Accumulating evidence indicates that microglia play a pivotal role in Alzheimer’s disease (AD). Normally, microglia monitor their environment and respond to pathogens or injuries by shifting into different activation states—ramping up to fight threats or switching into clean or repair modes. The ability to dynamically move between states and return to the baseline (homeostatic) state is crucial for a healthy brain. In AD, however, microglia may become stuck in pro-inflammatory states or fail to properly clear amyloid. Scientists are studying how microglia switch between states and whether restoring their normal function could slow disease progression.
As microglia mature, they begin producing immune checkpoint molecules such as Tim-3 and Lag-3. These checkpoint proteins act as brakes on the inflammatory response and help shut down inflammation once the threat is cleared, allowing microglia to return to their baseline state. Dr. Kuchroo and his colleagues first discovered Tim-3 in peripheral T cells—immune cells outside the brain that fight infections throughout the body—about 20 years ago. Later research revealed that microglia in the brain also produce Tim-3, suggesting that similar immune regulatory mechanisms operate both inside and outside the brain.
However, checkpoints can also cause problems. In cancer and chronic viral infections, too much checkpoint activity by Tim-3 and Lag-3 causes T cells to become “exhausted,” leading them to stop responding effectively to threats. This insight led to the development of therapeutic Tim-3 antibodies that block Tim-3 activity, essentially releasing the brake and allowing T cells to function again. One of these therapies is currently in clinical trials and on the FDA fast track for approval for two types of cancer.
The same mechanism may be at play in AD. If microglia checkpoints become overactive, microglia may become exhausted and fail to clear amyloid effectively, allowing the disease to progress. Conversely, if checkpoints fail to activate properly, microglia may remain stuck in damaging inflammatory states. Understanding how to modulate these checkpoint molecules could open new therapeutic avenues for AD.
This ambitious proposal consists of two aims. As part of a previous funding cycle, the Kuchroo lab generated several mouse models with Tim-3 and/or Lag-3 knocked out in all cells or specifically in microglia or T cells. As part of the first aim for this new proposal, they will cross their different knockout lines with amyloid and tau mouse models. Once created, they will measure amyloid or tau pathology, define inflammatory, immunological, and gene expression profiles, test microglial function, and assess cognitive abilities. This extensive study will provide a comprehensive picture of how Tim-3 and Lag-3 influence microglia and AD progression. For the second aim, they will confirm their findings by altering the levels of Tim-3 and Lag-3 using antibodies that will tag the proteins for removal by the immune system rather than a genetic knockout. They will use Tim-3 or Lag-3 antibodies, either individually or together, to slow or prevent disease progression. In addition, Dr. Kuchroo’s lab will develop and optimize different antibody delivery strategies to maximize brain specificity and minimize off-target effects. As part of this, they will test three different administration routes: injection into the bloodstream, the abdominal cavity, or directly into the brain.
This project ambitiously aims to build a comprehensive picture of how Tim-3 and Lag-3 contribute to AD, and then build on that work to develop therapeutic approaches to target them effectively. The work here will lay a firm foundation for future development of these therapies and help determine the most effective ways to deliver them. Collectively, this work will help accelerate subsequent steps toward a clinically viable treatment.
