Plant-made virus-like particle vaccines bearing the hemagglutinin of either seasonal (H1) or avian (H5) influenza have distinct patterns of interaction with human immune cells in vitro

Introduction The recent emergence of avian influenza strains has fuelled concern about pandemic preparedness since vaccines targeting these viruses are often poorly immunogenic. Weak antibody responses to vaccines have been seen across multiple platforms including plant-made VLPs. To better understand these differences, we compared the in vitro responses of human immune cells exposed to plant-made virus-like particle (VLP) vaccines targeting H1N1 (H1-VLP) and H5N1 (H5-VLP). Methods Peripheral blood mononuclear cells (PBMC) from healthy adults were stimulated ex vivo with 2-5 µg/mL VLPs bearing the hemagglutinin (HA) of either H1N1 (A/California/7/2009) or H5N1 (A/Indonesia/5/05). VLP-immune cell interactions were characterized by confocal microscopy and flow cytometry 30 min after stimulation with dialkylaminostyryl dye-labeled (DiD) VLP. Expression of CD69 and pro-inflammatory cytokines were used to assess innate immune activation 6 h after stimulation. Results H1- and H5-VLPs rapidly associated with all subsets of human PBMC but exhibited unique binding preferences and frequencies. The H1-VLP bound to 88.7 ± 1.6% of the CD19+ B cells compared to only 21.9 ± 1.8% bound by the H5-VLP. At 6 h in culture, CD69 expression on B cells was increased in response to H1-VLP but not H5-VLP (22.79 ± 3.42% vs. 6.15 ± 0.82% respectively: p