RNA loading of leukemic antigens into cord blood-derived dendritic cells for immunotherapy

CMRF-56(+) blood dendritic cells loaded with mRNA induce effective antigen-specific cytotoxic T-lymphocyte responses

There are numerous transcriptional, proteomic and functional differences between monocyte-derived dendritic cells (Mo-DC) and primary blood dendritic cells (BDC). The CMRF-56 monoclonal antibody (mAb) recognizes a cell surface marker, which is upregulated on BDC following overnight culture. Given its unique ability to select a heterogeneous population of BDC, we engineered a human chimeric (h)CMRF-56 IgG4 mAb to isolate primary BDC for potential therapeutic vaccination. The ability to select multiple primary BDC subsets from patients and load them with in vitro transcribed (IVT) mRNA encoding tumor antigen might circumvent the issues limiting the efficacy of Mo-DC. After optimizing and validating the purification of hCMRF-56(+) BDC, we showed that transfection of hCMRF-56(+) BDC with mRNA resulted in efficient mRNA translation and antigen presentation by myeloid BDC subsets, while preserving superior DC functions compared to Mo-DC. Immune selected and transfected hCMRF-56(+) BDC migrated very efficiently in vitro and as effectively as cytokine matured Mo-DC in vivo. Compared to Mo-DC, hCMRF-56(+) BDC transfected with influenza matrix protein M1 displayed superior MHC peptide presentation and generated potent antigen specific CD8(+) T-cell recall responses, while Wilms tumor 1 (WT1) transfected CMRF-56(+) BDC generated effective primary autologous cytotoxic T-cell responses. The ability of the combined DC subsets within hCMRF-56(+) BDC to present mRNA delivered tumor antigens merits phase I evaluation as a reproducible generic platform for the next generation of active DC immune therapies.

Umbilical cord blood-derived CD11c(+) dendritic cells could serve as an alternative allogeneic source of dendritic cells for cancer immunotherapy

Introduction

Allogenic dendritic cells (DCs) generated from healthy donors, who are complete or partially HLA-matched, have been used for clinical trials. One of the sources for allogenic DCs is umbilical cord blood (UCB) cells. However, as far as cord blood cells are concerned, looking at their naïve nature, there is a concern as to whether the DCs generated from them will have enough potential to elicit a proper T cell response. For this, we compared CD11c⁺ UCB-DCs/ Cytotoxic T lymphocytes (CTLs) with the conventional source, i.e. peripheral blood (PBL) monocyte DCs/CTLs, using various parameters.

Methods

CD11c⁺ DCs generated from the two sources were compared morphologically, phenotypically and functionally. Functional assays included antigen uptake, chemotactic migration and MLR (mixed lymphocyte reaction). The CTLs generated were examined for the activation markers, granzyme A & granzyme B, and IFN-γ secretion. MUC1 (STAPPVHNV) peptide-specific CTLs were quantified by Streptamer staining. In vitro CTL activity was assessed by their efficiency in killing MCF-7 cells. For in vivo CTL assay, a xenograft of MCF-7-luc-F5 cells in female NOD/SCID mice was employed. Regression of tumors in mice was monitored using an in vivo imaging system before and after ten days of CTL infusion. Statistical analysis of all the experiments between the two groups was evaluated by one-way ANOVA.

Results

The CD11c⁺ DCs from the two sources were morphologically and phenotypically similar. Their capacity to uptake antigen, migration towards CCL-19 and MLR activity were equivalent. UCB-CTLs had significantly higher levels of activation markers, number of MUC1 specific CTLs, IFN-γ secretion and IL-12p70/IL-10 ratio than that of PBL-CTLs. Hematoxylin and Eosin-stained tumor sections showed T cell infiltration, which was further confirmed by immunofluorescence staining. In vivo CTL activity was found to be similar with the two sources.

Conclusions

Our data demonstrate that CD11c⁺ UCB-DCs/CTLs are as potent as standard CD11c⁺ PBL-DC/CTLs and could therefore be used as an allogenic source for therapeutic purposes. The findings of this study could help in taking us one step closer towards the personalized therapy using DC based cancer vaccines.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0160-8) contains supplementary material, which is available to authorized users.

Transport, resealing, and re-poration dynamics of two-pulse electroporation-mediated molecular delivery

Electroporation is of interest for many drug-delivery and gene-therapy applications. Prior studies have shown that a two-pulse-electroporation protocol consisting of a short-duration, high-voltage first pulse followed by a longer, low-voltage second pulse can increase delivery efficiency and preserve viability. In this work the effects of the field strength of the first and second pulses and the inter-pulse delay time on the delivery of two different-sized Fluorescein-Dextran (FD) conjugates are investigated. A series of two-pulse-electroporation experiments were performed on 3T3-mouse fibroblast cells, with an alternating-current first pulse to permeabilize the cell, followed by a direct-current second pulse. The protocols were rationally designed to best separate the mechanisms of permeabilization and electrophoretic transport. The results showed that the delivery of FD varied strongly with the strength of the first pulse and the size of the target molecule. The delivered FD concentration also decreased linearly with the logarithm of the inter-pulse delay. The data indicate that membrane resealing after electropermeabilization occurs rapidly, but that a non-negligible fraction of the pores can be reopened by the second pulse for delay times on the order of hundreds of seconds. The role of the second pulse is hypothesized to be more than just electrophoresis, with a minimum threshold field strength required to reopen nano-sized pores or defects remaining from the first pulse. These results suggest that membrane electroporation, sealing, and re-poration is a complex process that has both short-term and long-term components, which may in part explain the wide variation in membrane-resealing times reported in the literature.

Exogenous addition of arachidonic acid to the culture media enhances the functionality of dendritic cells for their possible use in cancer immunotherapy

The development of dendritic cell based vaccines is a promising approach in cancer immunotherapy. For their successful use in the clinics, the propagation and functionality of DCs is crucial. We earlier established a two-step method for the large scale generation of DCs from umbilical cord blood derived MNCs/CD34+ cells. This work aims at improving their functionality based on the following observations: in vitro generated DCs can be less efficient in migration and other functional activities due to lower eicosanoid levels. The production of eicosanoids from Arachidonic Acid (AA) can be hampered due to suppression of the enzyme phospholipase A2 by IL-4, an essential cytokine required for the differentiation of DCs. We hypothesized that exogenous addition of AA to the culture media during DC generation may result in DCs with improved functionality. DCs were generated with and without AA. The two DC sets were compared by phenotypic analysis, morphology and functional assays like antigen uptake, MLR, CTL assay and in vitro and in vivo migration. Though there were no differences between the two types of DCs in terms of morphology, phenotype and antigen uptake, AA⁺ DCs exhibited an enhanced in vitro and in vivo migration, T cell stimulatory capacity, CTL activity and significantly higher transcript levels of COX-2. AA⁺ DCs also show a favorable Th1 cytokine profile than AA^- DCs. Thus addition of AA to the culture media is skewing the DCs towards the secretion of more IL-12 and less of IL-10 along with the restoration of eicosanoids levels in a COX-2 mediated pathway thereby enhancing the functionality of these cells to be used as a potent cellular vaccine. Taken together, these findings will be helpful in the better contriving of DC based vaccines for cancer immunotherapy.

mRNA-based dendritic cell vaccines

Cancer immunotherapy has been proposed as a powerful treatment modality. Active immunotherapy aspires to stimulate the patient's immune system, particularly T cells. These cells can recognize and kill cancer cells and can form an immunological memory. Dendritic cells (DCs) are the professional antigen-presenting cells of our immune system. They take up and process antigens to present them to T cells. Consequently, DCs have been investigated as a means to stimulate cancer-specific T-cell responses. An efficient strategy to program DCs is the use of mRNA, a well-defined and safe molecule that can be easily generated at high purity. Importantly, vaccines consisting of mRNA-modified DCs showed promising results in clinical trials. Therefore, we will introduce cancer immunotherapy and DCs and give a detailed overview on the application of mRNA to generate cancer-fighting DC vaccines.

Modeling dendritic cell vaccination for influenza prophylaxis: potential applications for niche populations

BACKGROUND

Cancer patients can exhibit negligible responses to prophylactic vaccinations, including influenza vaccination. To help address this issue, we developed in vitro and in vivo models of dendritic cell (DC) immunotherapy for the prevention of influenza virus infection.

METHODS

Human cord blood (CB)-derived or mouse splenocyte-derived DCs were loaded with purified recombinant hemagglutinin (rHA). T-cell responses to HA-loaded CB-derived DCs were determined by ELISpot. Protective efficacy was determined by vaccination of BALB/c mice with a single injection of 10(6) autologous DCs. DC migration to peripheral lymphoid organs was verified by carboxyfluorescein succinimidyl ester staining, and HA-specific antibody titers were determined by enzyme-linked immunosorbent assay. Mice were then challenged intranasally with BALB/c-adapted A/New Caledonia influenza virus derived from four consecutive lung pool passages. Antigen-presenting cell (APC) dysfunction was modeled using the MAFIA transgenic system, in which the Csf1r promoter conditionally drives AP20178-inducible Fas.

RESULTS

CB-derived human DCs were able to generate de novo T-cell responses against rHA, as determined by a system of rigorous controls. Mice vaccinated intraperitoneally developed HA titers detectable at serum dilutions of >1:1000. HA seroconverters survived virus challenge, whereas unvaccinated controls and vaccinated nonseroconverters lost weight and died. Furthermore, use of a model of APC-specific immunosuppression revealed that DC vaccination could generate HA-specific antibody titers under conditions in which protein vaccination could not.

CONCLUSIONS

The model demonstrates that DC immunotherapy for the prevention of influenza is feasible, and studies are underway to determine whether populations of immunosuppressed individuals might ultimately benefit from the procedure.

Umbilical cord blood: current status and future directions

Once considered biological waste, umbilical cord blood (UCB) has become an accepted source of haematopoietic stem cells (HSCs). With initial success in the pediatric setting, UCB transplantation continues to gain favor in the adult patient population. Novel approaches to UCB transplantation include use of two units and a variety of graft manipulations. Additional uses for UCB are currently being explored and include applications in regenerative medicine and immunotherapy.

A large number of mature and functional dendritic cells can be efficiently generated from umbilical cord blood-derived mononuclear cells by a simple two-step culture method

BACKGROUND

Advances in the past two decades in dendritic cell (DC) biology paved the way to exploit them as a promising tool in cancer immunotherapy. The prerequisite for DC vaccine preparations is large-scale in vitro generations of homogeneous, mature, and functional DCs. Frequent improvements are being made in the existing in vitro DC production protocols to achieve this goal. In our previous study we reported a large-scale generation of mature, functional DCs from umbilical cord blood (UCB) CD34+ cells. Here we report that this method can be used for the efficient generation of DCs from UCB mononuclear cells (MNCs) and thus the hematopoietic stem cell isolation step is not essential.

STUDY DESIGN AND METHODS

MNCs or CD34+ cells isolated from the same cord blood (CB) samples were used for the generation of DCs. DCs were characterized for morphology, phenotype, and functional assays including antigen uptake, chemotaxis, and mixed leukocyte reaction. Similarly DCs generated from the MNCs of same fresh and frozen CB units were compared.

RESULTS

The morphologic, phenotypic, and functional characterization of the DCs generated from various sets show that they were comparable in nature irrespective of the starting population used.

CONCLUSION

We conclude that the CD34+ isolation step is not essential for the generation of mature, functional DCs and thus can be eliminated. More importantly, we show that DCs can be generated with equal efficiency from the MNCs of frozen CB units. Our culture method will be useful for exploiting the potential of UCB as an additional source for allogeneic DCs in the clinical settings.

Recent advances in antigen-loaded dendritic cell-based strategies for treatment of minimal residual disease in acute myeloid leukemia

Therapeutic vaccination with dendritic cells (DCs) is recognized as an important experimental therapy for the treatment of minimal residual disease in acute myeloid leukemia. Many sources of leukemia-associated antigens and different methods for antigen loading of DCs have been used in an attempt to optimize anti-tumor responses. For instance, monocyte-derived DCs have been loaded with apoptotic whole-cell suspensions, necrotic cell lysates, tumor-associated peptides, eluted peptides and cellular DNA or RNA. Furthermore, monocyte-derived DCs can be chemically or electrically fused with leukemic blasts, and DCs have been cultured out of leukemic blasts. However, it remains a challenge in cancer immunotherapy to identify which of these methods is the most optimal for antigen loading and activation of DCs. This review discusses recent advances in DC research and the application of this knowledge towards new strategies for antigen loading of DCs in the treatment of minimal residual disease in acute myeloid leukemia.

Dendritic cells (DCs) can be successfully generated from leukemic blasts in individual patients with AML or MDS: an evaluation of different methods

Myeloid-leukemic cells (AML, MDS, CML) can be differentiated to leukemia-derived dendritic cell [DC (DCleu)] potentially presenting the whole leukemic antigen repertoire without knowledge of distinct leukemia antigens and are regarded as promising candidates for a vaccination strategy. We studied the capability of 6 serum-free DC culture methods, chosen according to different mechanisms, to induce DC differentiation in 137 cases of AML and 52 cases of MDS. DC-stimulating substances were cytokines ("standard-medium", "MCM-Mimic", "cytokine-method"), bacterial lysates ("Picibanil"), double-stranded RNA ["Poly (I:C)"] or a cytokine bypass method ("Ca-ionophore"). The quality/quantity of DC generated was estimated by flow cytometry studying (co) expressions of "DC"antigens, costimulatory, maturation, and blast-antigens. Comparing these methods on average 15% to 32% DC, depending on methods used, could be obtained from blast-containing mononuclear cells (MNC) in AML/MDS cases with a DC viability of more than 60%. In all, 39% to 64% of these DC were mature; 31% to 52% of leukemic blasts could be converted to DCleu and DCleu-proportions in the suspension were 2% to 70% (13%). Average results of all culture methods tested were comparable, however not every given case of AML could be differentiated to DC with 1 selected method. However performing a pre-analysis with 3 DC-generating methods (MCM-Mimic, Picibanil, Ca-ionophore) we could generate DC in any given case. Functional analyses provided proof, that DC primed T cells to antileukemia-directed cytotoxic cells, although an anti-leukemic reaction was not achieved in every case. In summary our data show that a successful, quantitative DC/DCleu generation is possible with the best of 3 previously tested methods in any given case. Reasons for different functional behaviors of DC-primed T cells must be evaluated to design a practicable DC-based vaccination strategy.

Clinical-scale elutriation as a means of enriching antigen-presenting cells and manipulating alloreactivity

BACKGROUND AIMS

Clinical-scale elutriation using the Elutra(c) has been shown to enrich monocytes reliably for immunotherapy protocols. Until now, a detailed assessment of the four (F1-F4) non-monocyte fractions derived from this process has not been performed.

METHODS

Using fluorescence-activated cell sorting (FACS), we performed phenotypic analyses to investigate the possible enrichment of T, B, natural killer (NK) and dendritic cells (DC) or their subsets in one or more Elutra fractions.

RESULTS

Blood DC were enriched up to 10-fold in some fractions (F3 and F4) compared with the pre-elutriation apheresis product. This increased the number of DC that could be isolated from a given cell number by immunomagnetic separation. It was also found that CD62L(-) effector memory CD4(+) T cells were enriched in later fractions. In four of five cases tested, cells from F3 demonstrated decreased alloreactive proliferation in a mixed lymphocyte reaction compared with cells from the apheresis product. B cells were enriched in F1 compared with the apheresis product.

CONCLUSIONS

In addition to providing enrichment of monocytes for the generation of DC, the Elutra enriches cell subsets that may be incorporated into and enhance existing immunotherapy and stem cell transplantation protocols.

De novo T-lymphocyte responses against baculovirus-derived recombinant influenzavirus hemagglutinin generated by a naive umbilical cord blood model of dendritic cell vaccination

Cancer patients and recipients of hematopoietic stem cell transplantation exhibit a negligible response to influenza vaccine. Toward the goal of addressing this issue, we developed an in vitro model of dendritic cell (DC) immunotherapy utilizing DCs generated from naïve umbilical cord blood (UCB). UCB DCs were loaded with purified rHA protein and used to stimulate autologous T-lymphocytes. Upon recall with HA-loaded autologous DC, a 4-10-fold increase in the number of IFN-gamma producing T-lymphocytes was observed in comparison to T-cells stimulated with control DCs. Antigen-specific T-cell functionality was determined by (51)Cr lytic assay. Using a peptide library of predicted HA binding epitopes, we mapped an HA-specific, DR15-restricted CD4 T-cell epitope and observed tetramer positive cells. This model demonstrates that HA-specific immune responses might possibly be generated in a de novo fashion and suggests that dendritic cell immunotherapy for the prevention of influenza in populations of immunosuppressed individuals could be feasible.

Effect of Tα1 on ESCC RNA-transfected human cord blood dendritic cells induced antitumor activity of cytotoxic T lymphocytes

AIM: To investigate effect of human cord blood dendritic cells (DCs) transfected with RNA of esophageal carcinoma cells on the proliferation of T lymphocyte and on the antitumor activity of cytotoxic T lymphocytes (CTL), and immunoa-djuvant effect of Tα1 on human cord blood dendritic cells.

METHODS: The RNA of T.Tn cells were prepared by TRIzol reagent. The cord blood monocytes were cultured to produce DCs with rhSCF, rhGM-CSF and rhlL-4. The DCs were collected and transfected with tumor cell total RNA. Tα1 was added in culture system to enhance the DCs vaccine. MHC-I, MHC-II and co-stimulatory molecules, CD54, CD80 and CD86 on the surface of DCs were analyzed by FCM. The mixed lymphocyte reaction (MLR) and cytotoxicity of CTLs to T.Tn cells was assayed using MTT colorimetry.

RESULTS: Compared with pre-transfection group, expressions of MHC-I, MHC-II, CD54, CD80 and CD86 (MHC-I: 70.36 ± 6.09vs 8.17 ± 1.93; MHC-II: 72.03 ± 5.32 vs 7.64 ± 5.33; CD54: 69.36 ± 7.33 vs 2.05 ± 2.03; CD80: 67.21 ± 6.77 vs 2.33 ± 1.65; CD86: 68.85 ± 7.41 vs 6.73 ± 1.97, P < 0.01) were significantly higher in DCs transfected with RNA of esophageal carcinoma cells; T cell proliferation was markedly enhanced (10 : 1: 4.77 ± 0.79 vs 1.65 ± 0.71; 50 : 1: 3.85 ± 0.57 vs 1.56 ± 0.13; 100 : 1: 2.89 ± 0.59 vs 1.19 ± 0.21, P < 0.05); and tumor cytolytic activities of cytotoxic T lymphocyte were effectively induced (10 : 1: 27.36 ± 8.93 vs 10.35 ± 2.93; 20 : 1: 44.55 ± 2.36 vs 11.77 ± 1.03; 50 : 1: 51.08 ± 4.92 vs 12.75 ± 1.49, P < 0.05). Tα1 enhanced significantly the surface molecule expression (MHC-I: 87.88 ± 9.13 vs 70.36 ± 6.09; MHC-II: 93.16 ± 3.34 vs 72.03 ± 5.32; CD54: 91.75 ± 3.84 vs 69.36 ± 7.33; CD80: 87.27 ± 8.68 vs 67.21 ± 6.77; CD86: 89.09 ± 6.86 vs 68.85 ± 7.41, P < 0.05), stimulation of proliferation (10 : 1: 8.31 ± 1.78 vs 4.77 ± 0.79; 50 : 1: 5.97 ± 0.14 vs 3.85 ± 0.57; 100 : 1: 4.03 ± 0.13vs 2.89 ± 0.59, P < 0.05) and activity of cytotoxic T lymphocytes (10 : 1: 47.66 ± 4.12 vs 27.36 ± 8.93; 20 : 1: 56.72 ± 7.24 vs44.55 ± 2.36; 50 : 1: 76.48 ± 3.47 vs 51.08 ± 4.92, P < 0.05).

CONCLUSION: DCs from human cord blood monocytes exhibit high expression of MHC and co-stimulatory molecules and enhances T lymphocyte capability after transfection with RNA of esophageal carcinoma. The vaccine of cord blood DCs with adjuvant of Tα1 may provide an effective and specific way for immunotherapy of esophageal carcinoma.

Tumor vaccine therapy against recrudescent tumor using dendritic cells simultaneously transfected with tumor RNA and granulocyte macrophage colony-stimulating factor RNA

Recently, dendritic cells (DC) transfected with tumor RNA have been used as a cancer vaccine. The efficacy of a cancer vaccine using DC transfected tumor RNA was examined. Of particular interest was whether a vaccine using DC transfected with recrudescent tumor RNA is effective for the treatment of a regrowing tumor after prior immunotherapy. In addition, the usefulness of co-transfection of granulocyte macrophage colony-stimulating factor (GM-CSF) mRNA to augment the DC vaccine was examined. CT26 tumor-bearing mice were immunized by s.c. injection with DC transfected with CT26 mRNA (DC-CT26). The cytotoxic activity against CT26 in mice immunized with DC-CT26 was significantly higher than that in the control group (P < 0.001) and was augmented by GM-CSF mRNA co-transfection (P < 0.05), resulting in remarkable therapeutic efficacy in CT26 s.c. tumor models. Cytotoxic T lymphocytes induced by the vaccination using DC transfected with mRNA from the recrudescent tumor showed a potent cytotoxicity against the recrudescent CT26 tumor cells, which was significantly higher than the cytotoxicity induced by the vaccination using DC-CT26 (P < 0.05). In addition, in a recrudescent tumor model, this vaccination suppressed the regrowing s.c. tumors, and was augmented by GM-CSF mRNA co-transfection (P < 0.05). These results suggested that vaccination therapy using DC simultaneously transfected with whole tumor RNA and GM-CSF mRNA could generate therapeutic immune responses even against recrudescent tumor after prior vaccination.

Cord blood CD34+ cells cultured with FLT3L, stem cell factor, interleukin-6, and IL-3 produce CD11c+CD1a-/c- myeloid dendritic cells

Methods that allow expansion of myeloid dendritic cells (MDCs) from CD34(+) cells are potentially important for boosting anti-leukemic responses after cord blood (CB) hematopoietic stem cell transplantation (HSCT). We showed that the combination of early-acting cytokines FLT3-ligand (FL), stem cell factor (SCF), interleukin (IL)-3, and IL-6 supported the generation of CD11c(+)CD16() CD1a()/c() MDCs from CB CD34(+) cells or CB myeloid precursors. Early-acting cytokine-derived MDCs were maintained within the myeloid CD33(+)CD14()CD15() precursors with a mean of 4 x 10(6) cells generated from 1-4 x 10(4) CB CD34(+) cells or myeloid precursors after 2 weeks. After 8-12 days of culture the MDCs expressed higher levels of HLA-DR antigen but lower levels of CD40 and CD86 antigen, compared to adult blood MDCs. At this stage of differentiation, the early-acting cytokine-derived MDCs had acquired the ability to induce greater allogeneic T cell proliferation than monocytes or granulocytes derived from same culture. Early-acting cytokine-derived MDCs exposed to the cytokine cocktail (CC) comprising IL-1beta, IL-6, tumor necrosis factor (TNF)-alpha, and prostaglandin E (PGE)-2, upregulated the surface co-stimulatory molecules CD40 and CD86 and enhanced allogeneic T cell proliferation, as is characteristic of MDCs maturation. The reliable production of MDCs from CB CD34(+) cells provides a novel way to study their lineage commitment pathway(s) and also a potential means of enriching CB with MDCs to improve prospects for DC immunotherapy following CB HSCT.

Leukemia: cord blood for allogeneic stem cell transplantation

PURPOSE OF REVIEW

Cord blood is considered an acceptable alternative to hematopoietic stem cells. This review focuses on clinical results of cord blood transplantation including factors associated with transplantation outcomes for aiding graft selection. Immunological analysis of T cell recovery processes and approaches to cellular therapy using cord blood-derived immune cells are also discussed.

RECENT FINDINGS

To resolve problems with cord blood transplantation, including high toxicity especially in the early phase after transplant and delayed engraftment, a reduced intensity regimen and double cord blood units from different donors are applied. For adequate graft selection, cell dose and human leukocyte antigen compatibility are important to reduce transplant-related toxicity, although the importance of human leukocyte antigen compatibility seems to disappear in leukemia patients because of a possible graft-versus-leukemia effect in a human leukocyte antigen-mismatched setting. Immune reconstitution after cord blood transplantation is also important to reduce the risk of infectious complication. Recent technologies make it possible to generate antigen-specific T cells from naïve T cells from cord blood in vitro.

SUMMARY

Stem cell sources are now available for almost all leukemia patients. The efficacy of cord blood transplantation warrants further clarification by larger clinical experience and well designed studies. Efforts to reduce toxicity and improve engraftment are still in progress.

Dendritic cell vaccination

There has been a surge of interest in the use of dendritic cell (DC) vaccination as cellular immunotherapy for numerous cancers. Despite some encouraging results, this therapeutic modality is far from being considered as a therapy for cancer. This review will first discuss preclinical DC vaccination in murine models of cancer, with an emphasis on comparative studies investigating different methods of antigen priming. We will then comment on the various murine DC subsets and how these relate to human DC preparations used for clinical studies. Finally, the methodology used to generate human DCs and some recent clinical trials in several cancers are reviewed.