An increasing amount of evidence suggests that immune responses may affect trophoblast functioning, which in turn may play a role in gestational disorders and fetal development. This systematic review offers the first summary of in vitro studies on the trophoblast response to immunological triggers, in conjunction with a risk of bias analysis. A search in Pubmed and Embase yielded 110 relevant studies. Primary trophoblasts were the most commonly used cell type, but trophoblast subtypes were not always defined. Similarly, the exact natures of trophoblast cell lines were sometimes unclear. Cytokines and Toll-like receptor agonists were often used as interventions, but most studies focused on a select few substances such as tumor necrosis factor-α and lipopolysaccharide. In regard to the outcome parameters, some important trophoblast functions, such as hormone production and barrier formation were underrepresented. Whether or not risk of bias was high varied strongly between types of bias. Risk of selection bias, for example, was usually low. However, none of the included studies mentioned blinding or plate randomization. Only a select few studies mentioned passage numbers, use of vehicle control or conflict of interest. In conclusion, better characterization of trophoblast subtypes and a broader range of studied interventions and outcome parameters would contribute to a more complete understanding of trophoblast responses to immune stimuli. Additionally, researchers are encouraged to replicate experiments and pay close attention when setting up and writing down methodologies, in order to improve the reproducibility and translatability of their work.
Placental dysregulation frequently results in pregnancy complications that impact fetal well-being and potentially predispose the infant to diseases later in life. Thus, efforts to understand the molecular mechanisms underlying placental disorders are crucial to aid the development of effective treatments to restore placental function. Currently, the most common methods used for trophoblast-specific gene modulation in the laboratory are transgenic animals and lentiviral trophectoderm transduction. The generation of transgenic animal lines is costly and requires a considerable amount of time to generate and maintain, while the integration preference of lentiviruses, actively transcribed genes, may result in genotoxicity. Therefore, there is much interest in the development of non-viral in vivo transfection techniques for use in both research and clinical settings. Herein, we describe a non-viral, minimally invasive method for in vivo placental gene modulation through sonoporation, an ultrasound-mediated transfection technique wherein the application of ultrasound on target tissues is used to direct the uptake of DNA vectors. In this method, plasmids are bound to lipid microbubbles, which are then injected into the maternal bloodstream and ultimately delivered to the placenta when subjected to low-frequency ultrasound. Syncytiotrophoblasts are directly exposed to maternal blood and, therefore highly accessible to therapeutic agents in the maternal circulation. This technique can be used to modulate gene expression and, subsequently, the function of the placenta, circumventing the requirement to generate transgenic animals. Sonoporation also offers a safer alternative to existing viral techniques, making it not only an advantageous research tool but also a potentially adaptable technique in clinical settings.