Crosstalk between dendriticcell subsets and implicationsfor dendritic cell-basedanticancer immunotherapyExpert Rev. Clin. Immunol. Early online, 1–12 (2014)

Ghaith Bakdash,Inge Schreurs,Gerty Schreibelt‡ andJurjen Tel*‡

Department of Tumor Immunology,

Radboud University Medical Centre and

Radboud Institute for Molecular Life

Sciences, Nijmegen, The Netherlands

*Author for correspondence:

Tel.: +31 243 617 600

Fax: +31 243 640 339

J.Tel@ncmls.ru.nl

‡Authors contributed equally

Dendritic cells (DCs) are a family of professional antigen-presenting cells that have anindispensable role in the initiation of innate and adaptive immune responses againstpathogens and tumor cells. The DC family is very heterogeneous. Two main types of naturallyoccurring DCs circulate in peripheral blood, each with its unique phenotypic and functionalcharacteristics: myeloid DCs and plasmacytoid. There is an ample number of studies that havefocused on the bi-directional crosstalk between DCs and natural killer cells or T cells.However, the crosstalk among the different DC subsets, in the context of infectious diseasesand cancer, has until now not received much attention. Here, we review all availableliterature that has dealt with the crosstalk between plasmacytoid and myeloid DCs and thepotential mode of action. Emphasis will be given to the therapeutic potential of thecombination of DC subsets for DC-based immunotherapy.

KEYWORDS: cancer • crosstalk • immunotherapy • myeloid DCs • plasmacytoid DCs

The human immune system is made up of awide variety of cell types to maintain immunehomeostasis. In this system, professionalantigen-presenting cells (APCs) control thetight balance between tolerance and immunity.All professional APCs express MHC class II-peptide complexes on their cell surface andexploit an efficient antigen-uptake machinery.Dendritic cells (DCs) represent a family ofprofessional APCs that are derived fromhematopoietic precursors and have the capacityto induce antigen-specific T-cell responses [1].Efficient T-cell priming is dependent on fullmaturation of DCs, which is evoked by therecognition of specific pathogen-associatedmolecular patterns by their distinct pathogenrecognition receptors (PRRs) [2–4]. DCs expressa large group of PRRs that includes C-typelectin receptors, NOD-like receptors, RIG-I-like receptors and DNA receptors [2,5], for thedetection of proteins, lipids, carbohydrates andnucleic acids that are pathogen specific and arenot expressed by the host [6,7]. The most wellknown family of PRRs is the Toll-like receptor(TLR) family. To date, in humans 10 differentTLRs have been identified [4,8]. TLR1, 2,

4–6 are all expressed on the cell surface,whereas the TLR3, 7–10 are expressed inendocytic compartments. TLR2/TLR1 andTLR2/TLR6 are heterodimers and recognizelipids and peptidoglycans. TLR4 recognizeslipid A of lipopolysaccharide and TLR5 recog-nizes bacterial flagellin [2,7,8]. TLR3 recognizesviral replication intermediate dsRNA. TLR7and 8 recognize ssRNA and TLR9 recognizesunmethylated CpG in bacterial and viral geno-mic DNA. Endogenous danger signals (e.g.,alarmins) are also able to trigger TLRs andthereby induce DC activation [9]. Alarmins arereleased following non-programmed cell death,and they restore the homeostasis by promotingtissue reconstruction.

DCs constantly monitor their surroundingenvironment for pathogens and have a highphagocytic capacity. Pathogens are internalizedby DCs upon encounter and thereafter aredegraded by enzymes to digest the pathogeninto smaller antigenic peptides to be presentedto naı̈ve T cells. DCs are equipped with andexploit several types of antigen capturemechanisms, for example, phagocytosis, pino-cytosis, receptor-mediated endocytosis and

informahealthcare.com 10.1586/1744666X.2014.912561 � 2014 Informa UK Ltd ISSN 1744-666X 1

Review

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

caveolin-dependent antigen internalization [10]. Extracellularantigens are encapsulated by the plasma membrane, which ena-bles the formation of an intracellular vacuole termed as phago-some or an endosome. The pool of early endosomes includesmultiple populations of early endosomes with different kinetics.Some early endosomes are very stable while some rapidly trans-form into late endosomes [11]. From the late endosomes anti-gens are loaded onto MHC class II molecules and transportedto the cell surface for antigen presentation to CD4+

T cells [11,12]. MHC class I molecules present intracellular anti-gens, which have been processed by the proteasome, to CD8+

T cells. DCs also have the unique ability to present exogenous-derived antigens in MHC class I molecules to CD8+ T cells viathe so-called cross-presentation process [13,14].

The capacity to migrate from non-lymphoid peripheral organsis one of the first properties attained by maturing DCs [15].Maturing DCs also upregulate the formation of MHC-peptide

complexes and the expression of these complexes along with theexpression of costimulatory molecules [15,16]. Concurrently, theendocytic capacity of maturing DCs is downregulated, whichprevents the reabsorption of the MHC-peptide complexes [15].During the maturation process, the chemokine receptor CCR7 isupregulated, which sensitizes DCs to the chemokine ligandsCCL19 and CCL21 that are expressed in the T-cell zones inlymphoid organs [17]. Functional maturation reaches its endpoint with DCs residing in T-cell-rich lymphoid tissues, and pre-senting the MHC-peptide complex to residing T cells [15].

Naı̈ve T cells are activated through multiple signals. Signalone is when a T-cell receptor recognizes a MHC-peptide com-plex, signal two is when CD28 on the T cell interacts withCD80 or CD86 on the DC, also known as costimulation [18].The combination of signal one and two stimulates T-cell pro-liferation. Signal three is a DC-derived cytokine signal(IL-12 and type I IFNs) that drives polarization of naı̈veT cells into a specific functional subset [19]. Homing instruc-tions by the DCs form a fourth signal [20]. This gives T cellsthe indication about the origin of the DCs and where thepathogen was encountered [21]. DCs that have not encountereda pathogen yet are known as immature and reside in tissueswith a high phagocytic capacity. Immature DCs are capable ofinducing Treg to preserve tolerance to foreign antigens andself-antigens [22]. Because immature DCs have a low expressionof MHC and costimulatory factors, they fail to stimulateT cells adequately, which leads to T-cell anergy [22].

Despite their indispensable role in eliciting an immuneresponse, DCs are a rather rare and heterogeneous type ofimmune cell. DC subtypes differ in phenotype and function,which may also depend on their localization. Every DC subsetexpresses a specialized combination of PRRs and is dividedinto different groups based on variable criteria [8,23]. Emergingevidence suggest that DC subsets have the capacity to cross-activate each other and thereby orchestrate full immune activa-tion against a wide variety of pathogens [24,25]. Here, we reviewthe bi-directional crosstalk between DC subsets and extrapolatethis to implications for DC-based immunotherapy.

Different subsets of DCDCs can broadly be categorized into two main subsets: bloodand lymphoid tissue DCs and inflammatory DCs (InfDC).Blood and lymphoid DCs are divided into two subsets: plasma-cytoid (pDCs) and myeloid (mDCs) DCs [26]. In humans,both subsets are defined as lineage (CD3, 14, 15, 19, 20, 56)negative, MHC class II (HLA-DR) positive, but differ in theexpression of CD11c (TABLE 1) [27]. Moreover, human pDCs arecharacterized by the specific expression of BDCA2,BDCA4 and ILT7 [28,29]. The human mDC subset can be fur-ther subdivided based on the expression of CD141+ (BDCA3)and CD1c+ (BDCA1). Transcriptional profiling revealed signif-icant differences between the human blood DC subsets [30],probably reflecting differences in their antigen-presenting capac-ities. Furthermore, mDCs and pDCs show clearly distinctresponses to products derived from pathogens, as a result of

Table 1. Phenotypical characteristics of humanblood dendritic cell subsets.

pDC mDC

BDCA1+ BDCA3+

Characteristic

markers

BDCA1 – + -

BDCA3 – – +

BDCA4 + – –

CD123 + ±

CD11c – + +

HLA-DR + + +

ILT7/CD85g + – –

Toll-like

receptors

TLR1 + + +

TLR2 – + +

TLR3 – + +

TLR4 – + ±

TLR5 – + ±

TLR6 ± + +

TLR7 + ± ±

TLR8 – + +

TLR9 + – –

TLR10 + + +

C-type lectin

receptors

BDCA2 + – –

CLEC9A/DNGR-1 – – +

DCIR + + –

DEC205/CD205 + + +

MMR/CD206 – – –

DC-SIGN/CD209 – – –

mDCs: Myeloid dendritic cells; pDCs: Plasmacytoid dendritic cells.

Review Bakdash, Schreurs, Schreibelt & Tel

doi: 10.1586/1744666X.2014.912561 Expert Rev. Clin. Immunol.

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

their distinct TLR expression profiles (TABLE 1) [4]. In a non-activated state, both mDCs and pDCs express regulatory mole-cules and have been associated with tolerance orTh2 responses [26,31,32]. Moreover, non-activated pDCs promoteTreg cell-mediated immunosuppression [33], and the presenceof pDCs and mDCs in tumors has been correlated with poorclinical outcome [34–36].

mDCs have the capacity to produce IL-12 in response tomicrobial stimuli through TLRs, and thereby induce Th1 andpotently prime cytotoxic T-cell responses [37,38]. Moreover,BDCA1+ mDCs were shown to respond to viral stimulation byproducing IL-27, which excels in inducing a cytotoxic profileof CD8+ T cells [39]. Furthermore, dependent on the stimulusused, BDCA1+ mDCs have also been shown to secrete low butsignificant amounts of type I IFNs, and thereby able to skewT-cell responses [40,41]. Nonetheless, it is generally accepted thatpDCs, in contrast, are the key effectors in innate immunitybecause of their capacity to produce large amounts of type IIFNs in response to bacterial or viral infections. Similar tomDC-derived IL-12, pDC-derived type I IFNs also participatein T-cell priming as Th1-inducing cytokines [31]. The vastamount of type I IFNs produced by pDCs inhibits viral repli-cation and contributes to the activation of B cells, T cells, NKcells and mDCs [42]. Although mDCs were initially describedas potent professional APCs, and regulators of specific T-cellresponses [8,43], increasing evidence suggest that human pDCsalso play a role in antigen cross-presentation and T-cellpriming [14,27,44–47]. Apart from their role in antigen presenta-tion and T-cell priming, blood DC subsets have also beenimplicated in direct cytotoxic activity [48,49]. mDCs derivedfrom peripheral blood from chronic hepatitis C patients wereable to induce apoptosis of CD4+ and CD8+ T cells in vitro[43]. We recently demonstrated that pDCs express cytotoxicmolecules and exert tumoricidal activity after stimulation withthe tick-borne encephalitis vaccine FSME [50]. Taken together,blood DC subsets are key players in the initiation and regula-tion of immune responses and are equipped with antigen-presenting and tumoricidal capacities [48,50,51].

Although monocytes are known for their potential to differ-entiate into DCs in vitro [52], it has been shown that this alsotakes place in vivo during inflammation [53]. These monocyte-derived InfDC are recruited to sites of inflammation caused bya pathogenic invasion [54], or inflammatory diseases such asasthma [55] and rheumatoid arthritis [56]. Similar to other DCs,InfDCs are capable of migrating to lymph nodes where theycan present antigens to both CD4+ and CD8+ T cells [53,55].Recently, the existence of this InfDCs in human inflammatoryfluids has been revealed, displaying a unique capacity of thissubset to induce Th17 effector cells [57].

Interaction between mDC & pDCOwing to their non-overlapping expression profile of TLR,pDC and mDC possess unique pathogen detectioncapacities (TABLE 1) [4,27]. This is also accompanied by distinctivecytokine productivity in response to TLR triggering. Whereas

pDCs are characterized by producing type I IFN and TNF-aupon stimulation, mDCs react mainly by producing IL-12.These complementary properties insinuate synergistic interac-tion between the two DC subsets. Indeed, it has been demon-strated that pDCs and mDCs are located in tight proximityin vivo under both steady state and inflammatoryconditions [58–60]. Furthermore, the variable sensitivity to differ-ent classes of pathogens implies that mDCs and pDCs mayactually cross-sensitize each other to achieve an optimalimmune response. Below, we will elaborately address on thiscrosstalk in the frames of infectious diseases and cancer.

mDC/pDC crosstalk in infectious diseases

A pioneering study by Fonteneau and colleagues clearly demon-strated that human HIV type 1 (HIV-1) is able to activatehuman pDCs, which in turn cross-activate bystander mDCs.Being a cellular target of HIV-1, pDCs respond to this virusby rapid maturation, characterized by upregulated expression ofthe maturation markers CD83 and CCR7 and the costimula-tory molecules CD80 and CD86. Moreover, HIV-1-activatedpDCs were found to produce the antiviral cytokine IFN-a andthe proinflammatory cytokine TNF-a. Consequently, HIV-1--stimulated pDCs gained enhanced migratory and T-cell activa-tory capacities and inducing maturation in accompanyingCD11c mDCs [61]. In stark contrast, mDCs only express T-celland macrophage chemoattractants, but do not mature inresponse to direct contact with HIV-1 [62], although this subsethas been shown to be equipped with the tools to recognizeHIV-1 components when infected with recombinant HIV-1--derived particles [40,63]. However, in case of an infection withwild-type HIV-1, it is believed that mDCs get activated in thepresence of bystander HIV-1-stimulated pDCs. This indirectroute of activation was shown to be partially mediated by thesoluble cytokines TNF-a, IFN-a and IFN-b, produced byHIV-1-activated pDCs (FIGURE 1A) [61]. Overall, this study pro-vided the first evidence for the central role of soluble cytokinesin mediating mDC/pDC crosstalk following viral infections.This notion was corroborated by demonstrating that pDC-secreted type I IFNs render monocyte-derived DCs (moDCs)sensitive to viral infections by upregulating the expression ofthe viral RNA sensors from the RIG-I-like family [64].

Another virus that was demonstrated to be cleared by theimmune system through a collaborative effort between pDCsand mDCs is the herpes simplex virus (HSV). In a mousemodel of cutaneous HSV infection, pDCs were recruited tolymph nodes where they matured and came in close contactwith resident mDCs. Although, pDCs are poor inducers ofCD8+ cytotoxic lymphocytes (CTL), in vivo depletion of pDCsresulted in debilitated CTL-mediated clearance of HSV [25].This was caused by lymph node-resident mDCs losing theircapacity to induce CTLs [25]. In pDC-depleted mice, thoselymph node-resident mDCs were shown to have a limitedcapacity to form clusters with T cells and impaired antigen pre-sentation, necessary to prime CTLs. The pDC-derived help sig-nal, vital for mDC functions, was shown to be mediated by

Crosstalk between DC subsets & implications for DC-based anticancer immunotherapy Review

informahealthcare.com doi: 10.1586/1744666X.2014.912561

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

HIV-1

HSV

CD2

CD40

pDC

pDC

pDCmDC

CpG

mDC

mDCIL-15

IL-12

CD40

CD40L

Listeria monocytogenes

CTL

Th1

T cell

T cell

? NOTCH? ICAM-1

?

CD80CD83CD86CCR7

CD40CD80TNFα

CD40CD80TNFα

S. aureusLPS

TNFα

TNFα

IFNα

IFNα

IFNα

IFNβTNFαA

B

C

Figure 1. Schematic overview of the different described mechanisms responsible for the crosstalk between the DC subsets.(A) Upon activation by HIV-1, human pDCs secrete IFN-a, IFN-b and TNF-a, which in turn induce the activation of human BDCA1+ mDCs.Murine pDCs cross-activate murine lymph node resident mDCs after HSV-induced activation, at least partially, through CD2 and CD40. (B)Murine mDCs produce IL-15 in response to Listeria monoctyogenes stimulation, which in an autocrine fashion drives CD40 expression, andsubsequently leads to the secretion of IL-12 via a CD40–CD40L pDC dependent interaction. (C) Activation of human BDCA1+ mDCs by LPSor Staphylococcus aureus induced the activation of pDCs that in part was regulated by TNF-a, ICAM-1 or NOTCH. Vice versa human pDCsactivated by CpG induced the activation of BDCA1+ mDCs partially through the soluble factors IFN-a and TNF-a.LPS: Lipopolysaccharide; mDCs: Myeloid dendritic cells; pDCs: Plasmacytoid dendritic cells.

Review Bakdash, Schreurs, Schreibelt & Tel

doi: 10.1586/1744666X.2014.912561 Expert Rev. Clin. Immunol.

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

the surface molecules CD2 and CD40 ligand (CD40L)(FIGURE 1A) [25]. In addition, pDC-derived IFN-a furtherenhanced mDC capacity to induce CTLs. Thus, in addition tothe described importance of soluble factors, physical interactionbetween pDCs and mDCs, mediated by surface molecules,plays a crucial role in the crosstalk between DC subsets [25].

The conspicuous contribution of both soluble elements andsurface molecules in mediating interactions between differentsubsets raised a lot of questions concerning mechanisms regulat-ing these interactions. An elegant study by Kuwajima and col-leagues addressed this issue and proposed a two-step interactionscheme between pDCs and mDCs. Upon infection with Listeriamonoctyogenes, murine mDCs would react by producing theproinflammatory cytokines IL-15, which is critical for DC mat-uration, and IL-12 that is important for initiatingTh1 responses and clearance of infection. However,IL-12 production was abolished upon pDC depletion. Theauthors revealed murine mDCs, expressing TLR9, respond tounmethylated CpG oligodeoxynucleotides (CpG), a prevalentbacterial component, by initially producing IL-15. Subse-quently, mDC-derived IL-15 induces the expression ofCD40 on mDCs themselves, allowing interaction with pDCsthrough CD40L on pDCs. Through this interaction, mDCs arestimulated to produce IL-12 [65]. Conclusively, synergistic effectsof pDC and mDCs interactions against Listeria infection aredependent on a soluble factor (IL-15), albeit acting in autocrinefashion, and cell surface molecules (CD40/CD40L) (FIGURE 1B).

Although pDCs are equipped with TLR9 that permits sens-ing a particular component (CpG), the absence of other bacte-rial sensors renders them unresponsive to bacterial stimulation.However, this functional disability could be circumventedthrough crosstalk with mDCs. Analogous to human mDCcross-activation by HIV-1-stimulated pDCs [61], the latter couldbe activated by the mere presence of bacteria-stimulatedmDCs [24]. This crosstalk between human mDCs and pDCswas shown to be cell–cell contact-dependent, whereas solublefactors such as TNF-a and IFN-a were revealed to bedispensable. Although CD40–CD40L interactions were shownto be central for murine mDC/pDC crosstalk [25,65],neutralizing this interaction between human DC subsets didnot yield any effects on mDC/pDC crosstalk. In an attemptto define the surface molecules that are actually mediatingthe subsets crosstalk, potential candidates of the TNF familyof receptors, such as CD40, CD27, OX-40L, 4–1BB,HVEML, CD30L, RANKL and GITRL, were confirmed notto be involved in the crosstalk process [66]. However, a possiblerole of ICAM-1 in this crosstalk is speculated (FIGURE 1C).ICAM-1 expression is upregulated on pDCs upon stimula-tion and its cognate ligands CD11a and CD11b are presenton the surface of mDCs. Neutralizing ICAM-1 interactionwith its ligands abolished mDC cross-maturation, albeit in adonor-dependent manner [66]. Although this study is not con-clusive, it highlights the role of adhesion molecules in DCsubsets interactions, an issue that should be addressed infuture studies.

Another cell contact-dependent communication routebetween human DC subsets involves g-secretase-mediatedmechanisms including the NOTCH pathway (FIGURE 1C) [59]. Sig-nal inhibition through these pathways resulted in abolishedpDC expression of CCL19, induced by lipopolysaccharide -treated mDCs. This finding clearly demonstrates that the mul-tifaceted effects of DC subsets crosstalk may occur through dif-ferent mechanisms and can be mediated via variable pathways.

The observed discrepancy between different studies over themechanisms underlying DC subsets crosstalk can be related toseveral factors. First of all, interspecies differences may explainwhy the two steps, IL-15/CD40L-dependent mechanism wascompletely nullified in a human setting as human blood DCs,in contrast to human splenic CD11c+ DC or in vitro-differenti-ated moDCs that have been shown to secrete IL-15 [67,68], werefound to neither secrete soluble IL-15 or express surface-boundIL-15 [66]. However, future studies should address the possibil-ity that this two-stepped model might be indeed valid inhumans, albeit mediated by elements other than IL-15 andCD40L. For instance, chemokines could play a role in mDC–pDC crosstalk, as was described for DC-NK cell crosstalk [69].Moreover, contradictory findings among human studies can beaccounted for by using different types of stimuli. Althoughboth bacterial and viral stimulation of DCs lead to DC matu-ration and cytokine production, they both induce a distinctexpression profile of soluble factors and surface molecules,which all bear the potential to mediate crosstalk with other DCsubsets. Finally, a very relevant factor that can justify variationsamong different observations is the applied experimental setup.In studies highlighting the involvement of soluble factors likeTNF-a and IFN-a in DC subsets crosstalk [24,61], both DCsubsets were cultured together and simultaneously exposed tothe stimulating factor (viral or bacterial). On the other hand,in studies emphasizing the role of surface molecules in thiscrosstalk [59,66], pDCs and mDCs were stimulated separately for16 h before being co-cultured following extensive washing.Based on this experimental setup, the possible effects of solublecytokines, which are secreted within this time frame, were over-looked. Such an in vitro approach is advocated by the sugges-tion that it reflects the in vivo situation as either one of theDC subsets would secrete soluble cytokines locally at the site ofinfection before migrating to the draining lymph node, wherecrosstalk with other DC subset takes place. However, such aproposal is refuted by the fact that mDCs and pDCs are inclose contact at tissues [60], where they get first-hand exposureto pathogens, and lymph nodes [59], where they can be simulta-neously exposed to pathogens brought over by other migratoryDCs. All these issues should be taken into account upondesigning new studies addressing DC subsets crosstalk.

The close proximity between pDCs and mDCs in tissuesand lymph nodes suggests that interaction between these twosubsets may take place through trogocytosis, a process involvingthe intercellular exchange of membrane patches containingmembrane-bound proteins between different cell types follow-ing immune synapse formation [70]. Not only was it

Crosstalk between DC subsets & implications for DC-based anticancer immunotherapy Review

informahealthcare.com doi: 10.1586/1744666X.2014.912561

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

demonstrated that T cells can acquire both MHC and costimu-latory molecules from APCs, but there is ample evidence thatthis transfer can take place into the opposite direction toDCs [71]. In analogy, it is possible that different DC subsetmay exchange membrane molecules through trogocytosis.Moreover, DC subsets may resort to a phenomenon termedcross-dressing, through which they can exchange surfacepeptide-MHC complexes [72]. Both trogocytosis and cross-dressing should be addressed in future studies investigating DCsubsets crosstalk.

pDC & mDC in cancer

DCs are crucial in conferring resistance against cancer throughmounting up tumor-specific cytotoxic responses. In addition tomDCs, pDCs were found in several human and murine can-cers like melanoma, head and neck cancer, ovarian cancer,breast cancer and myelogenous leukemia [34,73–76]. Dysfunc-tional DCs are also observed in the case of cancer. Upon co-culture with cancer cells (A549, SW480, Raji and Jurkat),mDCs demonstrated downregulated expression of MHC class Iand impaired CD8 T–cell-activating capacity [77]. Similarly,pDCs from multiple myeloma (MM) patients are also defectivein their antigen-presenting functions [78]. However, these func-tions could be restored by targeting pDCs with CpG, whichwas shown to improve the pDC immune function and inhibitMM cell growth [78].

In addition to the use of activating adjuvants, it is suggestedthat impaired DC functions could be improved by crosstalkbetween different DC subsets [25]. This was clearly demon-strated in a mouse model of HSV infection, where co-culturingmurine pDCs with impaired mDCs restored the capacity ofthe latter to induce HSV-specific cytotoxicity [25]. The sameprinciple can be extrapolated to promote the functions of dif-ferent DC subsets in the fight against cancer. Accumulatingdata clearly indicate that tumor-specific immune responses areshaped by cooperation between different DC subsets [79]. In amouse model of melanoma, where CpG was applied as a thera-peutic adjuvant, pDCs were shown to be indispensable inmediating the effects of CpG. pDCs were necessary to conferthe CpG-mediated upregulation of CD80 observed on mDCs,which maintained their central role in tumor-derived antigencross-presentation and the generation of long-term anti-tumorimmunity [79]. These findings are corroborated by anotherstudy demonstrating enhanced mDC priming ability under theeffect of pDCs [80]. Furthermore, immunizing mice with CpG-stimulated pDCs and mDCs resulted in an enhanced T-cellstimulation response against tumor, rendering mice resistant tofurther tumor challenge [80]. These synergistic effects wererevealed to be cell contact-dependent.

Another important element in the war against cancer is theinduction of sufficient NK and NKT cell responses. Interest-ingly, both pDC and mDC were revealed to be necessary forsynergistic activation of NKT cells [81,82]. CpG-stimulatedpDCs were shown to license NKT cells to interact withmDCs, which present a-galactosylceramide via CD1d to NKT

cells and trigger their activation as demonstrated by upregulatedexpression of CD69 and IFN-g [81,82]. Furthermore, anotherstudy unveiled a necessary role of both pDC and mDC ininducing functional NK cells, depending on the type of themicrobial stimulus [83]. Analogous to activated NKT cells,CD69 expression was upregulated by NK cells upon co-culturewith pDCs and mDCs after stimulation with influenza virus orCpG [83]. This enhanced CD69 expression was shown to betype I IFN- and TNF-dependent [83]. It was also found thattype I IFN is needed and sufficient for the enhancement ofNK cell cytolytic activity [83]. Next to that, mDCs stimulatedwith the TLR ligand poly(I:C) were able to induce NK cells toproduce IFN-g in a mechanism dependent on both cell-to-cellcontact and IL-12 [83]. Interestingly, interaction with NK cellsis bidirectional as IL-2-activated NK cells are able to inducematuration of mDCs and pDCs [83].

In addition to crosstalk between the classical mDCs andpDCs, interactions between these subsets and tissue-resident orInfDCs should also be addressed as a potential approach forDC-based cancer vaccines. InfDCs have been recently identifiedin tumor ascites and have displayed a unique capacity in pro-moting Th17-mediated inflammation [57]. Further characteriza-tion of this subset is required to determine whether it could beharnessed in future forms of cancer immunotherapy.

Although exploiting DC subset crosstalk in cancer immuno-therapy presents a very promising approach, the immunosup-pressive tumor microenvironment poses a major challengeagainst any potential clinical benefit of this approach. A keymediator of tumor-associated immunosuppression is therecently identified myeloid-derived suppressor cells. In additionto their capacity to directly inhibit T-cell cytotoxicity, myeloid-derived suppressor cells can also communicate with DCs lead-ing to DC function impairment and tumor progression [84].Furthermore, Treg, accumulating in tumor tissues and theperipheral circulation of cancer patients, are believed to con-tribute to the immune evasion of tumors [85]. Among the dif-ferent modes of action through which Treg exert suppression,they can interact with DCs and frustrate their T-cell stimula-tory functions [86]. Tumor-associated macrophages can also par-ticipate in immune dampening by producing IL-10, whichalters DC function prohibiting effective costimulation ofT cells [87]. Thus, DC interactions with the tumor-associatedinhibitory elements should be seriously addressed upon design-ing new DC-based vaccines.

Implications for immunotherapy of cancerThe decisive role of DCs in inducing immunity has been therationale for DC-based immunotherapy, in which DCs loadedwith tumor antigens are injected into cancer patients tostimulate T cells to eradicate tumors [88–90]. DC-basedimmunotherapy has been introduced in the clinic, and provedto be feasible, safe and non-toxic [91–96]. To date, virtually allclinical studies apply moDCs, differentiated ex vivo frommonocytes or CD34+ progenitors, for DC vaccination of can-cer patients [95,97,98]. Even though an abundant number of

Review Bakdash, Schreurs, Schreibelt & Tel

doi: 10.1586/1744666X.2014.912561 Expert Rev. Clin. Immunol.

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

vaccination studies demonstrated the immunogenicity of tumorantigen-loaded moDCs, the number of objective clinicalresponses has been limited, hampering its implementation asstandard treatment. It has been postulated that moDCs may beless effective for DC-based immunotherapy than naturallyoccurring DC subsets circulating in the blood. Therefore, otherDC subsets are being explored as alternatives for moDCs. Thetranslation of these unique blood DC subsets into immuno-therapy protocols was long hampered by the limited availabilityof clinical-grade components that induce DC activation. Previ-ously, we described that commonly available preventive vac-cines induce the activation of moDCs as well as humanpDCs [99,100], which allowed for the first time to explore theuse of rare TLR-activated blood DC subsets in feasibility trials.Recently, the first DC vaccination trial exploiting activatedhuman pDCs was performed in late-stage melanomapatients [46]. Although the trial was initially setup as a feasibilitystudy, and not designed to evaluate clinical outcome, retrospec-tive follow-up revealed that the overall survival of patients vac-cinated with autologous TLR-activated and tumor antigen-loaded pDCs was greatly increased compared with matchedcontrol patients treated with chemotherapy [46]. The great sur-vival benefit of vaccinated patients is especially interesting, sincethe induction of tumor antigen-specific cytotoxic T cells afterpDC vaccination occurred less frequently than after vaccinationwith moDCs. This suggests that besides induction of tumorantigen-specific T-cell responses, other mechanisms wereinvolved and crosstalk with other DC subsets, via cell–cell con-tact or soluble factors such as type I IFNs, is a likely candidate.

pDCs are known for their massive production of type I IFNsafter sensing viral or self nucleic acids at sites of inflammation.These IFNs could initiate protective immunity through matura-tion of resident mDCs and subsequent activation of infiltratingT cells and NK cells [101]. Because of their type I IFN production,properly activated pDCs might stimulate adjacent mDCs andenhance their ability to cross-prime CD8+ T cells, thereby induc-ing more efficient anti-tumor T-cell responses when comparedwith in vitro generated DCs. This notion is supported by twoindependent murine studies demonstrating that type I IFNs werecritical for the induction of anti-tumor immune responses [102,103].Throughout the years, systemic IFN-a administration has beenused as a treatment modality for various cancers, including high-risk melanoma [104,105]. Although, IFN-a has shown potent anti-tumor effects, this treatment modality has often been associatedwith severe toxicity-based side effects tampering its implementa-tion as a standard treatment [106]. In metastatic melanomapatients, administration of activated pDCs specifically inducedsystemic levels of type I IFNs and IFN-induced genes as theseresponses were absent in patients who received activatedmDCs [46]. Interestingly, none of these treated patients displayedany sign of toxicity or any other adverse effects, suggesting thatlocally produced type I IFN in the near proximity of T-cell prim-ing is safer then systemic administration and also beneficial forthe induction of anti-tumor responses. Whether these locally pro-duced type I IFNs act as a crosstalk mediator, leading to the

activation or modulation of the function of lymph node residentmDCs, remain to be determined. Next to having direct stimula-tory effects on mDCs, type I IFNs can also positively affect theability of mDCs to activate antigen-specific T cells. Multiplestudies demonstrated that type I IFNs were able to enhance anti-gen presentation by modulating antigen retention, routing andpresentation [103,107–109]. All together, these studies unambigu-ously demonstrate the powerful potential of pDC–mDCcrosstalk.

mDCs themselves are also potential candidates for DC-basedimmunotherapy. Recently, a Phase I trial was performed inwhich metastatic melanoma patients were vaccinated withautologous, ex vivo activated and tumor antigen-loadedBDCA1+ mDCs. Preliminary results confirm safety and feasi-bility of mDC-based vaccines and objective clinical responseswere observed in multiple patients [SCHREIBELT ET AL. MANUSCRIPT IN PREPA-

RATION]. These clinical responses coincided with the presence offunctional tumor antigen-specific T-cell responses, suggestingthat mDC and pDC might induce clinical responses in meta-static melanoma patients via different mechanisms; mDCs viadirect activation of tumor-specific T cells and pDCs by localproduction of type I IFNs.

These unexpected, but exciting findings urge for the develop-ment of clinical trials to further explore the mechanisms bywhich natural DCs to induce clinical responses in vivo and toexploit mDC–pDC crosstalk for cancer immunotherapy to fur-ther improve immunological and clinical outcome after DC-based cancer immunotherapy.

Expert commentary & five-year viewIn this review, we focused on pDCs, mDCs and their interac-tion during stimulation with pathogenic antigens, and how thiscrosstalk could be exploited for cancer immunotherapy. Basedon the expression of TLRs, subsets of DCs have specializedfunctions in the regulation of immune responses. pDCs, bythemselves, are able to induce T-cell response, however, whenco-cultured with other cells (mDC, lymph node DC, NK(T)cells and adaptive T cells), T-cell activation is enhanced. How-ever, the mechanisms responsible for pDC and mDC interac-tion remain controversial. Multiple studies suggest multiplemechanisms for interaction (CD40, ICAM1, NOTCH1, cell–cell contact and cytokines like TNF-a and IFN-a).

The applicability of multiple DC subsets in cancer therapyrelies on the understanding of the interaction between mDCs,pDCs and cancer cells. It has been found that cancer cells areable to (partially) inhibit DC function, resulting in a limitedCD8+ T-cell response. However, activating one DC subset canlead to the activation of the other subset. Furthermore, in lightof this review regarding pre-clinical findings on the bi-directional crosstalk between DC subsets, we believe that pDCsand mDCs should be combined together in one vaccine toexploit their functions simultaneously, which in our view willunlock their full potential for immunotherapeutic purposes.Yet, before we can exploit mDC–pDC synergy for DC vaccina-tion, optimal culture conditions need to be established. How

Crosstalk between DC subsets & implications for DC-based anticancer immunotherapy Review

informahealthcare.com doi: 10.1586/1744666X.2014.912561

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

long should cells be activated? Which clinical-grade stimuli/TLR ligands can be used to optimally activate both DC subsetswithout interfering with the activation of the other subset(s)?Should pDCs and mDCs be cultured and administeredtogether or separately? What ratio of mDCs and pDCs shouldbe chosen? To our knowledge, the use of multiple DC subsetsin human clinical trial vaccines has not been attempted before.Therefore, vaccination with multiple cell types may provide anovel strategy for DC-based vaccine development and hencemight improve the fight against cancer.

Recently, new therapeutic strategies, such as ipilimu-mab [110,111], vemurafenib [112,113] or multi-agent biochemother-apy combining standard chemotherapy or immunotherapy withbiologics such as IL-2 [114,115] or IFN-a [106] have obtained theUS FDA approval for treatment of metastatic melanoma. Forpatients with distant metastasis, ipilimumab recently proved tobe an effective treatment modality (20% of treated patientsbecame long-term survivors), resulting in its use as the newfirst-line treatment modality for metastatic melanoma patients.However, ipilimumab treatment is associated with severeimmune-related adverse effects, which could have a majorimpact on the quality of life. Ipilimumab is an antibodydirected against cytotoxic T-lymphocyte antigen 4 (CTLA4),which is a co-receptor expressed by activated T cells, memoryT cells and Treg. CTLA4 plays a crucial role in abrogatingimmunity and thereby provides a feedback mechanism to regu-late immune homeostasis [116]. Blockade of this inhibitory path-way results in enhanced T-cell activation, and has shown to beeffective in cancer immunotherapy. An important drawback oftreatment with anti-CTLA4 is the lack of specificity: the T-cellactivation threshold is lowered in an antigen non-specific man-ner. This is also apparent by the significant rate of toxicity pro-files of anti-CTLA4 antibodies consisting of diverse auto-

immune phenomena. However, toxicity does not accuratelypredict positive therapeutic outcome, indicating that manypatients will experience inflammatory pathology withoutbenefiting from an antitumor effect. Although randomized clin-ical trials are needed to further substantiate the clinical efficacyof naturally occurring DC subsets in anti-cancer immunother-apy, we believe that DC-based immunotherapy has majoradvantages over checkpoint inhibitors, as it is cheaper; andmore importantly is associated with only mild therapy-relatedside effects. Although only a limited number of studies investi-gated the quality of life during treatment, Leonhartsbergeret al. demonstrated that the quality of life of patients treatedwith DC-based immunotherapy, in terms of side effects andtoxicity, is better compared with that of chemotherapy and/orbiologic additives [94]. This is in our view an important param-eter that should be taken into account when designing treat-ment regimens for late-stage cancer patients, especially giventhe fact that there are only marginal variations in survival bene-fit between the different treatment modalities. On this basis,we advocate the use of natural DC subsets (rather thanmoDCs) for the next generation of DC-based vaccines for thevaccination of cancer patients.

Financial & competing interests disclosure

This work was supported by The Netherlands Organization for Scientific

Research (NWO) (Veni grant 86313024 to J Tel; Vidi grant

91776363 to IJMdV; 95103002 to IJMdV), Dutch Cancer Society

(KWF 2010–4722) and the Netherlands Institute for Regenerative Medi-

cine (NIRM, grant No. FES0908). The authors have no other relevant

affiliations or financial involvement with any organization or entity with

a financial interest in or financial conflict with the subject matter or

materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Different dendritic cell (DC) subsets possess distinct properties indicative of complementary effects.

• Collaboration between DC subsets is central for the eradication of microbial infections.

• Molecular mechanisms underlying DC subsets crosstalk remain debatable with strong evidence of the involvement of both soluble

cytokines and surface molecules.

• Tumor-specific immune responses are shaped by cooperation between different DC subsets.

• Utilizing the complementary qualities of DC subsets is pertinent for successful cancer immunotherapy.

References

Papers of special note have been highlighted as:

• of interest

•• of considerable interest

1. Banchereau J, Briere F, Caux C, et al.

Immunobiology of dendritic cells. Annu

Rev Immunol 2000;18:767-811

2. Teunissen MB, Haniffa M, Collin MP.

Insight into the immunobiology of human

skin and functional specialization of skin

dendritic cell subsets to innovate

intradermal vaccination design. Curr Top

Microbiol Immunol 2012;351:25-76

3. Banchereau J, Steinman RM. Dendritic cells

and the control of immunity. Nature 1998;

392(6673):245-52

4. Schreibelt G, Tel J, Sliepen KH, et al.

Toll-like receptor expression and function in

human dendritic cell subsets: implications

for dendritic cell-based anti-cancer

immunotherapy. Cancer Immunol

Immunother 2010;59(10):1573-82

5. Kawai T, Akira S. Toll-like receptors and

their crosstalk with other innate receptors in

infection and immunity. Immunity 2011;

34(5):637-50

6. Medzhitov R, Janeway CA Jr. Innate

immunity: the virtues of a nonclonal system

of recognition. Cell 1997;91(3):295-8

7. Palm NW, Medzhitov R. Pattern

recognition receptors and control of

adaptive immunity. Immunol Rev 2009;

227(1):221-33

Review Bakdash, Schreurs, Schreibelt & Tel

doi: 10.1586/1744666X.2014.912561 Expert Rev. Clin. Immunol.

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

8. Hemont C, Neel A, Heslan M, et al.

Human blood mDC subsets exhibit distinct

TLR repertoire and responsiveness. J Leukoc

Biol 2013;93(4):599-609

9. Bianchi ME. DAMPs, PAMPs and

alarmins: all we need to know about danger.

J Leukoc Biol 2007;81(1):1-5

10. Trombetta ES, Mellman I. Cell biology of

antigen processing in vitro and in vivo.

Annu Rev Immunol 2005;23:975-1028

11. Lakadamyali M, Rust MJ, Zhuang X.

Ligands for clathrin-mediated endocytosis

are differentially sorted into distinct

populations of early endosomes. Cell 2006;

124(5):997-1009

12. Burgdorf S, Kurts C. Endocytosis

mechanisms and the cell biology of antigen

presentation. Curr Opin Immunol 2008;

20(1):89-95

13. Lin ML, Zhan Y, Villadangos JA, Lew AM.

The cell biology of cross-presentation and

the role of dendritic cell subsets. Immunol

Cell Biol 2008;86(4):353-62

14. Nierkens S, Tel J, Janssen E, Adema GJ.

Antigen cross-presentation by dendritic cell

subsets: one general or all sergeants? Trends

Immunol 2013;34(8):361-70

15. Quah BJ, O’Neill HC. Maturation of

function in dendritic cells for tolerance and

immunity. J Cell Mol Med 2005;9(3):

643-54

16. Bakdash G, Sittig SP, van Dijk T, et al.

The nature of activatory and tolerogenic

dendritic cell-derived signal II. Front

Immunol 2013;4:53

17. Luther SA, Tang HL, Hyman PL, et al.

Coexpression of the chemokines ELC and

SLC by T zone stromal cells and deletion of

the ELC gene in the plt/plt mouse. Proc

Natl Acad Sci USA 2000;97(23):12694-9

18. Kalinski P, Hilkens CM, Wierenga EA,

Kapsenberg ML. T-cell priming by

type-1 and type-2 polarized dendritic cells:

the concept of a third signal. Immunol

Today 1999;20(12):561-7

19. Keppler SJ, Rosenits K, Koegl T, et al.

Signal 3 cytokines as modulators of primary

immune responses during infections: the

interplay of type I IFN and IL-12 in

CD8 T cell responses. PLoS One 2012;

7(7):e40865

20. Kalinski P. Dendritic cells in

immunotherapy of established cancer: roles

of signals 1, 2, 3 and 4. Curr Opin Investig

Drugs 2009;10(6):526-35

21. Sigmundsdottir H, Pan J, Debes GF, et al.

DCs metabolize sunlight-induced vitamin

D3 to ’program’ T cell attraction to the

epidermal chemokine CCL27. Nat

Immunol 2007;8(3):285-93

22. Chung CY, Ysebaert D, Berneman ZN,

Cools N. Dendritic cells: cellular mediators

for immunological tolerance. Clin Dev

Immunol 2013;2013:972865

23. Vremec D, Zorbas M, Scollay R, et al. The

surface phenotype of dendritic cells purified

from mouse thymus and spleen:

investigation of the CD8 expression by a

subpopulation of dendritic cells. J Exp Med

1992;176(1):47-58

24. Piccioli D, Sammicheli C, Tavarini S, et al.

Human plasmacytoid dendritic cells are

unresponsive to bacterial stimulation and

require a novel type of cooperation with

myeloid dendritic cells for maturation.

Blood 2009;113(18):4232-9

25. Yoneyama H, Matsuno K, Toda E, et al.

Plasmacytoid DCs help lymph node DCs to

induce anti-HSV CTLs. J Exp Med 2005;

202(3):425-35

26. Kassianos AJ, Hardy MY, Ju X, et al.

Human CD1c (BDCA-1)+ myeloid

dendritic cells secrete IL-10 and display an

immuno-regulatory phenotype and function

in response to Escherichia coli. Eur J

Immunol 2012;42(6):1512-22

27. Tel J, van der Leun AM, Figdor CG, et al.

Harnessing human plasmacytoid dendritic

cells as professional APCs. Cancer Immunol

Immunother 2012;61(8):1279-88

28. Piccioli D, Tavarini S, Borgogni E, et al.

Functional specialization of human

circulating CD16 and CD1c myeloid

dendritic-cell subsets. Blood 2007;109(12):

5371-9

29. Cao W, Rosen DB, Ito T, et al.

Plasmacytoid dendritic cell-specific receptor

ILT7-Fc epsilonRI gamma inhibits Toll-like

receptor-induced interferon production. J

Exp Med 2006;203(6):1399-405

30. Lindstedt M, Lundberg K, Borrebaeck CA.

Gene family clustering identifies functionally

associated subsets of human in vivo blood

and tonsillar dendritic cells. J Immunol

2005;175(8):4839-46

31. Kadowaki N, Antonenko S, Lau JY, Liu YJ.

Natural interferon alpha/beta-producing

cells link innate and adaptive immunity. J

Exp Med 2000;192(2):219-26

32. Farkas L, Kvale EO, Johansen FE, et al.

Plasmacytoid dendritic cells activate

allergen-specific TH2 memory cells:

modulation by CpG oligodeoxynucleotides.

J Allergy Clin Immunol 2004;114(2):

436-43

33. Conrad C, Meller S, Gilliet M.

Plasmacytoid dendritic cells in the skin: to

sense or not to sense nucleic acids. Semin

Immunol 2009;21(3):101-9

34. Treilleux I, Blay JY, Bendriss-Vermare N,

et al. Dendritic cell infiltration and

prognosis of early stage breast cancer. Clin

Cancer Res 2004;10(22):7466-74

35. Labidi-Galy SI, Sisirak V, Meeus P, et al.

Quantitative and functional alterations of

plasmacytoid dendritic cells contribute to

immune tolerance in ovarian cancer. Cancer

Res 2011;71(16):5423-34

36. Karthaus N, Torensma R, Tel J.

Deciphering the message broadcast by

tumor-infiltrating dendritic cells. Am J

Pathol 2012;181(3):733-42

37. Jarrossay D, Napolitani G, Colonna M,

et al. Specialization and complementarity in

microbial molecule recognition by human

myeloid and plasmacytoid dendritic cells.

Eur J Immunol 2001;31(11):3388-93

38. Nizzoli G, Krietsch J, Weick A, et al.

Human CD1c+ dendritic cells secrete high

levels of IL-12 and potently prime cytotoxic

T-cell responses. Blood 2013;122(6):932-42

39. de Groot R, van Beelen AJ, Bakdash G,

et al. Viral dsRNA-activated human

dendritic cells produce IL-27, which

selectively promotes cytotoxicity in naive

CD8+ T cells. J Leukoc Biol 2012;92(3):

605-10

40. Breckpot K, Escors D, Arce F, et al.

HIV-1 lentiviral vector immunogenicity is

mediated by Toll-like receptor 3 (TLR3)

and TLR7. J Virol 2010;84(11):5627-36

41. Goyvaerts C, Kurt de G, Van Lint S, et al.

Immunogenicity of targeted lentivectors.

Oncotarget 2014;5(3):704-15

•• This is the first feasibility study that

reports on the use of naturally occuring

plasmacytoid DCs in DC-based

immunotherapy for the treatment of

metastatic melanoma patients.

42. Shaw J, Wang YH, Ito T, et al.

Plasmacytoid dendritic cells regulate B-cell

growth and differentiation via CD70. Blood

2010;115(15):3051-7

43. Zhao L, Tyrrell DL. Myeloid dendritic cells

can kill T cells during chronic hepatitis C

virus infection. Viral Immunol 2013;26(1):

25-39

44. Di Pucchio T, Chatterjee B,

Smed-Sorensen A, et al. Direct

proteasome-independent cross-presentation

of viral antigen by plasmacytoid dendritic

cells on major histocompatibility complex

class I. Nat Immunol 2008;9:551-7

45. Hoeffel G, Ripoche AC, Matheoud D,

et al. Antigen crosspresentation by human

Crosstalk between DC subsets & implications for DC-based anticancer immunotherapy Review

informahealthcare.com doi: 10.1586/1744666X.2014.912561

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

plasmacytoid dendritic cells. Immunity

2007;27(3):481-92

46. Tel J, Aarntzen EH, Baba T, et al. Natural

human plasmacytoid dendritic cells induce

antigen-specific T-cell responses in

melanoma patients. Cancer Res 2013;73(3):

1063-75

47. Tel J, Schreibelt G, Sittig SP, et al. Human

plasmacytoid dendritic cells efficiently

cross-present exogenous Ags to CD8+

T cells despite lower Ag uptake than

myeloid dendritic cell subsets. Blood 2013;

121(3):459-67

48. Tel J, Anguille S, Waterborg CE, et al.

Tumoricidal activity of human dendritic

cells. Trends Immunol 2014;35(1):38-46

49. Roothans D, Smits E, Lion E, et al.

CD56 marks human dendritic cell subsets

with cytotoxic potential. Oncoimmunology

2013;2(2):e23037

50. Tel J, Smits EL, Anguille S, et al. Human

plasmacytoid dendritic cells are equipped

with antigen-presenting and tumoricidal

capacities. Blood 2012;120(19):3936-44

51. Lande R, Gilliet M. Plasmacytoid dendritic

cells: key players in the initiation and

regulation of immune responses. Ann N Y

Acad Sci 2010;1183:89-103

52. Sallusto F, Lanzavecchia A. Efficient

presentation of soluble antigen by cultured

human dendritic cells is maintained by

granulocyte/macrophage colony-stimulating

factor plus interleukin 4 and downregulated

by tumor necrosis factor alpha. J Exp Med

1994;179(4):1109-18

53. Leon B, Lopez-Bravo M, Ardavin C.

Monocyte-derived dendritic cells formed at

the infection site control the induction of

protective T helper 1 responses against

Leishmania. Immunity 2007;26(4):519-31

54. Greter M, Helft J, Chow A, et al. GM-CSF

controls nonlymphoid tissue dendritic cell

homeostasis but is dispensable for the

differentiation of inflammatory dendritic

cells. Immunity 2012;36(6):1031-46

55. Hammad H, Plantinga M, Deswarte K,

et al. Inflammatory dendritic cells – not

basophils – are necessary and sufficient for

induction of Th2 immunity to inhaled

house dust mite allergen. J Exp Med 2010;

207(10):2097-111

56. Campbell IK, van Nieuwenhuijze A,

Segura E, et al. Differentiation of

inflammatory dendritic cells is mediated by

NF-kappaB1-dependent GM-CSF

production in CD4 T cells. J Immunol

2011;186(9):5468-77

57. Segura E, Touzot M, Bohineust A, et al.

Human inflammatory dendritic cells induce

Th17 cell differentiation. Immunity 2013;

38(2):336-48

58. Nascimbeni M, Perie L, Chorro L, et al.

Plasmacytoid dendritic cells accumulate in

spleens from chronically HIV-infected

patients but barely participate in

interferon-alpha expression. Blood 2009;

113(24):6112-19

59. Perez-Cabezas B, Naranjo-Gomez M,

Ruiz-Riol M, et al. TLR-activated

conventional DCs promote gamma-

secretase-mediated conditioning of

plasmacytoid DCs. J Leukoc Biol 2012;

92(1):133-43

60. Vermi W, Lonardi S, Morassi M, et al.

Cutaneous distribution of plasmacytoid

dendritic cells in lupus erythematosus.

Selective tropism at the site of epithelial

apoptotic damage. Immunobiology 2009;

14(9-10):877-86

61. Fonteneau JF, Larsson M, Beignon AS,

et al. Human immunodeficiency virus

type 1 activates plasmacytoid dendritic cells

and concomitantly induces the bystander

maturation of myeloid dendritic cells.

J Virol 2004;78(10):5223-32

62. Izmailova E, Bertley FM, Huang Q, et al.

HIV-1 Tat reprograms immature dendritic

cells to express chemoattractants for

activated T cells and macrophages. Nat Med

2003;9(2):191-7

63. Tan PH, Beutelspacher SC, Xue SA, et al.

Modulation of human dendritic-cell

function following transduction with viral

vectors: implications for gene therapy. Blood

2005;105(10):3824-32

64. Kramer M, Schulte BM,

Eleveld-Trancikova D, et al. Cross-talk

between human dendritic cell subsets

influences expression of RNA sensors and

inhibits picornavirus infection. J Innate

Immun 2010;2(4):360-70

•• This paper elegantly demontrates that the

crosstalk between the plasmacytoid DCs

and myeloid DCs can lead to antigen

specific CD8+ CTLs and antitumor

immunity.

65. Kuwajima S, Sato T, Ishida K, et al.

Interleukin 15-dependent crosstalk between

conventional and plasmacytoid dendritic

cells is essential for CpG-induced immune

activation. Nat Immunol 2006;7(7):740-6

66. Cantisani R, Sammicheli C, Tavarini S,

et al. Surface molecules on stimulated

plasmacytoid dendritic cells are sufficient to

cross-activate resting myeloid dendritic cells.

Hum Immunol 2011;72(11):1018-21

67. Jonuleit H, Wiedemann K, Muller G, et al.

Induction of IL-15 messenger RNA and

protein in human blood-derived dendritic

cells: a role for IL-15 in attraction of T

cells. J Immunol 1997;158(6):2610-15

68. Ferlazzo G, Pack M, Thomas D, et al.

Distinct roles of IL-12 and IL-15 in human

natural killer cell activation by dendritic

cells from secondary lymphoid organs. Proc

Natl Acad Sci USA 2004;101(47):16606-11

69. Pallandre JR, Krzewski K, Bedel R, et al.

Dendritic cell and natural killer cell cross-

talk: a pivotal role of CX3CL1 in NK

cytoskeleton organization and activation.

Blood 2008;112(12):4420-4

70. Joly E, Hudrisier D. What is trogocytosis

and what is its purpose? Nat Immunol

2003;4(9):815

71. Ahmed KA, Xiang J. Mechanisms of cellular

communication through intercellular protein

transfer. J Cell Mol Med 2011;15(7):

1458-73

72. Wakim LM, Bevan MJ. Cross-dressed

dendritic cells drive memory CD8+ T-cell

activation after viral infection. Nature 2011;

471(7340):629-32

73. Salio M, Cella M, Vermi W, et al.

Plasmacytoid dendritic cells prime

IFN-gamma-secreting melanoma-specific

CD8 lymphocytes and are found in primary

melanoma lesions. Eur J Immunol 2003;

33(4):1052-62

• In this study the authors have assessed

and documented the quality of life of

patients that received DC vaccination.

Importantly, they demonstrated that this

non-toxic personalized treatment

maintains the quality of life of these

patients.

74. Hartmann E, Wollenberg B, Rothenfusser S,

et al. Identification and functional analysis of

tumor-infiltrating plasmacytoid dendritic

cells in head and neck cancer. Cancer Res

2003;63(19):6478-87

75. ZouW,Machelon V, Coulomb-L’Hermin A,

et al. Stromal-derived factor-1 in human

tumors recruits and alters the function of

plasmacytoid precursor dendritic cells. Nat

Med 2001;7(12):1339-46

76. Weigel BJ, Nath N, Taylor PA, et al.

Comparative analysis of murine

marrow-derived dendritic cells generated by

Flt3L or GM-CSF/IL-4 and matured with

immune stimulatory agents on the in vivo

induction of antileukemia responses. Blood

2002;100(12):4169-76

77. Seo MJ, Kim GR, Son YM, et al.

Interactions of dendritic cells with cancer

cells and modulation of surface molecules

Review Bakdash, Schreurs, Schreibelt & Tel

doi: 10.1586/1744666X.2014.912561 Expert Rev. Clin. Immunol.

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

affect functional properties of CD8+ T cells.

Mol Immunol 2011;48(15-16):1744-52

• This study demonstrated that commonly

available prophylactic vaccines are able to

stimulate and activate myeloid DCs,

circumventing the need for synthetic

GMP TLR ligands and thereby enabling

the use of TLR-activated DCs for DC-

based immunotherapy.

78. Chauhan D, Singh AV, Brahmandam M,

et al. Functional interaction of plasmacytoid

dendritic cells with multiple myeloma cells:

a therapeutic target. Cancer Cell 2009;

16(4):309-23

79. Nierkens S, den Brok MH, Garcia Z, et al.

Immune adjuvant efficacy of CpG

oligonucleotide in cancer treatment is

founded specifically upon TLR9 function in

plasmacytoid dendritic cells. Cancer Res

2011;71(20):6428-37

80. Lou Y, Liu C, Kim GJ, et al. Plasmacytoid

dendritic cells synergize with myeloid

dendritic cells in the induction of

antigen-specific antitumor immune

responses. J Immunol 2007;178(3):1534-41

81. Marschner A, Rothenfusser S, Hornung V,

et al. CpG ODN enhance antigen-specific

NKT cell activation via plasmacytoid dendritic

cells. Eur J Immunol 2005;35(8):2347-57

82. Montoya CJ, Jie HB, Al-Harthi L, et al.

Activation of plasmacytoid dendritic cells

with TLR9 agonists initiates invariant NKT

cell-mediated cross-talk with myeloid dendritic

cells. J Immunol 2006;177(2):1028-39

83. Gerosa F, Gobbi A, Zorzi P, et al. The

reciprocal interaction of NK cells with

plasmacytoid or myeloid dendritic cells

profoundly affects innate resistance

functions. J Immunol 2005;174(2):727-34

84. Ostrand-Rosenberg S, Sinha P, Beury DW,

Clements VK. Cross-talk between

myeloid-derived suppressor cells (MDSC),

macrophages, and dendritic cells enhances

tumor-induced immune suppression. Semin

Cancer Biol 2012;22(4):275-81

85. Whiteside TL. Regulatory T cell subsets in

human cancer: are they regulating for or

against tumor progression? Cancer Immunol

Immunother 2014;63(1):67-72

86. Lakshmi Narendra B, Eshvendar Reddy K,

Shantikumar S, Ramakrishna S. Immune

system: a double-edged sword in cancer.

Inflamm Res 2013;62(9):823-34

87. Cook J, Hagemann T. Tumour-associated

macrophages and cancer. Curr Opin

Pharmacol 2013;13(4):595-601

•• The findings described in this study

demonstrated the potential of checkpoint

inhibitors as alternative treatment

modalities for late stage melanoma

patients. Although a substantial number

of patients developed treatment related

severe adverse effects, still a group of

patients receiving this form of treatment

developed long term tumor control.

88. Banchereau J, Palucka AK. Dendritic cells

as therapeutic vaccines against cancer. Nat

Rev Immunol 2005;5(4):296-306

89. den Brok MH, Nierkens S, Figdor CG,

et al. Dendritic cells: tools and targets for

antitumor vaccination. Expert Rev Vaccines

2005;4(5):699-710

90. Tuyaerts S, Aerts JL, Corthals J, et al.

Current approaches in dendritic cell

generation and future implications for

cancer immunotherapy. Cancer Immunol

Immunother 2007;56(10):1513-37

91. Mackensen A, Herbst B, Chen JL, et al.

Phase I study in melanoma patients of a

vaccine with peptide-pulsed dendritic cells

generated in vitro from CD34(+)

hematopoietic progenitor cells. Int J Cancer

2000;86(3):385-92

92. Banchereau J, Palucka AK, Dhodapkar M,

et al. Immune and clinical responses in

patients with metastatic melanoma to CD34

(+) progenitor-derived dendritic cell vaccine.

Cancer Res 2001;61(17):6451-8

93. Schuler-Thurner B, Schultz ES, Berger TG,

et al. Rapid Induction of Tumor-specific

Type 1 T Helper Cells in Metastatic

Melanoma Patients by Vaccination with

Mature, Cryopreserved, Peptide-loaded

Monocyte-derived Dendritic Cells. J Exp

Med 2002;195(10):1279-88

94. Leonhartsberger N, Ramoner R,

Falkensammer C, et al. Quality of life

during dendritic cell vaccination against

metastatic renal cell carcinoma. Cancer

Immunol Immunother 2012;61(9):1407-13

95. de Vries IJ, Lesterhuis WJ,

Scharenborg NM, et al. Maturation of

dendritic cells is a prerequisite for inducing

immune responses in advanced melanoma

patients. Clin Cancer Res 2003;9(14):

5091-100

96. Wilgenhof S, Van Nuffel AM, Benteyn D,

et al. A phase IB study on intravenous

synthetic mRNA electroporated dendritic

cell immunotherapy in pretreated advanced

melanoma patients. Ann Oncol 2013;

24(10):2686-93

97. Nestle FO, Alijagic S, Gilliet M, et al.

Vaccination of melanoma patients with

peptide- or tumor lysate-pulsed dendritic

cells. Nat Med 1998;4(3):328-32

98. Dhodapkar MV, Krasovsky J, Steinman RM,

Bhardwaj N. Mature dendritic cells boost

functionally superior CD8(+) T-cell in

humans without foreign helper epitopes. J

Clin Invest 2000;105(6):R9-R14

99. Schreibelt G, Benitez-Ribas D,

Schuurhuis D, et al. Commonly used

prophylactic vaccines as an alternative for

synthetically produced TLR ligands to

mature monocyte-derived dendritic cells.

Blood 2010;116(4):564-74

100. de Vries IJ, Tel J, Benitez-Ribas D, et al.

Prophylactic vaccines mimic synthetic CpG

oligonucleotides in their ability to modulate

immune responses. Mol Immunol 2011;

48(6-7):810-17

101. Mathan TS, Figdor CG, Buschow SI.

Human plasmacytoid dendritic cells: from

molecules to intercellular communication

network. Front Immunol 2013;4:372

102. Diamond MS, Kinder M, Matsushita H,

et al. Type I interferon is selectively

required by dendritic cells for immune

rejection of tumors. J Exp Med 2011;

208(10):1989-2003

103. Fuertes MB, Kacha AK, Kline J, et al. Host

type I IFN signals are required for

antitumor CD8+ T cell responses through

CD8{alpha}+ dendritic cells. J Exp Med

2011;208(10):2005-16

104. Anguille S, Lion E, Willemen Y, et al.

Interferon-alpha in acute myeloid leukemia:

an old drug revisited. Leukemia 2011;25(5):

739-48

105. Ascierto PA, Gogas HJ, Grob JJ, et al.

Adjuvant interferon alfa in malignant

melanoma: an interdisciplinary and

multinational expert review. Crit Rev Oncol

Hematol 2013;85(2):149-61

106. Kirkwood JM, Bender C, Agarwala S, et al.

Mechanisms and management of toxicities

associated with high-dose interferon alfa-2b

therapy. J Clin Oncol 2002;20(17):3703-18

107. Lattanzi L, Rozera C, Marescotti D, et al.

IFN-alpha boosts epitope cross-presentation

by dendritic cells via modulation of

proteasome activity. Immunobiology 2011;

216(5):537-47

108. Lorenzi S, Mattei F, Sistigu A, et al. Type I

IFNs control antigen retention and survival

of CD8alpha(+) dendritic cells after uptake

of tumor apoptotic cells leading to

cross-priming. J Immunol 2011;186(9):

5142-50

109. Spadaro F, Lapenta C, Donati S, et al.

IFN-alpha enhances cross-presentation in

human dendritic cells by modulating

antigen survival, endocytic routing, and

processing. Blood 2012;119(6):1407-17

Crosstalk between DC subsets & implications for DC-based anticancer immunotherapy Review

informahealthcare.com doi: 10.1586/1744666X.2014.912561

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.

110. Hodi FS, O’Day SJ, McDermott DF, et al.

Improved survival with ipilimumab in

patients with metastatic melanoma. N Engl

J Med 2010;363(8):711-23

111. Robert C, Thomas L, Bondarenko I, et al.

Ipilimumab plus dacarbazine for previously

untreated metastatic melanoma. N Engl J

Med 2011;364(26):2517-26

112. Chapman PB, Hauschild A, Robert C, et al.

Improved survival with vemurafenib in

melanoma with BRAF V600E mutation.

N Engl J Med 2011;364(26):2507-16

113. Rochet NM, Kottschade LA, Markovic SN.

Vemurafenib for melanoma metastases to

the brain. N Engl J Med 2011;365(25):

2439-41

114. Schwartzentruber DJ, Lawson DH,

Richards JM, et al. gp100 peptide vaccine

and interleukin-2 in patients with advanced

melanoma. N Engl J Med 2011;364(22):

2119-27

115. Tarhini AA, Kirkwood JM, Gooding WE,

et al. Durable complete responses with

high-dose bolus interleukin-2 in patients

with metastatic melanoma who have

experienced progression after

biochemotherapy. J Clin Oncol 2007;

25(25):3802-7

116. Fong L, Small EJ. Anti-cytotoxic

T-lymphocyte antigen-4 antibody: the first

in an emerging class of immunomodulatory

antibodies for cancer treatment. J Clin

Oncol 2008;26(32):5275-83

Review Bakdash, Schreurs, Schreibelt & Tel

doi: 10.1586/1744666X.2014.912561 Expert Rev. Clin. Immunol.

Exp

ert R

evie

w o

f C

linic

al I

mm

unol

ogy

Dow

nloa

ded

from

info

rmah

ealth

care

.com

by

Rad

boud

Uni

vers

iteit

Nijm

egen

on

04/2

3/14

For

pers

onal

use

onl

y.