Fetuses in ZIKV-infected DENV-immune dams were normal sized, whereas fetal demise occurred in non-immune dams. normal sized, whereas fetal demise occurred in non-immune dams. Moreover, reduced ZIKV Kv3 modulator 4 RNA is present in the placenta and fetuses of ZIKV-infected DENV-immune dams. DENV cross-reactive CD8+ T cells expand in the maternal spleen and decidua of ZIKV-infected dams, their depletion increases ZIKV infection in the placenta and fetus, and results in fetal demise. The inducement of cross-reactive CD8+ T cells via peptide immunization or adoptive transfer results in decreased ZIKV infection in the placenta. Prior DENV immunity can protect against ZIKV infection during pregnancy in mice, and CD8+ T cells are sufficient for this cross-protection. This has implications for understanding the natural history of ZIKV in DENV-endemic areas and the development of optimal ZIKV vaccines. Introduction Zika virus (ZIKV) is a positive-stranded, enveloped, RNA flavivirus in the family that is transmitted by species mosquitoes and sexual contact. ZIKV was first isolated in 1947 from a sentinel rhesus macaque in Uganda, and for decades, sporadic human case reports in Africa and Asia were associated with a self-limiting febrile illness. Outbreaks of ZIKV infection beyond its original range were reported in 2007 in Micronesia and from 2013 to 2014 in French Polynesia, where infection was associated with development of GuillainCBarr syndrome (GBS)1. Recently, there was a major epidemic of ZIKV in the Western Hemisphere, which also was associated with GBS. Additionally, infection of pregnant women was confirmed to cause congenital ZIKV syndrome, which includes microcephaly and other birth defects2,3. A successful pregnancy requires the maternal immune system to recognize and tolerate fetal tissues. Nonetheless, pregnant mammals must still mount robust immune response to pathogens4C6. Some pathogens including ZIKV ostensibly evade the immune system and breach the maternalCfetal interface. The primary barrier between the maternal and fetal compartments during pregnancy is the fetally derived placenta that is adjacent to and intercalated with the maternal decidua. Fetal macrophages (Hofbauer cells), placental fibroblasts, fetal endothelial cells and syncytiotrophoblasts, together with decidual stromal cells, macrophages, and lymphocytes of maternal origin, protect the fetus from pathogens present in maternal blood7C9. Several studies in animal models have demonstrated vertical transmission of ZIKV and its tropism for placental cells, including trophoblasts, endothelial cells, and macrophages10C15. Once ZIKV crosses the placental barrier, it can infect Kv3 modulator 4 neuronal progenitor cells in the fetal brain10,12,16C18. ZIKV and the closely related flavivirus DENV co-circulate in the same geographic ranges and are transmitted by the same mosquitoes. ZIKV and the four serotypes of dengue virus (DENV1C4) share 55.1C56.3% amino acid sequence identity. The adaptive immune response to DENV and its roles in protection versus pathogenesis is complex and remains incompletely understood19. Epidemiological data indicate that following primary infection by one DENV serotype, a second an infection using a different DENV serotype might trigger a far more serious type of dengue disease, revealing potential assignments for antibodies (Abs) and T cells in DENV pathogenesis. Two hypotheses have already been proposed to describe this sensation: Ab-dependent improvement (ADE) and T cell primary antigenic sin (TOAS). Many reports support the ADE model20C24 as the function for T cells continues to be less clear. Certainly, latest data indicate defensive assignments for serotype-specific and cross-reactive T cells against DENV infection in mice31C37 and individuals25C30. The role of T cells in ZIKV immunity continues to be explored in animal choices also. In nonhuman primates, the top of the Compact disc8+ T cell activation correlates with ZIKV RNA decrease, suggesting a defensive function for Compact disc8+ T cells in managing ZIKV replication38. In mice, Compact disc8+ T Kv3 modulator 4 cells broaden, display high cytolytic activity, and mediate viral clearance39. Predicated on amino acidity series and structural commonalities between ZIKV and DENV, many groups show cross-reactivity between DENV and ZIKV in both humoral40C45 and mobile replies46C49. One research in nonhuman primates demonstrated that preceding DENV exposure led to a decrease in the length of time of ZIKV viremia in DENV-immune pets, suggesting cross-protection50, although another combined group reported even more natural ramifications of DENV immunity on ZIKV infection and disease Ifng pathogenesis51. Research in mice show that DENV/ZIKV cross-reactive Abs can boost ZIKV pathogenesis41,42, whereas DENV/ZIKV cross-reactive Compact disc8+ T cells drive back ZIKV an infection46,49,52. Nevertheless, no study provides examined (i) how prior DENV publicity affects maternal and fetal final result of ZIKV an infection in being pregnant and (ii) the contribution of Compact disc8+ T cells to safeguard against or pathogenesis of ZIKV an infection during pregnancy. Appropriately, we investigated the final results of ZIKV infection during pregnancy in non-immune and DENV-immune mice using short-term sequential infection choices. Contact with DENV conferred security against maternal Prior.