Pathogenesis of recent Lassa virus isolates from lineages II and VII in cynomolgus monkeys

Abstract

The area of Lassa virus (LASV) circulation is expanding, with the emergence of highly pathogenic new LASV lineages. Benin recently became an endemic country for LASV and has seen the emergence of a new LASV lineage (VII). The first two outbreaks in 2014 and 2016 showed a relatively high mortality rate compared to other outbreaks. We infected cynomolgus monkeys with two strains belonging to lineage II and lineage VII that were isolated from deceased patients during the 2016 outbreak in Benin. The lineage VII strain (L7) caused uniform mortality. Death was associated with uncontrolled viral replication, unbalanced inflammatory responses characterized by increased concentrations of pro- and anti-inflammatory mediators, and the absence of efficient immune responses, resembling the pathogenesis associated with the prototypic Josiah strain in monkeys. The lineage II strain (L2) showed apparently lower virulence than its counterpart, with a prolonged time to death and a lower mortality rate. Prolonged survival was associated with better control of viral replication, a moderate inflammatory response, and efficient T -cell responses. Transcriptomic analyses also highlighted important differences in the immune responses associated with the outcome. Both strains caused strong inflammation in several organs. Notably, meningitis and encephalitis were observed in the cerebral cortex and cerebellum in all monkeys, independently of the outcome. Due to their apparently high pathogenicity, emerging strains from lineage VII should be considered in preclinical vaccine testing. Lineage II would also be beneficial in pathogenesis studies to study the entire spectrum of Lassa fever severity.

Lassa virus persistence with high viral titers following experimental infection in its natural reservoir host, Mastomys natalensis

“…However, the presence of these antibodies did not prevent infection with LASV in the offspring. In concordance with reports on human Lassa fever cases and experiments with NHP 39,40,45 , nAbs only appeared very late (≥ 100 days post infection) in a few individuals and often at low titers. Most of the animals that possessed nAbs were still viremic and no apparent effect on virus clearance was detected, indicating that nAbs neither conferred protection nor did they impact the course of LASV infection.…”

“…Changes in the immune response, notably in the T cell activity, during this maturation process, could explain the shift in the infection phenotype from tolerance towards effective control. Studies in humans and in animal models have already described an association between a robust T cell response and successful LASV control [38][39][40][41] . However, further characterization of the innate and adaptive immune response of M. natalensis is required to fully explore the underlying mechanisms involved in the development of LASV persistence in its natural host.…”

Rapid protection induced by a single-shot Lassa vaccine in male cynomolgus monkeys

“…Vaccination against LASV is a major challenge in Western Africa, where yearly epidemics remain uncontrolled. We previously demonstrated the efficacy of MeV-NP against Lassa fever in cynomolgus monkeys immunized one month or one year before a LASV infection 23,24 , as well as its protective efficacy against recently isolated and highly divergent Lassa strains from lineages II and VII 24,27 . Here, we demonstrate that MeV-NP can protect cynomolgus monkeys with similar or even higher efficacy when the monkeys are immunized 16 or 8 days before a LASV infection.…”

“…Knowing that strong inflammatory responses are also markers of severe Lassa fever in cynomolgus monkeys 23,25,27 , we performed a multiplex analysis of several soluble mediators of inflammation on the samples collected during the experiment. Plasma concentrations of the pro-inflammatory cytokines IL-6 and TNF-α, as well as soluble FasL were all increased in the days preceding death in the CT and H + 1 animals but remained unchanged in the D-16 and D-8 animals, except for a transient increase in TNF-α concentrations on day 6 in the D-8 animals and, to a lesser extent, D-16 animals (Fig.…”

Structural conservation of Lassa virus glycoproteins and recognition by neutralizing antibodies

“…Here, we utilize the I53-50A subunit as a scaffold to generate and characterize GPC trimers of LASV genotypes beyond the prototypical lineage IV Josiah. We focus on lineages of public health concern including lineage II one of the most common lineages which circulates widely in southern Nigeria; lineage V, which circulates in Mali and has decreased pathogenicity compared to lineage IV; and lineage VI, a newly described lineage isolated from a nosocomial infection in Togo with comparable pathogenicity to lineage IV (Mateo et al, 2022; Safronetz et al, 2013). Establishing a single particle cryo-electron microscopy (cryoEM) GPC pipeline allowed us to generate unliganded high-resolution structures of these GPC trimers, revealing structural commonalities and subtle differences between these geographically distinct lineages.…”