Project Description

In recent decades, scientists have advanced various drug delivery modalities to overcome the blood-brain barrier (BBB), which excludes most neurotherapeutics from entering the central nervous system (CNS), in order to treat CNS disorders. The emerging brain virotherapy using AAV vectors was reported to be immunogenic and costly in manufacturing. In addition, it is rather perilous that therapeutic viruses have to be administered into cerebrospinal fluid. Hence, this year, our team aims to engineer HEK293T cells to produce engineered exosomes, which are extracellular vesicles naturally capable of traversing BBB, hereby providing a low-risk platform for CNS mRNA therapy . The engineering includes: 1. boosting the production of exosomes; 2. facilitating therapeutic RNA to be packaged into exosomes; 3. increasing targeting specificity to neurons with low leakage during the transport of RNA cargo 4. prolonging the expression of therapeutic RNAs in the neurons

Exosome biogenesis

This year, we decided to engineer human embryonic kidney cells (HEK293T) to produce engineered exosomes. we genetically modified HEK293T to increase the production of exosomes so that the resulting therapeutic exosomes could reach the CNS with an relatively effective dose after undergoing the circulating blood stream and the BBB.

RNA Packaging

Since exosomes have randomicity in substances packaging, we modified exosomes to be capable of packaging our designed therapeutic mRNA in larger amount. To achieve this goal, a RNA-protein interaction strategy was utilized. The L7Ae-C/D box and MS2-3 loop interactions were considered in our project.

Exosome targeting and delivery

Exosome has been known as a messenger responsible for intracellular communication where the exosomes can be endocytosed unspecifically by other tissues or cells. Therefore, from the perspective of therapy, the efficiency of this based-on-exosome mRNA therapy is probably to a large extent lowered. To lower this concern, increasing neuron-targeting specificity by RVG (rabies viral glycoprotein) and 2 gap junctions proteins--connexin 43 and connexin 36 were considered in project design.

RNA stabilization

In the light of the ubiquity of RNase and the delicacy of RNA, which pose the main impediments to mRNA therapy, we designed to utilize the 3' UTR fragment (non-immunogenic)of Venezuelan equine encephalitis virus (VEEV) to make therapeutic mRNA evade classical deadenylation degradation pathway.