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.

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.

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 replication-incompetent Rift Valley fever vaccine: chimeric virus-like particles protect mice and rats against lethal challenge.

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 G(N) and G(C), 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.

Identification and characterization of a human monoclonal antibody that potently neutralizes a broad panel of rabies virus isolates.

Rabies is a zoonosis that results in millions of human exposures worldwide each year. Human monoclonal antibodies (HuMAbs) that neutralize rabies virus may represent one viable strategy for post-exposure prophylaxis in humans, and have many advantages over current human or equine rabies immune globulin. Transgenic mice carrying human immunoglobulin genes were used to isolate human monoclonal antibodies that neutralized rabies virus. Several HuMAbs were identified that neutralized rabies virus variants from a broad panel of isolates of public health significance. HuMAb 17C7 was the most promising antibody identified because it neutralized all rabies virus isolates tested. HuMAb 17C7 recognizes a conformational epitope on the rabies virus glycoprotein which includes antigenic site III. HuMAb 17C7 protected hamsters from a lethal dose of rabies virus in a well-established in vivo model of post-exposure prophylaxis.

Human monoclonal antibodies directed against toxins A and B prevent Clostridium difficile-induced mortality in hamsters.

Clostridium difficile is the leading cause of nosocomial antibiotic-associated diarrhea, and recent outbreaks of strains with increased virulence underscore the importance of identifying novel approaches to treat and prevent relapse of Clostridium difficile-associated diarrhea (CDAD). CDAD pathology is induced by two exotoxins, toxin A and toxin B, which have been shown to be cytotoxic and, in the case of toxin A, enterotoxic. In this report we describe fully human monoclonal antibodies (HuMAbs) that neutralize these toxins and prevent disease in hamsters. Transgenic mice carrying human immunoglobulin genes were used to isolate HuMAbs that neutralize the cytotoxic effects of either toxin A or toxin B in cell-based in vitro neutralization assays. Three anti-toxin A HuMAbs (3H2, CDA1, and 1B11) could all inhibit the enterotoxicity of toxin A in mouse intestinal loops and the in vivo toxicity in a systemic mouse model. Four anti-toxin B HuMAbs (MDX-1388, 103-174, 1G10, and 2A11) could neutralize cytotoxicity in vitro, although systemic toxicity in the mouse could not be neutralized. Anti-toxin A HuMAb CDA1 and anti-toxin B HuMAb MDX-1388 were tested in the well-established hamster model of C. difficile disease. CDA1 alone resulted in a statistically significant reduction of mortality in hamsters; however, the combination treatment offered enhanced protection. Compared to controls, combination therapy reduced mortality from 100% to 45% (P<0.0001) in the primary disease hamster model and from 78% to 32% (P<0.0001) in the less stringent relapse model.