IntroductionBased on the advances in the treatment of multiple sclerosis (MS), currently available disease-modifying treatments (DMT) have positively influenced the disease course of MS. However, the efficacy of DMT is highly variable and increasing treatment efficacy comes with a more severe risk profile. Hence, the unmet need for safer and more selective treatments remains. Specifically restoring immune tolerance towards myelin antigens may provide an attractive alternative. In this respect, antigen-specific tolerisation with autologous tolerogenic dendritic cells (tolDC) is a promising approach.Methods and analysisHere, we will evaluate the clinical use of tolDC in a well-defined population of MS patients in two phase I clinical trials. In doing so, we aim to compare two ways of tolDC administration, namely intradermal and intranodal. The cells will be injected at consecutive intervals in three cohorts receiving incremental doses of tolDC, according to a best-of-five design. The primary objective is to assess the safety and feasibility of tolDC administration. For safety, the number of adverse events including MRI and clinical outcomes will be assessed. For feasibility, successful production of tolDC will be determined. Secondary endpoints include clinical and MRI outcome measures. The patients’ immune profile will be assessed to find presumptive evidence for a tolerogenic effect in vivo.Ethics and disseminationEthics approval was obtained for the two phase I clinical trials. The results of the trials will be disseminated in a peer-reviewed journal, at scientific conferences and to patient associations.Trial registration numbersNCT02618902andNCT02903537; EudraCT numbers: 2015-002975-16 and 2015-003541-26.

Background & Aim Dendritic cells (DC) have the capacity to induce potent tumor antigen-specific T-cell immunity. We have completed vaccination in the adjuvant setting in 77 cancer patients (acute myeloid leukemia (AML, n=30), metastatic breast cancer (MBC, n=12), glioblastoma multiforme (GBM, n=13), malignant pleural mesothelioma (MPM, n=10) and other solid tumors (n=12)) with autologous DC electroporated with mRNA encoding the nearly universal tumor-associated antigen Wilms’ tumor 1 protein (WT1). Methods, Results & Conclusion WT1-targeted DC vaccination was feasible and safe in all patients. The majority of the patients showed a positive delayed type hypersensitivity (DTH) response to the vaccine. Objective clinical responses were observed among all tumor types, including complete (CR) and/or molecular remissions or stable disease (SD) in the AML group, partial responses (PR) and SD in the GBM group and SD in the MBC and MPM groups. In AML patients in first CR, median overall survival (OS) calculated from time of diagnosis was 56.1 months (mo). Median OS from time of diagnosis of metastasis was 41.9 mo in MBC, 43.7 mo from diagnosis in GBM and 35.7 mo from start of therapy in MPM; this compares favorably to numbers reported in the literature, respectively 24.8 mo, 14.7 mo and 22 mo. In AML, long-term OS was correlated with WT1-specific polyfunctional CD8+ T-cells in the DTH reaction sites and long-term CR with polyepitope WT1-specific tetramer+ CD8+ T-lymphocytes. In solid tumors, PR or SD was correlated with interferon (IFN)-gamma+ and/or tumor necrosis factor (TNF)-alpha+ WT1-specific CD4+ and/or CD8+ T-cells; increased OS in the GBM+MPM cohorts was correlated with IFN-gamma+ WT1-specific CD4+ T-lymphocytes. In conclusion, WT1-targeted DC vaccination is feasible, safe and immunogenic, and displays relevant anti-tumor activity in patients with hematological and solid malignancies. Most importantly, this treatment modality can confer a significant survival benefit to the patients. Dendritic cells (DC) have the capacity to induce potent tumor antigen-specific T-cell immunity. We have completed vaccination in the adjuvant setting in 77 cancer patients (acute myeloid leukemia (AML, n=30), metastatic breast cancer (MBC, n=12), glioblastoma multiforme (GBM, n=13), malignant pleural mesothelioma (MPM, n=10) and other solid tumors (n=12)) with autologous DC electroporated with mRNA encoding the nearly universal tumor-associated antigen Wilms’ tumor 1 protein (WT1). WT1-targeted DC vaccination was feasible and safe in all patients. The majority of the patients showed a positive delayed type hypersensitivity (DTH) response to the vaccine. Objective clinical responses were observed among all tumor types, including complete (CR) and/or molecular remissions or stable disease (SD) in the AML group, partial responses (PR) and SD in the GBM group and SD in the MBC and MPM groups.

While emerging evidence indicates that dendritic cells (DC) play a central role in the pathogenesis of multiple sclerosis (MS), their modulation with immunoregulatory agents provides a prospect as disease-modifying therapy. We first investigated the effect of 1,25-dihydroxyvitamin D3 (vitD3) on monocyte-derived DC (mo-DC) from healthy controls and MS patients. VitD3 treatment of mo-DC resulted in a maturation-resistant phenotype and anti-inflammatory cytokine profile as compared to conventional immunogenic DC, in both healthy controls and MS patients. Importantly, vitD3-treated DC induced T cell hyporesponsiveness, as demonstrated by a reduced ability to induce interferon-γ secretion by allogeneic peripheral blood lymphocytes stimulated with vitD3-treated DC as compared with conventional DC. We also investigated the influence of cryopreservation on the phenotype and allogeneic T cell stimulatory capacity of vitD3-treated DC. Following a freeze-thaw cycle, vitD3-treated immature DC could be recovered with a 78% yield and 75% viability. Cryopreservation did not affect the expression of DC membrane markers by vitD3-treated DC nor their capacity to induce T cell hyporesponsiveness in an allogeneic mixed leukocyte reaction. The T cell hyporesponsiveness induced by vitD3-treated DC is antigen-specific since T cells retained their capacity to respond to an unrelated antigen, i.e. cytomegalovirus pp65-derived peptides, while being unresponsive to myelin-derived peptides following tolerization to a myelin oligodendrocyte glycoprotein (MOG)-derived peptide pool and a myelin basic protein (MBP)-derived peptide pool. Furthermore, these T cells did not reactivate upon rechallenge with fully mature conventional DC, demonstrating that this induced T cell hyporesponsiveness was robust. Based on our observations, it can be concluded that vitD3 treatment of DC results in the generation of highly potent tolerance-inducing DC (tolerogenic DC (tolDC)). Importantly, we demonstrate the feasibility of cryopreservation of these tolDC. In this perspective, our results contribute to large scale production and preservation of tolDC and further underscore their potential clinical applicability in order to correct the immunological imbalance in auto-immune disease in general and in MS in particular. Based on our observations, we are now preparing a phase I dose escalation clinical study with vitD3-treated DC pulsed with myelin antigen peptides in relapsing-remitting MS patients.

We have previously reported the clinical and immunological effects of vaccination with dendritic cells electroporated with WT1 mRNA (WT1/DC) in 10 patients with acute myeloid leukemia (AML) (Van Tendeloo et al. PNAS 2010). In the present study, we expanded on the initial results and investigated WT1/DC as an adjuvant treatment in 60 high-risk cancer patients.

The advent of new cell-based immunotherapies for leukemia offers treatment possibilities for certain leukemia subgroups. The wider acceptability of these new technologies in clinical practice will depend on its impact on survival and costs. Due to the small patient groups who have received it, these aspects have remained understudied. This non-randomized single-center study evaluated medical costs and survival for acute myeloid leukemia between 2005 and 2010 in 50 patients: patients treated with induction and consolidation chemotherapy (ICT) alone; patients treated with ICT plus allogeneic hematopoietic stem cell transplantation (HCT), which is the current preferred post-remission therapy in patients with intermediate- and poor-risk AML with few co-morbidities, and patients treated with ICT plus immunotherapy using autologous dendritic cells (DC) engineered to express the Wilms’ tumor protein (WT1). Total costs including post- consolidation costs on medical care at the hematology ward and outpatient clinic, pharmaceutical prescriptions, intensive care ward, laboratory tests and medical imaging were analyzed. Survival was markedly better in HCT and DC. HCT and DC were more costly than ICT. The median total costs for HCT and DC were similar. These results need to be confirmed to enable more thorough cost-effectiveness analyses, based on observations from multicenter, randomized clinical trials and preferably using quality-adjusted life-years as an outcome measure.

Dendritic cells (DC) have important functions in T cell immunity and T cell tolerance. Previously, it was believed that T cell unresponsiveness induced by immature DC (iDC) is caused by the absence of inflammatory signals in steady-state in vivo conditions and by the low expression levels of costimulatory molecules on iDC. However, a growing body of evidence now indicates that iDC can also actively maintain peripheral T cell tolerance by the induction and/or stimulation of regulatory T cell populations. In this study, we investigated the in vitro T cell stimulatory capacity of iDC and mature DC (mDC) and found that both DC types induced a significant increase in the number of transforming growth factor (TGF)-beta and interleukin (IL)-10 double-positive CD4(+) T cells within 1 week of autologous DC/T cell co-cultures. In iDC/T cell cultures, where antigen-specific T cell priming was significantly reduced as compared to mDC/T cell cultures, we demonstrated that the tolerogenic effect of iDC was mediated by soluble TGF-beta and IL-10 secreted by CD4(+)CD25(-)FOXP3(-) T cells. In addition, the suppressive capacity of CD4(+) T cells conditioned by iDC was transferable to already primed antigen-specific CD8(+) T cell cultures. In contrast, addition of CD4(+) T cells conditioned by mDC to primed antigen-specific CD8(+) T cells resulted in enhanced CD8(+) T cell responses, notwithstanding the presence of TGF-beta(+)/IL-10(+) T cells in the transferred fraction. In summary, we hypothesize that DC have an active role in inducing immunosuppressive cytokine-secreting regulatory T cells. We show that iDC-conditioned CD4(+) T cells are globally immunosuppressive, while mDC induce globally immunostimulatory CD4(+) T cells. Furthermore, TGF-beta(+)/IL-10(+) T cells are expanded by DC independent of their maturation status, but their suppressive function is dependent on immaturity of DC.

To date, Wilms' tumor protein (WT1) is acknowledged as a valuable target for active specific immunotherapy in several solid and hematological malignancies, such as leukemia. Preclinical data from our laboratory and that of Hans Stauss have already shown that WT1 RNA-electroporated dendritic cells (DC) stimulate WT1-specific T cells in vitro (Van Driessche A et al. Leukemia 2005; 19:1863–1871). Therefore, we started a phase I/II dose-escalation trial in which patients with acute myeloid leukemia (AML) in remission received intradermal injections with WT1 RNA-loaded DC. Feasibility, safety and immunogenicity of the vaccine were investigated. Seven patients received four biweekly DC vaccines. A delayed-type hypersensitivity (DTH) test was performed 2 weeks following the last vaccination. Patients underwent an apheresis and monocytes were isolated using CD14-labeled magnetic beads by CliniMACS. DC were generated in 6-day cultures in clinical-grade medium supplemented with serum, GM-CSF and IL-4 and maturated with PGE2 and TNF-a. Keyhole limpet hemocyanin (KLH) was added during maturation as a CD4+ helper antigen. Mature DC were harvested, electroporated with WT1 mRNA and used as vaccines. Patients were monitored for minimal residual disease (MRD) by analyzing WT1 RNA expression in peripheral blood by qRT-PCR. When the patient was HLA-A2+, tetramer staining was performed to detect WT1-specific CD8+ T cells. Before and after the vaccination cycle, peripheral blood was collected for immunomonitoring purposes. There was successful DC generation and vaccine production in all patients selected. No serious adverse events or toxicity was seen and all vaccinations were well tolerated. A decrease in WT1 RNA expression was observed during the course of the vaccination in 3/5 patients who had an increased WT1 mRNA level in peripheral blood at the start of DC vaccination. A vaccine-specific immune response was demonstrated in 7/7 patients by an in vivo DTH reaction both to KLH as well as to WT1. By tetramer analysis, detectable levels of WT1-specific CD8+ T cells could be demonstrated during the course of the vaccination both in the peripheral blood as well as in the expanded DTH-infiltrating T cells from the skin biopsies. Preliminary data from immunomonitoring in pre- and post-vaccination T cell samples from 3 patients show a mixed T helper (Th)1/Th2 response towards the KLH and the WT1 protein following vaccination. We conclude that vaccination of AML remission patients with WT1 RNA-loaded DC is feasible and safe. Furthermore, the vaccine elicits anti-vaccine T-cell responses in vivo and a decrease in WT1 RNA expression levels was observed during MRD monitoring in some vaccinated patients.

Leukemic cells exert immunosuppressive effects that interfere with dendritic cell (DC) function and hamper effective antileukemic immune responses. Here, we sought to enhance the immunogenicity of leukemic cells by loading them with the double-stranded (ds) RNA Toll-like receptor 3 (TLR3) ligand polyriboinosinic polyribocytidylic acid (poly(I:C)), mimicking viral infection of the tumor cells. Given the responsiveness of DC to TLR ligands, we hypothesized that the uptake of poly(I:C)-loaded leukemic cells by immature DC (iDC) would lead to DC activation. Primary acute myeloid leukemia (AML) cells and AML cell lines markedly responded to poly(I:C) electroporation by apoptosis, upregulation of TLR3 expression, enhanced expression of major histocompatibility complex (MHC) and costimulatory molecules and by production of type I interferons (IFN). Upon phagocytosis of poly(I:C)-electroporated AML cells, DC maturation and activation were induced as judged by an increased expression of MHC and costimulatory molecules, production of proinflammatory cytokines and an increase of T helper 1 (T(H)1)-polarizing capacity. These immune effects were suboptimal when AML cells were passively pulsed with poly(I:C), indicating the superiority of poly(I:C) transfection over pulsing. Our results demonstrate that poly(I:C) electroporation is a promising strategy to increase the immunogenicity of AML cells and to convert iDC into activated mature DC following the phagocytosis of AML cells.