“Off the shelf” allogeneic stem cell transplants and stem cell nano‐composites are being used for the treatment of degenerative bone diseases. However, major and minor histocompatibility antigens of therapeutic cell transplants can be recognized as foreign and lead to their rejection by the host immune system. If a host immune response is identified within the first week post‐transplant, immune modulating therapies could be applied to prevent graft failure and support engraftment. Ferumoxytol (Feraheme™) is an FDA approved iron oxide nanoparticle preparation for the treatment of anemia in patients. Ferumoxytol can be used “off label” as an magnetic resonance (MR) contrast agent, as these nanoparticles provide measurable signal changes on magnetic resonance imaging (MRI). In this focused review article, we will discuss three methods to localize and identify innate immune responses to stem cell transplants using ferumoxytol‐enhanced MRI, which are based on tracking stem cells, tracking macrophages or detecting mediators of cell death: (a) monitor MRI signal changes of ferumoxytol‐labeled stem cells in the presence or absence of innate immune responses, (b) monitor influx of ferumoxytol‐labeled macrophages into stem cell implants, and (c) monitor apoptosis of stem cell implants with caspase‐3 activatable nanoparticles. These techniques can detect transplant failure at an early stage, when immune‐modulating interventions can potentially preserve the viability of the cell transplants and thereby improve bone and cartilage repair outcomes. Approaches 1 and 2 are immediately translatable to clinical practice. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Cells at the Nanoscale Diagnostic Tools > Biosensing

Introduction: Fragile X syndrome (FXS) is a debilitating neurogenetic disorder that can result in a multitude of impairments in cognition, memory, and learning. Case Presentation: a 25-year-old male with FXS participated in this study. The participant obtained scores in the non-spectrum range on the Autism Diagnostic Observation Scale and obtained an full scale IQ score of 57 (Verbal IQ = 23 and Nonverbal IQ = 34) on the Stanford-Binet Intelligence Scales (SB-5). On the Vineland Adaptive Behavior Scales, 2nd Edition (VABS-2) he obtained a composite score of 66. Pre-scan serum cortisol reactivity was 16.45 mcg/dL. Following a [18F]flumazenil (5mCi) intravenous bolus injection, the participant was scanned without sedation on a hybrid PET-MR system (Signa, GE Healthcare, Waukesha, WI) for 60 mins. List mode PET data, structural and diffusion MRI (DWI), and MR spectroscopy (MRS) were acquired simultaneously. Quantitative PET and DWI measures were extracted from 83 pre-defined regions of interest. MRS data was collected from two 20 cc voxels (thalamus and dorsolateral prefrontal cortex). Conclusion: This is the first study to investigate neuromolecular behavior in FXS without the use of sedation using PET-MR. Mapping the neuromolecular differences in FXS can lead to targeted treatments that can significantly improve quality of life for families and individuals with intellectual disabilities.

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The cover image is based on the Focus Article Magnetic Resonance Imaging of Stem Cell–Macrophage Interactions with Ferumoxytol and Ferumoxytol‐Derived Nanoparticles by Hossein Nejadnik, Jessica Tseng, and Heike Daldrup‐Link. https://doi.org/10.1002/wnan.1552.