Engineering WT1-Encoding mRNA to Increase Translational Efficiency in Dendritic Cells.

Dendritic cells (DCs) are the orchestrators of the immune system and are frequently used in clinical trials in order to boost the immune system in cancer patients. Among several available techniques for DC modification, mRNA electroporation is an interesting technique due to the favorable characteristics of mRNA. Antigen expression level and duration can be increased by multiple optimizations of an antigen-encoding mRNA template. Here, we describe different molecular modifications to a WT1-encoding mRNA construct in order to increase antigen expression and the subsequent introduction of mRNA into DCs.

Disease progression in recurrent glioblastoma patients treated with the VEGFR inhibitor axitinib is associated with increased regulatory T cell numbers and T cell exhaustion.

BACKGROUND: Recurrent glioblastoma is associated with a poor overall survival. Antiangiogenic therapy results in a high tumor response rate but has limited impact on survival. Immunotherapy has emerged as an efficient treatment modality for some cancers, and preclinical evidence indicates that anti-VEGF(R) therapy can counterbalance the immunosuppressive tumor microenvironment. METHODS: We collected peripheral blood mononuclear cells (PBMC) of patients with recurrent glioblastoma treated in a randomized phase II clinical trial comparing the effect of axitinib with axitinib plus lomustine and analyzed the immunophenotype of PBMC, the production of cytokines and expression of inhibitory molecules by circulating T cells. RESULTS: PBMC of 18 patients were collected at baseline and at 6 weeks after initiation of study treatment. Axitinib increased the number of naïve CD8(+) T cells and central memory CD4(+) and CD8(+) T cells and reduced the TIM3 expression on CD4(+) and CD8(+) T cells. Patients diagnosed with progressive disease on axitinib had a significantly increased number of regulatory T cells and an increased level of PD-1 expression on CD4(+) and CD8(+) T cells. In addition, reduced numbers of cytokine-producing T cells were found in progressive patients as compared to patients responding to treatment. CONCLUSION: Our results suggest that axitinib treatment in patients with recurrent glioblastoma has a favorable impact on immune function. At the time of acquired resistance to axitinib, we documented further enhancement of a preexisting immunosuppression. Further investigations on the role of axitinib as potential combination partner with immunotherapy are necessary.

Current status and perspectives of immune-based therapies for hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a frequent cancer with a high mortality. For early stage cancer there are potentially curative treatments including local ablation, resection and liver transplantation. However, for more advanced stage disease, there is no optimal treatment available. Even in the case of a "curative" treatment, recurrence or development of a new cancer in the precancerous liver is common. Thus, there is an urgent need for novel and effective (adjuvant) therapies to treat HCC and to prevent recurrence after local treatment in patients with HCC. The unique immune response in the liver favors tolerance, which remains a genuine challenge for conventional immunotherapy in patients with HCC. However, even in this "immunotolerant" organ, spontaneous immune responses against tumor antigens have been detected, although they are insufficient to achieve significant tumor death. Local ablation therapy leads to immunogenic tumor cell death by inducing the release of massive amounts of antigens, which enhances spontaneous immune response. New immune therapies such as dendritic cell vaccination and immune checkpoint inhibition are under investigation. Immunotherapy for cancer has made huge progress in the last few years and clinical trials examining the use of immunotherapy to treat hepatocellular carcinoma have shown some success. In this review, we discuss the current status of and offer some perspectives on immunotherapy for hepatocellular carcinoma, which could change disease progression in the near future.

Intratumoral Delivery of TriMix mRNA Results in T-cell Activation by Cross-Presenting Dendritic Cells.

Modulating the activity of tumor-infiltrating dendritic cells (TiDC) provides opportunities for novel cancer interventions. In this article, we report on our study of the uptake of mRNA by CD8α(+) cross-presenting TiDCs upon its intratumoral (i.t.) delivery. We exploited this property to deliver mRNA encoding the costimulatory molecule CD70, the activation stimuli CD40 ligand, and constitutively active Toll-like receptor 4, referred to as TriMix mRNA. We show that TiDCs are reprogrammed to mature antigen-presenting cells that migrate to tumor-draining lymph nodes (TDLN). TriMix stimulated antitumor T-cell responses to spontaneously engulfed cancer antigens, including a neoepitope. We show in various mouse cancer models that i.t. delivery of TriMix mRNA results in systemic therapeutic antitumor immunity. Finally, we show that the induction of antitumor responses critically depends on TiDCs, whereas it only partially depends on TDLNs. As such, we provide a platform and a mechanistic rationale for the clinical testing of i.t. administration of TriMix mRNA.

mRNA-based dendritic cell vaccines.

Cancer immunotherapy has been proposed as a powerful treatment modality. Active immunotherapy aspires to stimulate the patient's immune system, particularly T cells. These cells can recognize and kill cancer cells and can form an immunological memory. Dendritic cells (DCs) are the professional antigen-presenting cells of our immune system. They take up and process antigens to present them to T cells. Consequently, DCs have been investigated as a means to stimulate cancer-specific T-cell responses. An efficient strategy to program DCs is the use of mRNA, a well-defined and safe molecule that can be easily generated at high purity. Importantly, vaccines consisting of mRNA-modified DCs showed promising results in clinical trials. Therefore, we will introduce cancer immunotherapy and DCs and give a detailed overview on the application of mRNA to generate cancer-fighting DC vaccines.

Long-term clinical outcome of melanoma patients treated with messenger RNA-electroporated dendritic cell therapy following complete resection of metastases.

PURPOSE: Melanoma patients with a high risk of recurrence may benefit from immunotherapy with mRNA-electroporated autologous monocyte-derived dendritic cells (DCs). Further benefit may be found in combining DC-therapy with interferon alfa-2b. PATIENTS AND METHODS: The long-term clinical outcome of AJCC stage III/IV melanoma patients who had no evidence of disease at the time of treatment with autologous mRNA-electroporated DCs in a single-center pilot clinical trial was analyzed. Antigen loading was accomplished by co-electroporation of mRNA encoding a fusion protein between MAGE-A1, -A3, -C2, Tyrosinase, MelanA/MART-1, or gp100, and an HLA class II-targeting sequence. DCs were administered by 4-6 bi-weekly intradermal injections. IFN-α-2b (5 MIU TIW) was initiated either at recurrence (cohort 1), concomitant with DCs (cohorts 2 and 3), or following the fourth DC administration (cohort 4). RESULTS: Thirty melanoma patients were recruited between April 2006 and June 2009. DC-related adverse events included grade 2 local injection site reactions in all patients, grade 2 fever and flu-like symptoms in one patient, and skin depigmentation in seven patients. After a median follow-up of over 6 years, the median relapse-free survival is 22 months (95% CI 12-32 months). Twelve patients have died. The median overall survival has not been reached; the 2-year and 4-year survival rates are 93 and 70%, respectively. CONCLUSIONS: Adjuvant therapy following the resection of melanoma metastases with autologous mRNA-electroporated DCs, combined with interferon alfa-2b, is tolerable and results in encouraging long-term overall survival rates justifying further evaluation in a randomized clinical trial.

Single-step antigen loading and maturation of dendritic cells through mRNA electroporation of a tumor-associated antigen and a TriMix of costimulatory molecules.

Dendritic cells (DC) are key players in several types of cancer vaccines. Large numbers of DC can easily be generated in closed systems from the monocyte fraction of the peripheral blood. They are the professional antigen-presenting cells, and electroporation of mRNA-encoding tumor antigens is a very efficient and a relatively simple way to load the DC with antigen. The co-electroporation of a tumor antigen of choice and the combination of 3 costimulatory molecules, including CD70, caTLR4, and CD40L (TriMix-DC), leads to fully potent antigen-presenting DC able to generate a broad immune response.Here we describe the in vitro transcription of the mRNA and the subsequent generation and electroporation of autologous DC used for the treatment of melanoma patients.

Design of an Optimized Wilms' Tumor 1 (WT1) mRNA Construct for Enhanced WT1 Expression and Improved Immunogenicity In Vitro and In Vivo.

Tumor antigen-encoding mRNA for dendritic cell (DC)-based vaccination has gained increasing popularity in recent years. Within this context, two main strategies have entered the clinical trial stage: the use of mRNA for ex vivo antigen loading of DCs and the direct application of mRNA as a source of antigen for DCs in vivo. DCs transfected with mRNA-encoding Wilms' tumor 1 (WT1) protein have shown promising clinical results. Using a stepwise approach, we re-engineered a WT1 cDNA-carrying transcription vector to improve the translational characteristics and immunogenicity of the transcribed mRNA. Different modifications were performed: (i) the WT1 sequence was flanked by the lysosomal targeting sequence of dendritic cell lysosomal-associated membrane protein to enhance cytoplasmic expression; (ii) the nuclear localization sequence (NLS) of WT1 was deleted to promote shuttling from the nucleus to the cytoplasm; (iii) the WT1 DNA sequence was optimized in silico to improve translational efficiency; and (iv) this WT1 sequence was cloned into an optimized RNA transcription vector. DCs electroporated with this optimized mRNA showed an improved ability to stimulate WT1-specific T-cell immunity. Furthermore, in a murine model, we were able to show the safety, immunogenicity, and therapeutic activity of this optimized mRNA. This work is relevant for the future development of improved mRNA-based vaccine strategies K.Molecular Therapy-Nucleic Acids (2013) 2, e134; doi:10.1038/mtna.2013.54; published online 19 November 2013.

Characterization of CD8+ T-cell responses in the peripheral blood and skin injection sites of melanoma patients treated with mRNA electroporated autologous dendritic cells (TriMixDC-MEL).

Treatment of melanoma patients with mRNA electroporated dendritic cells (TriMixDC-MEL) stimulates T-cell responses against the presented tumor-associated antigens (TAAs). In the current clinical trials, melanoma patients with systemic metastases are treated, requiring priming and/or expansion of preexisting TAA-specific T cells that are able to migrate to both the skin and internal organs. We monitored the presence of TAA-specific CD8(+) T cells infiltrating the skin at sites of intradermal TriMixDC-MEL injection (SKILs) and within the circulation of melanoma patients treated in two clinical trials. In 10 out of fourteen (71%) patients screened, CD8(+) T cells recognizing any of the four TAA presented by TriMixDC-MEL cellular vaccine were found in both compartments. In total, 30 TAA-specific T-cell responses were detected among the SKILs and 29 among peripheral blood T cells, of which 24 in common. A detailed characterization of the antigen specificity of CD8(+) T-cell populations in four patients indicates that the majority of the epitopes detected were only recognized by CD8(+) T cells derived from either skin biopsies or peripheral blood, indicating that some compartmentalization occurs after TriMix-DC therapy. To conclude, functional TAA-specific CD8(+) T cells distribute both to the skin and peripheral blood of patients after TriMixDC-MEL therapy.

Dendritic cells loaded with mRNA encoding full-length tumor antigens prime CD4+ and CD8+ T cells in melanoma patients.

It is generally thought that dendritic cells (DCs) loaded with full-length tumor antigen could improve immunotherapy by stimulating broad T-cell responses and by allowing treatment irrespective of the patient's human leukocyte antigen (HLA) type. To investigate this, we determined the specificity of T cells from melanoma patients treated with DCs loaded with mRNA encoding a full-length tumor antigen fused to a signal peptide and an HLA class II sorting signal, allowing presentation in HLA class I and II. In delayed-type hypersensitive (DTH)-biopsies and blood, we found functional CD8(+) and CD4(+) T cells recognizing novel treatment-antigen-derived epitopes, presented by several HLA types. Additionally, we identified a CD8(+) response specific for the signal peptide incorporated to elicit presentation by HLA class II and a CD4(+) response specific for the fusion region of the signal peptide and one of the antigens. This demonstrates that the fusion proteins contain newly created immunogenic sequences and provides evidence that ex vivo-generated mRNA-modified DCs can induce effector CD8(+) and CD4(+) T cells from the naive T-cell repertoire of melanoma patients. Thus, this work provides definitive proof that DCs presenting the full antigenic spectrum of tumor antigens can induce T cells specific for novel epitopes and can be administered to patients irrespective of their HLA type.

Preclinical evaluation of TriMix and antigen mRNA-based antitumor therapy.

The use of tumor-associated antigen (TAA) mRNA for therapeutic purposes is under active investigation. To be effective, mRNA vaccines need to deliver activation stimuli in addition to TAAs to dendritic cells (DC). In this study, we evaluated whether intranodal delivery of TAA mRNA together with TriMix, a mix of mRNA encoding CD40 ligand, constitutive active Toll-like receptor 4 and CD70, results in the in situ modification and maturation of DCs, hence, priming of TAA-specific T cells. We showed selective uptake and translation of mRNA in vivo by lymph node resident CD11c(+) cells. This process was hampered by codelivery of classical maturation stimuli but not by TriMix mRNA. Importantly, TriMix mRNA induced a T-cell-attracting and stimulatory environment, including recruitment of antigen-specific CD4(+) and CD8(+) T cells and CTLs against various TAAs. In several mouse tumor models, mRNA vaccination was as efficient in CTL induction and therapy response as vaccination with mRNA-electroporated DCs. Together, our findings suggest that intranodal administration of TAA mRNA together with mRNA encoding immunomodulating molecules is a promising vaccination strategy.

Epitope and HLA-type independent monitoring of antigen-specific T-cells after treatment with dendritic cells presenting full-length tumor antigens.

The efficacy of cancer immunotherapy can be improved by treatment with full-length tumor antigen and by combining several antigens. This approach allows the induction of a broad immune response irrespective of the patient's HLA type which at the same time challenges immune monitoring. Also, the number of available lymphocytes is most often limited and minimal in vitro restimulations of the lymphocytes should maintain information about the actual in vivo situation. To overcome these hurdles, we developed a method to measure the CD8(+) and CD4(+) T-cell responses directly ex vivo. Skin biopsies taken from dendritic cell (DC)-induced DTH reactions from melanoma patients participating in a DC-clinical trial served as lymphocyte source. Antigen-specificity of skin infiltrating lymphocytes was investigated by coculture with antigen-presenting autologous B cells and assessed for CD137 upregulation and enhanced cytokine secretion. Using this approach we could detect treatment-specific CD8(+) T-cells without restimulation in vitro. Upregulation of the activation marker CD137 correlated with the upregulation of the lytic marker CD107a. CD137 upregulation by treatment-specific CD4(+) lymphocytes however was more pronounced after antigen-specific in vitro restimulation. Both CD8(+) and CD4(+) lymphocytes could be further expanded using the same B cells as for screening allowing characterization of the recognized antigenic region. In addition, this technique can be extended to detect a broader array of T-cell functions and to monitor a large cohort of patients. We believe that this approach of direct ex vivo monitoring, irrespective of the patient's HLA-type or the recognized peptide, and using a limited number of lymphocytes is a valuable tool in the immune monitoring of current cellular immunotherapies.

Intravenous and intradermal TriMix-dendritic cell therapy results in a broad T-cell response and durable tumor response in a chemorefractory stage IV-M1c melanoma patient.

Dendritic cells (DCs) electroporated with mRNA encoding CD70, CD40L and a constitutively active toll-like receptor 4 (TriMix-DC) have an increased T-cell stimulatory capacity. In a prospective phase IB clinical trial, we treated melanoma patients with intradermal and intravenous injections of autologous TriMix-DC co-electroporated with mRNA encoding full-length MAGE-A3, MAGE-C2, tyrosinase and gp100. We report here the immunological and clinical results obtained in one patient with a particularly favorable outcome. This patient had stage IV-M1c melanoma with documented progression during dacarbazine chemotherapy and received 5 TriMix-DC injections. Following DC therapy, a broad CD8(+) T-cell response against multiple epitopes derived from all four treatment antigens was found in the blood and among T cells derived from DTH biopsy. In addition, CD4(+) T cells recognizing different MAGE-A3-derived epitopes were detected in DTH-derived cells. A spontaneous anti-MAGE-C2 CD8(+) T-cell response was present prior to TriMix-DC therapy and increased during treatment. The tumor response was assessed with 18-fluorodeoxyglucose-positron emission/computed tomography. We documented a partial tumor response according to RECIST criteria with a marked reduction in (18)F-FDG-uptake by lung, lymph node and bone metastases. The patient remains free from progression after 12 months of follow-up. This case report indicates that administration of autologous TriMix-DC by the combined intradermal and intravenous route can mediate a durable objective tumor response accompanied by a broad T-cell response in a chemorefractory stage IV-M1c melanoma patient.

Therapeutic vaccination with an autologous mRNA electroporated dendritic cell vaccine in patients with advanced melanoma.

The immunostimulatory capacity of dendritic cells is improved by co-electroporation with mRNA encoding CD40 ligand, constitutively active toll-like receptor 4, and CD70 (TriMix-DC). This pilot clinical trial evaluated the feasibility, safety, and immunogenicity of a therapeutic vaccination containing autologous TriMix-DC co-electroporated with mRNA encoding a human leukocyte antigen class II-targeting signal linked to 1 of 4 melanoma-associated antigens (MAGE-A3, MAGE-C2, tyrosinase, and gp100) in patients with advanced melanoma. Thirty-five American Joint Committee on Cancer stage III/IV melanoma patients received autologous TriMix-DC (4 administrations 2 weeks apart). Immune monitoring was performed by evaluating skin biopsies of delayed type IV hypersensitivity (DTH) reactions for presence of vaccinal antigen-specific DTH-infiltrating lymphocytes (DIL). Thereafter, patients could receive interferon-alpha-2b (IFN-α-2b) 5 MU subcutaneously 3 times weekly and additional TriMix-DC every 8 weeks. TriMix-DC-related adverse events comprised grade 2 local injection site reactions (all patients), and grade 2 fever and lethargy (2 patients). Vaccinal antigen-specific DIL were found in 0/6 patients tested at vaccine initiation and in 12/21 (57.1%) assessed after the fourth vaccine. A positive postvaccination DTH test correlated with IL-12p70 secretion capacity of TriMix-DC. No objective responses to TriMix-DC alone were seen according to RECIST. Twenty-nine patients received IFN-α-2b after the fourth vaccine without unexpected adverse events. During TriMix-DC/IFN-α-2b combination therapy, 1 partial response and 5 stable disease (disease control of >6 months with regression of metastases) were observed in 17 patients with evaluable disease at baseline. In conclusion, this study demonstrated that therapeutic vaccination with autologous TriMix-DC is feasible, safe, and immunogenic and can be combined with sequential IFN-α-2b.