Single-Injection Therapy Shows Promise in Reducing Alzheimer’s Plaques in Mice

The landscape of Alzheimer’s disease treatment is shifting, with scientists exploring innovative ways to not just manage symptoms, but to actively combat the disease’s underlying mechanisms. While recently approved monoclonal antibody therapies offer a promising, albeit limited, slowing of cognitive decline – typically around 10 additional months of independence for patients – they require frequent infusions. Now, research published in the journal Science on March 5th, details a potentially transformative approach: reprogramming brain cells to clear the amyloid plaques characteristic of Alzheimer’s, potentially with a single injection.

Engineering the Brain’s Natural Cleanup Crew

The new strategy, developed by researchers at Washington University School of Medicine in St. Louis, draws inspiration from the success of CAR-T cell therapy in cancer treatment. CAR-T therapy involves genetically modifying a patient’s own immune T cells to recognize and attack cancer cells. Instead of T cells, however, the WashU team focused on astrocytes, the most abundant type of cell in the brain. Astrocytes typically provide support and maintain a healthy environment for neurons, but researchers have now equipped them with a “homing device” – a chimeric antigen receptor, or CAR – that allows them to target and destroy specific substances. In this case, the target is amyloid beta, the protein that accumulates to form the plaques associated with Alzheimer’s disease.

These engineered CAR-astrocytes essentially become powerful cleaning cells, actively seeking out and removing the harmful proteins that contribute to cognitive decline. “This study marks the first successful attempt at engineering astrocytes to specifically target and remove amyloid beta plaques in the brains of mice with Alzheimer’s disease,” explained senior author Marco Colonna, MD, professor of Pathology at WashU Medicine. While further research is needed to optimize the approach and address potential side effects, the results represent a significant step toward developing a new immunotherapy for neurodegenerative diseases, and potentially even brain tumors.

Understanding Amyloid Plaques and the Brain’s Defense System

Alzheimer’s disease is characterized by the buildup of amyloid beta protein in the brain, forming plaques that disrupt normal brain function. These deposits trigger a cascade of damaging changes, ultimately leading to brain shrinkage and cognitive impairment. Normally, the brain has its own cleanup system, relying on immune cells called microglia to remove cellular waste. However, in neurodegenerative diseases like Alzheimer’s, microglia can become overwhelmed and lose their ability to effectively clear harmful material. The Alzheimer’s Association highlights the importance of understanding these processes to develop effective treatments.

The research team, led by first author Yun Chen, PhD, sought to alleviate the burden on microglia by harnessing the power of astrocytes. By introducing a gene that produces a CAR into astrocytes using a harmless virus, they were able to equip these cells with the ability to capture and engulf amyloid beta proteins. This effectively transformed astrocytes into specialized amyloid-clearing cells, concentrating their efforts on removing the harmful plaques in mice predisposed to developing Alzheimer’s.

Promising Results in Alzheimer’s-Prone Mice

The researchers tested their therapy on mice carrying genetic mutations that increase their risk of developing Alzheimer’s disease. These mice typically begin to develop amyloid beta plaques by around six months of age. The study involved two groups: one received the virus carrying the CAR gene before plaques appeared, while the other received the treatment after their brains were already filled with plaques. After three months, the results were evaluated.

In the younger mice, the engineered CAR-astrocytes successfully prevented plaque formation. By six months of age, while untreated mice had brains packed with amyloid plaques, the treated mice showed no detectable plaques. Even more encouragingly, in older mice that already had established plaques, the therapy reduced amyloid plaque levels by approximately 50% compared to mice that received a control virus without the CAR gene. This suggests the therapy can not only prevent plaque formation but also actively reduce existing plaque burden.

A Potential Shift Towards Single-Injection Therapies

Currently approved amyloid-targeting therapies, such as lecanemab (Leqembi®) and donanemab (Kisunla™), require frequent intravenous infusions – every two or four weeks, respectively – to maintain their effectiveness. As detailed in BioDrugs, these infusions can be a significant burden for patients. The CAR-astrocyte therapy, however, offers the potential for a single-injection treatment, which could dramatically improve patient convenience, and adherence. The researchers have filed a patent related to their CAR-astrocyte engineering method, signaling their intent to further develop and potentially commercialize this technology.

“Consistent with the antibody drug treatments, this new CAR-astrocyte immunotherapy is more effective when given in the earlier stages of the disease,” noted co-author David M. Holtzman, MD. “But where it differs, and where it could make a difference in clinical care, is in the single injection that successfully reduced the amount of harmful brain proteins in mice.”

Beyond Alzheimer’s: Potential Applications for Brain Tumors

The research team is now focused on refining the CAR-astrocyte therapy, aiming to improve the precision of targeting harmful proteins while minimizing disruption to normal brain cell activity. They also envision potential applications beyond Alzheimer’s disease. By modifying the CAR homing device to recognize markers found on brain tumors, astrocytes could potentially be redirected to directly destroy tumor cells. This innovative strategy could pave the way for new treatments for a range of brain disorders affecting the central nervous system.

The next steps involve rigorous preclinical testing to assess the safety and efficacy of the therapy in larger animal models. Researchers will also demand to address potential side effects and optimize the delivery method to ensure the CAR-astrocytes reach the targeted areas of the brain. Successful translation to human clinical trials will be crucial to determine whether this promising approach can offer a new hope for individuals affected by Alzheimer’s disease and other devastating neurological conditions. Understanding the biomarkers associated with Alzheimer’s, as discussed in JAMA, will be critical for identifying patients who may benefit most from this therapy.