Novel Insights on MRGPRX2-Mediated Hypersensitivity to Neuromuscular Blocking Agents And Fluoroquinolones

Neuromuscular blocking agents (NMBAs) like atracurium and rocuronium as well as fluoroquinolones (FQs) cause mast cell-mediated anaphylaxis by activating Mas-related G protein-coupled receptor X2 (MRGPRX2), but many questions remain unanswered. Here, we address three of them, namely whether primary human mast cells show similar activation by these drugs as murine mast cells and mast cell lines, how sugammadex protects from atracurium-induced MRGPRX2-mediated mast cell activation, and why some but not all patients treated with rocuronium develop anaphylaxis. We used peripheral blood-derived cultured mast cells from healthy donors and patients, assessed mast cell activation and degranulation by quantifying intracellular calcium and CD63 expression, respectively, and made use of MRGPRX2-silencing, via electroporation with Dicer-substrate small interfering RNAs, and single cell flow cytometric analyses. Atracurium, ciprofloxacin, and levofloxacin activated and degranulated primary human mast cells, but only MRGPRX2-positive and not MRGPRX2-negative or -silenced mast cells. Sugammadex attenuated the atracurium-induced and MRGPRX2-mediated activation and degranulation of human mast cells by reducing free atracurium levels. The mast cells of patients with IgE-independent anaphylaxis to rocuronium were similar, in their MRGPRX2 expression and function, to those of patients with IgE-mediated anaphylaxis. These findings further improve our understanding of the role and relevance of MRGPRX2-driven mast cell activation in anaphylactic reactions to NMBAs and FQs and may help to improve their prediction, prevention, and treatment.

CD56 Homodimerization and Participation in Anti-Tumor Immune Effector Cell Functioning: A Role for Interleukin-15

A particularly interesting marker to identify anti-tumor immune cells is the neural cell adhesion molecule (NCAM), also known as cluster of differentiation (CD)56. Namely, hematopoietic expression of CD56 seems to be confined to powerful effector immune cells. Here, we sought to elucidate its role on various killer immune cells. First, we identified the high motility NCAM-120 molecule to be the main isoform expressed by immune cells. Next, through neutralization of surface CD56, we were able to (1) demonstrate the direct involvement of CD56 in tumor cell lysis exerted by CD56-expressing killer cells, such as natural killer cells, gamma delta (γδ) T cells, and interleukin (IL)-15-cultured dendritic cells (DCs), and (2) reveal a putative crosstalk mechanism between IL-15 DCs and CD8 T cells, suggesting CD56 as a co-stimulatory molecule in their cell-to-cell contact. Moreover, by means of a proximity ligation assay, we visualized the CD56 homophilic interaction among cancer cells and between immune cells and cancer cells. Finally, by blocking the mitogen-activated protein kinase (MAPK) pathway and the phosphoinositide 3-kinase (PI3K)-Akt pathway, we showed that IL-15 stimulation directly led to CD56 upregulation. In conclusion, these results underscore the previously neglected importance of CD56 expression on immune cells, benefiting current and future immune therapeutic options.

Dendritic Cell-Based Immunotherapy of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a type of blood cancer characterized by the uncontrolled clonal proliferation of myeloid hematopoietic progenitor cells in the bone marrow. The outcome of AML is poor, with five-year overall survival rates of less than 10% for the predominant group of patients older than 65 years. One of the main reasons for this poor outcome is that the majority of AML patients will relapse, even after they have attained complete remission by chemotherapy. Chemotherapy, supplemented with allogeneic hematopoietic stem cell transplantation in patients at high risk of relapse, is still the cornerstone of current AML treatment. Both therapies are, however, associated with significant morbidity and mortality. These observations illustrate the need for more effective and less toxic treatment options, especially in elderly AML and have fostered the development of novel immune-based strategies to treat AML. One of these strategies involves the use of a special type of immune cells, the dendritic cells (DCs). As central orchestrators of the immune system, DCs are key to the induction of anti-leukemia immunity. In this review, we provide an update of the clinical experience that has been obtained so far with this form of immunotherapy in patients with AML.

Abstract B192: CD56 participation in immune effector cell activation and tumor cell eradication: A role for interleukin-15

Oncoimmunologists are in a constant search for more effective immunotherapeutic treatments, helping to cure cancer. In this respect, immune cell participation is a key issue. A particularly interesting marker to identify antitumor immune cells is the neural cell adhesion molecule (NCAM), known as CD56. Namely, hematopoietic expression of CD56 seems to be confined to activated immune cells exhibiting some level of cytotoxic properties (Van Acker et al., Frontiers in Immunology 2017). Unfortunately, the current knowledge on the expression and functional role of CD56 is very fragmented. Therefore, we sought to elucidate the role of CD56 expression on various killer immune cells. First, we identified the high motility NCAM-120 isoform to be the main subset on immune cells. Next, through neutralization of surface CD56, we were able to demonstrate for the first time a direct involvement of CD56 in tumor cell lysis exerted by CD56-expressing killer cells such as natural killer cells, gamma delta (γδ) T-cells and interleukin (IL)-15-cultured dendritic cells (DCs). We also detected a putative crosstalk mechanism, suggesting CD56 as a co-stimulatory molecule in the interaction between IL-15 DCs and CD8 T-cells. Finally, by blocking the mitogen-activated protein kinase (MAPK) pathway and the phosphoinositide 3-kinase (PI3K)–AKT pathway, with respectively trametinib and afuresertib, we confirmed our hypothesis that IL-15 stimulation directly leads to CD56 upregulation via the recruitment of shc, binding a phosphotyrosine residue on the IL-2/15Rβ chain. In conclusion, these results underscore the previously neglected importance of CD56 expression on immune cells, benefiting current and future immune therapeutic options.

Citation Format: Heleen H. Van Acker, Maarten Versteven, Hans De Reu, Peter Ponsaerts, Zwi N Berneman, Viggo F. Van Tendeloo, Evelien L. Smits. CD56 participation in immune effector cell activation and tumor cell eradication: A role for interleukin-15 [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B192.

Abstract B137: Preclinical evaluation of a Wilms’ tumor protein 1-targeted interleukin-15 dendritic cell vaccine: T-cell activity and batch production

Encouraging results from clinical trials demonstrate that dendritic cell (DC) vaccination is a valuable tool in cancer immunotherapy. Empowering DC vaccine immunogenicity to improve clinical outcome is at center stage in the rapidly evolving immunotherapeutic landscape. Developing a unique type of DC vaccine, so-called interleukin (IL)-15 DCs generated with IL-15 and strong immune stimulating maturation signals, we could demonstrate superior in vitro activities at both adaptive as well as innate immunity as compared to gold-standard IL-4 DCs. In this light, IL-15 DCs are capable of activating NK cells and gamma-delta T-cells, whereas IL-4 DCs are not. Designed to induce durable antitumor T-cell immunity, this pre-clinical research focuses on the improvement of Wilms’ Tumor protein 1 (WT1)-targeted T-cell activity. The WT1 antigen is overexpressed in a wide variety of human cancers and thus appears to fulfill the criteria of a universal tumor-associated antigen. The capacity of our novel IL-15 DCs to induce WT1-specific immunity is assessed using two in-house developed tumor antigen-specific T-cell assays. The first series of experiments demonstrate in a head-to-head comparison that WT1 mRNA-electroporated IL-15 DCs perform at least as well as IL-4 DCs in triggering a WT1 T-cell receptor (TCR)-transfected T-cell line. Using an autologous primary TCR-engineered CD8+ T-cell approach, we are now comparing their WT1-specific antitumor function. With its unique characteristics, including IL-15-transpresentation and interferon-gamma secretion, IL-15 DCs are expected to significantly promote WT1-specific T-cell-mediated tumor cell killing. Enabling its clinical application, we also evaluated the upscaled IL 15 DC vaccine production and cryopreservation processes. We were able to employ the three-day culture protocol in clinically suitable culture flasks. In addition, the use of an optimized cryopreservation medium results in a pre- to-post cryopreservation yield of 81.3 ± 7.4 % with a preserved phenotype and functionality. High-scale production and cryopreservation allows for the implementation of DC vaccination in multimodal treatment schedules. Underscoring the tumor antigen-specific T-cell-stimulating capacity among previously described superior characteristics and warranting batch production of patient-specific DC vaccines, further strengthens the impetus to bring WT1-loaded IL-15 DCs to the clinic.

Citation Format: Maarten Versteven, David Damoiseaux, Diana Campillo-Davo, Heleen Van Acker, Hans De Reu, Sébastien Anguille, Zwi N Berneman, Evelien L Smits, Viggo F Van Tendeloo, Eva Lion. Preclinical evaluation of a Wilms’ tumor protein 1-targeted interleukin-15 dendritic cell vaccine: T-cell activity and batch production [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B137.

BDCA1+CD14+ Immunosuppressive Cells in Cancer, a Potential Target?

Dendritic cell (DC) vaccines show promising effects in cancer immunotherapy. However, their efficacy is affected by a number of factors, including (1) the quality of the DC vaccine and (2) tumor immune evasion. The recently characterized BDCA1+CD14+ immunosuppressive cells combine both aspects; their presence in DC vaccines may directly hamper vaccine efficacy, whereas, in patients, BDCA1+CD14+ cells may suppress the induced immune response in an antigen-specific manner systemically and at the tumor site. We hypothesize that BDCA1+CD14+ cells are present in a broad spectrum of cancers and demand further investigation to reveal treatment opportunities and/or improvement for DC vaccines. In this review, we summarize the findings on BDCA1+CD14+ cells in solid cancers. In addition, we evaluate the presence of BDCA1+CD14+ cells in leukemic cancers. Preliminary results suggest that the presence of BDCA1+CD14+ cells correlates with clinical features of acute and chronic myeloid leukemia. Future research focusing on the differentiation from monocytes towards BDCA1+CD14+ cells could reveal more about their cell biology and clinical significance. Targeting these cells in cancer patients may improve the outcome of cancer immunotherapy.

The role of the common gamma-chain family cytokines in γδ T cell-based anti-cancer immunotherapy

Cytokines of the common gamma-chain receptor family, comprising interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15 and IL-21, are vital with respect to organizing and sustaining healthy immune cell functions. Supporting the anti-cancer immune response, these cytokines inspire great interest for their use as vaccine adjuvants and cancer immunotherapies. It is against this background that gamma delta (γδ) T cells, as special-force soldiers and natural contributors of the tumor immunosurveillance, also received a lot of attention the last decade. As γδ T cell-based cancer trials are coming of age, this present review focusses on the effects of the different cytokines of the common gamma-chain receptor family on γδ T cells with respect to boosting γδ T cells as a therapeutic target in cancer immunotherapy. This review also gathers data that IL-15 in particular exhibits key features for augmenting the anti-tumor activity of effector killer γδ T cells whilst overcoming the myriad of immune escape mechanisms used by cancer cells.

Interleukin-15-Cultured Dendritic Cells Enhance Anti-Tumor Gamma Delta T Cell Functions through IL-15 Secretion

Dendritic cell (DC) vaccination can be an effective post-remission therapy for acute myeloid leukemia (AML). Yet, current DC vaccines do not encompass the ideal stimulatory triggers for innate gamma delta (γδ) T cell anti-tumor activity. Promoting type 1 cytotoxic γδ T cells in patients with AML is, however, most interesting, considering these unconventional T cells are primed for rapid function and exert meaningful control over AML. In this work, we demonstrate that interleukin (IL)-15 DCs have the capacity to enhance the anti-tumoral functions of γδ T cells. IL-15 DCs of healthy donors and of AML patients in remission induce the upregulation of cytotoxicity-associated and co-stimulatory molecules on the γδ T cell surface, but not of co-inhibitory molecules, incite γδ T cell proliferation and stimulate their interferon-γ production in the presence of blood cancer cells and phosphoantigens. Moreover, the innate cytotoxic capacity of γδ T cells is significantly enhanced upon interaction with IL-15 DCs, both towards leukemic cell lines and allogeneic primary AML blasts. Finally, we address soluble IL-15 secreted by IL-15 DCs as the main mechanism behind the IL-15 DC-mediated γδ T cell activation. These results indicate that the application of IL-15-secreting DC subsets could render DC-based anti-cancer vaccines more effective through, among others, the involvement of γδ T cells in the anti-leukemic immune response.

Desirable cytolytic immune effector cell recruitment by interleukin-15 dendritic cells

Success of dendritic cell (DC) therapy in treating malignancies is depending on the DC capacity to attract immune effector cells, considering their reciprocal crosstalk is partially regulated by cell-contact-dependent mechanisms. Although critical for therapeutic efficacy, immune cell recruitment is a largely overlooked aspect regarding optimization of DC vaccination. In this paper we have made a head-to-head comparison of interleukin (IL)-15-cultured DCs and conventional IL-4-cultured DCs with regard to their proficiency in the recruitment of (innate) immune effector cells. Here, we demonstrate that IL-4 DCs are suboptimal in attracting effector lymphocytes, while IL15 DCs provide a favorable chemokine milieu for recruiting CD8⁺ T cells, natural killer (NK) cells and gamma delta (γδ) T cells. Gene expression analysis revealed that IL-15 DCs exhibit a high expression of chemokines involved in antitumor immune effector cell attraction, while IL-4 DCs display a more immunoregulatory profile characterized by the expression of Th2 and regulatory T cell-attracting chemokines. This is confirmed by functional data indicating an enhanced recruitment of granzyme B⁺ effector lymphocytes by IL-15 DCs, as compared to IL-4 DCs, and subsequent superior killing of tumor cells by the migrated lymphocytes. Elevated CCL4 gene expression in IL-15 DCs and lowered CCR5 expression on both migrated γδ T cells and NK cells, led to validation of increased CCL4 secretion by IL15 DCs. Moreover, neutralization of CCR5 prior to migration resulted in an important inhibition of γδ T cell and NK cell recruitment by IL-15 DCs. These findings further underscore the strong immunotherapeutic potential of IL-15 DCs.

CD56 in the Immune System: More Than a Marker for Cytotoxicity?

Over the past years, the phenotypic and functional boundaries distinguishing the main cell subsets of the immune system have become increasingly blurred. In this respect, CD56 (also known as neural cell adhesion molecule) is a very good example. CD56 is the archetypal phenotypic marker of natural killer cells but can actually be expressed by many more immune cells, including alpha beta T cells, gamma delta T cells, dendritic cells, and monocytes. Common to all these CD56-expressing cell types are strong immunostimulatory effector functions, including T helper 1 cytokine production and an efficient cytotoxic capacity. Interestingly, both numerical and functional deficiencies and phenotypic alterations of the CD56⁺ immune cell fraction have been reported in patients with various infectious, autoimmune, or malignant diseases. In this review, we will discuss our current knowledge on the expression and function of CD56 in the hematopoietic system, both in health and disease.

Interleukin-15 enhances the proliferation, stimulatory phenotype, and antitumor effector functions of human gamma delta T cells

Background

Adoptive immunotherapy is gaining momentum to fight malignancies, whereby γδ T cells have received recent attention as an alternative cell source as to natural killer cells and αβ T cells. The advent of γδ T cells is largely due to their ability to recognize and target tumor cells using both innate characteristic and T cell receptor (TCR)-mediated mechanisms, their capacity to enhance the generation of antigen-specific T cell responses, and their potential to be used in an autologous or allogeneic setting.

Methods

In this study, we explored the beneficial effect of the immunostimulatory cytokine interleukin (IL)-15 on purified γδ T cells and its use as a stimulatory signal in the ex vivo expansion of γδ T cells for adoptive transfer. The expansion protocol was validated both with immune cells of healthy individuals and acute myeloid leukemia patients.

Results

We report that the addition of IL-15 to γδ T cell cultures results in a more activated phenotype, a higher proliferative capacity, a more pronounced T helper 1 polarization, and an increased cytotoxic capacity of γδ T cells. Moreover γδ T cell expansion starting with peripheral blood mononuclear cells from healthy individuals and acute myeloid leukemia patients is boosted in the presence of IL-15, whereby the antitumor properties of the γδ T cells are strengthened as well.

Conclusions

Our results support the rationale to explore the use of IL-15 in clinical adoptive therapy protocols exploiting γδ T cells.

Generation and Cryopreservation of Clinical Grade Wilms' Tumor 1 mRNA-Loaded Dendritic Cell Vaccines for Cancer Immunotherapy

First described in the 1970s, dendritic cells (DC) are currently subjects of intense investigation to exploit their unique antigen-presenting and immunoregulatory capacities. In cancer, DC show promise to elicit or amplify immune responses directed against cancer cells by activating natural killer (NK) cells and tumor antigen-specific T cells. Wilms' tumor 1 (WT1) protein is a tumor-associated antigen that is expressed in a majority of cancer types and has been designated as an antigen of major interest to be targeted in clinical cancer immunotherapy trials. In this chapter, we describe the generation, cryopreservation, and thawing of clinical grade autologous monocyte-derived DC vaccines that are loaded with WT1 by messenger RNA (mRNA) electroporation. This in-house-developed transfection method gives rise to presentation of multiple antigen epitopes and can be used for all patients without restriction of human leukocyte antigen (HLA) type.

Bisphosphonates for cancer treatment: Mechanisms of action and lessons from clinical trials

A growing body of evidence points toward an important anti-cancer effect of bisphosphonates, a group of inexpensive, safe, potent, and long-term stable pharmacologicals that are widely used as osteoporosis drugs. To date, they are already used in the prevention of complications of bone metastases. Because the bisphosphonates can also reduce mortality in among other multiple myeloma, breast, and prostate cancer patients, they are now thoroughly studied in oncology. In particular, the more potent nitrogen-containing bisphosphonates have the potential to improve prognosis. The first part of this review will elaborate on the direct and indirect anti-tumoral effects of bisphosphonates, including induction of tumor cell apoptosis, inhibition of tumor cell adhesion and invasion, anti-angiogenesis, synergism with anti-neoplastic drugs, and enhancement of immune surveillance (e.g., through activation of γδ T cells and targeting macrophages). In the second part, we shed light on the current clinical position of bisphosphonates in the treatment of hematological and solid malignancies, as well as on ongoing and completed clinical trials investigating the therapeutic effect of bisphosphonates in cancer. Based on these recent data, the role of bisphosphonates is expected to further expand in the near future outside the field of osteoporosis and to open up new avenues in the treatment of malignancies.

Generation of a cord blood-derived Wilms Tumor 1 dendritic cell vaccine for AML patients treated with allogeneic cord blood transplantation

The poor survival rates of refractory/relapsed acute myeloid leukemia (AML) patients after haematopoietic cell transplantation (HCT) requires the development of additional immune therapeutic strategies. As the elicitation of tumor-antigen specific cytotoxic T lymphocytes (CTLs) is associated with reduced relapses and enhanced survival, enhanced priming of these CTLs using an anti-AML vaccine may result in long-term immunity against AML. Cord blood (CB), as allogeneic HCT source, may provide a unique setting for such post-HCT vaccination, considering its enhanced graft-versus-leukemia (GvL) effects and population of highly responsive naïve T cells. It is our goal to develop a powerful and safe immune therapeutic strategy composed of CB-HCT followed by vaccination with CB CD34⁺-derived dendritic cells (DCs) presenting the oncoprotein Wilms Tumor-1 (WT1), which is expressed in AML-blasts in the majority of patients. Here, we describe the optimization of a clinically applicable DC culture protocol. This two-step protocol consisting of an expansion phase followed by the differentiation toward DCs, enables us to generate sufficient cord blood-derived DCs (CBDCs) in the clinical setting. At the end of the culture, the CBDCs exhibit a mature surface phenotype, are able to migrate, express tumor antigen (WT1) after electroporation with mRNA encoding the full-length WT1 protein, and stimulate WT1-specific T cells.

Interleukin-15 Dendritic Cells Harness NK Cell Cytotoxic Effector Function in a Contact- and IL-15-Dependent Manner

The contribution of natural killer (NK) cells to the treatment efficacy of dendritic cell (DC)-based cancer vaccines is being increasingly recognized. Much current efforts to optimize this form of immunotherapy are therefore geared towards harnessing the NK cell-stimulatory ability of DCs. In this study, we investigated whether generation of human monocyte-derived DCs with interleukin (IL)-15 followed by activation with a Toll-like receptor stimulus endows these DCs, commonly referred to as "IL-15 DCs", with the capacity to stimulate NK cells. In a head-to-head comparison with "IL-4 DCs" used routinely for clinical studies, IL-15 DCs were found to induce a more activated, cytotoxic effector phenotype in NK cells, in particular in the CD56bright NK cell subset. With the exception of GM-CSF, no significant enhancement of cytokine/chemokine secretion was observed following co-culture of NK cells with IL-15 DCs. IL-15 DCs, but not IL-4 DCs, promoted NK cell tumoricidal activity towards both NK-sensitive and NK-resistant targets. This effect was found to require cell-to-cell contact and to be mediated by DC surface-bound IL-15. This study shows that DCs can express a membrane-bound form of IL-15 through which they enhance NK cell cytotoxic function. The observed lack of membrane-bound IL-15 on "gold-standard" IL-4 DCs and their consequent inability to effectively promote NK cell cytotoxicity may have important implications for the future design of DC-based cancer vaccine studies.

Empowering gamma delta T cells with antitumor immunity by dendritic cell-based immunotherapy

Gamma delta (γδ) T cells are the all-rounders of our immune-system with their major histocompatibility complex-unrestricted cytotoxicity, capacity to secrete immunosti-mulatory cytokines and ability to promote the generation of tumor antigen-specific CD8⁺ and CD4⁺ T cell responses. Dendritic cell (DC)-based vaccine therapy has the prospective to harness these unique features of the γδ T cells in the fight against cancer. In this review, we will discuss our current knowledge on DC-mediated γδ T cell activation and related opportunities for tumor immunologists.

Interleukin-15 dendritic cells as vaccine candidates for cancer immunotherapy

Owing to their professional antigen-presenting capacity and unique potential to induce tumor antigen-specific T cell immunity, dendritic cells (DCs) have attracted much interest over the past decades for therapeutic vaccination against cancer. Clinical trials have shown that the use of tumor antigen-loaded DCs in cancer patients is safe and that it has the potential to induce anti-tumor immunity which, in some cases, culminates in striking clinical responses. Unfortunately, in a considerable number of patients, DC vaccination is unable to mount effective anti-tumor immune responses and, if it does so, the resultant immunity is often insufficient to translate into tangible clinical benefit. This underscores the necessity to re-design and optimize the current procedures for DC vaccine manufacturing. A new generation of DC vaccines with improved potency has now become available for clinical use as a result of extensive pre-clinical research. One of the promising next-generation DC vaccine candidates are interleukin (IL)-15-differentiated DCs. In this commentary, we will compile the research data that have been obtained by our group and other groups with these so-called IL-15 DCs and summarize the evidence supporting the implementation of IL-15 DCs in DC-based cancer vaccination regimens.

Interleukin-15-induced CD56(+) myeloid dendritic cells combine potent tumor antigen presentation with direct tumoricidal potential

Dendritic cells (DCs) are the quintessential antigen-presenting cells of the human immune system and play a prime role in coordinating innate and adaptive immune responses, explaining the strong and still growing interest in their application for cancer immunotherapy. Much current research in the field of DC-based immunotherapy focuses on optimizing the culture conditions for in vitro DC generation in order to assure that DCs with the best possible immunogenic qualities are being used for immunotherapy. In this context, monocyte-derived DCs that are alternatively induced by interleukin-15 (IL-15 DCs) have attracted recent attention due to their superior immunostimulatory characteristics. In this study, we show that IL-15 DCs, in addition to potent tumor antigen-presenting function, possess tumoricidal potential and thus qualify for the designation of killer DCs. Notwithstanding marked expression of the natural killer (NK) cell marker CD56 on a subset of IL-15 DCs, we found no evidence of a further phenotypic overlap between IL-15 DCs and NK cells. Allostimulation and antigen presentation assays confirmed that IL-15 DCs should be regarded as bona fide myeloid DCs not only from the phenotypic but also from the functional point of view. Concerning their cytotoxic activity, we demonstrate that IL-15 DCs are able to induce apoptotic cell death of the human K562 tumor cell line, while sparing tumor antigen-specific T cells. The cytotoxicity of IL-15 DCs is predominantly mediated by granzyme B and, to a small extent, by tumor necrosis factor-α (TNF-α)-related apoptosis-inducing ligand (TRAIL) but is independent of perforin, Fas ligand and TNF-α. In conclusion, our data provide evidence of a previously unappreciated role for IL-15 in the differentiation of human monocytes towards killer DCs. The observation that IL-15 DCs have killer DC capacity lends further support to their implementation in DC-based immunotherapy protocols.

WT1-targeted dendritic cell vaccination as a postremission treatment to prevent or delay relapse in acute myeloid leukemia

2506

Background: Vaccination with tumor antigen-loaded dendritic cells (DC) holds promise for the adjuvant treatment of cancer. Methods: In a phase I/II trial, we investigated the effect of autologous DC vaccination in 17 patients with acute myeloid leukemia (AML) in remission but at very high risk of full relapse. Wilms’ tumor 1 protein (WT1) was chosen as immunotherapeutic target and introduced into the DC by mRNA electroporation. We are continuing a phase II trial, which is still recruiting. Results: Two out of 3 patients, who were in partial remission with chemotherapy-refractory disease, were brought into complete remission following 4 biweekly intradermal injections of WT1 mRNA-electroporated DC. In those 2 patients as well as in 6 other patients who were in complete remission but who had molecularly demonstrable residual disease, there was a return to normal of the AML-associated WT1 mRNA tumor marker following DC vaccination, compatible with reaching clinical and molecular remission in 8/17 patients. Among the 8 responders, there have been 2 relapses and 2 deaths. Of the 9 non-responders, 8 have relapsed and 7 have died. Of the 2 patients in partial remission who were brought into complete remission by DC vaccination, 1 has died following relapse. Median overall survival was 6 months in non-responders and 52 months in responders (p=0.0007). Median relapse-free survival was 3 months in non-responders as compared to 47 months in responders (p<0.0001). Clinical responses overall were correlated with elevated levels of activated natural killer (NK) cells post-vaccination. Long-term clinical responses, lasting for at least 3 years, were significantly correlated with an increase in polyepitope WT1-specific tetramer+ CD8+ T-cell frequencies. Conclusions: DC-based immunotherapy elicits both innate (NK) and adaptive (T cells) cellular responses correlated with clinical benefit. WT1 mRNA-transfected DC emerge as a feasible and effective strategy to control residual disease in AML, in particular as a post-remission treatment to prevent full relapse.

Endothelial microparticles (EMP) for the assessment of endothelial function: an in vitro and in vivo study on possible interference of plasma lipids

Background

Circulating endothelial microparticles (EMP) reflect the condition of the endothelium and are of increasing interest in cardiovascular and inflammatory diseases. Recently, increased numbers of EMP following oral fat intake, possibly due to acute endothelial injury, have been reported. On the other hand, the direct interference of lipids with the detection of EMP has been suggested. This study aimed to investigate the effect of lipid-rich solutions, commonly administered in clinical practice, on the detection, both in vitro and in vivo, of EMP.

Methods

For the in vitro assessment, several lipid-rich solutions were added to whole blood of healthy subjects (n = 8) and patients with coronary heart disease (n = 5). EMP (CD31+/CD42b−) were detected in platelet poor plasma by flow cytometry. For the in vivo study, healthy volunteers were evaluated on 3 different study-days: baseline evaluation, following lipid infusion and after a NaCl infusion. EMP quantification, lipid measurements and peripheral arterial tonometry were performed on each day.

Results

Both in vitro addition and in vivo administration of lipids significantly decreased EMP (from 198.6 to 53.0 and from 272.6 to 90.6/µl PPP, respectively, p = 0.001 and p = 0.012). The EMP number correlated inversely with the concentration of triglycerides, both in vitro and in vivo (r = −0.707 and −0.589, p<0.001 and p = 0.021, respectively). The validity of EMP as a marker of endothelial function is supported by their inverse relationship with the reactive hyperemia index (r = −0.758, p = 0.011). This inverse relation was confounded by the intravenous administration of lipids.

Conclusion

The confounding effect of high circulating levels of lipids, commonly found in patients that receive intravenous lipid-based solutions, should be taken into account when flow cytometry is used to quantify EMP.

Role of dendritic cells in HIV-immunotherapy

HIV remains one of the most important deadly infections today, due to the lack of a preventive vaccine and limited access to medical care in developing countries. In developed countries, antiretroviral therapy is available, but it can not eliminate the virus, implying that life-long therapy is necessary. Therefore, it is important that other strategies such as therapeutic vaccination will be developed to control virus replication or even eliminate the virus. The major obstacles towards such a strategy are the huge variability of the virus and the profound HIV-induced immune dysfunction. In this review we focus on dendritic cell based immunotherapies against HIV. To develop an efficient immunotherapy, several elements should be taken into account such as which antigen and loading strategy to use, how to deliver the immunogen, how to optimize the interaction between antigenic peptide and T cells and avoid tolerance. Clearly, to develop an immunotherapy to complement the effect of HAART, it is not sufficient to enhance T cell responses against a consensus sequence or against the prevailing plasma virus. Broad and potent immune response are needed to suppress the entire quasispecies, including the latent reservoir, and to prevent any escape.

Induction of complete and molecular remissions in acute myeloid leukemia by Wilms' tumor 1 antigen-targeted dendritic cell vaccination

Active immunization using tumor antigen-loaded dendritic cells holds promise for the adjuvant treatment of cancer to eradicate or control residual disease, but so far, most dendritic cell trials have been performed in end-stage cancer patients with high tumor loads. Here, in a phase I/II trial, we investigated the effect of autologous dendritic cell vaccination in 10 patients with acute myeloid leukemia (AML). The Wilms' tumor 1 protein (WT1), a nearly universal tumor antigen, was chosen as an immunotherapeutic target because of its established role in leukemogenesis and superior immunogenic characteristics. Two patients in partial remission after chemotherapy were brought into complete remission after intradermal administration of full-length WT1 mRNA-electroporated dendritic cells. In these two patients and three other patients who were in complete remission, the AML-associated tumor marker returned to normal after dendritic cell vaccination, compatible with the induction of molecular remission. Clinical responses were correlated with vaccine-associated increases in WT1-specific CD8+ T cell frequencies, as detected by peptide/HLA-A*0201 tetramer staining, and elevated levels of activated natural killer cells postvaccination. Furthermore, vaccinated patients showed increased levels of WT1-specific IFN-gamma-producing CD8+ T cells and features of general immune activation. These data support the further development of vaccination with WT1 mRNA-loaded dendritic cells as a postremission treatment to prevent full relapse in AML patients.