Measuring Melanoma-Specific Cytotoxic T Lymphocytes Elicited by Dendritic Cell Vaccines with a Tumor Inhibition Assay In Vitro

A Dendritic Cell Vaccine Combined With Radiotherapy Activates the Specific Immune Response in Patients With Esophageal Cancer

Dendritic cells (DC) are highly efficient antigen-presenting cells. DC may be used to create DC vaccines against cancer, but the optimal strategies remain to be elucidated. This study aimed to examine the benefits and adverse effects of using esophageal cancer cell antigens to stimulate DC to trigger the specific immune response in patients with esophageal cancer undergoing radiotherapy. This was an observational cohort study performed at Lianshui County People's Hospital between September 2010 and June 2012. Forty patients with esophageal cancer planned to receive radiotherapy were selected, and 28 received the DC vaccine. DC were isolated, loaded with antigens, and intradermally injected after being cultured for 1 week. One week after injection, the patients underwent a delayed-type hypersensitivity test. Serum Th1 cytokines [interleukin (IL)-2, IL-12, and interferon (IFN)-γ] and antigen-specific IFN-γCD8 T cells were tested before and after vaccination. Patients were followed up for 2 years. Adverse events were monitored. Patients in the vaccine group tolerated the DC vaccine. Levels of serum IL-2 (+92.4%), IL-12 (+70.9%), and IFN-γ (+214.3%) as well as the proportion of IFN-γCD8 T cells (3.0-16.4-fold) were significantly increased compared with baseline and the control group (all P<0.05). The 1- (82.1% vs. 50.0%, P=0.04) and 2-year survival (67.8% vs. 33.3%, P=0.04) was improved by vaccination. Only 2 patients showed mild fever. In conclusion, the DC vaccine triggered the specific immune response and induced the secretion of Th1 cytokines. The vaccine may lead to better survival, but this have to be confirmed. Adverse events were rare and mild.

Design of universal cancer vaccines using natural tumor vessel-specific antigens (SANTAVAC)

Vaccination against endothelial cells (ECs) lining the tumor vasculature represents one of the most attractive potential cancer immunotherapy options due to its ability to prevent solid tumor growth. Using this approach, target antigens can be derived from ECs and used to develop a universal cancer vaccine. Unfortunately, direct immunization with EC preparations can elicit autoimmune vasculitis in normal tissues. Recently, tumor-induced changes to the human EC surface were described that provided a basis for designing efficient EC-based vaccines capable of eliciting immune responses that targeted the tumor endothelium directly. This review examines these data from the perspective of designing EC-based cancer vaccines for the treatment of all solid tumors, including the antigen composition of vaccine formulations, the selection ECs for antigen derivation, the production and control of antigens, and the method for estimating vaccine efficacy and safety. As the vaccine preparation requires a specifically derived set of natural cell surface antigens, a new vaccine preparation concept was formulated. Antigen compositions prepared according to this concept were named SANTAVAC (Set of All Natural Target Antigens for Vaccination Against Cancer).

Tumor-induced endothelial cell surface heterogeneity directly affects endothelial cell escape from a cell-mediated immune response in vitro

Immune-mediated damage to tumor vessels is a potential means of preventing solid tumor progression. Antiangiogenic cancer vaccines capable of inducing this kind of damage include formulations comprised of endothelial cell-specific antigens. Identification of antigens capable of eliciting efficient vaccination is difficult because the endothelial cell phenotype is affected by surrounding tissues, including angiogenic stimuli received from surrounding tumor cells. Therefore, phenotype endothelial cell variations (heterogeneity) were examined in the context of the development of an efficient vaccine using mass spectrometry-based cell surface profiling. This approach was applied to primary human microvascular endothelial cell (HMEC) cultures proliferated under growth stimuli provided by either normal tissues (growth supplement from human hypothalamus) or cancer cells (MCF-7, LNCap and HepG2). It was found that tumors induced pronounced, tumor type-dependent changes to HMEC surface targets that in an in vitro model of human antiangiogenic vaccination directly facilitated HMEC escape from cytotoxic T cell-mediated cell death. Furthermore, it was found that tumors influenced the HMEC phenotype unidirectionally and that HMEC imunogenicity was reciprocal to the intensity of tumor-induced changes to the HMEC surface. These findings provide data for the design of tumor-specific endothelial cell based vaccines with sufficient immunogenicity without posing a risk to the elicitation of autoimmunity if administered in vivo.

Universal cancer vaccine: an update on the design of cancer vaccines generated from endothelial cells

Among the potential cancer immunotherapies, vaccination against antigens expressed by endothelial cells lining the tumor vasculature represents one of the most attractive options because this approach may prevent the growth of any solid tumor. Therefore, endothelial cells can be used as a source of antigens for developing a so-called "universal" cancer vaccine. Unfortunately, efficient endothelial cell-based cancer vaccines have not yet been developed because previous approaches utilized direct endothelial cell immunizations which is not effective and can result in the elicitation of autoimmune responses associated with systemic autoimmune vasculitis. Recently, the heterogeneity of the endothelial cell surface was defined using an in vitro system as a means of developing antiangiogenic cancer vaccines. This analysis demonstrated that tumors induced specific changes to the microvascular of human endothelial cell (HMEC) surface thereby providing a basis for the design of endothelial cell-based vaccines that directly target the tumor endothelium. (1) This commentary further describes HMEC heterogeneity from the perspective of designing an endothelial cell-based universal (for the treatment of all solid tumors) cancer vaccine with high immunogenicity that does not pose the risk of eliciting autoimmunity.

Taming cancer by inducing immunity via dendritic cells

Immunotherapy seeks to mobilize a patient's immune system for therapeutic benefit. It can be passive, i.e. transfer of immune effector cells (T cells) or proteins (antibodies), or active, i.e. vaccination. In cancer, passive immunotherapy can lead to some objective clinical responses, thus demonstrating that the immune system can reject tumors. However, passive immunotherapy is not expected to yield long-lived memory T cells that might control tumor outgrowth. Active immunotherapy with dendritic cell (DC)-based vaccines has the potential to induce both tumor-specific effector and memory T cells. Early clinical trials testing vaccination with ex vivo-generated DCs pulsed with tumor antigens provide a proof-of-principle that therapeutic immunity can be elicited. Yet, there is a need to improve their efficacy. The next generation of DC vaccines is expected to generate large numbers of high-avidity effector CD8(+) T cells and to overcome regulatory T cells. Therapeutic vaccination protocols will combine improved ex vivo DC vaccines with therapies that offset the suppressive environment established by tumors.

Cross-priming of cyclin B1, MUC-1 and survivin-specific CD8+ T cells by dendritic cells loaded with killed allogeneic breast cancer cells

Introduction

The ability of dendritic cells (DCs) to take up whole tumor cells and process their antigens for presentation to T cells ('cross-priming') is an important mechanism for induction of tumor specific immunity.

Methods

In vitro generated DCs were loaded with killed allogeneic breast cancer cells and offered to autologous naïve CD8⁺ T cells in 2-week and/or 3-week cultures. CD8⁺ T cell differentiation was measured by their capacity to secrete effector cytokines (interferon-γ) and kill breast cancer cells. Specificity was measured using peptides derived from defined breast cancer antigens.

Results

We found that DCs loaded with killed breast cancer cells can prime naïve CD8⁺ T cells to differentiate into effector cytotoxic T lymphocytes (CTLs). Importantly, these CTLs primed by DCs loaded with killed HLA-A*0201^- breast cancer cells can kill HLA-A*0201⁺ breast cancer cells. Among the tumor specific CTLs, we found that CTLs specific for HLA-A2 restricted peptides derived from three well known shared breast tumor antigens, namely cyclin B1, MUC-1 and survivin.

Conclusion

This ability of DCs loaded with killed allogeneic breast cancer cells to elicit multiantigen specific immunity supports their use as vaccines in patients with breast cancer.

Efficient generation of CD34+ progenitor-derived dendritic cells from G-CSF-mobilized peripheral mononuclear cells does not require hematopoietic stem cell enrichment

As a result of their potent antigen-presentation function, dendritic cells (DC) are important tools for cell therapy programs. In vitro-generated DC from enriched CD34+ hematopoietic stem cells (HSC; enriched CD34 DC) have already proven their efficiency in Phase I/II clinical trials. Here, we investigated whether enrichment of CD34+ HSC before the onset of culture was absolutely required for their differentiation into DC. With this aim, we developed a new two-step culture method. PBMC harvested from G-CSF-mobilized, healthy patients were expanded for 7 days during the first step, with early acting cytokines, such as stem cell factor, fetal liver tyrosine kinase 3 ligand (Flt-3L), and thrombopoietin. During the second step, expanded cells were then induced to differentiate into mature DC in the presence of GM-CSF, Flt-3L, and TNF-alpha for 8 days, followed by LPS exposure for 2 additional days. Our results showed that the rate of CD34+/CD38+/lineageneg cells increased 19.5+/-10-fold (mean+/-sd) during the first step, and the expression of CD14, CD1a, CD86, CD80, and CD83 molecules was up-regulated markedly following the second step. When compared with DC generated from enriched CD34+ cells, which were expanded for 7 days before differentiation, DC derived from nonenriched peripheral blood stem cells showed a similar phenotye but higher yields of production. Accordingly, the allogeneic stimulatory capacity of the two-step-cultured DC was as at least as efficient as that of enriched CD34 DC. In conclusion, we report herein a new two-step culture method that leads to high yields of mature DC without any need of CD34+ HSC enrichment.

Hyperthermia enhances CTL cross-priming

Dendritic cells (DCs) loaded with killed allogeneic melanoma cells can cross-prime naive CD8(+) T cells to differentiate into melanoma-specific CTLs in 3-wk cultures. In this study we show that DCs loaded with killed melanoma cells that were heated to 42 degrees C before killing are more efficient in cross-priming of naive CD8(+) T cells than DCs loaded with unheated killed melanoma cells. The enhanced cross-priming was demonstrated by several parameters: 1) induction of naive CD8(+) T cell differentiation in 2-wk cultures, 2) enhanced killing of melanoma peptide-pulsed T2 cells, 3) enhanced killing of HLA-A*0201(+) melanoma cells in a standard 4-h chromium release assay, and 4) enhanced capacity to prevent tumor growth in vitro in a tumor regression assay. Two mechanisms might explain the hyperthermia-induced enhanced cross-priming. First, heat-treated melanoma cells expressed increased levels of 70-kDa heat shock protein (HSP70), and enhanced cross-priming could be reproduced by overexpression of HSP70 in melanoma cells transduced with HSP70 encoding lentiviral vector. Second, hyperthermia resulted in the increased transcription of several tumor Ag-associated Ags, including MAGE-B3, -B4, -A8, and -A10. Thus, heat treatment of tumor cells permits enhanced cross-priming, possibly via up-regulation of both HSPs and tumor Ag expression.