Additional Authors: Cui J, Glass JJ, Chen L, Thurecht K, Li D, Whittaker MR, Quinn JF, Crampin E, Davis TP, Caruso F, De Rose R, Kent SJ

Aim The interaction of nanoparticles with primary human cells for downstream biomedical applications like drug and vaccine delivery is poorly understood.  The study of nanoparticle interactions with cells has been traditionally restricted to cell lines.   Characterising nanoparticle interactions with primary blood cells in their natural milieu may provide a more accurate assessment of how nanomedicines will behave.
 
Methods We developed multiple assays to assess how nanoparticles associate with primary human blood cells. Freshly-drawn anticoagulated blood was labelled with fluorochrome-conjugated antibodies against major phagocytic blood cells and other WBC subsets and incubated with fluorescently labelled nanoparticles before utilizing multiparametric flow cytometry to examine cell subsets.  The antibody panel used in this assay has been expanded to examine particleinduced immunoactivation of T-cells and dendritic cells.
 
Results This assay: 1. Enabled elucidation of nanoparticle properties (polymer molecular weight, size and charge) that alter association with white blood cells:  a. Particles composed entirely of polyethylene glycol (PEG) showed that smaller particle size but higher molecular weight PEG resulted in lowest cell association with phagocytic blood cells.   b. Charge of hyperbranched polymers (HBPs) dictates their association with different white blood cell subsets.  Cationic HBPs associated with most cell types while anionic HBPs preferentially associated with cells specialized for pathogen clearance and processing.  2. Allowed for the development of more complex T-cell and dendritic cell assays that assess particle-induced immunoactivation.  
 
Conclusion We have developed standardised flow-based assays to examine interactions of primary human blood cells with novel nanoparticles.  These assays are helping inform the design and development of future nanomedicines.