Heterologous Prime-Boost Immunizations with a Virosomal and an Alphavirus Replicon Vaccine

Oncolytic alphavirus replicons mediated recruitment and activation of T cells

Oncolytic viruses show promise in enhancing tumor immunogenicity by releasing immunogenic signals during tumor cell infection and lysis. In this study, we improved the virus-induced tumor immunogenicity of recombinant Semliki Forest virus (rSFV)-based replicon particles by encoding immunogenic cytokines such as C-X-C motif chemokine ligand 10 (CXCL10), FMS-like tyrosine kinase 3 ligand (Flt3L), or interferon-gamma (IFN-ƴ). Real-time imaging and flow cytometry of human cancer cell-based monolayer and spheroid cultures, using LNCaP or PANC-1 cells, revealed effective infection and transgene expression in both models. LNCaP cells exhibited higher and earlier rSFV infection compared to PANC-1 cells. While infected LNCaP cells effectively triggered immune recruitment and T cell activation even without encoding cytokines, PANC-1 cells demonstrated improved immune responses only when infected with replicons encoding cytokines, particularly IFN-ƴ, which enhanced tumor immunogenicity irrespective of cancer cell susceptibility to infection. Our study demonstrates that despite innate phenotypic disparities in cancer cells, rSFV-based replicons encoding cytokines can potentially generate effective immune responses in the tumor.

Rise of the RNA machines - self-amplification in mRNA vaccine design

mRNA vaccines have won the race for early COVID-19 vaccine approval, yet improvements are necessary to retain this leading role in combating infectious diseases. A next generation of self-amplifying mRNAs, also known as replicons, form an ideal vaccine platform. Replicons induce potent humoral and cellular responses with few adverse effects upon a minimal, single-dose immunization. Delivery of replicons is achieved with virus-like replicon particles (VRPs), or in nonviral vehicles such as liposomes or lipid nanoparticles. Here, we discuss innovative advances, including multivalent, mucosal, and therapeutic replicon vaccines, and highlight novelties in replicon design. As soon as essential safety evaluations have been resolved, this promising vaccine concept can transform into a widely applied clinical platform technology taking center stage in pandemic preparedness.

Heterologous prime-boost vaccine using antigen-loaded microparticles and adenovirus (encoding antigen) enhances cellular immune responses and antitumor activity

Heterologous prime-boost vaccines have the potential to promote higher immune responses than homologous prime-boost vaccines and were used in this murine study to investigate the effect on the magnitude of the cellular (and humoral) antigen-specific immune responses and antitumor efficacy when a microparticle formulation (prime) is combined with an adenoviral vaccine (boost). Specifically, the prime comprised chick egg ovalbumin (OVA; 25 µg/dose), used here as a model tumor antigen (TA), encapsulated in microparticles (∼700 nm diameter) made from the biodegradable polymer, 50:50 poly(lactic-co-glycolic acid) (PLGA); while attenuated adenovirus (type 5) encoding OVA (Ad5OVA; 108 PFU/dose) was employed as the boost. The ability of OVA-loaded microparticles to enhance OVA-specific antibody responses, OVA-specific CD3 + CD8 + T cell responses and antitumor activity (i.e., protection against OVA-expressing tumor-challenge) to the heterologous prime-boost vaccine was investigated; and it was found that this prime-boost combination could significantly enhance OVA-specific cellular responses compared to all other vaccination groups and was the only group to confer a significant survival advantage over the unvaccinated group (naïve) in a prophylactic animal tumor model. This finding illustrates the potential for combining TA-loaded PLGA-based microparticles with other vaccine formats to improve tumor-specific cellular immune responses.

Immunogenicity and protection against Mycobacterium avium with a heterologous RNA prime and protein boost vaccine regimen

Prophylactic efficacy of two different delivery platforms for vaccination against Mycobacterium avium (M. avium) were tested in this study; a subunit and an RNA-based vaccine. The vaccine antigen, ID91, includes four mycobacterial antigens: Rv3619, Rv2389, Rv3478, and Rv1886. We have shown that ID91+GLA-SE is effective against a clinical NTM isolate, M. avium 2-151 smt. Here, we extend these results and show that a heterologous prime/boost strategy with a repRNA-ID91 (replicon RNA) followed by protein ID91+GLA-SE boost is superior to the subunit protein vaccine given as a homologous prime/boost regimen. The repRNA-ID91/ID91+GLA-SE heterologous regimen elicited a higher polyfunctional CD4+ TH1 immune response when compared to the homologous protein prime/boost regimen. More significantly, among all the vaccine regimens tested only repRNA-ID91/ID91+GLA-SE induced IFN-γ and TNF-secreting CD8+ T cells. Furthermore, the repRNA-ID91/ID91+GLA-SE vaccine strategy elicited high systemic proinflammatory cytokine responses and induced strong ID91 and an Ag85B-specific humoral antibody response a pre- and post-challenge with M. avium 2-151 smt. Finally, while all prophylactic prime/boost vaccine regimens elicited a degree of protection in beige mice, the heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen provided greater pulmonary protection than the homologous protein prime/boost regimen. These data indicate that a prophylactic heterologous repRNA-ID91/ID91+GLA-SE vaccine regimen augments immunogenicity and confers protection against M. avium.

It Takes a Village: The Multifaceted Immune Response to Mycobacterium tuberculosis Infection and Vaccine-Induced Immunity

Despite co-evolving with humans for centuries and being intensely studied for decades, the immune correlates of protection against Mycobacterium tuberculosis (Mtb) have yet to be fully defined. This lapse in understanding is a major lag in the pipeline for evaluating and advancing efficacious vaccine candidates. While CD4+ T helper 1 (TH1) pro-inflammatory responses have a significant role in controlling Mtb infection, the historically narrow focus on this cell population may have eclipsed the characterization of other requisite arms of the immune system. Over the last decade, the tuberculosis (TB) research community has intentionally and intensely increased the breadth of investigation of other immune players. Here, we review mechanistic preclinical studies as well as clinical anecdotes that suggest the degree to which different cell types, such as NK cells, CD8+ T cells, γ δ T cells, and B cells, influence infection or disease prevention. Additionally, we categorically outline the observed role each major cell type plays in vaccine-induced immunity, including Mycobacterium bovis bacillus Calmette-Guérin (BCG). Novel vaccine candidates advancing through either the preclinical or clinical pipeline leverage different platforms (e.g., protein + adjuvant, vector-based, nucleic acid-based) to purposefully elicit complex immune responses, and we review those design rationales and results to date. The better we as a community understand the essential composition, magnitude, timing, and trafficking of immune responses against Mtb, the closer we are to reducing the severe disease burden and toll on human health inflicted by TB globally.

Semliki Forest virus-based immunotherapy for cancer

Introduction: Immunotherapy has been introduced as a modern alternative for the treatment of various cancers, including the stimulation of the immune system by introduction of immunostimulatory molecules. Application of viral and non-viral vectors have provided a substantial contribution to improved delivery and expression of these immunostimulators.Areas covered: Alphavirus vectors, based on Semliki Forest virus, have allowed immunization with self-replicating RNA, recombinant virus particles, and layered DNA/RNA vectors. The attractive features of alphaviruses comprise their broad host range and extreme RNA replication in infected cells resulting in very high recombinant protein expression levels providing enhanced immune responses and an excellent basis for immunotherapy.Expert opinion: Immunization studies in animal tumor models have elicited strong humoral and cellular immune response, have provided prophylactic protection against tumor challenges, and have generated therapeutic efficacy in tumor-bearing animals. Clinical trials have indicated safe use of alphavirus vectors, making them attractive for cancer immunotherapy.

An alphavirus-based therapeutic cancer vaccine: from design to clinical trial

Cancer immunotherapy has greatly advanced in recent years. Most immunotherapeutic strategies are based on the use of immune checkpoint blockade to unleash antitumor immune responses or on the induction or adoptive transfer of immune effector cells. We aim to develop therapeutic vaccines based on recombinant Semliki Forest virus vectors to induce tumor-specific effector immune cells. In this review, we describe our ongoing work on SFV-based vaccines targeted against human papillomavirus- and hepatitis C virus-related infections and malignancies, focusing on design, delivery, combination strategies, preclinical efficacy and product development for a first-in-man clinical trial with an HPV-specific vaccine.

Potent therapeutic efficacy of an alphavirus replicon DNA vaccine expressing human papilloma virus E6 and E7 antigens

Cervical cancer develops as a result of infection with high-risk human papillomavirus (HPV) through persistent expression of early proteins E6 and E7. Our group pioneered a recombinant viral vector system based on Semliki Forest virus (SFV) for vaccination against cervical cancer. The most striking benefit of this alphavirus vector-based vaccine platform is its high potency. DNA vaccines on the other hand, have a major advantage with respect to ease of production. In this study, the benefits associated with both SFV-based vaccines and DNA vaccines were combined with the development of a DNA-launched RNA replicon (DREP) vaccine targeting cervical cancer. Using intradermal delivery followed by electroporation, we demonstrated that DREP encoding for E6,7 (DREP-E6,7) induced effective, therapeutic antitumor immunity. While immunizations with a conventional DNA vaccine did not prevent tumor outgrowth, immunization with a 200-fold lower equimolar dose of DREP (0.05 µg of DREP) resulted in approximately 85% of tumor-free mice. To overcome the safety concern of potential malignant transformation at the vaccination site, we evaluated the anti-tumor effect of a DREP vaccine encoding a shuffled version of E7 (DREP-E7sh). DREP-E7sh delayed tumor growth yet not to the same extent as DREP-E6,7. In addition, inclusion of a helper cassette and an ER targeting signal (sigHelp) did not significantly further enhance the suppression of tumor outgrowth in the long term, albeit exhibiting better tumor control early after immunization. Collectively, this study points towards the clinical evaluation of DREP encoding HPV antigens as a potent immunotherapy for patients with HPV16 (pre)-malignancies.

Antigen design enhances the immunogenicity of Semliki Forest virus-based therapeutic human papillomavirus vaccines

Cellular immunity against cancer can be achieved with viral vector- and DNA-based immunizations. In preclinical studies, cancer vaccines are very potent, but in clinical trials these potencies are not achieved yet. Thus, a rational approach to improve cancer vaccines is warranted. We previously demonstrated that the relatively low intrinsic immunogenicity of DNA vaccines could be enhanced by inclusion of endoplasmic reticulum (ER) targeting and universal helper epitopes within the vaccine. We now evaluated whether an optimal antigen format, as defined in DNA vaccines, can further enhance the effectiveness of recombinant Semliki Forest virus (rSFV) vaccines. To this purpose, we generated, characterized and evaluated the efficacy of rSFV replicon particles expressing human papillomavirus E6 and/or E7 proteins fused to several helper T-cell epitopes and an ER targeting signal. Here, we show that inclusion of a helper cassette and an ER targeting signal enhanced protein stability and markedly augmented the frequencies of human papillomavirus-specific T cells. Even at an immunization dose of as low as 10(5) replicon particles, this novel vaccine achieved tumor regression and protection. Thus, even highly effective viral vector vaccines can benefit from an improved antigen format, based on the inclusion of defined helper epitopes and ER targeting.

Tattoo Delivery of a Semliki Forest Virus-Based Vaccine Encoding Human Papillomavirus E6 and E7

The skin is an attractive organ for immunization because of the presence of antigen-presenting cells. Intradermal delivery via tattooing has demonstrated superior vaccine immunogenicity of DNA vaccines in comparison to conventional delivery methods. In this study, we explored the efficacy of tattoo injection of a tumor vaccine based on recombinant Semliki Forest virus replicon particles (rSFV) targeting human papillomavirus (HPV). Tattoo injection of rSFV particles resulted in antigen expression in both the skin and draining lymph nodes. In comparison with intramuscular injection, the overall antigen expression determined at the site of administration and draining lymph nodes was 10-fold lower upon tattoo injection. Delivery of SFV particles encoding the E6 and E7 antigens of human papillomavirus type 16 (SFVeE6,7) via tattooing resulted in HPV-specific cytotoxic T cells and in vivo therapeutic antitumor response. Strikingly, despite the observed lower overall transgene expression, SFVeE6,7 delivered via tattoo injection resulted in higher or equal levels of immune responses as compared to intramuscular injection. The intrinsic immunogenic potential of tattooing provides a benefit for immunotherapy based on an alphavirus.

Liposomes as vaccine delivery systems: a review of the recent advances

Liposomes and liposome-derived nanovesicles such as archaeosomes and virosomes have become important carrier systems in vaccine development and the interest for liposome-based vaccines has markedly increased. A key advantage of liposomes, archaeosomes and virosomes in general, and liposome-based vaccine delivery systems in particular, is their versatility and plasticity. Liposome composition and preparation can be chosen to achieve desired features such as selection of lipid, charge, size, size distribution, entrapment and location of antigens or adjuvants. Depending on the chemical properties, water-soluble antigens (proteins, peptides, nucleic acids, carbohydrates, haptens) are entrapped within the aqueous inner space of liposomes, whereas lipophilic compounds (lipopeptides, antigens, adjuvants, linker molecules) are intercalated into the lipid bilayer and antigens or adjuvants can be attached to the liposome surface either by adsorption or stable chemical linking. Coformulations containing different types of antigens or adjuvants can be combined with the parameters mentioned to tailor liposomal vaccines for individual applications. Special emphasis is given in this review to cationic adjuvant liposome vaccine formulations. Examples of vaccines made with CAF01, an adjuvant composed of the synthetic immune-stimulating mycobacterial cordfactor glycolipid trehalose dibehenate as immunomodulator and the cationic membrane forming molecule dimethyl dioctadecylammonium are presented. Other vaccines such as cationic liposome-DNA complexes (CLDCs) and other adjuvants like muramyl dipeptide, monophosphoryl lipid A and listeriolysin O are mentioned as well. The field of liposomes and liposome-based vaccines is vast. Therefore, this review concentrates on recent and relevant studies emphasizing current reports dealing with the most studied antigens and adjuvants, and pertinent examples of vaccines. Studies on liposome-based veterinary vaccines and experimental therapeutic cancer vaccines are also summarized.

Self-replicating alphavirus RNA vaccines

Recombinant nucleic acids are considered as promising next-generation vaccines. These vaccines express the native antigen upon delivery into tissue, thus mimicking live attenuated vaccines without having the risk of reversion to pathogenicity. They also stimulate the innate immune system, thus potentiating responses. Nucleic acid vaccines are easy to produce at reasonable cost and are stable. During the past years, focus has been on the use of plasmid DNA for vaccination. Now mRNA and replicon vaccines have come into focus as promising technology platforms for vaccine development. This review discusses self-replicating RNA vaccines developed from alphavirus expression vectors. These replicon vaccines can be delivered as RNA, DNA or as recombinant virus particles. All three platforms have been pre-clinically evaluated as vaccines against a number of infectious diseases and cancer. Results have been very encouraging and propelled the first human clinical trials, the results of which have been promising.

Therapeutic vaccination against chronic hepatitis C virus infection

Approximately 170 million people worldwide are chronic carriers of Hepatitis C virus (HCV). To date, there is no prophylactic vaccine available against HCV. The standard-of-care therapy for HCV infection involves a combination of pegylated interferon-α and ribavirin. This therapy, which is commonly associated with side effects, has a curative rate varying from 43% (HCV genotype 1) to 80% (HCV genotype 2). In 2011, two direct-acting antiviral agents, telaprevir and boceprevir, were approved by the US Food and drug Administration and are now being used in combination with standard-of-care therapy in selected patients infected with HCV genotype 1. Although both drugs are promising, resulting in a shortening of therapy, these drugs also induce additional side effects and have reduced efficacy in patients who did not respond to standard-of-care previously. An alternative approach would be to treat HCV by stimulating the immune system with a therapeutic vaccine ideally aimed at (i) the eradication of HCV-infected cells and (ii) neutralization of infectious HCV particles. The challenge is to develop therapeutic vaccination strategies that are either at least as effective as antiviral drugs but with lower side effects, or vaccines that, when combined with antiviral drugs, can circumvent long-term use of these drugs thereby reducing their side effects. In this review, we summarize and discuss recent preclinical developments in the area of therapeutic vaccination against chronic HCV infection. Although neutralizing antibodies have been described to exert protective immunity, clinical studies on the induction of neutralizing antibodies in therapeutic settings are limited. Therefore, we will primarily discuss therapeutic vaccines which aim to induce effective cellular immune response against HCV.

From tumor immunosuppression to eradication: targeting homing and activity of immune effector cells to tumors

Unraveling the mechanisms used by the immune system to fight cancer development is one of the most ambitious undertakings in immunology. Detailed knowledge regarding the mechanisms of induction of tolerance and immunosuppression within the tumor microenvironment will contribute to the development of highly effective tumor eradication strategies. Research within the last few decades has shed more light on the matter. This paper aims to give an overview on the current knowledge of the main tolerance and immunosuppression mechanisms elicited within the tumor microenvironment, with the focus on development of effective immunotherapeutic strategies to improve homing and activity of immune effector cells to tumors.