Zika virus (ZIKV) infection of pregnant women can cause fetal microcephaly and other neurologic defects. We describe the development of a non-human primate model to better understand fetal pathogenesis. To reliably induce fetal infection at defined times, four pregnant rhesus macaques are inoculated intravenously and intraamniotically with ZIKV at gestational day (GD) 41, 50, 64, or 90, corresponding to first and second trimester of gestation. The GD41-inoculated animal, experiencing fetal death 7 days later, has high virus levels in fetal and placental tissues, implicating ZIKV as cause of death. The other three fetuses are carried to near term and euthanized; while none display gross microcephaly, all show ZIKV RNA in many tissues, especially in the brain, which exhibits calcifications and reduced neural precursor cells. Given that this model consistently recapitulates neurologic defects of human congenital Zika syndrome, it is highly relevant to unravel determinants of fetal neuropathogenesis and to explore interventions.

The capsular swelling or quellung reaction was reported almost 100 years ago and described the effect of Abs on the appearance of microbial capsules. Despite widespread use to assess Ab binding to capsules, relatively little is known as to the mechanism of this effect or its biological consequences. The fungus Cryptococcus neoformans is an attractive system to study capsule reactions because it has a large polysaccharide capsule that is readily visible by light microscopy. When viewed by differential interference contrast microscopy, binding of mAb to C. neoformans cells produced two distinct capsular reactions that depended on the Ab epitope specificity and the yeast serotype. In the first pattern, termed “rim,” the capsule appears transparent with a highly refractive outer edge. In the second pattern, termed “puffy,” the capsule appears opaque and lacks a highly refractive outer rim. mAbs that bind with a rim pattern suppress the overall rate of C3 deposition on the yeast via the classical and alternative complement pathways. In contrast, mAbs that bind with a puffy pattern do not affect C3 deposition. Protective and nonprotective IgM mAbs produce rim and puffy patterns, respectively. These results indicate that: 1) capsule reactions are a consequence of Ab-induced changes in capsular refractive index; 2) the type of capsule reaction depends on the Ab specificity; and 3) Ab-induced changes in refractive index correlate with biological activities important for host defense against C. neoformans. Our results provide the first evidence associating distinct capsule reaction patterns with Ab biological activity.

SummaryDespite substantial investments since the events of 2001, much work remains to prepare the nation for a chemical, biological, radiological or nuclear (CBRN) attack or to respond to an emerging infectious disease threat. Following a 2010 review of the US Public Health Emergency Medical Countermeasures Enterprise, FDA launched its Medical Countermeasures initiative (MCMi) to facilitate the development and availability of medical products to counter CBRN and emerging disease threats. As a regulatory agency, FDA has a unique and critical part to play in this national undertaking. Using a three‐pillar approach, FDA is addressing key challenges associated with the regulatory review process for medical countermeasures; gaps in regulatory science for MCM development and evaluation; and issues related to the legal, regulatory and policy framework for an effective public health response. Filling the gaps in the MCM Enterprise is a huge national undertaking, requiring the collaboration of all stakeholders, including federal partners, current and prospective developers of medical countermeasures, relevant research organizations, and state and local responders. Especially critical to success are an appreciation of the long timelines, risks and high costs associated with developing medical countermeasures – and the systems to deliver them – and the requisite support of all stakeholders, including national leadership.