SARS-CoV-2 spike-based virus-like particles incorporate influenza H1/N1 antigens and induce dual immunity in mice

A vaccine effective against both SARS-CoV-2 and influenza A (IAV) viruses could represent a cost-effective strategy to reduce their combined public health burden as well as potential complications arising from co-infection. Based on previous findings that full-length SARS-CoV-2 spike (S) expression can induce high-level, enveloped VLP (eVLP) production in CHO cells, we tested whether IAV H1N1 hemagglutinin (H1) and neuraminidase (N1) could also be displayed on these particles. We found that co-incorporation of the IAV surface antigens in spike VLPs (S-VLPs) was highly efficient: upon transient co-expression of S + H1 or S + H1 + N1 in CHO cells, the resulting VLPs contained similar amounts of the SARS-CoV-2 S and IAV antigens. The self-assembled bivalent (S/H1) and trivalent (S/H1/N1) VLPs released into the culture media were purified by single-step chromatography using a S-VLP affinity resin. Western blot analysis and immuno‑gold labeling transmission electron microscopy (TEM) of purified VLPs confirmed the coexistence of S, H1 and N1 antigens in the same particles. Finally, we demonstrated that two doses of adjuvanted bivalent and trivalent VLPs elicit specific functional antibodies and cellular immunity in a mouse model, suggesting potential for combined SARS-CoV-2/IAV vaccine development.