Robert B. Mandell

A Replication-incompetent Rift Valley Fever Vaccine: Chimeric Virus-like Particles Protect Mice and Rats Against Lethal Challenge

Abstract Virus-like particles (VLPs) present viral antigens in a native conformation and are effectively recognized by the immune system and therefore are considered as suitable and safe vaccine candidates against many viral diseases. Here we demonstrate that chimeric VLPs containing Rift Valley fever virus (RVFV) glycoproteins GN and GC, nucleoprotein N and the gag protein of Moloney murine leukemia virus represent an effective vaccine candidate against Rift Valley fever, a deadly disease in humans and livestock. Long-lasting humoral and cellular immune responses are demonstrated in a mouse model by the analysis of neutralizing antibody titers and cytokine secretion profiles. Vaccine efficacy studies were performed in mouse and rat lethal challenge models resulting in high protection rates. Taken together, these results demonstrate that replication-incompetent chimeric RVF VLPs are an efficient RVFV vaccine candidate.

Rho GTPases Modulate Entry of Ebola Virus and Vesicular Stomatitis Virus Pseudotyped Vectors

ABSTRACT To explore mechanisms of entry for Ebola virus (EBOV) glycoprotein (GP) pseudotyped virions, we used comparative gene analysis to identify genes whose expression correlated with viral transduction. Candidate genes were identified by using EBOV GP pseudotyped virions to transduce human tumor cell lines that had previously been characterized by cDNA microarray. Transduction profiles for each of these cell lines were generated, and a significant positive correlation was observed between RhoC expression and permissivity for EBOV vector transduction. This correlation was not specific for EBOV vector alone as RhoC also correlated highly with transduction of vesicular stomatitis virus GP (VSVG) pseudotyped vector. Levels of RhoC protein in EBOV and VSV permissive and nonpermissive cells were consistent with the cDNA gene array findings. Additionally, vector transduction was elevated in cells that expressed high levels of endogenous RhoC but not RhoA. RhoB and RhoC overexpression significantly increased EBOV GP and VSVG pseudotyped vector transduction but had minimal effect on human immunodeficiency virus (HIV) GP pseudotyped HIV or adeno-associated virus 2 vector entry, indicating that not all virus uptake was enhanced by expression of these molecules. RhoB and RhoC overexpression also significantly enhanced VSV infection. Similarly, overexpression of RhoC led to a significant increase in fusion of EBOV virus-like particles. Finally, ectopic expression of RhoC resulted in increased nonspecific endocytosis of fluorescent dextran and in formation of increased actin stress fibers compared to RhoA-transfected cells, suggesting that RhoC is enhancing macropinocytosis. In total, our studies implicate RhoB and RhoC in enhanced productive entry of some pseudovirions and suggest the involvement of actin-mediated macropinocytosis as a mechanism of uptake of EBOV GP and VSVG pseudotyped viral particles.

Rift Valley fever virus: an unrecognized emerging threat?

Rift Valley fever virus (RVFV) is an arthropod-borne pathogen that often results in severe morbidity and mortality in both humans and livestock. As its geographic range continues to spread, it presents a real threat to naïve populations around the world by accidental introduction (e.g., the result of increased world travel) or a bioterror event. The lack of prophylactic and therapeutic measures, the potential for human-to-human transmission, and the significant threat to livestock associated with RVFV make infection with these pathogens a serious public health concern. Rift Valley fever epizootics and epidemics might rapidly overwhelm the capacities of the public health and veterinary medical communities to provide rapid diagnostic testing, distribution of countermeasures and adequate medical care.

Rift Valley Fever Virus: A Real Bioterror Threat

Rift Valley fever virus is recognized as an important bioterror and agroterror threat to Western countries including the United States. Once introduced, the virus would be readily spread by native mosquito populations and potentially become endemic. While infection often results in severe morbidity and mortality in both humans and livestock, there are currently no FDA or USDA-licensed vaccines. The development of effective countermeasures and implementing surveillance and diagnostic capabilities are critical. Ultimately, the presence of RVFV would lead to severe long-term negative impacts for healthcare, agricultural and travel economic sectors.

Novel suspension cell-based vaccine production systems for Rift Valley fever virus-like particles.

Rift Valley fever virus (RVFV) is an arthropod-borne pathogen that often results in severe morbidity and mortality in both humans and livestock. As its geographic range continues to expand, it presents a real threat to naïve populations around the world by accidental introduction (e.g., the result of increased travel) or intentional release (e.g., a bioterror event). While there is a clear need for a safe and efficacious vaccine against this emerging and re-emerging pathogen, no FDA-approved vaccine is currently available. This need was addressed by the establishment of novel mammalian and insect suspension cell line systems for the efficient production of RVF virus-like particle (VLP)-based vaccine candidates. A direct comparison of the production of RVF VLPs in these systems was performed. Optimization and characterization resulted in a production platform suitable for scale-up. Furthermore, RVF VLP-based vaccines were tested in a lethal challenge model and showed full protection, demonstrating that RVF VLPs present promising RVFV vaccine candidates.

A systems approach to designing next generation vaccines: combining α-galactose modified antigens with nanoparticle platforms.

Innovative vaccine platforms are needed to develop effective countermeasures against emerging and re-emerging diseases. These platforms should direct antigen internalization by antigen presenting cells and promote immunogenic responses. This work describes an innovative systems approach combining two novel platforms, αGalactose (αGal)-modification of antigens and amphiphilic polyanhydride nanoparticles as vaccine delivery vehicles, to rationally design vaccine formulations. Regimens comprising soluble αGal-modified antigen and nanoparticle-encapsulated unmodified antigen induced a high titer, high avidity antibody response with broader epitope recognition of antigenic peptides than other regimen. Proliferation of antigen-specific CD4+ T cells was also enhanced compared to a traditional adjuvant. Combining the technology platforms and augmenting immune response studies with peptide arrays and informatics analysis provides a new paradigm for rational, systems-based design of next generation vaccine platforms against emerging and re-emerging pathogens.

Virus-Like Particle-Based vaccines for Rift Valley Fever Virus

There is a clear need for a vaccine to protect humans and livestock against the devastating consequences of Rift Valley fever (RVF) virus infections. Virus-like particles (VLPs), readily generated for many viruses by expression of their structural proteins, are a safe and immunogenic vaccine platform that has been approved for use as human vaccines. Pre-clinical studies have shown that RVF VLPs are highly immunogenic and efficacious in rodent models, and thus present a promising vaccine candidate for Rift Valley fever virus.