Vaccination of multiple myeloma patients with idiotype-pulsed dendritic cells: immunological and clinical aspects

Exploring cellular immunotherapy platforms in multiple myeloma

Despite major advances in therapeutic platforms, most patients with multiple myeloma (MM) eventually relapse and succumb to the disease. Among the novel therapeutic options developed over the past decade, genetically engineered T cells have a great deal of potential. Cellular immunotherapies, including chimeric antigen receptor (CAR) T cells, are rapidly becoming an effective therapeutic modality for MM. Marrow-infiltrating lymphocytes (MILs) derived from the bone marrow of patients with MM are a novel source of T cells for adoptive T-cell therapy, which robustly and specifically target myeloma cells. In this review, we examine the recent innovations in cellular immunotherapies, including the use of dendritic cells, and cellular tools based on MILs, natural killer (NK) cells, and CAR T cells, which hold promise for improving the efficacy and/or reducing the toxicity of treatment in patients with MM.

Dendritic Cell-Based Immunotherapy in Multiple Myeloma: Challenges, Opportunities, and Future Directions

Immunotherapeutic approaches, including adoptive cell therapy, revolutionized treatment in multiple myeloma (MM). As dendritic cells (DCs) are professional antigen-presenting cells and key initiators of tumor-specific immune responses, DC-based immunotherapy represents an attractive therapeutic approach in cancer. The past years, various DC-based approaches, using particularly ex-vivo-generated monocyte-derived DCs, have been tested in preclinical and clinical MM studies. However, long-term and durable responses in MM patients were limited, potentially attributed to the source of monocyte-derived DCs and the immunosuppressive bone marrow microenvironment. In this review, we briefly summarize the DC development in the bone marrow niche and the phenotypical and functional characteristics of the major DC subsets. We address the known DC deficiencies in MM and give an overview of the DC-based vaccination protocols that were tested in MM patients. Lastly, we also provide strategies to improve the efficacy of DC vaccines using new, improved DC-based approaches and combination therapies for MM patients.

DKK1 as a novel target for myeloma immunotherapy

Novel, potent tumor-associated antigens are needed to improve the efficacy of immunotherapy for myeloma. We demonstrated that active vaccination using the DKK1-DNA vaccine in the myeloma mouse model protected mice from developing myeloma and effectively treated established myeloma. Therefore, DKK1 could be developed as a novel vaccine for myeloma immunotherapy.

Autologous Hematopoietic Stem Cells Are a Preferred Source to Generate Dendritic Cells for Immunotherapy in Multiple Myeloma Patients

In multiple myeloma (MM), dendritic cells (DCs), and their precursors are prone to malignant cell-mediated regulation of function leading to low efficacy of DC vaccine. DCs taken directly from MM patient's body or derived from monocytes are fewer in numbers and are also dysfunctional. Here, we investigated the functionality of Hematopoietic stem cell-derived DCs (SC-DCs) from MM patients. Mature-MM-SC-DCs showed all essential functions like antigen uptake, allogenic T cells simulation and migration comparable to those derived from healthy donor (HD) samples. A comparison of Mo-DCs and SC-DCs obtained from the same MM patients' samples revealed that the expression of IL-6 was higher in the precursors of Mo-DCs leading to their impaired migration. In addition, expression of CCR7 which is responsible for DCs migration was found to be lower in MM-Mo-DCs. The chromatin permissiveness as observed by H3K4me³ histone modification at the Ccr7 promoter in MM-Mo-DCs was significantly lower than those in MM-SC-DCs. Levels of Zbtb46- a hall mark DC transcription factor mRNA was also found to be reduced in MM-Mo-DCs. Cytotoxic T cells generated from MM-SC-DCs from autologous naïve T cells exhibited reduced antitumor activity because the T cells were exhausted. Blocking of CTLA-4 on autologous T cells could partially restore T cell proliferation and activation. Thus, a combination of MM-SC-DC vaccine and anti-CTLA-4 antibody may serve as a better candidate for immunotherapy of MM. This study has implications in increasing the efficacy of cancer immunotherapy in MM.

Stem Cell Transplantation for Multiple Myeloma

BACKGROUND

Multiple myeloma (MM) is the second most common hematologic malignancy, affecting approximately 14,000 new patients in the United State per year. The median overall survival is 5 years, and cure is a realistic goal for only a small minority of patients.

METHODS

A review of the literature was conducted that focused on treatment strategies for MM involving administration of high doses of chemotherapy followed by autologous or allogeneic hematopoietic stem cell transplant.

RESULTS

For over three decades, the standard treatment for MM has been a regimen of melphalan and prednisone (MP). Complete responses (CRs) have been rare, and 50% of patients have had disease that was resistant to treatment with MP. Attempts have been made to improve the outcome of MM by administering other combinations of standard doses of chemotherapy, but these treatments are equivalent in terms of overall survival. For patients who are candidates, high-dose therapy followed by autologous stem cell transplantation results in higher CR rates and improved long-term survival compared to treatment with standard doses of chemotherapy alone. While this strategy represents an advance in the treatment of MM, evidence-based reviews indicate that there are a number of issues to consider regarding the induction therapy, the collection of stem cells, and the timing, type, and number of high-dose therapies to use in this type of treatment strategy.

CONCLUSIONS

Advances have been made in autologous transplantation, allogeneic transplantation, anti-MM agents, and immunotherapy for MM. Combining these different strategies to achieve synergistic responses is an exciting possibility.

Dendritic Cell Therapies for Hematologic Malignancies

Dendritic cells (DCs) are potent antigen-presenting cells that constitute a major component of the immune system’s role in the recognition, elimination, and tolerance of cancer. The unique immunologic capabilities of DCs have recently been harnessed for therapeutic use with the creation of DC-based anti-tumor vaccines, several of which have moved into testing in clinical trials for hematologic malignancies. This review summarizes how treatment strategies using DC-based anti-tumor vaccines are advancing immunotherapeutic options for these diseases.

Efficacy of host-dendritic cell vaccinations with or without minor histocompatibility antigen loading, combined with donor lymphocyte infusion in multiple myeloma patients

Donor lymphocyte infusions (DLI) can induce durable remissions in multiple myeloma (MM) patients, but this occurs rather infrequently. As the graft-versus-tumor (GvT) effect of DLI depends on the presence of host-dendritic cells (DCs), we tested in a phase I/II trial whether the efficacy of DLI could be improved by simultaneous vaccination with host-DCs. We also analyzed the possibility of further improving the GvT effect by loading the DCs with peptides of mismatched hematopoietic cell-specific minor histocompatibility antigens (mHags). Fifteen MM patients not responding to a first DLI were included. Eleven patients could be treated with a second equivalent dose DLI combined with DC vaccinations, generated from host monocytes (moDC). For four patients, the DC products did not meet the quality criteria. In four of the treated patients the DCs were loaded with host mHag peptides. Toxicity was limited and no acute GvHD occurred. Most patients developed objective anti-host T-cell responses and in one patient a distinct mHag-specific T-cell response accompanied a temporary clinical response. These findings confirm that DLI combined with host-DC vaccination, either unloaded or loaded with mHag peptides, is feasible, safe and capable of inducing host-specific T-cell responses. The limited clinical effects may be improved by developing more immunogenic DC products or by combining this therapy with immune potentiating modalities like checkpoint inhibitors.

Development of Novel Immunotherapies for Multiple Myeloma

Multiple myeloma (MM) is a disorder of terminally differentiated plasma cells characterized by clonal expansion in the bone marrow (BM). It is the second-most common hematologic malignancy. Despite significant advances in therapeutic strategies, MM remains a predominantly incurable disease emphasizing the need for the development of new treatment regimens. Immunotherapy is a promising treatment modality to circumvent challenges in the management of MM. Many novel immunotherapy strategies, such as adoptive cell therapy and monoclonal antibodies, are currently under investigation in clinical trials, with some already demonstrating a positive impact on patient survival. In this review, we will summarize the current standards of care and discuss major new approaches in immunotherapy for MM.

The Role of Immunotherapy in Multiple Myeloma

Multiple myeloma is the second most common hematologic malignancy. The treatment of this disease has changed considerably over the last two decades with the introduction to the clinical practice of novel agents such as proteasome inhibitors and immunomodulatory drugs. Basic research efforts towards better understanding of normal and missing immune surveillence in myeloma have led to development of new strategies and therapies that require the engagement of the immune system. Many of these treatments are under clinical development and have already started providing encouraging results. We, for the second time in the last two decades, are about to witness another shift of the paradigm in the management of this ailment. This review will summarize the major approaches in myeloma immunotherapies.

Idiotypic DNA vaccination for the treatment of multiple myeloma: safety and immunogenicity in a phase I clinical study

We report on the safety and immunogenicity of idiotypic DNA vaccination in a phase I, non-randomised, open-label study in patients with multiple myeloma. The study used DNA fusion gene vaccines encoding patient-specific single chain variable fragment, or idiotype (Id), linked to fragment C (FrC) of tetanus toxin. Patients in complete or partial response following high-dose chemotherapy and autologous stem cell transplant were vaccinated intramuscularly with 1 mg DNA on six occasions, beginning at least 6 months post-transplant; follow-up was to week 52. Fourteen patients were enrolled on study and completed vaccinations. Idiotypic DNA vaccines were well tolerated with vaccine-related adverse events limited to low-grade constitutional symptoms. FrC- and Id-specific T-cell responses were detected by ex vivo ELISPOT in 9/14 and 3/14 patients, respectively. A boost of pre-existing anti-FrC antibody (Ab) was detected by ELISA in 8/14 patients, whilst anti-Id Ab was generated in 1/13 patients. Overall, four patients (29 %) made an immune response to FrC and Id, with six patients (43 %) responding to FrC alone. Over the 52-week study period, serum paraprotein was undetectable, decreased or remained stable for ten patients (71 %), whilst ongoing CR/PR was maintained for 11 patients (79 %). The median time to progression was 38.0 months for 13/14 patients. Overall survival was 64 % after a median follow-up of 85.6 months.

Immunotherapy strategies in multiple myeloma

Multiple myeloma (MM) is a B-cell malignancy characterized by the clonal proliferation of malignant plasma cells in the bone marrow and the development of osteolytic bone lesions. MM has emerged as a paradigm within the cancers for the success of drug discovery and translational medicine. This article discusses immunotherapy as an encouraging option for the goal of inducing effective and long-lasting therapeutic outcome. Divided into two distinct approaches, passive or active, immunotherapy, which targets tumor-associated antigens has shown promising results in multiple preclinical and clinical studies.

Vaccination of multiple myeloma: Current strategies and future prospects

Tumor immunotherapy holds great promise in controlling multiple myeloma (MM) and may provide an alternative treatment modality to conventional chemotherapy for MM patients. For this reason, a major area of investigation is the development of cancer vaccines to generate myeloma-specific immunity. Several antigens that are able to induce specific T-cell responses are involved in different critical mechanisms for cell differentiation, inhibition of apoptosis, demethylation and proliferation. Strategies under development include infusion of vaccine-primed and ex vivo expanded/costimulated autologous T cells after high-dose melphalan, genetic engineering of autologous T cells with receptors for myeloma-specific epitopes, administration of dendritic cell/plasma cell fusions and administration expanded marrow-infiltrating lymphocytes. In addition, novel immunomodulatory drugs may synergize with immunotherapies. The task ahead is to evaluate these approaches in appropriate clinical settings, and to couple them with strategies to overcome mechanisms of immunoparesis as a means to induce more robust clinically significant immune responses.

Trial watch: Dendritic cell-based interventions for cancer therapy

Dendritic cells (DCs) occupy a central position in the immune system, orchestrating a wide repertoire of responses that span from the development of self-tolerance to the elicitation of potent cellular and humoral immunity. Accordingly, DCs are involved in the etiology of conditions as diverse as infectious diseases, allergic and autoimmune disorders, graft rejection and cancer. During the last decade, several methods have been developed to load DCs with tumor-associated antigens, ex vivo or in vivo, in the attempt to use them as therapeutic anticancer vaccines that would elicit clinically relevant immune responses. While this has not always been the case, several clinical studies have demonstrated that DC-based anticancer vaccines are capable of activating tumor-specific immune responses that increase overall survival, at least in a subset of patients. In 2010, this branch of clinical research has culminated with the approval by FDA of a DC-based therapeutic vaccine (sipuleucel-T, Provenge^®) for use in patients with asymptomatic or minimally symptomatic metastatic hormone-refractory prostate cancer. Intense research efforts are currently dedicated to the identification of the immunological features of patients that best respond to DC-based anticancer vaccines. This knowledge may indeed lead to personalized combination strategies that would extend the benefit of DC-based immunotherapy to a larger patient population. In addition, widespread enthusiasm has been generated by the results of the first clinical trials based on in vivo DC targeting, an approach that holds great promises for the future of DC-based immunotherapy. In this Trial Watch, we will summarize the results of recently completed clinical trials and discuss the progress of ongoing studies that have evaluated/are evaluating DC-based interventions for cancer therapy.

Dendritic cell cancer vaccines: from the bench to the bedside

The recognition that the development of cancer is associated with acquired immunodeficiency, mostly against cancer cells themselves, and understanding pathways inducing this immunosuppression, has led to a tremendous development of new immunological approaches, both vaccines and drugs, which overcome this inhibition. Both "passive" (e.g. strategies relying on the administration of specific T cells) and "active" vaccines (e.g. peptide-directed or whole-cell vaccines) have become attractive immunological approaches, inducing cell death by targeting tumor-associated antigens. Whereas peptide-targeted vaccines are usually directed against a single antigen, whole-cell vaccines (e.g. dendritic cell vaccines) are aimed to induce robust responsiveness by targeting several tumor-related antigens simultaneously. The combination of vaccines with new immuno-stimulating agents which target "immunosuppressive checkpoints" (anti-CTLA-4, PD-1, etc.) is likely to improve and maintain immune response induced by vaccination.

Phage idiotype vaccination: first phase I/II clinical trial in patients with multiple myeloma

Background

Multiple myeloma is characterized by clonal expansion of B cells producing monoclonal immunoglobulins or fragments thereof, which can be detected in the serum and/or urine and are ideal target antigens for patient-specific immunotherapies.

Methods

Using phage particles as immunological carriers, we employed a novel chemically linked idiotype vaccine in a clinical phase I/II trial including 15 patients with advanced multiple myeloma. Vaccines composed of purified paraproteins linked to phage were manufactured successfully for each patient. Patients received six intradermal immunizations with phage idiotype vaccines in three different dose groups.

Results

Phage idiotype was well tolerated by all study participants. A subset of patients (80% in the middle dose group) displayed a clinical response indicated by decrease or stabilization of paraprotein levels. Patients exhibiting a clinical response to phage vaccines also raised idiotype-specific immunoglobulins. Induction of a cellular immune response was demonstrated by a cytotoxicity assay and delayed type hypersensitivity tests.

Conclusion

We present a simple, time- and cost-efficient phage idiotype vaccination strategy, which represents a safe and feasible patient-specific therapy for patients with advanced multiple myeloma and produced promising anti-tumor activity in a subset of patients.

Role of allogeneic stem cell transplantation in multiple myeloma

Multiple myeloma is currently incurable using standard treatment regimens. While the introduction of high-dose chemotherapy with autologous stem cell rescue has been shown to increase overall survival when compared with chemotherapy alone, this strategy is palliative. Allogeneic stem cell transplantation provides the potential for long-term disease-free survival in a small proportion of patients, although its application has been limited by procedure-related mortality, reflecting the intensive myeloablative conditioning given. Recently, reduced intensity conditioning regimens have been developed in an attempt to reduce toxicity whilst preserving the allogeneic graft-versus-myeloma effect, therefore maintaining the potential for disease eradication. This review aims to examine the current position of allogeneic transplantation in the management of myeloma.

Immunotherapeutic approaches to treat multiple myeloma

Cellular immunotherapy can be an effective adjuvant treatment for multiple myeloma (MM), as demonstrated by induction of durable remissions after allogeneic stem cell transplantation. However, anti-myeloma immunity is often hampered by suppressive mechanisms in the tumor micro-environment resulting in relapse or disease progression. To overcome this immunosuppression, new cellular immunotherapies have been developed, based on the important effector cells in anti-myeloma immunity, namely T cells and natural killer cells. These effectors can be modulated to improve their functionality, activated by dendritic cell vaccines, or combined with immune stimulating antibodies or immunomodulatory drugs to enhance their efficacy. In this review, we discuss promising pre-clinical and clinical data in the field of cellular immunotherapy in MM. In addition, we address the potential of combining these strategies with other therapies to maximize clinical effects without increasing toxicity. The reviewed therapies might pave the way to effective personalized treatments for MM patients.

Immunotherapy strategies for multiple myeloma: the present and the future

Growing knowledge of the complexities of the immune system have led to a better understanding of how it can be harnessed for the purpose of anticancer therapy. Moreover, recent success with immunotherapies for solid tumors, combined with novel therapeutic strategies against myeloma, heighten excitement at the prospect of improving clinical outcomes for myeloma by improving antitumor immunity. Increased understanding of myeloma tumor-associated antigens, availability of more potent vaccines, expanded immune-modulating therapies, development of agents that block immune-suppressive pathways, increased sophistication of adoptive cell therapy techniques and capitalization upon standard autologous transplant are all important standalone or combination strategies that might ultimately improve prognosis of patients with multiple myeloma.

Cytotoxicity of tumor antigen specific human T cells is unimpaired by arginine depletion

Tumor-growth is often associated with the expansion of myeloid derived suppressor cells that lead to local or systemic arginine depletion via the enzyme arginase. It is generally assumed that this arginine deficiency induces a global shut-down of T cell activation with ensuing tumor immune escape. While the impact of arginine depletion on polyclonal T cell proliferation and cytokine secretion is well documented, its influence on chemotaxis, cytotoxicity and antigen specific activation of human T cells has not been demonstrated so far. We show here that chemotaxis and early calcium signaling of human T cells are unimpaired in the absence of arginine. We then analyzed CD8⁺ T cell activation in a tumor peptide as well as a viral peptide antigen specific system: (i) CD8⁺ T cells with specificity against the MART-1_{aa26–35*A27L} tumor antigen expanded with in vitro generated dendritic cells, and (ii) clonal CMV pp65_aa495–503 specific T cells and T cells retrovirally transduced with a CMV pp65_aa495–503 specific T cell receptor were analyzed. Our data demonstrate that human CD8⁺ T cell antigen specific cytotoxicity and perforin secretion are completely preserved in the absence of arginine, while antigen specific proliferation as well as IFN-γ and granzyme B secretion are severely compromised. These novel results highlight the complexity of antigen specific T cell activation and demonstrate that human T cells can preserve important activation-induced effector functions in the context of arginine deficiency.

Immunologic microenvironment and personalized treatment in multiple myeloma

INTRODUCTION

Multiple myeloma (MM) is characterized by generalized immune suppression and increased susceptibility to infections and secondary malignancies. Malignant plasma cells (PCs) modulate the bone marrow microenvironment to favor their own survival and proliferation. These events lead to a severe deregulation of immune effectors. Extensive studies have been conducted to unveil the mechanisms through which MM cells negatively modulate immunity and to develop therapeutical approaches for restoring an efficient anti-MM immune response.

AREAS COVERED

This review article covers both the immunosuppressive effects exerted by MM and the immunomodulatory potential of novel anti-MM agents. A brief overview on the most promising immunotherapeutic approaches in the field is also provided.

EXPERT OPINION

MM leads to a progressive impairment of the immune system. Different approaches have been evaluated or are currently under investigation to boost a specific anti-MM immune response. The discovery that anti-MM agents like bortezomib also retain immunomodulatory properties provides evidence to support the development of combined treatment modalities. In the next future, immunotherapy will be likely included in selective treatments in early stages or in the post-transplantation setting with non toxic modalities that control or clear the neoplastic clone.

Evolution of cellular immunotherapy: from allogeneic transplant to dendritic cell vaccination as treatment for multiple myeloma

The promise of cellular therapy as treatment for multiple myeloma is highlighted by the observation that allogeneic transplantation results in durable remissions in a subset of patients. The potency of the graft-versus-myeloma effect is supported by the decreased risk of relapse seen in patients with graft-versus-host disease and disease response following donor lymphocyte infusions. However, the lack of specificity of the alloreactive lymphocytes limits their therapeutic efficacy and results in significant treatment-related morbidity and mortality. A major area of investigation is the development of cancer vaccines to generate myeloma-specific immunity that selectively targets malignant cells while minimizing toxicity to normal tissues. Critical elements required to develop an effective vaccine strategy involve the identification of myeloma-associated antigens, enhancement of antigen presentation, and reversing the immunosuppressive milieu induced by the disease. Dendritic cells are potent APCs that represent an ideal platform for vaccination. Strategies for vaccine design include the loading of individual antigens as well as the use of whole tumor cells as a source of myeloma antigens. Vaccination has been examined in the postautologous transplant setting in which disease cytoreduction and depletion of Tregs is associated with enhanced vaccine response. Recent efforts have also included exploration of immune modulatory agents that target inhibitory pathways to enhance vaccine response and create a more durable antitumor immunity.

Optimizing dendritic cell vaccine for immunotherapy in multiple myeloma: tumour lysates are more potent tumour antigens than idiotype protein to promote anti-tumour immunity

Dendritic cells (DCs) are the most potent antigen-presenting cells and are the mediators of T cell immunity. Many investigators have explored the potential of using DCs as a vaccine for tumour-derived antigens in immunotherapy of B cell malignancies, and the results have been disappointing. To search for better tumour antigens to improve the efficacy of DC-based immunotherapy in myeloma, we evaluated and compared the efficacy of the vaccination of DCs pulsed with idiotype (Id) or tumour lysate in the 5TGM1 myeloma mouse model. Our results showed that Id- or tumour lysate-pulsed DC vaccines protected mice efficiently against developing myeloma, retarded tumour growth, induced tumour regression against established tumour and protected surviving mice from tumour rechallenge. The therapeutic responses were associated with an induction of strong humoral immune responses, including anti-Id or anti-lysate antibodies, and cellular immune responses including myeloma-specific CD8(+) cytotoxic T lymphocytes, CD4(+) type 1 T helper cells and memory T cells in mice receiving Id- or tumour lysate-pulsed DC vaccines. In addition, our studies showed that tumour lysate-pulsed DCs were more potent vaccines than the Id-pulsed DC vaccines to promote anti-tumour immunity in the model. This information will be important for improving the strategies of DC-based immunotherapy for patients with myeloma and other B cell tumours.

Optimizing dendritic cell-based immunotherapy: tackling the complexity of different arms of the immune system

Earlier investigations have revealed a surprising complexity and variety in the range of interaction between cells of the innate and adaptive immune system. Our understanding of the specialized roles of dendritic cell (DC) subsets in innate and adaptive immune responses has been significantly advanced over the years. Because of their immunoregulatory capacities and because very small numbers of activated DC are highly efficient at generating immune responses against antigens, DCs have been vigorously used in clinical trials in order to elicit or amplify immune responses against cancer and chronic infectious diseases. A better insight in DC immunobiology and function has stimulated many new ideas regarding the potential ways forward to improve DC therapy in a more fundamental way. Here, we discuss the continuous search for optimal in vitro conditions in order to generate clinical-grade DC with a potent immunogenic potential. For this, we explore the molecular and cellular mechanisms underlying adequate immune responses and focus on most favourable DC culture regimens and activation stimuli in humans. We envisage that by combining each of the features outlined in the current paper into a unified strategy, DC-based vaccines may advance to a higher level of effectiveness.

Novel strategies for immunotherapy in multiple myeloma: previous experience and future directions

Multiple myeloma (MM) is a life-threatening haematological malignancy for which standard therapy is inadequate. Autologous stem cell transplantation is a relatively effective treatment, but residual malignant sites may cause relapse. Allogeneic transplantation may result in durable responses due to antitumour immunity mediated by donor lymphocytes. However, morbidity and mortality related to graft-versus-host disease remain a challenge. Recent advances in understanding the interaction between the immune system of the patient and the malignant cells are influencing the design of clinically more efficient study protocols for MM. Cellular immunotherapy using specific antigen-presenting cells (APCs), to overcome aspects of immune incompetence in MM patients, has received great attention, and numerous clinical trials have evaluated the potential for dendritic cell (DC) vaccines as a novel immunotherapeutic approach. This paper will summarize the data investigating aspects of immunity concerning MM, immunotherapy for patients with MM, and strategies, on the way, to target the plasma cell more selectively. We also include the MM antigens and their specific antibodies that are of potential use for MM humoral immunotherapy, because they have demonstrated the most promising preclinical results.

Immunogenic targets for specific immunotherapy in multiple myeloma

Multiple myeloma remains an incurable disease although the prognosis has been improved by novel therapeutics and agents recently. Relapse occurs in the majority of patients and becomes fatal finally. Immunotherapy might be a powerful intervention to maintain a long-lasting control of minimal residual disease or to even eradicate disseminated tumor cells. Several tumor-associated antigens have been identified in patients with multiple myeloma. These antigens are expressed in a tumor-specific or tumor-restricted pattern, are able to elicit immune response, and thus could serve as targets for immunotherapy. This review discusses immunogenic antigens with therapeutic potential for multiple myeloma.

Cellular immunotherapy using dendritic cells against multiple myeloma

Cellular therapy with dendritic cells (DCs) is emerging as a useful immunotherapeutic tool to treat multiple myeloma (MM). DC-based idiotype vaccination was recently suggested to induce idiotype-specific immune responses in MM patients. However, the clinical results so far have been largely disappointing, and the clinical effectiveness of such vaccinations in MM still needs to be demonstrated. DC-based therapies against MM may need to be boosted with other sources of tumor-associated antigens, and potent DCs should be recruited to increase the effectiveness of treatment. DCs with both high migratory capacity and high cytokine production are very important for effective DC-based cancer vaccination in order to induce high numbers of Th1-type CD4⁺ T cells and CD8⁺ cytotoxic T lymphocytes. The tumor microenvironment is also important in the regulation of tumor cell growth, proliferation, and the development of therapeutic resistance after treatment. In this review, we discuss how the efficacy of DC vaccination in MM can be improved. In addition, novel treatment strategies that target not only myeloma cells but also the tumor microenvironment are urgently needed to improve treatment outcomes.

Safety of intradermal injection of monosodium urate crystals as a vaccine carrier in volunteers

Monosodium urate (MSU) crystals are known to induce gouty arthritis, but also evoke specific cell immunity and work as an adjuvant by delivering several kinds of binding proteins, including idiotypic cancer vaccine peptides into dendritic cells. To investigate the potency of MSU crystals as a cancer vaccine carrier in vivo, this preclinical study examined whether intradermal injection of MSU crystals was safe for healthy adults. Subjects comprised 12 volunteers. Four different dose levels of MSU crystals were injected as follows: 2 μg (n = 3), 20 μg (n = 3), 200 μg (n = 3), or 2000 μg (n = 3). At 24 hours after administration, documented erythema was seen around the injection site in a dose-dependent manner, particularly in all adults with MSU dose ≥200 μg. However, redness was limited to the grade I level of the National Cancer Institute toxicity criteria. Serum uric acid levels did not show any change before and after injection. Moreover, neither gouty arthritis nor tophi developed in any volunteers, indicating that intradermal injection of MSU crystals did not induce systemic inflammation at the doses that evoked significant local inflammation. These findings suggest that intradermal injection of MSU crystals is fundamentally safe and should be made available for clinical trials using MSU-crystal-conjugated cancer vaccines.

Immunotherapy using dendritic cells against multiple myeloma: how to improve?

Multiple myeloma (MM) is a good target disease in which one can apply cellular immunotherapy, which is based on the graft-versus-myeloma effect. This role of immune effector cells provides the framework for the development of immune-based therapeutic options that use antigen-presenting cells (APCs) with increased potency, such as dendritic cells (DCs), in MM. Current isolated idiotype (Id), myeloma cell lysates, myeloma dying cells, DC-myeloma hybrids, or DC transfected with tumor-derived RNA has been used for immunotherapy with DCs. Immunological inhibitory cytokines, such as TGF-β, IL-10, IL-6 and VEGF, which are produced from myeloma cells, can modulate antitumor host immune response, including the abrogation of DC function, by constitutive activation of STAT3. Therefore, even the immune responses have been observed in clinical trials, the clinical response was rarely improved following DC vaccinations in MM patients. We are going to discuss how to improve the efficacy of DC vaccination in MM.

Cellular therapy to treat haematological and other malignancies: progress and pitfalls

The recent Food and Drug Administration (FDA) approval of a cellular therapy to treat castration resistant prostate cancer has reinforced the potential of cellular therapy to consolidate current pharmacological approaches to treating cancer. The emergence of the cell manufacturing facility to facilitate clinical translation of these new methodologies allows greater access to these novel therapies. Here we review different strategies currently being explored to treat haematological malignancies with a focus on adoptive allogeneic or autologous transfer of antigen specific T cells, NK cells or dendritic cells. These approaches all aim to generate immunological responses against overexpressed tissue antigens, mismatched minor histocompatability antigens or tumour associated antigens. Current successes and limitations of these different approaches will be discussed with an emphasis on challenges encountered in generating long term engraftment, antigen selection and implementation as well as therapeutic immune monitoring of clinical responses, with examples from recent clinical trials.

Active vaccination with Dickkopf-1 induces protective and therapeutic antitumor immunity in murine multiple myeloma

Dickkopf-1 (DKK1), broadly expressed in myeloma cells but highly restricted in normal tissues, together with its functional roles as an osteoblast formation inhibitor, may be an ideal target for immunotherapy in myeloma. Our previous studies have shown that DKK1 (peptide)-specific CTLs can effectively lyse primary myeloma cells in vitro. The goal of this study was to examine whether DKK1 can be used as a tumor vaccine to elicit DKK1-specific immunity that can control myeloma growth or even eradicate established myeloma in vivo. We used DKK1-DNA vaccine in the murine MOPC-21 myeloma model, and the results clearly showed that active vaccination using the DKK1 vaccine not only was able to protect mice from developing myeloma, but it was also therapeutic against established myeloma. Furthermore, the addition of CpG as an adjuvant, or injection of B7H1-blocking or OX40-agonist Abs, further enhanced the therapeutic effects of the vaccine. Mechanistic studies revealed that DKK1 vaccine elicited a strong DKK1- and tumor-specific CD4+ and CD8+ immune responses, and treatment with B7H1 or OX40 Abs significantly reduced the numbers of IL-10-expressing and Foxp3+ regulatory T cells in vaccinated mice. Thus, our studies provide strong rationale for targeting DKK1 for immunotherapy of myeloma patients.

CMRF44+ Dendritic Cells from Peripheral Blood Stem Cell Harvests of Patients with Myeloma as Potential Cellular Vectors for Idiotype Vaccination

The optimal conditions required to harvest dendritic cells (DC) for immunotherapy were investigated in a series of preliminary investigations using peripheral blood stem cell (PBSC) harvests and blood from patients with myeloma. There was no difference in the number of DC (CMRF44+, CD19-, CD14-) in PBSC mobilized with G-CSF (mean 0.28%, n = 7) compared with GM-CSF (mean 0.24%, n = 6) and apheresis itself did not concentrate DC. In longitudinal studies (n = 10), the peak DC count (day 12 post PBSC harvest) did not correlate with the peak CD34+ cell count or white cell count. A simple affinity purification of DC resulted in a mean 63-fold purification. Affinity enriched suspensions from normal blood contained more DC (mean = 18.8%; n = 5) than those from patients with myeloma (mean = 9.9%; n = 13). The percentage of DC with a lymphoid phenotype (CD11c-, CDw123hi+) was significantly higher in G-CSF mobilized PBSC harvests (22.7%; n = 6) than in peripheral blood samples from patients with myeloma (7.0%; n = 13; p = 0.01). DC endocytosis was normal and did not change throughout the course of the disease. Neither DC numbers nor subsets changed significantly between days 1 and 3 of culture. Current mobilization procedures, optimized for PBSC, need to be altered when harvesting DC.

Lenalidomide enhances antigen-specific activity and decreases CD45RA expression of T cells from patients with multiple myeloma

The aim of this study was to investigate whether the specific T cell response against the multiple myeloma Ag HM1.24 is enhanced by the immunomodulatory drug lenalidomide (Revlimid). Ag-specific CD3(+)CD8(+) T cells against the HM1.24 Ag were expanded in vitro by dendritic cells in 29 healthy donors and 26 patients with plasma cell dyscrasias. Ag-specific activation was analyzed by IFN-γ, granzyme B, and perforin secretion using ELISA, ELISPOT assay, and intracellular staining, and generation of Ag-specific T cells was analyzed by tetramer staining. Expression of T cell maturation markers (CD45RA, CD45R0, CCR7, and CD28) was investigated by flow cytometry. We found that activation of HM1.24-specific T cells from healthy donors and patients with plasma cell dyscrasias was enhanced significantly by lenalidomide and furthermore that the impact of lenalidomide on T cells depends on the duration of the exposure. Notably, lenalidomide supports the downregulation of CD45RA on T cells upon activation, observed in healthy donors and in patients in vitro and also in patients during lenalidomide therapy in vivo. We showed for the first time, to our knowledge, that lenalidomide enhances the Ag-specific activation of T cells and the subsequent downregulation of CD45RA expression of T cells in vitro and in vivo.

Novel immunotherapies

Multiple myeloma is still a fatal disease. Despite advances in high-dose chemotherapy and stem-cell transplantation and the development of novel therapeutics, relapse of the underlying disease remains the primary cause of treatment failure. Strategies for posttransplantation immunomodulation are desirable for eradication of remaining tumor cells. To this end, immunotherapy aimed at inducing myeloma-specific immunity in patients has been explored. Idiotype protein, secreted by myeloma cells, has been the primary target for immunotherapy as it is the best defined tumor-specific antigen. This chapter focuses on novel immunotherapies that are being developed to treat patients with myeloma. I will discuss potential myeloma antigens, antigen-specific T cells, and their function on myeloma tumor cells, and T-cell-based and antibody-based immunotherapies for myeloma. Furthermore, clinical studies of T-cell-based immunotherapy in the form of vaccination, allogeneic stem-cell transplantation and donor lymphocyte infusions, with or without donor vaccination using patient-derived idiotype, and future application of donor-derived or patient-derived, antigen-specific T-cell infusion in this disease are also discussed. Based on the specificity of the immune effector molecules and cells, immunotherapies with specific T cells or therapeutic antibodies may represent novel strategies for the treatment of multiple myeloma in the near future.

Immunology and immunotherapeutic approaches in multiple myeloma

Immunotherapy for patients suffering from multiple myeloma is a lively and emerging field in cancer research. Immunotherapeutic approaches offer unique treatment opportunities for this, to date, mostly incurable disease. Respective basic findings and recent clinical approaches are introduced and discussed. Although several obstacles still need to be overcome, it appears that clinically efficient immunotherapies will become available for multiple myeloma patients in the future.

Transfer of influenza vaccine-primed costimulated autologous T cells after stem cell transplantation for multiple myeloma leads to reconstitution of influenza immunity: results of a randomized clinical trial

Severe immune deficiency follows autologous stem cell transplantation for multiple myeloma and is associated with significant infectious morbidity. This study was designed to evaluate the utility of a pretransplantation vaccine and infusion of a primed autologous T-cell product in stimulating specific immunity to influenza. Twenty-one patients with multiple myeloma were enrolled from 2007 to 2009. Patients were randomly assigned to receive an influenza-primed autologous T-cell product or a nonspecifically primed autologous T-cell product. The study endpoint was the development of hemagglutination inhibition titers to the strain-specific serotypes in the influenza vaccine. Enzyme-linked immunospot assays were performed to confirm the development of influenza-specific B-cell and T-cell immunity. Patients who received the influenza-primed autologous T-cell product were significantly more likely to seroconvert in response to the influenza vaccine (P = .001). Seroconversion was accompanied by a significant B-cell response. No differences were observed in the global quantitative recovery of T-cell and B-cell subsets or in global T-cell and B-cell function. The provision of a primed autologous T-cell product significantly improved subsequent influenza vaccine responses. This trial was registered at www.clinicaltrials.gov as #NCT00499577.

Optimizing dendritic cell-based immunotherapy in multiple myeloma: intranodal injections of idiotype-pulsed CD40 ligand-matured vaccines led to induction of type-1 and cytotoxic T-cell immune responses in patients

Vaccination with idiotype (Id) protein-pulsed dendritic cells (DCs) has been explored in multiple myeloma and the results have been disappointing. To improve the efficacy of DC vaccination in myeloma, we investigated the use of Id- and keyhole limpet haemocyanin (KLH)-pulsed, CD40 ligand-matured DCs administered intranodally. Nine patients with smouldering or stable myeloma without treatment were enrolled and DC vaccines were administered at weekly intervals for a total of four doses. Following vaccination, all patients mounted Id-specific gamma-interferon T-cell response. Interleukin-4 response was elicited in two, and skin delayed-type hypersensitivity reaction occurred in seven patients. More importantly, Id-specific cytotoxic T-cell responses were also detected in five patients. Most if not all patients mounted a positive T-cell response to KLH following vaccination. At 1-year follow-up, six of the nine patients had stable disease, while three patients had slowly progressive disease even during the vaccination period. At 5-year follow-up, four of the six patients continued with stable disease. No major side effects were noted. In summary, intranodal administration of Id-pulsed CD40 ligand-matured DCs was able to induce Id-specific T and B-cell responses in patients. Current efforts are geared towards breaking tumour-mediated immune suppression and improving clinical efficacy of this immunotherapy.

Dendritic cells, T-cells and their possible role in the treatment of leukaemia and lymphoma

The immune system has the ability to control and destroy malignant calls. This has been demonstrated by the graft versus leukaemia effect and the use of donor lymphocyte infusions in peripheral blood stem cell transplantation. Dendritic cells are potent antigen presenting cells and become activated after phagocytosing and processing antigen. During this process they up-regulate MHC, co-stimulatory and adhesion molecules and have the ability to stimulate naïve T-cells. Recent evidence has shown that dendritic cells can be loaded with tumour specific antigens and can be used to generate specific anti-tumour T-cell responses. Initial clinical studies using this technology have been promising and suggest that dendritic cells and T-lymphocytes can be utilised in developing therapies which target specific malignant clones.

Cellular immunotherapy of cancer

Standard therapies for many common cancers remain toxic and are often ineffective. Cellular immunotherapy has the potential to be a highly targeted alternative, with low toxicity to normal tissues but a high capacity to eradicate tumor. In this chapter we describe approaches that generate cellular therapies using active immunization with cells, proteins, peptides, or nucleic acids, as well as efforts that use adoptive transfer of effector cells that directly target antigens on malignant cells. Many of these approaches are proving successful in hematologic malignancy and in melanoma. In this chapter we discuss the advantages and limitations of each and how over the next decade investigators will attempt to broaden their reach, increase their efficacy, and simplify their application.

Idiotype-pulsed antigen-presenting cells following autologous transplantation for multiple myeloma may be associated with prolonged survival

Vaccines are attractive as consolidation therapy after autologous stem cell transplantation (ASCT) for multiple myeloma (MM). We report the results of a phase II trial of the immunotherapeutic, APC8020 (Mylovenge), given after ASCT for MM. We compared the results with that of other patients with MM who underwent ASCT at Mayo Clinic during the same time period. Twenty-seven patients were enrolled on the trial between July, 1998 and June, 2001, and the outcomes were compared to that of 124 consecutive patients transplanted during the same period, but not enrolled on the trial. The median (range) follow-up for patients still alive from the vaccine trial is 6.5 (2.9-8 years), and 7.1 (6-8 years) in the control group. The median age was 57.4 range (36.1-71.3) in the DB group and 56.4 (range, 30-69) in the trial group. Known prognostic factors including PCLI, B2M, and CRP were comparable between the groups. The median overall survival for the trial patients was 5.3 years (95% CI: 4.0 years-N/A) compared to 3.4 years (95% CI: 2.7-4.6 years) for the DB group (P = 0.02). The median time to progression and progression-free survival for the trial group was similar to the DB group. Although not a controlled trial, the vaccines given after ASCT appear to be associated with improved overall survival compared to historical controls. This approach warrants further investigation to confirm this and define the role of vaccine therapy in myeloma.

B7+ T Cells in Myeloma: an Acquired Marker of Prior Chronic Antigen Presentation

Murine T cells do not endogenously upregulate CD80 expression but rather acquire CD80 from antigen presenting cells (APC) during CD28 ligation. Murine CD80+ memory T cells undergo apoptosis in the presence of high levels of antigen while naive CD80+ T cells are capable of acting as APC and T cell:T cell ligation induces anergy and unresponsiveness to antigen rechallenge. Reversing T cell unresponsiveness may be a key factor in the development of immunotherapy strategies for patients with myeloma. We have determined that B7+ T cells (CD80+ or CD86+) are common in patients with myeloma (n = 45), can be either CD4 or CD8, tend to be associated with stable disease and are polyclonal memory T cells (CD45RO). CD80 mRNA expression was present in CD80+ monocytes but not in CD3+ cells with a similar level of CD80 antigen expression. CD80 and CD86 antigen expression was upregulated on B cells but not T cells during incubation with trimeric human CD40 ligand (huCD40LT) + IL-2. Although there was a gradual loss of expression during in vitro culture, CD80+ T cells could be purified for further study. We conclude that B7 expression is common on T cells of patients with myeloma but that this is acquired rather than endogenously produced. B7+ CD45RO+ T cells constitute a population of memory T cells chronically exposed to antigen and warrant further study.

Generation of Dendritic Cells from Positively Selected CD14 + Monocytes for Anti-tumor Immunotherapy

Peripheral blood CD14+ monocytes from multiple myeloma (MM) patients can be induced to differentiate into fully functional, mature, CD83+ dendritic cells (DCs) which are highly efficient in priming autologous T lymphocytes in response to the patient-specific tumor idiotype (Id). We have recently scaled up our manufacturing protocol for application in a phase I-II clinical trial of anti-Id vaccination with DCs in MM patients. Elegible patients received a series of by-monthly immunizations consisting of three subcutaneous and two intravenous injections of Id-keyhole limpet hemocyanin (KLH)-pulsed DCs (5 x -, 10 x -, 50 x 10(6) cells and 10 x -, 50 x 10(6) cells, respectively). To generate DCs, monocytes were labeled with clinical grade anti-CD14 conjugates and positively selected by immunomagnetic separation. Cells were then cultured, according to Good Manufacturing Practice guidelines, in FCS-free medium in cell culture bags, and differentiated to DCs with GM-CSF plus IL-4 followed by TNF-alpha or, more recently, by a cocktail of IL-1beta, IL-6, TNF-alpha and prostaglandin-E2. Before maturation, Mo-DCs were pulsed with the autologous Id as whole protein or Id (VDJ)-derived HLA class I restricted peptides. Ten MM patients, who had been treated with two courses of high-dose chemotherapy with peripheral blood stem cell support, entered into the clinical study. CD14+ monocytes were enriched from 16.1+/-5.7% to 95.5+/-3.2% (recovery 67.9+/-15%, viability > 97%). After cell culture, phenotypic analysis showed that 89.6+/-6.6% of the cells were mature DCs. We obtained 2.89+/-1 x 10(8) DCs/leukapheresis which represented 24.5+/-9% of the initial number of CD14+ cells. Notably, the cytokine cocktail induced a significantly higher percentage and yield (31+/-10.9 of initial CD14+ cells) of DCs than TNF-alpha alone, secretion of larger amounts of IL-12, potent stimulatory activity on allogeneic and autologous T cells. Storage in liquid nitrogen did not modify the phenotype or functional characteristics of pre-loaded DCs. The recovery of thawed, viable DCs, was 78+/-10%. Thus, positive selection of CD14+ monocytes allows the generation of a uniform population of mature pre-loaded DCs which can be cryopreserved with no effects on phenotype and function and are suitable for clinical trials. Based on these results, a DCs-based phase II trial of anti-Id vaccination with VDJ-derived HLA class I-restricted peptides and KLH is underway for lymphoma patients.

Dendritic Cells and their Potential Therapeutic Role in Haematological Malignancy

The generation of an effective immune response is dependent on the efficient capture and presentation of antigen by antigen-presenting cells. The most potent antigen-presenting cells are dendritic cells (DC). These cells have the capability of activating naive helper and cytotoxic T cells. In recent years it has been demonstrated that in vivo responses to a number of solid tumours can be generated by DC pulsed with either purified tumour antigen or whole tumour cell lysate. In addition, a number of in vivo studies using DC have also been attempted in solid tumours, with some encouraging results. In haematological malignancies, there is now strong evidence that previous T cell anergy can be reversed and significant anti-tumour immune responses generated, in vitro, against the majority of leukaemias. As far as in vivo studies in haematological malignancies are concerned, although T cell responses have been demonstrated in the majority of cases and some dramatic early clinical responses reported, overall results appear disappointing. However, considering the fact that many of these studies were performed in patients with advanced disease and that such therapeutic strategies are still in their infancy, the overall results are actually quite encouraging. Although there is a real potential for DC immunotherapy in the future, it is important to be realistic about the limitations and obstacles to its development. It is highly unlikely that any form of immunotherapy is going to be effective in advanced disease due to the physical bulk of tumour, the immunosuppressive effects of tumours themselves and to any secondary immunosuppression following standard cancer therapy. The potential for immunotherapy is likely to lie either in adjunctive therapy or for treating minimal residual disease. Even in those situations, one of the major obstacles to be overcome is the state of immunological anergy or tolerance that many tumours seem able to induce. Indeed, there is evidence that, under certain circumstances, DC themselves can present antigen in such a way as to produce this state of anergy. Although, in vitro manipulation of DC and T cells can generate tumour-specific T cells from previously "anergic" cells, once reintroduced in vivo, these cells will be re-exposed to the tumour environment with the risk of being rendered anergic again.

Clonal Cytotoxic T Cells in Myeloma

Multiple myeloma (MM) is a malignant disease characterized by accumulation of morphologically recognizable plasma cells producing immunoglobulin (Ig) in the bone marrow. The occurrence of clonal T cells in MM, as defined by the presence of rearrangements in the T-cell receptor (TCR)-beta chains detected on Southern blotting, is associated with an improved prognosis. This review aims to describe the various ways in which we have demonstrated the presence of such T cell clones, and to describe the phenotype of these cells. Finally, the specificities of these clinically important CD8+ T cell populations will be discussed in the context of immunotherapy.

Dendritic cell-based therapeutic vaccination against myeloma: vaccine formulation determines efficacy against light chain myeloma

Multiple myeloma is an incurable plasma cell malignancy. Immunotherapy in myeloma patients had limited success to date. We have previously demonstrated that dendritic cells (DCs) pulsed with autologous Ig Id induced Id-reactive CD8(+) T cells and protection against a myeloma tumor challenge. In this work, we studied the therapeutic efficacy of chemotherapy combined with different formulations of DC-based vaccines in mice bearing large plasma cell tumors. The comparative study demonstrated that s.c. injection of DCs loaded with Id coupled to keyhole limpet hemocyanin, s.c. injection of DCs loaded with irradiated tumor cells, and intratumoral injection of naive DCs were similarly effective in mediating tumor regression and long-term survival. However, whereas the Id-keyhole limpet hemocyanin-DC vaccine was inefficient against myeloma cells that lost expression of the Ig H chain, intratumoral injection of naive DCs and s.c. injection of DCs loaded with irradiated tumor cells were highly effective against cells producing L chains only. This may be of particular importance for patients with L chain myeloma. Given that T cells respond primarily to peptides derived from H chain CDRs, attempts to treat L chain disease with myeloma protein-pulsed DCs may be futile. Vaccination with tumor cell-loaded DCs may, however, induce an effective antitumor response.

Binding of monosodium urate crystals with idiotype protein efficiently promote dendritic cells to induce cytotoxic T cells

Monosodium urate (MSU) crystals have been reported to evoke specific cell immunity and to work as an adjuvant in a mouse model. The crystals also have another unique characteristic to bind with positively charged proteins, which could help to deliver some antigens into human dendritic cells (DC). We focused on the application of MSU crystals as not only an adjuvant but also as a carrier of positively charged antigenic protein to induce human cytotoxic T cells (CTL) efficiently in vitro. We selected human leukocyte antigen (HLA)-A2 expressing the multiple myeloma IM-9 cell line and its product idiotype (Id) protein as one of the best pairs of target cells and positively charged tumor-specific antigen, respectively. Following the sensitization of DC derived from HLA-A2-positive volunteers pulsed with tumor-specific monoclonal immunoglobulin G-Fab fragments (IM-9 Fab) attached to MSU crystals, the DC-stimulated CD8(+) T cells killed significantly more target cells (40.1 +/- 1.7%) than those stimulated by DC pulsed with MSU crystals alone (6.2 +/- 8.6%, P < 0.01) or IM-9 Fab alone (4.7 +/- 8.1%, P < 0.01). These cytotoxic effects of the DC-stimulated CD8(+) cells were reduced when MSU crystals were precoated with fetal bovine serum. In addition, we confirmed that MSU crystals facilitated human DC to express the maturation marker, CD83 and deliver (Fab')(2), attaching to the crystals by flow cytometer analysis. MSU crystals have distinct advantages of a protein carrier binding with positively charged proteins and delivering antigenic protein into DC, as well as an adjuvant promoting DC maturation and inducing CTL.

Activation of autologous leukemia-specific T cells in acute myeloid leukemia: monocyte-derived dendritic cells cocultured with leukemic blasts compared with leukemia-derived dendritic cells

In acute myeloid leukemia (AML) blasts can be differentiated into dendritic cell (DC) like cells (AML-DC). These cells have a mature DC-like phenotype, are strong stimulators in mixed leukocyte reactions and can be used to generate leukemia-specific cytotoxic T cells. However, recent reports about naturally existing leukemic DC with immunoregulatory dysfunctions in peripheral blood of AML patients caused concerns about the use of AML-DC for therapeutic purposes. Systematic intra-individual comparisons between AML-DC and non-leukemic DC derived from monocytes (MoDC) in AML patients are missing. Thus, we investigated the ability to generate MoDC from peripheral blood of 17 AML patients in first remission and their functional integrity to stimulate leukemia-specific T cells by simple coculture with leukemic blasts. Phenotypic analysis of AML-DC and MoDC from the same individual patients revealed that MoDC exhibit a more homogenous mature DC phenotype. Additionally, functional analysis demonstrated the ability of remission MoDC to activate autologous leukemia-specific T cells in 11 of 12 patients, whereas AML-DC led to a specific T cell activation in four of eight patients. The presented findings might have impact on the design of further therapeutic studies using autologous antigen-presenting cells.