Nature BE: Breaking through the blood-brain barrier, the new AAV variant helps treat brain tumors and central nervous system genetic diseases

I believe that everyone is no stranger to the term blood-brain barrier (BBB), in layman's terms, the blood-brain barrier is the "gate"
of the brain.
As the "secret place" of the human body, the brain controls a number of important functions of the human body, and the blood-brain barrier can keep out harmful substances such as toxins and pathogens that may exist in the blood and protect the safety of
brain tissue.

From this point of view, the blood-brain barrier has important biological significance
for maintaining the basic stability of the environment in brain tissue and maintaining the normal physiological state of the central nervous system.
Unfortunately, the tightly controlled blood-brain barrier has also become a barrier to the treatment of central nervous system (CNS) diseases
.

On October 10, 2022, Fengfeng Bei's team from the Department of Neurosurgery, Brigham and Women's Hospital, Harvard University, USA, published an online publication in the journal Nature Biomedical Engineering entitled : Variants of the adeno-associated virus serotype 9 with enhanced penetration of the blood-brain barrier in rodents and primates Research paper
.

The study reported a novel variant of adeno-associated virus (AAV), AAV.
CPP.
16, which has demonstrated more efficient delivery efficiency than previously developed delivery vehicles in preclinical animal tests, is able to break through the limitations of the blood-brain barrier and can be used to treat brain tumors (such as glioblastoma) and central nervous system genetic diseases
.

Over the past two decades, humans have made a series of milestone breakthroughs
in the field of gene therapy.
Gene therapy has also gradually become one of the hottest emerging therapies, especially adeno-associated virus (AAV) has become the preferred delivery vector for gene therapy and is also recognized as the most promising delivery vector
.

In previous studies, scientists have found that adeno-associated virus (AAV) can cross the blood-brain barrier in some cases, but normally, this delivery of AAV across the blood-brain barrier is inefficient and cannot meet the therapeutic needs
of gene therapy for the brain.
Therefore, Fengfeng Bei's team worked to optimize AAV, improve its potential
to cross the blood-brain barrier and deliver drugs.

In this latest study, to improve on existing AAVs, the team targeted cell-perforating peptides (CPPs), a group of short peptides
known to be able to cross biofilms such as the blood-brain barrier.
The team collected about 100 cell-permeable peptides and inserted them into various AAVs, then tested these recombinant AVVs one by one to find the most effective
.

After a series of tests and continuous optimization, the research team was very lucky to find the answer - AAV.
CPP.
16
。 Compared with the commonly used AAV9, AAV.
The delivery efficiency of CPP.
16 across the blood-brain barrier was significantly improved: about 6-249-fold improvement in brain infection efficiency in different mouse strains, and also about 5-fold improvement
in cynomolgus monkey models.

Immediately afterwards, the research team further tested the effectiveness of AAV.
CPP.
16, and they found that AAV.
CPP.
16 showed higher infection affinity in brain neuronal cells, astrocytes, and spinal cord neurons
.
In terms of safety, although intravenous AAV .
CPP.
16 can still infect peripheral organs, such as liver, muscle, heart and dorsal root ganglia, it does not cause significant sustained hepatotoxicity and dorsal root ganglion degeneration
.

So, what causes AAV.
CPP.
16 to have a high delivery efficiency across the blood-brain barrier? The researchers found that AAV.
CPP.
16 crosses the blood-brain barrier
by significantly increasing the transcytosis of epithelial cells not in a destructive manner.

What's more, Fengfeng Bei's team also explored the potential of
AAV.
CPP.
16 as a gene therapy vector to treat malignant gliomas.
The study using AAV.
CPP.
16 to deliver PD-L1 showed that compared with AAV9, the delivery effect of AAV.
CPP.
16 in the malignant glioma microenvironment was increased by about 17.
5 times, significantly increased CD8+T infiltration and IFNg secretion, and reduced Treg cell infiltration, thereby effectively improving the survival rate of tumor-bearing mice to 75%, and the survival rate of recurrent tumor models in long-term surviving mice reached 100%.

In addition, AAV.
CPP.
16-delivered HSV-TK1 therapy combined with intraperitoneal injection of GCV can significantly kill tumor cells, reduce tumor volume, and improve the survival rate of tumor-bearing mice to about 57%.

Professor Fengfeng Bei, corresponding author of the study, said the study was gratifying because it was one step
closer to successfully translating AAV-delivered drugs across the human blood-brain barrier.
This study also suggests that AAV can be used as an effective systemic drug delivery tool to fight gliomas or other central nervous system diseases
in need.

Fengfeng Bei holds a bachelor's degree from Tsinghua University, a master's degree from King's College London, a Ph.
D.
from University College London, and is currently an assistant professor in the Department of Neurosurgery at Harvard University Brigham and Women's Hospital, where his lab is dedicated to developing AAV gene delivery technology and is currently focusing on breaking through the blood-brain barrier
.
Based on this research, he also founded Brave Bio, a gene therapy startup that is currently in stealth mode and previously completed a seed round
of about $5 million.

In summary, this study obtained a variant of AVV with efficient cross-blood-brain barrier delivery capability by screening cell membrane peptides for combination with different AVVs.
CPP.
16
。 In mice and cynomolgus monkeys, AAV.
CPP.
16 showed high infection affinity between the brain and spinal cord and showed good therapeutic effect
in mouse malignant glioma models.
This research opens new doors
for the treatment of brain tumors such as glioblastoma and genetic diseases that affect the central nervous system.

Original source:

Yao， Y.
， Wang， J.
， Liu， Y.
et al.
Variants of the adeno-associated virus serotype 9 with enhanced penetration of the blood–brain barrier in rodents and primates.
Nat.
Biomed.
Eng (2022).
https：//doi.
org/10.
1038/s41551-022-00938-7.