Immunoengineered Particles As Artificial Immune Cells:  the Importance of Size and Shape

Biodegradable materials, including polymeric particles, can be engineered to mimic attributes of biological cells. Our lab is especially interested in the design and development of immunoengineered artificial antigen presenting cells (aAPCs). We construct biodegradable poly(lactic-co-glycolic acid) (PLGA) micro- and nanoparticles of various sizes and then alter their geometry through the use of an automated multidimensional film-stretching device. We functionalize the surface of these particles by conjugation of a biomimetic Signal 1 protein, an MHC Db IgG gp100 dimer that gives antigen specificity, and a Signal 2 protein, an anti-CD28 antibody as an activation signal. We have observed that the interaction of a T Cell with the surface of an aAPC can be dependent on the physical properties of the particle including its size and geometry. We find that with the same protein coverage, anisotropic particles as aAPCs are more potent than spherical aAPCs. In particular, oblate ellipsoids (disc shaped), with a large radius of curvature, lead to more effective aAPC activity than prolate ellipsoids (football shaped), which in turn are more effective than spherical particles. Size, another physical property, plays a similar role with microsphere-based aAPCs more effective than nanosphere-based aAPCs. Non-spherical, anisotropic shapes were particularly important for nanoscale aAPCs, and anisotropic shapes increased cytotoxic T Cell proliferation in vitro and in vivo, reduced non-specific cellular uptake in vitro, and led to longer blood circulation half-life in vivo. We find that microparticles synthesized utilizing a flow-focusing microfluidic device can lead to spherical and anisotropic aAPCs with a polydispersity index of 1.05, indicating a nearly uniform population. We also find that this technology can be extended to fabricate anisotropic particles coated with supported lipid bilayers. These hybrid particles can allow for spatially dynamic protein presentation that mimics the lateral diffusion of proteins in biological cell membranes. When evaluated in mouse models of melanoma, anisotropic aAPCs can reduce tumor growth and enhance survival. In addition, when PLGA aAPCs, that activate T cells, are combined with the checkpoint inhibitor anti-programmed death 1, that prevents downregulation of T cells, we find a synergistic effect and improved efficacy at treating melanoma. These biologically-inspired immunoengineered particles can engineer T cells in vivo and could be an enabling technology for cancer immunotherapy.