Recombinant fowlpox virus vector-based vaccines: expression kinetics, dissemination and safety profile following intranasal delivery

Recombinant single-cycle influenza virus with exchangeable pseudotypes allows repeated immunization to augment anti-tumour immunity with immune checkpoint inhibitors

Virus-based tumour vaccines offer many advantages compared to other antigen-delivering systems. They generate concerted innate and adaptive immune response, and robust CD8⁺ T cell responses. We engineered a non-replicating pseudotyped influenza virus (S-FLU) to deliver the well-known cancer testis antigen, NY-ESO-1 (NY-ESO-1 S-FLU). Intranasal or intramuscular immunization of NY-ESO-1 S-FLU virus in mice elicited a strong NY-ESO-1-specific CD8⁺ T cell response in lungs and spleen that resulted in the regression of NY-ESO-1-expressing lung tumour and subcutaneous tumour, respectively. Combined administration with anti-PD-1 antibody, NY-ESO-1 S-FLU virus augmented the tumour protection by reducing the tumour metastasis. We propose that the antigen delivery through S-FLU is highly efficient in inducing antigen-specific CD8⁺ T cell response and protection against tumour development in combination with PD-1 blockade.

IL-13Rα2 Regulates the IL-13/IFN-γ Balance during Innate Lymphoid Cell and Dendritic Cell Responses to Pox Viral Vector-Based Vaccination

We have shown that manipulation of IL-13 and STAT6 signaling at the vaccination site can lead to different innate lymphoid cell (ILC)/dendritic cell (DC) recruitment, resulting in high avidity/poly-functional T cells and effective antibody differentiation. Here we show that permanent versus transient blockage of IL-13 and STAT6 at the vaccination site can lead to unique ILC-derived IL-13 and IFN-γ profiles, and differential IL-13Rα2, type I and II IL-4 receptor regulation on ILC. Specifically, STAT6-/- BALB/c mice given fowl pox virus (FPV) expressing HIV antigens induced elevated ST2/IL-33R+ ILC2-derived IL-13 and reduced NKp46+/- ILC1/ILC3-derived IFN-γ expression, whilst the opposite (reduced IL-13 and elevated IFN-γ expression) was observed during transient inhibition of STAT6 signaling in wild type BALB/c mice given FPV-HIV-IL-4R antagonist vaccination. Interestingly, disruption/inhibition of STAT6 signaling considerably impacted IL-13Rα2 expression by ST2/IL-33R+ ILC2 and NKp46- ILC1/ILC3, unlike direct IL-13 inhibition. Consistently with our previous findings, this further indicated that inhibition of STAT6 most likely promoted IL-13 regulation via IL-13Rα2. Moreover, the elevated ST2/IL-33R+ IL-13Rα2+ lung ILC2, 24 h post FPV-HIV-IL-4R antagonist vaccination was also suggestive of an autocrine regulation of ILC2-derived IL-13 and IL-13Rα2, under certain conditions. Knowing that IL-13 can modulate IFN-γ expression, the elevated expression of IFN-γR on lung ST2/IL-33R+ ILC2 provoked the notion that there could also be inter-regulation of lung ILC2-derived IL-13 and NKp46- ILC1/ILC3-derived IFN-γ via their respective receptors (IFN-γR and IL-13Rα2) at the lung mucosae early stages of vaccination. Intriguingly, under different IL-13 conditions differential regulation of IL-13/IL-13Rα2 on lung DC was also observed. Collectively these findings further substantiated that IL-13 is the master regulator of, not only DC, but also different ILC subsets at early stages of viral vector vaccination, and responsible for shaping the downstream adaptive immune outcomes. Thus, thoughtful selection of vaccine strategies/adjuvants that can manipulate IL-13Rα2, and STAT6 signaling at the ILC/DC level may prove useful in designing more efficacious vaccines against different/chronic pathogens.

NF-κB as an Important Factor in Optimizing Poxvirus-Based Vaccines against Viral Infections

Poxviruses are large dsDNA viruses that are regarded as good candidates for vaccine vectors. Because the members of the Poxviridae family encode numerous immunomodulatory proteins in their genomes, it is necessary to carry out certain modifications in poxviral candidates for vaccine vectors to improve the vaccine. Currently, several poxvirus-based vaccines targeted at viral infections are under development. One of the important aspects of the influence of poxviruses on the immune system is that they encode a large array of inhibitors of the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which is the key element of both innate and adaptive immunity. Importantly, the NF-κB transcription factor induces the mechanisms associated with adaptive immunological memory involving the activation of effector and memory T cells upon vaccination. Since poxviruses encode various NF-κB inhibitor proteins, before the use of poxviral vaccine vectors, modifications that influence NF-κB activation and consequently affect the immunogenicity of the vaccine should be carried out. This review focuses on NF-κB as an essential factor in the optimization of poxviral vaccines against viral infections.

Expression of Two Foreign Genes by a Newcastle Disease Virus Vector From the Optimal Insertion Sites through a Combination of the ITU and IRES-Dependent Expression Approaches

Many Newcastle disease virus (NDV) strains have been developed as vectors to express a foreign gene (FG) for vaccine and cancer therapy purposes. The non-coding region between the phosphoprotein (P) and matrix protein (M) genes and the non-coding region behind the NP gene open reading frame (ORF) in the NDV genome have been identified as the optimal insertion sites for efficient FG expression through the independent transcription unit (ITU) and the internal ribosomal entry site (IRES) dependent expression approaches, respectively. To date, however, the majority of these NDV vectors express only a single or two FGs from suboptimal insertion sites in the NDV genome, obtaining various levels of FG expression. To improve the FG expression, we generated NDV LaSota vaccine strain-based recombinant viruses expressing two FGs, GFP, and RFP, from the identified optimal insertion sites through a combination of the ITU and IRES-dependent approaches. Biological assessments of the recombinant viruses indicated that the recombinants expressing two FGs were slightly attenuated with approximately one order of magnitude lower in virus titers when compared to the viruses containing a single FG. The FG expression efficiencies from the two-FG viruses were also lower than those from the single-FG viruses. However, the expression of two FGs from the optimal insertion sites was significantly (p < 0.05) higher than those from the suboptimal insertion sites. The expressions of FGs as monocistronic ITU were approximately 4-fold more efficient than those expressed by the bicistronic IRES-dependent approach. These results suggest that the NDV LaSota vector could efficiently express two FGs from the identified optimal insertions sites. The ITU strategy could be used for “vectoring” FGs in circumstances where high expression of gene products (e.g., antigens) is warranted, whereas, the IRES-dependent tactic might be useful when lower amounts of IRES-directed FG products are needed.

Mucosal and systemic SIV-specific cytotoxic CD4+ T cell hierarchy in protection following intranasal/intramuscular recombinant pox-viral vaccination of pigtail macaques

A HIV vaccine that provides mucosal immunity is urgently needed. We evaluated an intranasal recombinant Fowlpox virus (rFPV) priming vaccine followed by intramuscular Modified Vaccinia Ankara (rMVA) booster vaccine, both expressing SIV antigens. The vaccination generated mucosal and systemic SIV-specific CD4+ T cell mediated immunity and was associated with partial protection against high-dose intrarectal SIVmac251 challenge in outbred pigtail macaques. Three of 12 vaccinees were completely protected and these animals elicited sustained Gag-specific poly-functional, cytotoxic mucosal CD4+ T cells, complemented by systemic poly-functional CD4+ and CD8+ T cell immunity. Humoral immune responses, albeit absent in completely protected macaques, were associated with partial control of viremia in animals with relatively weaker mucosal/systemic T cell responses. Co-expression of an IL-4R antagonist by the rFPV vaccine further enhanced the breadth and cytotoxicity/poly-functionality of mucosal vaccine-specific CD4+ T cells. Moreover, a single FPV-gag/pol/env prime was able to induce rapid anamnestic gp140 antibody response upon SIV encounter. Collectively, our data indicated that nasal vaccination was effective at inducing robust cervico-vaginal and rectal immunity, although cytotoxic CD4+ T cell mediated mucosal and systemic immunity correlated strongly with 'complete protection', the different degrees of protection observed was multi-factorial.

Can an in vivo imaging system be used to determine localization and biodistribution of AAV5-mediated gene expression following subretinal and intravitreal delivery in mice?

Recombinant adeno associated viruses (AAV) are the most commonly used vectors in animal model studies of gene therapy for retinal diseases. The ability of a vector to localize and remain in the target tissue, and in this manner to avoid off-target effects beyond the site of delivery, is critical to the efficacy and safety of the treatment. The in vivo imaging system (IVIS) is a non-invasive imaging tool used for detection and quantification of bioluminescence activity in rodents. Our aim was to investigate whether IVIS can detect localization and biodistribution of AAV5 vector in mice following subretinal (SR) and intravitreal (IVT) injections. AAV5 carrying firefly luciferase DNA under control of the ubiquitous cytomegalovirus (CMV) promoter was injected unilaterally IVT or SR (in the central or peripheral retina) of forty-one mice. Luciferase activity was tracked for up to 60 weeks in the longest surviving animals, using repeated (up to 12 times) IVIS bioluminescence imaging. Luciferase presence was also confirmed immunohistochemically (IHC) and by PCR in representative animals. In the SR group, IVIS readings demonstrated luciferase activity in all (32/32) eyes, and luciferase presence was confirmed by IHC (4/4 eyes) and PCR (12/12 eyes). In the IVT group, IVIS readings demonstrated luciferase activity in 7/9 eyes, and luciferase presence was confirmed by PCR in 5/5 eyes and by IHC (2/2 eyes). In two SR-injected animals (one each from the central and peripheral injection sites), PCR detected luciferase presence in the ipsilateral optic nerves, a finding that was not detected by IVIS or IHC. Our results show that when evaluating SR delivery, IVIS has a sensitivity and specificity of 100% compared with the gold standard PCR. When evaluating IVT delivery, IVIS has a sensitivity of 78% and specificity of 100%. These finding confirm the ability of IVIS to detect in-vivo localized expression of AAV following SR delivery in the retina up to 60 weeks post-treatment, using repeated imaging for longitudinal evaluation, without fading of the biological signal, thereby replacing the need for post mortem processing in order to confirm vector expression. However, IVIS is probably not sensitive enough, compared with genome detection, to demonstrate biodistribution to the optic nerve, as it could not detect luciferase activity in ipsilateral optic nerves following SR delivery in mice.

Vector Order Determines Protection against Pathogenic Simian Immunodeficiency Virus Infection in a Triple-Component Vaccine by Balancing CD4+ and CD8+ T-Cell Responses

An effective AIDS vaccine should elicit strong humoral and cellular immune responses while maintaining low levels of CD4+ T-cell activation to avoid the generation of target cells for viral infection. The present study investigated two prime-boost regimens, both starting vaccination with single-cycle immunodeficiency virus, followed by two mucosal boosts with either recombinant adenovirus (rAd) or fowlpox virus (rFWPV) expressing SIVmac239 or SIVmac251 gag/pol and env genes, respectively. Finally, vectors were switched and systemically administered to the reciprocal group of animals. Only mucosal rFWPV immunizations followed by systemic rAd boost significantly protected animals against a repeated low-dose intrarectal challenge with pathogenic SIVmac251, resulting in a vaccine efficacy (i.e., risk reduction per exposure) of 68%. Delayed viral acquisition was associated with higher levels of activated CD8+ T cells and Gag-specific gamma interferon (IFN-γ)-secreting CD8+ cells, low virus-specific CD4+ T-cell responses, and low Env antibody titers. In contrast, the systemic rFWPV boost induced strong virus-specific CD4+ T-cell activity. rAd and rFWPV also induced differential patterns of the innate immune responses, thereby possibly shaping the specific immunity. Plasma CXCL10 levels after final immunization correlated directly with virus-specific CD4+ T-cell responses and inversely with the number of exposures to infection. Also, the percentage of activated CD69+ CD8+ T cells correlated with the number of exposures to infection. Differential stimulation of the immune response likely provided the basis for the diverging levels of protection afforded by the vaccine regimen.IMPORTANCE A failed phase II AIDS vaccine trial led to the hypothesis that CD4+ T-cell activation can abrogate any potentially protective effects delivered by vaccination or promote acquisition of the virus because CD4+ T helper cells, required for an effective immune response, also represent the target cells for viral infection. We compared two vaccination protocols that elicited similar levels of Gag-specific immune responses in rhesus macaques. Only the animal group that had a low level of virus-specific CD4+ T cells in combination with high levels of activated CD8+ T cells was significantly protected from infection. Notably, protection was achieved despite the lack of appreciable Env antibody titers. Moreover, we show that both the vector and the route of immunization affected the level of CD4+ T-cell responses. Thus, mucosal immunization with FWPV-based vaccines should be considered a potent prime in prime-boost vaccination protocols.