekova,An IL-2 paradox: blocking CD25 on T cells induces IL-2-drivenactivation of CD56(bright) NK cells, J. Immunol. 185 (2010)1311–1320.

[22] S.C. Wuest, J.H. Edwan, J.F. Martin, S. Han, J.S. Perry, C.M.Cartagena, E. Matsuura, D. Maric, T.A. Waldmann, B. Bielekova,A role for interleukin-2 trans-presentation in dendritic cell-mediated T cell activation in humans, as revealed by daclizumabtherapy, Nat. Med. 17 (2011) 604–609.

[23] J.T. Snyder, J. Shen, H. Azmi, J. Hou, D.H. Fowler, J.A.Ragheb, Direct inhibition of CD40L expression can contributeto the clinical efficacy of daclizumab independently of itseffects on cell division and Th1/Th2 cytokine production,Blood 109 (2007) 5399–5406.

[24] U. Oh, G. Blevins, C. Griffith, N. Richert, D. Maric, C.R. Lee, H.McFarland, S. Jacobson, Regulatory T cells are reduced duringanti-CD25 antibody treatment of multiple sclerosis, Arch. Neu-rol. 66 (2009) 471–479.

[25] B. Sadlack, H. Merz, H. Schorle, A. Schimpl, A.C. Feller, I.Horak, Ulcerative colitis-like disease in mice with a disruptedinterleukin-2 gene, Cell 75 (1993) 253–261.

[26] S. Higuma-Myojo, Y. Sasaki, S. Miyazaki, M. Sakai, A.Siozaki, N. Miwa, S. Saito, Cytokine profile of natural killercells in early human pregnancy, Am. J. Reprod. Immunol.54 (2005) 21–29.

[27] M.A. Zarife, E.A. Reis, T.M. Carmo, G.B. Lopes, E.C. Brandao,H.R. Silva, N. Santana, O.A. Martins-Filho, M.G. Reis, Increasedfrequency of CD56Bright NK-cells, CD3-CD16+CD56- NK-cells andactivated CD4+T-cells or B-cells in parallel with CD4+CDC25HighT-cells control potentially viremia in blood donors with HCV, J.Med. Virol. 81 (2009) 49–59.

[28] S.S. Farag, J.B. VanDeusen, T.A. Fehniger, M.A. Caligiuri, Biologyand clinical impact of human natural killer cells, Int. J. Hematol.78 (2003) 7–17.

[29] Z. Li, W.K. Lim, S.P. Mahesh, B. Liu, R.B. Nussenblatt, Cuttingedge: in vivo blockade of human IL-2 receptor induces expan-sion of CD56(bright) regulatory NK cells in patients with activeuveitis, J. Immunol. 174 (2005) 5187–5191.