Nano/microparticle Formulations for Universal Influenza Vaccines

Comparative study of acetalated-dextran microparticle fabrication methods for a clinically translatable subunit-based influenza vaccine

The most common influenza vaccines are inactivated viruses produced in chicken eggs, which is a time-consuming production method with variable efficacy due to mismatches of the vaccine strains to the dominant circulating strains. Subunit-based vaccines provide faster production times in comparison to the traditional egg-produced vaccines but often require the use of an adjuvant to elicit a highly protective immune response. However, the current FDA approved adjuvant for influenza vaccines (MF59) elicits a primarily helper T-cell type 2 (Th2)-biased humoral immune response. Adjuvants that can stimulate a Th1 cellular response are correlated to have more robust protection against influenza. The cyclic dinucleotide cGAMP has been shown to provide a potent Th1 response but requires the use of a delivery vehicle to best initiate its signalling pathway in the cytosol. Herein, acetalated dextran (Ace-DEX) was used as the polymer to fabricate microparticles (MPs) via double-emulsion, electrospray, and spray drying methods to encapsulate cGAMP. This study compared each fabrication method's ability to encapsulate and retain the hydrophilic adjuvant cGAMP. We compared their therapeutic efficacy to Addavax, an MF59-like adjuvant, and cGAMP Ace-DEX MPs provided a stronger Th1 response in vaccinated BALB/c mice. Furthermore, we compared Ace-DEX MPs to spray dried MPs composed from a commonly used polymer for drug delivery, poly(lactic-co-glycolic acid) (PLGA). We observed that all Ace-DEX MPs elicited similar humoral and cellular responses to the PLGA MPs. Overall, the results shown here indicate Ace-DEX can perform similarly to PLGA as a polymer for drug delivery and that spray drying can provide an efficient way to produce MPs to encapsulate cGAMP and stimulate the immune system.

Recent Advances, Approaches and Challenges in the Development of Universal Influenza Vaccines

Every year, influenza virus infections cause significant morbidity and mortality worldwide. They pose a substantial burden of disease, in terms of not only health but also the economy. Owing to the ability of influenza viruses to continuously evolve, annual seasonal influenza vaccines are necessary as a prophylaxis. However, current influenza vaccines against seasonal strains have limited effectiveness and require yearly reformulation due to the virus undergoing antigenic drift or shift. Vaccine mismatches are common, conferring suboptimal protection against seasonal outbreaks, and the threat of the next pandemic continues to loom. Therefore, there is a great need to develop a universal influenza vaccine (UIV) capable of providing broad and durable protection against all influenza virus strains. In the quest to develop a UIV that would obviate the need for annual vaccination and formulation, a multitude of strategies is currently underway. Promising approaches include targeting the highly conserved epitopes of haemagglutinin (HA), neuraminidase (NA), M2 extracellular domain (M2e) and internal proteins of the influenza virus. The identification and characterization of broadly neutralizing antibodies (bnAbs) targeting conserved regions of the viral HA protein, in particular, have provided important insight into novel vaccine designs and platforms. This review discusses universal vaccine approaches presently under development, with an emphasis on those targeting the highly conserved stalk of the HA protein, recent technological advancements used and the future prospects of a UIV in terms of its advantages, developmental obstacles and potential shortcomings.

Anti-microbial host factor HDAC6 is antagonised by the influenza A virus through host caspases and viral PA

Histone deacetylase 6 (HDAC6), through the repertoire of its substrate proteins, plays a critical role in human physiology, and an aberrant function of HDAC6 contributes to various pathophysiological conditions. HDAC6 is also known to be an anti-microbial host factor and has been implicated in restricting or clearing the infection of various human viral and bacterial pathogens. However, the state and the mechanisms of its antagonism in infected cells are not understood. Here, we demonstrate that influenza A virus (IAV) antagonises HDAC6 by recruiting both viral and host components. We found that HDAC6 mRNA expression, and consequently, the HDAC6 polypeptide expression is downregulated in human lung epithelial cells during early stage of IAV infection but can be rescued by depleting the expression of viral polymerase acidic (PA) protein, a subunit of IAV RNA polymerase. In addition, during later stage of the infection, the HDAC6 polypeptide undergoes caspase-mediated cleavage at two sites, generating two cleaved fragments. Both these fragments disappeared when the expression of caspase 3 was depleted in infected cells, whereas only second fragment disappeared when the expression of caspase 6 was depleted. But both fragments disappeared and the level of full-length HDAC6 polypeptide was rescued when the expression of PA was depleted in infected cells. Collectively, these data indicated that IAV antagonises the HDAC6 by decreasing its expression level in infected cells, both at mRNA and polypeptide level via PA gene, which has been implicated in auxiliary functions like degradation of host mRNA and induction of apoptosis.