Front. Immunol. Frontiers in Immunology Front. Immunol. 1664-3224 Frontiers Media S.A. 10.3389/fimmu.2017.00879 Immunology Review Enhancement of Adjuvant Functions of Natural Killer T Cells Using Nanovector Delivery Systems: Application in Anticancer Immune Therapy Ghinnagow Reem 1 2 3 4 5 Cruz Luis Javier 6 Macho-Fernandez Elodie 1 2 3 4 5 Faveeuw Christelle 1 2 3 4 5 Trottein François 1 2 3 4 5 * 1Univ. Lille, U1019 – UMR 8204 – CIIL – Centre d’Infection et d’Immunité de Lille, Lille, France 2Centre National de la Recherche Scientifique, UMR 8204, Lille, France 3Institut National de la Santé et de la Recherche Médicale U1019, Lille, France 4Hospitalier Universitaire de Lille, Lille, France 5Institut Pasteur de Lille, Lille, France 6Translational Nanobiomaterials and Imaging, Department of Radiology, Leiden University Medical Center, Leiden, Netherlands

Edited by: Paolo Dellabona, San Raffaele Hospital (IRCCS), Italy

Reviewed by: Tonya J. Webb, University of Maryland, Baltimore, United States; Alessandro Poggi, IRCCS AOU San Martino IST, Italy; Moriya Tsuji, Aaron Diamond AIDS Research Center, United States

 *Correspondence: François Trottein, francois.trottein@pasteur-lille.fr

Specialty section: This article was submitted to Cancer Immunity and Immunotherapy, a section of the journal Frontiers in Immunology

 27 07 2017 2017 8 879 01 06 2017 10 07 2017 Copyright © 2017 Ghinnagow, Cruz, Macho-Fernandez, Faveeuw and Trottein. 2017 Ghinnagow, Cruz, Macho-Fernandez, Faveeuw and Trottein

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Type I natural killer T (NKT) cells have gained considerable interest in anticancer immune therapy over the last decade. This “innate-like” T lymphocyte subset has the unique ability to recognize foreign and self-derived glycolipid antigens in association with the CD1d molecule expressed by antigen-presenting cells. An important property of these cells is to bridge innate and acquired immune responses. The adjuvant function of NKT cells might be exploited in the clinics. In this review, we discuss the approaches currently being used to target NKT cells for cancer therapy. In particular, we highlight ongoing strategies utilizing NKT cell-based nanovaccines to optimize immune therapy.

 natural killer T cells adjuvant α-galactosylceramide CTL response nanovaccines dendritic cells cancer R08046EE/RPT08003EEA and R13071EE/RPT13001EEA Institut National de la Santé et de la Recherche Médicale10.13039/501100001677 Centre National de la Recherche Scientifique10.13039/501100004794 University of Lille Nord de France Pasteur Institute of Lille Institut National du Cancer10.13039/501100006364 Introduction

Invariant or type I natural killer T cells (referred as NKT cells) represent a highly conserved subset of non-conventional T lymphocytes endowed with a remarkably broad range of immune effector and regulatory functions. These cells recognize foreign and self-derived glycolipid antigens presented by the monomorphic MHC/HLA class I-like molecule CD1d expressed by antigen-presenting cells, including dendritic cells (DCs) [for reviews, Ref. (1–5)]. NKT cells express on their surface a semi-invariant T cell receptor (TCR) composed by a unique TCR-α chain paired with a restricted number of β-chains. Rapidly after natural activation (inflammation, infection), NKT cells produce huge amounts of cytokines including T helper (Th)1-like (INF-γ), Th2-like (IL-4), Th17-like (IL-17, IL-22), and regulatory (IL-10) cytokines. This flexibility depends on the mode of stimulation, on the location and on the NKT cell subset challenged. Of note, NKT cells can be activated by direct TCR triggering and also via cytokines, without TCR engagement (5). With their ability to swiftly release cytokines, NKT cells have also the potential to lyse cellular targets following TCR recognition of lipid antigens (6). This property is important in immune surveillance against tumor cells and could be exploited for immune-based therapy. The role of NKT cells in various pathologies including cancer, infection, acute, and chronic inflammation and autoimmune diseases has been evidenced in experimental models and in humans (5). Along with their natural (beneficial or detrimental) role in pathological settings, NKT cells can also be manipulated by means of specific CD1d-restricted ligands. For instance, exposure of antigen-presenting cells to α-galactosylceramide (α-GalCer) triggers potent innate and acquired immune responses. Of particular interest is the exquisite capacity of NKT cells to promote DC maturation and, as a consequence, to trigger potent T and B cell responses (7). This unique property, and given that the CD1d/NKT axis is conserved in humans (with no HLA restriction), could be used in clinical situations, including cancer. There is a strong interest to exploit the adjuvant effects of α-GalCer or related glycolipid derivatives to develop more efficient NKT cell-based vaccines (8–10). We herein review the effects of α-GalCer in preclinical and clinical studies and discuss ongoing and future strategies that aim to optimize NKT cell-based antitumor therapy with a particular focus on nanovector delivery systems. These systems, particularly those allowing encapsulation of tumor antigens and α-GalCer derivatives (adjuvant), might realize maximal therapeutic benefit with minimal toxicity.

 Free α-GalCer in Antitumor Therapy: from Preclinical Studies to Clinical Development

Alpha-GalCer is a marine sponge-derived glycosphingolipid originally discovered in a screen for antitumor compounds (11, 12). This seminal discovery has led to the development of synthetic α-GalCer derivatives as a family of powerful glycolipid agonists for NKT cells in order to promote protective immune responses against infections and cancers (13–15). α-GalCer triggers a mixed response by NKT cells including the production of IFN-γ, a cytokine important in tumor immune surveillance and inhibition of angiogenesis. Different agonists with Th1-promoting functions (which appear to be more adapted for anticancer therapies) have been described (13, 16). Preclinical studies have highlighted the potent antitumor effect of α-GalCer and α-GalCer derivatives against solid tumors (sarcoma, melanoma and colon, prostate, and lung carcinoma) and hematological malignancies (lymphoma) (12, 17–21). Mechanisms involved include early production of IFN-γ by NKT cells and NK cells and secretion of IL-12 by DCs (20). This success has led to clinical trials in patients with advanced lung cancer. Free soluble α-GalCer was used. Unfortunately, no or low clinical benefits were reported among patients (22–24). These disappointing results might be due to the lower number of NKT cells in patients relative to healthy individuals and/or to their diminished (but reversible) activation threshold capacity (22–32). Hence, one concern in NKT cell-based therapy is the diminished NKT cell count and/or function, although this cannot be generalized to all advanced cancer patients. Various means of circumventing this potential drawback are being developed including infusion of autologous ex vivo-expanded NKT cells. This approach can lead to clinically relevant antitumor responses (33–39). In vivo transfer of NKT cells expressing chimeric antigen receptor in order to redirect their cytotoxicity against tumor cells has also been explored in preclinical studies. This approach may provide potent antitumor activity (40, 41). Moreover, the reprogramming of NKT cells to induced pluripotent stem cells and their subsequent re-differentiation into more functional NKT cells (compared with the parental cells) is opening up new avenues in this field (42, 43). Another reason that might explain disappointing clinical data relates to the uncontrolled delivery of α-GalCer, which might lead to suboptimal primary and secondary activation of NKT cells. This later issue prompted researchers to inoculate α-GalCer in a vectorized (cellular or acellular systems) form in order to better control the delivery of the active principle and to generate more efficient innate and acquired immune-based antitumor responses.

 Vectorization of α-GalCer in Cellular Systems

Cellular systems in which α-GalCer is incorporated can act as potent (NKT cell-based) cellular adjuvants. As described below, these cellular systems include DCs, non-antigen presenting cells, and cancer cells. Studies in mice have demonstrated that α-GalCer loaded in DCs has a higher ability to activate NKT cells and to trigger antitumor responses relative to α-GalCer injected in a free (non-vectorized) form (18, 44). In the same line, adoptive transfer of α-GalCer-loaded autologous peripheral blood mononuclear cells or DCs induced clinical benefits in some patients (lung cancer and head and neck cancer), an effect that correlates with IFN-γ production (23, 33, 34, 36, 45–49). Of note, adoptive transfer of autologous NKT cells along with α-GalCer-pulsed mononuclear cells or DCs led to encouraging clinical results in term of prolonged median overall survival time (35, 36, 50). This effect was associated with a significant infiltration of NKT cells into the tumor (36) Hence, this combination therapy led to significant clinical efficacy, although technical and economic issues still persist.

Taniguchi’s group was the first to exploit artificial adjuvant vectors (aAVCs) to enhance NKT cell-based antitumor responses (8). This system can induce both innate and long-term memory CD8+ T cell responses against cancer. For instance, inoculation (single dose) of allogeneic fibroblasts (used as a vector cell) into which tumor antigen mRNA and CD1d with α-GalCer were introduced led to a long-lasting antitumor response (51–54). The same group has designed a human aAVC consisting of embryonic kidney cells transfected with the human melanoma MART-1 antigen and CD1d and pulsed with α-GalCer. This cellular system promoted antitumor response in humanized mice (55). Mechanistically, it is likely that allogeneic cells are selectively taken up by DCs and that the subsequent cross-presentation of tumor antigens to CD8+ T cells and α-GalCer to NKT cell is critical in the promotion of strong and long-lasting tumor-specific cytotoxic CD8+ T lymphocytes (CTL) responses.

Tumor cells are rich sources of tumor antigens. However, due to the low immunogenicity of tumor antigens, combined adjuvants are requisite in order to develop cancer vaccines. Shimizu and collaborators were the first to evaluate the capacity of α-GalCer-pulsed tumor cells (melanoma) to act as a cellular adjuvant (56). Numerous studies have validated the efficacy of this strategy in therapeutical settings in the mouse system (solid tumor and hematological malignancies) (57–66). Mechanistically, inoculated α-GalCer-pulsed tumor cells are selectively taken up by DCs (as for aAVC), which have a unique capacity to cross-present antigens from dying cells. It is also possible that the killing of CD1d-expressing tumor cells by activated NKT cells leads to the release of tumor antigens and to their subsequent cross-presentation by DCs. Whatever the mechanism, it is likely that the presentation of both α-GalCer and tumor antigens by the same DC is critical in the development of the protective tumor-specific CTL-based antitumor response. Whether this strategy could be exploited in the human setting to harness cancer progression and recurrence, without inducing autoimmunity, is still unknown. Cooperative action of toll-like receptor (TLR) ligands and iNKT cells on DC function is a well-recognized phenomenon (67). Of interest, relative to inoculation of α-GalCer-loaded tumor cells alone, coadministration of α-GalCer-loaded tumor cells and TLR9 agonists augments the antitumor response (66).

Introduction of α-GalCer and tumor antigens in antigen-presenting cells has also been attempted in preclinical models. DCs expressing the mammary tumor-associated antigen Her-2 and pulsed with α-GalCer trigger potent antitumor responses (68). The use of different models of tumors revealed that this strategy was effective both in prophylactic and therapeutic settings (69). Of interest, vaccination with DCs transduced with OVA (used here as a model tumor antigen) plus CCL21, a chemokine that attracts both T cells and NKT cells, protects against OVA-expressing tumors (70). Finally, human embryonic stem cell-derived DCs genetically engineered to express CD1d can prime CD8+ T cells against tumor antigens (71). The potential benefit of this latter strategy in cancer immunotherapy is being studied. In conclusion, cell-based vaccines to optimize α-GalCer activity in vivo are promising although technical, logistical, and financial difficulties might limit the development of such vaccines.

 Vectorization of α-GalCer in Acellular Systems Definition of Nanovectors

Development of nanovectors (<1 μm) holds great potential for cancer immunotherapy, including antitumor vaccines (72–74). The interest of using nanosized carriers able to incorporate α-GalCer (with or without tumor antigen) to optimize NKT cell-based anticancer therapy has recently emerged. Encapsulation of α-GalCer into nanovectors might offer several advantages relative to soluble α-GalCer. This includes preferential internalization by antigen-presenting cells (due to the size), slower and sustained release of α-GalCer in CD1d-containing endosomes, and minimal side effects (due to the lower amount required for a similar biological effect). Moreover, compared to cell-based vectorization, nanovectors are less invasive and costly (no adoptive transfer). Nanovectors offer the unique opportunity to deliver both adjuvant (including α-GalCer) and tumor antigens to the same antigen-presenting cells, especially DCs (75–77). Nanovectors represent an interesting class of delivery vehicles able to induce potent and long-lasting immune responses (78, 79). Surprisingly enough, few studies have exploited this unique property to enhance the antitumor functions of NKT cells.

Nanovectors include a multiple range of particulate systems including (among others) virus-like particles, dendrimers, silica microspheres, micelles, nanogels, nanoemulsions, liposomes, carbon nanotubes, metallic nanoparticles, and polymeric nanoparticles, which include nanospheres and nanocapsules (Table 1 and not shown). The physical properties as well as the advantages and drawbacks of nanovectors are presented in Table 1. For vaccine development, a major goal is to target DCs. Uptake of nanovectors by DCs depends on several physicochemical properties including the size, shape, surface charge, hydrophobicity, and hydrophilicity of nanovectors. To target more selectively DCs, it is possible to arm nanovectors with ligands or antibodies on their surface. Among the different delivery systems for antigen encapsulation in vaccines, particularly for cancer therapy, polymeric nanoparticles have many advantages including low toxicity, high biodegradability, amenability to controlled release of the bioactive agents (antigen and adjuvant), preservation of their stability, and potential for surface functionalization (79, 80). Currently, there is a long list of polymers used to produce nanovectors including plasma albumin, chitosan, polyethyleneimine, polylactic acid, and polylactic-coglycolic acid (PLGA). PLGA is one of the most successful biocompatible and biodegradable polymers (approved for in vivo use by the United States Food and Drug Administration). PLGA-based nanoparticle systems are particularly interesting since they allow high antigen density, incorporation of different classes of molecules including proteins and lipids, ability to reach MHC I pathway after uptake by DCs, and slow release kinetics delivery (75, 81–85). Attempts have been made to incorporate α-GalCer in nanosized vectors, with or without tumor antigens (Table 2). Here, we detail the effect of vectorized α-GalCer in innate and acquired immune-based antitumor responses.

Physical properties, advantages and drawbacks of nanovectors.

Dendrimers 1.5–14.5 nm Chemical homogeneity, high, degree of surface functionality and versatility, controlled degradation Multistep syntheses, elevated cost
Micelles 10–100 nm Capacity and compatibility with the loaded drug, minimized cylotoxicity Low drug loading, low drug incorporation stability, limited targeting ability
Nanogels 20–200 nm Large Surface area, high capacity to absorb water and other biological fluids, functional modification of the surfaces to prevent rapid clearance by phagocytic cells Difficulties to remove the solvents and surfactants (toxicity)
Nanoemulsions ≈100 nm Stable structures. Large effective surface area (enhances the bioavailability of the active compound) Special application techniques (high pressure homogenizers, ultrasonics), expensive equipment. Emulsions require large amounts of surfactants (toxic)
Liposomes 400 nm to 5 μm Controlled release of the active principle (reduced side effect relative to the free form), economical production, good tolerability, specific targeting, can transport up to 10,000 active compounds Approved for clinical use Rapid clearance due to the reticuloendothelial system low-term stability
Multilamellar vesicles 200 nm to 1 μm
Large unilamellar vesicles 20 nm to 200 nm Possibility to incorporate PEG and antibodies/ligands onto the surface to lengthen blood circulation and target immune cells
Small unilamellar vesicles
Carbon nanotubesSingle-walled Radius of up to 1 nm Excellent chemical and thermal stability, ordered structure, high mechanical strength, high electrical and thermal conductivity, metallic or semimetallic behavior, high surface area, and bioavailability Lack of solubility in aqueous media (may be solved by chemical modification and functionalization), potential toxic effects, aggregate formation (alteration of their general physico-chemical properties)
Multi-walled (2–10 layers of graphene sheet) Diameter of >10 nm
Metallic nanoparticles 5–500 nm Biological capacity to catalyze reactions in aqueous media at standard temperature and pressure, use in molecular imaging Toxic chemicals, high-energy requirements of production
Polymeric nanoparticlesNanospheresContinuous matrix systems in which loaded drugs are generally dispersed in and entrapped by different binding systems 10 nm to 1 µm Slower and sustained release of the active principle (adjuvant, antigens), high physical stability, simple formulation, multifunctionality, incorporation (absorption or covalent conjugation) of hydrophilic polymers (e.g., PEG/PEO-chains, polysorbate 80 polysaccharides). Cationic systems enhance DC uptake, possibility to graft ligands or antibodies to enhance the targeting Quickly eliminated from the bloodstream (need specific design to escape the reticuloendothelial system cells)
NanocapsulesCore (hydrophobic or hydrophilic) structure surrounded by a polymeric shell in which the drugs are confined 10 nm to 1 µm Natural polymers (dextran, Chitosan, albumin, gelatin, starch) Copolymers (PFLA, PGA, PLGA) approved by the FDA for clinical use, multiple functionalization (PLGA nanoparticles) for use in cancer immunotherapy

Utilization of α-GalCer-encapsulated nanovectors to promote NKT cell activation and antitumor responses.

Nanovectors Antigen Targeting and NKT cell response Antitumor response Reference
Silica microspheres No Targeting of dendritic cells (DCs) and CD169-expressing macrophages (NKT) cell activation Not tested (86, 87)
Virus-like particles Lymphocytic choriomeningitis virus-derived peptide gp33 NKT cell activation gp33-specific CTL responseProtection against melanoma (prophylactic setting) (94)
Liposomes No Targeting of DCs (Mannose receptor, DC-SIGN) via surface oligomannose NKT cell activation (Thl biais) Not tested (91)
No Targeting of macrophages (sialoadhesin CD169) via glycan ligands NKT cell activation (mouse and human) Not tested (92)
No Targeting of antigen-presenting cells (octaarginine-modified liposomes) strong NKT cell response Antitumor effects (melanoma)Therapeutic setting (90)
Tyrosinase-related protein 2 (Trp2) NKT cell activation CTL response-antitumor effectsTherapeutic setting (97)
PLGA-based NPs (passive targeting) No Better primary activation of NKT cells (IFN-γ) Not tested (88, 89)
OVA NKT cell activation Higher CTL response relative to soluble OVA and α-GalCer and to TLR-based nanovaccineProtection against melanomaProphylactic and therapeutic settings (95, 96)
PLGA-based NPs (active targeting) No Targeting of DEC205-expressing DCsBetter primary activation of NKT cells compared to soluble α-GalCerReduced unresponsiveness of NKT cells upon restimulation Not tested (93)
OVA Same extent of NKT cell activation relative to NPs without OVA Robust OVA-specific CTL responseAntitumor effects (melanoma, lymphoma)Prophylactic and therapeutic settings (93)
Trp2Gp100 Targeting of Clec9a-expressing DCsNKT cell activationBetter primary and secondary activation of NKT cells CTL response against tumor self antigensAntitumor effects (melanoma)Prophylactic and therapeutic settings (107)
Melan A Targeting of CLEC9a-expressing DCsExpansion and activation of human NKT cells (expanded from PBMCs) Expansion of human Melan A-specific CD8+ T cells (107)
Vectorization of α-GalCer without Tumor Antigen

Preclinical studies suggest that α-GalCer vectorized in nanovectors is of potential interest. This relies mainly on passive (untargeted) and active (targeted) delivery of α-GalCer to antigen-presenting cells. For instance, silica microspheres coated with lipid bilayers plus α-GalCer target mouse CD169-expressing macrophages and DCs, both cell types being critical in the primary activation of NKT cells (86, 87). Others and we have demonstrated that PLGA-based nanoparticles are internalized by DCs to promote NKT cell activation (88, 89). Another study has shown that α-GalCer incorporated in octaarginine-modified liposomes are passively taken up by antigen-presenting cells and strongly activate NKT cells. This leads to therapeutic protection against B16F10 lung metastases (90). In order to optimize the targeting of α-GalCer to antigen-presenting cells, nanovectors can be armed with ligands or antibodies that bind to specific markers. For instance, liposomes decorated with oligomannose that binds to mannose receptor and DC-SIGN target DCs in vivo and potently stimulate NKT cells toward a Th1 direction (91). Encapsulating α-GalCer in liposomes bearing on their surface glycans specific for the sialoadhesin CD169 strongly activates NKT cells in vivo (92). Our recent data demonstrate that, relative to non-vectorized α-GalCer, α-GalCer incorporated into antibody-armed PLGA nanoparticles that target DCs increases NKT cell-based innate immune responses (93).

 Vectorization of α-GalCer and Tumor Antigens Passive (Untargeted) Delivery

Very few studies have been devoted so far to study the potential benefit of encapsulating α-GalCer and tumor antigens in nanosized vectors. A pioneer study from McKee and colleagues analyzed the consequences of α-GalCer and antigen co-encapsulation in antitumor responses (94). In this work, α-GalCer and the gp33 peptide derived from lymphocytic choriomeningitis virus (used as a model antigen) were incorporated into virus-like particles. This composite particle system induced a 10-fold more active gp33-specific CTL response, compared to free α-GalCer and gp33, and prophylactically protected against gp33-expressing melanoma. Mechanistically, it is likely that α-GalCer and gp33 are delivered in the endosomal compartment of antigen-presenting cells to load to CD1d and MHC Class I, respectively, thus favoring cross-presentation by DCs. Dölen and collaborators have recently demonstrated that encapsulating α-GalCer and OVA in PLGA-based nanoparticles is efficient to trigger antitumor responses (95). Of interest was the observation that the response was superior compared to TLR agonist and OVA co-encapsulation. More recently, using a similar strategy, Li and colleagues showed that the immune responses triggered by α-GalCer and OVA encapsulated in PLGA nanoparticles was longer compared to that induced by its soluble counterparts (96). Of note, both intranasal and intraperitoneal injection of nanovaccine triggered robust antigen-specific CD8+ T cell response. Of interest, Neumann and colleagues investigated the effect of α-GalCer and tumor antigens co-delivery on antitumor responses using a cationic liposome (97). The self-antigen tyrosinase-related protein 2 (Trp2) was used. The authors found that the liposomal formulation elicits potent antigen-specific CTL response and prevents tumor progression in a therapeutic setting. Collectively, encapsulation of α-GalCer and tumor antigens in nanovectors, including liposomes and PLGA NPs (Table 2), elicits antitumor responses in experimental models. In these settings (passive delivery), DCs and probably other antigen-presenting cells are critically important.

 Active (Targeted) Delivery in DCs

Our work was the first to investigate the consequences of active α-GalCer and tumor antigen delivery to DCs by means of multifunctional nanovectors. In light of the literature showing the unique ability of cross-priming DCs (CD8α+ DCs and BDCA3+ DCs in the mouse and human system, respectively) to initiate and maintain CTL responses (98–101), we decided to target this DC subset. Moreover, we and others showed that CD8α+ DCs are very potent to stimulate primary and secondary NKT cell activation (93, 102). Finally, the fact that NKT cells can substitute “classical” CD4+ Th cells to license the DCs for cross-priming represents another reason explaining our devised strategy (103). Since cross-priming DCs express specific markers on their surface, we armed PLGA-based nanoparticles with antibodies in order to target these cells in vivo. Although DEC205 is not entirely specific for cross-priming CD8α+ DCs, nanoparticles armed with anti-DEC205 antibodies and carrying both α-GalCer and OVA successfully led to antigen cross-presentation and to potent antitumor responses (93). Of interest, this strategy also led to a long lasting antigen-specific antibody response. The C-type lectin Clec9a (also known as DNGR1) is almost exclusively expressed by cross-priming mouse and human DCs and is known to confer potent CTL responses (104–106). Our recent data indicate that PLGA-based nanoparticles armed with anti-Clec9a antibodies and incorporating both α-GalCer and OVA can confer protection against OVA-expressing tumors (lymphoma) (107). We also investigated whether our vectorization/targeting strategy might break tolerance to tumor self-antigens, an important challenge for optimal antitumor therapy [for reviews see Ref. (108–112)]. Indeed, co-incorporation of α-GalCer and tumor melanoma-derived self-antigens (including Trp2) triggered a potent CD8+ T cell-mediated antitumor response (107). Hence, our vaccine strategy, probably by enhancing DC/NKT cell/naive CD8+ T cell interactions (Figure 1), abrogates self-tolerance and promotes effective antitumor CTL responses. Signals incorporated by DCs are critical to shape the functions of naive T lymphocytes, including CD8+ T cells. Because maturation processes of DCs due to direct innate sensor (such as TLR) signaling might be different to those triggered by NKT cells, it would be interesting to compare the efficacy of TLR-based and NKT cell-based targeted nanovaccines in cancer therapies (Figure 2). Co-administration of soluble α-GalCer and TLR agonists with antigen was shown to enhance the CD8+ T cell response with augmented effect on tumor progression, relative to antigen mixed with an adjuvant alone (113). Therefore, encapsulation of both TLR ligands and α-GalCer derivatives in antibody-armed nanovectors might additively or synergistically enhance the responses, a hypothesis that needs further investigations.

Schematic “ménage à trois” between CD8α+ DC, natural killer T (NKT) cells, and naive CD8+ T cells. (1) Anti-Clec9a-armed nanoparticles that carry α-GalCer and tumor antigen are taken up by CD8α+ DC via the endocytic receptor Clec9a. (2) The active components are delivered in the endosomes and presented via MHC class I (peptide) and CD1d (α-GalCer) to naïve CD8+ T cells and NKT cells, respectively. (3) In response to TCR triggering, NKT cells activate the maturation of CD8α+ dendritic cells (DCs) through cytokines and costimulatory (CD40) molecules. (4) Mature DCs transmit signals to naïve CD8+ T cells, which, in turn, differentiate into CTLs. (5) CTLs destroy tumor cells. Note that α-GalCer is acquired and presented by DCs that are also actively engaged in presenting peptides to T cells. This scheme does not consider reciprocal interactions between NKT cells and CD8+ T cells.

Promotion of CD8+ T cell responses upon direct [toll-like receptor (TLR)-based] and/or indirect [natural killer T (NKT) cell based] dendritic cell (DC) activation. Direct activation. Nanoparticles bearing TLR agonists are internalized by DCs (i.e., those that excel in cross-presentation) and activate endosomal TLRs (such as TLR3, TLR7/8, or TLR9). This rapidly leads to DC maturation and to the production of inflammatory cytokines and costimulatory molecules that in turn promote the differentiation and expansion of naïve CD8+ T cells. Indirect activation. In this setting, the delivery of α-GalCer in DCs leads to the exposition of the glycolipid on the cell surface in association with the CD1d molecule (at this stage, the DC is still immature). TCR triggering in NKT cells leads to the release of cytokines and to the expression of costimulatory (CD40) molecules culminating in DC maturation. In turn, mature DCs activate naïve CD8+ T cells. Direct and indirect activation. One may suppose that the two effects are additive, or even synergistic, to promote optimal CD8+ T cell responses that control tumor progression.

 Concluding Remarks and Future Perspectives

Growing evidences demonstrate that α-GalCer (or α-GalCer derivatives) might be successfully used in cancer therapy. However, innovative strategies to better manipulate the adjuvant properties and the antitumor potentials of NKT cells are required. Among them, optimization of delivery systems that contain α-GalCer and tumor antigens to optimally activate NKT cell-based immune responses remains an important goal. Cell-based vaccines that promote strong and long-lasting CTL responses offer an interesting immunotherapeutic strategy for the future although concerns still exist (cost, invasive procedure). Nanovectors that passively or actively target (cross-priming) DCs are also of clinical interest. Future studies will aim to enhance the efficacy of delivery systems in order to improve cell targeting and to optimize the delivery of the active principles (α-GalCer and tumor antigens) in the right cellular compartment. Such development will require the use of more sophisticated nanovectors to improve surgical strikes and possibly the targeting of other (DC expressed) specific molecules. Complementary approaches including strategies that boost the number/function of NKT cells in patients (transfer of functional NKT cells) and/or that aim to control immune suppression (e.g., check point blockers, immunomodulatory drugs) are of interest. Moreover, combination of NKT cell and TLR agonists might amplify the strength and the quality of the immune response in patients. An important area for future research is the development of humanized mouse models to accurately replicate the NKT cell response in humans. It is likely that, in a near future, the use of nanovector-based medicine will optimize antitumor responses for the sake of cancer patients, in combination with conventional immunotherapy.

 Author Contributions

All authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.

 Conflict of Interest Statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

We apologize to colleagues whose works could not be cited due to space constraints.

Funding. This work was supported by the INSERM, the CNRS, the University of Lille Nord de France, the Pasteur Institute of Lille, and the Institut National du Cancer (INCa, projets libres) under reference R08046EE/RPT08003EEA and R13071EE/RPT13001EEA.

 Abbreviations

NKT, natural killer T; DCs, dendritic cells; TCR, T cell receptor; α-GalCer, α-galactosylceramide; CAR, chimeric antigen receptor; aAVC, artificial adjuvant vector; PLGA, polylactic-coglycolic acid; CTL, cytotoxic CD8+ T lymphocyte; TLR, toll-like receptor; Trp2, tyrosinase-related protein 2.

 References Taniguchi M Harada M Kojo S Nakayama T Wakao H. The regulatory role of Valpha14 NKT cells in innate and acquired immune response. Annu Rev Immunol (2003) 21:483–513.10.1146/annurev.immunol.21.120601.14105712543936 Bendelac A Savage PB Teyton L. The biology of NKT cells. Annu Rev Immunol (2007) 25:297–336.10.1146/annurev.immunol.25.022106.14171117150027 Berzins SP Smyth MJ Baxter AG. Presumed guilty: natural killer T cell defects and human disease. Nat Rev Immunol (2011) 11:131–42.10.1038/nri290421267014 Rossjohn J Pellicci DG Patel O Gapin L Godfrey DI. Recognition of CD1d-restricted antigens by natural killer T cells. Nat Rev Immunol (2012) 12:845–57.10.1038/nri332823154222 Brennan PJ Brigl M Brenner MB. Invariant natural killer T cells: an innate activation scheme linked to diverse effector functions. Nat Rev Immunol (2013) 13:101–17.10.1038/nri336923334244 Metelitsa LS. Anti-tumor potential of type-I NKT cells against CD1d-positive and CD1d-negative tumors in humans. Clin Immunol (2011) 140:119–29.10.1016/j.clim.2010.10.00521095162 Hermans IF Silk JD Gileadi U Salio M Mathew B Ritter G NKT cells enhance CD4+ and CD8+ T cell responses to soluble antigen in vivo through direct interaction with dendritic cells. J Immunol (2003) 171:5140–7.10.4049/jimmunol.171.10.514014607913 Fujii S-I Shimizu K Okamoto Y Kunii N Nakayama T Motohashi S NKT cells as an ideal anti-tumor immunotherapeutic. Front Immunol (2013) 4:409.10.3389/fimmu.2013.0040924348476 Cerundolo V Silk JD Masri SH Salio M. Harnessing invariant NKT cells in vaccination strategies. Nat Rev Immunol (2009) 9:28–38.10.1038/nri245119079136 Mattarollo SR Smyth MJ. NKT cell adjuvants in therapeutic vaccines against hematological cancers. Oncoimmunology (2013) 2:e22615.10.4161/onci.2261523482240 Kobayashi E Motoki K Uchida T Fukushima H Koezuka Y. KRN7000, a novel immunomodulator, and its antitumor activities. Oncol Res (1995) 7:529–34.8866665 Kawano T Cui J Koezuka Y Toura I Kaneko Y Motoki K CD1d-restricted and TCR-mediated activation of valpha14 NKT cells by glycosylceramides. Science (1997) 278:1626–9.10.1126/science.278.5343.16269374463 Carreño LJ Saavedra-Ávila NA Porcelli SA. Synthetic glycolipid activators of natural killer T cells as immunotherapeutic agents. Clin Transl Immunology (2016) 5:e69.10.1038/cti.2016.1427195112 Kharkwal SS Arora P Porcelli SA. Glycolipid activators of invariant NKT cells as vaccine adjuvants. Immunogenetics (2016) 68:597–610.10.1007/s00251-016-0925-y27377623 East JE Kennedy AJ Webb TJ. Raising the roof: the preferential pharmacological stimulation of Th1 and th2 responses mediated by NKT cells. Med Res Rev (2014) 34:45–76.10.1002/med.2127623239102 Li X Fujio M Imamura M Wu D Vasan S Wong C-H Design of a potent CD1d-binding NKT cell ligand as a vaccine adjuvant. Proc Natl Acad Sci U S A (2010) 107:13010–5.10.1073/pnas.100666210720616071 Nakagawa R Motoki K Ueno H Iijima R Nakamura H Kobayashi E Treatment of hepatic metastasis of the colon26 adenocarcinoma with an alpha-galactosylceramide, KRN7000. Cancer Res (1998) 58:1202–7. Toura I Kawano T Akutsu Y Nakayama T Ochiai T Taniguchi M. Cutting edge: inhibition of experimental tumor metastasis by dendritic cells pulsed with alpha-galactosylceramide. J Immunol (1999) 163:2387–91.10452972 Shin T Nakayama T Akutsu Y Motohashi S Shibata Y Harada M Inhibition of tumor metastasis by adoptive transfer of IL-12-activated Valpha14 NKT cells. Int J Cancer (2001) 91:523–8.10.1002/1097-0215(20010215)91:4<523::AID-IJC1087>3.0.CO;2-L11251976 Smyth MJ Crowe NY Pellicci DG Kyparissoudis K Kelly JM Takeda K Sequential production of interferon-gamma by NK1.1(+) T cells and natural killer cells is essential for the antimetastatic effect of alpha-galactosylceramide. Blood (2002) 99:1259–66.10.1182/blood.V99.4.125911830474 Nowak M Arredouani MS Tun-Kyi A Schmidt-Wolf I Sanda MG Balk SP Defective NKT cell activation by CD1d+ TRAMP prostate tumor cells is corrected by interleukin-12 with α-galactosylceramide. PLoS One (2010) 5:e11311.10.1371/journal.pone.001131120593019 Giaccone G Punt CJ Ando Y Ruijter R Nishi N Peters M A phase I study of the natural killer T-cell ligand alpha-galactosylceramide (KRN7000) in patients with solid tumors. Clin Cancer Res (2002) 8:3702–9.1247357910.1155/2007/89017 Schneiders FL Scheper RJ von Blomberg BME Woltman AM Janssen HLA van den Eertwegh AJM Clinical experience with α-galactosylceramide (KRN7000) in patients with advanced cancer and chronic hepatitis B/C infection. Clin Immunol (2011) 140:130–41.10.1016/j.clim.2010.11.01021169066 Exley MA Nakayama T. NKT-cell-based immunotherapies in clinical trials. Clin Immunol (2011) 140:117–8.10.1016/j.clim.2011.04.015 Tahir SM Cheng O Shaulov A Koezuka Y Bubley GJ Wilson SB Loss of IFN-gamma production by invariant NK T cells in advanced cancer. J Immunol (2001) 167:4046–50.10.4049/jimmunol.167.7.404611564825 Yanagisawa K Seino K Ishikawa Y Nozue M Todoroki T Fukao K. Impaired proliferative response of V alpha 24 NKT cells from cancer patients against alpha-galactosylceramide. J Immunol (2002) 168:6494–9.10.4049/jimmunol.168.12.649412055270 Dhodapkar MV Geller MD Chang DH Shimizu K Fujii S-I Dhodapkar KM A reversible defect in natural killer T cell function characterizes the progression of premalignant to malignant multiple myeloma. J Exp Med (2003) 197:1667–76.10.1084/jem.2002165012796469 Fujii S Shimizu K Klimek V Geller MD Nimer SD Dhodapkar MV. Severe and selective deficiency of interferon-gamma-producing invariant natural killer T cells in patients with myelodysplastic syndromes. Br J Haematol (2003) 122:617–22.10.1046/j.1365-2141.2003.04465.x12899717 Molling JW Kölgen W van der Vliet HJJ Boomsma MF Kruizenga H Smorenburg CH Peripheral blood IFN-gamma-secreting Valpha24+Vbeta11+ NKT cell numbers are decreased in cancer patients independent of tumor type or tumor load. Int J Cancer (2005) 116:87–93.10.1002/ijc.20998 Molling JW Langius JAE Langendijk JA Leemans CR Bontkes HJ van der Vliet HJJ Low levels of circulating invariant natural killer T cells predict poor clinical outcome in patients with head and neck squamous cell carcinoma. J Clin Oncol (2007) 25:862–8.10.1200/JCO.2006.08.578717327607 Konishi J Yamazaki K Yokouchi H Shinagawa N Iwabuchi K Nishimura M. The characteristics of human NKT cells in lung cancer – CD1d independent cytotoxicity against lung cancer cells by NKT cells and decreased human NKT cell response in lung cancer patients. Hum Immunol (2004) 65:1377–88.10.1016/j.humimm.2004.09.003 Gorini F Azzimonti L Delfanti G Scarfò L Scielzo C Bertilaccio MT Invariant NKT cells contribute to chronic lymphocytic leukemia surveillance and prognosis. Blood (2017) 129:3440–51.10.1182/blood-2016-11-75106528465341 Chang DH Osman K Connolly J Kukreja A Krasovsky J Pack M Sustained expansion of NKT cells and antigen-specific T cells after injection of alpha-galactosyl-ceramide loaded mature dendritic cells in cancer patients. J Exp Med (2005) 201:1503–17.10.1084/jem.2004259215867097 Motohashi S Ishikawa A Ishikawa E Otsuji M Iizasa T Hanaoka H A phase I study of in vitro expanded natural killer T cells in patients with advanced and recurrent non-small cell lung cancer. Clin Cancer Res (2006) 12:6079–86.10.1158/1078-0432.CCR-06-011417028247 Kunii N Horiguchi S Motohashi S Yamamoto H Ueno N Yamamoto S Combination therapy of in vitro-expanded natural killer T cells and alpha-galactosylceramide-pulsed antigen-presenting cells in patients with recurrent head and neck carcinoma. Cancer Sci (2009) 100:1092–8.10.1111/j.1349-7006.2009.01135.x19302288 Yamasaki K Horiguchi S Kurosaki M Kunii N Nagato K Hanaoka H Induction of NKT cell-specific immune responses in cancer tissues after NKT cell-targeted adoptive immunotherapy. Clin Immunol (2011) 138:255–65.10.1016/j.clim.2010.11.01421185787 de Lalla C Rinaldi A Montagna D Azzimonti L Bernardo ME Sangalli LM Invariant NKT cell reconstitution in pediatric leukemia patients given HLA-haploidentical stem cell transplantation defines distinct CD4+ and CD4- subset dynamics and correlates with remission state. J Immunol (2011) 186:4490–9.10.4049/jimmunol.100374821357532 Casorati G de Lalla C Dellabona P. Invariant natural killer T cells reconstitution and the control of leukemia relapse in pediatric haploidentical hematopoietic stem cell transplantation. Oncoimmunology (2012) 1:355–7.10.4161/onci.1839922737613 Exley MA Friedlander P Alatrakchi N Vriend L Yue SC Sasada T Adoptive transfer of invariant NKT cells as immunotherapy for advanced melanoma: a phase 1 clinical trial. Clin Cancer Res (2017) 25:3510–19.10.1158/1078-0432.CCR-16-0600 Heczey A Liu D Tian G Courtney AN Wei J Marinova E Invariant NKT cells with chimeric antigen receptor provide a novel platform for safe and effective cancer immunotherapy. Blood (2014) 124:2824–33.10.1182/blood-2013-11-54123525049283 Tian G Courtney AN Jena B Heczey A Liu D Marinova E CD62L+ NKT cells have prolonged persistence and antitumor activity in vivo. J Clin Invest (2016) 126:2341–55.10.1172/JCI8347627183388 Kitayama S Zhang R Liu T-Y Ueda N Iriguchi S Yasui Y Cellular adjuvant properties, direct cytotoxicity of re-differentiated Vα24 invariant NKT-like cells from human induced pluripotent stem cells. Stem Cell Reports (2016) 6:213–27.10.1016/j.stemcr.2016.01.005 Yamada D Iyoda T Vizcardo R Shimizu K Sato Y Endo TA Efficient regeneration of human Vα24(+) invariant natural killer T cells and their anti-tumor activity in vivo. Stem Cells (2016) 34:2852–60.10.1002/stem.2465 Nishimura T Kitamura H Iwakabe K Yahata T Ohta A Sato M The interface between innate and acquired immunity: glycolipid antigen presentation by CD1d-expressing dendritic cells to NKT cells induces the differentiation of antigen-specific cytotoxic T lymphocytes. Int Immunol (2000) 12:987–94.10.1093/intimm/12.7.98710882410 Nieda M Okai M Tazbirkova A Lin H Yamaura A Ide K Therapeutic activation of Valpha24+Vbeta11+ NKT cells in human subjects results in highly coordinated secondary activation of acquired and innate immunity. Blood (2004) 103:383–9.10.1182/blood-2003-04-115514512316 Ishikawa A Motohashi S Ishikawa E Fuchida H Higashino K Otsuji M A phase I study of alpha-galactosylceramide (KRN7000)-pulsed dendritic cells in patients with advanced and recurrent non-small cell lung cancer. Clin Cancer Res (2005) 11:1910–7.10.1158/1078-0432.CCR-04-145315756017 Motohashi S Nagato K Kunii N Yamamoto H Yamasaki K Okita K A phase I-II study of alpha-galactosylceramide-pulsed IL-2/GM-CSF-cultured peripheral blood mononuclear cells in patients with advanced and recurrent non-small cell lung cancer. J Immunol (2009) 182:2492–501.10.4049/jimmunol.080012619201905 Nicol AJ Tazbirkova A Nieda M. Comparison of clinical and immunological effects of intravenous and intradermal administration of α-galactosylceramide (KRN7000)-pulsed dendritic cells. Clin Cancer Res (2011) 17:5140–51.10.1158/1078-0432.CCR-10-310521653690 Nagato K Motohashi S Ishibashi F Okita K Yamasaki K Moriya Y Accumulation of activated invariant natural killer T cells in the tumor microenvironment after α-galactosylceramide-pulsed antigen presenting cells. J Clin Immunol (2012) 32:1071–81.10.1007/s10875-012-9697-922534863 Dellabona P Casorati G de Lalla C Montagna D Locatelli F. On the use of donor-derived iNKT cells for adoptive immunotherapy to prevent leukemia recurrence in pediatric recipients of HLA haploidentical HSCT for hematological malignancies. Clin Immunol (2011) 140:152–9.10.1016/j.clim.2010.11.01521185785 Fujii S Goto A Shimizu K. Antigen mRNA-transfected, allogeneic fibroblasts loaded with NKT-cell ligand confer antitumor immunity. Blood (2009) 113:4262–72.10.1182/blood-2008-08-17644619164596 Shimizu K Asakura M Shinga J Sato Y Kitahara S Hoshino K Invariant NKT cells induce plasmacytoid dendritic cell (DC) cross-talk with conventional DCs for efficient memory CD8+ T cell induction. J Immunol (2013) 190:5609–19.10.4049/jimmunol.130003323630347 Fujii S-I Shimizu K. Immunotherapy with artificial adjuvant vector cells: harnessing both arms of the immune response. Oncoimmunology (2013) 2:e23432.10.4161/onci.23432 Shimizu K Yamasaki S Shinga J Sato Y Watanabe T Ohara O Systemic DC activation modulates the tumor microenvironment and shapes the long-lived tumor-specific memory mediated by CD8+ T cells. Cancer Res (2016) 76:3756–66.10.1158/0008-5472.CAN-15-321927371739 Shimizu K Mizuno T Shinga J Asakura M Kakimi K Ishii Y Vaccination with antigen-transfected, NKT cell ligand-loaded, human cells elicits robust in situ immune responses by dendritic cells. Cancer Res (2013) 73:62–73.10.1158/0008-5472.CAN-12-075923108144 Shimizu K Kurosawa Y Taniguchi M Steinman RM Fujii S-I. Cross-presentation of glycolipid from tumor cells loaded with alpha-galactosylceramide leads to potent and long-lived T cell mediated immunity via dendritic cells. J Exp Med (2007) 204:2641–53.10.1084/jem.2007045817923500 Shimizu K Goto A Fukui M Taniguchi M Fujii S. Tumor cells loaded with alpha-galactosylceramide induce innate NKT and NK cell-dependent resistance to tumor implantation in mice. J Immunol (2007) 178:2853–61.10.4049/jimmunol.178.5.285317312129 Chung Y Qin H Kang C-Y Kim S Kwak LW Dong C. An NKT-mediated autologous vaccine generates CD4 T-cell dependent potent antilymphoma immunity. Blood (2007) 110:2013–9.10.1182/blood-2006-12-06130917581919 Choi YS Hoory T Monie A Wu A Connolly D Hung C-F. alpha-Galactosylceramide enhances the protective and therapeutic effects of tumor cell based vaccines for ovarian tumors. Vaccine (2008) 26:5855–63.10.1016/j.vaccine.2008.08.02718771701 Mattarollo SR West AC Steegh K Duret H Paget C Martin B NKT cell adjuvant-based tumor vaccine for treatment of myc oncogene-driven mouse B-cell lymphoma. Blood (2012) 120:3019–29.10.1182/blood-2012-04-42664322932803 Hunn MK Farrand KJ Broadley KWR Weinkove R Ferguson P Miller RJ Vaccination with irradiated tumor cells pulsed with an adjuvant that stimulates NKT cells is an effective treatment for glioma. Clin Cancer Res (2012) 18:6446–59.10.1158/1078-0432.CCR-12-070423147997 Mattarollo SR Steegh K Li M Duret H Foong Ngiow S Smyth MJ. Transient Foxp3(+) regulatory T-cell depletion enhances therapeutic anticancer vaccination targeting the immune-stimulatory properties of NKT cells. Immunol Cell Biol (2013) 91:105–14.10.1038/icb.2012.5823090488 Hong S Lee H Jung K Lee SM Lee S-J Jun HJ Tumor cells loaded with α-galactosylceramide promote therapeutic NKT-dependent anti-tumor immunity in multiple myeloma. Immunol Lett (2013) 156:132–9.10.1016/j.imlet.2013.10.00224148970 Hunn MK Hermans IF. Exploiting invariant NKT cells to promote T-cell responses to cancer vaccines. Oncoimmunology (2013) 2:e23789.10.4161/onci.2378923734325 Gibbins JD Ancelet LR Weinkove R Compton BJ Painter GF Petersen TR An autologous leukemia cell vaccine prevents murine acute leukemia relapse after cytarabine treatment. Blood (2014) 124:2953–63.10.1182/blood-2014-04-56895625237205 Dong T Yi T Yang M Lin S Li W Xu X Co-operation of α-galactosylceramide-loaded tumour cells and TLR9 agonists induce potent anti-tumour responses in a murine colon cancer model. Biochem J (2016) 473:7–19.10.1042/BJ2015012926450924 Hermans IF Silk JD Gileadi U Masri SH Shepherd D Farrand KJ Dendritic cell function can be modulated through cooperative actions of TLR ligands and invariant NKT cells. J Immunol (2007) 178:2721–9.10.4049/jimmunol.178.5.272117312114 Ko H-J Kim Y-J Kim Y-S Chang W-S Ko S-Y Chang S-Y A combination of chemoimmunotherapies can efficiently break self-tolerance and induce antitumor immunity in a tolerogenic murine tumor model. Cancer Res (2007) 67:7477–86.10.1158/0008-5472.CAN-06-463917671218 Fukushima S Hirata S Motomura Y Fukuma D Matsunaga Y Ikuta Y Multiple antigen-targeted immunotherapy with alpha-galactosylceramide-loaded and genetically engineered dendritic cells derived from embryonic stem cells. J Immunother (2009) 32:219–31.10.1097/CJI.0b013e318194b63b19242378 Matsuyoshi H Hirata S Yoshitake Y Motomura Y Fukuma D Kurisaki A Therapeutic effect of alpha-galactosylceramide-loaded dendritic cells genetically engineered to express SLC/CCL21 along with tumor antigen against peritoneally disseminated tumor cells. Cancer Sci (2005) 96:889–96.10.1111/j.1349-7006.2005.00123.x16367909 Zeng J Shahbazi M Wu C Toh HC Wang S. Enhancing immunostimulatory function of human embryonic stem cell-derived dendritic cells by CD1d overexpression. J Immunol (2012) 188:4297–304.10.4049/jimmunol.110234322407918 Craparo EF Bondì ML. Application of polymeric nanoparticles in immunotherapy. Curr Opin Allergy Clin Immunol (2012) 12:658–64.10.1097/ACI.0b013e3283588c57 Smith DM Simon JK Baker JR. Applications of nanotechnology for immunology. Nat Rev Immunol (2013) 13:592–605.10.1038/nri348823883969 Serda RE. Particle platforms for cancer immunotherapy. Int J Nanomedicine (2013) 8:1683–96.10.2147/IJN.S31756 Cruz LJ Tacken PJ Fokkink R Joosten B Stuart MC Albericio F Targeted PLGA nano- but not microparticles specifically deliver antigen to human dendritic cells via DC-SIGN in vitro. J Control Release (2010) 144:118–26.10.1016/j.jconrel.2010.02.013 Ghotbi Z Haddadi A Hamdy S Hung RW Samuel J Lavasanifar A. Active targeting of dendritic cells with mannan-decorated PLGA nanoparticles. J Drug Target (2011) 19:281–92.10.3109/1061186X.2010.49946320590403 Waeckerle-Men Y Groettrup M. PLGA microspheres for improved antigen delivery to dendritic cells as cellular vaccines. Adv Drug Deliv Rev (2005) 57:475–82.10.1016/j.addr.2004.09.007 Bachmann MF Jennings GT. Vaccine delivery: a matter of size, geometry, kinetics and molecular patterns. Nat Rev Immunol (2010) 10:787–96.10.1038/nri286820948547 Park Y-M Lee SJ Kim YS Lee MH Cha GS Jung ID Nanoparticle-based vaccine delivery for cancer immunotherapy. Immune Netw (2013) 13:177.10.4110/in.2013.13.5.17724198742 Alyautdin R Khalin I Nafeeza MI Haron MH Kuznetsov D. Nanoscale drug delivery systems and the blood-brain barrier. Int J Nanomedicine (2014) 9:795–811.10.2147/IJN.S5223624550672 Fahmy TM Demento SL Caplan MJ Mellman I Saltzman WM. Design opportunities for actively targeted nanoparticle vaccines. Nanomedicine (Lond) (2008) 3:343–55.10.2217/17435889.3.3.34318510429 Mundargi RC Babu VR Rangaswamy V Patel P Aminabhavi TM. Nano/micro technologies for delivering macromolecular therapeutics using poly(D,L-lactide-co-glycolide) and its derivatives. J Control Release (2008) 125:193–209.10.1016/j.jconrel.2007.09.01318083265 Lü J-M Wang X Marin-Muller C Wang H Lin PH Yao Q Current advances in research and clinical applications of PLGA-based nanotechnology. Expert Rev Mol Diagn (2009) 9:325–41.10.1586/erm.09.15 Lee Y-R Lee Y-H Im S-A Kim K Lee C-K. Formulation and characterization of antigen-loaded PLGA nanoparticles for efficient cross-priming of the antigen. Immune Netw (2011) 11:163–8.10.4110/in.2011.11.3.163 Silva AL Soema PC Slütter B Ossendorp F Jiskoot W. PLGA particulate delivery systems for subunit vaccines: linking particle properties to immunogenicity. Hum Vaccin Immunother (2016) 12:1056–69.10.1080/21645515.2015.111771426752261 Barral P Polzella P Bruckbauer A van Rooijen N Besra GS Cerundolo V CD169(+) macrophages present lipid antigens to mediate early activation of iNKT cells in lymph nodes. Nat Immunol (2010) 11:303–12.10.1038/ni.185320228797 Barral P Sánchez-Niño MD van Rooijen N Cerundolo V Batista FD. The location of splenic NKT cells favours their rapid activation by blood-borne antigen. EMBO J (2012) 31:2378–90.10.1038/emboj.2012.8722505026 Thapa P Zhang G Xia C Gelbard A Overwijk WW Liu C Nanoparticle formulated alpha-galactosylceramide activates NKT cells without inducing anergy. Vaccine (2009) 27:3484–8.10.1016/j.vaccine.2009.01.04719200815 Macho Fernandez E Chang J Fontaine J Bialecki E Rodriguez F Werkmeister E Activation of invariant Natural Killer T lymphocytes in response to the α-galactosylceramide analogue KRN7000 encapsulated in PLGA-based nanoparticles and microparticles. Int J Pharm (2012) 423:45–54.10.1016/j.ijpharm.2011.04.06821575695 Nakamura T Yamazaki D Yamauchi J Harashima H. The nanoparticulation by octaarginine-modified liposome improves α-galactosylceramide-mediated antitumor therapy via systemic administration. J Control Release (2013) 171:216–24.10.1016/j.jconrel.2013.07.00423860186 Ishii M Kojima N. Effective stimulation of invariant natural killer T cells by oligomannose-coated liposomes. Int Immunopharmacol (2013) 15:685–92.10.1016/j.intimp.2013.03.00923535021 Kawasaki N Vela JL Nycholat CM Rademacher C Khurana A van Rooijen N Targeted delivery of lipid antigen to macrophages via the CD169/sialoadhesin endocytic pathway induces robust invariant natural killer T cell activation. Proc Natl Acad Sci U S A (2013) 110:7826–31.10.1073/pnas.121988811023610394 Macho-Fernandez E Cruz LJ Ghinnagow R Fontaine J Bialecki E Frisch B Targeted delivery of α-galactosylceramide to CD8α+ dendritic cells optimizes type I NKT cell-based antitumor responses. J Immunol (2014) 193:961–9.10.4049/jimmunol.130302924913977 McKee SJ Young VL Clow F Hayman CM Baird MA Hermans IF Virus-like particles and α-galactosylceramide form a self-adjuvanting composite particle that elicits anti-tumor responses. J Control Release (2012) 159:338–45.10.1016/j.jconrel.2012.02.01522386518 Dölen Y Kreutz M Gileadi U Tel J Vasaturo A van Dinther EAW Co-delivery of PLGA encapsulated invariant NKT cell agonist with antigenic protein induce strong T cell-mediated antitumor immune responses. Oncoimmunology (2015) 5:e1068493.10.1080/2162402X.2015.106849326942088 Li B Siuta M Bright V Koktysh D Matlock BK Dumas ME Improved proliferation of antigen-specific cytolytic T lymphocytes using a multimodal nanovaccine. Int J Nanomedicine (2016) 11:6103–21.10.2147/IJN.S11243227895483 Neumann S Young K Compton B Anderson R Painter G Hook S. Synthetic TRP2 long-peptide and α-galactosylceramide formulated into cationic liposomes elicit CD8+ T-cell responses and prevent tumour progression. Vaccine (2015) 33:5838–44.10.1016/j.vaccine.2015.08.08326363382 Crozat K Guiton R Contreras V Feuillet V Dutertre C-A Ventre E The XC chemokine receptor 1 is a conserved selective marker of mammalian cells homologous to mouse CD8alpha+ dendritic cells. J Exp Med (2010) 207:1283–92.10.1084/jem.2010022320479118 Bachem A Güttler S Hartung E Ebstein F Schaefer M Tannert A Superior antigen cross-presentation and XCR1 expression define human CD11c+CD141+ cells as homologues of mouse CD8+ dendritic cells. J Exp Med (2010) 207:1273–81.10.1084/jem.2010034820479115 Poulin LF Salio M Griessinger E Anjos-Afonso F Craciun L Chen J-L Characterization of human DNGR-1+ BDCA3+ leukocytes as putative equivalents of mouse CD8alpha+ dendritic cells. J Exp Med (2010) 207:1261–71.10.1084/jem.2009261820479117 Jongbloed SL Kassianos AJ McDonald KJ Clark GJ Ju X Angel CE Human CD141+ (BDCA-3)+ dendritic cells (DCs) represent a unique myeloid DC subset that cross-presents necrotic cell antigens. J Exp Med (2010) 207:1247–60.10.1084/jem.2009214020479116 Arora P Baena A Yu KOA Saini NK Kharkwal SS Goldberg MF A single subset of dendritic cells controls the cytokine bias of natural killer T cell responses to diverse glycolipid antigens. Immunity (2014) 40:105–16.10.1016/j.immuni.2013.12.00424412610 Semmling V Lukacs-Kornek V Thaiss CA Quast T Hochheiser K Panzer U Alternative cross-priming through CCL17-CCR4-mediated attraction of CTLs toward NKT cell-licensed DCs. Nat Immunol (2010) 11:313–20.10.1038/ni.184820190758 Sancho D Mourão-Sá D Joffre OP Schulz O Rogers NC Pennington DJ Tumor therapy in mice via antigen targeting to a novel, DC-restricted C-type lectin. J Clin Invest (2008) 118:2098–110.10.1172/JCI3458418497879 Picco G Beatson R Taylor-Papadimitriou J Burchell JM. Targeting DNGR-1 (CLEC9A) with antibody/MUC1 peptide conjugates as a vaccine for carcinomas. Eur J Immunol (2014) 44:1947–55.10.1002/eji.20134407624648154 Tullett KM Lahoud MH Radford KJ. Harnessing human cross-presenting CLEC9A(+)XCR1(+) dendritic cells for immunotherapy. Front Immunol (2014) 5:239.10.3389/fimmu.2014.00239 Ghinnagow R De Meester J Cruz LJ Aspord C Corgnac S Macho-Fernandez E Co-delivery of the NKT agonist α-galactosylceramide and tumor antigens to cross-priming dendritic cells breaks tolerance to self-antigens and promotes antitumor responses. Oncoimmunology (in press). Klebanoff CA Acquavella N Yu Z Restifo NP. Therapeutic cancer vaccines: are we there yet? Immunol Rev (2011) 239:27–44.10.1111/j.1600-065X.2010.00979.x21198663 Andersen BM Ohlfest JR. Increasing the efficacy of tumor cell vaccines by enhancing cross priming. Cancer Lett (2012) 325:155–64.10.1016/j.canlet.2012.07.01222809568 Palucka K Banchereau J. Dendritic-cell-based therapeutic cancer vaccines. Immunity (2013) 39:38–48.10.1016/j.immuni.2013.07.00423890062 Chen DS Mellman I. Oncology meets immunology: the cancer-immunity cycle. Immunity (2013) 39:1–10.10.1016/j.immuni.2013.07.01223890059 Pol J Bloy N Buqué A Eggermont A Cremer I Sautès-Fridman C Trial watch: peptide-based anticancer vaccines. Oncoimmunology (2015) 4:e974411.10.4161/2162402X.2014.97441126137405 Coelho-Dos-Reis JG Huang J Tsao T Pereira FV Funakoshi R Nakajima H Co-administration of α-GalCer analog and TLR4 agonist induces robust CD8(+) T-cell responses to PyCS protein and WT-1 antigen and activates memory-like effector NKT cells. Clin Immunol (2016) 168:6–15.10.1016/j.clim.2016.04.01427132023