Insect-Specific Chimeric Viruses Potentiated Antiviral Responses and Inhibited Pathogenic Alphavirus Growth in Mosquito Cells

Most alphaviruses are transmitted by mosquito vectors and infect a wide range of vertebrate hosts, with a few exceptions. Eilat virus (EILV) in this genus is characterized by a host range restricted to mosquitoes. Its chimeric viruses have been developed as safe and effective vaccine candidates and diagnostic tools. Here, we investigated the interactions between these insect-specific viruses (ISVs) and mosquito cells, unveiling their potential roles in determining vector competence and arbovirus transmission. By RNA sequencing, we found that these ISVs profoundly modified host cell gene expression profiles. Two EILV-based chimeras, consisting of EILV's nonstructural genes and the structural genes of Chikungunya virus (CHIKV) or Venezuelan equine encephalitis virus (VEEV), namely, EILV/CHIKV (E/C) and EILV/VEEV (E/V), induced more intensive transcriptome regulation than parental EILV and activated different antiviral mechanisms in host cells. We demonstrated that E/C robustly promoted antimicrobial peptide production and E/V strongly upregulated the RNA interference pathway components. This also highlighted the intrinsic divergences between CHIKV and VEEV, representatives of the Old World and New World alphaviruses. In contrast, EILV triggered a limited antiviral response. We further showed that initial chimera infections efficiently inhibited subsequent pathogenic alphavirus replication, especially in the case of E/V infection, which almost prevented VEEV and Sindbis virus (SINV) superinfections. Altogether our study provided valuable information on developing ISVs as biological control agents. 

IMPORTANCE Mosquito-borne alphaviruses can cause emerging and reemerging infectious diseases, posing a considerable threat to human and animal health worldwide. However, no specific antivirals or commercial vaccines are currently available. Therefore, it is vital to develop biological control measures to contain virus transmission. Insect-specific EILV and its chimeras are supposed to induce superinfection exclusion owing to the close phylogenetical relationship with pathogenic alphaviruses. These viruses might also, like bacterial symbionts, modulate mosquito hosts' vector competence for arboviruses. However, little is known about the responses of mosquitoes or mosquito cells to ISV infections. Here, we found that EILV barely elicited antiviral defenses in host cells, while its chimeras, namely, E/C and E/V, potentiated the responses via different mechanisms. Furthermore, we showed that initial chimera infections could largely inhibit subsequent pathogenic alphavirus infections. Taken together, our study proposed insect-specific chimeras as a promising candidate for developing biological control measures against pathogenic alphaviruses. 

© 2022 Tan et al.