Recent Advances and Current Challenges in Tumor Immunology and Immunotherapy

Mathematical modeling identifies Lck as a potential mediator for PD-1 induced inhibition of early TCR signaling

Programmed cell death-1 (PD-1) is an inhibitory immune checkpoint receptor that negatively regulates the functioning of T cell. Although the direct targets of PD-1 were not identified, its inhibitory action on the TCR signaling pathway was known much earlier. Recent experiments suggest that the PD-1 inhibits the TCR and CD28 signaling pathways at a very early stage ─ at the level of phosphorylation of the cytoplasmic domain of TCR and CD28 receptors. Here, we develop a mathematical model to investigate the influence of inhibitory effect of PD-1 on the activation of early TCR and CD28 signaling molecules. Proposed model recaptures several quantitative experimental observations of PD-1 mediated inhibition. Model simulations show that PD-1 imposes a net inhibitory effect on the Lck kinase. Further, the inhibitory effect of PD-1 on the activation of TCR signaling molecules such as Zap70 and SLP76 is significantly enhanced by the PD-1 mediated inhibition of Lck. These results suggest a critical role for Lck as a mediator for PD-1 induced inhibition of TCR signaling network. Multi parametric sensitivity analysis explores the effect of parameter uncertainty on model simulations.

Non-genetic engineering of cytotoxic T cells to target IL-4 receptor enhances tumor homing and therapeutic efficacy against melanoma

Adoptive transfer of cytotoxic T lymphocytes (CTLs) has been used as an immunotherapy in melanoma. However, the tumor homing and therapeutic efficacy of transferred CTLs against melanoma remain unsatisfactory. Interleukin-4 receptor (IL-4R) is commonly up-regulated in tumors including melanoma. Here, we studied whether IL-4R-targeted CTLs exhibit enhanced tumor homing and therapeutic efficacy against melanoma. CTLs isolated from mice bearing melanomas were non-genetically engineered with IL4RPep-1, an IL-4R-binding peptide, using a membrane anchor composed of dioleylphosphatidylethanolamine. Compared to control CTLs, IL-4R-targeted CTLs showed higher binding to melanoma cells and in vivo tumor homing. They also exerted a more rapid and robust effector response, including increased cytokine secretion and cytotoxicity against melanoma cells and enhanced reprogramming of M2-type macrophages to M1-type macrophages. Moreover, IL-4R-targeted CTLs efficiently inhibited melanoma growth and reversed the immunosuppressive tumor microenvironment. These results suggest that non-genetically engineered CTLs targeting IL-4R have potential as an adoptive T cell therapy against melanoma.

Use of transfer factor in immunosuppressed surgical patients

ABSTRACT Objective : to evaluate the action of Transfer Factor on the immune response of patients with malignant neoplasm submitted to surgery, chemotherapy and radiotherapy. Method: we analyzed the variations of leukocytes, total lymphocytes, T-lymphocytes and CD4 counts in 60 patients submitted to immunostimulation with a single, daily dose of 0.5mg sublingual Transfer Factor, started simultaneously with chemotherapy and/or radiotherapy. Results: there were statistically significant increases in the counts of all cell lines studied, more pronounced after 12 months of use of the medication. Conclusion: the Transfer Factor restored immune response and showed no side effects.

Interrogating Cellular Functions with Designer Janus Particles

Janus particles have two distinct surfaces or compartments. This enables novel applications that are impossible with homogeneous particles, ranging from the engineering of active colloidal metastructures to creating multimodal therapeutic materials. Recent years have witnessed a rapid development of novel Janus structures and exploration of their applications, particularly in the biomedical arena. It, therefore, becomes crucial to understand how Janus particles with surface or structural anisotropy might interact with biological systems and how such interactions may be exploited to manipulate biological responses. This perspective highlights recent studies that have employed Janus particles as novel toolsets to manipulate, measure, and understand cellular functions. Janus particles have been shown to have biological interactions different from uniform particles. Their surface anisotropy has been used to control the cell entry of synthetic particles, to spatially organize stimuli for the activation of immune cells, and to enable direct visualization and measurement of rotational dynamics of particles in living systems. The work included in this perspective showcases the significance of understanding the biological interactions of Janus particles and the tremendous potential of harnessing such interactions to advance the development of Janus structure-based biomaterials.

Current trends in cancer vaccines--a bioinformatics perspective

Cancer vaccine development is in the process of becoming reality in future, due to successful phase II/III clinical trials. However, there are still problems due to the specificity of tumor antigens and weakness of tumor associated antigens in eliciting an effective immune response. Computational models to assess the vaccine efficacy have helped to improve and understand what is necessary for personalized treatment. Further research is needed to elucidate the mechanisms of activation of antigen specific cytotoxic T lymphocytes, decreased TREG number functionality and antigen cascade, so that overall improvement in vaccine efficacy and disease free survival can be attained. T cell epitomic based in sillico approaches might be very effective for the design and development of novel cancer vaccines.

Cancer vaccines: state of the art of the computational modeling approaches

Cancer vaccines are a real application of the extensive knowledge of immunology to the field of oncology. Tumors are dynamic complex systems in which several entities, events, and conditions interact among them resulting in growth, invasion, and metastases. The immune system includes many cells and molecules that cooperatively act to protect the host organism from foreign agents. Interactions between the immune system and the tumor mass include a huge number of biological factors. Testing of some cancer vaccine features, such as the best conditions for vaccine administration or the identification of candidate antigenic stimuli, can be very difficult or even impossible only through experiments with biological models simply because a high number of variables need to be considered at the same time. This is where computational models, and, to this extent, immunoinformatics, can prove handy as they have shown to be able to reproduce enough biological complexity to be of use in suggesting new experiments. Indeed, computational models can be used in addition to biological models. We now experience that biologists and medical doctors are progressively convinced that modeling can be of great help in understanding experimental results and planning new experiments. This will boost this research in the future.

Enhanced delivery of T cells to tumor after chemotherapy using membrane-anchored, apoptosis-targeted peptide

Chemotherapy-induced apoptosis of tumor cells enhances the antigen presentation and sensitizes tumor cells to T cell-mediated cytotoxicity. Here we harnessed the apoptosis of tumor cells as a homing signal for the delivery of T cells to tumor. Jurkat T cells were anchored with ApoPep-1, an apoptosis-targeted peptide ligand, using the biocompatible anchor for membrane (BAM), an oleyl acid derivative. The ApoPep-1-BAM conjugate was efficiently anchored to cell membrane, while little anchoring was obtained with ApoPep-1 alone. The retention period of the ApoPep-1-BAM conjugate on cell membrane was approximately 80 and 40 min in the absence and presence of serum, respectively. ApoPep-1 was resistant to degradation in serum until 2h. The apoptosis-targeted T cells that were anchored with the ApoPep-1-BAM preferentially bound to apoptotic tumor cells over living cells. When intravenously injected into tumor-bearing mice, the number of apoptosis-targeted T cells and in vivo fluorescence signals by the homing of the cells to doxorubicin-treated tumor were higher than those of untargeted T cells. Accumulation of apoptosis-targeted T cells at other organs such as liver was not detected. These results suggest that the chemotherapy-induced apoptosis and subsequent enhancement of T cell delivery to tumor by the membrane anchoring of the apoptosis-targeted peptide could be a novel strategy for cancer immunotherapy.

Adoptive cell transfer therapy for malignant gliomas

To date, various adoptive immunotherapies have been attempted for treatment of malignant gliomas using nonspecific and/or specific effector cells. Since the late 1980s, with the development of rIL-2, the efficacy of lymphokine-activated killer (LAK) cell therapy with or without rIL-2 for malignant gliomas had been tested with some modifications in therapeutic protocols. With advancements in technology, ex vivo expanded tumor specific cytotoxic T-lymphocytes (CTL) or those lineages were used in clinical trials with higher tumor response rates. In addition, combinations of those adoptive cell transfer using LAK cells, CTLs or natural killer (NK) cells with autologous tumor vaccine (ATV) therapy were attempted. Also, a strategy of high-dose (or lymphodepleting) chemotherapy followed by adoptive cell transfer has been drawing attentions recently. The most important role of these clinical studies using cell therapy was to prove that these ex vivo expanded effector cells could kill tumor cells in vivo. Although recent clinical results could demonstrate radiologic tumor shrinkage in a number of cases, cell transfer therapy alone has been utilized less frequently, because of the high cost of ex vivo cell expansion, the short duration of antitumor activity in vivo, and the recent shift of interest to vaccine immunotherapy. Nevertheless, NK cell therapy using specific feeder cells or allergenic NK cell lines have potentials to be a good choice of treatment because of easy ex vivo expansion and their efficacy especially when combined with vaccine therapy as they are complementary to each other. Also, further studies are expected to clarify the efficacy of the high-dose chemotherapy followed by a large scale cell transfer therapy as a new therapeutic strategy for malignant gliomas.

Indoleamine 2,3-dioxygenase and immune tolerance in ovarian cancer

PURPOSE OF REVIEW

Ovarian cancer is the leading cause of cancer death among gynecologic malignancies despite significant advances in cytoreductive surgery and chemotherapy, and novel therapeutic approaches are urgently needed. Immunotherapy is one of these strategies; however, its clinical applications have shown limited efficacy. This may be attributed to tumor-induced immune tolerance, and much attention has been paid to overcoming these immune resistance mechanisms. This review focuses on the immunoregulatory enzyme indoleamine 2,3-dioxygenase (IDO) and shows the role of IDO and its clinical potential in ovarian cancer.

RECENT FINDINGS

IDO suppresses the proliferation of effector T cells or natural killer cells and their killer functions. In ovarian cancer, high IDO expression in tumor cells was correlated with a reduced number of tumor-infiltrating lymphocytes. The IDO expression was also correlated with advanced surgical stage and impaired survival. Preclinical studies in mice demonstrated that oral administration of IDO inhibitors suppressed peritoneal dissemination and potentiated the antitumor efficacy of chemotherapeutic agents.

SUMMARY

IDO induces immune tolerance and promotes ovarian cancer progression. Tumoral IDO expression is correlated with impaired clinical outcome. IDO inhibition may therefore be a promising strategy to restore host antitumor immunity and to enhance the antitumor potential of current chemotherapy or immunotherapy for advanced ovarian cancer.

Bryostatin-I: a dendritic cell stimulator for chemokines induction and a promising adjuvant for a peptide based cancer vaccine

Bryostatin-1 (Bryo-1), a PKC modulator, was previously shown to activate monocytes and lymphocytes to produce cytokines. In this report, we investigated the adjuvanticity of Bryo-1 both in vitro and in vivo. First, Bryo-1 was found to induce the release of CCL2 and CCL3 from mouse bone marrow-derived dendritic cells (BMDC) in a dose-dependent manner. As little as 0.1nM Bryo-I induced release of chemokines from BMDC and the maximal induction could be achieved at 5-10nM. Both PKC and ERK inhibitors attenuated the release of CCL2 and CCL3. Consistently, Western blot indicated that Bryo-I activated ERK in a dose- and time-dependent manner. Experiments with the NF-κB inhibitor, MG-132, demonstrated that NF-κB was involved in the induction of CCL2 but not CCL3. Because chemokines have been demonstrated to have profound effects on immune reactions by regulating the trafficking of DC and other lymphocytes into lymphoid organs, Bryo-I was tested as an adjuvant in an E7 peptide (MHC class I-restricted peptide epitope derived from human papillomavirus (HPV) 16 E7 protein)-based cancer vaccine. Mice immunized by s.c. injection with Bryo-I/E7 had enlarged draining lymph nodes and showed an antigen specific T-cell response demonstrated by the release of IFN-γ from isolated splenocytes and in vivo CTL activity. Finally, immunization with Bryo-I/E7 totally prevented the E7-expressing TC-1 tumor growth in mice. In conclusion, for the first time, we demonstrated that Bryo-I induced chemokine release from dendritic cell and was an effective adjuvant for peptide cancer vaccine.

Tresyl-based conjugation of protein antigen to lipid nanoparticles increases antigen immunogenicity

The present studies were aimed at investigating the engineering of NPs with protein-conjugated-surfactant at their surface. In order to increase the immunogenicity of a protein antigen, Brij 78 was functionalized by tresyl chloride and then further reacted with the primary amine of the model proteins ovalbumin (OVA) or horseradish peroxide (HRP). The reaction yielded Brij 78-OVA and Brij 78-HRP conjugates which were then used directly to form NP-OVA or NP-HRP using a one-step warm oil-in-water microemulsion precursor method with emulsifying wax as the oil phase, and Brij 78 and the Brij 78-OVA or Brij 78-HRP conjugate as surfactants. Similarly, Brij 700 was conjugated to HIV p24 antigen to yield Brij 700-p24 conjugate. The utility of these NPs for enhancing the immune responses to protein-based vaccines was evaluated in vivo using ovalbumin (OVA) as model protein and p24 as a relevant HIV antigen. In separate in vivo studies, female BALB/c mice were immunized by subcutaneous (s.c.) injection with NP-OVA and NP-p24 formulations along with several control formulations. These results suggested that with multiple antigens, covalent attachment of the antigen to the NP significantly enhanced antigen-specific immune responses. This facile covalent conjugation and incorporation method may be utilized to further incorporate other protein antigens, even multiple antigens, into an enhanced vaccine delivery system.

Role of sorafenib and sunitinib in the induction of expressions of NKG2D ligands in nasopharyngeal carcinoma with high expression of ABCG2

BACKGROUND

Sorafenib and sunitinib are novel small molecule tyrosine kinase inhibitors with multiple targets on tumor cells, which have been demonstrated to be beneficial in the treatment of several carcinomas. Combining the usage of molecular targeted agents and adoptive cellular immunotherapy (ACI) against drug-resistant relapse nasopharyngeal carcinoma which had no standard therapeutic regimen was investigated by our research in order to study whether synergistic effects exist and related mechanisms.

METHODS

Human multidrug-resistant nasopharyngeal carcinoma cell line CNE2/DDP with high and low expressions of ABCG(2) (abbreviated to ABCG (2) (High) CNE2/DDP and ABCG (2) (Low) CNE2/DDP) cells and NK cells were isolated by magnetic activated cell sorting, and the purity of isolated cells was detected by flow cytometry. mRNA expressions of drug-resistant gene ABCG(2), Bcl-2, MDR1, MRP and MGMT in ABCG (2) (High) CNE2/DDP and ABCG (2) (Low) CNE2/DDP cells were detected by reverse transcription polymerase chain reaction (RT-PCR). Drug sensitivity of two kinds of cells to fluorouracil, cisplatin, vincristine, carboplatin, epirubicin, daunorubicin, paclitaxel, mitomycin, sorafenib, and sunitinib were detected by MTT assay. FCM was used to evaluate the expressions of NKG2D ligands (NKG2DLs,) on target cells before and after incubated with sorafenib and sunitinib. Subsequently, the cytotoxic sensitivity of incubated and un-incubated ABCG (2) (High) CNE2/DDP and ABCG (2) (Low) CNE2/DDP cells to NK cells was measured by CytoTox 96(®) Non-Radioactive Cytotoxicity Assay.

RESULTS

The results revealed that target cells' cytotoxic sensitivity to natural killer (NK) cells increased in association with up-regulation of NKG2DLs on tumor cells after incubation with sorafenib and sunitinib. Furthermore, up-regulation in sunitinib group was much higher than in sorafenib group when it came to the expressions of NKG2DLs on tumor cells. For another, ABCG (2) (High) CNE2/DDP was much more sensitive to the regulation than ABCG (2) (Low) CNE2/DDP.

CONCLUSIONS

Our research revealed for the first time that sorafenib and sunitinib could up-regulate NKG2DLs on tumor cells resulting in markedly increased tumor cells cytotoxic sensitivity to NK cells, which suggested that combining usage of molecular targeted agents and ACI may result in great benefits in clinical practice for the therapy-resistant cases and drug-resistant relapse.

Microarray-based gene expression analysis as a process characterization tool to establish comparability of complex biological products: scale-up of a whole-cell immunotherapy product

Whole-cell immunotherapies and other cellular therapies have shown promising results in clinical trials. Due to the complex nature of the whole cell product and of the sometimes limited correlation of clinical potency with the proposed mechanism of action, these cellular immunotherapy products are generally not considered well characterized. Therefore, one major challenge in the product development of whole cell therapies is the ability to demonstrate comparability of product after changes in the manufacturing process. Such changes are nearly inevitable with increase in manufacturing experience leading to improved and robust processes that may have higher commercial feasibility. In order to comprehensively assess the impact of the process changes on the final product, and thus establish comparability, a matrix of characterization assays (in addition to lot release assays) assessing the various aspects of the cellular product are required. In this study, we assessed the capability of DNA-microarray-based, gene-expression analysis as a characterization tool using GVAX cancer immunotherapy cells manufactured by Cell Genesys, Inc. The GVAX immunotherapy product consists two prostate cancer cell lines (CG1940 and CG8711) engineered to secrete human GM-CSF. To demonstrate the capability of the assay, we assessed the transcriptional changes in the product when produced in the presence or absence of fetal bovine serum, and under normal and hypoxic conditions, both changes intended to stress the cell lines. We then assessed the impact of an approximately 10-fold process scale-up on the final product at the transcriptional level. These data were used to develop comparisons and statistical analyses suitable for characterizing culture reproducibility and cellular product similarity. Use of gene-expression data for process characterization proved to be a reproducible and sensitive method for detecting differences due to small or large changes in culture conditions as might be encountered in process scale-up or unanticipated bioprocess failures. Gene expression analysis demonstrated that cell products of representative lots under the same production process and at the same production scale were statistically identical. Large process changes that resulted from the artificial stress conditions used (absence of FBS and induction of hypoxia) displayed profoundly different gene expression patterns. We propose the use of simple t-test analysis in combination with the herein introduced expression ratio with mean intensity (ERMI) analysis as useful tools for process characterization by global gene expression analysis.

Immunotherapy for cancer: synthetic carbohydrate-based vaccines

Aberrant glycosylation of glycoproteins and glycolipids of cancer cells, which correlates with poor survival rates, is being exploited for the development of immunotherapies for cancer. In particular, advances in the knowledge of cooperation between the innate and adaptive system combined with the implementation of efficient synthetic methods for assembly of oligosaccharides and glycopeptides is providing avenues for the rationale design of vaccine candidates. In this respect, fully synthetic vaccine candidates show great promise because they incorporate only those elements requires for relevant immune responses, and hence do not suffer from immune suppression observed with classical carbohydrate-protein conjugate vaccines. Such vaccines are chemically well-defined and it is to be expected that they can be produced in a reproducible fashion. In this feature article, recent advances in the development of fully synthetic sub-unit carbohydrate-based cancer vaccines will be discussed.

Role of the immunosuppressive enzyme indoleamine 2,3-dioxygenase in the progression of ovarian carcinoma

OBJECTIVE

Indoleamine 2,3-dioxygenase (IDO) is a tryptophan-catabolizing enzyme that induces immune tolerance. The purpose of the present study is to investigate IDO expression and its functional role in ovarian cancer cells in vitro and in vivo.

METHODS

IDO expression was immunohistochemically scored in surgically-resected ovarian cancer tissues (n=60), and its association with tumor-infiltrating lymphocyte (TIL) count or patient survival was analyzed. Next, IDO cDNA was transfected into the human ovarian carcinoma cell line SKOV3, establishing stable clones of IDO-overexpressing cells (SK-IDO). SK-IDO cells were characterized in vitro as well as in vivo using a nude mouse xenograft model.

RESULTS

High IDO expression in tumor cells was found in 34 (56.7%) cases and was correlated with a reduced number of CD8+ TIL. Patients with high IDO expression had significantly impaired overall and progression-free survival compared to patients with no or low IDO expression. There were no significant differences in in vitro cell proliferation, migration, invasion, or chemosensitivity to paclitaxel between the SK-IDO and control vector-transfected (SK-pcDNA) cells. However, tumor peritoneal dissemination was significantly increased in SK-IDO-xenografted mice compared to SK-pcDNA-xenografted mice. This tumor-progressive effect in SK-IDO-xenografted mice was abrogated by oral administration of the IDO inhibitor 1-methyl-tryptophan (1-MT). Finally, treatment with weekly i.p. paclitaxel combined with daily administration of 1-MT significantly prolonged the survival of the SK-IDO-xenografted mice compared to treatment with paclitaxel alone.

CONCLUSIONS

These results suggest that IDO is involved in ovarian cancer progression in vivo and may be a promising therapeutic target for advanced ovarian cancer.

Identification of tumor-associated, MHC class II-restricted phosphopeptides as targets for immunotherapy

The activation and recruitment of CD4(+) T cells are critical for the development of efficient antitumor immunity and may allow for the optimization of current cancer immunotherapy strategies. Searching for more optimal and selective targets for CD4(+) T cells, we have investigated phosphopeptides, a new category of tumor-derived epitopes linked to proteins with vital cellular functions. Although MHC I-restricted phosphopeptides have been identified, it was previously unknown whether human MHC II molecules present phosphopeptides for specific CD4(+) T cell recognition. We first demonstrated the fine specificity of human CD4(+) T cells to discriminate a phosphoresidue by using cells raised against the candidate melanoma antigen mutant B-Raf or its phosphorylated counterpart. Then, we assessed the presence and complexity of human MHC II-associated phosphopeptides by analyzing 2 autologous pairs of melanoma and EBV-transformed B lymphoblastoid lines. By using sequential affinity isolation, biochemical enrichment, mass spectrometric sequencing, and comparative analysis, a total of 175 HLA-DR-associated phosphopeptides were characterized. Many were derived from source proteins that may have roles in cancer development, growth, and metastasis. Most were expressed exclusively by either melanomas or transformed B cells, suggesting the potential to define cell type-specific phosphatome "fingerprints." We then generated HLA-DRbeta1*0101-restricted CD4(+) T cells specific for a phospho-MART-1 peptide identified in both melanoma cell lines. These T cells showed specificity for phosphopeptide-pulsed antigen-presenting cells as well as for intact melanoma cells. This previously undescribed demonstration of MHC II-restricted phosphopeptides recognizable by human CD4(+) T cells provides potential new targets for cancer immunotherapy.

Central role of tumor-associated CD8+ T effector/memory cells in restoring systemic antitumor immunity

Sustained delivery of IL-12 and GM-CSF to tumors induces the activation of tumor-resident CD8(+) T effector/memory cells (Tem) followed by cytotoxic CD8(+) T effector cell expansion. To determine whether the secondary effectors expanded from tumor-associated Tem or were primed de novo, activation kinetics of tumor-draining lymph node (TDLN) CD8(+) T cells were analyzed. Treatment promoted a 4-fold increase in the numbers of TDLN CD8(+) T cells displaying a CD69(+)CCR5(+)CD62L(-) periphery-homing effector phenotype by day 4 posttherapy. Pulse labeling of tumor and TDLN T cells with BrdU confirmed that proliferation occurred exclusively within the draining lymph nodes between days 1 and 4 with subsequent migration of primed CD8(+) T effectors to tumors on day 7. Day 4 CD8(+) T effector cells preferentially homed to and lysed experimental, but not control, tumors, establishing tumor specificity. To determine whether the secondary CD8(+) T effector cell response was dependent on activation of tumor-resident CD8(+) Tem, mice that were selectively depleted of tumor-infiltrating CD8(+) T cells were treated and monitored for T effector priming. In the absence of tumor-resident CD8(+) Tem, T effector cell expansion was completely abrogated in the TDLN, revealing that restoration of CD8(+) Tem function was critical to the induction of secondary T effectors. T cell priming failed to occur in IFN-gamma or perforin knockout mice, demonstrating that the requirement for Tem activation was associated with induction of Tem cytotoxicity. These data confirm that intratumoral IL-12 plus GM-CSF induces de novo priming of tumor-specific CD8(+) T effector cells in the TDLN and establish the critical role of preexisting intratumoral CD8(+) Tem in driving this process.

The effects of salt on the physicochemical properties and immunogenicity of protein based vaccine formulated in cationic liposome

Recently, we have developed a simple and potent therapeutic cancer vaccine consisting of a cationic lipid and a peptide antigen. In this report, we expanded the utility of this formulation to protein based vaccines. First, we formulated the human papillomavirus (HPV) 16 E7 protein (E7) in different doses of DOTAP liposome. The results showed that these formulations failed to regress an established tumor. However, when sodium chloride (30 mM) was added to the DOTAP (100 nmol)/E7 (20 microg) formulation, anti-tumor activity was generated in the immunized mice. Correlatively, 30 mM NaCl in the DOTAP/E7 protein formulation increased the particle size from approximately 350 to 550 nm, decreased the protein loading capacity (from 95 to 90%), and finally increased the zeta potential (from 29 to 38 mV). Next, a model protein antigen ovalbumin (OVA) was formulated in different doses of DOTAP liposomes. Similarly, the results showed that 20 microg OVA formulated in 200 nmol DOTAP with 30 mM NaCl had the best OVA-specific antibody response, including both IgG(1) and IgG(2a), suggesting both Th1 and Th2 immune responses were generated by this formulation. In conclusion, we have expanded the application of cationic DOTAP liposome formulation to protein based vaccines and also identified that small amounts of salt could change the physicochemical properties of the vaccine formulation and enhance the activity of the DOTAP/protein based vaccine. The enhancement of immune responses by salt is possibly due to its interference of the electrostatic interaction between the cationic lipid and the protein antigen to facilitate the antigen release from the carrier and at the same time activate the antigen presenting cells.

Reactive oxygen species play a central role in the activity of cationic liposome based cancer vaccine

Recently, we developed a simple and potent therapeutic liposome cancer vaccine consisting of a peptide antigen and a cationic lipid. The molecular mechanism of the adjuvanticity of cationic liposome was studied and described in the current report. First, cationic DOTAP liposome, but not the neutral liposome DOPC, was shown to generate reactive oxygen species (ROS) in mouse bone marrow-derived dendritic cells (BMDC). ROS generation by DOTAP was required for ERK and p38 activation and downstream chemokine/cytokine induction. Furthermore, ROS were shown to be involved in the expression of the co-stimulatory molecules CD86/CD80 induced by DOTAP. However, as the DOTAP concentration increased from 50 to 800 microM, the apoptotic marker Annexin V and ROS double positive cells increased, suggesting that high dose of DOTAP-generated ROS causes cell apoptosis. In vivo, optimal amount of ROS in the draining lymph nodes (DLN) and anti-tumor (HPV positive TC-1 tumor) activity induced by E7 peptide (antigen derived from E7 oncoprotein of human papillomavirus (HPV) type 16) formulated in 100 nmol DOTAP were attenuated by incorporating DOPC in the formulation, suggesting that ROS are essential for the vaccine induced anti-tumor activity. Moreover, 600 nmol DOTAP/E7 generated huge amount of ROS in the DLN and showed no activity of tumor regression. Interestingly, 600 nmol DOTAP/E7-induced ROS were tuned down to the same level induced by 100 nmol DOTAP/E7 by adding DOPC in the formulation and this formulation showed tumor regression activity. In conclusion, DOTAP is an active DC stimulator resulting in the activation of ERK and p38 and induction of chemokines, cytokines and co-stimulatory molecules mediated by appropriate amount of ROS. Our data elucidated an important mechanism of adjuvant activity of cationic liposome and could facilitate rational design of synthetic lipid based adjuvants and vaccine formulation.