An inactivated recombinant Lassa virus (LASV) and rabies vaccine candidate was developed that protects both mice and guinea pigs from Lassa fever. The vaccine also elicits a lasting humoral response against both LASV and rabies virus in both animal models. The novel vaccine, which uses a rabies virus–derived vector, expresses a codon-optimized LASV glycoprotein, according to Tiago Abreu Mota, a doctoral student at Jefferson University, Philadelphia, and his colleagues.
Lassa fever, a World Health Organization priority disease with a biosafety level of 4, is a hemorrhagic fever caused by the Lassa virus, which has no approved vaccine or potent antiviral treatment, according to the report published online in. So the development of a vaccine would be an important step in protecting the West African population from this deadly disease, which infects an estimated 100,000-300,000 people annually. As many as 80% of Lassa fever exposures are mildly symptomatic and thus go unreported; however, the case fatality rate of full-blown Lassa fever has been reported to reach as high as 50%, according to Mr. Mota and his colleagues.
An advantage to the new vaccine is that it is inactivated and thus could potentially be used in pregnant women and immunosuppressed patients, both of which are major risk groups for Lassa fever, according to the researchers. The vaccine could also protect against rabies, which is another major health concern in the regions affected by the Lassa virus.
In terms of mechanism of action, the vaccine did not induce virus-neutralizing antibodies, but rather appeared to trigger cell-mediated protection through activating natural killer cells to promote significantly more killing of virus-infected cells than nontriggered NK cells (P less than .01), as seen through in vitro testing.
The ability to assay for this form of vaccine effectiveness was a key development, according to the researchers. “The neutralizing antibody has been something of a gold standard in vaccine development. High levels are usually a good indication that the immune reaction is strong enough to deflect viral disease. In the case of Lassa virus, however, neutralizing antibodies have not been very good surrogates, since they are produced in much lower quantities. ... The new surrogate of protection will aid in the development of a more potent vaccine against Lassa virus,” according to aby Jefferson University.
This work was supported by various grants from the National Institutes of Health. Mr. Mota and two of his colleagues are inventors on a U.S. provisional patent application for a recombinant Lassa-rabies vaccine.
SOURCE: Mota TA et al. Nat Commun. 2018;9:4223. .