Vertical transmission of African-lineage Zika virus through the fetal membranes in a rhesus macaque (Macaca mulatta) model

Clade IIb Mpox virus (MPXV) vertical transmission and fetal demise in a pregnant rhesus macaque model

Infection with clade I Mpox virus (MPXV) results in adverse pregnancy outcomes, yet the potential for vertical transmission resulting in fetal harm with clade IIb MPXV, the clade that is currently circulating in the Western Hemisphere, remains unknown. We sought to establish a pregnant rhesus macaque model of clade IIb MPXV infection with early gestation inoculation to understand if infection results in vertical transmission and adverse pregnancy outcomes. Three pregnant rhesus macaques were inoculated intradermally with 1.5 x 105 plaque forming units (PFU) of clade IIb MPXV near gestational day (GD) 30 and animals were monitored for viremia and maternal and fetal well-being. Animals were euthanized to collect tissues at 5, 14, or 25 days post-inoculation (dpi). Tissues were evaluated for viral DNA (vDNA) loads, infectious virus titers, histopathology, MPXV mRNA and protein localization, as well as MPXV protein co-localization with placental cells including, Hofbauer cells, mesenchymal stromal cells, endothelial cells, and trophoblasts. vDNA was detected in maternal blood and skin lesions by 5 dpi. Lack of fetal heartbeat was observed at 14 or 25 dpi for two dams indicating fetal demise; the third dam developed significant vaginal bleeding at 5 dpi and was deemed an impending miscarriage. vDNA was detected in placental and fetal tissue in both fetal demise cases. MPXV localized to placental villi by ISH and IHC. Clade IIb MPXV infection in pregnant rhesus macaques results in vertical transmission to the fetus and adverse pregnancy outcomes, like clade I MPXV. This suggests that clade IIb MPXV infection in human pregnancy poses a danger to maternal and fetal health as well. Further studies are needed to determine whether antiviral therapy with tecovirimat will prevent vertical transmission and improve pregnancy outcomes.

Role of non-human primate models in accelerating research and developing countermeasures against Zika virus infection

Zika virus, a mosquito-transmitted orthoflavivirus, has become a pathogen of global health concern ever since the virus caused an epidemic in Brazil in 2015 associated with approximately 700 000 laboratory-confirmed cases of congenital microcephaly. The subsequent spread of the epidemic in 2016 resulted in a wide spectrum of congenital neurological, ophthalmological, and developmental abnormalities across the Americas, Africa, and Asia. In this context, non-human primate models have become essential tools for Zika virus research to understand the pathogenesis of congenital brain injury and perinatal complications and for developing and testing medical countermeasures such as vaccines, diagnostics, and therapeutics. Fetal brain injury has been observed across various non-human primate species and is influenced by factors such as the Zika virus strain, gestational age at inoculation, and inoculation dose and route. Miscarriages are also seen as common outcomes of first trimester Zika virus infections. This Series paper reviews the diverse non-human primate models currently used for Zika virus research to mitigate the public health effects of future Zika virus epidemics.

Zika virus-induced fetal demise is driven by strain- and dose-specific RLR-driven activation of the interferon response in the decidua, placenta, and fetus in Ifnar1 -/- mice

Congenital Zika syndrome (CZS), the set of fetal and neonatal complications associated with Zika virus (ZIKV) infection in pregnancy, was first noted during the outbreak in the Americas in 2015-16. However, there was an unequal distribution of ZIKV cases and severe outcomes in all areas where ZIKV emerged in the Americas, demonstrating that the risk of CZS varied over space and time. Recently, we demonstrated that phenotypic heterogeneity existed between closely-related ZIKV strains. All ZIKV strains tested infected the placenta but varied in their capacity to cause overt fetal harm. Here, we further characterized the relative contributions of virus genotype and infecting dose of two phenotypically distinct ZIKV strains across multiple timepoints in gestation in pregnant mice that lack type-I interferon receptor function ( Ifnar1 -/- ). To better understand the underlying causes of adverse fetal outcomes, we used RNA sequencing to compare ZIKV-infected and uninfected tissues. We found that ZIKV infection triggers retinoic acid-inducible gene I (RIG-I)-like receptor-mediated activation of the interferon response at the maternal-fetal interface. However, modest chemical inhibition of RIG-I activation in the decidua and placenta did not protect against fetal demise. Instead, the fetal interferon response was significantly associated with fetal demise. Together, these findings suggest that the response to ZIKV at the maternal-fetal interface can vary depending on the infecting ZIKV genotype and dose, and that the fetal immune response is an important mediator of fetal harm.

IMPORTANCE

Previously, we used a mouse model of ZIKV infection during pregnancy to assess the pathogenic potential to the fetus of a panel of five, low-passage ZIKV strains representing the viral genetic diversity in the Americas. We found that phenotypic heterogeneity existed between these closely-related ZIKV strains. Here, we show that this heterogeneity is driven by retinoic acid-inducible gene I (RIG-I)-like receptor-mediated activation of the interferon response at the maternal-fetal interface. We used chemical inhibition of the RIG-I pathway and measured the transcriptional activity of interferon stimulated genes in fetuses to demonstrate that the fetal immune response may contribute to fetal demise.

Nanoparticle-mediated delivery of placental gene therapy via uterine artery catheterization in a pregnant rhesus macaque

Nanoparticles offer promise as a mechanism to non-invasively deliver targeted placental therapeutics. Our previous studies utilizing intraplacental administration demonstrate efficient nanoparticle uptake into placental trophoblast cells and overexpression of human IGF1 (hIGF1). Nanoparticle-mediated placental overexpression of hIGF1 in small animal models of placental insufficiency and fetal growth restriction improved nutrient transport and restored fetal growth. The objective of this pilot study was to extend these studies to the pregnant nonhuman primate and develop a method for local delivery of nanoparticles to the placenta via maternal blood flow from the uterine artery. Nanoparticles containing hIGF1 plasmid driven by the placenta-specific PLAC1 promoter were delivered to a mid-gestation pregnant rhesus macaque via a catheterization approach that is clinically used for uterine artery embolization. Maternal-fetal interface, fetal and maternal tissues were collected four days post-treatment to evaluate the efficacy of hIGF1 treatment in the placenta. The uterine artery catheterization procedure and nanoparticle treatment was well tolerated by the dam and fetus through the four-day study period following catheterization. Nanoparticles were taken up by the placenta from maternal blood as plasmid-specific hIGF1 expression was detected in multiple regions of the placenta via in situ hybridization and qPCR. The uterine artery catheterization approach enabled successful delivery of nanoparticles to maternal circulation in close proximity to the placenta with no concerns to maternal or fetal health in this short-term feasibility study. In the future, this delivery approach can be used for preclinical evaluation of the long-term safety and efficacy of nanoparticle-mediated placental therapies in a rhesus macaque model.

Fetal Zika virus inoculation in macaques revealed control of the fetal viral load during pregnancy

BACKGROUND

Early pregnancy Zika virus (ZIKV) infection is associated with major brain damage in fetuses, leading to microcephaly in 0.6-5.0% of cases, but the underlying mechanisms remain largely unknown.

METHODS

To understand the kinetics of ZIKV infection during fetal development in a nonhuman primate model, four cynomolgus macaque fetuses were exposed in utero through echo-guided intramuscular inoculation with 103 PFU of ZIKV at 70-80 days of gestation, 2 controls were mock inoculated. Clinical, immuno-virological and ultrasound imaging follow-ups of the mother/fetus pairs were performed until autopsy after cesarean section 1 or 2 months after exposure (n = 3 per group).

RESULTS

ZIKV was transmitted from the fetus to the mother and then replicate in the peripheral blood of the mother from week 1 to 4 postexposure. Infected fetal brains tended to be smaller than those of controls, but not the femur lengths. High level of viral RNA ws found after the first month in brain tissues and placenta. Thereafter, there was partial control of the virus in the fetus, resulting in a decreased number of infected tissue sections and a decreased viral load. Immune cellular and humoral responses were effectively induced.

CONCLUSIONS

ZIKV infection during the second trimester of gestation induces short-term brain injury, and although viral genomes persist in tissues, most of the virus is cleared before delivery.

Mpox virus (MPXV) vertical transmission and fetal demise in a pregnant rhesus macaque model

Infection with clade I Mpox virus (MPXV) results in adverse pregnancy outcomes, yet the potential for vertical transmission resulting in fetal harm with clade IIb MPXV, the clade that is currently circulating in the Western Hemisphere, remains unknown. We established a rhesus macaque model of vertical MPXV transmission with early gestation inoculation. Three pregnant rhesus macaques were inoculated intradermally with 1.5 × 10^5 plaque forming units (PFU) of clade IIb MPXV near gestational day (GD) 30 and animals were monitored for viremia and maternal and fetal well-being. Animals were euthanized to collect tissues at 5, 14, or 25 days post-inoculation (dpi). Tissues were evaluated for viral DNA (vDNA) loads, infectious virus titers, histopathology, MPXV mRNA and protein localization, as well as MPXV protein co-localization with placental cells including, Hofbauer cells, mesenchymal stromal cells, endothelial cells, and trophoblasts. vDNA was detected in maternal blood and skin lesions by 5 dpi. Lack of fetal heartbeat was observed at 14 or 25 dpi for two dams indicating fetal demise; the third dam developed significant vaginal bleeding at 5 dpi and was deemed an impending miscarriage. vDNA was detected in placental and fetal tissue in both fetal demise cases. MPXV localized to placental villi by ISH and IHC. Clade IIb MPXV infection in pregnant rhesus macaques results in vertical transmission to the fetus and adverse pregnancy outcomes, like clade I MPXV. Further studies are needed to determine whether antiviral therapy with tecovirimat will prevent vertical transmission and improve pregnancy outcomes.

One Sentence Summary

Clade IIb Mpox virus infection of pregnant rhesus macaques results in vertical transmission from mother to fetus and adverse pregnancy outcomes.

Decidual leukocytes respond to African lineage Zika virus infection with mild anti-inflammatory changes during acute infection in rhesus macaques

Zika virus (ZIKV) can be vertically transmitted during pregnancy resulting in a range of adverse pregnancy outcomes. The decidua is commonly found to be infected by ZIKV, yet the acute immune response to infection remains understudied in vivo. We hypothesized that in vivo African-lineage ZIKV infection induces a pro-inflammatory response in the decidua. To test this hypothesis, we evaluated the decidua in pregnant rhesus macaques within the first two weeks following infection with an African-lineage ZIKV and compared our findings to gestationally aged-matched controls. Decidual leukocytes were phenotypically evaluated using spectral flow cytometry, and cytokines and chemokines were measured in tissue homogenates from the decidua, placenta, and fetal membranes. The results of this study did not support our hypothesis. Although ZIKV RNA was detected in the decidual tissue samples from all ZIKV infected dams, phenotypic changes in decidual leukocytes and differences in cytokine profiles suggest that the decidua undergoes mild anti-inflammatory changes in response to that infection. Our findings emphasize the immunological state of the gravid uterus as a relatively immune privileged site that prioritizes tolerance of the fetus over mounting a pro-inflammatory response to clear infection.