Plant-derived virus-like particle vaccines drive cross-presentation of influenza A hemagglutinin peptides by human monocyte-derived macrophages

A growing body of evidence supports the importance of T cell responses to protect against severe influenza, promote viral clearance and ensure long-term immunity. Plant-derived virus-like particle (VLP) vaccines bearing influenza hemagglutinin (HA) have been shown to elicit strong humoral and CD4+ T cell responses in both pre-clinical and clinical studies. To better understand the immunogenicity of theses vaccines, we tracked the intracellular fate of a model HA (A/California/07/2009 H1N1) in human monocyte-derived macrophages (MDMs) following delivery either as VLPs (H1-VLP) or in soluble form. High-resolution tandem mass spectrometry identified 131 HA-derived peptides associated with MHC I in the H1-VLP-treated MDMs. Together with immunostaining and microscopy results, these data suggest that HA delivery to antigen-presenting cells on plant-derived VLPs facilitates antigen uptake, endosomal processing and cross-presentation. These observations may help explain the broad and cross-reactive immune responses generated by these vaccines.