Vaccination against SARS-CoV-2 using extracellular blebs derived from spike protein-expressing dendritic cells

COVID-19 has caused significant morbidity and mortality worldwide but also accelerated the clinical use of emerging vaccine formulations. To address the current shortcomings in the prevention and treatment of SARS-CoV-2 infection, UC Irvine researchers have developed a novel vaccine platform that closely mimics dendritic cells (DCs) in antigen presentation and T-cell stimulation in a cell-free and tunable manner. Genetically engineered DCs that express the SARS-CoV-2 spike protein (S) were chemically converted into extracellular blebs (EBs). The resulting EBs elicited potentially protective humoral immunity in vivo, indicated by the production of antibodies that potently neutralized S-pseudotyped virus, presenting EBs as a promising and safe vaccine.

Preparation and characterization of EBs derived from SARS-CoV-2
spike protein (S)-expressing DC2.4 cells

A) Lentiviral transduction of DC2.4 cells for S expression, followed by blebbing and vaccination of the syngeneic mice. Briefly, DC2.4 cells were transduced with S-expressing lentivirus prior to puromycin selection. DC2.4 S cells were then treated with blebbing buffer to produce EBs. The micro-sized EBs were isolated by centrifugation and used to vaccinate the animals, followed by assays for antibody binding to S and neutralization of S-pseudotyped virus. B) DC2.4 cells, DC2.4 S cells, DC2.4 EBs, and DC2.4 S EBs were analyzed for S expression by flow cytometry. C) 2.5 × 10⁵ DC2.4 S cells and DC2.4 S EBs at a surface area equivalent to 2.5 × 10⁵ DC2.4 S cells were lysed, and their S contents were quantified by ELISA.