Dendritic cell vaccines in melanoma: From promise to proof?

Langerhans Cells in Sentinel Lymph Nodes from Melanoma Patients

BACKGROUND

Langerhans cells (LCs) are professional Dendritic Cells (DCs) involved in immunoregulatory functions. At the skin level, LCs are immature. In response to tissue injuries, they migrate to regional Lymph Nodes (LNs), reaching a full maturation state. Then, they become effective antigen-presenting cells (APCs) that induce anti-cancer responses. Notably, melanoma patients present several DC alterations in the Sentinel Lymph Node (SLN), where primary antitumoral immunity is generated. LCs are the most represented DCs subset in melanoma SLNs and are expected to play a key role in the anti-melanoma response. With this paper, we aim to review the current knowledge and future perspectives regarding LCs and melanoma.

METHODS

A systematic review was carried out according to the PRISMA statement using the PubMed (MEDLINE) library from January 2004 to January 2024, searching for original studies discussing LC in melanoma.

RESULTS

The final synthesis included 15 articles. Several papers revealed significant LCs-melanoma interactions.

CONCLUSIONS

Melanoma immune escape mechanisms include SLN LC alterations, favoring LN metastasis arrival/homing and melanoma proliferation. The SLN LCs of melanoma patients are defective but not irreversibly, and their function may be restored by appropriate stimuli. Thus, LCs represent a promising target for future immunotherapeutic strategies and cancer vaccines.

Cryomicroneedles for transdermal cell delivery

Cell therapies for the treatment of skin disorders could benefit from simple, safe and efficient technology for the transdermal delivery of therapeutic cells. Conventional cell delivery by hypodermic-needle injection is associated with poor patient compliance, requires trained personnel, generates waste and has non-negligible risks of injury and infection. Here, we report the design and proof-of-concept application of cryogenic microneedle patches for the transdermal delivery of living cells. The microneedles are fabricated by stepwise cryogenic micromoulding of cryogenic medium with pre-suspended cells, and can be easily inserted into porcine skin and dissolve after deployment of the cells. In mice, cells delivered by the cryomicroneedles retained their viability and proliferative capability. In mice with subcutaneous melanoma tumours, the delivery of ovalbumin-pulsed dendritic cells via the cryomicroneedles elicited higher antigen-specific immune responses and led to slower tumour growth than intravenous and subcutaneous injections of the cells. Biocompatible cryomicroneedles may facilitate minimally invasive cell delivery for a range of cell therapies.

Plasmacytoid dendritic cells and their therapeutic activity in cancer

In the last decade several studies provided evidence that plasmacytoid dendritic cells (pDCs) infiltrate human neoplasms with poor prognosis. However, the role of tumor-associated pDCs remains controversial. Various studies indicate that pDCs play an immuno-suppressive role and facilitate tumor progression in both animal models and humans. In contrast, others found that the presence of activated tumor-associated pDCs results in tumor regression in mice. Given these findings, understanding pDC function in tumor biology is an important necessity and may pave the way for novel therapeutic strategies to fight malignancies.

Oncolytic Rhabdovirus Vaccine Boosts Chimeric Anti-DEC205 Priming for Effective Cancer Immunotherapy

Prime-boost vaccination employing heterologous viral vectors encoding an antigen is an effective strategy to maximize the antigen-specific immune response. Replication-deficient adenovirus serotype 5 (Ad5) is currently being evaluated clinically in North America as a prime in conjunction with oncolytic rhabdovirus Maraba virus (MG1) as a boost. The use of an oncolytic rhabdovirus encoding a tumor antigen elicits a robust anti-cancer immune response and extends survival in murine models of cancer. Given the prevalence of pre-existing immunity to Ad5 globally, we explored the potential use of DEC205-targeted antibodies as an alternative agent to prime antigen-specific responses ahead of boosting with an oncolytic rhabdovirus expressing the same antigen. We found that a prime-boost vaccination strategy, consisting of an anti-DEC205 antibody fused to the model antigen ovalbumin (OVA) as a prime and oncolytic rhabdovirus-OVA as a boost, led to the formation of a robust antigen-specific immune response and improved survival in a B16-OVA tumor model. Overall, our study shows that anti-DEC205 antibodies fused to cancer antigens are effective to prime oncolytic rhabdovirus-boosted cancer antigen responses and may provide an alternative for patients with pre-existing immunity to Ad5 in humans.

Vaccination with dendritic cells pulsed ex vivo with gp100 peptide-decorated liposomes enhances the efficacy of anti PD-1 therapy in a mouse model of melanoma

BACKGROUND

Targeting antigens to dendritic cells (DCs) via nanoparticles is a powerful strategy which improves the efficacy of ex vivo antigen-pulsed DC vaccines.

METHODS

In this study, liposomes were first decorated with gp100_25-33 self-antigen and then characterized. Then, DCs were pulsed ex vivo with liposomal gp100 and injected subcutaneously in mice bearing B16F10 established melanoma tumors in combination with anti-PD-1 therapy.

RESULTS

Treatment with liposomal pulsed DC vaccine elicited the strongest anticancer immunity and enhanced intratumoral immune responses based on infiltration of gp100-specific CD4+ and CD8+ T cells to the tumor leading to significant tumor growth regression and prolonged survival rate. Treatment with liposomal pulsed DC vaccine also markedly enhanced specific cytotoxic T lymphocytes (CTL) responses with a significant higher titer of IFN-γ in the spleen. Moreover, a significant increase of PD-1 expressing CD8+ tumor infiltrating lymphocytes (TILs) was detected in tumors.

CONCLUSION

Our results demonstrate an optimum dose of liposomal gp100 significantly increases the efficacy of anti-PD-1 therapy in mice and might be an effective strategy to overcome resistance to anti-PD-1 therapy.

The Tumor Microenvironment Innately Modulates Cancer Progression

Cancer development and progression occurs in concert with alterations in the surrounding stroma. Cancer cells can functionally sculpt their microenvironment through the secretion of various cytokines, chemokines, and other factors. This results in a reprogramming of the surrounding cells, enabling them to play a determinative role in tumor survival and progression. Immune cells are important constituents of the tumor stroma and critically take part in this process. Growing evidence suggests that the innate immune cells (macrophages, neutrophils, dendritic cells, innate lymphoid cells, myeloid-derived suppressor cells, and natural killer cells) as well as adaptive immune cells (T cells and B cells) contribute to tumor progression when present in the tumor microenvironment (TME). Cross-talk between cancer cells and the proximal immune cells ultimately results in an environment that fosters tumor growth and metastasis. Understanding the nature of this dialog will allow for improved therapeutics that simultaneously target multiple components of the TME, increasing the likelihood of favorable patient outcomes.

Personalized Dendritic Cell Vaccines-Recent Breakthroughs and Encouraging Clinical Results

With the advent of combined immunotherapies, personalized dendritic cell (DC)-based vaccination could integrate the current standard of care for the treatment of a large variety of tumors. Due to their proficiency at antigen presentation, DC are key coordinators of the innate and adaptive immune system, and have critical roles in the induction of antitumor immunity. However, despite proven immunogenicity and favorable safety profiles, DC-based immunotherapies have not succeeded at inducing significant objective clinical responses. Emerging data suggest that the combination of DC-based vaccination with other cancer therapies may fully unleash the potential of DC-based cancer vaccines and improve patient survival. In this review, we discuss the recent efforts to develop innovative personalized DC-based vaccines and their use in combined therapies, with a particular focus on ovarian cancer and the promising results of mutanome-based personalized immunotherapies.

CD40L coding oncolytic adenovirus allows long-term survival of humanized mice receiving dendritic cell therapy

Dendritic cells (DCs) are crucial players in promoting immune responses. Logically, adoptive DC therapy is a promising approach in cancer immunotherapy. One of the major obstacles in cancer immunotherapy in general is the immunosuppressive tumor microenvironment, which hampers the maturation and activation of DCs. Therefore, human clinical outcomes with DC therapy alone have been disappointing. In this study, we use fully serotype 3 oncolytic adenovirus Ad3-hTERT-CMV-hCD40L, expressing human CD40L, to modulate the tumor microenvironment with subsequently improved function of DCs. We evaluated the synergistic effects of Ad3-hTERT-CMV-hCD40L and DCs in the presence of human peripheral blood mononuclear cells ex vivo and in vivo. Tumors treated with Ad3-hTERT-CMV-hCD40L and DCs featured greater antitumor effect compared with unarmed virus or either treatment alone. 100% of humanized mice survived to the end of the experiment, while mice in all other groups died by day 88. Moreover, adenovirally-delivered CD40L induced activation of DCs, leading to induction of Th1 immune responses. These results support clinical trials with Ad3-hTERT-CMV-hCD40L in patients receiving DC therapy.

Therapeutic DNA Vaccines for Human Papillomavirus and Associated Diseases

Human papillomavirus (HPV) has long been recognized as the causative agent of cervical cancer. High-risk HPV types 16 and 18 alone are responsible for over 70% of all cases of cervical cancers. More recently, HPV has been identified as an etiological factor for several other forms of cancers, including oropharyngeal, anogenital, and skin. Thus, the association of HPV with these malignancies creates an opportunity to control these HPV lesions and HPV-associated malignancies through immunization. Strategies to prevent or to therapeutically treat HPV infections have been developed and are still pushing innovative boundaries. Currently, commercial prophylactic HPV vaccines are widely available, but they are not able to control established infections or lesions. As a result, there is an urgent need for the development of therapeutic HPV vaccines, to treat existing infections, and to prevent the development of HPV-associated cancers. In particular, DNA vaccination has emerged as a promising form of therapeutic HPV vaccine. DNA vaccines have great potential for the treatment of HPV infections and HPV-associated cancers due to their safety, stability, simplicity of manufacturability, and ability to induce antigen-specific immunity. This review focuses on the current state of therapeutic HPV DNA vaccines, including results from recent and ongoing clinical trials, and outlines different strategies that have been employed to improve their potencies. The continued progress and improvements made in therapeutic HPV DNA vaccine development holds great potential for innovative ways to effectively treat HPV infections and HPV-associated diseases.

T-cell Landscape in a Primary Melanoma Predicts the Survival of Patients with Metastatic Disease after Their Treatment with Dendritic Cell Vaccines

Tumor-infiltrating lymphocytes appear to be a predictor of survival in many cancers, including cutaneous melanoma. We applied automated multispectral imaging to determine whether density and distribution of T cells within primary cutaneous melanoma tissue correlate with survival of metastatic melanoma patients after dendritic cell (DC) vaccination. CD3(+) T cell infiltration in primary tumors from 77 metastatic melanoma patients was quantified using the ratio of intratumoral versus peritumoral T-cell densities (I/P ratio). Patients with longer survival after DC vaccination had stronger T-cell infiltration than patients with shorter survival in a discovery cohort of 19 patients (P = 0.000026) and a validation cohort of 39 patients (P = 0.000016). I/P ratio was the strongest predictor of survival in a multivariate analysis including M substage and serum lactate dehydrogenase level. To evaluate I/P ratio as a predictive biomarker, we analyzed 19 chemotherapy-treated patients. Longer survival times of DC-vaccinated compared with chemotherapy-treated patients was observed for high (P = 0.000566), but not low (P = 0.154) I/P ratios. In conclusion, T-cell infiltration into primary melanoma is a strong predictor of survival after DC vaccination in metastatic melanoma patients who, on average, started this therapy several years after primary tumor resection. The infiltration remains predictive even after adjustment for late-stage prognostic markers. Our findings suggest that the I/P ratio is a potential predictive biomarker for treatment selection. Cancer Res; 76(12); 3496-506. ©2016 AACR.

Prophylactic vaccines are potent activators of monocyte-derived dendritic cells and drive effective anti-tumor responses in melanoma patients at the cost of toxicity

Dendritic cell (DC)-based immunotherapy is explored worldwide in cancer patients, predominantly with DC matured with pro-inflammatory cytokines and prostaglandin E₂. We studied the safety and efficacy of vaccination with monocyte-derived DC matured with a cocktail of prophylactic vaccines that contain clinical-grade Toll-like receptor ligands (BCG, Typhim, Act-HIB) and prostaglandin E₂ (VAC-DC). Stage III and IV melanoma patients were vaccinated via intranodal injection (12 patients) or combined intradermal/intravenous injection (16 patients) with VAC-DC loaded with keyhole limpet hemocyanin (KLH) and mRNA encoding tumor antigens gp100 and tyrosinase. Tumor antigen-specific T cell responses were monitored in blood and skin-test infiltrating-lymphocyte cultures. Almost all patients mounted prophylactic vaccine- or KLH-specific immune responses. Both after intranodal injection and after intradermal/intravenous injection, tumor antigen-specific immune responses were detected, which coincide with longer overall survival in stage IV melanoma patients. VAC-DC induce local and systemic CTC grade 2 and 3 toxicity, which is most likely caused by BCG in the maturation cocktail. The side effects were self-limiting or resolved upon a short period of systemic steroid therapy. We conclude that VAC-DC can induce functional tumor-specific responses. Unfortunately, toxicity observed after vaccination precludes the general application of VAC-DC, since in DC maturated with prophylactic vaccines BCG appears to be essential in the maturation cocktail.

Combined cytotoxic activity of an infectious, but non-replicative herpes simplex virus type 1 and plasmacytoid dendritic cells against tumour cells

Malignant melanoma is an aggressive tumour of the skin with increasing incidence, frequent metastasis and poor prognosis. At the same time, it is an immunogenic type of cancer with spontaneous regressions. Most recently, the tumoricidal effect of plasmacytoid dendritic cells (pDC) and their capacity to overcome the immunosuppressive tumour microenvironment are being investigated. In this respect, we studied the effect of the infectious, but replication-deficient, herpes simplex virus 1 (HSV-1) d106S vaccine strain, which lacks essential immediate early genes, in pDC co-cultures with 11 melanoma cell lines. We observed a strong cytotoxic activity, inducing apoptotic and necrotic cell death in most melanoma cell lines. The cytotoxic activity of HSV-1 d106S plus pDC was comparable to the levels of cytotoxicity induced by natural killer cells, but required only a fraction of cells with effector : target ratios of 1 : 20 (P < 0·05). The suppressive activity of cell-free supernatants derived from virus-stimulated pDC was significantly neutralized using antibodies against the interferon-α receptor (P < 0·05). In addition to type I interferons, TRAIL and granzyme B contributed to the inhibitory effect of HSV-1 d106S plus pDC to a minor extent. UV-irradiated viral stocks were significantly less active than infectious particles, both in the absence and presence of pDC (P < 0·05), indicating that residual activity of HSV-1 d106S is a major component and sensitizes the tumour cells to interferon-producing pDC. Three leukaemic cell lines were also susceptible to this treatment, suggesting a general anti-tumour effect. In conclusion, the potential of HSV-1 d106S for therapeutic vaccination should be further evaluated in patients suffering from different malignancies.

Tumor cell lysates as immunogenic sources for cancer vaccine design

Autologous dendritic cells (DCs) loaded with tumor-associated antigens (TAAs) are a promising immunological tool for cancer therapy. These stimulate the antitumor response and immunological memory generation. Nevertheless, many patients remain refractory to DC approaches. Antigen (Ag) delivery to DCs is relevant to vaccine success, and antigen peptides, tumor-associated proteins, tumor cells, autologous tumor lysates, and tumor-derived mRNA have been tested as Ag sources. Recently, DCs loaded with allogeneic tumor cell lysates were used to induce a potent immunological response. This strategy provides a reproducible pool of almost all potential Ags suitable for patient use, independent of MHC haplotypes or autologous tumor tissue availability. However, optimizing autologous tumor cell lysate preparation is crucial to enhancing efficacy. This review considers the role of cancer cell-derived lysates as a relevant source of antigens and as an activating factor for ex vivo therapeutic DCs capable of responding to neoplastic cells. These promising therapies are associated with the prolonged survival of advanced cancer patients.

Intranodal vaccination with mRNA-optimized dendritic cells in metastatic melanoma patients

Autologous dendritic cell (DC) therapy is an experimental cellular immunotherapy that is safe and immunogenic in patients with advanced melanoma. In an attempt to further improve the therapeutic responses, we treated 15 patients with melanoma, with autologous monocyte-derived immature DC electroporated with mRNA encoding CD40 ligand (CD40L), CD70 and a constitutively active TLR4 (caTLR4) together with mRNA encoding a tumor-associated antigen (TAA; respectively gp100 or tyrosinase). In addition, DC were pulsed with keyhole limpet hemocyanin (KLH) that served as a control antigen. Production of this DC vaccine with high cellular viability, high expression of co-stimulatory molecules and MHC class I and II and production of IL-12p70, was feasible in all patients. A vaccination cycle consisting of three vaccinations with up to 15×106 DC per vaccination at a biweekly interval, was repeated after 6 and 12 months in the absence of disease progression. mRNA-optimized DC were injected intranodally, because of low CCR7 expression on the DC, and induced de novo immune responses against control antigen. T cell responses against tyrosinase were detected in the skin-test infiltrating lymphocytes (SKIL) of two patients. One mixed tumor response and two durable tumor stabilizations were observed among 8 patients with evaluable disease at baseline. In conclusion, autologous mRNA-optimized DC can be safely administered intranodally to patients with metastatic melanoma but showed limited immunological responses against tyrosinase and gp100.

Favorable overall survival in stage III melanoma patients after adjuvant dendritic cell vaccination

Melanoma patients with regional metastatic disease are at high risk for recurrence and metastatic disease, despite radical lymph node dissection (RLND). We investigated the immunologic response and clinical outcome to adjuvant dendritic cell (DC) vaccination in melanoma patients with regional metastatic disease who underwent RLND with curative intent. In this retrospective study, 78 melanoma patients with regional lymph node metastasis who underwent RLND received autologous DCs loaded with gp100 and tyrosinase and were analyzed for functional tumor-specific T cell responses in skin-test infiltrating lymphocytes. The study shows that adjuvant DC vaccination in melanoma patients with regional lymph node metastasis is safe and induced functional tumor-specific T cell responses in 71% of the patients. The presence of functional tumor-specific T cells was correlated with a better 2-year overall survival (OS) rate. OS was significantly higher after adjuvant DC vaccination compared to 209 matched controls who underwent RLND without adjuvant DC vaccination, 63.6 mo vs. 31.0 mo (p = 0.018; hazard ratio 0.59; 95%CI 0.42-0.84). Five-year survival rate increased from 38% to 53% (p < 0.01). In summary, in melanoma patients with regional metastatic disease, who are at high risk for recurrence and metastatic disease after RLND, adjuvant DC vaccination is well tolerated. It induced functional tumor-specific immune responses in the majority of patients and these were related to clinical outcome. OS was significantly higher compared to matched controls. A randomized clinical trial is needed to prospectively validate the efficacy of DC vaccination in the adjuvant setting.

Therapeutic antitumor efficacy of tumor-derived autophagosome (DRibble) vaccine on head and neck cancer

Purpose

Vaccines play important roles in antitumor biotherapy. Autophagy in tumor cells plays a critical role in depredating proteins, including tumor-specific antigens and tumor-associated antigens. We aimed to induce and collect tumor-derived autophagosomes (DRibbles) from tumor cells as a novel antitumor vaccine by inhibiting the functions of proteasomes and lysosomes.

Materials and methods

DRibbles were prepared and their morphological and autophagic properties characterized. Dendritic cells (DCs) generated from the bone marrow monocytes of mice were cocultured with DRibbles, then surface molecules of DCs and B cells, as well as apoptosis of DCs, were determined by flow cytometry. Meanwhile, functional properties of the DRibble-DCs were examined by mixed lymphocyte reactions and animal experiments.

Results

The diameter of autophagic nanoparticles with spherical and double-membrane structure was between 200 nm and 500 nm. DRibbles resulted in the upregulation of costimulatory molecules CD40 and CD86 as well as major histocompatibility complex (MHC)-I molecules on DCs, but not MHC-II. The expressions of CD40, CD80, and CD86 and that of MHC-II molecules on B cells were also upregulated. Moreover, suppression of tumor growth and lifetime prolongation was observed in DRibble-DC-vaccinated tumor-bearing mice.

Conclusion

Our results demonstrate that naïve T cells can be activated effectively by DC cross-presenting antigens on upregulated MHC-I, suggesting that DRibbles be deployed as an effective antitumor vaccine for head and neck cancer immunotherapy in clinical trials.

Antibodies targeting Clec9A promote strong humoral immunity without adjuvant in mice and non-human primates

Targeting antigens to dendritic cell (DC) surface receptors using antibodies has been successfully used to generate strong immune responses and is currently in clinical trials for cancer immunotherapy. Whilst cancer immunotherapy focuses on the induction of CD8(+) T-cell responses, many successful vaccines to pathogens or their toxins utilize humoral immunity as the primary effector mechanism. Universally, these approaches have used adjuvants or pathogen material that augment humoral responses. However, adjuvants are associated with safety issues. One approach, successfully used in the mouse, to generate strong humoral responses in the absence of adjuvant is to target antigen to Clec9A, also known as DNGR-1, a receptor on CD8α(+) DCs. Here, we address two issues relating to clinical application. First, we address the issue of variable adjuvant-dependence for different antibodies targeting mouse Clec9A. We show that multiple sites on Clec9A can be successfully targeted, but that strong in vivo binding and provision of suitable helper T cell determinants was essential for efficacy. Second, we show that induction of humoral immunity to CLEC9A-targeted antigens is extremely effective in nonhuman primates, in an adjuvant-free setting. Our findings support extending this vaccination approach to humans and offer important insights into targeting design.

Restoring immunosurveillance by dendritic cell vaccines and manipulation of the tumor microenvironment

Cancer cells evolve from normal cells throughout life and are usually recognized by our immune system and destroyed, a process called immunosurveillance. Unfortunately, in some instances cancer cells paralyze our immune system, resulting in outgrowth and spreading of the tumor. Understanding the complexity of immunomodulation by tumors is important for the development of therapeutical strategies. Nowadays, various approaches have been developed to enhance anti-tumor immune responses and abrogate the immune dampening effect of the tumor and its surrounding environment, including dendritic cell-based vaccines, therapies to counteract myeloid derived suppressor cell function within the tumor and antagonists of inhibitory signaling pathways to overcome 'immune checkpoints'. The challenge is now to find the right combination of immune based therapies to fully restore immune function and provide a more efficacious and enduring anti-tumor response.

Tracking targeted bimodal nanovaccines: immune responses and routing in cells, tissue, and whole organism

Dendritic cells (DCs) are the most potent antigen-presenting cells (APCs), involved in the induction of immunity and currently exploited for antitumor immunotherapies. An optimized noninvasive imaging modality capable of determining and quantifying DC-targeted nanoparticle (NP) trajectories could provide valuable information regarding therapeutic vaccine outcome. Here, targeted poly(d,l-lactide-co-glycolide) nanoparticles (PLGA NPs) recognizing DC receptors were equipped with superparamagnetic iron oxide particles (SPIO) or gold nanoparticles with fluorescently labeled antigen. The fluorescent label allowed for rapid analysis and quantification of DC-specific uptake of targeted PLGA NPs in comparison to uptake by other cells. Transmission electron microscopy (TEM) showed that a fraction of the encapsulated antigen reached the lysosomal compartment of DCs, where SPIO and gold were already partially released. However, part of the PLGA NPs localized within the cytoplasm, as confirmed by confocal microscopy. DCs targeted with NPs carrying SPIO or fluorescent antigen were detected within lymph nodes as early as 1 h after injection by magnetic resonance imaging (MRI). Despite the fact that targeting did not markedly affect PLGA NP biodistribution on organism and tissue level, it increased delivery of NPs to DCs residing in peripheral lymph nodes and resulted in enhanced T cell proliferation. In conclusion, two imaging agents within a single carrier allows tracking of targeted PLGA NPs at the subcellular, cellular, and organismal levels, thereby facilitating the rational design of in vivo targeted vaccination strategies.

Direct type I IFN but not MDA5/TLR3 activation of dendritic cells is required for maturation and metabolic shift to glycolysis after poly IC stimulation

Type I interferons (IFNs) play an important role in direct antiviral defense as well as linking the innate and adaptive immune responses. On dendritic cells (DCs), IFNs facilitate their activation and contribute to CD8(+) and CD4(+) T cell priming. However, the precise molecular mechanism by which IFNs regulate maturation and immunogenicity of DCs in vivo has not been studied in depth. Here we show that, after in vivo stimulation with the TLR ligand poly IC, IFNs dominate transcriptional changes in DCs. In contrast to direct TLR3/mda5 signaling, IFNs are required for upregulation of all pathways associated with DC immunogenicity. In addition, metabolic pathways, particularly the switch from oxidative phosphorylation to glycolysis, are also regulated by IFNs and required for DC maturation. These data provide evidence for a metabolic reprogramming concomitant with DC maturation and offer a novel mechanism by which IFNs modulate DC maturation.

Tumor antigen-/cytokine-pulsed dendritic cells in therapy against lymphoma

Adoptive cell therapy using dendritic cells (DCs) is a strategy to deliver tumor antigens in cancer immunotherapy. Co-delivery of antigens to DC with essential components like genes encoding cytokines, chemokines, and other molecules or stimulation with recombinant cytokines is a potential method for designing an effective tumor vaccine protocol. Here, we describe the stimulation of purified splenic- or bone marrow-derived DC with recombinant interleukin-15 (IL-15) in the presence of intact soluble antigen from metastatic lymphoma tumor cells in an experimental animal model.

The use of dendritic cells for peptide-based vaccination in cancer immunotherapy

Effective antitumor immunity requires the generation and persistence of functional tumor-specific T-cell responses. Among the critical factors that often control these responses is how the antigen is delivered and presented to T cells. The use of peptide-based vaccination has been found to be a promising means to induce antitumor T-cell responses but with limited effects even if the peptide is co-delivered with a potent adjuvant. This limited response could be due to cancer-induced dysfunction in dendritic cells (DC), which play a central role in shaping the quantity and quality of antitumor immunity. Therefore, DC-based peptide delivery of tumor antigen is becoming a potential approach in cancer immunotherapy. In this approach, autologous DC are generated from their precursors in bone marrow or peripheral blood mononuclear cells, loaded with tumor antigen(s) and then infused back to the tumor-bearing host in about 7 days. This DC-based vaccination can act as an antigen delivery vehicle as well as a potent adjuvant, resulting in measurable antitumor immunity in several cancer settings in preclinical and clinical studies. This chapter focuses on DC-based vaccination and how this approach can be more efficacious in cancer immunotherapy.Effective antitumor immunity requires the generation and persistence of functional tumor-specific T-cell responses. Among the critical factors that often control these responses is how the antigen is delivered and presented to T cells. The use of peptide-based vaccination has been found to be a promising means to induce antitumor T-cell responses but with limited effects even if the peptide is co-delivered with a potent adjuvant. This limited response could be due to cancer-induced dysfunction in dendritic cells (DC), which play a central role in shaping the quantity and quality of antitumor immunity. Therefore, DC-based peptide delivery of tumor antigen is becoming a potential approach in cancer immunotherapy. In this approach, autologous DC are generated from their precursors in bone marrow or peripheral blood mononuclear cells, loaded with tumor antigen(s) and then infused back to the tumor-bearing host in about 7 days. This DC-based vaccination can act as an antigen delivery vehicle as well as a potent adjuvant, resulting in measurable antitumor immunity in several cancer settings in preclinical and clinical studies. This chapter focuses on DC-based vaccination and how this approach can be more efficacious in cancer immunotherapy.

CD8(+) T-cell priming and boosting: more antigen-presenting DC, or more antigen per DC?

RNA transfection is a standard method to load dendritic cells (DC) with antigen for therapeutic cancer vaccination. While electroporation yields high transfection efficiency and satisfying expression levels, lipofection results in only few cells expressing high amounts of antigen. We compared antigen loading of human monocyte-derived DC by MelanA RNA electroporation and lipofection. No differences in phenotype or migrational capacity were detected, but lipofected DC induced stronger cytokine secretion by antigen-specific T cells and were superior in priming and boosting of MelanA-specific CD8(+) T cells. Interestingly, T cells stimulated with the differently transfected DC did not differ in their functional avidity. To determine whether the amount of antigen per cell is indeed responsible for the superiority of the lipofected DC, we increased the amount of MelanA RNA fivefold and mixed those DC with mock-electroporated ones to mimic the antigen distribution of lipofected cells. This significantly improved the stimulatory capacity, indicating that indeed the amount of antigen per cell seems to be the responsible feature for the observed superiority of lipofected DCs. These data suggest that a few DC that express high amounts of antigen are more immunogenic than many DC expressing lower amounts, although this needs to be tested in a two-armed immunogenicity trial.

Preparation of tumor antigen-loaded mature dendritic cells for immunotherapy

While clinical studies have established that antigen-loaded DC vaccines are safe and promising therapy for tumors, their clinical efficacy remains to be established. The method described below, prepared in accordance with Good Manufacturing Process (GMP) guidelines, is an optimization of the most common ex vivo preparation method for generating large numbers of DCs for clinical studies. Our method utilizes the synthetic TLR 3 agonist Polyinosinic-Polycytidylic Acid-poly-L-lysine Carboxymethylcellulose (Poly-ICLC) to stimulate the DCs. Our previous study established that Poly-ICLC is the most potent individual maturation stimulus for human DCs as assessed by an upregulation of CD83 and CD86, induction of interleukin-12 (IL-12), tumor necrosis factor (TNF), interferon gamma-induced protein 10 (IP-10), interleukmin 1 (IL-1), and type I interferons (IFN), and minimal interleukin 10 (IL-10) production. DCs are differentiated from frozen peripheral blood mononuclear cells (PBMCs) obtained by leukapheresis. PBMCs are isolated by Ficoll gradient centrifugation and frozen in aliquots. On Day 1, PBMCs are thawed and plated onto tissue culture flasks to select for monocytes which adhere to the plastic surface after 1-2 hr incubation at 37 °C in the tissue culture incubator. After incubation, the lymphocytes are washed off and the adherent monocytes are cultured for 5 days in the presence of interleukin-4 (IL-4) and granulocyte macrophage-colony stimulating factor (GM-CSF) to differentiate to immature DCs. On Day 6, immature DCs are pulsed with the keyhole limpet hemocyanin (KLH) protein which serves as a control for the quality of the vaccine and may boost the immunogenicity of the vaccine. The DCs are stimulated to mature, loaded with peptide antigens, and incubated overnight. On Day 7, the cells are washed, and frozen in 1 ml aliquots containing 4-20 x 10(6) cells using a controlled-rate freezer. Lot release testing for the batches of DCs is performed and must meet minimum specifications before they are injected into patients.

Adjuvant vaccination with melanoma antigen-pulsed dendritic cells in stage III melanoma patients

Dendritic cells may be successfully used to induce in vivo-specific anti-tumor responses when combined with the appropriate antigen in the appropriate context. The purpose of this study was to evaluate efficacy of peptide-loaded DC vaccine in high-risk stage III melanoma patients after lymph node dissection (LND). HLA-A2+, -A1+, or -A3+ melanoma patients (N=22), stage III, N1b-N3, received 5–16 (median: 11) DC vaccines loaded with MHC class-I-restricted melanoma peptides respective to the patient’s haplotype, and with autologous tumor lysate, if available. Vaccinated patients were matched to unvaccinated stage III controls (22 of 869) by sex, number of metastatic lymph nodes, extracapsular involvement, LND type, Breslow stage, and ulceration. Vaccination elicited cutaneous delayed-type hypersensitivity (DTH) or/and IFN-γ-producing CD8+ cell response to melanoma peptides in 15 of 22 patients. Three-year overall survival (OS) rate was 68.2% in the vaccinated group versus 25.7% in the control group, P value accounting for matching: 0.0290. In a Cox regression model, hazard ratio (HR) for death of vaccinated patients was 0.31 [95% confidence interval (CI): 0.10–0.94]. The corresponding values for 3-year disease-free survival rate were 40.9 versus 14.5%, P=0.1083; HR of recurrence for vaccinated, 0.46 (95% CI: 0.18–1.22). There was no grade>1 toxicity. The DC/peptide vaccine was well tolerated and elicited immune responses to melanoma antigens. Vaccinated patients had significantly longer OS after LND than the matched controls, but a significant improvement in the primary endpoint DFS was not achieved.

Importance of helper T-cell activation in dendritic cell-based anticancer immunotherapy

Dendritic cell-based anticancer immunotherapy is feasible, safe and results in the induction of tumor-specific immune responses, at least in a fraction of vaccinated patients. The concomitant activation of cytotoxic and helper T cells, by loading DCs with peptides or electroporating them with the corresponding mRNAs, may further enhance vaccine-induced antitumor responses.

Functional OCT4-specific CD4+ and CD8+ T cells in healthy controls and ovarian cancer patients

The identification of growth and differentiation pathways that are responsible for the proliferation and survival of cancer stem cells (CSCs) has opened avenues for the discovery of novel therapeutic targets. In the initial phase of an anticancer immune response, T cells specific for tumor-associated antigens develop in patients and, at least under selected circumstances, are able to eliminate malignant cells. However, it remains unknown whether CSC-specific T cells are also operational. We found naturally occurring multifunctional CD4⁺ and CD8⁺ T cells specific for the stem cell marker OCT4 among the peripheral blood mononuclear cells (PBMCs) of both healthy individuals and ovarian cancer patients. Moreover, lymphocytes isolated from the ascites of patients affected by ovarian malignancies also contained OCT4-specific T cells. OCT4-reactive CD4⁺ T cells did not produce interferon γ (IFNγ) and IFNγ-inducible protein 10 (IP-10) but were capable of proliferation upon stimulation with dendritic cells (DCs) loaded with an OCT4-derived peptide or OCT4 mRNA. OCT4-reactive CD8⁺ cells did not proliferate in response to a similar challenge, yet produced IP-10 as well as sufficient amounts of IFNγ to induce IP-10 . Furthermore, CD8⁺ cytotoxic T cells were able to release their lysosomal components, as indicated by the mobilization of CD107a. These results demonstrate the existence of anti-CSC specific T cells in ovarian cancer patients.

Simultaneous activation of T helper function can augment the potency of dendritic cell-based cancer immunotherapy

PURPOSE

Simultaneous activation of T helper 1 (Th1) cell function has crucial roles in induction of potent cytotoxic T lymphocyte (CTL) responses in cancer immunotherapy. Here, we investigated whether dendritic cell (DC)-based vaccines loaded with both tumor-associated antigen (TAA)-derived MHC class I and pan-MHC class II peptides could elicit more potent CTL responses through simultaneous activation of Th1 function and reduction in CD4(+) regulatory T (Treg) cell proliferation.

METHODS

C57BL/6 mice bearing LLC1, a mouse Lewis lung cancer cell line, were subcutaneously administered DCs loaded with both LLC-derived MHC class I (MUT1&2) and LLC-unrelated pan-MHC class II (PADRE) peptides (DC-MUT1&2-PADRE). In assays using samples from advanced lung cancer patients, peripheral blood mononuclear cells were stimulated with autologous DCs loaded with both MUC1 MHC class I and PADRE peptides (DC-MUC1-PADRE) in vitro. Subsequently, TAA-specific CTL responses and the population of CD4(+) Treg cells were analyzed.

RESULTS

The population of spleen CD4(+) PADRE-specific cells producing interferon-gamma (IFNγ) was significantly increased by DC-MUT1&2-PADRE administration. Vaccinations with DC-MUT1&2-PADRE decreased the population of CD4(+) Treg cells in spleen and augmented CTL responses, effectively leading to suppression of tumor growth. In assays with human samples, CD4(+) Treg cells were induced less frequently, and MUC1-specific cytotoxicity was enhanced by stimulation with DC-MUC1-PADRE compared with that by stimulation with DC-MUC1 alone.

CONCLUSIONS

Simultaneous activation of Th1 function by DCs loaded with both TAA-derived MHC class I and PADRE peptides augments TAA-specific CTL responses while reducing Treg cell proliferation.

mRNA: From a chemical blueprint for protein production to an off-the-shelf therapeutic

Two decades ago, mRNA became the focus of research in molecular medicine and was proposed as an active pharmaceutical ingredient for the therapy of cancer. In this regard, mRNA has been mainly used for ex vivo modification of antigen-presenting cells (APCs), such as dendritic cells (DCs). This vaccination strategy has proven to be safe, well tolerated and capable of inducing tumor antigen-specific immune responses. Recently, the direct application of mRNA for in situ modification of APCs, hence immunization was shown to be feasible and at least as effective as DC-based immunization in pre-clinical models. It is believed that application of mRNA as an off-the-shelf vaccine represents an important step in the development of future cancer immunotherapeutic strategies. Here, we will discuss the use of ex vivo mRNA-modified DCs and “naked mRNA” for cancer immunotherapy focusing on parameters such as the employed DC subtype, DC activation stimulus and route of immunization. In addition, we will provide an overview on the clinical trials published so far, trying to link their outcome to the aforementioned parameters.

New generation of dendritic cell vaccines

Dendritic cells (DC) play a pivotal role in the induction and regulation of immune responses, including the induction of cytotoxic T lymphocytes (CTL) responses. These are essential for the eradication of cancers and pathogens including HIV and malaria, for which there are currently no effective vaccines. New developments in our understanding of DC biology have identified the key DC subset responsible for CTL induction, which is now an attractive candidate to target for vaccination. These DC are characterized by expression of novel markers Clec9A and XCR1, and a specialized capacity to cross-present antigen (Ag) from tumors and pathogens that do not directly infect DC. New generation DC vaccines that specifically target the cross-presenting DC in vivo have already demonstrated potential in preclinical animal models but the challenge remains to translate these findings into clinically efficacous vaccines in man. This has been greatly facilitated by the recent identification of the equivalent Clec9A(+) XCR1(+) cross-presenting DC in human lymphoid tissues and peripheral tissues that are key sites for vaccination administration. These findings combined with further studies on DC subset biology have important implications for the design of new CTL-mediated vaccines.

Generation of hypoallergenic neoglycoconjugates for dendritic cell targeted vaccination: a novel tool for specific immunotherapy

The incidence of allergic disorders and asthma continuously increased over the past decades, consuming a considerable proportion of the health care budget. Allergen-specific subcutaneous immunotherapy represents the only intervention treating the underlying causes of type I allergies, but still suffers from unwanted side effects and low compliance. There is an urgent need for novel approaches improving safety and efficacy of this therapy. In the present study we investigated carbohydrate-mediated targeting of allergens to dermal antigen-presenting cells and its influence on immunogenicity and allergenicity. Mannan, high (40 kDa) and low (6 kDa) molecular weight dextran, and maltodextrin were covalently attached to ovalbumin and papain via mild carbohydrate oxidation resulting in neoglycocomplexes of various sizes. In particular, mannan-conjugates were efficiently taken up by dendritic cells in vivo leading to elevated humoral immune responses against the protein moiety and a shift from IgE to IgG. Beyond providing an adjuvant effect, papain glycocomplexes also proved to mask B-cell epitopes, thus rendering the allergen derivative hypoallergenic.

The present data demonstrate that carbohydrate-modified allergens combine targeting of antigen presenting cells with hypoallergenicity, offering the potential for low dose allergen-specific immunotherapy while concomitantly reducing the risk of side effects.

In vivo imaging of therapy-induced anti-cancer immune responses in humans

Immunotherapy aims to re-engage and revitalize the immune system in the fight against cancer. Research over the past decades has shown that the relationship between the immune system and human cancer is complex, highly dynamic, and variable between individuals. Considering the complexity, enormous effort and costs involved in optimizing immunotherapeutic approaches, clinically applicable tools to monitor therapy-induced immune responses in vivo are most warranted. However, the development of such tools is complicated by the fact that a developing immune response encompasses several body compartments, e.g., peripheral tissues, lymph nodes, lymphatic and vascular systems, as well as the tumor site itself. Moreover, the cells that comprise the immune system are not static but constantly circulate through the vascular and lymphatic system. Molecular imaging is considered the favorite candidate to fulfill this task. The progress in imaging technologies and modalities has provided a versatile toolbox to address these issues. This review focuses on the detection of therapy-induced anticancer immune responses in vivo and provides a comprehensive overview of clinically available imaging techniques as well as perspectives on future developments. In the discussion, we will focus on issues that specifically relate to imaging of the immune system and we will discuss the strengths and limitations of the current clinical imaging techniques. The last section provides future directions that we envision to be crucial for further development.

Vaccination with mRNA-electroporated dendritic cells induces robust tumor antigen-specific CD4+ and CD8+ T cells responses in stage III and IV melanoma patients

PURPOSE

Electroporation of dendritic cells (DC) with mRNA encoding tumor-associated antigens (TAA) has multiple advantages compared to peptide loading. We investigated the immunologic and clinical responses to vaccination with mRNA-electroporated DC in stage III and IV melanoma patients.

EXPERIMENTAL DESIGN

Twenty-six stage III HLA*02:01 melanoma patients scheduled for radical lymph node dissection (stage III) and 19 melanoma patients with irresectable locoregional or distant metastatic disease (referred to as stage IV) were included. Monocyte-derived DC, electroporated with mRNA encoding gp100 and tyrosinase, were pulsed with keyhole limpet hemocyanin and administered intranodally. TAA-specific T-cell responses were monitored in blood and skin-test infiltrating lymphocyte (SKIL) cultures.

RESULTS

Comparable numbers of vaccine-induced CD8(+) and/or CD4(+) TAA-specific T-cell responses were detected in SKIL cultures; 17/26 stage III patients and 11/19 stage IV patients. Strikingly, in this population, TAA-specific CD8(+) T cells that recognize multiple epitopes and produce elevated levels of IFNγ upon antigenic challenge in vitro, were significantly more often observed in stage III patients; 15/17 versus 3/11 stage IV patients, P = 0.0033. In stage IV patients, one mixed and one partial response were documented. The presence or absence of IFNγ-producing TAA-specific CD8(+) T cells in stage IV patients was associated with marked difference in median overall survival of 24.1 months versus 11.0 months, respectively.

CONCLUSION

Vaccination with mRNA-electroporated DC induces a broad repertoire of IFNγ producing TAA-specific CD8(+) and CD4(+) T-cell responses, particularly in stage III melanoma patients.

Maturation of human iDCs by IL-18 plus PGE2, but not by each stimulus alone, induced migration toward CCL21 and the secretion of IL-12 and IFN-γ

Dendritic cells (DCs) are potent antigen-presenting cells that initiate the primary immune response and whose functional properties in vivo depend on the maturation stimulus. We describe the functional properties of human monocyte-derived DCs after the maturation of immature DCs (iDCs) for 2 days with LPS (100 ng/ml), PGE2 (1 μg/ml), CD40L (1 μg/ml) or IL-18 (200 ng/ml) and with CD40L+PGE2 and IL-18+PGE2 mixtures at the same concentrations as above. Neither IL-18 nor PGE2 alone stimulated IL-12 or IFN-γ secretion. When administered simultaneously to 1×10(6)iDCs/ml, IL-18+PGE2 induced the secretion of 131.4±6.7 pg IL-12/ml and 355±87 pg IFN-γ/ml but there was no detectable IL-10 secretion. However, PGE2 alone stimulated the secretion of 208±89 pg IL-10/ml whereas IL-18 alone did not stimulate the secretion of IL-10, IL-12, TNF-α or INF-γ. When the mixture of CD40L+PGE2 was used, only migration toward CCL19 and CCL21 was induced. CD40L did not stimulate the secretion of IL-10, IL-12, TNF-α or IFN-γ and did not stimulate migration toward CCL19 or CCL21. The extent of stimulation of T cell proliferation was essentially the same for all stimuli at the concentrations given above. New properties such as IL-12 and INF-γ secretion and migration toward CCL21 emerged when a mixture of IL-18+PGE2 was employed. These data show that when the pairs of stimuli reported here were used simultaneously their effect was not additive. This system can be used to prepare mDCs with properties useful for cell therapy and also as a model to investigate the mechanisms of cytokine secretion and cell migration.

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.

Melanoma vaccines

There is much renewed activity in the testing of vaccines that target metastatic melanoma, driven by successes in other areas, most notably prostate cancer. Yet, sound evidence that any stand-alone vaccination approach has clinical benefit against melanoma remains lacking. With phase III studies showing no efficacy of promising whole-cell vaccines and heat shock proteins, peptide and dendritic cell vaccines remain the most common approaches. A major obstacle to progress is the lack of any surrogate measures in phase II studies that associate meaningfully with clinical benefit, and this is further complicated by phase III evidence in prostate cancer that immunologic monitoring, tumor response rates, or even times to tumor progression may not accurately predict survival benefit. The area with the most progress has been in combining vaccines with other systemic immunostimulatory agents. Although no vaccine has been found which fulfills the prediction from murine models that they can enhance the efficacy of ipilimumab, combining a peptide vaccination with high-dose interleukin 2 was shown to enhance complete and overall response rates compared with interleukin 2 alone. These promising combinations continue to struggle with the same unresolved issues that have plagued melanoma vaccines from the beginning-what are the best antigens to target, what are the best methods of vaccination, and what constitutes a sufficient immune response to be of value? Virtually no progress has been made toward answering these questions.

Antigen-specific versus antigen-nonspecific immunotherapeutic approaches for human melanoma: the need for integration for optimal efficacy?

Due to its immunogenecity and evidence of immune responses resulting in tumor regression, metastatic melanoma has been the target for numerous immunotherapeutic approaches. Unfortunately, based on the clinical outcomes, even the successful induction of tumor-specific responses does not correlate with efficacy. Immunotherapies can be divided into antigen-specific approaches, which seek to induce T cells specific to one or several known tumor associated antigens (TAA), or with antigen-nonspecific approaches, which generally activate T cells to become nonspecifically lytic effectors. Here the authors critically review the different immunotherapeutic approaches in melanoma.

Targeting Dendritic Cells in vivo for Cancer Therapy

Monoclonal antibodies that recognize cell surface molecules have been used deliver antigenic cargo to dendritic cells (DC) for induction of immune responses. The encouraging anti-tumor immunity elicited using this immunization strategy suggests its suitability for clinical trials. This review discusses the complex network of DC, the functional specialization of DC subsets, the immunological outcomes of targeting different DC subsets and their cell surface receptors, and the requirements for the induction of effective anti-tumor CD4 and CD8 T cell responses that can recognize tumor-specific antigens. Finally, we review preclinical experiments and the progress toward targeting human DC in vivo.

Experience with synthetic vaccines for cancer and persistent virus infections in nonhuman primates and patients

Synthetic vaccines, in particular long synthetic peptides of approximately 25-50 amino acids in length, are attractive for HIV vaccine development and for induction of therapeutic immune responses in patients with (pre-)malignant disorders. In the case of preventive vaccine development against HIV, no major success has been achieved, but the possibilities are by no means exhausted. A long peptide vaccine consisting of 13 overlapping peptides, which together cover the entire length of the two oncogenic proteins E6 and E7 of high-risk human papilloma virus type 16 (HPV16), caused complete regression of all lesions and eradication of virus in 9 out of 20 women with high-grade vulvar intraepithelial neoplasia, a therapy-resistant preneoplastic disorder. The nature and strength of the vaccine-prompted T cell responses were significantly correlated with the clinical response. Synthetic peptide vaccines are attractive, because they allow rational improvement of vaccine design and detailed pharmacokinetic and pharmacodynamic studies not possible with conventional vaccines. Improvements are possible by addition or conjugation of adjuvants, notably TLR ligands, to the synthetic peptides.

Boosting antibody responses by targeting antigens to dendritic cells

Delivering antigens directly to dendritic cells (DCs) in situ, by injecting antigens coupled to antibodies specific for DC surface molecules, is a promising strategy for enhancing vaccine efficacy. Enhanced cytotoxic T cell responses are obtained if an adjuvant is co-administered to activate the DC. Such DC targeting is also effective at enhancing humoral immunity, via the generation of T follicular helper cells. Depending on the DC surface molecule targeted, antibody production can be enhanced even in the absence of adjuvants. In the case of Clec9A as the DC surface target, enhanced antibody production is a consequence of the DC-restricted expression of the target molecule. Few other cells absorb the antigen-antibody construct, therefore, it persists in the bloodstream, allowing sustained antigen presentation, even by non-activated DCs.

Early identification of antigen-specific immune responses in vivo by [18F]-labeled 3'-fluoro-3'-deoxy-thymidine ([18F]FLT) PET imaging

Current biomarkers are unable to adequately predict vaccine-induced immune protection in humans with infectious disease or cancer. However, timely and adequate assessment of antigen-specific immune responses is critical for successful vaccine development. Therefore, we have developed a method for the direct assessment of immune responses in vivo in a clinical setting. Melanoma patients with lymph node (LN) metastases received dendritic cell (DC) vaccine therapy, injected intranodally, followed by [(18)F]-labeled 3'-fluoro-3'-deoxy-thymidine ([(18)F]FLT) PET at varying time points after vaccination. Control LNs received saline or DCs without antigen. De novo immune responses were readily visualized in treated LNs early after the prime vaccination, and these signals persisted for up to 3 wk. This selective [(18)F]FLT uptake was markedly absent in control LNs, although tracer uptake in treated LNs increased profoundly with as little as 4.5 × 10(5) DCs. Immunohistochemical staining confirmed injected DC dispersion to T-cell areas and resultant activation of CD4(+) and CD8(+) T cells. The level of LN tracer uptake significantly correlates to the level of circulating antigen-specific IgG antibodies and antigen-specific proliferation of T cells in peripheral blood. Furthermore, this correlation was not observed with [(18)F]-labeled fluoro-2-deoxy-2-D-glucose. Therefore, [(18)F]FLT PET offers a sensitive tool to study the kinetics, localization, and involvement of lymphocyte subsets in response to vaccination. This technique allows for early discrimination of responding from nonresponding patients in anti-cancer vaccination and aid physicians in individualized decisionmaking.

Current vaccination strategies for prostate cancer

CONTEXT

The first therapeutic cancer vaccine demonstrating effectiveness in a phase 3 study was approved by the US Food and Drug Administration on 29 April 2010. The pivotal trial demonstrated overall survival (OS) benefit in patients treated with antigen-loaded leukapheresis cells compared with a control infusion. Results of other prostate cancer (PCa) vaccination strategies are awaited, as this approach may herald a new era in the care for patients with advanced PCa.

OBJECTIVE

Consider effectiveness and safety of vaccination strategies in the treatment of PCa.

EVIDENCE ACQUISITION

We searched three bibliographic databases (January 1995 through October 2010) for randomised phase 2 and 3 studies of vaccination strategies for PCa based on predetermined relevant Medical Subject Heading terms and free text terms.

EVIDENCE SYNTHESIS

Data from 3 randomised phase 3 and 10 randomised phase 2 vaccination trials are discussed with respect to clinical outcome in terms of progression-free survival and OS, toxicity, prostate-specific antigen (PSA) response, and immunologic response. Three phase 3 trials (D9901, D9902A, and D9902B) that enrolled a total of 737 patients, all controlled and double-blinded, tested the efficacy of sipuleucel-T. The largest of these three trials, called Immunotherapy for Prostate Adenocarcinoma Treatment (IMPACT), has demonstrated safety and effectiveness of sipuleucel-T (now marketed as Provenge) as measured by prolonged survival of 512 asymptomatic patients with metastatic castration-resistant PCa (mCRPC). The study showed a 4.1-mo median survival benefit in the sipuleucel-T vaccine-treated group compared with the control group (25.8 vs 21.7 mo; hazard ratio [HR]: 0.78; 95% confidence interval [CI], 0.62-0.98; p=0.032) and extended 3-yr survival (31.7% vs 23.0%). In contrast, two phase 3 vaccination trials with a whole-tumour-cell mixture of two PCa cell lines (GVAX) and testing GVAX either alone or in combination with chemotherapy versus chemotherapy alone (VITAL1 and 2) were terminated prematurely based on futility and increased deaths. Other phase 2 vaccination trials testing different types of vaccines in castration-resistant PCa patients have been reported with variable outcomes. Notably, a controlled, double-blind, randomised phase 2 vaccine trial of PROSTVAC-VF, a recombinant viral vector containing complementary DNA encoding PSA, in 125 patients with chemotherapy-naïve, minimally symptomatic mCRPC also demonstrated safety but no significant effect on the time to disease progression. In comparison with controls (n=40), PROSTVAC-VF-treated patients (n=82) experienced longer median survival of 8.5 mo (25.1 vs 16.6 mo; HR: 0.56; 95% CI, 0.37-0.85; p=0.0061) and extended 3-yr survival (30% vs 17%). In general, PCa vaccines are perceived to have less toxicity compared with current cytotoxic or targeted therapies. Evaluation of clinical efficacy of different vaccination strategies (eg, protein-, peptide- and DNA-based vaccines) in the context of properly designed and controlled phase 3 studies is warranted.

CONCLUSIONS

Cancer vaccines represent a new paradigm in the treatment of PCa. The IMPACT trial showed improved survival but no difference in time to disease progression in mCRPC patients with minimal tumour burden. Observations in phase 2 and 3 trials pave the way for other vaccination approaches for this disease, raise questions regarding the most appropriate clinical trial designs, and underscore the importance of identifying biomarkers for antitumour effect to better implement such therapies.

Human dendritic cells transfected with amplified MUC1 mRNA stimulate cytotoxic T lymphocyte responses against pancreatic cancer in vitro

BACKGROUND AND AIM

Mucin (MUC) 1 is an epithelial cell glycoprotein that is aberrantly overexpressed in many adenocarcinomas, including pancreatic cancer (PC), providing an ideal tumor-associated antigen and target for immunotherapy. In this study, we investigated whether the cytotoxic T lymphocytes (CTLs) induced by dendritic cells (DCs) transfected with amplified MUC1 mRNA could respond against PC in vitro.

METHODS

Amplified mRNA encoding MUC1 were transfected into DCs using electroporation with an optimized setting and the MUC1 expression were evaluated by quantitative real-time polymerase chain reaction and Western blot. The MUC1 specific CTL responses were measured using the standard chromium 51 (51Cr)-release assays and the interferon-γ release assay.

RESULTS

Dendritic cells could be transfected with amplified MUC1 mRNA efficiently. The transfected DCs were remarkably effective in stimulating MUC1-specific CTL responses in vitro. The function of MUC1 specific CTLs, induced by MUC1 mRNA-transfected DCs, was restricted by major histocompatibility complex (MHC) class I antigen presentation.

CONCLUSION

The CTL responses stimulated by DCs transfected with MUC1 mRNA could only recognize and lyse HLA-A2+/MUC1+ PC and other target cells under restriction by MHC class I-specific antigen presentation, providing a preclinical rationale for using MUC1 as a target structure for immunotherapeutic strategies against PC.

DC maturation and function are not altered by melanoma-derived immunosuppressive soluble factors

BACKGROUND

Although melanoma can elicit robust tumor antigen-specific immune responses, advanced melanoma is associated with immune tolerance. We have previously described several mechanisms of melanoma-induced immunosuppression, including the skewing of the immune response towards a Th2 cytokine profile and the induction of regulatory T cells. Since dendritic cells (DCs) are potentially important players that can direct other cells of the immune system towards a cytotoxic, humoral, or regulatory phenotype, we hypothesized that melanoma-produced factors directly affect the maturation and function of DCs, influencing the nature and magnitude of the resulting immune response.

MATERIALS AND METHODS

To test this hypothesis, immature myeloid-derived DCs (mdDCs) were derived with cytokines from CD14+ peripheral blood mononuclear cells (PBMCs) and exposed to 20% melanoma-conditioned media (MCM). After 2 d, the expression of maturation markers and the function of these mdDCs, measured by cytokine production, the amount of endocytosis, expression of the inhibitory molecule indoleamine 2,3-dioxygenase (IDO), and the ability to stimulate T cells were determined.

RESULTS

We found that incubation with MCM did not inhibit the expression of maturation markers or IDO, the production of cytokines, the amount of antigen uptake, or the ability to induce T cell proliferation in mixed-lymphocyte reactions by mdDC.

CONCLUSIONS

These results suggest that the immunosuppressive effects of melanoma-produced factors are independent of directly measurable changes in mdDC function or maturation in vitro.

Immunotherapy for cutaneous malignancy

BACKGROUND

Immunotherapy for cutaneous malignancy involves manipulating the immune system to treat and prevent skin cancer. Although initial efforts were fraught with low success rates and technical challenges, more-recent endeavors have yielded response rates approaching 50% for treating metastatic melanoma. Many of these advances are a result of increasing knowledge of the immune system's intricacies and continued progress in laboratory techniques.

OBJECTIVE

To review our current understanding of the skin immune system and discuss how these factors contribute to the host response to malignancy and to report the current state of immunotherapeutic techniques.

MATERIALS AND METHODS

An extensive PubMed literature search was conducted in topics involving immunotherapy with specific relevance to cutaneous malignancy using the MeSH terms "immunotherapy" and "skin cancer."

RESULTS

Despite initially poor patient responses to these treatment modalities, recent gains in scientific knowledge and clinical intervention protocols have brought immunotherapy to the forefront of prospective skin cancer therapeutics, particularly for advanced melanoma.

CONCLUSIONS

Current treatment options for advanced cutaneous malignancies such as melanoma are low in efficacy. Immunotherapies have the potential to provide novel approaches to address this, particularly when used in combination. The authors have indicated no significant interest with commercial supporters.