Assistant Professor University of Maryland Rockville, Maryland, United States
Introduction:: Lymphatic vessels are critical for tissue homeostasis and adaptive immunity, as they are the natural conduit between peripheral tissues and the lymph nodes, where the immune response is shaped. Because particulates are primarily shuttled via lymphatic vessels, lymphatics have received considerable attention as targets for drug delivery in the context of immune modulation. We have investigated how nanoparticle material properties like surface chemistry affect their transport into lymphatic vessels and to the lymph nodes, along with the transport mechanisms used by lymphatic endothelial cells (LECs) underlying nanoparticle transport into lymphatics.
Materials and Methods:: Nanoparticles were functionalized with PEG at different densities and with different charges with sizes between 40-200 nm in size. We used an in vitro model of lymphatic transport as well as in vivo model using intradermal injections to assess nanoparticle transport across lymphatic endothelial cells and to the down-stream draining lymph nodes over time.
Results, Conclusions, and Discussions:: We have found that surface chemistry of nanoparticles affects their transport into lymphatic vessels and to the downstream lymph nodes. We have shown that nanoparticles densely coated with polyethylene glycol (PEG) have highest transported across lymphatic endothelial cells (LECs) and accumulation in the lymph nodes, a close to 2-fold increase compared to nanoparticles coated with a low density of PEG. In vivo, LECs constantly experience transmural, or interstitial flow. We found that exposing LECs to flow levels representative of those experienced by LECs in vivo, increased transport of PEG-coated nanoparticles 5-fold after 6h. We have also found that the density of the PEG coating affects the cellular transport processes involved, specifically macropinocytosis and that inhibition of macropinocytosis markedly reduces transport of 100 nm low density PEGylated and 40 nm densely PEGylated nanoparticles. To quantify contributions of different transport pathways in nanoparticle transport across LECs, we transformed the transport pathways into a system of differential equations that we used to extrapolate kinetic parameters describing the transport of nanoparticles across the LEC barrier. This computational model is one of the first to describe transport kinetics across lymphatic vessels, and offers some of the first quantitative values for coefficients to describe nanoparticles transport across LECs.In summary, our computational, in-vitro, and in-vivo results indicate that nanoparticle surface charge, PEG conformation, and size are key criteria for nanoparticle design for effective lymphatic delivery with a dense, neutrally charged coating of PEG maximizing transport across LEC barriers and transport to lymph nodes. Our results are the first to provide specific surface chemistry design parameters to maximize nanoparticle transport by lymphatics, and thus maximize lymph node targeting. Our work thus lays the foundation for future development of more effective immunotherapies and vaccines.
