Prime-boost vaccination with a combination of proteosome-degradable and wild-type forms of two influenza proteins leads to augmented CTL response

Recalling the Future: Immunological Memory Toward Unpredictable Influenza Viruses

Persistent and durable immunological memory forms the basis of any successful vaccination protocol. Generation of pre-existing memory B cell and T cell pools is thus the key for maintaining protective immunity to seasonal, pandemic and avian influenza viruses. Long-lived antibody secreting cells (ASCs) are responsible for maintaining antibody levels in peripheral blood. Generated with CD4⁺ T help after naïve B cell precursors encounter their cognate antigen, the linked processes of differentiation (including Ig class switching) and proliferation also give rise to memory B cells, which then can change rapidly to ASC status after subsequent influenza encounters. Given that influenza viruses evolve rapidly as a consequence of antibody-driven mutational change (antigenic drift), the current influenza vaccines need to be reformulated frequently and annual vaccination is recommended. Without that process of regular renewal, they provide little protection against “drifted” (particularly H3N2) variants and are mainly ineffective when a novel pandemic (2009 A/H1N1 “swine” flu) strain suddenly emerges. Such limitation of antibody-mediated protection might be circumvented, at least in part, by adding a novel vaccine component that promotes cross-reactive CD8⁺ T cells specific for conserved viral peptides, presented by widely distributed HLA types. Such “memory” cytotoxic T lymphocytes (CTLs) can rapidly be recalled to CTL effector status. Here, we review how B cells and follicular T cells are elicited following influenza vaccination and how they survive into a long-term memory. We describe how CD8⁺ CTL memory is established following influenza virus infection, and how a robust CTL recall response can lead to more rapid virus elimination by destroying virus-infected cells, and recovery. Exploiting long-term, cross-reactive CTL against the continuously evolving and unpredictable influenza viruses provides a possible mechanism for preventing a disastrous pandemic comparable to the 1918-1919 H1N1 “Spanish flu,” which killed more than 50 million people worldwide.

Universal influenza vaccines: from viruses to nanoparticles

INTRODUCTION

The current seasonal influenza vaccine confers only limited protection due to waning antibodies or the antigenic shift and drift of major influenza surface antigens. A universal influenza vaccine which induces broad cross-protection against divergent influenza viruses with a comparable or better efficacy to seasonal influenza vaccines against matched strains will negate the need for an annual update of vaccine strains and protect against possible influenza pandemics.

AREAS COVERED

In this review, we summarize the recent progress in nanoparticle-based universal influenza vaccine development. We compared the most potent nanoparticle categories, focusing on how they encapsulate conserved influenza epitopes, stimulate the innate and adaptive immune systems, exhibit antigen depot effect, extend the period for antigen-processing and presentation, and exert an intrinsic adjuvant effect on inducing robust immune responses.

EXPERT COMMENTARY

The development of an effective universal influenza vaccine is an urgent task. Traditional influenza vaccine approaches are not sufficient for preventing recurrent epidemics or occasional pandemics. Nanoparticles are compatible with different immunogens and immune stimulators and can overcome the intrinsically low immunogenicity of conserved influenza virus antigens. We foresee that an affordable universal influenza vaccine will be available within ten years by integrating nanoparticles with other targeted delivery and controlled release technology.

Intracellular degradation and localization of NS1 of tick-borne encephalitis virus affect its protective properties

Currently, many DNA vaccines against infectious diseases are in clinical trials; however, their efficacy needs to be improved. The potency of DNA immunogen can be optimized by targeting technologies. In the current study, to increase the efficacy of NS1 encoded by plasmid, proteasome targeting was applied. NS1 variants with or without translocation sequence and with ornithine decarboxylase as a signal of proteasomal degradation were tested for expression, localization, protein turnover, proteasomal degradation and protection properties. Deletion of translocation signal abrogated presentation of NS1 on the cell surface and increased proteasomal processing of NS1. Fusion with ornithine decarboxylase led to an increase of protein turnover and the proteasome degradation rate of NS1. Immunization with NS1 variants with increased proteasome processing protected mice from viral challenge only partially; however, the survival time of infected mice was prolonged in these groups. These data can give a presupposition for formulation of specific immune therapy for infected individuals.

Feasibility analysis of p62 (SQSTM1)-encoding DNA vaccine as a novel cancer immunotherapy

Cancer immunotherapy is a thriving field, but its clinical achievements are modest so far. One of its major hurdles seems to be finding a feasible cancer antigen as a target for immune response. After many years of research, three major criteria for choice of tumor antigens emerged. An antigen should be: (i) immunogenic; (ii) essential for cancers cells (to avoid its loss through immunoediting), but dispensable for normal tissues to reduce the risk of toxicity, and (iii) overexpressed in tumors as compared to the normal tissues. Here we argue that p62 (SQSTM1), a protein involved in autophagy and signal transduction, fits all the above criteria and can be chosen as a novel cancer antigen. Accordingly, we carried out an extensive study and found antitumor and antimetastatic activity of p62-encoding DNA vaccine in five types of commonly used transplantable tumor models of mice and rats, and spontaneous tumors in several dogs. Given that toxicity of p62 vaccine was minimal, if any, we believe that p62-encoding vaccine merits further clinical development.

Protective Efficacy of the Conserved NP, PB1, and M1 Proteins as Immunogens in DNA- and Vaccinia Virus-Based Universal Influenza A Virus Vaccines in Mice

The conventional hemagglutinin (HA)- and neuraminidase (NA)-based influenza vaccines need to be updated most years and are ineffective if the glycoprotein HA of the vaccine strains is a mismatch with that of the epidemic strain. Universal vaccines targeting conserved viral components might provide cross-protection and thus complement and improve conventional vaccines. In this study, we generated DNA plasmids and recombinant vaccinia viruses expressing the conserved proteins nucleoprotein (NP), polymerase basic 1 (PB1), and matrix 1 (M1) from influenza virus strain A/Beijing/30/95 (H3N2). BALB/c mice were immunized intramuscularly with a single vaccine based on NP, PB1, or M1 alone or a combination vaccine based on all three antigens and were then challenged with lethal doses of the heterologous influenza virus strain A/PR/8/34 (H1N1). Vaccines based on NP, PB1, and M1 provided complete or partial protection against challenge with 1.7 50% lethal dose (LD50) of PR8 in mice. Of the three antigens, NP-based vaccines induced protection against 5 LD50 and 10 LD50 and thus exhibited the greatest protective effect. Universal influenza vaccines based on the combination of NP, PB1, and M1 induced a strong immune response and thus might be an alternative approach to addressing future influenza virus pandemics.

Broad-spectrum anti-tumor and anti-metastatic DNA vaccine based on p62-encoding vector

Autophagy plays an important role in neoplastic transformation of cells and in resistance of cancer cells to radio- and chemotherapy. p62 (SQSTM1) is a key component of autophagic machinery which is also involved in signal transduction. Although recent empirical observations demonstrated that p62 is overexpressed in variety of human tumors, a mechanism of p62 overexpression is not known. Here we report that the transformation of normal human mammary epithelial cells with diverse oncogenes (RAS, PIK3CA and Her2) causes marked accumulation of p62. Based on this result, we hypothesized that p62 may be a feasible candidate to be an anti-cancer DNA vaccine. Here we performed a preclinical study of a novel DNA vaccine encoding p62. Intramuscularly administered p62-encoding plasmid induced anti-p62 antibodies and exhibited strong antitumor activity in four models of allogeneic mouse tumors - B16 melanoma, Lewis lung carcinoma (LLC), S37 sarcoma, and Ca755 breast carcinoma. In mice challenged with Ca755 cells, p62 treatment had dual effect: inhibited tumor growth in some mice and prolonged life in those mice which developed tumor size similar to control. P62-encoding plasmid has demonstrated its potency both as a preventive and therapeutic vaccine. Importantly, p62 vaccination drastically suppressed metastasis formation: in B16 melanoma where tumor cells where injected intravenously, and in LLC and S37 sarcoma with spontaneous metastasis. Overall, we conclude that a p62-encoding vector(s) constitute(s) a novel, effective broad-spectrum antitumor and anti-metastatic vaccine feasible for further development and clinical trials.

A novel DNA vaccine technology conveying protection against a lethal herpes simplex viral challenge in mice

While there are a number of licensed veterinary DNA vaccines, to date, none have been licensed for use in humans. Here, we demonstrate that a novel technology designed to enhance the immunogenicity of DNA vaccines protects against lethal herpes simplex virus 2 (HSV-2) challenge in a murine model. Polynucleotides were modified by use of a codon optimization algorithm designed to enhance immune responses, and the addition of an ubiquitin-encoding sequence to target the antigen to the proteasome for processing and to enhance cytotoxic T cell responses. We show that a mixture of these codon-optimized ubiquitinated and non-ubiquitinated constructs encoding the same viral envelope protein, glycoprotein D, induced both B and T cell responses, and could protect against lethal viral challenge and reduce ganglionic latency. The optimized vaccines, subcloned into a vector suitable for use in humans, also provided a high level of protection against the establishment of ganglionic latency, an important correlate of HSV reactivation and candidate endpoint for vaccines to proceed to clinical trials.

The multifaceted effect of PB1-F2 specific antibodies on influenza A virus infection

PB1-F2 is a small influenza A virus (IAV) protein encoded by an alternative reading frame of the PB1 gene. During IAV infection, antibodies to PB1-F2 proteins are induced. To determine their function and contribution to virus infection, three distinct approaches were employed: passive transfer of anti-PB1-F2 MAbs and polyclonal antibodies, active immunization with PB1-F2 peptides and DNA vaccination with plasmids expressing various parts of PB1-F2. Mostly N-terminal specific antibodies were detected in polyclonal sera raised to complete PB1-F2. Passive and active immunization revealed that antibodies recognizing the N-terminal part of the PB1-F2 molecule have no remarkable effect on the course of IAV infection. Interestingly antibodies against the C-terminal region of PB1-F2, obtained by immunization with KLH-PB1-F2 C-terminal peptide or DNA immunization with pC-ter.PB1-F2 plasmid, partially protected mice against virus infection. To our knowledge, this is the first report demonstrating the biological relevance of humoral immunity against PB1-F2 protein in vivo.

Simultaneous immunisation with a Wilms' tumour 1 epitope and its ubiquitin fusions results in enhanced cell mediated immunity and tumour rejection in C57BL/6 mice

Protein fusion to ubiquitin results in its targeting to proteasome and processing through MHC class I pathway. We used this approach to induce cytotoxic T lymphocyte (CTL) response against a MHC class I epitope. Therefore, two known proteasome targeting systems, "ubiquitin fusion degradation" (UFD) and "N-end rule", were used to immunise C57BL/6 mice. Two plasmids encoding an epitope from Wilms' Tumour 1 (WT1-126), fused N-terminally to ubiquitin, were constructed. They were designated as "pUbVVPT" and "pUbGRPT", targeting the fused epitope to UFD and N-end pathways, respectively. A plasmid encoding WT1-126 without ubiquitin fusion (pPT) was also constructed as control. Three mice groups were immunised using these constructs (UGR, UVV and PT groups). Two other groups received mixed immunisations of pUbVVPT or pUbGRPT plus pPT plasmids (UVV+PT and UGR+PT). All mice received a WT1-126 peptide booster. Lymphoproliferative responses following stimulation with WT1-126 were observed in all immunisation groups, with mice receiving the mixture of plasmids eliciting the highest proliferation (UVV+PT>UGR+PT>PT). Moreover, In vivo cytotoxicity assay results revealed highest specific lysis of target cells in UVV+PT group. Tumour growth was decreased in all immunised groups, and was completely abrogated in UGR+PT group. In addition, T(H)1 type cytokines patterns were detected from all immunised groups and WT1-126-specific IFNγ producing lymphocytes were developed in them. These results suggest that the delivery of ubiquitin-fused epitopes along with epitopes alone can be used to optimise the effect of DNA vaccines on the induction of anti-tumour immunity.

Regulation of Immunogen Processing: Signal Sequences and Their Application for the New Generation of DNA-Vaccines

Immunization with naked genes (DNA-immunization) is a perspective modern approach to prophylactic as well as therapeutic vaccination against pathogens, as well as cancer and allergy. A panel of DNA immunogens has been developed, some are already in the clinical trials. However, the immunogenicity of DNA vaccines, specifically of those applied to humans, needs a considerable improvement. There are several approaches to increase DNA vaccine immunogenicity. One approach implies the modifications of the encoded immunogen that change its processing and presentation, and thus the overall pattern of anti-immunogen response. For this, eukaryotic expression vectors are constructed that encode the chimeric proteins composed of the immunogen and specialized targeting or signal sequences. The review describes a number of signals that if fused to immunogen, target it into the predefined subcellular compartments. The review gives examples of their application for DNA-immunization.

Towards a Brucella vaccine for humans

There is currently no licensed vaccine for brucellosis in humans. Available animal vaccines may cause disease and are considered unsuitable for use in humans. However, the causative pathogen, Brucella, is among the most common causes of laboratory-acquired infections and is a Center for Disease Control category B select agent. Thus, human vaccines for brucellosis are required. This review highlights the considerations that are needed in the journey to develop a human vaccine, including animal models, and includes an assessment of the current status of novel vaccine candidates.

Importance of mRNA secondary structural elements for the expression of influenza virus genes

Development of novel vaccines and therapeutics often requires efficient expression of recombinant viral proteins. Here we show that mutations in essential functional regions of conserved influenza proteins NP and NS1, lead to reduced expression of these genes in vitro. According to in silico analysis, these mRNA regions possess distinct secondary structures sensitive to mutations. We identified a novel structural feature within a region in NS1 mRNA that encodes amino acids essential for NS1 function. Mutations altering this mRNA element lead to significantly reduced protein expression. Conversely, expression was not affected by mutations resulting in amino acid substitutions, when they were designed to preserve this secondary RNA structural element. Furthermore, altering this structure significantly reduced RNA transcription without affecting mRNA stability. Therefore, distinct internal secondary structures of viral mRNA may be important for viral gene expression. If such elements encode amino acids essential for the protein function, then early selection against mutations in this region will be beneficial for the virus. This might point at yet another mechanism of viral evolution, especially for RNA viruses. Finally, introducing mutations into viral genes while preserving their secondary RNA structure, suggests a new method for the generation of efficiently expressed recombinants of viral proteins.

Development of a vaccine against pandemic influenza viruses: current status and perspectives

The constant threat of a new influenza pandemic, which may be caused by a highly pathogenic avian influenza virus, necessitates the development of a vaccine capable of providing efficient, long-term, and cost-effective protection. Proven avenues for the development of vaccines against seasonal influenza as well as novel approaches have been explored over the past decade. Whereas significant insights are consistently being made, the generation of a highly efficient and cross-protective vaccine against the future pandemic influenza strain remains as the ultimate goal in the field. In this review, we re-examine these efforts and outline the scientific, political, and economic problems that befall this area of biotechnological research.

The proteosomal degradation of fusion proteins cannot be predicted from the proteosome susceptibility of their individual components

It is assumed that the proteosome-processing characteristics of fusion constructs can be predicted from the sum of the proteosome sensitivity of their components. In the present study, we observed that a fusion construct consisting of proteosome-degradable proteins does not necessarily result in a proteosome-degradable chimera. Conversely, fusion of proteosome-resistant proteins may result in a proteosome-degradable composite. We previously demonstrated that conserved influenza proteins can be unified into a single fusion antigen that is protective, and that vaccination with combinations of proteosome-resistant and proteosome-degradable antigens resulted in an augmented T-cell response. In the present study we constructed proteosome-degradable mutants of conserved influenza proteins NP, M1, NS1, and M2. These were then fused into multipartite proteins in different positions. The stability and degradation profiles of these fusion constructs were demonstrated to depend on the relative position of the individual proteins within the chimeric molecule. Combining unstable sequences of either NP and M1 or NS1 and M2 resulted in either rapidly proteosome degraded or proteosome-resistant bipartite fusion mutants. However, further unification of the proteosome-degradable forms into a single four-partite fusion molecule resulted in relatively stable chimeric proteins. Conversely, the addition of proteosome-resistant wild-type M2 to proteosome-resistant NP-M1-NS1 fusion protein lead to the decreased stability of the resulting four-partite multigene products, which in one case was clearly proteosome dependent. Additionally, a highly destabilized form of M1 failed to destabilize the wild-type NP. Collectively, we did not observe any additive effect leading to proteosomal degradation/nondegradation of a multigene construct.