FastDC derived from human monocytes within 48 h effectively prime tumor antigen-specific cytotoxic T cells

A comprehensive battery of flow cytometric immunoassays for the in vitro testing of chemical effects in human blood cells

Background

There is a growing need for immunological assays to test toxic and modulatory effects of chemicals. The assays should be easy to use, reproducible and superior to cell line-based assays. We have therefore developed a comprehensive portfolio of assays based on primary human blood cells that are suitable for testing chemical effects.

Methods

The flow cytometry-based assays were designed to target a wide range of human peripheral blood mononuclear cells and whole blood, including T cells, NK cells, B cells, basophils and innate-like T cells such as γδT, MAIT and NKT cells. We have selected a set of activation markers for each immune cell, e.g: CD154 (T cells), CD137, CD107a (NK cells), CD63 (basophils), CD69, CD83 (B cells), CD69, IFN-γ (MAIT cells) and we selected cell specific stimuli: aCD3 antibodies (T cells); E. coli and cytokines IL-12/15/18 (MAIT cells); CpG ODN2006, R848 or aCD40 antibodies (B cells), fMLP or aFcϵR1 (basophils) or K562 cells (NK cells).

Results

By selecting immune cell-specific markers and cell-specific stimuli, we were able to induce particular immune responses from the targeted immune cells. For example, the response to stimulation with anti-CD3 antibodies was in 36.8% of CD107a+CD8+ cells. Cytokine stimulation induced the production of IFN-γ in 30% of MAIT cells. After stimulation with E. coli, around 50% of MAIT cells produced TNF. About 40% of basophils responded to aFcƐR1 stimulation. Similar activation ranges were achieved in K562-stimulated NK cells.

Conclusion

Our test portfolio covers the most relevant immune cells present in human blood, providing a solid basis for in vitro toxicity and immunomodulatory testing of chemicals. By using human blood, the natural composition of cells found in the blood can be determined and the effects of chemicals can be detected at the cellular level.

Isolation of Neoantigen-Specific Human T Cell Receptors from Different Human and Murine Repertoires

Simple Summary

T cell-based immunotherapy has achieved remarkable clinical responses in patients with cancer. Neoepitope-specific T cells can specifically recognize mutated tumor cells and have led to tumor regression in mouse models and clinical studies. However, isolating neoepitope-specific T cell receptors (TCRs) from the patients’ own repertoire has shown limited success. Sourcing T cell repertoires, other than the patients’ own, has certain advantages: the availability of larger amounts of blood from healthy donors, circumventing tumor-related immunosuppression in patients, and including different donors to broaden the pool of specific T cells. Here, for the first time, a side-by-side comparison of three different TCR donor repertoires, including patients and HLA-matched allogenic healthy human repertoires, as well as repertoires of transgenic mice, is performed. Our results support recent studies that using not only healthy donor T cell repertoires, but also transgenic mice might be a viable strategy for isolating TCRs with known specificity directed against neoantigens for adoptive T cell therapy.

Abstract

(1) Background: Mutation-specific T cell receptor (TCR)-based adoptive T cell therapy represents a truly tumor-specific immunotherapeutic strategy. However, isolating neoepitope-specific TCRs remains a challenge. (2) Methods: We investigated, side by side, different TCR repertoires—patients’ peripheral lymphocytes (PBLs) and tumor-infiltrating lymphocytes (TILs), PBLs of healthy donors, and a humanized mouse model—to isolate neoepitope-specific TCRs against eight neoepitope candidates from a colon cancer and an ovarian cancer patient. Neoepitope candidates were used to stimulate T cells from different repertoires in vitro to generate neoepitope-specific T cells and isolate the specific TCRs. (3) Results: We isolated six TCRs from healthy donors, directed against four neoepitope candidates and one TCR from the murine T cell repertoire. Endogenous processing of one neoepitope, for which we isolated one TCR from both human and mouse-derived repertoires, could be shown. No neoepitope-specific TCR could be generated from the patients’ own repertoire. (4) Conclusion: Our data indicate that successful isolation of neoepitope-specific TCRs depends on various factors such as the heathy donor’s TCR repertoire or the presence of a tumor microenvironment allowing neoepitope-specific immune responses of the host. We show the advantage and feasibility of using healthy donor repertoires and humanized mouse TCR repertoires to generate mutation-specific TCRs with different specificities, especially in a setting when the availability of patient material is limited.

Autologous Dendritic Cells in Combination With Chemotherapy Restore Responsiveness of T Cells in Breast Cancer Patients: A Single-Arm Phase I/II Trial

Introduction

Animal studies and preclinical studies in cancer patients suggest that the induction of immunogenic cell death (ICD) by neoadjuvant chemotherapy with doxorubicin and cyclophosphamide (NAC-AC) recovers the functional performance of the immune system. This could favor immunotherapy schemes such as the administration of antigen-free autologous dendritic cells (DCs) in combination with NAC-AC to profit as cryptic vaccine immunogenicity of treated tumors.

Objective

To explore the safety and immunogenicity of autologous antigen-free DCs administered to breast cancer patients (BCPs) in combination with NAC-AC.

Materials and Methods

A phase I/II cohort clinical trial was performed with 20 BCPs treated with NAC-AC [nine who received DCs and 11 who did not (control group)]. The occurrence of adverse effects and the functional performance of lymphocytes from BCPs before and after four cycles of NAC-AC receiving DCs or not were assessed using flow cytometry and compared with that from healthy donors (HDs). Flow cytometry analysis using manual and automated algorithms led us to examine functional performance and frequency of different lymphocyte compartments in response to a stimulus in vitro. This study was registered at clinicaltrials.gov (NCT03450044).

Results

No grade II or higher adverse effects were observed associated with the transfer of DCs to patients during NAC-AC. Interestingly, in response to the in vitro stimulation, deficient phosphorylation of Zap70 and AKT proteins observed before chemotherapy in most patients’ CD4 T cells significantly recovered after NAC-AC only in patients who received DCs.

Conclusions

The transfer of autologous DCs in combination with NAC-AC in BCPs is a safe procedure. That, in BCPs, the administration of DCs in combination with NAC-AC favors the recovery of the functional capacity of T cells suggests that this combination may potentiate the adjuvant effect of ICD induced by NAC-AC on T cells and, hence, potentiate the immunogenicity of tumors as cryptic vaccines.

Insights Into Dendritic Cells in Cancer Immunotherapy: From Bench to Clinical Applications

Dendritic cells (DCs) are efficient antigen-presenting cells (APCs) and potent activators of naïve T cells. Therefore, they act as a connective ring between innate and adaptive immunity. DC subsets are heterogeneous in their ontogeny and functions. They have proven to potentially take up and process tumor-associated antigens (TAAs). In this regard, researchers have developed strategies such as genetically engineered or TAA-pulsed DC vaccines; these manipulated DCs have shown significant outcomes in clinical and preclinical models. Here, we review DC classification and address how DCs are skewed into an immunosuppressive phenotype in cancer patients. Additionally, we present the advancements in DCs as a platform for cancer immunotherapy, emphasizing the technologies used for in vivo targeting of endogenous DCs, ex vivo generated vaccines from peripheral blood monocytes, and induced pluripotent stem cell-derived DCs (iPSC-DCs) to boost antitumoral immunity.

Monocytes complexed to platelets differentiate into functionally deficient dendritic cells

In addition to their role in hemostasis, platelets store numerous immunoregulatory molecules such as CD40L, TGFβ, β2-microglobulin, and IL-1β and release them upon activation. Previous studies indicate that activated platelets form transient complexes with monocytes, especially in HIV infected individuals and induce a proinflammatory monocyte phenotype. Because monocytes can act as precursors of dendritic cells (DCs) during infection/inflammation as well as for generation of DC-based vaccine therapies, we evaluated the impact of activated platelets on monocyte differentiation into DCs. We observed that in vitro cultured DCs derived from platelet-monocyte complexes (PMCs) exhibit reduced levels of molecules critical to DC function (CD206, dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin, CD80, CD86, CCR7) and reduced antigen uptake capacity. DCs derived from PMCs also showed reduced ability to activate naïve CD4+ and CD8+ T cells, and secrete IL-12p70 in response to CD40L stimulation, resulting in decreased ability to promote type-1 immune responses to HIV antigens. Our results indicate that formation of complexes with activated platelets can suppress the development of functional DCs from such monocytes. Disruption of PMCs in vivo via antiplatelet drugs such as Clopidogrel/Prasugrel or the application of platelet-free monocytes for DCs generation in vitro, may be used to enhance immunization and augment the immune control of HIV.

DCs-based therapies: potential strategies in severe SARS-CoV-2 infection

Pneumonia caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is spreading globally. There have been strenuous efforts to reveal the mechanisms that the host defends itself against invasion by this virus. The immune system could play a crucial role in virus infection. Dendritic cell as sentinel of the immune system plays an irreplaceable role. Dendritic cells-based therapeutic approach may be a potential strategy for SARS-CoV-2 infection. In this review, the characteristics of coronavirus are described briefly. We focus on the essential functions of dendritic cell in severe SARS-CoV-2 infection. Basis of treatment based dendritic cells to combat coronavirus infections is summarized. Finally, we propose that the combination of DCs based vaccine and other therapy is worth further study.

Usefulness of IL-21, IL-7, and IL-15 conditioned media for expansion of antigen-specific CD8+ T cells from healthy donor-PBMCs suitable for immunotherapy

Clonal anergy and depletion of antigen-specific CD8+ T cells are characteristics of immunosuppressed patients such as cancer and post-transplant patients. This has promoted translational research on the adoptive transfer of T cells to restore the antigen-specific cellular immunity in these patients. In the present work, we compared the capability of PBMCs and two types of mature monocyte-derived DCs (moDCs) to prime and to expand ex-vivo antigen-specific CD8+ T cells using culture conditioned media supplemented with IL-7, IL-15, and IL-21. The data obtained suggest that protocols involving moDCs are as efficient as PBMCs-based cultures in expanding antigen-specific CD8+ T cell to ELA and CMV model epitopes. These three gamma common chain cytokines promote the expansion of naïve-like and central memory CD8+ T cells in PBMCs-based cultures and the expansion of effector memory T cells when moDCs were used. Our results provide new insights into the use of media supplemented with IL-7, IL-15, and IL-21 for the in-vitro expansion of early-differentiated antigen-specific CD8+ T cells for immunotherapy purposes.

Rapid Expansion of Highly Functional Antigen-Specific T Cells from Patients with Melanoma by Nanoscale Artificial Antigen-Presenting Cells

PURPOSE

Generation of antigen-specific T cells from patients with cancer employs large numbers of peripheral blood cells and/or tumor-infiltrating cells to generate antigen-presenting and effector cells commonly requiring multiple rounds of restimulation ex vivo. We used a novel paramagnetic, nanoparticle-based artificial antigen-presenting cell (nano-aAPC) that combines anti-CD28 costimulatory and human MHC class I molecules that are loaded with antigenic peptides to rapidly expand tumor antigen-specific T cells from patients with melanoma.

EXPERIMENTAL DESIGN

Nano-aAPC-expressing HLA-A*0201 molecules and costimulatory anti-CD28 antibody and HLA-A*0201 molecules loaded with MART-1 or gp100 class I-restricted peptides were used to stimulate CD8 T cells purified from the peripheral blood of treatment-naïve or PD-1 antibody-treated patients with stage IV melanoma. Expanded cells were restimulated with fresh peptide-pulsed nano-aAPC at day 7. Phenotype analysis and functional assays including cytokine release, cytolysis, and measurement of avidity were conducted.

RESULTS

MART-1-specific CD8 T cells rapidly expanded up to 1,000-fold by day 14 after exposure to peptide-pulsed nano-aAPC. Expanded T cells had a predominantly stem cell memory CD45RA⁺/CD62L⁺/CD95⁺ phenotype; expressed ICOS, PD-1, Tim3, and LAG3; and lacked CD28. Cells from patients with melanoma were polyfunctional; highly avid; expressed IL2, IFNγ, and TNFα; and exhibited cytolytic activity against tumor cell lines. They expanded 2- to 3-fold after exposure to PD-1 antibody in vivo, and expressed a highly diverse T-cell receptor V beta repertoire.

CONCLUSIONS

Peptide-pulsed nano-aAPC rapidly expanded polyfunctional antigen-specific CD8 T cells with high avidity, potent lytic function, and a stem cell memory phenotype from patients with melanoma.

Ex vivo dendritic cell generation-A critical comparison of current approaches

Dendritic cells (DCs) are professional antigen-presenting cells, required for the initiation of naïve and memory T cell responses and regulation of adaptive immunity. The discovery of DCs in 1973, which culminated in the Nobel Prize in Physiology or Medicine in 2011 for Ralph Steinman and colleagues, initially focused on the identification of adherent mononuclear cell fractions with uniquely stellate dendritic morphology, followed by key discoveries of their critical immunologic role in initiating and maintaining antigen-specific immunity and tolerance. The medical promise of marshaling these key capabilities of DCs for therapeutic modulation of antigen-specific immune responses has guided decades of research in hopes to achieve genuine physiologic partnership with the immune system. The potential uses of DCs in immunotherapeutic applications include cancer, infectious diseases, and autoimmune disorders; thus, methods for rapid and reliable large-scale production of DCs have been of great academic and clinical interest. However, difficulties in obtaining DCs from lymphoid and peripheral tissues, low numbers and poor survival in culture, have led to advancements in ex vivo production of DCs, both for probing molecular details of DC function as well as for experimenting with their clinical utility. Here, we review the development of a diverse array of DC production methodologies, ranging from cytokine-based strategies to genetic engineering tools devised for enhancing DC-specific immunologic functions. Further, we explore the current state of DC therapies in clinic, as well as emerging insights into physiologic production of DCs inspired by existing therapies.

Human Dendritic Cells: Their Heterogeneity and Clinical Application Potential in Cancer Immunotherapy

Dendritic cells (DC) are professional antigen presenting cells, uniquely able to induce naïve T cell activation and effector differentiation. They are, likewise, involved in the induction and maintenance of immune tolerance in homeostatic conditions. Their phenotypic and functional heterogeneity points to their great plasticity and ability to modulate, according to their microenvironment, the acquired immune response and, at the same time, makes their precise classification complex and frequently subject to reviews and improvement. This review will present general aspects of the DC physiology and classification and will address their potential and actual uses in the management of human disease, more specifically cancer, as therapeutic and monitoring tools. New combination treatments with the participation of DC will be also discussed.

IL-15 Generates IFN-γ-producing Cells Reciprocally Expressing Lymphoid-Myeloid Markers during Dendritic Cell Differentiation

Recently, interest in IL-15-differentiated cells has increased; however, the phenotypic definition of IL-15-differentiated bone marrow-derived cells (IL-15-DBMCs) is still under debate, particularly the generation of IFN-γ-producing innate cells such as premature NK (pre-mNK) cells, natural killer dendritic cells (NKDCs), interferon-producing killer dendritic cells (IKDCs), and type 1 innate lymphoid cells (ILC1s), all of which are IL-15-dependent. Here, we revisited the immunophenotypic characteristics of IFN-γ-producing IL-15-DBMCs and their functional role in the control of intracellular Mycobacterium tuberculosis (Mtb) infection. When comparing the cytokine levels between bone marrow-derived dendritic cells (BMDCs) and IL-15-DBMCs upon stimulation with various TLR agonists, only the CD11c^int population of IL-15-DBMCs produced significant levels of IFN-γ, decreased levels of MHC-II, and increased levels of B220. Neither BMDCs nor IL-15-DBMCs were found to express DX5 or NK1.1, which are representative markers for the NK cell lineage and IKDCs. When the CD11c^intB220⁺ population of IL-15-DBMCs was enriched, the Thy1.2⁺Sca-1⁺ population showed a marked increase in IFN-γ production. In addition, while depletion of the B220⁺ and Thy1.2⁺ populations of IL-15-DBMCs, but not the CD19⁺ population, inhibited IFN-γ production, enrichment of these cell populations increased IFN-γ. Ultimately, co-culture of sorted IFN-γ-producing B220⁺Thy1.2⁺ IL-15-DBMCs with Mtb-infected macrophages resulted in control of the intracellular growth of Mtb via the IFN-γ-nitric oxide axis in a donor cell number-dependent manner. Taken together, the results indicate that IFN-γ-producing IL-15-DBMCs could be redefined as CD11c^intB220⁺Thy1.2⁺Sca-1⁺ cells, which phenotypically resemble both IKDCs and ILC1s, and may have therapeutic potential for controlling infectious intracellular bacteria such as Mtb.

Chemotherapy and radiation therapy elicits tumor specific T cell responses in a breast cancer patient

Background

Experimental evidence and clinical studies in breast cancer suggest that some anti-tumor therapy regimens generate stimulation of the immune system that accounts for tumor clinical responses, however, demonstration of the immunostimulatory power of these therapies on cancer patients continues to be a formidable challenge. Here we present experimental evidence from a breast cancer patient with complete clinical response after 7 years, associated with responsiveness of tumor specific T cells.

Methods

T cells were obtained before and after anti-tumor therapy from peripheral blood of a 63-years old woman diagnosed with ductal breast cancer (HER2/neu+++, ER-, PR-, HLA-A*02:01) treated with surgery, followed by paclitaxel, trastuzumab (suspended due to cardiac toxicity), and radiotherapy. We obtained a leukapheresis before surgery and after 8 months of treatment. Using in vitro cell cultures stimulated with autologous monocyte-derived dendritic cells (DCs) that produce high levels of IL-12, we characterize by flow cytometry the phenotype of tumor associated antigens (TAAs) HER2/neu and NY-ESO 1 specific T cells. The ex vivo analysis of the TCR-Vβ repertoire of TAA specific T cells in blood and Tumor Infiltrating Lymphocytes (TILs) were performed in order to correlate both repertoires prior and after therapy.

Results

We evidence a functional recovery of T cell responsiveness to polyclonal stimuli and expansion of TAAs specific CD8+ T cells using peptide pulsed DCs, with an increase of CTLA-4 and memory effector phenotype after anti-tumor therapy. The ex vivo analysis of the TCR-Vβ repertoire of TAA specific T cells in blood and TILs showed that whereas the TCR-Vβ04-02 clonotype is highly expressed in TILs the HER2/neu specific T cells are expressed mainly in blood after therapy, suggesting that this particular TCR was selectively enriched in blood after anti-tumor therapy.

Conclusions

Our results show the benefits of anti-tumor therapy in a breast cancer patient with clinical complete response in two ways, by restoring the responsiveness of T cells by increasing the frequency and activation in peripheral blood of tumor specific T cells present in the tumor before therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2625-2) contains supplementary material, which is available to authorized users.

Monocyte-derived dendritic cells from cirrhotic patients retain similar capacity for maturation/activation and antigen presentation as those from healthy subjects

Few studies have investigated the impact of liver cirrhosis on dendritic cell function. The purpose of this study was to compare the activation and antigen-presentation capacity of monocyte-derived dendritic cells (MoDC) from cirrhotic patients (CIR) relative to healthy donors (HD). MoDC from CIR and HD were matured, phenotyped, irradiated and pulsed with 15mer peptides for two hepatocellular carcinoma-related antigens, alphafetoprotein and glypican-3, then co-cultured with autologous T-cells. Expanded T-cells were evaluated by interferon-gamma ELISPOT and intracellular staining. 15 CIR and 7 HD were studied. While CD14+ monocytes from CIR displayed enhanced M2 polarization, under MoDC-polarizing conditions, we identified no significant difference between HD and CIR in maturation-induced upregulation of co-stimulation markers. Furthermore, no significant differences were observed between CIR and HD in subsequent expansion of tumor antigen-specific IFNγ+ T-cells.

CONCLUSION

MoDCs isolated from cirrhotic individuals retain similar capacity for in vitro activation, maturation and antigen-presentation as those from healthy donors.

The N-N non-covalent domain of the nucleocapsid protein of type 2 porcine reproductive and respiratory syndrome virus enhances induction of IL-10 expression

Porcine reproductive and respiratory syndrome virus (PRRSV) usually establishes a prolonged infection and causes an immunosuppressive state. It has been proposed that IL-10 plays an important role in PRRSV-induced immunosuppression. However, this mechanism has not been completely elucidated. In this study, we found that transfection of 3D4/2 macrophages with the N protein gene of type 2 PRRSV significantly upregulated IL-10 expression at the transcriptional level. Moreover, alanine substitution mutation analysis revealed that the N protein residues 33-37, 65-68 and 112-123 were related to the upregulation of IL-10 promoter activity. Recombinant PRRSV with mutations at residues 33-37 in the N protein (rQ33-5A and rS36A) recovered from corresponding infectious cDNA clones and induced significantly lower levels of IL-10 production in infected monocyte-derived dendritic cells, as compared with their revertants rQ33-5A(R) and rS36A(R), and the wild-type recombinant PRRSV strain rNT/wt. These data indicate that the type 2 PRRSV N protein plays an important role in IL-10 induction and the N-N non-covalent domain is associated with this activity.

Fast monocyte-derived dendritic cell-based immunotherapy

Recent reports have described a new strategy for differentiation and maturation of monocyte (Mo)-derived dendritic cells (DC) within only 48-72 h of in vitro culture (fast-DC). Mature fast-DC are as effective as mature standard-DC (generated in 7-10 days of in vitro culture) in priming and propagation of antigen-specific T-cell responses. The use of fast-DC not only reduces labor and supply cost, as well as workload and time, but also increases the DC yield from Mo, which may facilitate DC-based immunotherapy for cancer patients. Detailed protocols for generation, pulsing with different antigen sources, and transduction with adenoviral vector of Mo-derived mature fast-DC as well as using of fast-DC for priming and propagation of antigen-specific cytotoxic T-cell effectors will be described here.

DNA methylation dynamics during ex vivo differentiation and maturation of human dendritic cells

Background

Dendritic cells (DCs) are important mediators of innate and adaptive immune responses, but the gene networks governing their lineage differentiation and maturation are poorly understood. To gain insight into the mechanisms that promote human DC differentiation and contribute to the acquisition of their functional phenotypes, we performed genome-wide base-resolution mapping of 5-methylcytosine in purified monocytes and in monocyte-derived immature and mature DCs.

Results

DC development and maturation were associated with a great loss of DNA methylation across many regions, most of which occurs at predicted enhancers and binding sites for known transcription factors affiliated with DC lineage specification and response to immune stimuli. In addition, we discovered novel genes that may contribute to DC differentiation and maturation. Interestingly, many genes close to demethylated CG sites were upregulated in expression. We observed dynamic changes in the expression of TET2, DNMT1, DNMT3A and DNMT3B coupled with temporal locus-specific demethylation, providing possible mechanisms accounting for the dramatic loss in DNA methylation.

Conclusions

Our study is the first to map DNA methylation changes during human DC differentiation and maturation in purified cell populations and will greatly enhance the understanding of DC development and maturation and aid in the development of more efficacious DC-based therapeutic strategies.

Preparation of triple-negative breast cancer vaccine through electrofusion with day-3 dendritic cells

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) in human immune system. DC-based tumor vaccine has met with some success in specific malignancies, inclusive of breast cancer. In this study, we electrofused MDA-MB-231 breast cancer cell line with day-3 DCs derived from peripheral blood monocytes, and explored the biological characteristics of fusion vaccine and its anti-tumor effects in vitro. Day-3 mature DCs were generated from day-2 immature DCs by adding cocktails composed of TNF-α, IL-1β, IL-6 and PEG₂. Day-3 mature DCs were identified and electofused with breast cancer cells to generate fusion vaccine. Phenotype of fusion cells were identified by fluorescence microscope and flow cytometer. The fusion vaccine was evaluated for T cell proliferation, secretion of IL-12 and IFN-γ, and induction of tumor-specific CTL response. Despite differences in morphology, day-3 and day-7 DC expressed similar surface markers. The secretion of IL-12 and IFN-γ in fusion vaccine group was much higher than that in the control group. Compared with control group, DC-tumor fusion vaccine could better stimulate the proliferation of allogeneic T lymphocytes and kill more breast cancer cells (MDA-MB-231) in vitro. Day-3 DCs had the same function as the day-7 DCs, but with a shorter culture period. Our findings suggested that day-3 DCs fused with whole apoptotic breast cancer cells could elicit effective specific antitumor T cell responses in vitro and may be developed into a prospective candidate for adoptivet immunotherapy.

Day 3 Poly (I:C)-activated dendritic cells generated in CellGro for use in cancer immunotherapy trials are fully comparable to standard Day 5 DCs

BACKGROUND

Dendritic cells (DCs) are professional antigen-presenting cells that are capable of inducing immune responses. DC-based vaccines are normally generated using a standard 5- to 7-day protocol. To shorten the DC-based vaccine production for use in cancer immunotherapy, we have developed a fast DC protocol by comparing standard DCs (Day 5 DCs) and fast DCs (Day 3 DCs).

METHODS

We tested the generation of Day 5 versus Day 3 DCs using CellGro media and subsequent activation by two activation stimuli: Poly (I:C) and LPS. We evaluated DC morphology, viability, phagocyte activity, cytokine production and ability to stimulate antigen-specific T cells.

RESULTS

Day 5 and Day 3 DCs exhibited similar phagocytic capacity. Poly (I:C)-activated Day 5 DCs expressed higher levels of the costimulatory and surface molecules CD80, CD86 and HLA-DR compared to Poly (I:C)-activated Day 3 DCs. Nevertheless, LPS-activated Day 5 and Day 3 DCs were phenotypically similar. Cytokine production was generally stronger when LPS was used as the maturation stimulus, and there were no significant differences between Day 5 and Day 3 DCs. Importantly, Day 5 and Day 3 DCs were able to generate comparable numbers of antigen-specific CD8(+) T cells. The number of Tregs induced by Day 5 and Day 3 DCs was also comparable.

CONCLUSION

We identified monocyte-derived DCs generated in CellGro for 3 days and activated using Poly (I:C) similarly potent in most functional aspects as DCs produced by the standard 5 day protocol. These results provide the rationale for the evaluation of faster protocols for DC generation in clinical trials.

Antigen-specific activation and cytokine-facilitated expansion of naive, human CD8+ T cells

Antigen-specific priming of human, naive T cells has been difficult to assess. Owing to the low initial frequency in the naive cell pool of specific T cell precursors, such an analysis has been obscured by the requirements for repeated stimulations and prolonged culture time. In this protocol, we describe how to evaluate antigen-specific priming of CD8(+) cells 10 d after a single specific stimulation. The assay provides reference conditions, which result in the expansion of a substantial population of antigen-specific T cells from the naive repertoire. Various conditions and modifications during the priming process (e.g., testing new cytokines, co-stimulators and so on) can now be directly compared with the reference conditions. Factors relevant to achieving effective priming include the dendritic cell preparation, the T cell preparation, the cell ratio at the time of priming, the serum source used for the experiment and the timing of addition and concentration of the cytokines used for expansion. This protocol is relevant for human immunology, vaccine biology and drug development.

Dendritic cell-based immunity and vaccination against hepatitis C virus infection

Hepatitis C virus (HCV) has chronically infected an estimated 170 million people worldwide. There are many impediments to the development of an effective vaccine for HCV infection. Dendritic cells (DC) remain the most important antigen-presenting cells for host immune responses, and are capable of either inducing productive immunity or maintaining the state of tolerance to self and non-self antigens. Researchers have recently explored the mechanisms by which DC function is regulated during HCV infection, leading to impaired antiviral T-cell responses and so to persistent viral infection. Recently, DC-based vaccines against HCV have been developed. This review summarizes the current understanding of DC function during HCV infection and explores the prospects of DC-based HCV vaccine. In particular, it describes the biology of DC, the phenotype of DC in HCV-infected patients, the effect of HCV on DC development and function, the studies on new DC-based vaccines against HCV infection, and strategies to improve the efficacy of DC-based vaccines.

Identification of a novel peptide derived from the M-phase phosphoprotein 11 (MPP11) leukemic antigen recognized by human CD8+ cytotoxic T lymphocytes

BACKGROUND AND OBJECTIVES

There is an urgent need for the development of leukemia-targeted immunotherapeutic approaches using defined leukemia-associated antigens that are preferentially expressed by most leukemia subtypes and absent or minimally expressed in vital tissues. M-phase phosphoprotein 11 protein (MPP11) is extensively overexpressed in leukemic cells and therefore is considered an attractive target for leukemia T cell therapy. We sought to identify potential CD8+ cytotoxic T lymphocytes that specifically recognised peptides derived from the MPP11 antigen.

METHODS

A computer-based epitope prediction program SYFPEITHI, was used to predict peptides from the MPP11 protein that bind to the most common HLA- A*0201 molecule. Peptide binding capacity to the HLA-A*0201 molecule was measured using the T2 TAP-deficient, HLA-A*0201-positive cell line. Dendritic cells were pulsed with peptides and then used to generate CD8+ cytotoxic T lymphocytes (CTL). The CML leukemic cell line K562-A2.1 naturally expressing the MPP11 antigen and engineered to express the HLA-A*0201 molecule was used as the target cell.

RESULTS

We have identified a potential HLA-A*0201 binding epitope (STLCQVEPV) named MPP-4 derived from the MPP11 protein which was used to generate a CTL line. Interestingly, this CTL line specifically recognized peptide-loaded target cells in both ELISPOT and cytotoxic assays. Importantly, this CTL line exerted a cytotoxic effect towards the CML leukemic cell line K562-A2.1.

CONCLUSION

This is the first study to describe a novel epitope derived from the MPP11 antigen that has been recognized by human CD8+ CTL.

A rapid culture technique produces functional dendritic-like cells from human acute myeloid leukemia cell lines

Most anti-cancer immunotherapeutic strategies involving dendritic cells (DC) as vaccines rely upon the adoptive transfer of DC loaded with exogenous tumour-peptides. This study utilized human acute myeloid leukemia (AML) cells as progenitors from which functional dendritic-like antigen presenting cells (DLC) were generated, that constitutively express tumour antigens for recognition by CD8⁺ T cells. DLC were generated from AML cell lines KG-1 and MUTZ-3 using rapid culture techniques and appropriate cytokines. DLC were evaluated for their cell-surface phenotype, antigen uptake and ability to stimulate allogeneic responder cell proliferation, and production of IFN-γ; compared with DC derived from normal human PBMC donors. KG-1 and MUTZ-3 DLC increased expression of CD80, CD83, CD86, and HLA-DR, and MUTZ-3 DLC downregulated CD14 and expressed CD1a. Importantly, both KG-1 and MUTZ-3-derived DLC promoted proliferation of allogeneic responder cells more efficiently than unmodified cells; neither cells incorporated FITC-labeled dextran, but both stimulated IFN-γ production from responding allogeneic CD8⁺ T cells. Control DC produced from PBMC using the FastDC culture also expressed high levels of critical cell surface ligands and demonstrated good APC function. This paper indicates that functional DLC can be cultured from the AML cell lines KG-1 and MUTZ-3, and FastDC culture generates functional KG-1 DLC.

Generation of CD19-chimeric antigen receptor modified CD8+ T cells derived from virus-specific central memory T cells

The adoptive transfer of donor T cells that have been genetically modified to recognize leukemia could prevent or treat leukemia relapse after allogeneic HSCT (allo-HSCT). However, adoptive therapy after allo-HSCT should be performed with T cells that have a defined endogenous TCR specificity to avoid GVHD. Ideally, T cells selected for genetic modification would also have the capacity to persist in vivo to ensure leukemia eradication. Here, we provide a strategy for deriving virus-specific T cells from CD45RA(-)CD62L(+)CD8(+) central memory T (T(CM)) cells purified from donor blood with clinical grade reagents, and redirect their specificity to the B-cell lineage marker CD19 through lentiviral transfer of a gene encoding a CD19-chimeric Ag receptor (CAR). Virus-specific T(CM) were selectively transduced by exposure to the CD19 CAR lentivirus after peptide stimulation, and bi-specific cells were subsequently enriched to high purity using MHC streptamers. Activation of bi-specific T cells through the CAR or the virus-specific TCR elicited phosphorylation of downstream signaling molecules with similar kinetics, and induced comparable cytokine secretion, proliferation, and lytic activity. These studies identify a strategy for tumor-specific therapy with CAR-modified T cells after allo-HSCT, and for comparative studies of CAR and TCR signaling.

Human dendritic cells infected with the nonpathogenic Mopeia virus induce stronger T-cell responses than those infected with Lassa virus

The events leading to death in severe cases of Lassa fever (LF) are unknown. Fatality seems to be linked to high viremia and immunosuppression, and cellular immunity, rather than neutralizing antibodies, appears to be essential for survival. We previously compared Lassa virus (LV) with its genetically close but nonpathogenic homolog Mopeia virus (MV), which was used to model nonfatal LF. We showed that strong and early activation of antigen-presenting cells (APC) may play a crucial role in controlling infection. Here we developed an in vitro model of dendritic-cell (DC)-T-cell coculture in order to characterize human T-cell responses induced by MV- or LV-infected DCs. Our results show very different responses to infection with LV and MV. MV strongly and durably stimulated CD8(+) and CD4(+) T cells, showing early and high activation, a strong proliferative response, and acquisition of effector and memory phenotypes. Furthermore, robust and functional CD4(+) and CD8(+) cytotoxic T lymphocytes (CTL) were generated. LV, however, induced only weak memory responses. Thus, this study allows an improved understanding of the pathogenesis and immune mechanisms involved in the control of human LV.

Generation of functional monocyte-derived fast dendritic cells suitable for clinical application in the absence of interleukin-6

To develop dendritic cells (DCs)-based immunotherapy for cancer patients, it is necessary to have a standardized, reproducible, fast, and easy to use protocol for in vitro generation of fully functional DCs. Recently, a new strategy was described for differentiation and maturation of human monocyte (Mo)-derived fast-DCs with full T cell stimulatory capacity within only 48-72 h of in vitro culture. Interleukin (IL)-6 plus tumour necrosis factor (TNF)-α, IL-1β, and prostaglandin (PG)-E(2) were used in this strategy to induce maturation of the generated DCs. The present study further modifies this strategy by excluding IL-6 from the cytokines cocktail used for DCs maturation. The results showed that maturation of fast-DCs without IL-6 did not significantly alter the morphology, phenotype and the yield of mature DCs (P > 0.05, compared with those generated with IL-6). Moreover, fast-DCs generated without IL-6 are functional antigen presenting cells, have the ability to induce tetanus toxoid-specific autologous T cell proliferation, and are suitable for gene delivery through adenoviral vector transduction as those generated with IL-6 (P > 0.05). In conclusion, the present study proves that fully mature and functional Mo-derived fast-DCs can be generated in vitro without adding IL-6, which not only reduces the number of required recombinant cytokines, but may also resemble DCs development in vivo more closely.

Third generation dendritic cell vaccines for tumor immunotherapy

This review summarizes our studies of the past several years on the development of third generation dendritic cell (DC) vaccines. These developments have implemented two major innovations in DC preparation: first, young DCs are prepared within 3 days and, second, the DCs are matured with the help of Toll-like receptor agonists, imbuing them with the capacity to produce bioactive IL-12 (p70). Based on phenotype, chemokine-directed migration, facility to process and present antigens, and stimulatory capacity to polarize Th1 responses in CD4+ T cells, induce antigen-specific CD8+ CTL and activate natural killer cells, these young mDCs display all the important properties needed for initiating good antitumor responses in a vaccine setting.

Three-day dendritic cells for vaccine development: antigen uptake, processing and presentation

BACKGROUND

Antigen-loaded dendritic cells (DC) are capable of priming naïve T cells and therefore represent an attractive adjuvant for vaccine development in anti-tumor immunotherapy. Numerous protocols have been described to date using different maturation cocktails and time periods for the induction of mature DC (mDC) in vitro. For clinical application, the use of mDC that can be generated in only three days saves on the costs of cytokines needed for large scale vaccine cell production and provides a method to produce cells within a standard work-week schedule in a GMP facility.

METHODS

In this study, we addressed the properties of antigen uptake, processing and presentation by monocyte-derived DC prepared in three days (3d mDC) compared with conventional DC prepared in seven days (7d mDC), which represent the most common form of DC used for vaccines to date.

RESULTS

Although they showed a reduced capacity for spontaneous antigen uptake, 3d mDC displayed higher capacity for stimulation of T cells after loading with an extended synthetic peptide that requires processing for MHC binding, indicating they were more efficient at antigen processing than 7d DC. We found, however, that 3d DC were less efficient at expressing protein after introduction of in vitro transcribed (ivt)RNA by electroporation, based on published procedures. This deficit was overcome by altering electroporation parameters, which led to improved protein expression and capacity for T cell stimulation using low amounts of ivtRNA.

CONCLUSIONS

This new procedure allows 3d mDC to replace 7d mDC for use in DC-based vaccines that utilize long peptides, proteins or ivtRNA as sources of specific antigen.

Short-term cultured, interleukin-15 differentiated dendritic cells have potent immunostimulatory properties

Background

Optimization of the current dendritic cell (DC) culture protocol in order to promote the therapeutic efficacy of DC-based immunotherapy is warranted. Alternative differentiation of monocyte-derived DCs using granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin (IL)-15 has been propagated as an attractive strategy in that regard. The applicability of these so-called IL-15 DCs has not yet been firmly established. We therefore developed a novel pre-clinical approach for the generation of IL-15 DCs with potent immunostimulatory properties.

Methods

Human CD14⁺ monocytes were differentiated with GM-CSF and IL-15 into immature DCs. Monocyte-derived DCs, conventionally differentiated in the presence of GM-CSF and IL-4, served as control. Subsequent maturation of IL-15 DCs was induced using two clinical grade maturation protocols: (i) a classic combination of pro-inflammatory cytokines (tumor necrosis factor-α, IL-1β, IL-6, prostaglandin E₂) and (ii) a Toll-like receptor (TLR)7/8 agonist-based cocktail (R-848, interferon-γ, TNF-α and prostaglandin E₂). In addition, both short-term (2-3 days) and long-term (6-7 days) DC culture protocols were compared. The different DC populations were characterized with respect to their phenotypic profile, migratory properties, cytokine production and T cell stimulation capacity.

Results

The use of a TLR7/8 agonist-based cocktail resulted in a more optimal maturation of IL-15 DCs, as reflected by the higher phenotypic expression of CD83 and costimulatory molecules (CD70, CD80, CD86). The functional superiority of TLR7/8-activated IL-15 DCs over conventionally matured IL-15 DCs was evidenced by their (i) higher migratory potential, (ii) advantageous cytokine secretion profile (interferon-γ, IL-12p70) and (iii) superior capacity to stimulate autologous, antigen-specific T cell responses after passive peptide pulsing. Aside from a less pronounced production of bioactive IL-12p70, short-term versus long-term culture of TLR7/8-activated IL-15 DCs resulted in a migratory profile and T cell stimulation capacity that was in favour of short-term DC culture. In addition, we demonstrate that mRNA electroporation serves as an efficient antigen loading strategy of IL-15 DCs.

Conclusions

Here we show that short-term cultured and TLR7/8-activated IL-15 DCs fulfill all pre-clinical prerequisites of immunostimulatory DCs. The results of the present study might pave the way for the implementation of IL-15 DCs in immunotherapy protocols.

Induction of inducible CD4+CD25+Foxp3+ regulatory T lymphocytes by porcine reproductive and respiratory syndrome virus (PRRSV)

Increases in numbers or activities of regulatory T lymphocytes (Tregs) have been linked to the establishments of several persistent infections. It has been previously shown that porcine reproductive and respiratory syndrome virus (PRRSV) can negatively modulate the host immune responses, resulting in persistent infection and secondary immunodeficiency. Recently, the existence of porcine CD4(+)CD25(+) Tregs has been demonstrated. We investigated the effect of PRRSV on the CD4(+)CD25(+) Tregs. The CD4(+)CD25(+)Foxp3(+) T lymphocytes in the peripheral blood mononuclear cells (PBMCs) were identified, using the anti-human anti-Foxp3 monoclonal antibody. In vitro culture of porcine PBMC in the presence of PRRSV, but not classical swine fever virus, significantly increased the numbers of Foxp3(+) lymphocytes, particularly in the CD4(+)CD25(high) subpopulation. The time-course study revealed that PRRSV significantly increased the numbers of viral-specific CD4(+)CD25(high)Foxp3(+) subpopulation in the culture starting from 12h through the end of the observation period. Consistent to the results obtained by flow cytometry, enhanced Foxp3 gene expression was observed in the PBMC cultured with PRRSV in a time-course manner. The presence of monocyte-derived DC in the co-culture significantly enhanced the induction of CD4(+)CD25(+) Foxp3(+) T lymphocytes. The PRRSV-induced CD4(+)CD25(high) T lymphocytes exhibited suppressive activity when co-cultured with PHA-activated, autologous peripheral blood leukocytes, indicating the suppressive activity of the PRRSV-specific Tregs. In addition, PRRSV exposure significantly increased the numbers of PRRSV-specific CD4(+)CD25(+)Foxp3(+) subpopulation in the PBMC of infected pigs at 10 days post-infection. In summary, the results indicated that PRRSV could increase the numbers of viral-specific, inducible regulatory T lymphocytes in the porcine PBMC, both in vitro and in vivo. The findings suggested the novel immunomodulatory mechanism induced by PRRSV.

Effect of ex vivo culture duration on phenotype and cytokine production by mature dendritic cells derived from peripheral blood monocytes

BACKGROUND

To generate clinical-grade dendritic cells (DCs) ex vivo for immunotherapy trials, peripheral blood monocytes are typically cultured in granulocyte-macrophage-colony-stimulating factor (GM-CSF) and interleukin (IL)-4 and then matured using one or more agents. Duration of the initial DC culture is one important variable that has not been systematically evaluated for its effect on the characteristics of the final mature DC product.

STUDY DESIGN

DCs were generated from elutriated peripheral blood monocytes by incubation in medium containing 2000 units per mL each of GM-CSF and IL-4 for 3 to 7 days, followed by maturation with lipopolysaccharide and interferon-gamma (IFN-gamma). DC yield, viability, flow cytometric phenotype, and cytokine production were evaluated.

RESULTS

The percentage yield and viability of mature DCs were similar after GM-CSF/IL-4 culture for 3 or 7 days. In either case, mature DCs expressed abundant CD80, CD86, CD83, and CCR7, but 3-day DCs expressed these antigens in a more consistent and homogeneous manner. Mature 3-day DCs produced much more IL-12 and less IL-10 after restimulation with CD40L-LTK than 7-day DCs. The former were also more effective in presenting immunogenic peptides to CD8 T cells. Analogous changes in cytokine production were observed in mature DCs prepared using lower concentrations of GM-CSF/IL-4 or when the alternative maturation cocktails poly(I:C)/IFN-gamma and soluble CD40L/IFN-gamma were used.

CONCLUSION

Extended initial culture of DCs in GM-CSF/IL-4 does not affect yield or viability of subsequently matured DCs, but can adversely affect their ability to homogeneously express high levels of functionally important surface molecules such as CD83 and CCR7 and to produce IL-12.

Identification of a WT1 protein-derived peptide, WT1, as a HLA-A 0206-restricted, WT1-specific CTL epitope

The Wilms' tumor gene WT1 is overexpressed in various kinds of hematopoietic malignancies as well as solid cancers, and this protein has been demonstrated to be an attractive target antigen for cancer immunotherapy. WT1-specific CTL epitopes with a restriction of HLA-A 2402 or HLA-A 0201 have been already identified. In the present study it has been demonstrated that a 9-mer WT1-derived WT1(187) peptide, which had already been shown to elicit a WT1-specific CTL response with a restriction of HLA-A 0201, can also elicit a CTL response with a restriction of HLA-A 0206. In all three different HLA-A 0206(+) healthy donors examined, WT1(187) peptide-specific CTL could be generated from peripheral blood mononuclear cells, and the CTL showed cytotoxic activity that depended on dual expression of WT1 and HLA-A 0206 molecules. The present study describes the first identification of a HLA-A 0206-restricted, WT1-specific CTL epitope. The present results should help to broaden the application of WT1 peptide-based immunotherapy from only HLA-A 0201-positive to HLA-A 0206-positive cancer patients as well.

Dendritic cell-based cancer vaccination: quo vadis?

Dendritic cells (DCs) play a central role in the initiation and regulation of primary immune responses. DCs loaded with tumor-associated antigens induce anti-tumoral cytotoxic T cells in vitro and in vivo. However, clinical trials using ex vivo-generated DCs have failed to demonstrate clinical efficacy. This review summarizes recent advances in concepts and techniques that are providing new impulses to DC-based cancer vaccination. Improvements in protocols for ex vivo-generation of DCs, innovations in immunomonitoring, strategies to overcome tumor-induced immunosuppression and insights into the mutual beneficial effects of vaccines and chemotherapy are all considered. Furthermore, we highlight novel developments in cell-free vaccines targeting DCs in vivo.

Generation of mature dendritic cells with unique phenotype and function by in vitro short-term culture of human monocytes in the presence of interleukin-4 and interferon-beta

Dendritic cell (DC)-based immunotherapy has been utilized for the treatment of not only a number of human malignancies but also a select group of infectious diseases. Conventional techniques for the generation and maturation of DCs require 7 days of in vitro culture, which prompted us to seek alternative methods that would hasten the generation of functional human myeloid DCs in vitro. Following the use of a number of cytokines/growth factors, we found that in vitro culture of purified human monocytes, in media containing interleukin (IL)-4, together with interferon (IFN)-beta for 24 hrs, followed by the addition of non-specific antigenic stimuli, such as keyhole limpet hemocyanin (KLH), lipopolysaccharide (LPS), or inactivated human immunodeficiency virus (HIV)-1 induced the monocytes to differentiated by 3 days into mature DCs (4B-DCs). These 4B-DCs expressed high levels of CD83 and CD11c, as well as markers of immune activation, including CD80 and CD86, human leukocyte antigen (HLA) class I and II, and CD14, but not CD1a. Anti-CD14 blocking antibody interfered with generation of 4B-DCs by LPS, but not by KLH or HIV-1. Interestingly, 4B-DCs, but not conventional DCs generated using macrophage-colony stimulating factor and IL-4 (G4-DCs), expressed OX40 and OX40L. 4B-DCs showed phagocytic activity, and spontaneously produced IL-12 and tumor necrosis factor (TNF)-alpha, but not IL-10. 4B-DCs promoted proliferation of allogeneic naïve CD4(+) T cells, producing IFN-(lambda) at lower levels than those stimulated with G4-DCs. 4B-DCs were more potent stimulators of allogeneic bulk CD8(+) T cells producing IFN-(lambda) than G4-DCs. These data indicate that 4B-DCs are unique and may provide a relatively more rapid alternative tool for potential clinical use, as compared with conventional G4-DCs.

Current approaches in dendritic cell generation and future implications for cancer immunotherapy

The discovery of tumor-associated antigens, which are either selectively or preferentially expressed by tumors, together with an improved insight in dendritic cell biology illustrating their key function in the immune system, have provided a rationale to initiate dendritic cell-based cancer immunotherapy trials. Nevertheless, dendritic cell vaccination is in an early stage, as methods for preparing tumor antigen presenting dendritic cells and improving their immunostimulatory function are continuously being optimized. In addition, recent improvements in immunomonitoring have emphasized the need for careful design of this part of the trials. Still, valuable proofs-of-principle have been obtained, which favor the use of dendritic cells in subsequent, more standardized clinical trials. Here, we review the recent developments in clinical DC generation, antigen loading methods and immunomonitoring approaches for DC-based trials.

Accelerated in vitro differentiation of blood monocytes into dendritic cells in human sepsis

Summary Sepsis-induced immune depression is characterized by infection susceptibility and monocyte early deactivation. Because monocytes are precursors for dendritic cells (DC), alterations in their differentiation into DC may contribute to defective immune responses in septic patients. We therefore investigated the ability of monocytes to differentiate into functional DC in vitro in patients undergoing surgery for peritonitis. Monocytes from 20 patients collected immediately after surgery (D0), at week 1 and at weeks 3-4 and from 11 control donors were differentiated into immature DC. We determined the phenotype of monocytes and derived DC, and analysed the ability of DC to respond to microbial products and to elicit T cell responses in a mixed leucocyte reaction (MLR). We show that, although monocytes from septic patients were deactivated with decreased responses to lipopolysaccharide (LPS) and peptidoglycan and low human leucocyte antigen D-related (HLA-DR) expression, they expressed the co-stimulatory molecule CD80, CD40 and CCR7. Monocytes collected from patients at D0 and week 1 differentiated faster into DC with early loss of CD14 expression. Expression of HLA-DR increased dramatically in culture to reach control levels, as did responses of DC to LPS and peptidoglycan. However, although patient and control immature DC had similar abilities to induce T cell proliferation in MLR, maturation of DC derived from patients did not increase T cell responses. These results show that circulating monocytes from septic patients express markers of activation and/or differentiation despite functional deactivation, and differentiate rapidly into phenotypically normal DC. These DC fail, however, to increase their T cell activation abilities upon maturation.

Contact-activated monocytes: efficient antigen presenting cells for the stimulation of antigen-specific T cells

Mature dendritic cells (DCs) are potent antigen presenting cells (APCs) that have been used in vaccine studies and adoptive immunotherapy protocols. For many clinical studies DCs are derived from monocytes in the presence of cytokines, which are expensive and often unavailable for clinical use. Here we describe a cytokine independent method for the differentiation of monocytes into APCs for the reactivation of antigen-specific memory T cells from both healthy donors and cancer patients. Contact activation of monocytes resulted in secretion of proinflammatory cytokines, such as IL-8, and increased cell surface expression of costimulatory molecules. To determine if activated monocytes (actMo) like DC can reactivate antigen-specific CTL, they were transduced with adenoviral vectors encoding the subdominant Epstein Barr virus antigens, latent membrane proteins (LMP) 1 and 2, which are expressed in Epstein Barr virus-positive malignancies. Stimulation of peripheral blood mononuclear cells with LMP1- and LMP2-expressing actMo activated LMP1- and LMP2-specific T cells, which could be further expanded with LMP1 or LMP2 expressing lymphoblastoid cell lines. The use of actMo as APCs simplifies the production/manufacture of antigen-specific T cells for clinical trials.

Interferon-γ dose-dependently inhibits prostaglandin E2-mediated dendritic-cell-migration towards secondary lymphoid organ chemokines

Monocyte-derived human dendritic cells (MoDCs) are increasingly applied as cellular vaccines for cancer patients. Important features for their efficacy include high migratory responsiveness to lymph node-chemokines and most likely their ability to produce bioactive IL-12 p70 upon subsequent contact with CD40 ligand-expressing T-cells. The current standard DC-maturation cocktail for clinical trials is inflammatory cytokines (TNF-alpha, IL-1beta and IL-6) combined with prostaglandin E(2) (PGE(2)), inducing phenotypically mature MoDCs with high migratory responsiveness to CCR7 ligands. This cocktail does not, however, induce or prime for production of IL-12 p70. Addition of IFN-gamma to PGE(2)-containing maturation cocktails has been shown to prime for substantial production of IL-12 p70 by subsequent CD40 ligation, but the impact of IFN-gamma on phenotypic maturation and migratory responsiveness induced by PGE(2)-containing inflammatory stimuli still remains elusive. Here, we demonstrate that addition of IFN-gamma to the standard maturation cocktail decreased CCR7 mRNA and down-regulated CCR7 expression on MoDCs in a dose-dependent manner. Moreover, addition of IFN-gamma was found to suppress MoDC-migration towards the CCR7-ligands CCL19 and CCL21. These novel findings indicate that addition of IFN-gamma to DC-maturation stimuli may have no beneficial impact on MoDC-vaccine efficiency and further implicate IFN-gamma as a negative feedback factor in DC migration towards draining lymph nodes when full-blown Th1-type responses are established. Such mechanism may restrict an uncontrolled and potentially harmful amplification of the adaptive Th1 response.

In vitro methods for generating CD8+ T-cell clones for immunotherapy from the naïve repertoire

Innovations in gene discovery and the analysis of gene expression are facilitating the identification of a growing number of antigens that could potentially be targeted for immunotherapy of tumors. Methods to reliably generate antigen-specific T-cell responses in vitro would be useful not only to screen candidate antigens for immunogenicity prior to embarking on in vivo vaccination trials, but also to generate T-cell lines or clones that could be used directly for adoptive immunotherapy approaches. Although many techniques have proven successful for expanding ex vivo effector cells from antigen-specific memory CD8(+) cells that have been primed in vivo, methods to reliably generate high-avidity CTL clones from the naïve repertoire have not been well described. Various methods for the induction and expansion of antigen-specific CD8(+) CTL clones from healthy A2(+) donors were compared, using WT1 as a model tumor-associated antigen for which there is a low frequency of precursor T cells in naïve individuals. In contrast to the well-studied Melan-A/MART-1 (Melan-A) A2-restricted response, for which the CD8(+) T-cell precursor frequency in the naïve repertoire is unusually high, successful expansion of WT1-specific CD8(+) T cells appeared to be more dependent upon cell culture conditions. In particular, primary stimulation with autologous peptide-loaded monocyte-derived DC generated in 48 h (DC2d) was more effective in expanding WT1-reactive populations of CTL than stimulation with DC generated using the more standard week-long protocol (DC7d). Adding supplemental IL-7 2 to 3 days after initiation of a stimulation cycle expanded antigen-specific cells within CTL lines more efficiently than including the cytokine from the beginning of the cycle. Following primary stimulation with peptide-loaded mature DC, subsequent restimulation with peptide-loaded PBMC as the stimulators was more effective at expanding antigen-specific cells than repeated stimulation with mature DC. Using these techniques, high-avidity CTL clones specific for an A()0201-restricted epitope of WT1 have been generated from nearly all normal A2(+) donors tested. Such clones have been demonstrated to be capable of recognizing and lysing leukemic cells, and will soon be tested for therapeutic activity in clinical trials of adoptive immunotherapy in patients with relapsed leukemia after transplantation.