Lymph node acts as an important physiological site for immune responses and cancer metastasis. With its biological roles, lymph node targeting can be applied for visualization of sentinel lymph nodes, treatment of lymph node metastasis, and activation of immune responses. In here, we focused on retention, distribution and cellular uptake of liposomes in lymphatic system after subcutaneous injection to examine its property in vivo. Among many nano-sized delivery systems, we chose liposome since it is FDA-approved, safe nanoparticle currently used in clinical applications. We engineered surface characteristics of liposomes and the effect was monitored in mouse lymph nodes.
To modulate the surface characteristics of liposomes, we introduced lipids from positively charged (1,2-dioleoyl-3-trimethylammonium-propane, (DOTAP)) to negatively charged (phosphatidylglycerol, (PG) and phosphatidylserine (PS)) into the phosphatidylcholine backbone. Additionally, liposome bilayer fluidity and effect of mannose were examined together. To monitor the liposomes, we labeled liposomes with fluorescent dyes and measured lymph node fluorescence signal until 24hr after injection. Distribution and interactions with immune cells were also seen by immunofluorescence and FACS analysis respectively.
Taken together, positive charge introduced by DOTAP reduced trafficking and retention of liposomes in lymph nodes after 24hr. Also, DOTAP-liposomes showed low level of cellular uptake by macrophages and dendritic cells. Negatively charged liposomes (PG-liposome and PS-liposome) showed high level of drainage, retention and cellular uptake by macrophages and dendritic cells. Interestingly, mannose-liposome showed low level of drainage and retention but relatively high amount of cellular uptake. This study showed comparative results of charges and targeting ligand in lymphatic delivery and showed structural variability can control lymphatic drainage and cellular uptake in vivo. Each surface characteristics can be applied for optimization of functional agents in different applications.