A Novel Breast/Ovarian Cancer Peptide Vaccine Platform That Promotes Specific Type-1 but not Treg/Tr1-type Responses

Quantitative MRI cell tracking of immune cell recruitment to tumors and draining lymph nodes in response to anti-PD-1 and a DPX-based immunotherapy

DPX is a unique T cell activating formulation that generates robust immune responses (both clinically and preclinically) which can be tailored to various cancers via the use of tumor-specific antigens and adjuvants. While DPX-based immunotherapies may act complementary with checkpoint inhibitors, combination therapy is not always easily predictable based on individual therapeutic responses. Optimizing these combinations can be improved by understanding the mechanism of action underlying the individual therapies. Magnetic Resonance Imaging (MRI) allows tracking of cells labeled with superparamagnetic iron oxide (SPIO), which can yield valuable information about the localization of crucial immune cell subsets. In this work, we evaluated the use of a multi-echo, single point MRI pulse sequence, TurboSPI, for tracking and quantifying cytotoxic T lymphocytes (CTLs) and myeloid lineage cells (MLCs). In a subcutaneous cervical cancer model (C3) we compared untreated mice to mice treated with either a single therapy (anti-PD-1 or DPX-R9F) or a combination of both therapies. We were able to detect, using TurboSPI, significant increases in CTL recruitment dynamics in response to combination therapy. We also observed differences in MLC recruitment to therapy-draining (DPX-R9F) lymph nodes in response to treatment with DPX-R9F (alone or in combination with anti-PD-1). We demonstrated that the therapies presented herein induced time-varying changes in cell recruitment. This work establishes that these quantitative molecular MRI techniques can be expanded to study a number of cancer and immunotherapy combinations to improve our understanding of longitudinal immunological changes and mechanisms of action.

Therapeutic vaccines for aggressive B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most common aggressive B-cell lymphoma and highly heterogeneous disease. With the standard immunochemotherapy, anti-CD20 antibody rituximab (R-) plus CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) chemotherapy, 30-40% of DLBCLs are refractory to initial immunochemotherapy or experience relapse post-therapy with poor clinical outcomes despite salvage therapies. Mechanisms underlying chemoresistance and relapse are heterogeneous across DLBCL and within individual patients, representing hurdles for targeted therapies targeting a specific oncogenic signaling pathway. In recent years, paradigm-shifting immunotherapies have shown impressive efficacy in various cancer types regardless of underlying oncogenic mechanisms. Vaccines are being developed for DLBCL to build protective immunity against relapse after first complete remission and to promote antitumor immune responses synergizing with immune checkpoint inhibitors to treat refractory/relapsed patients. This article provides a brief review of current progress in vaccine development in DLBCL and discussion on immunologic mechanisms underlying the therapeutic effectiveness and resistance.

Generation of highly activated, antigen-specific tumor-infiltrating CD8+ T cells induced by a novel T cell-targeted immunotherapy

The induction of tumor-targeted, cytotoxic T lymphocytes has been recognized as a key component to successful immunotherapy. DPX-based treatment was previously shown to effectively recruit activated CD8⁺ T cells to the tumor. Herein, we analyze the unique phenotype of the CD8⁺ T cells recruited into the tumor in response to DPX-based therapy, and how combination with checkpoint inhibitors impacts T cell response. C3-tumor-bearing mice were treated with cyclophosphamide (CPA) for seven continuous days every other week, followed by DPX treatment along with anti-CTLA-4 and/or anti-PD-1. Efficacy, immunogenicity, and CD8⁺ T cells tumor infiltration were assessed. The expression of various markers, including checkpoint markers, peptide specificity, and proliferation and activation markers, was determined by flow cytometry. tSNE analysis of the flow data revealed a resident phenotype of CD8⁺ T cells (PD-1⁺TIM-3⁺CTLA-4⁺) within untreated tumors, whereas DPX/CPA treatment induced recruitment of a novel population of CD8⁺ T cells (PD-1⁺TIM-3⁺CTLA-4⁻) within tumors. Combination of anti-CTLA-4 (ipilimumab) with DPX/CPA versus DPX/CPA alone significantly increased survival and inhibition of tumor growth, without changing overall systemic immunogenicity. Addition of checkpoint inhibitors did not significantly change the phenotype of the newly recruited cells induced by DPX/CPA. Yet, anti-CTLA-4 treatment in combination with DPX/CPA enhanced a non-antigen specific response within the tumor. Finally, the tumor-recruited CD8⁺ T cells induced by DPX/CPA were highly activated, antigen-specific, and proliferative, while resident phenotype CD8⁺ T cells, seemingly initially exhausted, were reactivated with combination treatment. This study supports the potential of combining DPX/CPA with ipilimumab to further enhance survival clinically.

Up-to-date role of biologics in the management of respiratory syncytial virus

INTRODUCTION

Respiratory syncytial virus (RSV) is a leading cause of severe lower respiratory tract disease in young children and a substantial contributor to respiratory tract disease throughout life. Despite RSV being a high priority for vaccine development, there is currently no safe and effective vaccine available. There are many challenges to developing an RSV vaccine and there are limited antiviral drugs or biologics available for the management of infection. In this article, we review the antiviral treatments, vaccination strategies along with alternative therapies for RSV.

AREAS COVERED

This review is a summary of the current antiviral and RSV vaccination approaches noting strategies and alternative therapies that may prevent or decrease the disease severity in RSV susceptible populations.

EXPERT OPINION

This review discusses anti-RSV strategies given that no safe and efficacious vaccines are available, and therapeutic treatments are limited. Various biologicals that target for RSV are considered for disease intervention, as it is likely that it may be necessary to develop separate vaccines or therapeutics for each at-risk population.

The respiratory syncytial virus vaccine landscape: lessons from the graveyard and promising candidates

The global burden of disease caused by respiratory syncytial virus (RSV) is increasingly recognised, not only in infants, but also in older adults (aged ≥65 years). Advances in knowledge of the structural biology of the RSV surface fusion glycoprotein have revolutionised RSV vaccine development by providing a new target for preventive interventions. The RSV vaccine landscape has rapidly expanded to include 19 vaccine candidates and monoclonal antibodies (mAbs) in clinical trials, reflecting the urgency of reducing this global health problem and hence the prioritisation of RSV vaccine development. The candidates include mAbs and vaccines using four approaches: (1) particle-based, (2) live-attenuated or chimeric, (3) subunit, (4) vector-based. Late-phase RSV vaccine trial failures highlight gaps in knowledge regarding immunological protection and provide lessons for future development. In this Review, we highlight promising new approaches for RSV vaccine design and provide a comprehensive overview of RSV vaccine candidates and mAbs in clinical development to prevent one of the most common and severe infectious diseases in young children and older adults worldwide.

A Respiratory Syncytial Virus Vaccine Based on the Small Hydrophobic Protein Ectodomain Presented With a Novel Lipid-Based Formulation Is Highly Immunogenic and Safe in Adults: A First-in-Humans Study

Background

Respiratory syncytial virus infection can cause lower respiratory tract infection in older adults comparable to influenza, but no vaccines are available.

Methods

This was a randomized, observer-blinded, first-in-humans study of a novel synthetic RSV antigen based on the ectodomain of the small hydrophobic glycoprotein (SHe) of RSV subgroup A, formulated with either the lipid and oil-based vaccine platform DepoVax (DPX-RSV[A]) or alum (RSV[A]-Alum), in healthy, 50-64-year-old individuals. Two dose levels (10 or 25 µg) of SHe with each formulation were compared to placebo. A booster dose was administered on day 56.

Results

There was no indication that the vaccine was unsafe. Mild pain, drowsiness, and muscles aches were the most common solicited adverse events (AEs), and the frequencies of the AEs did not increase after dose 2. Robust anti-SHe-specific immune responses were demonstrated in the DPX-RSV(A) 10-μg and 25-μg groups (geometric mean titer, approximately 10-fold and 100-fold greater than that of placebo at days 56 and 236, respectively), and responses were sustained in the DPX-RSV(A) 25-μg group at day 421. Responses to the RSV(A)-Alum vaccines were very low.

Conclusions

A novel antigen from the SH protein of RSV, formulated in a lipid and oil-based vaccine platform, was highly immunogenic, with sustained antigen-specific antibody responses, and had an acceptable safety profile.

Unique depot formed by an oil based vaccine facilitates active antigen uptake and provides effective tumour control

Background

Oil emulsions are commonly used as vaccine delivery platforms to facilitate slow release of antigen by forming a depot at the injection site. Antigen is trapped in the aqueous phase and as the emulsion degrades in vivo the antigen is passively released. DepoVax™ is a unique oil based delivery system that directly suspends the vaccine components in the oil diluent that forces immune cells to actively take up components from the formulation in the absence of passive release. The aim of this study was to use magnetic resonance imaging (MRI) with additional biological markers to evaluate and understand differences in clearance between several different delivery systems used in peptide-based cancer vaccines.

Methods

C57BL/6 mice were implanted with a cervical cancer model and vaccinated 5 days post-implant with either DepoVax (DPX), a water-in-oil emulsion (w/o), a squalene oil-in-water emulsion (squal o/w) or a saponin/liposome emulsion (sap/lip) containing iron oxide-labeled targeted antigen. MRI was then used to monitor antigen clearance, the site of injection, tumour and inguinal lymph node volumes and other gross anatomical changes. HLA-A2 transgenic mice were also vaccinated to evaluate immune responses of human directed peptides.

Results

We demonstrated differences in antigen clearance between DPX and w/o both in regard to how quickly the antigen was cleared and the pattern in which it was cleared. We also found differences in lymph node responses between DPX and both squal o/w and sap/lip.

Conclusions

These studies underline the unique mechanism of action of this clinical stage vaccine delivery system.

Electronic supplementary material

The online version of this article (10.1186/s12929-018-0413-9) contains supplementary material, which is available to authorized users.

Using lymph node swelling as a potential biomarker for successful vaccination

There is currently a lack of biomarkers to help properly assess novel immunotherapies at both the preclinical and clinical stages of development. Recent work done by our group indicated significant volume changes in the vaccine draining right lymph node (RLN) volumes of mice that had been vaccinated with DepoVaxTM, a lipid-based vaccine platform that was developed to enhance the potency of peptide-based vaccines. These changes in lymph node (LN) volume were unique to vaccinated mice.To better assess the potential of volumetric LN markers for multiple vaccination platforms, we evaluated 100 tumor bearing mice and assessed their response to vaccination with either a DepoVax based vaccine (DPX) or a water-in-oil emulsion (w/o), and compared them to untreated controls. MRI was used to longitudinally monitor LN and tumor volumes weekly over 4 weeks. We then evaluated changes in LN volumes occurring in response to therapy as a potential predictive biomarker for treatment success.We found that for both vaccine types, DPX and w/o, the %RLN volumetric increase over baseline and the ratio of RLN/LLN were strong predictors of successful tumor suppression (LLN is left inguinal LN). The area under the curve (AUC) was greatest, between 0.75-0.85, two (%RLN) or three (RLN/LLN) weeks post-vaccination. For optimized critical thresholds we found these biomarkers consistently had sensitivity >90% and specificity >70% indicating strong prognostic potential. Vaccination with DepoVax had a more pronounced effect on draining lymph nodes than w/o emulsion vaccines, which correlated with a higher anti-tumor activity in DPX-treated mice.

Using MRI cell tracking to monitor immune cell recruitment in response to a peptide-based cancer vaccine

PURPOSE

MRI cell tracking can be used to monitor immune cells involved in the immunotherapy response, providing insight into the mechanism of action, temporal progression of tumor growth, and individual potency of therapies. To evaluate whether MRI could be used to track immune cell populations in response to immunotherapy, CD8⁺ cytotoxic T cells, CD4⁺ CD25⁺ FoxP3⁺ regulatory T cells, and myeloid-derived suppressor cells were labeled with superparamagnetic iron oxide particles.

METHODS

Superparamagnetic iron oxide-labeled cells were injected into mice (one cell type/mouse) implanted with a human papillomavirus-based cervical cancer model. Half of these mice were also vaccinated with DepoVax^TM (ImmunoVaccine, Inc., Halifax, Nova Scotia, Canada), a lipid-based vaccine platform that was developed to enhance the potency of peptide-based vaccines.

RESULTS

MRI visualization of CD8⁺ cytotoxic T cells, regulatory T cells, and myeloid-derived suppressor cells was apparent 24 h post-injection, with hypointensities due to iron-labeled cells clearing approximately 72 h post-injection. Vaccination resulted in increased recruitment of CD8⁺ cytotoxic T cells, and decreased recruitment of myeloid-derived suppressor cells and regulatory T cells to the tumor. We also found that myeloid-derived suppressor cell and regulatory T cell recruitment were positively correlated with final tumor volume.

CONCLUSION

This type of analysis can be used to noninvasively study changes in immune cell recruitment in individual mice over time, potentially allowing improved application and combination of immunotherapies. Magn Reson Med 80:304-316, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Type III hypersensitivity reactions to a B cell epitope antigen are abrogated using a depot forming vaccine platform

Peptide antigens are combined with an adjuvant in order to increase immunogenicity in vivo. The immunogenicity and safety of a RSV vaccine formulated in a novel oil-based platform, DepoVax™ (DPX), was compared to an alum formulation. A peptide B cell epitope derived from RSV small hydrophobic ectodomain (SHe) served as the antigen. Both vaccines induced SHe-specific antibodies after immunization of mice. A single dose of the DPX-based formulation resulted in anti-SHe titres for up to 20 weeks. Boosting with Alum-SHe, but not with DPX-SHe, led to unexpected clinical signs such as decreased activity, cyanosis and drop in body temperature in mice but not in rabbits. The severity of adverse reactions correlated with magnitude of SHe-specific IgG immune responses and decreased complement component 3 plasma levels, indicating a type III hypersensitivity reaction. By RP-HPLC analysis, we found that only 8-20% of the antigen was found to be adsorbed to alum in vitro, indicating that this antigen is likely released systemically upon injection in vivo. Clinical signs were not observed in rabbits, indicating the response correlates with peptide dose relative to size of animal. These results suggest that peptide antigens targeted to produce B cell mediated response may result in increased incidence of type III hypersensitivity reactions when delivered in non-depot forming vaccines. The DPX formulation induced strong antibody titres to the antigen without causing adverse events, likely due to the strength of the depot in vivo, and demonstrates the potential safety and immunogenicity of this platform for B cell peptide antigens.

A novel immunization approach for dengue infection based on conserved T cell epitopes formulated in calcium phosphate nanoparticles

Dengue virus (DV) is the etiologic agent of dengue fever, the most significant mosquito-borne viral disease in humans. Most DV vaccine approaches are focused on generating antibody mediated responses; one such DV vaccine is approved for use in humans but its efficacy is limited. While it is clear that T cell responses play important role in DV infection and subsequent disease manifestations, fewer studies are aimed at developing vaccines that induce robust T cells responses. Potent T cell based vaccines require 2 critical components: the identification of specific T cell stimulating MHC associated peptides, and an optimized vaccine delivery vehicle capable of simultaneously delivering the antigens and any required adjuvants. We have previously identified and characterized DV specific HLA-A2 and -A24 binding DV serotypes conserved epitopes, and the feasibility of an epitope based vaccine for DV infection. In this study, we build on those previous studies and describe an investigational DV vaccine using T cell epitopes incorporated into a calcium phosphate nanoparticle (CaPNP) delivery system. This study presents a comprehensive analysis of functional immunogenicity of DV CaPNP/multipeptide formulations in vitro and in vivo and demonstrates the CaPNP/multipeptide vaccine is capable of inducing T cell responses against all 4 serotypes of DV. This synthetic vaccine is also cost effective, straightforward to manufacture, and stable at room temperature in a lyophilized form. This formulation may serve as an effective candidate DV vaccine that protects against all 4 serotypes as either a prophylactic or therapeutic vaccine.

Combination of poly I:C and Pam3CSK4 enhances activation of B cells in vitro and boosts antibody responses to protein vaccines in vivo

Vaccines that can rapidly induce strong and robust antibody-mediated immunity could improve protection from certain infectious diseases for which current vaccine formulations are inefficient. For indications such as anthrax and influenza, antibody production in vivo is a correlate of efficacy. Toll-like receptor (TLR) agonists are frequently studied for their role as vaccine adjuvants, largely because of their ability to enhance initiation of immune responses to antigens by activating dendritic cells. However, TLRs are also expressed on B cells and may contribute to effective B cell activation and promote differentiation into antigen-specific antibody producing plasma cells in vivo. We sought to discover an adjuvant system that could be used to augment antibody responses to influenza and anthrax vaccines. We first characterized an adjuvant system in vitro which consisted of two TLR ligands, poly I:C (TLR3) and Pam3CSK4 (TLR2), by evaluating its effects on B cell activation. Each agonist enhanced B cell activation through increased expression of surface receptors, cytokine secretion and proliferation. However, when B cells were stimulated with poly I:C and Pam3CSK4 in combination, further enhancement to cell activation was observed. Using B cells isolated from knockout mice we confirmed that poly I:C and Pam3CSK4 were signaling through TLR3 and TLR2, respectively. B cells activated with Poly I:C and Pam3CSK4 displayed enhanced capacity to stimulate allogeneic CD4⁺ T cell activation and differentiate into antibody-producing plasma cells in vitro. Mice vaccinated with influenza or anthrax antigens formulated with poly I:C and Pam3CSK4 in DepoVax^™ vaccine platform developed a rapid and strong antigen-specific serum antibody titer that persisted for at least 12 weeks after a single immunization. These results demonstrate that combinations of TLR adjuvants promote more effective B cell activation in vitro and can be used to augment antibody responses to vaccines in vivo.

Anti-PD-1 increases the clonality and activity of tumor infiltrating antigen specific T cells induced by a potent immune therapy consisting of vaccine and metronomic cyclophosphamide

BACKGROUND

Future cancer immunotherapies will combine multiple treatments to generate functional immune responses to cancer antigens through synergistic, multi-modal mechanisms. In this study we explored the combination of three distinct immunotherapies: a class I restricted peptide-based cancer vaccine, metronomic cyclophosphamide (mCPA) and anti-PD-1 treatment in a murine tumor model expressing HPV16 E7 (C3).

METHODS

Mice were implanted with C3 tumors subcutaneously. Tumor bearing mice were treated with mCPA (20 mg/kg/day PO) for seven continuous days on alternating weeks, vaccinated with HPV16 E749-57 peptide antigen formulated in the DepoVax (DPX) adjuvanting platform every second week, and administered anti-PD-1 (200 μg/dose IP) after each vaccination. Efficacy was measured by following tumor growth and survival. Immunogenicity was measured by IFN-γ ELISpot of spleen, vaccine draining lymph nodes and tumor draining lymph nodes. Tumor infiltration was measured by flow cytometry for CD8α+ peptide-specific T cells and RT-qPCR for cytotoxic proteins. The clonality of tumor infiltrating T cells was measured by TCRβ sequencing using genomic DNA.

RESULTS

Untreated C3 tumors had low expression of PD-L1 in vivo and anti-PD-1 therapy alone provided no protection from tumor growth. Treatment with DPX/mCPA could delay tumor growth, and tri-therapy with DPX/mCPA/anti-PD-1 provided long-term control of tumors. We found that treatment with DPX/mCPA/anti-PD-1 enhanced systemic antigen-specific immune responses detected in the spleen as determined by IFN-γ ELISpot compared to those in the DPX/mCPA group, but immune responses in tumor-draining lymph nodes were not increased. Although no increases in antigen-specific CD8α+ TILs could be detected, there was a trend for increased expression of cytotoxic genes within the tumor microenvironment as well as an increase in clonality in mice treated with DPX/mCPA/anti-PD-1 compared to those with anti-PD-1 alone or DPX/mCPA. Using a library of antigen-specific CD8α+ T cell clones, we found that antigen-specific clones were more frequently expanded in the DPX/mCPA/anti-PD-1 treated group.

CONCLUSIONS

These results demonstrate how the efficacy of anti-PD-1 may be improved by combination with a potent and targeted T cell activating immune therapy.

Using MRI to evaluate and predict therapeutic success from depot-based cancer vaccines

In the preclinical development of immunotherapy candidates, understanding the mechanism of action and determining biomarkers that accurately characterize the induced host immune responses is critical to improving their clinical interpretation. Magnetic resonance imaging (MRI) was used to evaluate in vivo changes in lymph node size in response to a peptide-based cancer vaccine therapy, formulated using DepoVax (DPX). DPX is a novel adjuvant lipid-in-oil-based formulation that facilitates enhanced immune responses by retaining antigens at the injection site for extended latencies, promoting increased potentiation of immune cells. C57BL/6 mice were implanted with C3 (HPV) tumor cells and received either DPX or control treatments, 5 days post-implantation. Complete tumor eradication occurred in DPX-vaccinated animals and large volumetric increases were observed in the vaccine-draining right inguinal lymph node (VRILN) in DPX mice, likely corresponding to increased localized immune response to the vaccine. Upon evaluating the relative measure of vaccine-potentiated immune activation to tumor-induced immune response (VRILN/VLILN), receiver-operating characteristic (ROC) curves revealed an area under the curve (AUC) of 0.90 (±0.07), indicating high specificity and sensitivity as a predictive biomarker of vaccine efficacy. We have determined that for this tumor model, early MRI lymph node volumetric changes are predictive of depot immunotherapeutic success.

Peptide vaccines in breast cancer: The immunological basis for clinical response

This review discusses peptide-based vaccines in breast cancer, immune responses and clinical outcomes, which include studies on animal models and phase I, phase I/II, phase II and phase III clinical trials. Peptide-based vaccines are powerful neoadjuvant immunotherapies that can directly target proteins expressed in tumor cells, mainly tumor-associated antigens (TAAs). The most common breast cancer TAA epitopes are derived from MUC1, HER2/neu and CEA proteins. Peptides derived from TAAs could be successfully used to elicit CD8 and CD4 T cell-specific responses. Thus, choosing peptides that adapt to natural variations of human leukocyte antigen (HLA) genes is critical. The most attractive advantage is that the target response is more specific and less toxic than for other therapies and vaccines. Prominent studies on NeuVax - E75 (epitope for HER2/neu and GM-CSF) in breast cancer and DPX-0907 (HLA-A2-TAAs) expressed in breast cancer, ovarian and prostate cancer have shown the efficacy of peptide-based vaccines as neoadjuvant immunotherapy against cancer. Future peptide vaccine strategies, although a challenge to be applied in a broad range of breast cancers, point to the development of degenerate multi-epitope immunogens against multiple targets.

Survivin-targeted immunotherapy drives robust polyfunctional T cell generation and differentiation in advanced ovarian cancer patients

DepoVax™ is an innovative and strongly immunogenic vaccine platform. Survivin is highly expressed in many tumor types and has reported prognostic value. To generate tumor-specific immune response, a novel cancer vaccine was formulated in DepoVax platform (DPX-Survivac) using survivin HLA class I peptides. Safety and immune potency of DPX-Survivac was tested in combination with immune-modulator metronomic cyclophosphamide in ovarian cancer patients. All the patients receiving the therapy produced antigen-specific immune responses; higher dose vaccine and cyclophosphamide treatment generating significantly higher magnitude responses. Strong T cell responses were associated with differentiation of naïve T cells into central/effector memory (CM/EM) and late differentiated (LD) polyfunctional antigen-specific CD4⁺ and CD8⁺ T cells. This approach enabled rapid de novo activation/expansion of vaccine antigen-specific CD8⁺ T cells and provided a strong rationale for further testing to determine clinical benefits associated with this immune activation. These data represent vaccine-induced T cell activation in a clinical setting to a self-tumor antigen previously described only in animal models.

Metronomic cyclophosphamide enhances HPV16E7 peptide vaccine induced antigen-specific and cytotoxic T-cell mediated antitumor immune response

In clinical trials, metronomic cyclophosphamide (CPA) is increasingly being combined with vaccines to reduce tumor-induced immune suppression. Previous strategies to modulate the immune system during vaccination have involved continuous administration of low dose chemotherapy, studies that have posed unique considerations for clinical trial design. Here, we evaluated metronomic CPA in combination with a peptide vaccine targeting HPV16E7 in an HPV16-induced tumor model, focusing on the cytotoxic T-cell response and timing of low dose metronomic CPA (mCPA) treatment relative to vaccination. Mice bearing C3 tumors were given metronomic CPA on alternating weeks in combination with immunization with a DepoVax vaccine containing HPV16E7_49-57 peptide antigen every 3 weeks. Only the combination therapy provided significant long-term control of tumor growth. The efficacy of the vaccine was uncompromised if given at the beginning or end of a cycle of metronomic CPA. Metronomic CPA had a pronounced lymphodepletive effect on the vaccine draining lymph node, yet did not reduce the development of antigen-specific CD8⁺ T cells induced by vaccination. This enrichment correlated with increased cytotoxic activity in the spleen and increased expression of cytotoxic gene signatures in the tumor. Immunity could be passively transferred through CD8⁺ T cells isolated from tumor-bearing mice treated with the combinatorial treatment regimen. A comprehensive survey of splenocytes indicated that metronomic CPA, in the absence of vaccination, induced transient lymphodepletion marked by a selective expansion of myeloid-derived suppressor cells. These results provide important insights into the multiple mechanisms of metronomic CPA induced immune modulation in the context of a peptide cancer vaccine that may be translated into more effective clinical trial designs.

Clearance of depot vaccine SPIO-labeled antigen and substrate visualized using MRI

Immunotherapies, including peptide-based vaccines, are a growing area of cancer research, and understanding their mechanism of action is crucial for their continued development and clinical application. Exploring the biodistribution of vaccine components may be key to understanding this action. This work used magnetic resonance imaging (MRI) to characterize the in vivo biodistribution of the antigen and oil substrate of the vaccine delivery system known as DepoVax(TM). DepoVax uses a novel adjuvanted lipid-in-oil based formulation to solubilise antigens and promote a depot effect. In this study, antigen or oil were tagged with superparamagnetic iron oxide (SPIO), making them visible on MR images. This enables tracking of individual vaccine components to determine changes in biodistribution. Mice were injected with SPIO-labeled antigen or SPIO-labeled oil, and imaged to examine clearance of labeled components from the vaccine site. The SPIO-antigen was steadily cleared, with nearly half cleared within two months post-vaccination. In contrast, the SPIO-oil remained relatively unchanged. The biodistribution of the SPIO-antigen component within the vaccine site was heterogeneous, indicating the presence of active clearance mechanisms, rather than passive diffusion or drainage. Mice injected with SPIO-antigen also showed MRI contrast for several weeks post-vaccination in the draining inguinal lymph node. These results indicate that MRI can visualize the in vivo longitudinal biodistribution of vaccine components. The sustained clearance is consistent with antigen up-take and trafficking by immune cells, leading to accumulation in the draining lymph node, which corresponds to the sustained immune responses and reduced tumor burden observed in vaccinated mice.

Therapeutic vaccines and cancer: focus on DPX-0907

In an attempt to significantly enhance immunogenicity of peptide cancer vaccines, we developed a novel non-emulsion depot-forming vaccine platform called DepoVax™ (DPX). Human leukocyte antigen (HLA)-A2 restricted peptides naturally presented by cancer cells were used as antigens to create a therapeutic cancer vaccine, DPX-0907. In a phase I clinical study, the safety and immune-activating potential of DPX-0907 in advanced-stage breast, ovarian, and prostate cancer patients were examined, following encouraging results in HLA-A2 transgenic mice. The DPX-0907 vaccine was shown to be safe and well tolerated, with injection-site reactions being the most commonly reported adverse event. Vaccinated cancer patients exhibited a 61% immune response rate, with higher response rates in the breast and ovarian cancer patient cohorts. In keeping with the higher immune efficacy of this vaccine platform, antigen-specific responses were detected in 73% of immune responders after just one vaccination. In 83% of responders, peptide-specific T-cells were detected at two or more time points post-vaccination, with 64% of these patients showing evidence of immune persistence. Immune monitoring also demonstrated the generation of antigen-specific T-cell memory, with the ability to secrete multiple type 1 cytokines. The novel DPX formulation promotes multifunctional effector/memory responses to peptide-based tumor-associated antigens. The data support the capacity of DPX-0907 to elicit type-1 biased immune responses, warranting further clinical development of the vaccine. In this review, we discuss the rationale for developing DPX-based therapeutic cancer vaccine(s), with a focus on DPX-0907, aimed at inducing efficient anti-tumor immunity that may eventually be shown to prolong patient survival.

Tumor Inhibition by DepoVax-Based Cancer Vaccine Is Accompanied by Reduced Regulatory/Suppressor Cell Proliferation and Tumor Infiltration

A successful cancer vaccine needs to overcome the effects of immune-suppressor cells such as Treg lymphocytes, suppressive cytokine-secreting Tr1 cells, and myeloid-derived suppressor cells (MDSCs), while enhancing tumor-specific immune responses. Given the relative poor efficacy associated with current cancer vaccines, a novel vaccine platform called DepoVax^TM (DPX) was developed. C3 tumor-challenged mice were immunized with HPV-E7 peptide in DPX- or conventional-emulsion- (CE-) based vaccine. While control mice showed marked increase in Treg/MDSCs in spleen and blood, in mice treated with DPX-E7 the levels remained similar to tumor-free naive mice. Such differences were also seen within the tumor. Antigen-specific IL10-secreting CD4/CD8 T cells and TGF-β⁺CD8⁺ T cell frequencies were increased significantly in CE-treated and control mice in contrast to DPX-E7-immunized mice. Analysis of tumor-infiltrating cells revealed higher frequency of suppressor cells in untreated controls than in DPX-E7 group while the converse was true for tumor-infiltrating CD8 T cells. Immunization of tumor-bearing HLA-A2 transgenic mice with human vaccine DPX-0907, a peptide-based vaccine for breast/ovarian/prostate cancers, showed efficient induction of immune response to cancer peptides despite the presence of suppressor cells. Thus, this study provides the rationale for using DPX-based cancer vaccines in immune-suppressed cancer patients, to induce effective anticancer immunity.

Cell recruitment and antigen trafficking in afferent lymph after injection of antigen and poly(I:C) containing liposomes, in aqueous or oil-based formulations

After vaccination, innate cell populations transport antigen from the tissue, via the afferent lymphatic vessels, into the local lymph node where they provide critical signals for the generation of an adaptive immune response. The present study uses a unique lymphatic cannulation model to examine, in real time, changes in afferent lymph after injection of a liposome-based delivery system, incorporating diptheria toxoid (DT) and the innate stimulator, poly(I:C). There was a dramatic but temporal recruitment of innate cell populations over time, with neutrophils and monocytes peaking at 6h and 28h post vaccination respectively. The number of dendritic cells (DC) did not increase over the 198h time period, while lymphocytes were slightly elevated at the latest times, indicating the start of an adaptive response. Monocytes and neutrophils were the predominant cell types transporting antigen at the early time points while DC were the most dominant antigen-carrying cells after 78h, predominantly the Sirp-α(high) DC subtype. Resuspending liposomes in oil instead of aqueous solutions has recently been shown to dramatically increase the level and persistence of an immune response and forms the basis of the novel adjuvant formulations, Vaccimax© and Depovax©. In the present study, formulation of the DT and poly(I:C) containing liposomes in an oil carrier dramatically reduced antigen transport to the draining lymph nodes. Examination of the injection site revealed the creation of an ectopic lymphoid tissue with prominent antigen foci and organized lymphoid cells, providing a possible mechanism for the persistence of an immune response in liposome-in-oil adjuvant formulation. Together, the present studies demonstrate the real-time innate in vivo response to vaccination of two novel liposome-based adjuvant systems and the dramatic effect of different carrier formulations.

First-in-man application of a novel therapeutic cancer vaccine formulation with the capacity to induce multi-functional T cell responses in ovarian, breast and prostate cancer patients

Background

DepoVax^TM is a novel non-emulsion depot-forming vaccine platform with the capacity to significantly enhance the immunogenicity of peptide cancer antigens. Naturally processed HLA-A2 restricted peptides presented by breast, ovarian and prostate cancer cells were used as antigens to create a therapeutic cancer vaccine, DPX-0907.

Methods

A phase I clinical study was designed to examine the safety and immune activating potential of DPX-0907 in advanced stage breast, ovarian and prostate cancer patients. A total of 23 late stage cancer patients were recruited and were divided into two dose/volume cohorts in a three immunization protocol.

Results

DPX-0907 was shown to be safe with injection site reactions being the most commonly reported adverse event. All breast cancer patients (3/3), most of ovarian (5/6) and one third of prostate (3/9) cancer patients exhibited detectable immune responses, resulting in a 61% immunological response rate. Immune responses were generally observed in patients with better disease control after their last prior treatment. Antigen-specific responses were detected in 73% of immune responders (44% of evaluable patients) after the first vaccination. In 83% of immune responders (50% of evaluable patients), peptide-specific T cell responses were detected at ≥2 time points post vaccination with 64% of the responders (39% of evaluable patients) showing evidence of immune persistence. Immune monitoring also demonstrated the generation of antigen-specific T cell memory with the ability to secrete multiple Type 1 cytokines.

Conclusions

The novel DepoVax formulation promotes multifunctional effector memory responses to peptide-based tumor associated antigens. The data supports the capacity of DPX-0907 to elicit Type-1 biased immune responses, warranting further clinical development of the vaccine. This study underscores the importance of applying vaccines in clinical settings in which patients are more likely to be immune competent.

Trial Registration

ClinicalTrials.gov NCT01095848

A novel self-assembled nanoparticle vaccine with HIV-1 Tat₄₉₋₅₇/HPV16 E7₄₉₋₅₇ fusion peptide and GM-CSF DNA elicits potent and prolonged CD8⁺ T cell-dependent anti-tumor immunity in mice

Peptide-based vaccines derived from the E7 protein of human papillomavirus (HPV) type 16 were developed to induce effective T cell responses against established cervical cancer, but have met with limited clinical success. It is necessary to develop novel peptide-based strategies to substantially improve the immune response against HPV16-related cancer. In this study, we aimed to design a novel peptide-based self-assembled nanoparticle HPV16 vaccine by combining the cell-penetrating peptide HIV-1 Tat(49-57) that was fused with the HPV16 E7(49-57) cytotoxic T lymphocyte (CTL) epitope and the granulocyte-macrophage colony stimulating factor (GM-CSF) gene, and to investigate how it improves the immune response and the therapeutic outcome ex vivo and in vivo. Nanoparticles were prepared and identified by transmission electron microscopy (TEM), gel retardation and DNase I protection assays. This type of vaccine formulation formed the 20-80 nm nanoparticles, and greatly improved epitope-specific immunity both ex vivo and in vivo. Importantly, this vaccine type was associated with decreased tumor growth and enhanced long-term survival in the prophylactic and therapeutic mouse models. The underlying mechanisms were determined to involve priming of enhanced frequency of CD8(+) memory T subtype cells. These results suggest that the nanoparticle Tat-E7/pGM-CSF represents a promising novel approach to enhance the potency of peptide-based cervical cancer vaccines, and this vaccine design strategy may act as a useful reference for research of virus-associated diseases and specific tumor immunotherapies.

ADAM metallopeptidase domain 17 (ADAM17) is naturally processed through major histocompatibility complex (MHC) class I molecules and is a potential immunotherapeutic target in breast, ovarian and prostate cancers

Selection of suitable antigens is critical for the development of cancer vaccines. Most desirable are over-expressed cell surface proteins that may serve as targets for both antibodies and T cells, thus maximizing a concerted immune response. Towards this goal, we characterized the relevance of tumour necrosis factor-α-converting enzyme (ADAM17) for such targeted therapeutics. ADAM17 is one of the several metalloproteinases that play a key role in epidermal growth factor receptor (EGFR) signalling and has recently emerged as a new therapeutic target in several tumour types. In the present study, we analysed the expression profile of ADAM17 in a variety of normal and cancer cells of human origin and found that this protein is over-expressed on the surface of several types of cancer cells compared to the normal counterparts. Furthermore, we analysed the presentation of a human leucocyte antigen (HLA)-A2-restricted epitope from ADAM17 protein to specific T cells established from normal donors as well as ovarian cancer patients. Our analysis revealed that the HLA-A2-restricted epitope is processed efficiently and presented by various cancer cells and not by normal cells. Tumour-specific T cell activation results in the secretion of both interferon-γ and granzyme B that can be blocked by HLA-A2 specific antibodies. Collectively, our data present evidence that ADAM17 can be a potential target antigen to devise novel immunotherapeutic strategies against ovarian, breast and prostate cancer.

A liposome-based platform, VacciMax, and its modified water-free platform DepoVax enhance efficacy of in vivo nucleic acid delivery

Nucleic acid vaccines represent a promising alternative to killed bacterial antigen, recombinant protein or peptide vaccines for infectious diseases and cancer immunotherapy. Although significant advances are made with DNA vaccines in animal studies, there are severe limitations to deliver these vaccines effectively and considerable reservations exist about current methods used. In this study, a liposome-based vaccine platform, VacciMax (VM), and its modified water-free version, DepoVax (DPX), were tested for their ability to improve in vivo delivery of plasmid DNA (pDNA), mRNA and siRNA. Subcutaneously injected pDNA for IL12 and pDNA as well as mRNA for green fluorescent protein (GFP) in VM/DPX significantly enhanced their in vivo expression. Enhanced IL12 secretion and GFP expression was restricted to CD11b(+) and CD11c(+) antigen-presenting cells, but not B cells. Further, significant inhibition of plasmid/antigen-induced IL12 secretion was seen after injection of IL12-siRNA in VM. These findings suggest VM and DPX to be promising means of delivering nucleic acid vaccines in vivo, and warrant further studies on their role in inducing effective immune responses.