Lipid Based Delivery System Targeting To The Immune Cells

In the past few decades liposomes have a variety of medical applications,including molecular imaging, drug delivery, and targeted therapy. Lipidstructure has great potential for improved modified to improvepharmacokinetic performance. Conventional liposomes are easily uptakeby the reticuloendothelial system, through the EPR effect to achievepassive targeting to liver, lung and other specific organs; long-circulatingliposomes modified with high hydrophilic groups, made them escapingfrom RES, extending blood circulation time, increasing the drug releasetime. But most of the liposomes need targeting motif modification toreduce the toxicity and organs specific enrichment. At present, the studyof lymphatic targeted liposomes is poor, in many diseases, the treatmentfailure is due in part to occult disease residing in the lymph nodes, anddose-limiting toxicities of existing protocols that prevent patients fromreceiving full recommended regimens. Our study focuses on the use ofartificial ligand peptide or APCs degrading peptide, targeting the specificlymphocytes to the effect for corresponding disease treatment or prevention.In the peptide ligands targeting liposomes study, we focused on theCD40/CD40L pathway. Many autoimmune diseases associated with thispathway over activated, such as multiple sclerosis (MS). We designedpeptide ligands of CD40L, hoping to block the CD40/CD40L pathwayand eliminate the CD40L+T cells for therapy. Stealth liposomes ascytotoxic drugs carriers have been studied well, and peptide modified onliposomes surface is commonly used. We combined the specific ligand toCD40L on liposomes containing cytotoxic drugs, then achieving bothsignal blockage and T cells depleting effect.We used computer-aided screening to determine the protein interactionpockects, and with Antodock software to grading the potential candidatepeptides. Then surface plasmon resonance technology was used to screenthe ligands at the molecular level. After got the candidate peptides, westudied their binding abilities to target CD40L+cells, and finalized atargeting peptide. In vitro experiment showed that peptide-modifiedmethotrexate liposomes could target CD40L+T cells to kill them morethan conventional liposomes. And in vivo study with EAE model(CD40/CD40L pathway over activated) showed targeting liposomes alsohad better therapeutic effect. In another T cell epitopes liposomes study, the natural degrading processof exogenous antigen by antigen presenting cell was used. Epitopes wereproduced naturally presenting on the peptide antigen-presenting cellsurface. Now, T cells epitopes could only be harvested by artificial elutedor by computer aid design and then chemically synthesize. But all thesemethods are time-consuming and costly. Our research is considering the Tcell epitopes as a black box, assembling the membrane fragmentscontaining epitopes/MHC-II complexes into liposomes. Then we study ifthis complex system could have partially APC functions to activate Tcells. As liposomes are good membrane proteins carrier, it could maintainthe biological activity of epitopes/MHC-II complexes. Meanwhile,liposomes is a pseudo cell system, this could keep the antigen-presentingfunctions of membrane patches well.In this study, OVA was used as a model antigen, dendritic cells (DC) wereused as a model antigen-presenting cells. Via the in vitro processing, OVAepitopes were presented on DC surface to form epitopes/MHC-IIcomplexes. Subsequently we extracted epitopes/MHC-II complexes,reconsititued them on the surface of liposomes, so called immuneliposomes targeting CD4+T cells. In vitro, the liposomes could promoteMF2.2D9T cells secrete IL-2, and induce primary CD4+T cellproliferation. In vivo, it could cause OVA-specific humoral immunity. The mice immunized with this liposomes, could have anti-OVAexpressing tumor properties, both humoral and cellular immunity isinvolved. In all, we prepared a natural T cell epitopes containingliposomes, which maintained partially immunological activity, targetingCD4+T cells, and might be used as a preventive cancer vaccine.