No abstract

Massive worldwide serological testing for SARS-CoV-2 is needed to determine the extent of virus exposure in a particular region, the ratio of symptomatic to asymptomatic infected persons, and the duration and extent of immunity after infection. To achieve this, the development and production of reliable and cost-effective SARS-CoV-2 antigens is critical. We report the bacterial production of the peptide S-RBDN318-V510, which contains the receptor-binding domain of the SARS-CoV-2 spike protein (region of 193 amino acid residues from asparagine-318 to valine-510) of the SARS-CoV-2 spike protein. We purified this peptide using a straightforward approach involving bacterial lysis, his-tag-mediated affinity chromatography, and imidazole-assisted refolding. The antigen performances of S-RBDN318-V510 and a commercial full-length spike protein were compared in ELISAs. In direct ELISAs, where the antigen was directly bound to the ELISA surface, both antigens discriminated sera from non-exposed and exposed individuals. However, the discriminating resolution was better in ELISAs that used the full-spike antigen than the S-RBDN318-V510. Attachment of the antigens to the ELISA surface using a layer of anti-histidine antibodies gave equivalent resolution for both S-RBDN318-V510 and the full-length spike protein. Results demonstrate that ELISA-functional SARS-CoV-2 antigens can be produced in bacterial cultures, and that S-RBDN318-V510 may represent a cost-effective alternative to the use of structurally more complex antigens in serological COVID-19 testing.

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Tumor-on-chips have become an effective resource in cancer research. However, their widespread use remains limited due to issues related to their practicality in fabrication and use. To address some of these limitations, we introduce a 3D-printed chip, which is large enough to host ~1 cm3 of tissue and fosters well-mixed conditions in the liquid niche, while still enabling the formation of the concentration profiles that occur in real tissues due to diffusive transport. We compared the mass transport performance in its rhomboidal culture chamber when empty, when filled with GelMA/alginate hydrogel microbeads, or when occupied with a monolithic piece of hydrogel with a central channel, allowing communication between the inlet and outlet. We show that our chip filled with hydrogel microspheres in the culture chamber promotes adequate mixing and enhanced distribution of culture media. In proof-of-concept pharmacological assays, we biofabricated hydrogel microspheres containing embedded Caco2 cells, which developed into microtumors. Microtumors cultured in the device developed throughout the 10-day culture showing >75% of viability. Microtumors subjected to 5-fluorouracil treatment displayed <20% cell survival and lower VEGF-A and E-cadherin expression than untreated controls. Overall, our tumor-on-chip device proved suitable for studying cancer biology and performing drug response assays.