Chikungunya virus (CHIKV) is an emerging arbovirus associated with several recent large-scale epidemics. The 2005–2006 epidemic on Reunion island that resulted in approximately 266,000 human cases was associated with a strain of CHIKV with a mutation in the envelope protein gene (E1-A226V). To test the hypothesis that this mutation in the epidemic CHIKV (strain LR2006 OPY1) might influence fitness for different vector species, viral infectivity, dissemination, and transmission of CHIKV were compared in Aedes albopictus, the species implicated in the epidemic, and the recognized vector Ae. aegypti. Using viral infectious clones of the Reunion strain and a West African strain of CHIKV, into which either the E1–226 A or V mutation was engineered, we demonstrated that the E1-A226V mutation was directly responsible for a significant increase in CHIKV infectivity for Ae. albopictus, and led to more efficient viral dissemination into mosquito secondary organs and transmission to suckling mice. This mutation caused a marginal decrease in CHIKV Ae. aegypti midgut infectivity, had no effect on viral dissemination, and was associated with a slight increase in transmission by Ae. aegypti to suckling mice in competition experiments. The effect of the E1-A226V mutation on cholesterol dependence of CHIKV was also analyzed, revealing an association between cholesterol dependence and increased fitness of CHIKV in Ae. albopictus. Our observation that a single amino acid substitution can influence vector specificity provides a plausible explanation of how this mutant virus caused an epidemic in a region lacking the typical vector. This has important implications with respect to how viruses may establish a transmission cycle when introduced into a new area. Due to the widespread distribution of Ae. albopictus, this mutation increases the potential for CHIKV to permanently extend its range into Europe and the Americas.

Zika virus (ZIKV) has recently emerged as an explosive pandemic associated with severe neuropathology in newborns and adults1. There are no ZIKV-specific treatments or preventatives; thus, development of a safe and effective vaccine is a high priority. Messenger RNA (mRNA) has emerged as a versatile and highly effective platform to deliver vaccine antigens and therapeutic proteins2,3. Here, we demonstrate that a single low-dose intradermal immunization with lipid nanoparticle-encapsulated nucleoside-modified mRNA (mRNA-LNP) encoding the pre-membrane and envelope (prM-E) glycoproteins of a 2013 ZIKV outbreak strain elicited potent and durable neutralizing antibody responses in mice and non-human primates. Immunization with 30 μg of nucleoside-modified ZIKV mRNA-LNPs protected mice from ZIKV challenges at 2 weeks or 5 months post-vaccination, and a single dose of 50 μg was sufficient to protect non-human primates from a challenge at 5 weeks post-vaccination. These data demonstrate that nucleoside-modified mRNA-LNPs elicit rapid and durable protective immunity and thus represent a new and promising vaccine candidate for the global fight against ZIKV.

Highlights d Human B cells specific for a novel epitope on influenza A groups 1 and 2 d Crystallography locates the epitope at the interface of the hemagglutinin head domains d Robust protection by antibodies to this epitope, dependent on IgG subclass d Protective, cross-group antibodies are encoded by diverse sets of Ig gene segments

The recent outbreak of Chikungunya virus (CHIKV) on several islands in the Indian Ocean and in India has focused attention on this reemerging virus and highlighted the need for development of new tools to study vector-virus-host interactions. We have constructed and characterized, in cell culture, Aedes aegypti and Ae. albopictus mosquitoes, infectious cDNA clones of CHIKV using a recent isolate from La Réunion Island. Comparison of the growth kinetics and infection rates of the viral isolate CHIKV strain LR2006 OPY1 (CHIKV-LR) and a full-length infectious clone (CHIKV-LR ic) indicate that the infectious clone has retained the viral phenotypes of the original isolate. Infectious clones that express green fluorescent protein (GFP) were also produced and characterized in cell culture and in Aedes mosquitoes. The CHIKV-LR 5'GFP infected Ae. aegypti and Ae. albopictus mosquitoes at a similar rate to the original virus and to the full length infectious clone. The CHIKV-LR 3'GFP only infected Ae. albopictus mosquitoes at similar rates. The development of these authentic infectious clones will enable targeted studies of the molecular determinants of infection, pathogenesis and transmission competence by Ae. aegypti and Ae. albopictus mosquitoes.

SUMMARY Chikungunya virus (CHIKV) is a mosquito-transmitted RNA virus that causes acute febrile infection associated with polyarthralgia in humans. Mechanisms of protective immunity against CHIKV are poorly understood, and no effective therapeutics or vaccines are available. We isolated and characterized human monoclonal antibodies (mAbs) that neutralize CHIKV infectivity. Among the 30 mAbs isolated, 13 had broad and ultrapotent neutralizing activity (IC50 < 10 ng/mL), and all of these mapped to domain A of the E2 envelope protein. Potent inhibitory mAbs blocked post-attachment steps required for CHIKV membrane fusion, and several were protective in a lethal challenge model in immunocompromised mice, even when administered at late time points after infection. These highly protective mAbs could be considered for prevention or treatment of CHIKV infection, and their epitope location in domain A of E2 could be targeted for rational structure-based vaccine development.

Human B cell antigen-receptor (BCR) repertoires reflect repeated exposures to evolving influenza viruses; new exposures update the previously generated B cell memory (Bmem) population. Despite structural similarity of hemagglutinins (HAs) from the two groups of influenza A viruses, cross-reacting antibodies (Abs) are uncommon. We analyzed Bmem compartments in three unrelated, adult donors and found frequent cross-group BCRs, both HA-head directed and non-head directed. Members of a clonal lineage from one donor had a BCR structure similar to that of a previously described Ab, encoded by different gene segments. Comparison showed that both Abs contacted the HA receptor-binding site through long heavy-chain third complementarity determining regions. Affinities of the clonal-lineage BCRs for historical influenza-virus HAs from both group 1 and group 2 viruses suggested that serial responses to seasonal influenza exposures had elicited the lineage and driven affinity maturation. We propose that appropriate immunization regimens might elicit a comparably broad response.

Although oxidative tissue injury often accompanies viral infection, there is little understanding of how it influences virus replication. We show that multiple hepatitis C virus (HCV) genotypes are exquisitely sensitive to oxidative membrane damage, a property distinguishing them from other pathogenic RNA viruses. Lipid peroxidation, regulated in part through sphingosine kinase 2, severely restricts HCV replication in Huh-7 cells and primary human hepatoblasts. Endogenous oxidative membrane damage lowers the 50% effective concentration of direct-acting antivirals, suggesting critical regulation of the conformation of the NS3/4A protease and NS5B polymerase, membrane-bound HCV replicase components. Resistance to lipid peroxidation maps genetically to trans-membrane and membrane-proximal residues within these proteins, and is essential for robust replication in cell culture, as exemplified by the atypical JFH1 strain. Thus, the typical, wild-type HCV replicase is uniquely regulated by lipid peroxidation, providing a novel mechanism for attenuating replication in stressed tissue and possibly facilitating long-term viral persistence.

Between 2005 and 2007 Chikungunya virus (CHIKV) caused its largest outbreak/epidemic in documented history. An unusual feature of this epidemic is the involvement of Ae. albopictus as a principal vector. Previously we have demonstrated that a single mutation E1-A226V significantly changed the ability of the virus to infect and be transmitted by this vector when expressed in the background of well characterized CHIKV strains LR2006 OPY1 and 37997. However, in the current study we demonstrate that introduction of the E1-A226V mutation into the background of an infectious clone derived from the Ag41855 strain (isolated in Uganda in 1982) does not significantly increase infectivity for Ae. albopictus. In order to elucidate the genetic determinants that affect CHIKV sensitivity to the E1-A226V mutation in Ae. albopictus, the genomes of the LR2006 OPY1 and Ag41855 strains were used for construction of chimeric viruses and viruses with a specific combination of point mutations at selected positions. Based upon the midgut infection rates of the derived viruses in Ae. albopictus and Ae. aegypti mosquitoes, a critical role of the mutations at positions E2-60 and E2-211 on vector infection was revealed. The E2-G60D mutation was an important determinant of CHIKV infectivity for both Ae. albopictus and Ae. aegypti, but only moderately modulated the effect of the E1-A226V mutation in Ae. albopictus. However, the effect of the E2-I211T mutation with respect to mosquito infections was much more specific, strongly modifying the effect of the E1-A226V mutation in Ae. albopictus. In contrast, CHIKV infectivity for Ae. aegypti was not influenced by the E2-1211T mutation. The occurrence of the E2-60G and E2-211I residues among CHIKV isolates was analyzed, revealing a high prevalence of E2-211I among strains belonging to the Eastern/Central/South African (ECSA) clade. This suggests that the E2-211I might be important for adaptation of CHIKV to some particular conditions prevalent in areas occupied by ECSA stains. These newly described determinants of CHIKV mosquito infectivity for Ae. albopictus and Ae. aegypti are of particular importance for studies aimed at the investigation of the detailed mechanisms of CHIKV adaptations to its vector species.