An attenuated Zika virus NS4B protein mutant is a potent inducer of antiviral immune responses.

Live attenuated vaccines (LAVs) are one of the most important strategies to control flavivirus diseases. The flavivirus nonstructural (NS) 4B proteins are a critical component of both the virus replication complex and evasion of host innate immunity. Here we have used site-directed mutagenesis of residues in the highly conserved N-terminal and central hydrophobic regions of Zika virus (ZIKV) NS4B protein to identify candidate attenuating mutations. Three single-site mutants were generated, of which the NS4B-C100S mutant was more attenuated than the other two mutants (NS4B-C100A and NS4B-P36A) in two immunocompromised mouse models of fatal ZIKV disease. The ZIKV NS4B-C100S mutant triggered stronger type 1 interferons and interleukin-6 production, and higher ZIKV-specific CD4+ and CD8+ T-cell responses, but induced similar titers of neutralization antibodies compared with the parent wild-type ZIKV strain and a previously reported candidate ZIKV LAV with a 10-nucleotide deletion in 3'-UTR (ZIKV-3'UTR-Δ10). Vaccination with ZIKV NS4B-C100S protected mice from subsequent WT ZIKV challenge. Furthermore, either passive immunization with ZIKV NS4B-C100S immune sera or active immunization with ZIKV NS4B-C100S followed by the depletion of T cells affords full protection from lethal WT ZIKV challenge. In summary, our results suggest that the ZIKV NS4B-C100S mutant may serve as a candidate ZIKV LAV due to its attenuated phenotype and high immunogenicity.

Memory T Cells in Flavivirus Vaccination.

Flaviviruses include many medically important viruses, such as Dengue virus (DENV), Japanese encephalitis (JEV), tick-borne encephalitis (TBEV), West Nile (WNV), yellow fever (YFV), and Zika viruses (ZIKV). Currently, there are licensed human vaccines for DENV, JEV, TBEV and YFV, but not for WNV or ZIKV. Memory T cells play a central role in adaptive immunity and are important for host protection during flavivirus infection. In this review, we discuss recent findings from animal models and clinical trials and provide new insights into the role of memory T cells in host protective immunity upon vaccination with the licensed flavivirus vaccines.