Summary Zika virus (ZIKV), which emerged in regions endemic to Dengue virus (DENV), is vertically transmitted and results in adverse pregnancy outcomes. Antibodies to DENV can cross-react with ZIKV, but whether these antibodies influence ZIKV vertical transmission remains unclear. Here, we find that DENV antibodies increase ZIKV infection of placental macrophages (Hofbauer cells [HCs]) from 10% to over 80% and enhance infection of human placental explants. ZIKV-anti-DENV antibody complexes increase viral binding and entry into HCs but also result in blunted type I IFN, proinflammatory cytokine and antiviral responses. Additionally, ZIKV infection of HCs and human placental explants are enhanced in an IgG subclass-dependent manner, and targeting FcRn reduces ZIKV replication in human placental explants. Collectively, these findings support a role for pre-existing DENV antibodies in enhancement of ZIKV infection of select placental cell types and indicate that pre-existing immunity to DENV should be considered when addressing in ZIKV vertical transmission.

The importance of fetal placental macrophages (Hofbauer cell [HCs]) is underscored by their appearance 18 d postconception and maintenance through term; however, how human HCs evolve during healthy pregnancy and how microenvironment and ontogeny impact phenotype and function remain unknown. In this study, we comprehensively classify human HCs ex vivo, interrogate phenotypic plasticity, and characterize antiviral immune responses through gestation. Activated HCs were abundant in early pregnancy and decreased by term; molecular signatures emphasize inflammatory phenotypes early in gestation. Frequency of HCs with regulatory phenotypes remained high through term. Furthermore, term HCs exhibited blunted responses to stimulation, indicating reduced plasticity. IFN-l1 is a key placental IFN that appeared less protective than IFN-a, suggesting a potential weakness in antiviral immunity. Ligand-specific responses were temporally regulated: we noted an absence of inflammatory mediators and reduced antiviral gene transcription following RIG-I activation at term despite all HCs producing inflammatory mediators following IFN-g plus LPS stimulation. Collectively, we demonstrate sequential, evolving immunity as part of the natural history of HCs through gestation.

While the majority of influenza-infected individuals show no or mild symptomatology, pregnant women are at higher risk of complications and infection-associated mortality. Although enhanced lung pathology and dysregulated hormones are thought to underlie adverse pregnancy outcomes following influenza infection, how pregnancy confounds long-term maternal anti-influenza immunity remains to be elucidated. Previously, we linked seasonal influenza infection to clinical observations of adverse pregnancy outcomes, enhanced lung and placental histopathology, and reduced control of viral replication in lungs of infected pregnant mothers. Here, we expand on this work and demonstrate that lower infectious doses of the pandemic A/California/07/2009 influenza virus generated adverse gestational outcomes similar to higher doses of seasonal viruses. Mice infected during pregnancy demonstrated lower hemagglutination inhibition and neutralizing antibody titers than non-pregnant animals until 63 days post infection. These differences in humoral immunity suggest that pregnancy impacts antibody maturation mechanisms without alterations to B cell frequency or antibody secretion. This is further supported by transcriptional analysis of plasmablasts, which demonstrate downregulated B cell metabolism and post-translational modification systems only among pregnant animals. In sum, these findings corroborate a link between adverse pregnancy outcomes and severe pathology observed during pandemic influenza infection. Furthermore, our data propose that pregnancy directly confounds humoral responses following influenza infection which resolves post-partem. Additional studies are required to specify the involvement of plasmablast metabolism with early humoral immunity abnormalities to best guide vaccination strategies and improve our understanding of the immunological consequences of pregnancy.

Quantitative variations in CTLA4 expression, due to genetic polymorphisms, are associated with various human autoimmune conditions, including type 1 diabetes (T1D). Extensive studies have demonstrated that CTLA4 is not only essential for the suppressive role of regulatory T (Treg) cells, but also required for intrinsic control of conventional T (Tconv) cells. We report that a modest insufficiency of CTLA4 in mice, which mimics the effect of some human CTLA4 genetic polymorphisms, accompanied by a T1D-permissive MHC locus, was sufficient to induce juvenile-onset diabetes on an otherwise T1D-resistant genetic background. Reduction in CTLA4 levels had an unanticipated effect in promoting Treg cell function both in vivo and in vitro. It led to an increase in Treg memory in both lymphoid and nonlymphoid target tissue. Conversely, modulating CTLA4 by either RNAi or antibody blockade promoted effector memory (TEM) formation in the Tconv compartment. The CD4+ TEM cells, including those within target tissue, produced IL17 or IFNγ. Blocking IL7 signaling reduced the Th17 autoimmune compartment, but did not suppress the T1D induced by CTLA4 insufficiency. Enhanced effector memory formation in both Tconv and Treg lineages may underpin the apparently dichotomized impact of CTLA4 insufficiency on autoimmune pathogenesis. Therefore, while the presence of CTLA4 plays a critical role in controlling homeostasis of T cells, its quantitative variation may impose diverse or even opposing effects on distinct lineages of T cells, an optimal sum of which is necessary for preservation of T-cell immunity while suppressing tissue damage.

In 2019, >90% of new HIV infections in infants globally occurred vertically. Studies suggest intrauterine transmission most often occurs in the third trimester; however, there are no mechanistic studies to support these observations. We therefore obtained early/mid-gestation and term placentae from 20 HIV/Hepatitis B/CMV negative women. Isolated primary placental macrophages (Hofbauer cells [HCs]) were exposed to HIV-1BaL and/or interferon (IFN)-α, IFN-β, IFN-λ1, and RIG-I-like receptor (RLR) agonists. qRT-PCR, FACS, ELISA, Luminex, and Western blot analyses determined expression of activation markers, co-receptors, viral antigen, cytokines, antiviral genes, and host proteins. Early gestation HCs express higher levels of CCR5 and exhibit a more activated phenotype. Despite downregulation of CCR5, term HCs were more susceptible to HIV replication. Early gestation HCs displayed a more activated phenotype than term HCs and HIV exposure lead to the further up-regulation of T-cell co-stimulatory and MHC molecules. Limited HIV replication in early/mid gestation HCs was associated with increased secretion of anti-inflammatory cytokines, chemokines, and a more robust antiviral immune response. In contrast, term HCs were more susceptible to HIV replication, associated with dampening of IFN-induced STAT1 and STAT2 protein activation. Treatment of early/mid gestation and term HCs, with type I IFNs or RLR agonists reduced HIV replication, underscoring the importance of IFN and RLR signaling in inducing an antiviral state. Viral recognition and antiviral immunity in early gestation HCs may prevent in utero HIV infection, whereas diminished antiviral responses at term can facilitate transmission. Defining mechanisms and specific timing of vertical transmission are critical for the development of specific vaccines and antiviral therapeutics to prevent new HIV infections in children globally.

A severe consequence of adult Zika virus (ZIKV) infection is Guillain-Barré Syndrome (GBS), where autoreactive antibodies attack peripheral and central nervous systems (CNS) resulting in neuro-ocular pathology and fatal complications. During virally induced GBS, autoimmune brain demyelination and macular degeneration correlate with low virus neutralization and elevated antibody-mediated infection among Fcγ-R bearing cells. The use of interferon-deficient mice for ZIKV studies limits elucidation of antibody-dependent enhancement (ADE) and long-term pathology (≥120 days), due to high lethality post-infection. Here we used immunocompetent BALB/c mice, which generate robust humoral immune responses, to investigate long-term impacts of ZIKV infection. A high infectious dose (1x10 6 FFU per mouse) of ZIKV was administered intravenously. Control animals received a single dose of anti-IFNAR blocking monoclonal antibody and succumbed to lethal neurological pathology within 13 days. Immunocompetent mice exhibited motor impairment such as arthralgia, as well as ocular inflammation resulting in retinal vascular damage, and corneal edema. This pathology persisted 100 days after infection with evidence of chronic inflammation in immune-privileged tissues, demyelination in the hippocampus and motor cortex regions of the brain, and retinal/corneal hyperplasia. Anti-inflammatory transcriptional responses were tissue-specific, likely contributing to differential pathology in these organs. Pathology in immunocompetent animals coincided with weakly neutralizing antibodies and increased ADE among ZIKV strains (PRVABC59, FLR, and MR766) and all Dengue virus (DENV) serotypes. These antibodies were autoreactive to GBS-associated gangliosides. This study highlights the importance of longevity studies in ZIKV infection and confirms the role of anti-ganglioside antibodies in ZIKV-induced neuro-ocular disease.

Zika virus (ZIKV) causes moderate to severe neuro-ocular sequelae, with symptoms ranging from conjunctivitis to Guillain-Barré Syndrome (GBS). Despite the international threat ZIKV poses, no licensed vaccine exists. As ZIKV and DENV are closely related, antibodies against one virus have demonstrated the ability to enhance the other. To examine if vaccination can confer robust, long-term protection against ZIKV, preventing neuro-ocular pathology and long-term inflammation in immune-privileged compartments, BALB/c mice received two doses of unadjuvanted inactivated whole ZIKV vaccine (ZVIP) intramuscularly (IM) or cutaneously with dissolving microneedle patches (MNP). MNP immunization induced significantly higher B and T cell responses compared to IM vaccination, resulting in increased antibody titers with greater avidity for ZPIV as well as increased numbers of IFN-γ, TNF-α, IL-and IL-4 secreting T cells. When compared to IM vaccination, antibodies generated by cutaneous vaccination demonstrated greater neutralization activity, increased cross-reactivity with Asian and African lineage ZIKV strains (PRVABC59, FLR, and MR766) and Dengue virus (DENV) serotypes, limited ADE, and lower reactivity to GBS-associated gangliosides. MNP vaccination effectively controlled viremia and inflammation, preventing neuro-ocular pathology. Conversely, IM vaccination exacerbated ocular pathology, resulting in uncontrolled, long-term inflammation. Importantly, neuro-ocular pathology correlated with anti-ganglioside antibodies implicated in demyelination and GBS. This study highlights the importance of longevity studies in ZIKV immunization, and the need of exploring alternative vaccination platforms to improve the quality of vaccine-induced immune responses.

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