Efficient in vitro and in vivo transfection of self-amplifying mRNA with linear poly(propylenimine) and poly(ethylenimine-propylenimine) random copolymers as non-viral carriers

Messenger RNA (mRNA) based vaccines have been introduced worldwide to combat the Covid-19 pandemic. These vaccines consist of non-amplifying mRNA formulated in lipid nanoparticles (LNPs). Consequently, LNPs are considered benchmark non-viral carriers for nucleic acid delivery. However, the formulation and manufacturing of these mRNA-LNP nanoparticles are expensive and time-consuming. Therefore, we used self-amplifying mRNA (saRNA) and synthesized novel polymers as alternative non-viral carrier platform to LNPs, which enable a simple, rapid, one-pot formulation of saRNA-polyplexes. Our novel polymer-based carrier platform consists of randomly concatenated ethylenimine and propylenimine comonomers, resulting in linear, poly(ethylenimine-ran-propylenimine) (L-PEIx-ran-PPIy) copolymers with controllable degrees of polymerization. Here we demonstrate in multiple cell lines, that our saRNA-polyplexes show comparable to higher in vitro saRNA transfection efficiencies and higher cell viabilities compared to formulations with Lipofectamine MessengerMAX™ (LFMM), a commercial, lipid-based carrier considered to be the in vitro gold standard carrier. This is especially true for our in vitro best performing saRNA-polyplexes with N/P 5, which are characterised with a size below 100 nm, a positive zeta potential, a near 100% encapsulation efficiency, a high retention capacity and the ability to protect the saRNA from degradation mediated by RNase A. Furthermore, an ex vivo hemolysis assay with pig red blood cells demonstrated that the saRNA-polyplexes exhibit negligible hemolytic activity. Finally, a bioluminescence-based in vivo study was performed over a 35-day period, and showed that the polymers result in a higher and prolonged bioluminescent signal compared to naked saRNA and L-PEI based polyplexes. Moreover, the polymers show different expression profiles compared to those of LNPs, with one of our new polymers (L-PPI250) demonstrating a higher sustained expression for at least 35 days after injection.

Chitin-mediated blockade of chitinase-like proteins reduces tumor immunosuppression, inhibits lymphatic metastasis and enhances anti-PD-1 efficacy in complementary TNBC models

BACKGROUND

Chitinase-like proteins (CLPs) play a key role in immunosuppression under inflammatory conditions such as cancer. CLPs are enzymatically inactive and become neutralized upon binding of their natural ligand chitin, potentially reducing CLP-driven immunosuppression. We investigated the efficacy of chitin treatment in the context of triple-negative breast cancer (TNBC) using complementary mouse models. We also evaluated the immunomodulatory influence of chitin on immune checkpoint blockade (ICB) and compared its efficacy as general CLP blocker with blockade of a single CLP, i.e. chitinase 3-like 1 (CHI3L1).

METHODS

Female BALB/c mice were intraductally injected with luciferase-expressing 4T1 or 66cl4 cells and systemically treated with chitin in combination with or without anti-programmed death (PD)-1 ICB. For single CLP blockade, tumor-bearing mice were treated with anti-CHI3L1 antibodies. Metastatic progression was monitored through bioluminescence imaging. Immune cell changes in primary tumors and lymphoid organs (i.e. axillary lymph nodes and spleen) were investigated through flow cytometry, immunohistochemistry, cytokine profiling and RNA-sequencing. CHI3L1-stimulated RAW264.7 macrophages were subjected to 2D lymphatic endothelial cell adhesion and 3D lymphatic integration in vitro assays for studying macrophage-mediated lymphatic remodeling.

RESULTS

Chitin significantly reduced primary tumor progression in the 4T1-based model by decreasing the high production of CLPs that originate from tumor-associated neutrophils (TANs) and Stat3 signaling, prominently affecting the CHI3L1 and CHI3L3 primary tumor levels. It reduced immunosuppressive cell types and increased anti-tumorigenic T-cells in primary tumors as well as axillary lymph nodes. Chitin also significantly reduced CHI3L3 primary tumor levels and immunosuppression in the 66cl4-based model. Compared to anti-CHI3L1, chitin enhanced primary tumor growth reduction and anti-tumorigenicity. Both treatments equally inhibited lymphatic adhesion and integration of macrophages, thereby hampering lymphatic tumor cell spreading. Upon ICB combination therapy, chitin alleviated anti-PD-1 resistance in both TNBC models, providing a significant add-on reduction in primary tumor and lung metastatic growth compared to chitin monotherapy. These add-on effects occurred through additional increase in CD8α+ T-cell infiltration and activation in primary tumor and lymphoid organs.

CONCLUSIONS

Chitin, as a general CLP blocker, reduces CLP production, enhances anti-tumor immunity as well as ICB responses, supporting its potential clinical relevance in immunosuppressed TNBC patients.

Lipid Nanoparticle Encapsulation Empowers Poly(I:C) to Activate Cytoplasmic RLRs and Thereby Increases Its Adjuvanticity

Poly(I:C) is a synthetic analogue of dsRNA capable of activating both TLR3 and RLRs, such as MDA-5 and RIG-I, as pathogen recognition receptors. While poly(I:C) is known to provoke a robust type I IFN, type III IFN, and Th1 cytokine response, its therapeutic use as a vaccine adjuvant is limited due to its vulnerability to nucleases and poor uptake by immune cells. is encapsulated poly(I:C) into lipid nanoparticles (LNPs) containing an ionizable cationic lipid that can electrostatically interact with poly(I:C). LNP-formulated poly(I:C) triggered both lysosomal TLR3 and cytoplasmic RLRs, in vitro and in vivo, whereas poly(I:C) in an unformulated soluble form only triggered endosomal-localized TLR3. Administration of LNP-formulated poly(I:C) in mouse models led to efficient translocation to lymphoid tissue and concurrent innate immune activation following intramuscular (IM) administration, resulting in a significant increase in innate immune activation compared to unformulated soluble poly(I:C). When used as an adjuvant for recombinant full-length SARS-CoV-2 spike protein, LNP-formulated poly(I:C) elicited potent anti-spike antibody titers, surpassing those of unformulated soluble poly(I:C) by orders of magnitude and offered complete protection against a SARS-CoV-2 viral challenge in vivo, and serum from these mice are capable of significantly reducing viral infection in vitro.

Lipid Nanoparticle Delivery Alters the Adjuvanticity of the TLR9 Agonist CpG by Innate Immune Activation in Lymphoid Tissue

Pharmacological strategies to activate innate immune cells are of great relevance in the context of vaccine design and anticancer immune therapy, to mount broad immune responses able to clear infection and malignant cells. Synthetic CpG oligodeoxynucleotides (CpG-ODNs) are short single-stranded DNA molecules containing unmethylated CpG dinucleotides and a phosphorothioate backbone. Class B CpG ODNs activate robust innate immune responses through a TLR9-dependent NF-κB signaling pathway. This feature is attractive to exploit in the context of vaccine design and cancer immunotherapy. Soluble CpG-ODNs cause hepatic toxicity, which reduces its therapeutic applicability. The formulation of class B CpG ODN1826 in lipid nanoparticles (LNPs) containing an ionizable cationic lipid that complexes CpG through electrostatic interaction is reported. Upon local administration, LNP-formulated CpG drains to lymph nodes and triggers robust innate immune activation. Unformulated, soluble, CpG, by contrast, is unable to induce robust innate activation in draining lymph nodes and is distributed systemically. In a vaccination setting, LNP-formulated CpG, admixed with a protein antigen, induces higher antigen-specific antibody titers and T cell responses than antigen admixed with unformulated soluble CpG.

Evaluation of a self-amplifying mRNA reporter vaccine in explant models of broiler chickens

In order to minimize animal loss and economical loss, industrial poultry is heavily vaccinated against infectious agents. mRNA vaccination is an effective vaccination platform, yet little to no comprehensive, comparative studies in avians can be found. Nevertheless, poultry mRNA vaccination could prove to be very interesting due to the relatively low production cost, especially true when using self-amplifying mRNA (saRNA), and their extreme adaptability to new pathogens. The latter could be particularly useful when new pathogens join the stage or new variants arise. As a first step toward the investigation of saRNA vaccines in poultry, this study evaluates a luciferase-encoding saRNA in avian tracheal explants, conjunctival explants, primary chicken cecal cells and 18-day embryonated eggs. Naked saRNA in combination with RNase inhibitor and 2 different lipid-based formulations, that is, ionizable lipid nanoparticles (LNPs) and Lipofectamine Messenger Max, were evaluated. The saRNA-LNP formulation led to the highest bioluminescent signal in the tracheal explants, conjunctival explants and cecal cell cultures. A dose-response experiment with these saRNA-LNPs (33-900 ng/well) in these avian organoids and cells showed a nonlinear dose-response relationship. After in ovo administration, the highest dose of the saRNA-LNPs (5 µg) resulted in a visual expression as a weak bioluminescence signal could be seen. The other delivery approaches did not lead to a visual saRNA expression in the embryos. In conclusion, effective entry of saRNA encapsulated in LNPs followed by successful saRNA translation in poultry was established. Hence, mRNA vaccination in poultry could be possible, but further in vivo testing is needed.

Xenogeneic equine stem cells activate anti-tumor adaptive immunity in a 4T1-based intraductal mouse model for triple-negative breast cancer: proof-of-principle

Triple-negative breast cancer (TNBC) remains difficult to treat, especially due to ineffective immune responses. Current treatments mainly aim at a cytotoxic effect, whereas (stem) cell therapies are being investigated for their immune stimulatory capacities to initiate the anti-tumor immunity. Here, a thoroughly characterized, homogenous and non-tumorigenic mixture of equine mesenchymal stem cells (eMSCs) harvested from horse peripheral blood as innovative xenogeneic immunomodulators were tested in a 4T1-based intraductal mouse model for TNBC. The eMSCs significantly reduced 4T1 progression upon systemic injection, with induction of inflammatory mediators and T-cell influx in primary tumors, already after a single dose. These xenogeneic anti-cancer effects were not restricted to MSCs as systemic treatment with alternative equine epithelial stem cells (eEpSCs) mimicked the reported disease reduction. Mechanistically, effective eMSC treatment did not rely on the spleen as systemic entrapment site, whereas CD4+ and CD8α+ T-cell infiltration and activation were critical. These results show that eMSCs and potentially also other equine stem cell types can be a valuable TNBC treatment strategy for further (pre)clinical evaluation.

One cisplatin dose provides durable stimulation of anti-tumor immunity and alleviates anti-PD-1 resistance in an intraductal model for triple-negative breast cancer

Aggressive triple-negative breast cancer (TNBC) is classically treated with chemotherapy. Besides direct tumor cell killing, some chemotherapeutics such as cisplatin provide additional disease reduction through stimulation of anti-tumor immunity. The cisplatin-induced immunomodulation in TNBC was here investigated in-depth using immunocompetent intraductal mouse models. Upon primary tumor transition to invasive carcinoma, cisplatin was injected systemically and significantly reduced tumor progression. Flow cytometric immunophenotyping was corroborated by immunohistochemical analyses and revealed both differential immune cell compositions and positivity for their programmed death (PD)-1 and PD-ligand (L)1 markers across body compartments, including the primary tumor, axillary lymph nodes and spleen. As key findings, a significant decrease in immunosuppressive and a concomitant increase in anti-tumor lymphocytic cell numbers were observed in the axillary lymph nodes and spleen, highlighting their importance in cisplatin-stimulated anti-tumor immunity. These immunomodulatory effects were already established following the first cisplatin dose, indicating that early cisplatin-mediated events may determine (immuno)therapeutic outcome. Furthermore, a single cisplatin dose sufficed to alleviate anti-PD-1 resistance in a 4T1-based model, providing add-on disease reduction without toxic side effects as seen upon multiple cisplatin dosing. Overall, these results highlight cisplatin as immunotherapeutic ally in TNBC, providing durable immunostimulation, even after a single dose.

Choroid plexus-derived extracellular vesicles exhibit brain targeting characteristics

The brain is protected against invading organisms and other unwanted substances by tightly regulated barriers. However, these central nervous system (CNS) barriers impede the delivery of drugs into the brain via the blood circulation and are therefore considered major hurdles in the treatment of neurological disorders. Consequently, there is a high need for efficient delivery systems that are able to cross these strict barriers. While most research focuses on the blood-brain barrier (BBB), the design of drug delivery platforms that are able to cross the blood-cerebrospinal fluid (CSF) barrier, formed by a single layer of choroid plexus epithelial cells, remains a largely unexplored domain. The discovery that extracellular vesicles (EVs) make up a natural mechanism for information transfer between cells and across cell layers, has stimulated interest in their potential use as drug delivery platform. Here, we report that choroid plexus epithelial cell-derived EVs exhibit the capacity to home to the brain after peripheral administration. Moreover, these vesicles are able to functionally deliver cargo into the brain. Our findings underline the therapeutic potential of choroid plexus-derived EVs as a brain drug delivery vehicle via targeting of the blood-CSF interface.

A dual-antigen self-amplifying RNA SARS-CoV-2 vaccine induces potent humoral and cellular immune responses and protects against SARS-CoV-2 variants through T cell-mediated immunity

Self-amplifying RNA vaccines may induce equivalent or more potent immune responses at lower doses compared to non-replicating mRNA vaccines via amplified antigen expression. In this paper, we demonstrate that 1 μg of an LNP-formulated dual-antigen self-amplifying RNA vaccine (ZIP1642), encoding both the S-RBD and N antigen, elicits considerably higher neutralizing antibody titers against Wuhan-like Beta B.1.351 and Delta B.1.617.2 SARS-CoV-2 variants compared to those of convalescent patients. In addition, ZIP1642 vaccination in mice expanded both S- and N-specific CD3+CD4+ and CD3+CD8+ T cells and caused a Th1 shifted cytokine response. We demonstrate that the induction of such dual antigen-targeted cell-mediated immune response may provide better protection against variants displaying highly mutated Spike proteins, as infectious viral loads of both Wuhan-like and Beta variants were decreased after challenge of ZIP1642 vaccinated hamsters. Supported by these results, we encourage redirecting focus toward the induction of multiple antigen-targeted cell-mediated immunity in addition to neutralizing antibody responses to bypass waning antibody responses and attenuate infectious breakthrough and disease severity of future SARS-CoV-2 variants.

Regulatory guidelines and preclinical tools to study the biodistribution of RNA therapeutics

The success of the messenger RNA-based COVID-19 vaccines of Moderna and Pfizer/BioNTech marks the beginning of a new chapter in modern medicine. However, the rapid rise of mRNA therapeutics has resulted in a regulatory framework that is somewhat lagging. The current guidelines either do not apply, do not mention RNA therapeutics, or do not have widely accepted definitions. This review describes the guidelines for preclinical biodistribution studies of mRNA/siRNA therapeutics and highlights the relevant differences for mRNA vaccines. We also discuss the role of in vivo RNA imaging techniques and other assays to fulfill and/or complement the regulatory requirements. Specifically, quantitative whole-body autoradiography, microautoradiography, mass spectrometry-based assays, hybridization techniques (FISH, bDNA), PCR-based methods, in vivo fluorescence imaging, and in vivo bioluminescence imaging, are discussed. We conclude that this new and rapidly evolving class of medicines demands a multi-layered approach to fully understand its biodistribution and in vivo characteristics.

Mucosal Vaccination Against Periodontal Disease: Current Status and Opportunities

Approximately 9 out of 10 adults have some form of periodontal disease, an infection-induced inflammatory disease of the tooth-supporting tissues. The initial form, gingivitis, often remains asymptomatic, but this can evolve into periodontitis, which is typically associated with halitosis, oral pain or discomfort, and tooth loss. Furthermore, periodontitis may contribute to systemic disorders like cardiovascular disease and type 2 diabetes mellitus. Control options remain nonspecific, time-consuming, and costly; largely relying on the removal of dental plaque and calculus by mechanical debridement. However, while dental plaque bacteria trigger periodontal disease, it is the host-specific inflammatory response that acts as main driver of tissue destruction and disease progression. Therefore, periodontal disease control should aim to alter the host's inflammatory response as well as to reduce the bacterial triggers. Vaccines may provide a potent adjunct to mechanical debridement for periodontal disease prevention and treatment. However, the immunopathogenic complexity and polymicrobial aspect of PD appear to complicate the development of periodontal vaccines. Moreover, a successful periodontal vaccine should induce protective immunity in the oral cavity, which proves difficult with traditional vaccination methods. Recent advances in mucosal vaccination may bridge the gap in periodontal vaccine development. In this review, we offer a comprehensive overview of mucosal vaccination strategies to induce protective immunity in the oral cavity for periodontal disease control. Furthermore, we highlight the need for additional research with appropriate and clinically relevant animal models. Finally, we discuss several opportunities in periodontal vaccine development such as multivalency, vaccine formulations, and delivery systems.

Antibody-Mediated Targeting of Antigens to Intestinal Aminopeptidase N Elicits Gut IgA Responses in Pigs

Many pathogens enter the host via the gut, causing disease in animals and humans. A robust intestinal immune response is necessary to protect the host from these gut pathogens. Despite being best suited for eliciting intestinal immunity, oral vaccination remains a challenge due to the gastrointestinal environment, a poor uptake of vaccine antigens by the intestinal epithelium and the tolerogenic environment pervading the gut. To improve uptake, efforts have focused on targeting antigens towards the gut mucosa. An interesting target is aminopeptidase N (APN), a conserved membrane protein present on small intestinal epithelial cells shown to mediate epithelial transcytosis. Here, we aimed to further optimize this oral vaccination strategy in a large animal model. Porcine APN-specific monoclonal antibodies were generated and the most promising candidate in terms of epithelial transcytosis was selected to generate antibody fusion constructs, comprising a murine IgG1 or porcine IgA backbone and a low immunogenic antigen: the F18-fimbriated E. coli tip adhesin FedF. Upon oral delivery of these recombinant antibodies in piglets, both mucosal and systemic immune responses were elicited. The presence of the FedF antigen however appeared to reduce these immune responses. Further analysis showed that F18 fimbriae were able to disrupt the antigen presenting capacity of intestinal antigen presenting cells, implying potential tolerogenic effects of FedF. Altogether, these findings show that targeted delivery of molecules to epithelial aminopeptidase N results in their transcytosis and delivery to the gut immune systems. The results provide a solid foundation for the development of oral subunit vaccines to protect against gut pathogens.

Strategies for controlling the innate immune activity of conventional and self-amplifying mRNA therapeutics: Getting the message across

The recent approval of messenger RNA (mRNA)-based vaccines to combat the SARS-CoV-2 pandemic highlights the potential of both conventional mRNA and self-amplifying mRNA (saRNA) as a flexible immunotherapy platform to treat infectious diseases. Besides the antigen it encodes, mRNA itself has an immune-stimulating activity that can contribute to vaccine efficacy. This self-adjuvant effect, however, will interfere with mRNA translation and may influence the desired therapeutic outcome. To further exploit its potential as a versatile therapeutic platform, it will be crucial to control mRNA's innate immune-stimulating properties. In this regard, we describe the mechanisms behind the innate immune recognition of mRNA and provide an extensive overview of strategies to control its innate immune-stimulating activity. These strategies range from modifications to the mRNA backbone itself, optimization of production and purification processes to the combination with innate immune inhibitors. Furthermore, we discuss the delicate balance of the self-adjuvant effect in mRNA vaccination strategies, which can be both beneficial and detrimental to the therapeutic outcome.

Squaric Ester-Based, pH-Degradable Nanogels: Modular Nanocarriers for Safe, Systemic Administration of Toll-like Receptor 7/8 Agonistic Immune Modulators

Small-molecular Toll-like receptor 7/8 (TLR7/8) agonists hold promise as immune modulators for a variety of immune therapeutic purposes including cancer therapy or vaccination. However, due to their rapid systemic distribution causing difficult-to-control inflammatory off-target effects, their application is still problematic, in particular systemically. To address this problem, we designed and robustly fabricated pH-responsive nanogels serving as versatile immunodrug nanocarriers for safe delivery of TLR7/8-stimulating imidazoquinolines after intravenous administration. To this aim, a primary amine-reactive methacrylamide monomer bearing a pendant squaric ester amide is introduced, which is polymerized under controlled RAFT polymerization conditions. Corresponding PEG-derived squaric ester amide block copolymers self-assemble into precursor micelles in polar protic solvents. Their cores are amine-reactive and can sequentially be transformed by acid-sensitive cross-linkers, dyes, and imidazoquinolines. Remaining squaric ester amides are hydrophilized affording fully hydrophilic nanogels with profound stability in human plasma but stimuli-responsive degradation upon exposure to endolysosomal pH conditions. The immunomodulatory behavior of the imidazoquinolines alone or conjugated to the nanogels was demonstrated by macrophages in vitro. In vivo, however, we observed a remarkable impact of the nanogel: After intravenous injection, a spatially controlled immunostimulatory activity was evident in the spleen, whereas systemic off-target inflammatory responses triggered by the small-molecular imidazoquinoline analogue were absent. These findings underline the potential of squaric ester-based, pH-degradable nanogels as a promising platform to permit intravenous administration routes of small-molecular TLR7/8 agonists and, thus, the opportunity to explore their adjuvant potency for systemic vaccination or cancer immunotherapy purposes.

Sterilizing Immunity against SARS-CoV-2 Infection in Mice by a Single-Shot and Lipid Amphiphile Imidazoquinoline TLR7/8 Agonist-Adjuvanted Recombinant Spike Protein Vaccine*

The search for vaccines that protect from severe morbidity and mortality because of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19) is a race against the clock and the virus. Here we describe an amphiphilic imidazoquinoline (IMDQ-PEG-CHOL) TLR7/8 adjuvant, consisting of an imidazoquinoline conjugated to the chain end of a cholesterol-poly(ethylene glycol) macromolecular amphiphile. It is water-soluble and exhibits massive translocation to lymph nodes upon local administration through binding to albumin, affording localized innate immune activation and reduction in systemic inflammation. The adjuvanticity of IMDQ-PEG-CHOL was validated in a licensed vaccine setting (quadrivalent influenza vaccine) and an experimental trimeric recombinant SARS-CoV-2 spike protein vaccine, showing robust IgG2a and IgG1 antibody titers in mice that could neutralize viral infection in vitro and in vivo in a mouse model.

OMO-1 reduces progression and enhances cisplatin efficacy in a 4T1-based non-c-MET addicted intraductal mouse model for triple-negative breast cancer

c-MET is considered a driver of cancer progression, impacting tumor growth and tumor-supporting stroma. Here, we investigated the therapeutic efficacy of OMO-1, a potent and selective c-MET inhibitor, in an immunocompetent intraductal mouse model for triple-negative breast cancer (TNBC). OMO-1 reduced non-c-MET addicted 4T1 tumor progression dose dependently as monotherapeutic and provided additional disease reduction in combination with cisplatin. At the stromal level, OMO-1 significantly reduced neutrophil infiltration in 4T1 tumors, promoted immune activation, and enhanced cisplatin-mediated reduction of tumor-associated macrophages. OMO-1 treatment also reduced 4T1 tumor hypoxia and increased expression of pericyte markers, indicative for vascular maturation. Corroborating this finding, cisplatin delivery to the 4T1 primary tumor was enhanced upon OMO-1 treatment, increasing cisplatin DNA-adduct levels and tumor cell death. Although verification in additional cell lines is warranted, our findings provide initial evidence that TNBC patients may benefit from OMO-1 treatment, even in cases of non-c-MET addicted tumors.

Lipid-Polyglutamate Nanoparticle Vaccine Platform

Peptide-based subunit vaccines are attractive in view of personalized cancer vaccination with neo-antigens, as well as for the design of the newest generation of vaccines against infectious diseases. Key to mounting robust antigen-specific immunity is delivery of antigen to antigen-presenting (innate immune) cells in lymphoid tissue with concomitant innate immune activation to promote antigen presentation to T cells and to shape the amplitude and nature of the immune response. Nanoparticles that co-deliver both peptide antigen and molecular adjuvants are well suited for this task. However, in the context of peptide-based antigen, an unmet need exists for a generic strategy that allows for co-encapsulation of peptide and molecular adjuvants due to the stark variation in physicochemical properties based on the amino acid sequence of the peptide. These properties also strongly differ from those of many molecular adjuvants. Here, we devise a lipid nanoparticle (LNP) platform that addresses these issues. Key in our concept is poly(l-glutamic acid) (PGA), which serves as a hydrophilic backbone for conjugation of, respectively, peptide antigen (Ag) and an imidazoquinoline (IMDQ) TLR7/8 agonist as a molecular adjuvant. Making use of the PGA's polyanionic nature, we condensate PGA-Ag and PGA-IMDQ into LNP by electrostatic interaction with an ionizable lipid. We show in vitro and in vivo in mouse models that LNP encapsulation favors uptake by innate immune cells in lymphoid tissue and promotes the induction of Ag-specific T cells responses both after subcutaneous and intravenous administration.

Corticosteroids and cellulose purification improve, respectively, the in vivo translation and vaccination efficacy of sa-mRNAs

Synthetic mRNAs are an appealing platform with multiple biomedical applications ranging from protein replacement therapy to vaccination. In comparison with conventional mRNA, synthetic self-amplifying mRNAs (sa-mRNAs) are gaining interest because of their higher and longer-lasting expression. However, sa-mRNAs also elicit an innate immune response, which may complicate their clinical application. Approaches to reduce the innate immunity of sa-mRNAs have not been studied in detail. Here we investigated, in vivo, the effect of several innate immune inhibitors and a novel cellulose-based mRNA purification approach on the type I interferon (IFN) response and the translation and vaccination efficacy of our formerly developed sa-mRNA vaccine against Zika virus. Among the investigated inhibitors, we found that corticosteroids and especially topical application of clobetasol at the sa-mRNA injection site was the most efficient in suppressing the type I IFN response and increasing the translation of sa-mRNA. However, clobetasol prevented formation of antibodies against sa-mRNA-encoded antigens and should therefore be avoided in a vaccination context. Residual dsRNA by-products of the in vitro transcription reaction are known inducers of immediate type I IFN responses. We additionally demonstrate a drastic reduction of these dsRNA by-products upon cellulose-based purification, reducing the innate immune response and improving sa-mRNA vaccination efficacy.

In Vivo Validation of a Reversible Small Molecule-Based Switch for Synthetic Self-Amplifying mRNA Regulation

Synthetic mRNA therapeutics have the potential to revolutionize healthcare, as they enable patients to produce therapeutic proteins inside their own bodies. However, convenient methods that allow external control over the timing and magnitude of protein production after in vivo delivery of synthetic mRNA are lacking. In this study, we validate the in vivo utility of a synthetic self-amplifying mRNA (RNA replicon) whose expression can be turned off using a genetic switch that responds to oral administration of trimethoprim (TMP), a US Food and Drug Administration (FDA)-approved small-molecule drug. After intramuscular electroporation, the engineered RNA replicon exhibited dose-dependent and reversible expression of its encoded protein upon TMP administration. The TMP serum level needed for maximal downregulation of protein translation was approximately 45-fold below that used in humans for therapeutic purposes. To demonstrate the therapeutic potential of the technology, we injected mice with a TMP-responsive RNA replicon encoding erythropoietin (EPO) and successfully controlled the timing and magnitude of EPO production as well as changes in hematocrit. This work demonstrates the feasibility of controlling mRNA kinetics in vivo, thereby broadly expanding the clinical versatility of mRNA therapeutics.

The Opposing Effect of Type I IFN on the T Cell Response by Non-modified mRNA-Lipoplex Vaccines Is Determined by the Route of Administration

mRNA-lipoplex vaccines are currently being explored in phase II clinical trials for the treatment of patients with advanced solid tumors. Mechanistically, these mRNA-lipoplex vaccines are characterized by the induction of type I interferon (IFN) centered innate responses. Earlier studies have identified type I IFNs as major regulators of the T cell response instigated by mRNA-lipoplex vaccines. However, stimulatory or, in contrast, profound inhibitory effects of type I IFNs were described depending on the study. In this mouse study, we demonstrated that the opposing roles of type I IFN signaling on the magnitude of the vaccine-evoked T cell responses is dependent on the route of mRNA-lipoplex administration and is regulated at the level of the T cells rather than indirectly through modulation of dendritic cell function. This study helps to understand the double-edged sword character of type I IFN induction upon mRNA-based vaccine treatment and may contribute to a more rational design of mRNA vaccination regimens.

Imidazoquinoline-Conjugated Degradable Coacervate Conjugate for Local Cancer Immunotherapy

Strategies that can reduce the harmful side effects of potent immunomodulatory drugs are in high demand to facilitate clinical translation of the newest generation of immunotherapy. Indeed, uncontrolled triggering of the immune system can lead to life-threatening cascade reactions, such as e.g. cytokine storm. In particular, drug formulations that combine simplicity and degradability are of formidable relevance. Imidazoquinolines are an excellent example of such small molecule immunomodulatory drugs that exhibit in unformulated form a highly undesirable pharmacokinetic profile. Imidazoquinolines are potent inducers of type I interferons that are of great interest in the context of anticancer and antiviral therapy through triggering of Toll like receptors 7 and 8. In this work we aimed to alter the pharmacokinetic profile of imidazoquinolines using a simple, yet efficient, strategy that holds high potential for clinical translation. Hereto, we conjugated an imidazoquinoline to the backbone of poly(aspartate) and further formulated this into a degradable coacervate through complex coacervation with a nontoxic degradable polycation. The intrinsic TLR activity of the imidazoquinoline was well preserved and our formulation strategy offered spatial control over its biological activity in vivo.

Immune cells as tumor drug delivery vehicles

This review article describes the use of immune cells as potential candidates to deliver anti-cancer drugs deep within the tumor microenvironment. First, the rationale of using drug carriers to target tumors and potentially decrease drug-related side effects is discussed. We further explain some of the current limitations when using nanoparticles for this purpose. Next, a comprehensive step-by-step description of the migration cascade of immune cells is provided as well as arguments on why immune cells can be used to address some of the limitations associated with nanoparticle-mediated drug delivery. We then describe the benefits and drawbacks of using red blood cells, platelets, granulocytes, monocytes, macrophages, myeloid-derived suppressor cells, T cells and NK cells for tumor-targeted drug delivery. An additional section discusses the versatility of nanoparticles to load anti-cancer drugs into immune cells. Lastly, we propose increasing the circulatory half-life and development of conditional release strategies as the two main future pillars to improve the efficacy of immune cell-mediated drug delivery to tumors.

Potent and Prolonged Innate Immune Activation by Enzyme-Responsive Imidazoquinoline TLR7/8 Agonist Prodrug Vesicles

Synthetic immune-stimulatory drugs such as agonists of the Toll-like receptors (TLR) 7/8 are potent activators of antigen-presenting cells (APCs), however, they also induce severe side effects due to leakage from the site of injection into systemic circulation. Here, we report on the design and synthesis of an amphiphilic polymer-prodrug conjugate of an imidazoquinoline TLR7/8 agonist that in aqueous medium forms vesicular structures of 200 nm. The conjugate contains an endosomal enzyme-responsive linker enabling degradation of the vesicles and release of the TLR7/8 agonist in native form after endocytosis, which results in high in vitro TLR agonist activity. In a mouse model, locally administered vesicles provoke significantly more potent and long-lasting immune stimulation in terms of interferon expression at the injection site and in draining lymphoid tissue compared to a nonamphiphilic control and the native TLR agonist. Moreover, the vesicles induce robust activation of dendritic cells in the draining lymph node in vivo.

Comparative Profiling of Metastatic 4T1- vs. Non-metastatic Py230-Based Mammary Tumors in an Intraductal Model for Triple-Negative Breast Cancer

The transition of ductal carcinoma in situ (DCIS) to invasive carcinoma (IC) in breast cancer can be faithfully reproduced by the intraductal mouse model. Envisaging to use this model for therapeutic testing, we aimed to in-depth characterize the tumor immunity associated with the differential progression of two types of intraductal tumors. More specifically, we focused on triple-negative breast cancer (TNBC) and intraductally inoculated luciferase-expressing metastatic 4T1 and locally invasive Py230 cells in lactating mammary glands of syngeneic BALB/c and C57BL/6 female mice, respectively. Although the aggressive 4T1 cells rapidly formed solid tumors, Py230 tumors eventually grew to a similar size through enhanced proliferation. Yet, ductal tumor cell breakthrough and metastasis occurred earlier in the 4T1- compared to the Py230-based intraductal model and was associated with high expression of matrix metalloproteinase (MMP)-9, vascular endothelial growth factor (VEGF), chitinase 3-like 1 (CHI3L1) and lipocalin 2 (LCN2) as well as an increased influx of immune cells (mainly macrophages, neutrophils and T-cells). Moreover, activated cytotoxic T-cells, B-cells and programmed death-1 (PD-1)-positive cells were more prominent in the 4T1-based intraductal model in line with enhanced pro-inflammatory cytokine and gene expression profiles. Py230-based tumors showed a more immunosuppressed anti-inflammatory profile with a high amount of regulatory T-cells, which may account for the decreased T-cell activation but increased proliferation compared to the 4T1-based tumors. Taken together, our results highlight the differential immunological aspects of aggressive metastatic and non-aggressive intraductal progression of 4T1- vs. Py230-based tumors, providing a base for future studies to explore therapy using these intraductal TNBC models.

Potent Lymphatic Translocation and Spatial Control Over Innate Immune Activation by Polymer-Lipid Amphiphile Conjugates of Small-Molecule TLR7/8 Agonists

Uncontrolled systemic inflammatory immune triggering has hampered the clinical translation of several classes of small-molecule immunomodulators, such as imidazoquinoline TLR7/8 agonists for vaccine design and cancer immunotherapy. By taking advantage of the inherent serum-protein-binding property of lipid motifs and their tendency to accumulate in lymphoid tissue, we designed amphiphilic lipid-polymer conjugates that suppress systemic inflammation but provoke potent lymph-node immune activation. This work provides a rational basis for the design of lipid-polymer amphiphiles for optimized lymphoid targeting.

Expression Kinetics and Innate Immune Response after Electroporation and LNP-Mediated Delivery of a Self-Amplifying mRNA in the Skin

In this work, we studied the expression kinetics and innate immune response of a self-amplifying mRNA (sa-RNA) after electroporation and lipid-nanoparticle (LNP)-mediated delivery in the skin of mice. Intradermal electroporation of the sa-RNA resulted in a plateau-shaped expression, with the plateau between day 3 and day 10. The overall protein expression of sa-RNA was significantly higher than that obtained after electroporation of plasmid DNA (pDNA) or non-replication mRNAs. Moreover, using IFN-β reporter mice, we elucidated that intradermal electroporation of sa-RNA induced a short-lived moderate innate immune response, which did not affect the expression of the sa-RNA. A completely different expression profile and innate immune response were observed when LNPs were used. The expression peaked 24 h after intradermal injection of sa-RNA-LNPs and subsequently showed a sharp drop. This drop might be explained by a translational blockage caused by the strong innate immune response that we observed in IFN-β reporter mice shortly (4 h) after intradermal injection of sa-RNA-LNPs. A final interesting observation was the capacity of sa-RNA-LNPs to transfect the draining lymph nodes after intradermal injection.

Improving the Repeatability and Efficacy of Intradermal Electroporated Self-Replicating mRNA

Local administration of naked self-replicating mRNA (sr-mRNA) in the skin or muscle using electroporation is effective but hampered by low repeatability. In this manuscript, we demonstrated that intradermal electroporation of sr-mRNA in combination with a protein-based RNase inhibitor increased the expression efficiency, success rate, and repeatability of the data. The RNase inhibitor should be added just before administration because storage of the inhibitor together with the sr-mRNA at −80°C resulted in a partial loss of the beneficial effect. Furthermore, the location of intradermal electroporation also had a major effect on the expression of the sr-mRNA, with the highest and longest expression observed at the tail base of the mice. In contrast with previous work, we did not observe a beneficial effect of calcium ions on the efficacy of naked sr-mRNA after intradermal injection. Finally, another important finding was that the traditional representation of in vivo bioluminescence data as means in logarithmic graphs can mask highly variable data. A more truthful representation can be obtained by showing the individual data points or by displaying median values in combination with interquartile ranges. In conclusion, intradermal sr-mRNA electroporation can be improved by adding an RNase inhibitor and injecting at the tail base.

Nanoparticle-Conjugate TLR7/8 Agonist Localized Immunotherapy Provokes Safe Antitumoral Responses

Localized therapeutic modalities that subvert the tumor microenvironment from immune-suppressive to pro-immunogenic can elicit systemic antitumor immune responses that induce regression of directly treated as well as nontreated distal tumors. A key toward generating robust antitumor T cell responses is the activation of dendritic cells (DCs) in the tumor microenvironment. Treatment with agonists triggering various pattern recognition receptors is very efficient to activate DCs, yet suffers from the induction of serious immune-related adverse effects, which is closely linked to their unfavorable PK/PD profile causing systemic immune activation and cytokine release. Here, it is reported that nanoparticle conjugation of a highly potent TLR7/8 agonist restricts immune activation to the tumor bed and its sentinel lymph nodes without hampering therapeutic antitumor efficacy. On a mechanistic level, it is confirmed that localized treatment with a nanoparticle-conjugated TLR7/8 agonist leads to potent activation of DCs in the sentinel lymph nodes and promotes proliferation of tumor antigen-specific CD8 T cells. Furthermore, therapeutic improvement upon combination with anti-PDL1 checkpoint inhibition and Flt3L, a growth factor that expands and mobilizes DCs from the bone marrow, is demonstrated. The findings provide a rational base for localized tumor engineering by nanomedicine strategies that provide spatial control over immune-activation.

Anti-inflammatory signaling by mammary tumor cells mediates prometastatic macrophage polarization in an innovative intraductal mouse model for triple-negative breast cancer

Background

Murine breast cancer models relying on intraductal tumor cell inoculations are attractive because they allow the study of breast cancer from early ductal carcinoma in situ to metastasis. Using a fully immunocompetent 4T1-based intraductal model for triple-negative breast cancer (TNBC) we aimed to investigate the immunological responses that guide such intraductal tumor progression, focusing on the prominent role of macrophages.

Methods

Intraductal inoculations were performed in lactating female mice with luciferase-expressing 4T1 mammary tumor cells either with or without additional RAW264.7 macrophages, mimicking basal versus increased macrophage-tumor cell interactions in the ductal environment. Imaging of 4T1-derived luminescence was used to monitor primary tumor growth and metastases. Tumor proliferation, hypoxia, disruption of the ductal architecture and tumor immune populations were determined immunohistochemically. M1- (pro-inflammatory) and M2-related (anti-inflammatory) cytokine levels were determined by Luminex assays and ELISA to investigate the activation state of the macrophage inoculum. Levels of the metastatic proteins matrix metalloproteinase 9 (MMP-9) and vascular endothelial growth factor (VEGF) as well as of the immune-related disease biomarkers chitinase 3-like 1 (CHI3L1) and lipocalin 2 (LCN2) were measured by ELISA to evaluate disease progression at the protein level.

Results

Mice intraductally co-injected with macrophages showed severe splenomegaly with faster ductal breakthrough of tumor cells and increased metastases in axillary lymph nodes and lungs. These mice showed higher M1-related cytokines in the early disease stages (at 1 to 3 weeks post-inoculation) due to the pro-inflammatory nature of RAW264.7 macrophages with increased Ly6G-positive neutrophils and decreased anti-inflammatory macrophages in the tumor microenvironment. However, upon metastasis (at 5 weeks post-inoculation), a prominent increase in M2-related cytokine levels was detected and established a tumor microenvironment with similar immune populations and cytokine responses as in mice which received only 4T1 tumor cells. The observed tumor-associated immune responses and the increased metastasis were associated with significantly induced local and systemic levels of MMP-9, VEGF, CHI3L1 and LCN2.

Conclusions

The current experimental study with an innovative immunocompetent intraductal model for TNBC pinpoints towards a metastasis-supporting M1 to M2 macrophage polarization in the mammary ducts mediated by 4T1-derived signaling. We propose to explore this process as immunotherapeutic target.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0860-x) contains supplementary material, which is available to authorized users.

Off-Target and Tumor-Specific Accumulation of Monocytes, Macrophages and Myeloid-Derived Suppressor Cells after Systemic Injection

Solid tumors frequently coexist with a degree of local chronic inflammation. Recruited myeloid cells can therefore be considered as interesting vehicles for tumor-targeted delivery of therapeutic agents. Using in vivo imaging, the short-term accumulation of systemically injected monocytes, macrophages and myeloid-derived suppressor cells (MDSCs) was compared in mice bearing fat pad mammary carcinomas. Monocytes and macrophages demonstrated almost identical in vivo and ex vivo distribution patterns with maximal tumor-associated accumulation seen 48 hours after injection that remained stable over the 4-day follow-up period. However, a substantial accumulation of both cell types was also seen in the liver, spleen and lungs albeit decreasing over time in all three locations. The MDSCs exhibited a similar distribution pattern as the monocytes and macrophages, but demonstrated a better relative on-target fraction over time. Overall, our findings highlight off-target cell accumulation as a major obstacle in the use of myeloid cells as vehicles for therapeutic tumor-targeted agents and indicate that their short-term on-target accumulation is mainly of nonspecific nature.

Comparison of the Expression Kinetics and Immunostimulatory Activity of Replicating mRNA, Nonreplicating mRNA, and pDNA after Intradermal Electroporation in Pigs

Synthetic mRNA is becoming increasingly popular as an alternative to pDNA-based gene therapy. Currently, multiple synthetic mRNA platforms have been developed. In this study we investigated the expression kinetics and the changes in mRNA encoding cytokine and chemokine levels following intradermal electroporation in pigs of pDNA, self-replicating mRNA, and modified and unmodified mRNA. The self-replicating mRNA tended to induce the highest protein expression, followed by pDNA, modified mRNA, and unmodified mRNA. Interestingly, the self-replicating mRNA was able to maintain its high expression levels during at least 12 days. In contrast, the expression of pDNA and the nonreplicating mRNAs dropped after respectively one and two days. Six days after intradermal electroporation a dose-dependent expression was observed for all vectors. Again, also at lower doses, the self-replicating mRNA tended to show the highest expression. All the mRNA vectors, including the modified mRNA, induced elevated levels of mRNA encoding cytokines and chemokines in the porcine skin after intradermal electroporation, while no such response was noticed after intradermal electroporation of the pDNA vector.

Evaluation of a xenogeneic vascular endothelial growth factor-2 vaccine in two preclinical metastatic tumor models in mice

In this study, a xenogeneic DNA vaccine encoding for human vascular endothelial growth factor receptor-2 (hVEGFR-2) was evaluated in two murine tumor models, the B16-F10 melanoma and the EO771 breast carcinoma model. The vaccine was administered by intradermal injection followed by electroporation. The immunogenicity and the biological efficacy of the vaccine were tested in (1) a prophylactic setting, (2) a therapeutic setting, and (3) a therapeutic setting combined with surgical removal of the primary tumor. The tumor growth, survival, and development of an immune response were followed. The cellular immune response was measured by a bioluminescence-based cytotoxicity assay with vascular endothelial growth factor-2 (VEGFR-2)-expressing target cells. Humoral immune responses were quantified by enzyme-linked immunosorbent assay (ELISA). Ex vivo bioluminescence imaging and immunohistological observation of organs were used to detect (micro)metastases. A cellular and humoral immune response was present in prophylactically and therapeutically vaccinated mice, in both tumor models. Nevertheless, survival in prophylactically vaccinated mice was only moderately increased, and no beneficial effect on survival in therapeutically vaccinated mice could be demonstrated. An influx of CD3+ cells and a slight decrease in VEGFR-2 were noticed in the tumors of vaccinated mice. Unexpectedly, the vaccine caused an increased quantity of early micrometastases in the liver. Lung metastases were not increased by the vaccine. These early liver micrometastases did however not grow into macroscopic metastases in either control or vaccinated mice when allowed to develop further after surgical removal of the primary tumor.

Immunogenicity and safety of xenogeneic vascular endothelial growth factor receptor-2 DNA vaccination in mice and dogs

Vascular endothelial growth factor receptor-2 (VEGFR-2) is an attractive target in oncology due to its crucial role in angiogenesis. In this study a DNA vaccine coding for human VEGFR-2 was evaluated in healthy mice and dogs, administered by intradermal injection and electroporation. In mice, three doses and vaccination schedules were evaluated. Cellular immune responses were measured by intracellular IFN-gamma staining and a cytotoxicity assay and antibodies by ELISA. Safety was assessed by measuring regulatory T cells and myeloid derived suppressor cells and a wound healing assay. The vaccine was subsequently evaluated in dogs, which were vaccinated three times with 100μg. Cellular immune responses were measured by intracellular IFN-gamma staining and antibodies by a flow cytometric assay. In mice, maximal cellular responses were observed after two vaccinations with 5μg. Humoral responses continued to increase with higher dose and number of vaccinations. No abnormalities in the measured safety parameters were observed. The vaccine was also capable of eliciting a cellular and humoral immune response in dogs. No adverse effects were observed, but tolerability of the electroporation was poor. This study will facilitate the evaluation of the vaccine in tumor bearing animals, ranging from rodent models to dogs with spontaneous tumors.

Comparison of the Adipose and Luminal Mammary Gland Compartment as Orthotopic Inoculation Sites in a 4T1-Based Immunocompetent Preclinical Model for Triple-Negative Breast Cancer

Breast tumorigenesis is classically studied in mice by inoculating tumor cells in the fat pad, the adipose compartment of the mammary gland. Alternatively, the mammary ducts, which constitute the luminal mammary gland compartment, also provide a suitable inoculation site to induce breast cancer in murine models. The microenvironments in these compartments influence tumor cell progression, yet this effect has not been investigated in an immunocompetent context. Here, we compared both mammary gland compartments as distinct inoculation sites, taking into account the immunological aspect by inoculating 4T1 tumor cells in immunocompetent mice. Following tumor cell inoculation in the adipose compartment of non-pretreated/naive, hormonally pretreated/naive and non-pretreated/lactating mice, the primary tumors developed similarly. However, a slower onset of primary tumor growth was found after inoculations in the luminal compartment of non-pretreated/lactating mice. Despite this difference in tumor development rate, metastasis to the liver and lungs was equally observed and was accompanied by lymphatic spreading of tumor cells and progressive splenomegaly with both inoculation types. Chitinase 3-like 1 (CHI3L1) and lipocalin 2 (LCN2) served as innovative biomarkers for disease progression showing increased levels in primary tumors and sera of the non-pretreated/lactating inoculation groups. A slower increase in circulating CHI3L1 but not LCN2 levels, was observed after inoculations in the luminal compartment which corroborated the slower tumor development at this inoculation site. Our results highlight the critical impact of different mammary gland compartments on tumor development in syngeneic murine models and support the use of novel tumor progression biomarkers in an immune-competent environment.

Immunological, anti-angiogenic and clinical effects of intratumoral interleukin 12 electrogene therapy combined with metronomic cyclophosphamide in dogs with spontaneous cancer: A pilot study

The immunological, anti-angiogenic and clinical effects of metronomic cyclophosphamide and 3 consecutive intratumoral interleukin (IL)-12 gene therapy (electrogene therapy (EGT)) treatments were evaluated in 6 dogs with spontaneous cancer. In all dogs, a decrease in peripheral leukocytes 2 days after IL-12 EGT coincided with erythema and swelling of the tumor. In the tumor, a transient increase in IL-12 levels was measured, whereas a continuous increase in interferon γ (IFNγ) and thrombospondin 1 (TSP-1) were determined in contrast to a continuous decrease in vascular endothelial growth factor (VEGF). In the serum, a transient increase in IL-12 and IL-10 levels were noted in contrast to a transient decrease in VEGF and TSP-1. The treatment resulted in a significant anti-angiogenic effect. Although all primary tumors continued to progress in time, this progression was slower than before treatment according to the contrast-enhanced ultrasound data. Besides the encouraging immunostimulatory and anti-angiogenic effects observed in all dogs we also noticed in 4 out of 6 dogs clinically relevant improvements in quality of life and weight. These results hold great promise for combinatorial strategies of IL-12 EGT and metronomic chemotherapy with conventional antitumor (immuno)therapies.

Intratumoural interleukin 12 gene therapy stimulates the immune system and decreases angiogenesis in dogs with spontaneous cancer

Interleukin 12 (IL-12) is a powerful immunostimulatory cytokine with a strong antitumoural activity. In this work, the immunological, anti-angiogenic and clinical effects of three consecutive intratumoural IL-12 electrogene therapy (EGT) treatments were evaluated in nine dogs with spontaneous cancer. In all the dogs, tumour biopsies and blood samples were taken prior, during and after the intratumoural IL-12 EGT (on days 1, 8, 35 and 1, 3, 8, 15, 35, respectively). An initial decrease in immune cells was followed by an increase above baseline 1-3 weeks after treatment initiation. Interestingly, the decrease in peripheral leukocytes 2 days after the first intratumoural IL-12 EGT coincided with erythema and tumour swelling. Transient increases of IL-12 and interferon γ were measured in the serum and the tumour tissue, whereas IL-10 transiently increased only in the serum. The effect of intratumoural IL-12 EGT on the levels of IL-24 and vascular endothelial growth factor in the sera and tumour biopsies differed per dog. Via contrast-enhanced ultrasound (US) (on days 1, 8 and 35), we demonstrated that intratumoural IL-12 EGT resulted in a significant decrease of the relative blood volume and blood flow speed in the tumour compared with baseline. Metastases were present in two dogs. In one of these dogs, IL-12 EGT of the primary tumour caused a transient partial regression of the metastases, but not of the primary tumour. The second dog with metastases did not survive long enough to complete the entire treatment cycle. Despite encouraging immunostimulatory and anti-angiogenic effects after intratumoural IL-12 EGT, no clinically relevant outcomes were observed in this study, as persistent tumour regression could not be obtained. On the other hand, the laboratory and US results hold great promise for combinatorial strategies of intratumoural IL-12 EGT with conventional antitumour (immuno)therapies.

Coadministration of a Plasmid Encoding HIV-1 Gag Enhances the Efficacy of Cancer DNA Vaccines

DNA vaccination holds great promise for the prevention and treatment of cancer and infectious diseases. However, the clinical ability of DNA vaccines is still controversial due to the limited immune response initially observed in humans. We hypothesized that electroporation of a plasmid encoding the HIV-1 Gag viral capsid protein would enhance cancer DNA vaccine potency. DNA electroporation used to deliver plasmids in vivo, induced type I interferons, thereby supporting the activation of innate immunity. The coadministration of ovalbumin (OVA) and HIV-1 Gag encoding plasmids modulated the adaptive immune response. This strategy favored antigen-specific Th1 immunity, delayed B16F10-OVA tumor growth and improved mouse survival in both prophylactic and therapeutic vaccination approaches. Similarly, a prophylactic DNA immunization against the melanoma-associated antigen gp100 was enhanced by the codelivery of the HIV-1 Gag plasmid. The adjuvant effect was not driven by the formation of HIV-1 Gag virus-like particles. This work highlights the ability of both electroporation and the HIV-1 Gag plasmid to stimulate innate immunity for enhancing cancer DNA vaccine immunogenicity and demonstrates interesting tracks for the design of new translational genetic adjuvants to overcome the current limitations of DNA vaccines in humans.

Immunological and angiogenic markers during metronomic temozolomide and cyclophosphamide in canine cancer patients

Metronomic chemotherapy stimulates the immune response via depletion of regulatory T cells (Tregs) and suppresses angiogenesis by modulating the secretion of thrombospondin-1 (TSP-1) and vascular endothelial growth factor (VEGF). In this study, blood was collected from 10 healthy dogs and from 30 canine cancer patients before and 2 and 4 weeks after treatment with metronomic temozolomide (6.6 mg m^-2 ), cyclophosphamide (12.5 mg m^-2 ) or cyclophosphamide and temozolomide. The percentage of circulating CD25⁺ Foxp3⁺ CD4⁺ Tregs and the plasma levels of TSP-1 and VEGF were measured. There was a significant difference in the percentage of Tregs between cancer patients and healthy dogs. A significant decrease in Tregs was noted in patients treated with metronomic cyclophosphamide and the combination. Treatment with temozolomide had no effect on the percentage of Tregs. TSP-1 and VEGF levels were, respectively, significantly lower and higher in cancer patients than in healthy dogs, but they were not influenced by any of the studied metronomic treatment regimens.

N(1)-methylpseudouridine-incorporated mRNA outperforms pseudouridine-incorporated mRNA by providing enhanced protein expression and reduced immunogenicity in mammalian cell lines and mice

Messenger RNA as a therapeutic modality is becoming increasingly popular in the field of gene therapy. The realization that nucleobase modifications can greatly enhance the properties of mRNA by reducing the immunogenicity and increasing the stability of the RNA molecule (the Kariko paradigm) has been pivotal for this revolution. Here we find that mRNAs containing the N(1)-methylpseudouridine (m1Ψ) modification alone and/or in combination with 5-methylcytidine (m5C) outperformed the current state-of-the-art pseudouridine (Ψ) and/or m5C/Ψ-modified mRNA platform by providing up to ~44-fold (when comparing double modified mRNAs) or ~13-fold (when comparing single modified mRNAs) higher reporter gene expression upon transfection into cell lines or mice, respectively. We show that (m5C/)m1Ψ-modified mRNA resulted in reduced intracellular innate immunogenicity and improved cellular viability compared to (m5C/)Ψ-modified mRNA upon in vitro transfection. The enhanced capability of (m5C/)m1Ψ-modified mRNA to express proteins may at least partially be due to the increased ability of the mRNA to evade activation of endosomal Toll-like receptor 3 (TLR3) and downstream innate immune signaling. We believe that the (m5C/)m1Ψ-mRNA platform presented here may serve as a new standard in the field of modified mRNA-based therapeutics.

Can dendritic cells improve whole cancer cell vaccines based on immunogenically killed cancer cells?

Immunogenic cell death (ICD) offers interesting opportunities in cancer cell (CC) vaccine manufacture, as it increases the immunogenicity of the dead CC. Furthermore, fusion of CCs with dendritic cells (DCs) is considered a superior method for generating whole CC vaccines. Therefore, in this work, we determined in naive mice whether immunogenically killed CCs per se (CC vaccine) elicit an antitumoral immune response different from the response observed when immunogenically killed CCs are associated with DCs through fusion (fusion vaccine) or through co-incubation (co-incubation vaccine). After tumor inoculation, the type of immune response in the prophylactically vaccinated mice differed between the groups. In more detail, fusion vaccines elicited a humoral anticancer response, whereas the co-incubation and CC vaccine mainly induced a cellular response. Despite these differences, all three approaches offered a prophylactic protection against tumor development in the murine mammary carcinoma model. In summary, it can be concluded that whole CC vaccines based on immunogenically killed CCs may not necessarily require association with DCs to elicit a protective anticancer immune response. If this finding can be endorsed in other cancer models, the manufacture of CC vaccines would greatly benefit from this new insight, as production of DC-based vaccines is laborious, time-consuming and expensive.

Non-classical proIL-1beta activation during mammary gland infection is pathogen-dependent but caspase-1 independent

Infection of the mammary gland with live bacteria elicits a pathogen-specific host inflammatory response. To study these host-pathogen interactions wild type mice, NF-kappaB reporter mice as well as caspase-1 and IL-1beta knockout mice were intramammarily challenged with Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The murine mastitis model allowed to compare the kinetics of the induced cytokine protein profiles and their underlying pathways. In vivo and ex vivo imaging showed that E. coli rapidly induced NF-kappaB inflammatory signaling concomitant with high mammary levels of TNF-alpha, IL-1 alpha and MCP-1 as determined by multiplex analysis. In contrast, an equal number of S. aureus bacteria induced a low NF-kappaB activity concomitant with high mammary levels of the classical IL-1beta fragment. These quantitative and qualitative differences in local inflammatory mediators resulted in an earlier neutrophil influx and in a more extensive alveolar damage post-infection with E. coli compared to S. aureus. Western blot analysis revealed that the inactive proIL-1beta precursor was processed into pathogen-specific IL-1beta fragmentation patterns as confirmed with IL-1beta knockout animals. Additionally, caspase-1 knockout animals allowed to investigate whether IL-1beta maturation depended on the conventional inflammasome pathway. The lack of caspase-1 did not prevent extensive proIL-1beta fragmentation by either of S. aureus or E. coli. These non-classical IL-1beta patterns were likely caused by different proteases and suggest a sentinel function of IL-1beta during mammary gland infection. Thus, a key signaling nodule can be defined in the differential host innate immune defense upon E. coli versus S. aureus mammary gland infection, which is independent of caspase-1.

Combination of interleukin-12 gene therapy, metronomic cyclophosphamide and DNA cancer vaccination directs all arms of the immune system towards tumor eradication

In this work a combination therapy that acts upon the immune suppressive, the innate and specific arms of the immune system is proposed. This combination therapy, which consists of intratumoral interleukin-12 (IL-12) gene therapy, human tyrosinase (hTyr) DNA vaccination and metronomic cyclophosphamide (CPX), was evaluated in a B16-F10 mouse model. The following groups were compared: (1) no treatment, (2) control vector, (3) intratumoral IL-12 gene therapy, (4) intratumoral IL-12 gene therapy+metronomic CPX, (5) intratumoral IL-12 gene therapy+metronomic CPX+hTyr DNA vaccination. Next to clinical efficacy and safety, we characterized acute effects of IL-12 and anti-tumor immune response after a second tumor challenge. All treatment groups showed increased survival and higher cure rates than control groups. Survival of non-cured mice was increased when metronomic CPX was combined with IL-12 gene therapy. Furthermore, mice that received metronomic CPX had significantly lower percentages of regulatory T cells. Addition of the hTyr DNA vaccine increased cure rate and resulted in increased survival compared to other treatment groups. We also demonstrated that the manifest necrosis within days after IL-12 gene therapy is at least partly due to IL-12 mediated activation of NK cells. All cured mice were resistant to a second challenge. A humoral memory response against the tumor cells was observed in all groups that received IL-12 gene therapy, while a cellular memory response was observed only in the vaccinated mice. In conclusion, every component of this combination treatment contributed a unique immunologic trait with associated clinical benefits.

Various ways to improve whole cancer cell vaccines

Immunotherapy based on whole cancer cell vaccines is regarded as a promising avenue for cancer treatment. However, limited efficacy in the first human clinical trials calls for more optimized whole cancer cell vaccines and better patient selection. It is suggested that whole cancer cell vaccines consist preferably of immunogenically killed autologous cancer stem cells associated with dendritic cells. Adjuvants should stimulate both immune effector cells and memory cells, which could be achieved through their correct dosage and timing of administration. There are indications that whole cancer cell vaccination is less effective in patients who are immunocompromised, who have specific genetic defects in their immune or cancer cells, as well as in patients in an advanced cancer stage. However, such patients form the bulk of enrolled patients in clinical trials, prohibiting an objective evaluation of the true potential of whole cancer cell immunotherapy. Each key point will be discussed.