The diverging roles of dendritic cells in kidney allotransplantation

Transplantation Reviews xxx (2015) xxx–xxx

Contents lists available at ScienceDirect

Transplantation Reviews

j ourna l homepage: www.e lsev ie r .com/ locate / t r re

The diverging roles of dendritic cells in kidney allotransplantation☆

Manuel Alfredo Podestà⁎, David Cucchiari, Claudio PonticelliNephrology and Dialysis Unit, Humanitas Clinical and Research Center, Via Manzoni 56, 20089, Rozzano – Milano, Italy

a b s t r a c t

Dendritic cells (DCs) are a family of antigen presenting cells that play a paramount role in bridging innate andadaptive immunity. In murine models several subtypes of DCs have been identified, including classical DCs,monocyte-derived DCs, and plasmacytoid DCs. Quiescent, immature DCs and some subtypes of plasmacytoidcells favor the expression of regulatory T cells, but in an inflammatory milieu DCs become mature and afterintercepting the antigenmigrate to lymphatic systemwhere they present the antigen to naïve T cells. Transplantrejection largely depends on the phenotype and maturation of DCs. The ischemia–reperfusion injury causes therelease of endogenous molecules that are recognized as danger signals by the pattern recognition receptor ofthe innate immunity with subsequent activation of inflammatory cells and mediators. In this environment DCsbecomemature andmigrate to lymphonodeswhere they present the alloantigen to T cells and direct their differ-entiation towards Th1 and Th17 effector cells. On the other hand, manipulation of DCs may favor T cell differen-tiation towards tolerant Th2 and T regulators (Treg). Experimental studies in murine models showed thepossibility of inducing an operational tolerance by injecting immature tolerogenicDCs. Recently, such a possibilityhas been also confirmed in primates. Although manipulation of DCs may represent an important step ahead inkidney transplantation, a number of technical and ethical issues should be solved before its clinical application.

© 2015 Elsevier Inc. All rights reserved.

1. Introduction

In 1868 Paul Langherans, still a student, first described branchedcells resembling neurons in the skin [1]. For many years the functionof these cells remained an enigma, although their frequent presence ininflammatory granulomas led to hypothesize a possible protective roleof these cells against infection. In 1973 Ralph Steinman and ZanvilCohn, by using phase-contrast light microscopy, identified a noveltype of cells in adherent cell populations prepared from mouse periph-eral lymphoid organs. These cells represented only 0.1–1.6% of the totalnucleated cells and had strange morphological features. The nucleuswas large, retractile, contorted in shape, with two or more small nucle-oli. The abundant cytoplasm contained many large spherical mitochon-dria. The cells had characteristic movements and showed branchedprojections. The authors proposed the term dendritic cells (DCs) forthis novel cell type [2,3] and demonstrated their importance in stimu-lating the leukocyte reaction [4]. Since then, further studies elucidatedthe origin of DCs and their central role in immune regulation.

2. Ontogenesis and functions of DCs

DCs are a family of professional antigen-presenting cells (APCs). DCscan be found in the skin and mucosal tissues (Langerhans cells), in

☆ Funding: No support has been provided for this paper.⁎ Corresponding author at: Istituto Clinico Humanitas IRCCS, Via Manzoni 56, 20089

Rozzano – Milano, Italy. Tel.: +39 3420036285.E-mail address: [email protected] (M.A. Podestà).

http://dx.doi.org/10.1016/j.trre.2015.04.0010955-470X/© 2015 Elsevier Inc. All rights reserved.

Please cite this article as: Podestà MA, et al, The diverging roles of dendrdx.doi.org/10.1016/j.trre.2015.04.001

parenchymal organs and gastrointestinal apparatus, in thymus, lymphnodes and in blood. Anatomically-wise, DCs may be divided in “resi-dent” lymphoid tissue and “migratory” non-lymphoid tissue DCs. Al-though the ontogenesis of human DCs is still poorly defined, murinemodels provided great insight on their different roles. Multiple subsetsof DCs have been identified in mouse (Table 1). They could be roughlydivided in classical DCs (cDCs), monocyte-derived DCs (moDCs) andplasmacytoid DCs (pDCs) (Fig. 1). The term “myeloid” is often used todistinguish all types of DCs from pDCs, which were originally describedas lymphoid.

Classical DCs can be further divided into two subsets characterizedby either CD8α/CD103 (cDC type 2) or CD11b (cDC type 1) expression.CD8α+ (found in lymphoid tissues) and CD103+ (found in non-lymphoid tissues) cDCs are the best characterized murine DCs subsetand seem to play a major role in antigen presentation to CD8+ T-cellsthrough MHC-I. CD11b+ DCs in contrast are more ill-defined andshow superior induction of CD4+ T-cell proliferation [5]. cDCsmay orig-inate from both myeloid and lymphoid precursor, but are more fre-quently derived from a common monocyte-DC precursors in the bonemarrow [6]. However, the fact that DCs acquire the expression of themarker CD8α only after their maturation may suggest that some DCscome from lymphoid cells that acquire the CD8+ phenotype on CD40-CD40L engagement [7].

Monocyte-derived DCs, also known as inflammatory DCs, are a het-erogeneous group of cells that are originated from phlogistic monociticinfiltrates, as supported by their expression of CD64/FcγRI [8,9] in addi-tion to CD11c, CD11b and Ly6C [10]. These cells produce TNFα and iNOSand were shown to favor Th17 polarization [11].

itic cells in kidney allotransplantation, Transplant Rev (2015), http://

Table 1Characterization of murine and human DCs subsets identified by the most commonly employed cellular markers.

Localization Origin DC subset Markers (mouse) Markers (human) Proposed function

Lymphoid tissue Myeloid cDC type 1 CD11b,CD11c [5,13]

CD1c (BDCA-1) [11] Induction of CD4+ T-cell proliferation

Myeloid cDC type 2 CD8α,CD11c [5,13]

CD141 (BDCA-3) [11] Antigen presentation to CD8+ T-cells

Myeloid moDC CD11c,CD11b,Ly6C,CD64 [9,10]

CD11c, CD14 [11,22] Inflammation, tissue repair

Plasmacytoid pDC mPDCA1,CD4,CD45RA [13,14]

CD303 (BDCA-2),CD304(BDCA-4),CD123 (IL-3R) [21]

Interferon production, tolerance (?)

Kidney Myeloid cDC type 1 CD11b,CX3CR1,F4/80,SIRPα [17]

CD1c (BDCA-1) [24] Induction of CD4+ T-cell proliferation

Myeloid cDC type 2 CD103 [17] CD141 (BDCA-3) [26] Antigen presentation to CD8+ T-cellsMyeloid moDC CD209 (DC-SIGN)

CD1c (BDCA-1)CD68 [24]

Inflammation, tissue repair

Plasmacytoid pDC CD303 (BDCA-2)CD123 (IL-3R) [24]

Interferon production, tolerance (?)

2 M.A. Podestà et al. / Transplantation Reviews xxx (2015) xxx–xxx

PlasmacytoidDCs are circulatingdendritic cellsmainly found in lym-phoid organs and characterized by a well developed secretory appara-tus that produces high doses of type I interferon upon viral infections[12]. pDCs express high levels of mPDCA1, but display a rather low ex-pression of CD11c or CD14, which distinguishes them from cDCs ormonocytes, respectively [13,14].

While it is relatively simple to purify DCs from lymphoid organs,consistent efforts were required to identify and characterize non-

Fig. 1. Schematic representation of DCs subsets and their main functions. cDCs are originated fr(CD8α+/CD103+ type 2 and CD11b+ type 1) that share common features with human BDCA-3+

liferation,while type 2 cDCs play amajor role in antigen presentation to CD8+ T-cells. moDCs arcirculating DCs that produce high doses of type I interferon upon viral infections.

Please cite this article as: Podestà MA, et al, The diverging roles of dendrdx.doi.org/10.1016/j.trre.2015.04.001

lymphoid tissue DCs. Renal resident DCs have been localized in closeproximity to peritubular capillaries in mice by identification of CD11cthrough immunohistochemistry [15]. These cDCs are originated frombone marrow progenitors, but a derivation from circulating Ly6C+

monocytes, which infiltrate the kidney upon inflammation, has alsobeen considered [16]. CD11c+ renal cDCs can be further divided intwo different subsets, based on the expression of either CD103 orCD11b, CX3CR1 and F40/80 [17].

om a commonmonocyte-DC precursor, and can be further divided in two subsets in miceand BDCA-1+ DCs respectively. Type 1 cDCs show superior induction of CD4+ T-cell pro-e originated from inflammatorymonocitic infiltrates and favor Th17 polarization. pDCs are

itic cells in kidney allotransplantation, Transplant Rev (2015), http://

3M.A. Podestà et al. / Transplantation Reviews xxx (2015) xxx–xxx

Mouse and human DCs system share some similarities; howevermurine markers such as CD8α and CD11b are not expressed on humancDCs. Consistent efforts have been directed towards the creation of aunified classification (Table 1). For instance, based on transcriptomicand functional studies, human CD1c+/BDCA1+ lymphoid tissue-resident and human CD207− CD14+ non-lymphoid cDCs have beengrouped as CD11b+-like cDCs, while it was demonstrated that CD141/BDCA3+ shares a distinct gene signature with mouse CD8α+ cDCs[18–20]. pDCs in humans are characterized by the expression ofCD123/IL-3R, CD303/BDCA-2 and CD304/BDCA-4, and by the absenceof the common myeloid markers [21]. Human moDCs have been onlyrecently identified in psoriatic skin and malignant ascites, but their fullcharacterization remains somewhat controversial [22,23].

Woltman et al. reported the first detailed analysis of DC subsets inthe human kidney. They described two different subsets of myeloidDCs in donor pre-transplant biopsies, defined by either positive stainingfor BDCA-1+, CD68+ andDC-SIGN+ (moDCs) or single positive stainingfor BDCA-1+ (cDCs type 1) [24,25]. In addition, the authors also detecteda minor population of BDCA-2+ plasmacytoid DCs in tubulointerstitialareas. Interestingly, none of these cellular subsets were positive forDC-LAMP, thus indicating that renal DCs are immature [24]. BDCA-3+

cDCs were identified in kidney biopsies from patients with activelupus nephritis, although they were not present in normal kidneys [26].

3. DCs as regulators of the immune response

The ability of DCs to regulate immunity is dependent on their matu-ration in an inflammatory milieu. Pathogen associated molecular pat-terns (PAMPs) and danger associated molecular patterns (DAMPs) arerecognized by Toll-like receptors (TLRs) and other receptors of the in-nate immunity, such as NOD-like and RIG-I receptors. TLRs activate anumber of adapter proteins (i.e. MyD88, IRAK, TRAM, TRAF, TRIF) thatmediate specific protein–protein interactions eventually leading to theformation of transcription factors—nuclear factor kinase B, interferonregulator3, mitogen-activated protein3—which induce or inhibit thegenes that organize the inflammatory response [27]. A variety of factorsfavoring an inflammatory environment can induce maturation of DCs,including bacterial-derived antigens, viral products, inflammatory cyto-kines, CD40/CD40L engagement. Mature DCs exert three distinctive

Fig. 2.Maturation andmigration of DCs: from a tolerant to an immunogenic phenotype. In a quical tolerance. However, in presence of pathogen aggression or release of endogenous substanceother receptors of the innate immune recognition system. These receptors recruit adapter protfactor kB and interferon regulator 3. These transcription factors can induce genes that orchestramature and migrate to lymphonodes where they present the antigen to the T cells so allowing

Please cite this article as: Podestà MA, et al, The diverging roles of dendrdx.doi.org/10.1016/j.trre.2015.04.001

functions: (i) a sentinel role in which antigens are captured and pre-sented, (ii) a migratory function, in which DCs move to theT-dependent areas of lymphoid organs and bind antigen-specific Tcells, (iii) an activation role, inwhich T-cell growth and effector functionare induced (Fig. 2). Interestingly, DCsmay present captured antigen onboth MHC-I andMHC-II class molecules. The former mechanism, whichrelies on endocytosis and proteasome processing, leads to CD8+ T-cellactivation through a process termed cross-presentation, which enablesimmune response against intracellular pathogens. In contrast, MHC-IImolecules assembly is attained through lysosome breakdown ofendocytic vesicles, which results in antigen presentation and activationof CD4+T-cells. This function is tightly controlled by a number of factorsleading to DCsmaturation, such as Toll-like receptor (TLR) signaling andexposure to inflammatory cytokines [28].

On the other hand, immature DCs may induce tolerance by immuneresponse down-regulation. When antigens are experimentally deliv-ered to DCs without maturation stimuli, MHC–peptide complexes areformed in the steady state. Naïve T cells, after recognizing their ligandson these DCs, divide repeatedly but are then deleted [29] and favor thegeneration of Foxp3+ T regulators (Tregs), which can be specific for ei-ther self- or non-self antigens [30]. Furthemore, thymoid DCs presentself-antigens to naïve T-cells, inducing the process of clonal deletionand positively selecting natural Tregs [31].

Thus, DCs can no longer be considered as a homogeneous cell typeperforming a single function of defense against pathogens and foreignantigens. Their phenotype and function depend on white cell lineagesand maturation stimuli that can activate divergent arms of the immunesystem. Further studies will be required to fully elucidate the role ofhuman subsets of DCs.

4. Innate immunity in allotransplant

Innate immunity plays a pivotal role in initiating an autoimmune re-sponse and in defending against oncogenic events [32,33]. In allotrans-plantation, innate immunity can be triggered in the donor even beforethe transplant. In the case of deceased donor the sympathetic systemhyperactivity, associated with brain death, causes a generalized ische-mia aggravated by the use of vasoconstrictor agents, which are neces-sary to sustain the circulation. After clamping the kidney vessels, the

iescent environment DCs release cytokines that can favor the development of immunolog-s by stressed cells, themolecular patterns of PAMPs or DAMPs are recognized by TLRs andeins which activate several kinases that amplify the signal, leading to activation of nuclearte the immune and inflammatory response. In an inflammatory environment, DCs becomethe activation of the adaptive immunity.

itic cells in kidney allotransplantation, Transplant Rev (2015), http://

4 M.A. Podestà et al. / Transplantation Reviews xxx (2015) xxx–xxx

short warm ischemia and the longer cold ischemia further reduce theoxygen and energetic supply leading to generation of reactive oxygenspecies, intra-cellular acidosis caused by the increased production oflactic acid from anaerobic glycolysis, and cell swelling caused by the im-paired function of ATP-dependent sodium–potassium pumps [34].These changes can cause damage to all cellular components thatmay ul-timately result in cell cycle arrest and even cell death.

The reperfusion of an ischemic kidney may result in further inflam-mation and oxidative damage, a paradoxical phenomenon termed is-chemia–reperfusion injury (IRI). The microvascular injury caused byischemia enhances fluid filtration and leukocyte plugging in capillariesand in postcapillary venules. After reperfusion, damaged endothelialcells secrete additional reactive oxygen species and favor the releaseof inflammatory mediators and proteolytic enzymes. Among them,caspases can mediate apoptosis in a significant number of sub-lethallyinjured cells. In addition to endothelial cells, proximal tubular epithelialcells are particularly vulnerable to the toxic effects of reperfusion andtend to undergo more necrosis in comparison with the less sensitivesegments, because they have higher metabolic demands [35,36]. Thedying cells release in the extra-cellular space endogenous moleculesthat are recognized as DAMPs from the pattern recognition receptorsof the innate immunity.

5. DCs as the bridge between innate and adaptive immunity

IRI and inflammation are the essential steps that lead to maturationof DCs in kidney transplant. Even before undergoing necrosis, damagedcells release several DAMPs, among which the best studied are High-Mobility Group Box 1 Protein (HMGB1) and heat-shock proteins(HSPs), such as HSP72. Generation of reactive oxygen species (ROS)can moreover damage extra-cellular proteins, creating fragments ofhyaluronan, fibronectin and heparan sulfate that can elicit TLRs-mediated DCs activation [37]. Upon receptor engagement with theseDAMPs, DCs modify their phenotype, increasing expression of MHC-related proteins, which are essential to intercept the antigen. In addi-tion, upon challenge with DAMPs, DCs express chemokine receptorsthat lead them to the T-dependent zone of secondary lymphoid organs,where the interaction between innate and adaptive immunity finallyoccurs. Their capacity to migrate, their constitutive expression MHC-Iand MHC-II, as well as co-stimulatory and adhesion molecules, makeDCs ideal cells for the activation of naïve T cells [38]. An importantrole is played by interleukin 12 [39] and chemokine receptors thathelp DCs to migrate into the T-cell zone of lymphoid organs [40].

Complement can also contribute to the link between innate andadaptive immunity: for instance, the component C3 can modulatecell-mediated response [41]. Moreover, the C3d component binds tothe CR2 receptor on the surface of follicular DCs and favors the interac-tion with the CR2-associated antigen on B cells, triggering antibody-mediated response [42]. The C5a component expressed on DCs favorstheir maturation and their capacity of activate T cells [43]. The terminalcomponents C5b-C9 bind to APC andhelp them in the direct recognitionof the antigen [44].

Thus, DCs are critical early initiators of innate immunity in the kid-ney and orchestrate inflammation subsequent to IRI. They are capableof inducing sterile inflammation after reperfusion directly through theproduction of proinflammatory cytokines and other soluble inflamma-tory mediators or indirectly through activation of effector T lympho-cytes and natural killer T cells (NKT), innate-like lymphocytes thatbind to glycolipid antigens presented by CD1d [45].

T-cell activation byDCs requires two signals: thefirst one is providedby the contact between the MHC-mounted antigen and the specificT-cell receptor (TCR). The second signal of co-stimulation is generatedby the contact between molecules of the B7 group on the surface ofDCs (CD80 and CD86) and adhesion molecules on the surface of theT cell (CD28). The presence of co-stimulatory molecules is a typical pre-rogative of DCs [46,47] and their absence favors tolerance, leading to

Please cite this article as: Podestà MA, et al, The diverging roles of dendrdx.doi.org/10.1016/j.trre.2015.04.001

deletion of the T clone or generation of Tregs. Nevertheless, matureDCs can transfer these molecules to other immune cells (i.e. B-cellsand monocytes) that can operate as APCs [48,49]. The antigen may bepresented to T cells by the donor DCs (direct pathway), by the recipientDCs in case of donor DCs depletion (indirect pathway) or by a passage ofalloantigen from donor to recipient DCs (semidirect pathays).

T cell polarization is of paramount importance in determining the ef-fect of the immune response on the allograft. Differentiation towardsthe pro-inflammatory Th1 and Th17 phenotypes has a pivotal role in re-jection, whereas Th2 and Treg polarization results in a protective effecton the transplanted organ. This polarization is guided byDCs and is con-trolled by cytokines, transcription factors and environmental factors.

Aside from TCR and B7-group signaling, other DCs receptors seem togreatly influence microenvironment and skew T-cell polarization.Sphingosine-1 phosphate (S1P), a sphingolipid produced byphosphorilation of sphngosine, is the natural ligand for a family of fiveG-protein coupled receptors. The absence of S1P3 on DCs preventstheir maturation and skews T-cell polarization towards a Th2 pheno-type, thus attenuating IRI [50]. These findings suggest the importanceof DCs S1P3 in modulating T cell function and support the developmentof S1P3 antagonist in tolerance induction in organ transplantation.

6. The dual role of DCs in rejection

Monocyte–macrophages have been found as the predominant cellu-lar infiltrate in kidney allograft rejection and represent amajor outcomeindicator [51,52]. Zuidwijk et al. analyzed and quantifiedDC subsets in asetting of acute rejection, finding an exceptionally high number of ma-ture renal DC-SIGN+ myeloid DCs (moDCs), which exceeded the renalBDCA-1+ (type 1) cDCs. The increased moDC/cDC ratio supports thetheory of a monocitic infiltration of the kidney in the setting of acute re-jection, with subsequent local differentiation to moDCs. The density ofboth myeloid subsets of mature DCs was associated with high inflam-mation score of the Banff 07 classification, graft interstitial fibrosis/tubular atrophy and loss of renal function in the long term [53], showingthat both myeloid subsets are involved in acute allograft rejection.Plasmacytoid DCs have been frequently associated to tolerance induc-tion [54,55]. However, pDCs were found to be increased in acuteallograft rejection, and their density appeared to correlate with inflam-mation and chronic injury [53].

Experimental studies suggest that localization of DCs may influencetheir function: graft-resident DCs and locally recruited systemic DCsmay indeed exert different roles that can influence the outcome of thekidney allograft. Studies in rat showed that renal cold IRI caused lossof graft DCs and progressive infiltration of host DC and CD4+ T cellswith effector/effector-memory phenotypes. These changes in graft/host DC populations were associated with development of tubulo-interstitial lesions, suggesting that graft–resident DCsmight have a pro-tective role while infiltrating host DCs exert deleterious effects on graftfunction [56].

In addition to origin and localization, also soluble mediators of themicroenvironment are likely to influence DCs phenotype and functionin the kidney. In conditions of cellular stress such as hypoxia/IRI, aden-osine extracellular concentrations increase by enhanced conversion ofATP. Adenosine, acting on several specific receptors (i.e. A1AR, A2AR,A2BR and A3R), mediates adaptation to hypoxia, conferring an anti-inflammatory state and a protective effect at cellular level [57]. By con-trast, ATP released by apoptotic cells acts as both a DAMP and a chemo-attractant for neutrophils and monocytes [58]. The enzymatic conver-sion steps from ATP to adenosine are regulated by two enzymes, CD39and CD73 [59].

Activation of A2AR expressed on DCs and T cells suppresses the im-mune response in allograft rejection [60]. Consistent with this finding,the expression of human CD39 in transgenic mice enhances the conver-sion of extracellular ATP to adenosine, and was shown to be protectivein a murine renal transplant model characterized by prolonged cold

itic cells in kidney allotransplantation, Transplant Rev (2015), http://

5M.A. Podestà et al. / Transplantation Reviews xxx (2015) xxx–xxx

ischemia [61]. Recent experimental data also showed that DCs tolerizedwith an A2AR agonist suppress NKT cell activation in vivo, attenuatingIRI [62]. These studies demonstrated that renal interstitial DCs pheno-type is determined at least in part by the expression of A2AR.

In summary, in organ transplantation DCs have a central role in ini-tiating alloantigen-specific immunity, but they may also favor an oper-ational tolerance. These contrasting effects of DCs depend on theirorigin and state of quiescence or maturation as well as by their locationand the chemical composition of the surrounding microenvironment.

7. Manipulation of DCs in allotransplant recipients

Tolerogenic DCs with immunoregulatory functions have been con-sidered as a possible target to induce and maintain immune tolerance.Inmurinemodels, adoptive transfusions of tolerogenic DCs could obtainan expansion of Tregs and reduced allotransplant sensitization in differ-ent types of transplants [63–65]. Other approaches explored in animalmodels comprised the inhibition of DCs maturation with agents suchas vascular–endothelial growth factor [66], IL-10 [67], laquinimoid[68], shikonin [69], honokiol [70], immunoglobulins [71] and phospho-diesterase inhibitors [72]. Alternatively, drugs favoring the productionof Tregs have been employed. A promising class of drugs is representedby mTOR inhibitors [73,74]. A combination therapy has been recentlyused to obtain an operational tolerance in primates: in Rhesusmacaque,pre-transplant intravenous infusion of tolerogenic DCs, together withmTOR inhibitor rapamycin and the B7-CD28 co-stimulation blockingagent CTLA4-Igcould significantly prolong kidney allograft survival incomparison with control monkeys not receiving DCs [75].

In the clinical setting, a French multicenter study is evaluating thepotential role of 1,25-α-dihydroxyvitamin D in renal transplantation,which may interfere with DCs maturation and T cell differentiation[76]. There are some encouraging data on mTOR inhibitors clinical ap-plication. Rapamycin administration to dialysis patients waiting fortransplantation was able to expand the production of Tregs [77]. In ad-dition, the conversion from cyclosporine to rapamycin increased thenumber of tolerogenic DCs and Tregs in renal transplant recipients[78]. Increasing attention has been paid to pDCs: as already stated,even though their capacity to prime T cell responses after infection orimmunization has been well demonstrated, these DCs may also exertan opposite tolerogenic role in different systems. Plasmacytoid DCsthat migrate to the thymus upon the influence of CCR9 and in the ab-sence of TLR signaling can drive CD4+CD25+FoxP3+ Treg development[55,79]. Some data speak in favor of a tolerogenic effect of pDCs. Amongpediatric liver-transplant recipients with rejection, the number of pDCswas significantly lower and the ratio cDCs/pDCswas significantly higherthan the ones in non rejecting patients [80]. Conversely, precursor pDCwas significantly higher in operationally tolerant pediatric liver trans-plant recipients than in those with maintenance immunosuppressionand correlated with the Treg frequency [81]. Pallotta et al. found thatindoleamine2,3-dioxygenase (IDO)was involved in intracellular signal-ing events responsible for the self-amplification and maintenance of astably regulatory phenotype in pDCs and showed that IDO has a tonic,non-enzymatic function that contributes to TGF-β-driven tolerance innon-inflammatory contexts [82]. Although a broad definition ofsteady-state pDCs as tolerogenic is premature [83], these cells seem toexert better tolerogenic effect in comparison with cDCs and may repre-sent possible targets for obtaining an operational tolerance in organtransplantation [84].

Despite this favorable data, ex vivomanipulation of DCs is limited bysome factors, such as the high cost and the long time needed to handlein laboratory. Moreover, before assessing their role in clinical trials anumber of problems should be better clarified including cell isolationand purification techniques, source, timing, route, frequency and doseof administration [85]. Some possible adverse events should be takeninto account. Maturation of tolerogenic DCs after in vivo injection orthe presence of a contaminant cell product could lead to the

Please cite this article as: Podestà MA, et al, The diverging roles of dendrdx.doi.org/10.1016/j.trre.2015.04.001

development of sensitization of the recipient to the donor antigens[86]. Also, the interaction between immunosuppressive drugs and DCsand the related increased risks of infection and cancer should be takeninto account.

Acknowledgments

The authors would like to thank prof. Meroni PL for his precious sug-gestions and critics on the manuscript.

Disclosures: CP served as a consultant of Novartis Italy until Decem-ber 31, 2011. He received honoraria from Novartis, Janssen-Cilag,Astellas. MAP and DC declare no conflicts of interest.

References

[1] Langerhans P. Ueber die Nerven der menschlichen haut. Arch Für Pathol Anat Phys-iol Für Klin Med 1868;44:325–37. http://dx.doi.org/10.1007/BF01959006.

[2] Steinman RM, Cohn ZA. Identification of a novel cell type in peripheral lymphoid or-gans of mice. I. Morphology, quantitation, tissue distribution. J Exp Med 1973;137:1142–62.

[3] Steinman RM, Cohn ZA. Identification of a novel cell type in peripheral lymphoid or-gans of mice. II. Functional properties in vitro. J Exp Med 1974;139:380–97.

[4] Steinman RM, Witmer MD. Lymphoid dendritic cells are potent stimulators of theprimarymixed leukocyte reaction inmice. Proc Natl Acad Sci U S A 1978;75:5132–6.

[5] Dudziak D, Kamphorst AO, Heidkamp GF, et al. Differential antigen processing bydendritic cell subsets in vivo. Science 2007;315:107–11. http://dx.doi.org/10.1126/science.1136080.

[6] Manz MG, Traver D, Miyamoto T, Weissman IL, Akashi K. Dendritic cell potentials ofearly lymphoid and myeloid progenitors. Blood 2001;97:3333–41.

[7] Anjuère F, Martínez del Hoyo G, Martín P, Ardavín C. Langerhans cells acquire aCD8+ dendritic cell phenotype on maturation by CD40 ligation. J Leukoc Biol2000;67:206–9.

[8] Mildner A, Yona S, Jung S. A close encounter of the third kind: monocyte-derivedcells. Adv Immunol 2013;120:69–103. http://dx.doi.org/10.1016/B978-0-12-417028-5.00003-X.

[9] Guilliams M, Henri S, Tamoutounour S, et al. From skin dendritic cells to a simplifiedclassification of human and mouse dendritic cell subsets. Eur J Immunol 2010;40:2089–94. http://dx.doi.org/10.1002/eji.201040498.

[10] Kool M, Soullié T, van Nimwegen M, et al. Alum adjuvant boosts adaptive immunityby inducing uric acid and activating inflammatory dendritic cells. J Exp Med 2008;205:869–82. http://dx.doi.org/10.1084/jem.20071087.

[11] Haniffa M, Collin M, Ginhoux F. Ontogeny and functional specialization of dendriticcells in human andmouse. Adv Immunol 2013;120:1–49. http://dx.doi.org/10.1016/B978-0-12-417028-5.00001-6.

[12] Siegal FP, Kadowaki N, Shodell M, et al. The nature of the principal type 1 interferon-producing cells in human blood. Science 1999;284:1835–7.

[13] Lindenmeyer M, Noessner E, Nelson PJ, Segerer S. Dendritic cells in experimentalrenal inflammation—part I. Nephron Exp Nephrol 2011;119:e83–90. http://dx.doi.org/10.1159/000332029.

[14] Blasius AL, Giurisato E, Cella M, Schreiber RD, Shaw AS, Colonna M. Bone marrowstromal cell antigen 2 is a specific marker of type I IFN-producing cells in thenaive mouse, but a promiscuous cell surface antigen following IFN stimulation. JImmunol 2006;177:3260–5.

[15] Krüger T, Benke D, Eitner F, et al. Identification and functional characterization ofdendritic cells in the healthy murine kidney and in experimental glomerulonephri-tis. J Am Soc Nephrol 2004;15:613–21.

[16] Rogers NM, Ferenbach DA, Isenberg JS, Thomson AW, Hughes J. Dendritic cells andmacrophages in the kidney: a spectrum of good and evil. Nat Rev Nephrol 2014;10:625–43. http://dx.doi.org/10.1038/nrneph.2014.170.

[17] Ginhoux F, Liu K, Helft J, et al. The origin and development of nonlymphoid tissueCD103+ DCs. J Exp Med 2009;206:3115–30. http://dx.doi.org/10.1084/jem.20091756.

[18] Klechevsky E, Morita R, Liu M, et al. Functional specializations of human epidermalLangerhans cells and CD14+ dermal dendritic cells. Immunity 2008;29:497–510.http://dx.doi.org/10.1016/j.immuni.2008.07.013.

[19] Crozat K, Guiton R, GuilliamsM, et al. Comparative genomics as a tool to reveal func-tional equivalences between human and mouse dendritic cell subsets. Immunol Rev2010;234:177–98. http://dx.doi.org/10.1111/j.0105-2896.2009.00868.x.

[20] Robbins SH, Walzer T, Dembélé D, et al. Novel insights into the relationships be-tween dendritic cell subsets in human andmouse revealed by genome-wide expres-sion profiling. Genome Biol 2008;9:R17. http://dx.doi.org/10.1186/gb-2008-9-1-r17.

[21] Dzionek A, Fuchs A, Schmidt P, et al. BDCA-2, BDCA-3, and BDCA-4: three markersfor distinct subsets of dendritic cells in human peripheral blood. J Immunol 2000;165:6037–46.

[22] Segura E, Touzot M, Bohineust A, et al. Human inflammatory dendritic cells induceTh17 cell differentiation. Immunity 2013;38:336–48. http://dx.doi.org/10.1016/j.immuni.2012.10.018.

[23] Hänsel A, Günther C, Ingwersen J, et al. Human slan (6-sulfo LacNAc) dendritic cellsare inflammatory dermal dendritic cells in psoriasis and drive strong TH17/TH1 T-cell responses. J Allergy Clin Immunol 2011;127:787–794.e1–9. http://dx.doi.org/10.1016/j.jaci.2010.12.009.

itic cells in kidney allotransplantation, Transplant Rev (2015), http://

6 M.A. Podestà et al. / Transplantation Reviews xxx (2015) xxx–xxx

[24] Woltman AM, de Fijter JW, Zuidwijk K, et al. Quantification of dendritic cell subsetsin human renal tissue under normal and pathological conditions. Kidney Int 2007;71:1001–8. http://dx.doi.org/10.1038/sj.ki.5002187.

[25] Noessner E, Lindenmeyer M, Nelson PJ, Segerer S. Dendritic cells in human renal in-flammation—part II. Nephron Exp Nephrol 2011;119:e91–8. http://dx.doi.org/10.1159/000332032.

[26] Fiore N, Castellano G, Blasi A, et al. Immature myeloid and plasmacytoid dendriticcells infiltrate renal tubulointerstitium in patients with lupus nephritis. MolImmunol 2008;45:259–65. http://dx.doi.org/10.1016/j.molimm.2007.04.029.

[27] Kawai T, Akira S. The role of pattern-recognition receptors in innate immunity: up-date on Toll-like receptors. Nat Immunol 2010;11:373–84. http://dx.doi.org/10.1038/ni.1863.

[28] Mildner A, Jung S. Development and function of dendritic cell subsets. Immunity2014;40:642–56. http://dx.doi.org/10.1016/j.immuni.2014.04.016.

[29] Steinman RM, Hawiger D, Nussenzweig MC. Tolerogenic dendritic cells. Annu RevImmunol 2003;21:685–711. http://dx.doi.org/10.1146/annurev.immunol.21.120601.141040.

[30] Mahnke K, Schmitt E, Bonifaz L, Enk AH, Jonuleit H. Immature, but not inactive: thetolerogenic function of immature dendritic cells. Immunol Cell Biol 2002;80:477–83.http://dx.doi.org/10.1046/j.1440-1711.2002.01115.x.

[31] Chung CYJ, Ysebaert D, Berneman ZN, Cools N. Dendritic cells: cellular mediators forimmunological tolerance. Clin Dev Immunol 2013;2013:972865. http://dx.doi.org/10.1155/2013/972865.

[32] Waldner H. The role of innate immune responses in autoimmune disease develop-ment. Autoimmun Rev 2009;8:400–4. http://dx.doi.org/10.1016/j.autrev.2008.12.019.

[33] Banchereau J, Palucka AK. Dendritic cells as therapeutic vaccines against cancer. NatRev Immunol 2005;5:296–306. http://dx.doi.org/10.1038/nri1592.

[34] Ponticelli CE. The impact of cold ischemia time on renal transplant outcome. KidneyInt 2015;87(2):272–5. http://dx.doi.org/10.1038/ki.2014.359.

[35] Cavaillé-Coll M, Bala S, Velidedeoglu E, et al. Summary of FDAworkshop on ischemiareperfusion injury in kidney transplantation. Am J Transplant 2013;13:1134–48.http://dx.doi.org/10.1111/ajt.12210.

[36] Ponticelli C. Ischaemia–reperfusion injury: a major protagonist in kidney transplan-tation. Nephrol Dial Transplant 2014;29:1134–40. http://dx.doi.org/10.1093/ndt/gft488.

[37] Land WG. Emerging role of innate immunity in organ transplantation part II: poten-tial of damage-associated molecular patterns to generate immunostimulatory den-dritic cells. Transplant Rev (Orlando) 2012;26:73–87. http://dx.doi.org/10.1016/j.trre.2011.02.003.

[38] Cella M, Jarrossay D, Facchetti F, et al. Plasmacytoid monocytes migrate to inflamedlymph nodes and produce large amounts of type I interferon. Nat Med 1999;5:919–23. http://dx.doi.org/10.1038/11360.

[39] Trinchieri G. Interleukin-12 and the regulation of innate resistance and adaptive im-munity. Nat Rev Immunol 2003;3:133–46. http://dx.doi.org/10.1038/nri1001.

[40] Cyster JG. Leukocyte migration: scent of the T zone. Curr Biol 2000;10:R30–3.[41] Dunkelberger JR, Song W-C. Role and mechanism of action of complement in regu-

lating T cell immunity. Mol Immunol 2010;47:2176–86. http://dx.doi.org/10.1016/j.molimm.2010.05.008.

[42] Carroll MC, Isenman DE. Regulation of humoral immunity by complement. Immuni-ty 2012;37:199–207. http://dx.doi.org/10.1016/j.immuni.2012.08.002.

[43] Peng Q, Li K, Wang N, et al. Dendritic cell function in allostimulation is modulated byC5aR signaling. J Immunol 2009;183:6058–68. http://dx.doi.org/10.4049/jimmunol.0804186.

[44] Zhou W, Farrar CA, Abe K, et al. Predominant role for C5b-9 in renal ischemia/reper-fusion injury. J Clin Invest 2000;105:1363–71. http://dx.doi.org/10.1172/JCI8621.

[45] Li L, Okusa MD. Macrophages, dendritic cells, and kidney ischemia–reperfusion inju-ry. Semin Nephrol 2010;30:268–77. http://dx.doi.org/10.1016/j.semnephrol.2010.03.005.

[46] Schwartz RH. Costimulation of T lymphocytes: the role of CD28, CTLA-4, and B7/BB1in interleukin-2 production and immunotherapy. Cell 1992;71:1065–8.

[47] McLellan AD, Sorg RV, Williams LA, Hart DN. Human dendritic cells activate T lym-phocytes via a CD40: CD40 ligand-dependent pathway. Eur J Immunol 1996;26:1204–10. http://dx.doi.org/10.1002/eji.1830260603.

[48] Game DS, Rogers NJ, Lechler RI. Acquisition of HLA-DR and costimulatory moleculesby T cells from allogeneic antigen presenting cells. Am J Transplant 2005;5:1614–25.http://dx.doi.org/10.1111/j.1600-6143.2005.00916.x.

[49] Wood KJ, Zaitsu M, Goto R. Cell mediated rejection. Methods Mol Biol 2013;1034:71–83. http://dx.doi.org/10.1007/978-1-62703-493-7_3.

[50] Bajwa A, Huang L, Ye H, et al. Dendritic cell sphingosine 1-phosphate receptor-3 reg-ulates Th1-Th2 polarity in kidney ischemia–reperfusion injury. J Immunol 2012;189:2584–96. http://dx.doi.org/10.4049/jimmunol.1200999.

[51] Girlanda R, Kleiner DE, Duan Z, et al. Monocyte infiltration and kidney allograft dys-function during acute rejection. Am J Transplant 2008;8:600–7. http://dx.doi.org/10.1111/j.1600-6143.2007.02109.x.

[52] Matheson PJ, Dittmer ID, Beaumont BW, Merrilees MJ, Pilmore HL. The macrophageis the predominant inflammatory cell in renal allograft intimal arteritis. Transplanta-tion 2005;79:1658–62.

[53] Zuidwijk K, de Fijter JW,MallatMJK, et al. Increased influx ofmyeloid dendritic cells dur-ing acute rejection is associatedwith interstitialfibrosis and tubular atrophy andpredictspoor outcome. Kidney Int 2012;81:64–75. http://dx.doi.org/10.1038/ki.2011.289.

[54] Colonna M, Trinchieri G, Liu Y-J. Plasmacytoid dendritic cells in immunity. NatImmunol 2004;5:1219–26. http://dx.doi.org/10.1038/ni1141.

[55] Martín-Gayo E, Sierra-Filardi E, Corbí AL, Toribio ML. Plasmacytoid dendritic cellsresident in human thymus drive natural Treg cell development. Blood 2010;115:5366–75. http://dx.doi.org/10.1182/blood-2009-10-248260.

Please cite this article as: Podestà MA, et al, The diverging roles of dendrdx.doi.org/10.1016/j.trre.2015.04.001

[56] Ozaki KS, Kimura S, NalesnikMA, et al. The loss of renal dendritic cells and activationof host adaptive immunity are long-term effects of ischemia/reperfusion injury fol-lowing syngeneic kidney transplantation. Kidney Int 2012;81:1015–25. http://dx.doi.org/10.1038/ki.2011.458.

[57] Morello S, Ito K, Yamamura S, et al. IL-1 beta and TNF-alpha regulation of the aden-osine receptor (A2A) expression: differential requirement for NF-kappa B binding tothe proximal promoter. J Immunol 2006;177:7173–83.

[58] Elliott MR, Chekeni FB, Trampont PC, et al. Nucleotides released by apoptotic cells actas a find-me signal to promote phagocytic clearance. Nature 2009;461:282–6.http://dx.doi.org/10.1038/nature08296.

[59] Sitkovsky MV, Lukashev D, Apasov S, et al. Physiological control of immune responseand inflammatory tissue damage by hypoxia-inducible factors and adenosine A2Areceptors. Annu Rev Immunol 2004;22:657–82. http://dx.doi.org/10.1146/annurev.immunol.22.012703.104731.

[60] Sevigny CP, Li L, Awad AS, et al. Activation of adenosine 2A receptors attenuates al-lograft rejection and alloantigen recognition. J Immunol 2007;178:4240–9.

[61] Crikis S, Lu B, Murray-Segal LM, et al. Transgenic overexpression of CD39 protectsagainst renal ischemia–reperfusion and transplant vascular injury. Am J Transplant2010;10:2586–95. http://dx.doi.org/10.1111/j.1600-6143.2010.03257.x.

[62] Li L, Huang L, Ye H, et al. Dendritic cells tolerized with adenosine A2AR agonist atten-uate acute kidney injury. J Clin Invest 2012;122:3931–42. http://dx.doi.org/10.1172/JCI63170.

[63] Wu W, Shan J, Li Y, et al. Adoptive transfusion of tolerance dendritic cells prolongs thesurvival of cardiac allograft: a systematic review of 44 basic studies in mice. J Evid-Based Med 2012;5:139–53. http://dx.doi.org/10.1111/j.1756-5391.2012.01191.x.

[64] Zhou Y, Shan J, Li Y, et al. Adoptive transfusion of tolerance dendritic cells prolongsthe survival of skin allografts inmice: a systematic review. J Evid-BasedMed 2013;6:90–103. http://dx.doi.org/10.1111/jebm.12035.

[65] Xia MJ, Shan J, Li YP, et al. Adoptive transfusion of tolerogenic dendritic cells pro-longs the survival of liver allograft: a systematic review. J Evid-Based Med 2014;7:135–46. http://dx.doi.org/10.1111/jebm.12094.

[66] Gabrilovich DI, Chen HL, Girgis KR, et al. Production of vascular endothelial growthfactor by human tumors inhibits the functional maturation of dendritic cells. NatMed 1996;2:1096–103.

[67] Steinbrink K, Wölfl M, Jonuleit H, Knop J, Enk AH. Induction of tolerance by IL-10-treated dendritic cells. J Immunol 1997;159:4772–80.

[68] Jolivel V, Luessi F, Masri J, et al. Modulation of dendritic cell properties by laquinimodas a mechanism for modulating multiple sclerosis. Brain J Neurol 2013;136:1048–66. http://dx.doi.org/10.1093/brain/awt023.

[69] Lee C-C, Wang C-N, Lai Y-T, et al. Shikonin inhibits maturation of bone marrow-derived dendritic cells and suppresses allergic airway inflammation in a murinemodel of asthma. Br J Pharmacol 2010;161:1496–511. http://dx.doi.org/10.1111/j.1476-5381.2010.00972.x.

[70] Li C-Y, Chao LK, Wang S-C, et al. Honokiol inhibits LPS-induced maturation and in-flammatory response of human monocyte-derived dendritic cells. J Cell Physiol2011;226:2338–49. http://dx.doi.org/10.1002/jcp.22576.

[71] Bayry J, Lacroix-Desmazes S, Carbonneil C, et al. Inhibition of maturation and func-tion of dendritic cells by intravenous immunoglobulin. Blood 2003;101:758–65.http://dx.doi.org/10.1182/blood-2002-05-1447.

[72] Heystek HC, Thierry A-C, Soulard P,Moulon C. Phosphodiesterase 4 inhibitors reducehuman dendritic cell inflammatory cytokine production and Th1-polarizing capaci-ty. Int Immunol 2003;15:827–35.

[73] Taner T, Hackstein H, Wang Z, Morelli AE, Thomson AW. Rapamycin-treated,alloantigen-pulsed host dendritic cells induce ag-specific T cell regulation and pro-long graft survival. Am J Transplant 2005;5:228–36. http://dx.doi.org/10.1046/j.1600-6143.2004.00673.x.

[74] Horibe EK, Sacks J, Unadkat J, et al. Rapamycin-conditioned, alloantigen-pulsed den-dritic cells promote indefinite survival of vascularized skin allografts in associationwith T regulatory cell expansion. Transpl Immunol 2008;18:307–18. http://dx.doi.org/10.1016/j.trim.2007.10.007.

[75] Ezzelarab MB, Zahorchak AF, Lu L, et al. Regulatory dendritic cell infusion prolongskidney allograft survival in nonhuman primates. Am J Transplant 2013;13:1989–2005. http://dx.doi.org/10.1111/ajt.12310.

[76] Penna G, Adorini L. 1 Alpha,25-dihydroxyvitamin D3 inhibits differentiation, matu-ration, activation, and survival of dendritic cells leading to impaired alloreactive Tcell activation. J Immunol 2000;164:2405–11.

[77] Afzali B, Edozie FC, Fazekasova H, et al. Comparison of regulatory T cells in hemodi-alysis patients and healthy controls: implications for cell therapy in transplantation.Clin J Am Soc Nephrol 2013;8:1396–405. http://dx.doi.org/10.2215/CJN.12931212.

[78] Stallone G, Pontrelli P, Infante B, et al. Rapamycin induces ILT3(high)ILT4(high) den-dritic cells promoting a new immunoregulatory pathway. Kidney Int 2014;85:888–97. http://dx.doi.org/10.1038/ki.2013.337.

[79] Hadeiba H, Sato T, Habtezion A, Oderup C, Pan J, Butcher EC. CCR9 expression definestolerogenic plasmacytoid dendritic cells able to suppress acute graft-versus-host dis-ease. Nat Immunol 2008;9:1253–60. http://dx.doi.org/10.1038/ni.1658.

[80] Gupta A, Kumar CA, NingappaM, et al. Elevatedmyeloid: plasmacytoid dendritic cellratio associates with late, but not early, liver rejection in children induced with rab-bit anti-human thymocyte globulin. Transplantation 2009;88:589–94. http://dx.doi.org/10.1097/TP.0b013e3181b11f12.

[81] Tokita D, Mazariegos GV, Zahorchak AF, et al. High PD-L1/CD86 ratio onplasmacytoid dendritic cells correlates with elevated T-regulatory cells in livertransplant tolerance. Transplantation 2008;85:369–77. http://dx.doi.org/10.1097/TP.0b013e3181612ded.

[82] Pallotta MT, Orabona C, Volpi C, et al. Indoleamine 2,3-dioxygenase is a signalingprotein in long-term tolerance by dendritic cells. Nat Immunol 2011;12:870–8.http://dx.doi.org/10.1038/ni.2077.

itic cells in kidney allotransplantation, Transplant Rev (2015), http://

7M.A. Podestà et al. / Transplantation Reviews xxx (2015) xxx–xxx

[83] Reizis B, Bunin A, Ghosh HS, Lewis KL, Sisirak V. Plasmacytoid dendritic cells: recentprogress and open questions. Annu Rev Immunol 2011;29:163–83. http://dx.doi.org/10.1146/annurev-immunol-031210-101345.

[84] Rogers NM, Isenberg JS, Thomson AW. Plasmacytoid dendritic cells: no longer anenigma and now key to transplant tolerance? Am J Transplant 2013;13:1125–33.http://dx.doi.org/10.1111/ajt.12229.

Please cite this article as: Podestà MA, et al, The diverging roles of dendrdx.doi.org/10.1016/j.trre.2015.04.001

[85] Ezzelarab M, Thomson AW. Tolerogenic dendritic cells and their role in transplanta-tion. Semin Immunol 2011;23:252–63. http://dx.doi.org/10.1016/j.smim.2011.06.007.

[86] Moreau A, Varey E, Bériou G, et al. Tolerogenic dendritic cells and negative vaccina-tion in transplantation: from rodents to clinical trials. Front Immunol 2012;3:218.http://dx.doi.org/10.3389/fimmu.2012.00218.

itic cells in kidney allotransplantation, Transplant Rev (2015), http://