SUMMARY CD8+ T cells protect against and promote the pathogenesis of some flaviviruses, but their role in Zika virus (ZIKV) infection is unknown. We developed mice lacking the type I interferon receptor specifically in a subset of myeloid cells (LysMCre+IFNARfl/fl C57BL/6 (H-2b) mice) as a model for ZIKV infection and used it to evaluate CD8+ T cell responses to ZIKV. 26 and 15 CD8+ T cell-reactive peptides for ZIKV African (MR766) and Asian (FSS13025) lineage strains respectively were identified and validated. CD8+ T cells from infected mice were polyfunctional and mediated cytotoxicity. Adoptive transfer of ZIKV-immune CD8+ T cells reduced viral burdens, whereas their depletion led to higher tissue burdens and CD8−/− mice displayed higher mortality to ZIKV-infection. Collectively, these results demonstrate that CD8+ T cells protect against ZIKV infection. Further, this study provides an immunocompetent mouse model for investigating ZIKV-specific T cell responses.

The transcription factor Twist1 induces Epithelial-Mesenchymal Transition and extracellular matrix degradation to promote tumor metastasis. Although Twist1 also plays a role in embryonic vascular development and tumor angiogenesis, the molecular mechanisms that underlie these processes are not as well understood. Here, we report a novel function for Twist1 in modifying the tumor microenvironment to promote progression. We found that expression of Twist1 in human mammary epithelial cells potently promoted angiogenesis. Surprisingly, Twist1 expression did not increase the secretion of the common pro-angiogenic factors VEGF and bFGF, but rather induced expression of the macrophage chemoattractant CCL2. Attenuation of endogenous Twist1 in vivo blocked macrophage recruitment and angiogenesis, whereas exogenous CCL2 rescued the ability of tumor cells lacking Twist1 to attract macrophages and promote angiogenesis. Macrophage recruitment also was essential for the ability of Twist1-expressing cells to elicit a strong angiogenic response. Together, our findings show how Twist1 recruits stromal macrophages through CCL2 induction to promote angiogenesis and tumor progression. Since Twist1 expression has been associated with poor survival in many human cancers, this finding suggests that anti-CCL2 therapy may offer a rational strategy to treat Twist1-positive metastatic cancers.

Several Zika virus (ZIKV) vaccines designed to elicit protective antibody (Ab) responses are currently under rapid development, but the underlying mechanisms that control the magnitude and quality of the Ab response remain unclear. Here, we investigated the CD4+ T cell response to primary intravenous and intravaginal infection with ZIKV. Using the LysMCre+Ifnar1fl/fl (myeloid type I IFN receptor-deficient) C57BL/6 mouse models, we identified six I-Ab-restricted ZIKV epitopes that stimulated CD4+ T cells with a predominantly cytotoxic Th1 phenotype in mice primed with ZIKV. Intravenous and intravaginal infection with ZIKV effectively induced follicular helper and regulatory CD4+ T cells. Treatment of mice with a CD4+ T cell-depleting Ab reduced the plasma cell, germinal center B cell, and IgG responses to ZIKV without affecting the CD8+ T cell response. CD4+ T cells were required to protect mice from a lethal dose of ZIKV after infection intravaginally, but not intravenously. However, adoptive transfer and peptide immunization experiments showed a role for memory CD4+ T cells in ZIKV clearance in mice challenged intravenously. These results demonstrate that CD4+ T cells are required mainly for the generation of a ZIKV-specific humoral response but not for an efficient CD8+ T cell response. Thus, CD4+ T cells could be important mediators of protection against ZIKV, depending on the infection or vaccination context.

SUMMARY Interferon-regulatory factors (IRFs) are a family of transcription factors (TFs) that translate viral recognition into antiviral responses, including type I interferon (IFN) production. Dengue virus (DENV) and other clinically important flaviviruses are suppressed by type I IFN. While mice lacking the type I IFN receptor (Ifnar1−/−) succumb to DENV infection, we found that mice deficient in three TFs controlling type I IFN production, Irf3−/−xIrf5−/−xIrf7−/− triple knockout (TKO), survive DENV challenge. DENV infection of TKO mice resulted in minimal type I IFN production but a robust type II IFN (IFNγ) response. Using loss-of-function approaches for various molecules, we demonstrate that the IRF-3, -5, -7-independent pathway utilizes predominantly IFNγ, and to a lesser degree type I IFNs. This pathway signals via IRF-1 to stimulate IL-12 production and IFNγ response. These results reveal a key antiviral role for IRF-1 by activating both type I and II IFN responses during DENV infection.