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Immune checkpoint blockade (ICB) has changed the therapeutic landscape of oncology but its impact is limited by primary or secondary resistance. ICB resistance has been related to a lack of T cells infiltrating into the tumor. Strategies to overcome this hurdle have so far focused on the tumor microenvironment, but have mostly overlooked the role of tumor-draining lymph nodes (TDLN). Whereas for CTLA-4 blockade TDLN have long since been implicated due to its perceived mechanism-of-action involving T cell priming, only recently has evidence been emerging showing TDLN to be vital for the efficacy of PD-1 blockade as well. TDLN are targeted by developing tumors to create an immune suppressed pre-metastatic niche which can lead to priming of dysfunctional antitumor T cells. In this review, we will discuss the evidence that therapeutic targeting of TDLN may ensure sufficient antitumor T cell activation and subsequent tumor infiltration to facilitate effective ICB. Indeed, waves of tumor-specific, proliferating stem cell-like, or progenitor exhausted T cells, either newly primed or reinvigorated in TDLN, are vital for PD-1 blockade efficacy. Both tumor-derived migratory dendritic cell (DC) subsets and DC subsets residing in TDLN, and an interplay between them, have been implicated in the induction of these T cells, their imprinting for homing and subsequent tumor control. We propose that therapeutic approaches, involving local delivery of immune modulatory agents for optimal access to TDLN, aimed at overcoming hampered DC activation, will enable ICB by promoting T cell recruitment to the tumor, both in early and in advanced stages of cancer. [ABSTRACT FROM AUTHOR]

Priming of CD8+ T cells by dendritic cells (DCs) is crucial for the generation of effective antitumor immune responses. Here, we describe a liposomal vaccine carrier that delivers tumor antigens to human CD169/Siglec-1+ antigen-presenting cells using gangliosides as targeting ligands. Ganglioside-liposomes specifically bound to CD169 and were internalized by in vitro-generated monocyte-derived DCs (moDCs) and macrophages and by ex vivo-isolated splenic macrophages in a CD169-dependent manner. In blood, high-dimensional reduction analysis revealed that ganglioside-liposomes specifically targeted CD14+ CD169+ monocytes and Axl+ CD169+ DCs. Liposomal codelivery of tumor antigen and Toll-like receptor ligand to CD169+ moDCs and Axl+ CD169+ DCs led to cytokine production and robust cross-presentation and activation of tumor antigen-specific CD8+ T cells. Finally, Axl+ CD169+ DCs were present in cancer patients and efficiently captured ganglioside-liposomes. Our findings demonstrate a nanovaccine platform targeting CD169+ DCs to drive antitumor T cell responses. [ABSTRACT FROM AUTHOR]

Whereas TLR9 agonists are recognized as powerful stimulators of antitumor immunity, GM-CSF has had mixed reviews. In previously reported randomized trials we assessed the effects of local immune modulation in early-stage melanoma with CpG-B alone or with GM-CSF. Here we discuss the added value of GM-CSF and show sex-related differences. [ABSTRACT FROM AUTHOR]

Background: Immune regulated pathways influence both breast cancer (BrC) development and response to (neo) adjuvant chemotherapy. The sentinel lymph node (SLN), as the first metastatic site, is also the first site where BrCinduced suppression of immune effector subsets occurs. Since intricate knowledge of the phenotypic and functional status of these immune effector subsets is lacking, we set out to map the immune landscape of BrC SLN. Methods: Viable LN cells from BrC SLN (n = 58) were used for detailed flowcytometry-assisted mapping of the immune landscape of BrC SLN in a comparative analysis with healthy (i.e. prophylactic mastectomy-derived) axillary lymph nodes (HLN, n = 17). Findings were related to clinicopathological characteristics. Results: Our data show that BrC-induced immune suppression in tumor-involved SLN, as evidenced by increased Treg and MDSC rates as well as by a generalized state of T cell anergy, coincides with hampered activation of LN-resident (LNR) dendritic cell (DC) subsets rather than of migratory DC subsets. Importantly, suppression of these LN-resident DC subsets preceded profoundly disabled T cell effector functions in tumor-involved SLN. Furthermore, we provide evidence that the suppressed state of LNR-cDC is not only related to nodal involvement but is also related to high-risk breast cancer subtypes that lack expression of hormone receptors and may be a negative predictor of disease-free survival. Conclusion: These data thus provide new insights in the mechanisms underlying loco-regional immune suppression induced by BrC and how these relate to clinical outcome. They identify the LNR-cDC subset as a pivotal regulatory node in cellular immune suppressive pathways and therefore as a promising therapeutic target to combat immune suppression and secure the induction of effective antitumor immunity, e.g. in combination with neo-adjuvant chemotherapy. [ABSTRACT FROM AUTHOR]

In patients with cancer, the functionality of Dendritic Cells (DC) is hampered by high levels of tumor-derived suppressive cytokines, which interfere with DC development and maturation. Poor DC development can limit the efficacy of immune checkpoint blockade and in vivo vaccination approaches. Interference in intracellular signaling cascades downstream from the receptors of major tumor-associated suppressive cytokines like IL-10 and IL-6, might improve DC development and activation, and thus enhance immunotherapy efficacy. We performed exploratory functional screens on arrays consisting of >1000 human kinase peptide substrates to identify pathways involved in DC development and its inhibition by IL-10 or IL-6. The resulting alterations in phosphorylation of the kinome substrate profile pointed to glycogen-synthase kinase-3β (GSK3β) as a pivotal kinase in both DC development and suppression. GSK3β inhibition blocked human DC differentiation in vitro, which was accompanied by decreased levels of IL-12p70 secretion, and a reduced capacity for T cell priming. More importantly, adenoviral transduction of monocytes with a constitutively active form of GSK3β induced resistance to the suppressive effects of IL-10 and melanoma-derived supernatants alike, resulting in improved DC development, accompanied by up-regulation of co-stimulatory markers, an increase in CD83 expression levels in mature DC, and diminished release of IL-10. Moreover, adenovirus-mediated intratumoral manipulation of this pathway in an in vivo melanoma model resulted in DC activation and recruitment, and in improved immune surveillance and tumor control. We propose the induction of constitutive GSK3β activity as a novel therapeutic means to bolster DC functionality in the tumor microenvironment. [ABSTRACT FROM AUTHOR]

The human bone marrow (BM) gives rise to all distinct blood cell lineages, including CD1c+ (cDC2) and CD141+ (cDC1) myeloid dendritic cells (DC) and monocytes. These cell subsets are also present in peripheral blood (PB) and lymphoid tissues. However, the difference between the BM and PB compartment in terms of differentiation state and immunological role of DC is not yet known. The BM may represent both a site for development as well as a possible effector site and so far, little is known in this light with respect to different DC subsets. Using genome-wide transcriptional profiling we found clear differences between the BM and PB compartment and a location-dependent clustering for cDC2 and cDC1 was demonstrated. DC subsets from BM clustered together and separate from the corresponding subsets from PB, which similarly formed a cluster. In BM, a common proliferating and immature differentiating state was observed for the two DC subsets, whereas DC from the PB showed a more immune-activated mature profile. In contrast, BM-derived slan+ non-classical monocytes were closely related to their PB counterparts and not to DC subsets, implying a homogenous prolife irrespective of anatomical localization. Additional functional tests confirmed these transcriptional findings. DC-like functions were prominently exhibited by PB DC. They surpassed BM DC in maturation capacity, cytokine production, and induction of CD4+ and CD8+ T cell proliferation. This first study on myeloid DC in healthy human BM offers new information on steady state DC biology and could potentially serve as a starting point for further research on these immune cells in healthy conditions as well as in diseases. [ABSTRACT FROM AUTHOR]

Antigen exposure to oral mucosa is generally thought to lead to immune tolerance induction. However, very little is known about the subset composition and function of dendritic cells (DC) migrating from human oral mucosa. Here we show that migratory DC from healthy human gingival explants consist of the same phenotypic subsets in the same frequency distribution as DC migrating from human skin. The gingival CD1a+ Langerhans cell and interstitial DC subsets lacked CXCR4 expression in contrast to their cutaneous counterparts, pointing to different migration mechanisms, consistent with previous observations in constructed skin and gingival equivalents. Remarkably, without any exogenous conditioning, gingival explants released higher levels of inflammatory cytokines than human skin explants, resulting in higher DC migration rates and a superior ability of migrated DC to prime allogeneic T cells and to induce type-1 effector T cell differentiation. From these observations we conclude that rather than an intrinsic ability to induce T cell tolerance, DC migrating from oral mucosa may have a propensity to induce effector T cell immunity and maintain a high state of alert against possible pathogenic intruders in the steady state. These findings may have implications for oral immunization strategies. [ABSTRACT FROM AUTHOR]

Cutaneous antigen presenting cells (APCs) are critical for the induction and regulation of skin immune responses. The human skin contains phenotypically and functionally distinct APCs subsets that are present at two separated locations. While CD1ahigh LCs form a dense network in the epidermis, the CD14+ and CD1a+ APCs reside in the dermal compartment. A better understanding of the biology of human skin APC subsets is necessary for the improvement of vaccine strategies that use the skin as administration route. In particular, progress in the characterization of uptake and activatory receptors will certainly improve APC-targeting strategies in vaccination. Here we performed a detailed analysis of the expression and function of glycan-binding and pattern-recognition receptors in skin APC subsets. The results demonstrate that under steady state conditions human CD1a+ dermal dendritic cells (DCs) were phenotypically most mature as measured by the expression of CD83 and CD86, whereas the CD14+ cells showed a higher expression of the CLRs DC-SIGN, mannose receptor and DCIR and had potent antigen uptake capacity. Furthermore, steady state LCs showed superior antigen cross-presentation as compared to the dermal APC subsets. Our results also demonstrate that the TLR3 ligand polyribosinic-polyribocytidylic acid (pI:C) was the most potent stimulator of cytokine production by both LCs and dDCs. These studies warrant further exploration of human CD1a+ dDCs and LCs as target cells for cancer vaccination to induce anti-tumor immune responses. [ABSTRACT FROM AUTHOR]

The CD34+ MUTZ-3 acute myeloid leukemia cell line has been used as a dendritic cell (DC) differentiation model. This cell line can be cultured into Langerhans cell (LC) or interstitial DC-like cells using the same cytokine cocktails used for the differentiation of their primary counterparts. Currently, there is an increasing interest in the study and clinical application of DC generated in the presence of IFNα, as these IFNα-DC produce high levels of inflammatory cytokines and have been suggested to be more potent in their ability to cross-present protein antigens, as compared to the more commonly used IL-4-DC. Here, we report on the generation of IFNα-induced MUTZ-DC. We show that IFNα MUTZ-DC morphologically and phenotypically display characteristic DC features and are functionally equivalent to “classic” IL-4 MUTZ-DC. IFNα MUTZ-DC ingest exogenous antigens and can subsequently cross-present HLA class-I restricted epitopes to specific CD8+ T cells. Importantly, mature IFNα MUTZ-DC express CCR7, migrate in response to CCL21, and are capable of priming naïve antigen-specific CD8+ T cells. In conclusion, we show that the MUTZ-3 cell line offers a viable and sustainable model system to study IFNα driven DC development and functionality. [ABSTRACT FROM AUTHOR]

Tumors abuse myeloid plasticity to re-direct dendritic cell (DC) differentiation from T cell stimulatory subsets to immune-suppressive subsets that can interfere with anti-tumor immunity. Lined by a dense network of easily accessible DC the skin is a preferred site for the delivery of DC-targeted vaccines. Various groups have recently been focusing on functional aspects of DC subsets in the skin and how these may be affected by tumor-derived suppressive factors. IL-6, Prostaglandin-E2, and IL-10 were identified as factors in cultures of primary human tumors responsible for the inhibited development and activation of skin DC as well as monocyte-derived DC. IL-10 was found to be uniquely able to convert fully developed DC to immature macrophage-like cells with functional M2 characteristics in a physiologically highly relevant skin explant model in which the phenotypic and functional traits of "crawl-out" DC were studied. Mostly from mouse studies, the JAK2/STAT3 signaling pathway has emerged as a "master switch" of tumor-induced immune suppression. Our lab has additionally identified p38-MAPK as an important signaling element in human DC suppression, and recently validated it as such in ex vivo cultures of single-cell suspensions from melanoma metastases. Through the identification of molecular mechanisms and signaling events that drive myeloid immune suppression in human tumors, more effective DC-targeted cancer vaccines may be designed. [ABSTRACT FROM AUTHOR]

In cancer patients pervasive systemic suppression of Dendritic Cell (DC) differentiation and maturation can hinder vaccination efficacy. In this study we have extensively characterized migratory DC subsets from human skin and studied how their migration and T cell-stimulatory abilities were affected by conditioning of the dermal microenvironment through cancer-related suppressive cytokines. To assess effects in the context of a complex tissue structure, we made use of a near-physiological skin explant model. By 4-color flow cytometry, we identified migrated Langerhans Cells (LC) and five dermis-derived DC populations in differential states of maturation. From a panel of known tumor-associated suppressive cytokines, IL-10 showed a unique ability to induce predominant migration of an immature CD14+CD141+DC-SIGN+ DC subset with low levels of co-stimulatory molecules, up-regulated expression of the co-inhibitory molecule PD-L1 and the M2-associated macrophage marker CD163. A similarly immature subset composition was observed for DC migrating from explants taken from skin overlying breast tumors. Whereas predominant migration of mature CD1a+ subsets was associated with release of IL-12p70, efficient Th cell expansion with a Th1 profile, and expansion of functional MART-1-specific CD8+ T cells, migration of immature CD14+ DDC was accompanied by increased release of IL-10, poor expansion of CD4+ and CD8+ T cells, and skewing of Th responses to favor coordinated FoxP3 and IL-10 expression and regulatory T cell differentiation and outgrowth. Thus, high levels of IL-10 impact the composition of skin-emigrated DC subsets and appear to favor migration of M2-like immature DC with functional qualities conducive to T cell tolerance. [ABSTRACT FROM AUTHOR]

Background: New treatment modalities are needed for the treatment of cancers of the head and neck region (HNSCC). Survivin is important for the survival and proliferation of tumor cells and may therefore provide a target for immunotherapy. Here we focused on the ex vivo presence and in vitro induction of survivin specific T cells. Methods: Tetramer staining and ELIspot assays were used to document the presence of survivin specific T cells in patient derived material, and to monitor the presence and persistence of survivin specific T cells after repeated in vitro stimulation with autologous dendritic cells. Results: Ex vivo analysis showed the presence of survivin-specific T cells in the peripheral blood (by tetramer analysis) and in the draining lymph node (by ELIspot analysis) in a HNSCC and a locally advanced breast cancer patient respectively. However, we were unable to maintain isolated survivin specific T cells for prolonged periods of time. For the in vitro generation of survivin specific T cells, monocyte derived DC were electroporated with mRNA encoding full length survivin or a survivin mini-gene together with either IL21 or IL12 mRNA. Western blotting and immunohistochemical staining of dendritic cell cytospin preparations confirmed translation of the full length survivin protein. After repeated stimulation we observed an increase, followed by a decrease, of the number of survivin specific T cells. FACS sorted or limiting dilution cloned survivin specific T cells could not be maintained on feeder mix for prolonged periods of time. Protein expression analysis subsequently showed that activated, but not resting T cells contain survivin protein. Conclusions: Here we have shown that survivin specific T cells can be detected ex vivo in patient derived material. Furthermore, survivin specific T cells can be induced in vitro using autologous dendritic cells with enforced expression of survivin and cytokines. However, we were unable to maintain enriched or cloned survivin specific T cells for prolonged periods of time. Endogenous expression of survivin in activated T cells and subsequent fratricide killing might explain our in vitro observations. We therefore conclude that survivin, although it is a universal tumor antigen, might not be the ideal target for immunotherapeutic strategies for the treatment of cancer of the head and neck [ABSTRACT FROM AUTHOR]

Interleukin (IL)-10 is a major cancer-related immunosuppressive factor, exhibiting a unique ability to hamper the maturation of dendritic cells (DCs). We have previously reported that IL-10 induces the conversion of activated, migratory CD1a+ DCs found in the human skin to CD14+CD141+ macrophage-like cells. Here, as a model of tumor-conditioned DC maturation, we functionally assessed CD14- and CD14+ DCs that matured in vitro upon exposure to IL-10. IL-10-induced CD14+ DCs were phenotypically characterized by a low maturation state as well as by high levels of BDCA3 and DC-SIGN, and as such they closely resembled CD14+ cells infiltrating melanoma metastases. Compared with DC matured under standard conditions, CD14+ DCs were found to express high levels of B7-H1 on the cell surface, to secrete low levels of IL- 12p70, to preferentially induce TH2 cells, to have a lower allogeneic TH cell and tumor antigen-specific CD8+ T-cell priming capacity and to induce proliferative T-cell anergy. In contrast to their CD14+ counterparts, CD14- monocyte-derived DCs retained allogeneic TH priming capacity but induced a functionally anergic state as they completely abolished the release of effector cytokines. Transcriptional and cytokine release profiling studies indicated a more profound angiogenic and pro-invasive signature of CD14+ DCs as compared with DCs matured in standard conditions or CD14- DCs matured in the presence of IL-10. Importantly, signal transducer and activator of transcription 3 (STAT3) depletion by RNA interference prevented the development of the IL-10-associated CD14+ phenotype, allowing for normal DC maturation and providing a potential means of therapeutic intervention. [ABSTRACT FROM AUTHOR]

Background: Dendritic cells (DCs) comprise heterogeneous populations of cells, which act as central orchestrators of the immune response. Applicability of primary DCs is restricted due to their scarcity and therefore DC models are commonly employed in DC-based immunotherapy strategies and in vitro tests assessing DC function. However, the interrelationship between the individual in vitro DC models and their relative resemblance to specific primary DC populations remain elusive. Objective: To describe and assess functionality and applicability of the available in vitro DC models by using a genome-wide transcriptional approach. Methods: Transcriptional profiling was performed with four commonly used in vitro DC models (MUTZ-3-DCs, monocyte-derived DCs, CD34-derived DCs and Langerhans cells (LCs)) and nine primary DC populations (dermal DCs, LCs, blood and tonsillar CD123+, CD1c+and CD141+DCs, and blood CD16+DCs). Results: Principal Component Analysis showed that transcriptional profiles of each in vitro DC model most closely resembled CD1c+and CD141+tonsillar myeloid DCs (mDCs) among primary DC populations. Thus, additional differentiation factors may be required to generate model DCs that more closely resemble other primary DC populations. Also, no model DC stood out in terms of primary DC resemblance. Nevertheless, hierarchical clustering showed clusters of differentially expressed genes among individual DC models as well as primary DC populations. Furthermore, model DCs were shown to differentially express immunologically relevant transcripts and transcriptional signatures identified for each model DC included several immune-associated transcripts. Conclusion: The unique transcriptional profiles of in vitro DC models suggest distinct functionality in immune applications. The presented results will aid in the selection of an appropriate DC model for in vitro assays and assist development of DC-based immunotherapy. [ABSTRACT FROM AUTHOR]

Epidermal Langerhans cells (LC) and dermal interstitial dendritic cells (IDC) were found to express the ATP-binding cassette (ABC) transporter breast cancer resistance protein (BCRP; ABCG2). Also, low BCRP expression was present on CD34+ blood DC precursors and expression was increased upon their differentiation to LC. The CD34+ acute myeloid leukemia-derived DC cell line MUTZ3 can be cultured into LC or IDC, depending on the cytokine cocktail used. Introduction of functional BCRP in MUTZ3 progenitor cells through retroviral transduction resulted in the emergence of typical LC-characteristics in IDC cultures; the majority of cells remained negative for the IDC-specific C-type lectin DC-SIGN, but rather displayed enhanced expression of the LC-specific C-type lectin Langerin and characteristic high expression levels of CD1a. BCRP-induced skewing toward LC-like differentiation coincided with early RelB expression in 'IDC', derived from MUTZ3-BCRP, and depended on endogenous transforming growth factor beta (TGF-β) production. Intriguingly, cellular BCRP localization differed between skin LC and IDC, and a more cytoplasmic BCRP localization, as observed in primary skin LC, seemed to relate to LC-like differentiation in IDC cultures upon BCRP introduction in MUTZ3 progenitors. Together these data support a role for BCRP in preferential LC differentiation from CD34+ myeloid DC progenitors. [ABSTRACT FROM AUTHOR]

Dendritic cells (DCs) are promising antigen presenting cells for cancer treatment. Previously, we showed that the combination of monophosphoryl lipid A (MPLA) with IFNγ generates mature DCs that produce IL-12 and polarize CD4+ T cells towards a Th1 phenotype. Here, we extended these observations by showing that the DCs generated with the clinical grade maturation cocktail of MPLA/IFNγ induce superior tumour antigen-specific CD8+ CTL responses compared to the cytokine cocktail matured DCs that are currently used in the clinic. MPLA/IFNγ DCs can induce CTL responses in healthy individuals as well as in melanoma patients. The CTL induction was mainly dependent on the IL-12 produced by the MPLA/IFNγ DCs. The high amounts of induced CTLs are functional as they produce IFNγ and lyse target cells and this cytolytic activity is antigen specific and HLA restricted. Furthermore, the CTLs proved to kill tumour cells expressing endogenous tumour antigen in vitro. Therefore, MPLA/IFNγ DCs are very promising for the use in future cancer immunotherapy. [ABSTRACT FROM AUTHOR]

The field of tumor vaccination is currently undergoing a shift in focus, from individualized tailor-made vaccines to more generally applicable vaccine formulations. Although primarily predicated by financial and logistic considerations, stemming from a growing awareness that clinical development for wide-scale application can only be achieved through backing from major pharmaceutical companies, these new approaches are also supported by a growing knowledge of the intricacies and minutiae of antigen presentation and effector T-cell activation. Here, the development of whole-cell tumor and dendritic cell (DC)-based vaccines from an individualized autologous set-up to a more widely applicable allogeneic approach will be discussed as reflected by translational studies carried out over the past two decades at our laboratories and clinics in the vrije universiteit medical center (VUmc) in Amsterdam, The Netherlands. [ABSTRACT FROM AUTHOR]

Dendritic cell (DC)-based immunotherapy faces new challenges because the efficacy of DC vaccines in clinical trials has been inconsistent. Strategies to improve immune responses induced by DC are currently being explored. We have recently shown the feasibility of generating fully functional DC from acute myeloid leukaemic (AML) blasts, but with varying expression levels of the important costimulatory molecule CD86. To overcome this variability, we developed a novel bispecific diabody that simultaneously and agonistically targeted CD40 on AML-DC and CD28 on naïve T cells. Beside optimization of CD28-mediated signalling, the resulting cellular cross-linking was also hypothesized to increase the strength and duration of T cell/AML-DC interactions, thus increasing T-cell responsiveness to AML antigens. The αCD40/αCD28-bispecific diabody was found to bind to its target antigens and provoked increased T-cell–DC cluster formation. The αCD40/αCD28 diabody is capable of increasing T-cell proliferation induced by AML-DC as well as the induction of DC maturation. Importantly, priming efficacy of tumour-specific cytotoxic T cells can also be improved by cross-linking AML-DC and T cells with the αCD40/αCD28 diabody. We propose that the αCD40/αCD28-bispecific diabody can serve as a potent therapeutic tool to effectively augment anti-tumour T-cell responses elicited by AML-DC. [ABSTRACT FROM AUTHOR]

The adoptive transfer of in vitro-induced and expanded tumor-specific cytotoxic T lymphocytes (CTL) presents a promising immunotherapeutic approach for the treatment of cancer. The in vitro induction of tumor-reactive CTL requires repeated stimulation of CTL precursors with dendritic cells (DC). To circumvent problems like scarcity of blood DC precursors and donor variability, it would be attractive to use DC from a non-autologous, unlimited source. DCs derived from the human acute myeloid leukemia (AML) cell line MUTZ-3 are attractive candidates since these DCs closely resemble monocyte-derived DC (MoDC) in terms of phenotype and T cell stimulatory capacity. Here we demonstrate that functional CTL clones could be generated against multiple tumor-associated antigens, i.e., human telomerase reverse transcriptase (hTERT), ErbB3-binding protein-1 (Ebp1), carcinoembryonic antigen (CEA) and Her-2/ neu, by stimulating CD8β+ CTL precursors with peptide-loaded allogeneic, HLA-A2-matched MUTZ-3-derived DC. A consistent induction capacity, as determined by MHC tetramer-binding, was found in multiple donors and comparable to autologous peptide-loaded MoDC. Functional characterization at the clonal level revealed the priming of CTL that recognized endogenously processed epitopes on tumor cell lines in an HLA-A2-restricted fashion. Our data indicate that MUTZ-3-derived DC can be used as stimulator cells for in vitro priming and expansion of functional TAA-specific effector CTL. MUTZ-3-derived DCs thus represent a ready and standardized source of allogeneic DC to generate CTL for therapeutic adoptive transfer strategies. [ABSTRACT FROM AUTHOR]

Tumors that lack T cell infiltration are less likely to respond to immune checkpoint inhibition and could benefit from cancer vaccination for the initiation of anti-tumor T cell responses. An attractive vaccine strategy is in vivo targeting of dendritic cells (DCs), key initiators of antigen-specific T cell responses. In this study we generated apoptotic tumor cell-derived extracellular vesicles (ApoEVs), which are potentially an abundant source of tumor-specific neo-antigens and other tumor-associated antigens (TAAs), and which can be manipulated to express DC-targeting ligands for efficient antigen delivery. Our data demonstrates that by specifically modifying the glycocalyx of tumor cells, high-mannose glycans can be expressed on their cell surface and on extracellular vesicles derived after the induction of apoptosis. High-mannose glycans are the natural ligands of dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), a dendritic cell associated C-type lectin receptor (CLR), which has the ability to efficiently internalize its cargo and direct it to both major histocompatibility complex (MHC)-I and MHC-II pathways for the induction of CD8+ and CD4+ T cell responses, respectively. Compared to unmodified ApoEVs, ApoEVs carrying DC-SIGN ligands are internalized to a higher extent, resulting in enhanced priming of tumor-specific CD8+ T cells. This approach thus presents a promising vaccination strategy in support of T cell-based immunotherapy of cancer. [ABSTRACT FROM AUTHOR]

To mount a strong anti-tumor immune response, non T cell inflamed (cold) tumors may require combination treatment encompassing vaccine strategies preceding checkpoint inhibition. In vivo targeted delivery of tumor-associated antigens (TAA) to dendritic cells (DCs), relying on the natural functions of primary DCs in situ, represents an attractive vaccination strategy. In this study we made use of a full-length MART-1 expressing C/B-chimeric adenoviral vector, consisting of the Ad5 capsid and the Ad3 knob (Ad5/3), which we previously showed to selectively transduce DCs in human skin and lymph nodes. Our data demonstrate that chimeric Ad5/3 vectors encoding TAA, and able to target human DCs in situ, can be used to efficiently induce expansion of functional tumor-specific CD8+ effector T cells, either from a naïve T cell pool or from previously primed T cells residing in the melanoma-draining sentinel lymph nodes (SLN). These data support the use of Ad3-knob containing viruses as vaccine vehicles for in vivo delivery. "Off-the-shelf" DC-targeted Ad vaccines encoding TAA could clearly benefit future immunotherapeutic approaches. [ABSTRACT FROM AUTHOR]

A number of studies point to an aberrant differentiation and accumulation of CD14+PD-L1+M2-macrophage-like cells in the microenvironment of cervical cancer, which promote immunosuppressive conditions and are associated with tumor invasion, angiogenesis and metastasis. Therapeutic targeting of these macrophages may tip the balance in favor of antitumor immunity. Cervical cancer is the fourth most common cancer among women worldwide and is caused by a persistent infection and subsequent integration of high-risk types of the human papillomavirus. Continuous expression of the viral oncoproteins E6 and E7 has been shown essential to maintain the transformed state of infected keratinocytes. As these non-self oncoproteins are immunogenic, cervical cancer requires a highly immune suppressed tumor microenvironment to metastasize through lymphovascular space invasion (LVSI) to the pelvic tumor-draining lymph nodes (TDLN). Unraveling the mechanisms underlying this immune suppression may uncover novel therapeutic targets aimed at loco-regional control of cervical cancer. [ABSTRACT FROM AUTHOR]

The generation and loading of dendritic cells (DC)ex-vivofor tumor vaccination purposes is laborious and costly. Direct intradermal (i.d.) administration of tumor-associated antigens could be an attractive alternative approach, provided that efficient uptake and cross-presentation by appropriately activated skin DCs can be achieved. Here, we compare the efficiency ofi.d. delivery of relatively small apoptotic blebs (diameter ∼0.1–1 μm) derived from MART-1 transduced acute myeloid leukemia (AML) HL60 cells, to that of larger apoptotic cell remnants (ACR; 2–10 μm) in a physiologically highly relevant human skin explant model. Injection of either fluorescently-labelled ACRs or blebs alone did not affect the number or distribution of migrated DC subsets from skin biopsies after 48 hours, but resulted in a general up-regulation of the co-stimulatory molecules CD83 and CD86 on skin DCs that had ingested apoptotic material. We have previously shown thati.d. administration of GM-CSF and IL-4 resulted in preferential migration of a mature and highly T cell-stimulatory CD11hiCD1a+CD14−dermal DC subset. Here, we found that co-injection of GM-CSF and IL-4 together with either ACRs or blebs resulted in uptake efficiencies within this dermal DC subset of 7.6% (±6.1%) and 19.1% (±15.9%), respectively, thus revealing a significantly higher uptake frequency of blebs (P< 0.02). Intradermal delivery of tumor-derived blebs did not affect the T-cell priming and TH-skewing abilities of migratory skin DC. Nevertheless, in contrast to i.d. administration of ACR, the injection of blebs lead to effective cross-presentation of MART-1 to specific CD8+effector T cells. We conclude that apoptotic bleb-based vaccines delivered through the skin may offer an attractive, and broadly applicable, cancer immunotherapy. [ABSTRACT FROM PUBLISHER]

Dendritic cell (DC)–targeting vaccines show great promise in increasing antitumor immunity. Glycan-engineered vaccines facilitate both DC targeting and increased uptake by DCs for processing and presentation to CD4+ and CD8+ T cells to induce tumor-specific T-cell responses. However, the complexity of various DC subsets in skin tissues, expressing different glycan-binding receptors that can mediate vaccine uptake or drainage of vaccines via lymphatics directly to the lymph node–resident DCs, complicates the success of vaccines. Moreover, the influx of inflammatory immune cells to the site of vaccination, such as monocytes that differentiate to DCs and coexpress glycan-binding receptors, may contribute to the strength of DC-targeting glycovaccines for future clinical use. [ABSTRACT FROM AUTHOR]

CD14+ dendritic cells (DCs) present in the dermis of human skin represent a large subset of dermal DCs (dDCs) that are considered macrophage-like cells with poor antigen (cross)-presenting capacity and limited migratory potential to the lymph nodes. CD14+ dDC highly express DC-specific ICAM-3-grabbing non-integrin (DC-SIGN), a receptor containing potent endocytic capacity, facilitating intracellular routing of antigens to major histocompatibility complex I and II (MHC-I andII) loading compartments for the presentation to antigen-specific CD8+ and CD4+ T cells. Here we show using a human skin explant model that the in situ targeting of antigens to DC-SIGN using glycan-modified liposomes enhances the antigen-presenting capacity of CD14+ dDCs. Intradermal vaccination of liposomes modified with the DC-SIGN-targeting glycan LewisX, containing melanoma antigens (MART-1 or Gp100), accumulated in CD14+ dDCs and resulted in enhanced Gp100- or MART-1-specific CD8+ T-cell responses. Simultaneous intradermal injection of the cytokines GM-CSF and IL-4 as adjuvant enhanced the migration of the skin DCs and increased the expression of DC-SIGN on the CD14+ and CD1a+ dDCs. These data demonstrate that human CD14+ dDCs exhibit potent cross-presenting capacity when targeted in situ through DC-SIGN. [ABSTRACT FROM AUTHOR]

CD1d-restricted invariant natural killer T (iNKT) cells constitute an important immunoregulatory T cell subset that can be activated by the synthetic glycolipid α-galactosylceramide (α-GalCer) and initiate antitumor immune responses. As cancer patients are frequently treated with aminobisphosphonates (NBP), it is relevant to determine possible effects of NBP on CD1d-restricted glycolipid Ag-presentation to iNKT cells. We report a striking reduction of α-GalCer-induced iNKT cell activation by monocyte derived dendritic cells (moDC) upon their exposure to NBP during maturation. We found that production of apolipoprotein E (apoE), which is a known facilitator of trans-membrane transport of exogenously derived glycolipids, was significantly diminished in moDC exposed to NBP. As the inhibitory effect of NBP on iNKT cell activation was alleviated by exogenous apoE, our data indicate that reduced apoE production by antigen presenting cells (APC) through NBP limits glycolipid-induced iNKT cell activation. This should be taken into account in the design of iNKT cell-based anti-cancer therapies. [ABSTRACT FROM AUTHOR]

The generation of effector CD8+ T cells with lytic capacity is crucial for tumor control. Dendritic cells (DCs) provide important signals to promote naive CD8+ T cell priming and activation of effector T cells. Here, we report that the Notch pathway has an important role in both these processes in human CD8+ T cells. Activated monocyte-derived DCs express Notch ligands Jaggedi and Delta-like4, whereas naive CD8+ T cells express Notch2. The role for Notch signaling in CD8+ T cell priming was determined using an ex-vivo model system in which tumor antigen-specific primary CD8+ T cell responses were measured. Inhibition of Notch using γ-secretase inhibitors or soluble Delta-like4-Fc during activation reduced expansion of antigen-specific CD8+ T cells, which was mirrored by decreased frequencies of interferon (IFN)-γ-, tumor necrosis factor-α-, and granzymeB-producing CD8+ T cells. Moreover, T cells primed when Notch signaling was prevented are functionally low-avidity T cells. In addition, Notch partially regulates established effector T cell function. Activation-induced Notch signaling is needed for IFN-γ release but not for cytolytic activity. These data indicate that Notch signaling controls human CD8+ T cell priming and also influences effector T cell functions. This may provide important information for designing new immunotherapies for treatment of cancer. [ABSTRACT FROM AUTHOR]

TLR agonists are attractive candidate adjuvants for therapeutic cancer vaccines as they can induce a balanced humoral and T cell-mediated immune response. With a dense network of dendritic cells (DCs) and draining lymphatics, the skin provides an ideal portal for vaccine delivery. Beside direct DC activation, TLR agonists may also induce DC activation through triggering the release of inflammatory mediators by accessory cells in the skin microenvironment. Therefore, a human skin explant model was used to explore the in vivo potential of intradermally delivered TLR agonists to stimulate Langerhans cells and dermal DCs in their natural complex tissue environment. The skin-emigrated DCs were phenotyped and analyzed for T cell stimulatory capacity. We report that, of six tested TLR-agonists, the TLR2 and -3 agonists peptidoglycan (PGN) and polyribosinic-polyribocytidylic acid (Poly I:C) were uniquely able to enhance the T cell-priming ability of skin-emigrated DCs, which, in the case of PGN, was accompanied by Th1 polarization. The enhanced priming capacity of Poly I:C-stimulated DCs was associated with a strong upregulation of appropriate costimulatory molecules, including CD70, whereas that of PGN-stimulated DCs was associated with the release of a broad array of proinflammatory cytokines. Transcriptional profiling further supported the notion that the PGN- and Poly I:C-induced effects were mediated through binding to TLR2/nucleotide-binding oligomerization domain 2 and TLR3/MDA5, respectively. These data warrant further exploration of PGN and Poly I:C, alone or in combination, as DC-targeted adjuvants for intradermal cancer vaccines. [ABSTRACT FROM AUTHOR]

Abstract: Cancer immunotherapy requires potent tumor-specific CD8+ and CD4+ T-cell responses, initiated by dendritic cells (DCs). Tumor antigens can be specifically targeted to DCs in vivo by exploiting their expression of C-type lectin receptors (CLR), which bind carbohydrate structures on antigens, resulting in internalization and antigen presentation to T-cells. We explored the potential of glycan-modified liposomes to target antigens to DCs to boost murine and human T-cell responses. Since DC-SIGN is a CLR expressed on DCs, liposomes were modified with DC-SIGN-binding glycans Lewis (Le)B or LeX. Glycan modification of liposomes resulted in increased binding and internalization by BMDCs expressing human DC-SIGN. In the presence of LPS, this led to 100-fold more efficient presentation of the encapsulated antigens to CD4+ and CD8+ T-cells compared to unmodified liposomes or soluble antigen. Similarly, incubation of human moDC with melanoma antigen MART-1-encapsulated liposomes coated with LeX in the presence of LPS led to enhanced antigen-presentation to MART-1-specific CD8+ T-cell clones. Moreover, this formulation drove primary CD8+ T-cells to differentiate into high numbers of tetramer-specific, IFN-γ-producing effector T-cells. Together, our data demonstrate the potency of a glycoliposome-based vaccine targeting DC-SIGN for CD4+ and CD8+ effector T-cell activation. This approach may offer improved options for treatment of cancer patients and opens the way to in situ DC-targeted vaccination. [Copyright &y& Elsevier]

Abstract: Vγ9Vδ2-T cells constitute a proinflammatory lymphocyte subpopulation with established antitumor activity. Phosphoantigens activate Vγ9Vδ2-T cells in vivo and in vitro. We studied whether the antitumor activity of Vγ9Vδ2-T cells can be potentiated by invariant NKT cells (iNKT), an important immunoregulatory T cell subset. When activated by the glycolipid α-galactosylceramide (α-GalCer), iNKT produce large amounts of cytokines involved in antitumor immune responses. Monocyte-derived dendritic cells were loaded with both phosphoantigens (using aminobisphosphonates) and α-GalCer during maturation and subsequently co-cultured with Vγ9Vδ2-T and iNKT cells. Aminobisphosphonates dose-dependently enhanced Vγ9Vδ2-T cell activation, and this was potentiated by α-GalCer-induced iNKT co-activation. iNKT co-activation also enhanced the IFN-γ production and cytolytic potential of Vγ9Vδ2-T cells against tumor cells. Using transwell experiments and neutralizing antibodies cross-talk between iNKT and Vγ9Vδ2-T cells was found to be mediated by TNF-α. Our data provide a rationale for combining both activating ligands to improve Vγ9Vδ2-T cell based approaches in cancer-immunotherapy. [Copyright &y& Elsevier]

Abstract: The sentinel lymph node (SLN) is an emerging focus for immunological research in breast cancer. Cryopreservation of SLN single-cell suspensions allows for simultaneous phenotypic multi-parameter analyses and minimizes operator dependent variability. This is of particular importance for immunomonitoring of large multicenter trials. However, little data are available regarding the influence of cryopreservation on phenotypic characteristics of lymph node dendritic cells and T cells. In this study we assessed the feasibility of cryopreservation of viable SLN cell samples for flowcytometric analysis, by comparing quantitative analyses of SLN cell samples after freeze-thawing with direct analysis of fresh SLN cell samples. SLN were collected from nine breast cancer patients. From each SLN cell sample, half was used for immediate analysis and half was analyzed after cryopreservation and thawing. Conventional dendritic cell (cDC) and T cell subsets were quantified and phenotypically characterized by flow cytometry. The observed frequencies of both CD1a+ and CD1a−CD11c+CD14− cDC subsets showed significant correlation between the fresh and frozen-thawed samples. Similar high correlations were found for CD83 and CD86 expression markers on the more frequent (>0.2%) CD1a+ and CD1a−CD11c+CD14− cDC subset, but not on the low-frequency (<0.2%) CD1a+CD11c+CD14+ cDC subset. CD4/CD8 T cell ratios were comparable and were significantly correlated pre- and post-freezing. Regulatory CD4+CD25hi T cell frequencies and their FoxP3 expression levels were significantly higher after freezing–thawing than in the freshly analyzed samples. Nevertheless, a highly significant correlation was found for both parameters pre- and post-freezing. Cryopreservation and thawing seems a valid and practical alternative to direct analysis of fresh viable lymph node cells, without introducing cryo-dependent variance between SLN samples. However, enumeration of low-frequency cell populations and assessment of their marker expression levels are less reliable after cryopreservation and should be assessed and considered in the design of each clinical trial. [Copyright &y& Elsevier]

To increase (tumor) vaccine efficacy, there is an urgent need for phenotypic and functional characterization of human dendritic cell (DC) subsets residing in lymphoid tissues. In this study we identified and functionally tested 4 human conventional DC (cDC) subsets within skin-draining sentinel lymph nodes (SLNs) from early-stage melanoma patients. These SLNs were all tumor negative and were removed on average 44 days after excision of the primary melanoma. As such, they were considered representative of steady-state conditions. On comparison with skin-migrated cDC, 2 CD1a+ subsets were identified as most likely skin-derived CD11cint Langerhans cells (LC) with intracellular langerin and E-cadherin expression or as CD11chi dermal DCs with variable expression of langerin. Two other CD1a- LN-residing cDC subsets were characterized as CD14-BDCA3hiCD103- and CD14+BDCA3loCD103+, respectively. Whereas the CD1a+ skin-derived subsets displayed greater levels of phenotypic maturation, they were associated with lower levels of inflammatory cytokine release and were inferior in terms of allogeneic T-cell priming and IFNγ induction. Thus, despite their higher maturation state, skin-derived cDCs (and LCs in particular) proved inferior T-cell activators compared with the CD1a- cDC subsets residing in melanoma-draining LNs. These observations should be considered in the design of DC-targeting immunotherapies. [ABSTRACT FROM AUTHOR]

In situ delivery of tumor-associated antigen (TAA) genes into dendritic cells (DC) has great potential as a generally applicable tumor vaccination approach. Although adenoviruses (Ad) are an attractive vaccine vehicle in this regard, Ad-mediated transduction of DCs is hampered by the lack of expression of the Ad receptor CAR on the DC surface. DC activation also requires interaction of CD40 with its ligand CD40L to generate protective T-cell-mediated tumor immunity. Therefore, to create a strategy to target Ads to DCs in vivo, we constructed a bispecific adaptor molecule with the CAR ectodomain linked to the CD40L extracellular domain via a trimerization motif (CFm40L). By targeting Ad to CD40 with the use of CFm40L, we enhanced both transduction and maturation of cultured bone marrow-derived DCs. Moreover, we improved transduction efficiency of DCs in lymph node and splenic cell suspensions in vitro and in skin and vaccination site-draining lymph nodes in vivo. Furthermore, CD40 targeting improved the induction of specific CD8+T cells along with therapeutic efficacy in a mouse model of melanoma. Taken together, our findings support the use of CD40-targeted Ad vectors encoding full-length TAA for in vivo targeting of DCs and high-efficacy induction of antitumor immunity. [ABSTRACT FROM AUTHOR]

Abstract: As the induction of contact hypersensitivity is the result of a series of cellular processes, including maturation and migration of epidermal dendritic cells (Langerhans cells (LC)), a battery of assays based on these in vivo events might provide a robust in vitro predictability model for distinguishing sensitizers from non-sensitizers. Therefore, assays with read-out for changes in CD86 expression and CXCL8 secretion were compared with a novel functional assay based on the in vitro migratory behaviour of LC. In all three assays LC derived from the human myeloid-leukaemia-cell-line MUTZ-3 (MUTZ-LC) were used. Exposure of MUTZ-LC to a panel of five sensitizers and three non-sensitizers resulted in increased CD86 expression in only 3/5 sensitizers, but also in 1/3 non-sensitizers. In contrast, CXCL8 secretion was uniformly increased after exposure to all sensitizers, but not after exposure to non-sensitizers. In a transwell migration assay, preferential migration of sensitizer-exposed MUTZ-LC towards CXCL12 was observed (5/5 sensitizers), whereas non-sensitizer-exposed MUTZ-LC only migrated towards CCL5 (3/3 non-sensitizers). In conclusion, the novel MUTZ-LC migration assay and analysis of CXCL8 secretion proved to be more successful than analysis of CD86 in predicting sensitizers from non-sensitizers and therefore warrant further investigation in the field of in vitro assay development. [Copyright &y& Elsevier]

Abstract: Targeting viral vectors encoding tumor-associated antigens to dendritic cells (DCs) in vivo is likely to enhance the effectiveness of immunotherapeutic cancer vaccines. We have previously shown that genetic modification of adenovirus (Ad) 5 to incorporate CD40 ligand (CD40L) rather than native fiber allows selective transduction and activation of DCs in vitro. Here, we examine the capacity of this targeted vector to induce immune responses to the tumor antigen CEA in a stringent in vivo canine model. CD40-targeted Ad5 transduced canine DCs via the CD40-CD40L pathway in vitro, and following vaccination of healthy dogs, CD40-targeted Ad5 induced strong anti-CEA cellular and humoral responses. These data validate the canine model for future translational studies and suggest targeting of Ad5 vectors to CD40 for in vivo delivery of tumor antigens to DCs is a feasible approach for successful cancer therapy. [Copyright &y& Elsevier]

ATP-binding cassette (ABC) transporters are known for their involvement in clinical multidrug resistance (MDR) and their physiological defensive functions in barrier organs. More recently, attention has been focused on their possible involvement in the regulation of immune responses following the identification of their substrates as known immunomodulating agents (e.g. prostaglandins, leukotrienes and cyclic nucleotides) and their functional expression in various immune effector cells, most notably in dendritic cells (DCs). This review addresses the possible roles of ABC transporters in DC development and function, as well as the putative immunostimulatory potential of their cytostatic substrates and how this knowledge might benefit DC-based chemo-immunotherapies. [Copyright &y& Elsevier]

Abstract: Dendritic cell (DC) migration to draining lymph nodes is important for the initiation of an effective immune response. Recently we reported that the human ATP-binding cassette (ABC) transporter multidrug resistance protein 4 (MRP4 and ABCC4) is required for the migration of human DC. Since the ABC transporter MRP1 (ABCC1) was previously shown to play a role in both human and mouse DC migration, we here studied whether Mrp4 is similarly required for DC migration in mice and whether the absence of Mrp4 interferes with the generation of an immune response. Immunological responses were compared in wild-type FVB (FVBwt), FVB Mrp4 knockout (KO) or FVB Mrp4/5 double knockout (dKO) mice. Skin, a preferred immunization site, was analyzed for DC markers, as well as for Mrp1 and Mrp4 expression. Whereas Mrp1 was abundantly present within FVBwt skin, only few Mrp4 expressing cells were detected. In addition, no Mrp4 protein expression was detected on in vitro cultured FVBwt bone marrow-derived DC (BM-DC). DC migration from murine ear skin was unaltered between FVBwt and MRP4/5 dKO animals. The absence of Mrp4 also had no effect on immune responses upon allergen sensitization, immunization or oral tolerance induction. We thus conclude that in contrast to its human counterpart, murine Mrp4 is not involved in DC migration, nor indeed, in the generation of an effective immune response. These data reveal disparities in the physiological role of ABC transporters between species, which may derive from differences in substrate specificity. [Copyright &y& Elsevier]

Abstract: CD1d-restricted natural killer T (NKT) cells are involved in the regulation of various immune responses, and have been shown to inhibit viral replication in animal hepatitis models when activated by the glycolipid α-galactosylceramide (α-GalCer, KRN7000). Previous studies have indicated that α-GalCer-induced activation of the immune system requires both CD1d expression by antigen-presenting cells as well as (normal) numbers of NKT cells. Discrepancies exist over circulating numbers of human invariant Vα24+Vβ11+ NKT cells during hepatitis C virus (HCV) infection. Here, by cross-sectional analysis and longitudinal analysis of patients undergoing effective combination antiviral therapy, we demonstrate that circulating Vα24+Vβ11+ NKT cell numbers are not decreased during active HCV infection. Importantly, as we also show that CD1d is expressed at comparable levels by peripheral blood monocytes and CD1c+ myeloid dendritic cells (DC) of healthy individuals and HCV-infected patients, these data indicate that all ingredients for evaluating the antiviral effects of the Vα24+Vβ11+ NKT cell ligand α-GalCer in HCV-infected patients are present. [Copyright &y& Elsevier]

Adenoviral (Ad) transduction of dendritic cells (DC) is a promising vaccination strategy. However, clinical applicability of Ad vectors is hampered by the necessity to use high titers of infectious Ad particles for efficient DC transduction. Here, we report on the production of a bacterially expressed bispecific conjugate, consisting of a fusion of recombinant single-chain (sc) mAb Fv fragments, which bind and neutralize the Ad fiber knob (through the S11 mAb scFv) and retarget Ad to CD40 on the DC surface (through the G28-5 mAb scFv). We show that this bispecific scFv fusion protein significantly enhances transduction efficiency of monocyte-derived DC (MoDC), reduces the amount of virus needed for a given level of transduction, and increases the ability of MoDC to activate CTL in an antigen specific manner. This single-component conjugate may prove to be a valuable immunotherapeutic tool for the targeting of Ad to DC in vivo. [Copyright &y& Elsevier]