High-density preculture of PBMCs restores defective sensitivity of circulating CD8 T cells to virus- and tumor-derived antigens

Technical pitfalls when collecting, cryopreserving, thawing, and stimulating human T-cells

The collection, cryopreservation, thawing, and culture of peripheral blood mononuclear cells (PBMCs) can profoundly influence T cell viability and immunogenicity. Gold-standard PBMC processing protocols have been developed by the Office of HIV/AIDS Network Coordination (HANC); however, these protocols are not universally observed. Herein, we have explored the current literature assessing how technical variation during PBMC processing can influence cellular viability and T cell immunogenicity, noting inconsistent findings between many of these studies. Amid the mounting concerns over scientific replicability, there is growing acknowledgement that improved methodological rigour and transparent reporting is required to facilitate independent reproducibility. This review highlights that in human T cell studies, this entails adopting stringent standardised operating procedures (SOPs) for PBMC processing. We specifically propose the use of HANC's Cross-Network PBMC Processing SOP, when collecting and cryopreserving PBMCs, and the HANC member network International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) PBMC Thawing SOP when thawing PBMCs. These stringent and detailed protocols include comprehensive reporting procedures to document unavoidable technical variations, such as delayed processing times. Additionally, we make further standardisation and reporting recommendations to minimise and document variability during this critical experimental period. This review provides a detailed overview of the challenges inherent to a procedure often considered routine, highlighting the importance of carefully considering each aspect of SOPs for PBMC collection, cryopreservation, thawing, and culture to ensure accurate interpretation and comparison between studies.

Performance and Stability of New Class of Fetal Bovine Sera (FBS) and Its Lyophilized Form in ELISpot and FluoroSpot Assays: Applications for Monitoring the Immune Response in Vaccine, and Cell and Gene Immunotherapy in Clinical Trials

Interferon-gamma (IFNγ) ELISpot and FluoroSpot are widely used assays to detect functional cell responses in immunotherapy clinical studies. Recognized for their importance in vaccine development studies to quantitate immune responses, these assays have more recently risen to the forefront in cell and gene therapy as well as cancer immunotherapy fields where responses against cancer neoantigens are not easily detectable above assay background. Here, we test a new class of fetal bovine serum (FBS), CultraPure FBS, in ex vivo ELISpot and FluoroSpot assays and cultured FluoroSpot assays following in vitro expansion. Several CultraPure FBS lots that have been specially formulated through the process of lyophilization (lyo-FBS) were compared to liquid CultraPure FBS. We stimulated human PBMCs with antigen-specific peptide pools diluted in media supplemented with liquid CultraPure FBS or lyo-FBS and found equivalent cytokine production with negligible to no assay background with both liquid and lyo-FBS formats. Moreover, the lyo-FBS showed lot-to-lot consistency and 90-day refrigerated (4 °C) stability in both ex vivo direct and in vitro cultured assays. In addition, we present here a method using lyo-FBS for the expansion of low-frequency antigen-specific T cells, mimicking the low frequency seen with cancer neoantigens by utilizing a cultured FluoroSpot assay. Our results demonstrate the presence of Granzyme B, interferon-gamma (IFNγ), and tumor necrosis factor (TNF) production by antigen-specific polyfunctional T cells following a 9-day culture using media supplemented with lyo-FBS.

Optimization of Peripheral Blood Mononuclear Cell Processing for Improved Clinical ELISpot Assay Performance

Cell and gene therapies have demonstrated impressive therapeutic efficacy in various human diseases. Nevertheless, cellular immune response directed against these therapeutic agents is an obstacle for achieving long-lasting clinical efficacy. Therefore, it is crucial to develop robust assays to accurately monitor cellular immunogenicity towards these therapies. Enzyme-linked immunospot (ELISpot) assay is one of the primarily used methods for measuring cellular immune response in clinical programs, which requires isolation of the peripheral blood mononuclear cells (PBMCs). The quality of this clinical material is one of the most critical factors that impact the robust assessment of cellular immune responses. The optimal blood sample processing conditions, however, remain poorly understood. In this study, we examined the impact of blood sample processing time on the performance characteristics of ELISpot to measure antigen-specific cellular responses. Blood samples that were processed after overnight delay resulted in a loss of ELISpot signals. We subsequently optimized several parameters of sample processing, and successfully recovered ELISpot signals for the blood samples that are processed within 32 h. Furthermore, several mitigation strategies were employed that would potentially address the impact of granulocyte contamination on detection of antigen-specific cellular responses. Our investigation provides an extension of sample processing window for clinical studies and is significant for resolving the logistical challenge of whole blood sample shipment for timely PBMC preparation in cell/gene therapy clinical studies.

Evaluation of Cellular Immune Response to Adeno-Associated Virus-Based Gene Therapy

The number of approved or investigational late phase viral vector gene therapies (GTx) has been rapidly growing. The adeno-associated virus vector (AAV) technology continues to be the most used GTx platform of choice. The presence of pre-existing anti-AAV immunity has been firmly established and is broadly viewed as a potential deterrent for successful AAV transduction with a possibility of negative impact on clinical efficacy and a connection to adverse events. Recommendations for the evaluation of humoral, including neutralizing and total antibody based, anti-AAV immune response have been presented elsewhere. This manuscript aims to cover considerations related to the assessment of anti-AAV cellular immune response, including review of correlations between humoral and cellular responses, potential value of cellular immunogenicity assessment, and commonly used analytical methodologies and parameters critical for monitoring assay performance. This manuscript was authored by a group of scientists involved in GTx development who represent several pharma and contract research organizations. It is our intent to provide recommendations and guidance to the industry sponsors, academic laboratories, and regulatory agencies working on AAV-based GTx viral vector modalities with the goal of achieving a more consistent approach to anti-AAV cellular immune response assessment.

A high-throughput screening RT-qPCR assay for quantifying surrogate markers of immunity from PBMCs

Immunoassays that quantitate cytokines and other surrogate markers of immunity from peripheral blood mononuclear cells (PBMCs), such as flow cytometry or Enzyme-Linked Immunosorbent Spot (ELIspot), allow highly sensitive measurements of immune effector function. However, those assays consume relatively high numbers of cells and expensive reagents, precluding comprehensive analyses and high-throughput screening (HTS). To address this issue, we developed a sensitive and specific reverse transcription-quantitative PCR (RT-qPCR)-based HTS assay, specifically designed to quantify surrogate markers of immunity from very low numbers of PBMCs. We systematically evaluated the volumes and concentrations of critical reagents within the RT-qPCR protocol, miniaturizing the assay and ultimately reducing the cost by almost 90% compared to current standard practice. We assessed the suitability of this cost-optimized RT-qPCR protocol as an HTS tool and determined the assay exceeds HTS uniformity and signal variance testing standards. Furthermore, we demonstrate this technique can effectively delineate a hierarchy of responses from as little as 50,000 PBMCs stimulated with CD4⁺ or CD8⁺ T cell peptide epitopes. Finally, we establish that this HTS-optimized protocol has single-cell analytical sensitivity and a diagnostic sensitivity equivalent to detecting 1:10,000 responding cells (i.e., 100 Spot Forming Cells/10⁶ PBMCs by ELIspot) with over 90% accuracy. We anticipate this assay will have widespread applicability in preclinical and clinical studies, especially when samples are limited, and cost is an important consideration.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (third edition)

The third edition of Flow Cytometry Guidelines provides the key aspects to consider when performing flow cytometry experiments and includes comprehensive sections describing phenotypes and functional assays of all major human and murine immune cell subsets. Notably, the Guidelines contain helpful tables highlighting phenotypes and key differences between human and murine cells. Another useful feature of this edition is the flow cytometry analysis of clinical samples with examples of flow cytometry applications in the context of autoimmune diseases, cancers as well as acute and chronic infectious diseases. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid. All sections are written and peer-reviewed by leading flow cytometry experts and immunologists, making this edition an essential and state-of-the-art handbook for basic and clinical researchers.

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.

Photochemical Internalization Enhanced Vaccination Is Safe, and Gives Promising Cellular Immune Responses to an HPV Peptide-Based Vaccine in a Phase I Clinical Study in Healthy Volunteers

Background and Aims

Photochemical internalization (PCI) is a technology for inducing release of endocytosed antigens into the cell cytosol via a light-induced process. Preclinical experiments have shown that PCI improves MHC class I antigen presentation, resulting in strongly enhanced CD8+ T-cell responses to polypeptide antigens. In PCI vaccination a mixture of the photosensitizing compound fimaporfin, vaccine antigens, and an adjuvant is administered intradermally followed by illumination of the vaccination site. This work describes an open label, phase I study in healthy volunteers, to assess the safety, tolerability, and immune response to PCI vaccination in combination with the adjuvant poly-ICLC (Hiltonol) (ClinicalTrials.gov Identifier: NCT02947854).

Methods

The primary objective of the study was to assess the safety and local tolerance of PCI mediated vaccination, and to identify a safe fimaporfin dose for later clinical studies. A secondary objective was to analyze the immunological responses to the vaccination. Each subject received 3 doses of HPV16 E7 peptide antigens and two doses of Keyhole Limpet Hemocyanin (KLH) protein. A control group received Hiltonol and vaccine antigens only, whereas the PCI groups in addition received fimaporfin + light. Local and systemic adverse effects were assessed by standard criteria, and cellular and humoral immune responses were analyzed by ELISpot, flow cytometry, and ELISA assays.

Results

96 healthy volunteers were vaccinated with fimaporfin doses of 0.75–50 µg. Doses below 17.5 µg were safe and tolerable, higher doses exhibited local tolerability issues in some study subjects, mainly erythema, and pain during illumination. There were few, and only mild and expected systemic adverse events. The employment of PCI increased the number of subjects exhibiting a T-cell response to the HPV peptide vaccine about 10-fold over what was achieved with the antigen/Hiltonol combination without PCI. Moreover, the use of PCI seemed to result in a more consistent and multifunctional CD8+ T-cell response. An enhancement of the humoral immune response to KLH vaccination was also observed.

Conclusions

Using PCI in combination with Hiltonol for intradermal vaccination is safe at fimaporfin doses below 17.5 µg, and gives encouraging immune responses to peptide and protein based vaccination.

Guidelines for the use of flow cytometry and cell sorting in immunological studies (second edition)

These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer-reviewed by leading experts in the field, making this an essential research companion.

SIMON, an Automated Machine Learning System, Reveals Immune Signatures of Influenza Vaccine Responses

Machine learning holds considerable promise for understanding complex biological processes such as vaccine responses. Capturing interindividual variability is essential to increase the statistical power necessary for building more accurate predictive models. However, available approaches have difficulty coping with incomplete datasets which is often the case when combining studies. Additionally, there are hundreds of algorithms available and no simple way to find the optimal one. In this study, we developed Sequential Iterative Modeling "OverNight" (SIMON), an automated machine learning system that compares results from 128 different algorithms and is particularly suitable for datasets containing many missing values. We applied SIMON to data from five clinical studies of seasonal influenza vaccination. The results reveal previously unrecognized CD4⁺ and CD8⁺ T cell subsets strongly associated with a robust Ab response to influenza Ags. These results demonstrate that SIMON can greatly speed up the choice of analysis modalities. Hence, it is a highly useful approach for data-driven hypothesis generation from disparate clinical datasets. Our strategy could be used to gain biological insight from ever-expanding heterogeneous datasets that are publicly available.

Building upon the success of CART19: chimeric antigen receptor T cells for hematologic malignancies

Chimeric antigen receptor T cell (CART) therapy has dramatically changed the therapeutic prospects for B cell malignancies. Over the last decade CD19-redirected CART have demonstrated the ability to induce deep, long-lasting remissions and possibly cure patients with relapsing B cell neoplasms. Such impressive results with CART19 fostered efforts to expand this technology to other incurable malignancies that naturally do not express CD19, such as acute myeloid leukemia (AML), Hodgkin lymphoma (HL) and multiple myeloma (MM). However, to reach this goal, several hurdles have to be overcome, in particular: (i) the apparent lack of suitable targets as effective as CD19; (ii) the immunosuppressive tumor microenvironment; (iii) intra-tumoral heterogeneity and antigen-negative relapses. Therefore, new strategies that allow safer and more potent CART platforms are under development and may provide grounds for new exciting breakthroughs in the field.

In silico and ex vivo approaches indicate immune pressure on capsid and non-capsid regions of coxsackie B viruses in the human system

Coxsackie B Virus (CBV) infection has been linked to the aetiology of type 1 diabetes (T1D) and vaccination has been proposed as prophylaxis for disease prevention. Serum neutralising antibodies and the presence of viral protein and RNA in tissues have been common tools to examine this potential disease relationship, whilst the role of anti-CBV cytotoxic T cell responses and their targets have not been studied. To address this knowledge gap, we augmented conventional HLA-binding predictive algorithm-based epitope discovery by cross-referencing epitopes with sites of positive natural selection within the CBV3 viral genome, identified using mixed effects models of evolution. Eight epitopes for the common MHC class I allele HLA-A*0201 occur at sites that appear to be positively selected. Furthermore, such epitopes span the viral genome, indicating that effective anti-viral responses may not be restricted to the capsid region. To assess the spectrum of IFNy responses in non-diabetic subjects and recently diagnosed type 1 diabetes (T1D) patients, we stimulated PBMC ex vivo with pools of synthetic peptides based on component-restricted sequences identified in silico. We found responders were more likely to recognize multiple rather than a single CBV peptide pool, indicating that the natural course of infection results in multiple targets for effector memory responses, rather than immunodominant epitopes or viral components. The finding that anti-CBV CD8 T cell immunity is broadly targeted has implications for vaccination strategies and studies on the pathogenesis of CBV-linked diseases.

Regulatory perspective on in vitro potency assays for human T cells used in anti-tumor immunotherapy

The adaptive immune system is known to play an important role in anti-neoplastic responses via induction of several effector pathways, resulting in tumor cell death. Because of their ability to specifically recognize and kill tumor cells, the potential use of autologous tumor-derived and genetically engineered T cells as adoptive immunotherapy for cancer is currently being explored. Because of the variety of potential T cell-based medicinal products at the level of starting material and manufacturing process, product-specific functionality assays are needed to ensure quality for individual products. In this review, we provide an overview of in vitro potency assays suggested for characterization and release of different T cell-based anti-tumor products. We discuss functional assays, as presented in scientific advices and literature, highlighting specific advantages and limitations of the various assays. Because the anticipated in vivo mechanism of action for anti-tumor T cells involves tumor recognition and cell death, in vitro potency assays based on the cytotoxic potential of antigen-specific T cells are most evident. However, assays based on other T cell properties may be appropriate as surrogates for cytotoxicity. For all proposed assays, biological relevance of the tests and correlation of the read-outs with in vivo functionality need to be substantiated with sufficient product-specific (non-)clinical data. Moreover, further unraveling the complex interaction of immune cells with and within the tumor environment is expected to lead to further improvement of the T cell-based products. Consequently, increased knowledge will allow further optimized guidance for potency assay development.

Chimeric antigen receptor T-cell therapies for lymphoma

New therapies are needed for patients with Hodgkin or non-Hodgkin lymphomas that are resistant to standard therapies. Indeed, unresponsiveness to standard chemotherapy and relapse after autologous stem-cell transplantation are indicators of an especially poor prognosis. Chimeric antigen receptor (CAR) T cells are emerging as a novel treatment modality for these patients. Clinical trial data have demonstrated the potent activity of anti-CD19 CAR T cells against multiple subtypes of B-cell lymphoma, including diffuse large-B-cell lymphoma (DLBCL), follicular lymphoma, mantle-cell lymphoma, and marginal-zone lymphoma. Importantly, anti-CD19 CAR T cells have impressive activity against chemotherapy-refractory lymphoma, inducing durable complete remissions lasting >2 years in some patients with refractory DLBCL. CAR-T-cell therapies are, however, associated with potentially fatal toxicities, including cytokine-release syndrome and neurological toxicities. CAR T cells with novel target antigens, including CD20, CD22, and κ-light chain for B-cell lymphomas, and CD30 for Hodgkin and T-cell lymphomas, are currently being investigated in clinical trials. Centrally manufactured CAR T cells are also being tested in industry-sponsored multicentre clinical trials, and will probably soon become a standard therapy. Herein, we review the clinical efficacy and toxicity of CAR-T-cell therapies for lymphoma, and discuss their limitations and future directions with regard to toxicity management, CAR designs and CAR-T-cell phenotypes, conditioning regimens, and combination therapies.

Checkpoint Inhibitors and Other Immune Therapies for Hodgkin and Non-Hodgkin Lymphoma

OPINION STATEMENT

Treatment for relapsed/refractory (R/R) Hodgkin and non-Hodgkin lymphoma remains challenging. The introduction of rituximab to B cell non-Hodgkin lymphoma (B-NHL) treatment significantly improved patients' response rate and survival; however, approximately one third of patients with diffuse large B cell lymphoma, the most common B-NHL subtype, still have a relapse or become refractory after first-line therapy. More recently, antibody therapies and small-molecule inhibitors were approved for treating R/R lymphomas; these agents include brentuximab vedotin, ibrutinib, and idelalisib. Immune checkpoint inhibitors and other immune therapies are emerging treatments currently being evaluated in various clinical trials for their efficacy against lymphoid malignancies. Striking results from these treatment modalities have been observed in solid tumors, and evidence is accumulating to support their use in various lymphomas. The most exciting results from immune checkpoint inhibitor therapy have been seen in patients with R/R Hodgkin lymphoma, in whom the overall response rate has reached 60-80 %. Results in NHL are more similar to those seen in other solid malignancies, ranging between 20 and 40 %, depending on the histology. Formal approval of these drugs is being awaited, as are the results of combination therapy with checkpoint inhibitors and other treatment modalities, including conventional chemotherapy, small-molecule inhibitors, and other immune therapies. Although response rates have been promising, attention must be paid to the management of unique immune-related adverse events, which warrant close monitoring in some cases. Identification of biomarkers that predict response or severe adverse events using either the tumor specimen or peripheral blood would aid in selecting patients suited for these types of treatment as well as determining the ideal sequence of treatment within the realm of immune therapies.

Expansion of cancer germline antigen-specific cytotoxic T lymphocytes for immunotherapy

The cancer germline antigens MAGE-A1, MAGE-A3, and NY-ESO-1 can be used to target relapsed or therapy-resistant malignant solid tumors, and previous studies have demonstrated that these antigens can be epigenetically upregulated on the surface of tumor cells following exposure to low-dose demethylating chemotherapy agents, such as decitabine. The extent to which cancer germline antigen cytotoxic T lymphocytes can be reliably expanded from healthy donors has not been well characterized, specifically in terms of whether these T cells consistently kill antigen-bearing targets or simply produce interferon-γ in the presence of the antigen. Cancer germline antigen cytotoxic T lymphocytes were generated using conventional method and high-density lymphocyte culture method. We demonstrate that there is no difference in the extent of antigen-specific killing with or without CD25 depletion when interleukin-21 is added to the cultures. Cancer germline antigen-specific killer cells could be expanded from 8/12 healthy donors using overlapping peptide mixes derived from MAGE-A1, MAGE-A3, and NY-ESO-1 and from 7/9 healthy donors using HLA-restricted epitopes. Furthermore, cytotoxic T lymphocyte derived from 4/5 patients displayed specific cytotoxicity of target cells expressing respective cancer germline antigen and HLA partially matched tumor lines. High-density lymphocyte culture prior to stimulation with cancer germline antigen peptides resulted in antigen-specific cytotoxic T lymphocyte from healthy donors and patients from whom cancer germline antigen cytotoxic T lymphocyte culture with conventional methods was not feasible. These data demonstrate that MAGE-A1-, MAGE-A3-, and NY-ESO-1-specific T cells with antigen-specific cytotoxicity can be cultured from healthy donors and patient-derived cells making adoptive immunotherapy with these cytotoxic T lymphocyte feasible.

A rapid method for quantifying cytoplasmic versus nuclear localization in endogenous peripheral blood leukocytes by conventional flow cytometry

A biochemical system and method have been developed to enable the quantitative measurement of cytoplasmic versus nuclear localization within cells in whole blood. Compared with the analyses of nuclear localization by western blot or fluorescence microscopy, this system saves a lot of time and resources by eliminating the necessity of purification and culturing steps, and generates data that are free from the errors and artifacts associated with using tumor cell lines or calculating nuclear signals from 2D images. This user‐friendly system enables the analysis of cell signaling within peripheral blood cells in their endogenous environment, including measuring the kinetics of nuclear translocation for transcription factors without requiring protein modifications. We first demonstrated the efficiency and specificity of this system for targeting nuclear epitopes, and verified the results by fluorescence microscopy. Next, the power of the technique to analyze LPS‐induced signaling in peripheral blood monocytes was demonstrated. Finally, both FoxP3 localization and IL‐2‐induced STAT5 signaling in regulatory T cells were analyzed. We conclude that this system can be a useful tool for enabling multidimensional molecular‐biological analyses of cell signaling within endogenous peripheral blood cells by conventional flow cytometry. © 2017 The Authors. Cytometry Part A Published by Wiley Periodicals, Inc. on behalf of ISAC.

Current and future immunotherapeutic approaches in Hodgkin lymphoma

Hodgkin lymphoma (HL) has become a highly curable malignancy even in advanced stages when treated adequately. However, relapsed or refractory disease and treatment-related toxicity constitute a significant clinical challenge. Innovative approaches are thus needed to improve treatment of these mainly young patients. In HL lesions, very few malignant Hodgkin and Reed-Sternberg (HRS) cells are embedded in an immunosuppressive microenvironment of reactive cells. Novel approaches such as bispecific antibodies, antibody-drug conjugates, immune-checkpoint inhibitors or adoptive cellular therapies are currently being investigated with promising results in relapsed or refractory patients. Encouraging response rates and a favorable toxicity profile have recently been reported in early phase clinical trials with antibodies blocking the programed-death receptor 1 (PD1). This review will summarize the current clinical knowledge on mechanism, safety and efficacy of the different agents and discuss potential future strategies, which are partly already investigated within clinical trials.

Induction of CD4(+) Regulatory and Polarized Effector/helper T Cells by Dendritic Cells

Dendritic cells (DCs) are considered to play major roles during the induction of T cell immune responses as well as the maintenance of T cell tolerance. Naive CD4(+) T cells have been shown to respond with high plasticity to signals inducing their polarization into effector/helper or regulatory T cells. Data obtained from in vitro generated bone-marrow (BM)-derived DCs as well as genetic mouse models revealed an important but not exclusive role of DCs in shaping CD4(+) T cell responses. Besides the specialization of some conventional DC subsets for the induction of polarized immunity, also the maturation stage, activation of specialized transcription factors and the cytokine production of DCs have major impact on CD4(+) T cells. Since in vitro generated BM-DCs show a high diversity to shape CD4(+) T cells and their high similarity to monocyte-derived DCs in vivo, this review reports data mainly on BM-DCs in this process and only touches the roles of transcription factors or of DC subsets, which have been discussed elsewhere. Here, recent findings on 1) the conversion of naive into anergic and further into Foxp3(-) regulatory T cells (Treg) by immature DCs, 2) the role of RelB in steady state migratory DCs (ssmDCs) for conversion of naive T cells into Foxp3(+) Treg, 3) the DC maturation signature for polarized Th2 cell induction and 4) the DC source of IL-12 for Th1 induction are discussed.

Immune responses to WT1 in patients with AML or MDS after chemotherapy and allogeneic stem cell transplantation

Wilms' tumor gene 1 (WT1) is overexpressed in leukemia and WT1-derived CD8(+) T-cell epitopes for immunotherapies targeting WT1 have been defined. Here, we analyzed expression of WT1 in 226 peripheral blood and bone marrow samples from patients with acute myeloid leukemia or myelodysplastic syndrome (AML/MDS) before and after allogeneic stem cell transplantation (SCT). Transcripts were assessed by quantitative polymerase chain reaction, and WT1-specific CD8+ cytotoxic T cells (CTL) were monitored by tetramer staining and enzyme-linked immunospot (ELISPOT) assays. Reduction of WT1 levels correlated with a longer survival (p < 0.01). Increment of WT1 transcripts eventually resulted in relapse and subsequent death of the patients. In patients with longer survival and continuous complete remission (cCR) after SCT, higher and enduring frequencies of WT1-specific CTL than in patients developing a relapse were detected. These cells were effector T cells secreting interferon gamma and granzyme B. In summary, WT1 is a suitable marker for the detection of minimal residual disease after SCT or chemotherapy. A rising WT1 signal correlated with a dismal prognosis of the patients. WT1-specific CD8(+) T cells might contribute to the maintenance of a cCR. Targeting WT-1 by peptide/protein vaccination as well as adoptive transfer of genetically modified T cells are future options in the individualized therapy for AML/MDS patients.