Patients with coronavirus disease‐2019 may be discharged based on clinical resolution of symptoms, and evidence for viral RNA clearance from the upper respiratory tract. Understanding the severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) viral clearance profile is crucial to establish a re‐testing plan on discharge and ending isolation of patients. We aimed to evaluate the number of days that a patient needed to achieve undetectable levels of SARS‐CoV‐2 in upper respiratory tract specimens (nasopharyngeal swab and/or an oropharyngeal swab). The clearance and persistence of viral RNA was evaluated in two groups of positive patients: those who achieved two negative reverse transcription‐polymerase chain reaction (RT‐PCR) tests and those who kept testing positive. Patients were organized thereafter in two subgroups, mild illness patients discharged home and inpatients who had moderate to severe illness. Results from RT‐PCR tests were then correlated with results from the evaluation of the immune response. The study evidenced that most patients tested positive for more than 2 weeks and that persistence of viral RNA is not necessarily associated with severe disease but may result from a weaker immune response instead.

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Gene delivery targeting mitochondria has the potential to transform the therapeutic landscape of mitochondrial genetic diseases. Taking advantage of the nonuniversal genetic code used by mitochondria, a plasmid DNA construct able to be specifically expressed in these organelles was designed by including a codon, which codes for an amino acid only if read by the mitochondrial ribosomes. In the present work, gemini surfactants were shown to successfully deliver plasmid DNA to mitochondria. Gemini surfactant-based DNA complexes were taken up by cells through a variety of routes, including endocytic pathways, and showed propensity for inducing membrane destabilization under acidic conditions, thus facilitating cytoplasmic release of DNA. Furthermore, the complexes interacted extensively with lipid membrane models mimicking the composition of the mitochondrial membrane, which predicts a favored interaction of the complexes with mitochondria in the intracellular environment. This work unravels new possibilities for gene therapy toward mitochondrial diseases.

Gene knockdown has emerged as an important tool for cancer gene therapy as well as for viral infections and dominantly inherited genetic disorders. The generation of suitable siRNA delivery systems poses some challenges, namely, to avoid nuclease degradation, to surpass the cytoplasmic membrane, and to release the nucleic acids into the cytosol. Aiming at evaluating the ability of thermoresponsive block copolymers formed by units of N-isopropylacrylamide and of (3-acrylamidopropyl)trimethylammonium chloride to efficiently deliver siRNAs, an extensive study was performed with four different copolymers using a human fibrosarcoma cell line as cell model. The silencing ability and cytotoxicity of the generated copolymer-based siRNA delivery systems were found to be dependent on the cloud point of the polymer, which corresponds to the transition temperature at which the aggregation or precipitation of the polymer molecules becomes thermodynamically more favorable than their solubilization. In the present study, a system capable of delivering siRNAs efficiently, specifically and without presenting relevant cytotoxicity, even in the presence of serum, was developed. Confocal fluorescence experiments showed that the ability of the generated systems to silence the target gene is related to some extent to nucleic acid internalization, being also dependent on polymer/siRNA dissociation at 37 °C. Thus, a delicate balance between nucleic acid internalization and intracellular release must be met in order to reach an ideal knockdown efficiency. The special features and potential for manipulation of the N-isopropylacrylamide-based copolymers make them suitable materials for the design and synthesis of new and promising siRNA delivery systems.

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