Nucleic acid-based vaccines such as viral vectors, plasmid DNA, and mRNA are being developed as a means to address a number of unmet medical needs that current vaccine technologies have been unable to address. Here, we describe a cationic nanoemulsion (CNE) delivery system developed to deliver a self-amplifying mRNA vaccine. This nonviral delivery system is based on Novartis's proprietary adjuvant MF59, which has an established clinical safety profile and is well tolerated in children, adults, and the elderly. We show that nonviral delivery of a 9 kb self-amplifying mRNA elicits potent immune responses in mice, rats, rabbits, and nonhuman primates comparable to a viral delivery technology, and demonstrate that, relatively low doses (75 µg) induce antibody and T-cell responses in primates. We also show the CNE-delivered self-amplifying mRNA enhances the local immune environment through recruitment of immune cells similar to an MF59 adjuvanted subunit vaccine. Lastly, we show that the site of protein expression within the muscle and magnitude of protein expression is similar to a viral vector. Given the demonstration that self-amplifying mRNA delivered using a CNE is well tolerated and immunogenic in a variety of animal models, we are optimistic about the prospects for this technology.

RNA-based vaccines have recently emerged as a promising alternative to the use of DNA-based and viral vector vaccines, in part because of the potential to simplify how vaccines are made and facilitate a rapid response to newly emerging infections. SAM vaccines are based on engineered self-amplifying mRNA (SAM) replicons encoding an Ag, and formulated with a synthetic delivery system, and they induce broad-based immune responses in preclinical animal models. In our study, in vivo imaging shows that after the immunization, SAM Ag expression has an initial gradual increase. Gene expression profiling in injection-site tissues from mice immunized with SAM-based vaccine revealed an early and robust induction of type I IFN and IFN-stimulated responses at the site of injection, concurrent with the preliminary reduced SAM Ag expression. This SAM vaccine-induced type I IFN response has the potential to provide an adjuvant effect on vaccine potency, or, conversely, it might establish a temporary state that limits the initial SAM-encoded Ag expression. To determine the role of the early type I IFN response, SAM vaccines were evaluated in IFN receptor knockout mice. Our data indicate that minimizing the early type I IFN responses may be a useful strategy to increase primary SAM expression and the resulting vaccine potency. RNA sequence modification, delivery optimization, or concurrent use of appropriate compounds might be some of the strategies to finalize this aim.

The major inducible 70-kDa heat shock protein (hsp72) binds measles virus (MV) nucleocapsids and increases MV gene expression. The cytoplasmic tail of the MV N protein (N(TAIL)) contains three hydrophobic domains (Box-1-3) that are potential targets of hsp72 interaction. Low affinity binding to Box-3 is correlated to hsp72-dependent stimulation of MV minireplicon reporter gene expression whereas interactions between hsp72 and Box-1 and/or -2 have not been documented. The present work showed that virus deficient in Box-3/hsp72 interaction retains the ability to form nucleocapsid/hsp72 complexes, identifying Box-2 but not Box-1 as a mediator of high affinity hsp72 binding. Box-2 is the binding site for the viral P protein X domain (XD), where P tethers the viral polymerase to nucleocapsid in support of transcription and genome replication, and competitive inhibition of XD binding to N(TAIL) by hsp72 was shown. Recognition of a common binding site by P and hsp72 represents a potential mechanism for host cell modulation of viral gene expression.

Transient hyperthermia such as that experienced during febrile episodes increases expression of the major inducible 70-kDa heat shock protein (hsp72). Despite the relevance of febrile episodes to viral pathogenesis and the multiple in vitro roles of heat shock proteins in viral replication and gene expression, the in vivo significance of virus-heat shock protein interactions is unknown. The present work determined the in vivo relationship between hsp72 levels and neurovirulence of an hsp72-responsive virus using the mouse model of measles virus (MV) encephalitis. Transgenic C57BL/6 mice were created to constitutively overexpress hsp72 in neurons, and these mice were inoculated intracranially with Edmonston MV (Ed MV) at 42 h of age. The mean viral RNA burden in brain was approximately 2 orders of magnitude higher in transgenic animals than in nontransgenic animals 2 to 4 weeks postinfection, and this increased burden was associated with a fivefold increase in mortality. Mice were also challenged with an Ed MV variant exhibiting an attenuated in vitro response to hsp72-dependent stimulation of viral transcription (Ed N-522D). This virus exhibited an attenuated neuropathogenicity in transgenic mice, where mortality and viral RNA burdens were not significantly different from nontransgenic mice infected with either Ed N-522D or parent Ed MV. Collectively, these results indicate that hsp72 levels can serve as a host determinant of viral neurovirulence in C57BL/6 mice, reflecting the direct influence of hsp72 on viral gene expression.Cellular heat shock proteins (HSPs) are recognized for their function as molecular chaperones that facilitate protein folding and trafficking (22) and for their ability to bind native proteins, resulting in altered activity of the substrate (18). Multiple families of HSPs are recognized and are classified according to their mass, with members of the 70-kDa family being expressed at high basal and/or stress-inducible levels in multiple tissues. In particular, the major inducible 70-kDa HSP (i.e., hsp72, also known as hsp70) exhibits a wide range of expression levels in the cytosol, being readily induced by physiological stimuli, such as fever (32,44). This dynamic range of expression and numerous roles in protein metabolism make hsp72 a potentially significant variable that could influence the outcome of viral replication in an animal host. In vitro studies suggest that hsp72 and the constitutively expressed isoform can directly modulate gene expression of several mammalian RNA and DNA viruses by supporting viral core protein maturation and/or assembly into nucleocapsid particles (11,12,30,31), by mediating assembly and/or activity of viral polymerase/replication complexes (7, 29, 45), or by mediating nuclear trafficking of viral preintegration complexes in the case of retroviruses (1). Despite the relevance of hsp72 to viral replication within the cell and the physiological relevance of elevated hsp72 to viral infection of an animal host, the biological (in vivo) significance of virus-hsp...

Although live-attenuated measles virus (MV) vaccines have been used successfully for over 50 years, the target cells that sustain virus replication in vivo are still unknown. We generated a reverse genetics system for the live-attenuated MV vaccine strain Edmonston-Zagreb ( IMPORTANCE Even though MV strain Edmonston-Zagreb has long been used as a live-attenuated vaccine (LAV) to protect against measles, nothing is known about the primary cells in which the virus replicates in vivo.This is vital information given the push to move toward needle-free routes of vaccination, since vaccine virus replication is essential for vaccination efficacy. We have generated a number of recombinant MV strains expressing enhanced green fluorescent protein. The virus that best mimicked the nonrecombinant vaccine virus was formulated according to protocols for production of commercial vaccine virus batches, and was subsequently used to assess viral tropism in nonhuman primates. The virus primarily replicated in professional antigen-presenting cells, which may explain why this LAV is so immunogenic and efficacious.

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The major inducible 70-kDa heat shock protein (hsp72) increases measles virus (MV) transcription and genome replication. This stimulatory effect is attributed to hsp72 interaction with two highly conserved hydrophobic domains in the nucleocapsid protein (N) C terminus of Edmonston MV. These domains are known as Box-2 and Box-3. A single amino acid substitution in Box-3 of Edmonston MV (i.e., N522D) disrupts hsp72 binding. The prevalence of the N522D substitution in contemporary wild-type MV isolates suggests that this sequence has been positively selected. The present work determined if the N522D substitution enhances viral fitness and the degree to which any fitness advantage is influenced by hsp72 levels. Both parent Edmonston MV (Ed N) and an N522D substitution mutant (Ed N-522D) exhibited similar growth on Vero and murine neuroblastoma cells and in cotton rat lung, although Ed N-522D virus exhibited an attenuated in vitro response to hsp72 overexpression. In contrast, mixed infections showed a significantly reduced in vitro and in vivo fitness of Ed N-522D virus. Results support the involvement of additional selectional pressures that maintain the circulation of virus containing N-522D despite the cost to viral fitness.The measles virus (MV) RNA genome is packaged by the viral nucleocapsid protein (N) to form a helical nucleocapsid. The carboxyl-terminal 125 amino acids of the 525-amino-acid N protein (i.e., N TAIL ) is exposed on the surface of the nucleocapsid (8, 9). Sequence variability in the N protein C terminus reflects the fact that this protein domain is intrinsically disordered, imparting structural plasticity that allows it to mediate interactions with a variety of cellular and viral binding partners that include the viral P protein (1, 2, 10), the major inducible 70-kDa heat shock protein (hsp72) (29, 30), the cellular nucleoprotein receptor (12, 13), and interferon-responsive factor 3 (24). Binding events are localized to patches of hydrophobic amino acid side groups whose sequence is well conserved relative to the hypervariable sequence that is otherwise characteristic of N TAIL (4). These regions of exposed hydrophobicity are referred to as Box-1, Box-2, and Box-3.Stable complex formation between the viral P protein and N TAIL involves both high-affinity binding to Box-2 and lowaffinity binding to . By also binding the viral L protein, P tethers the viral L protein to the nucleocapsid template in support of transcription and genome replication, and it is this essential function that is the probable basis for constraints in Box-2 and Box-3 sequence variability. hsp72 also exhibits a high binding affinity for Box-2 and a low binding affinity for Box-3, a fact that would allow hsp72 to destabilize P/N TAIL complexes (29,30). It has been postulated that it is necessary to diminish the affinity between P and N TAIL in order to promote the repetitive cycle of binding and release that underlies polymerase processivity (2). Such a model could explain the increases in MV transcription and genome replic...

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