Antibodies can now be re-engineered to work inside cells, not just on their surface, using AI-guided redesign of their binding fragments so they remain stable in the intracellular environment and can directly bind disease-driving proteins such as those involved in neurodegenerative disorders.
ACCESS Health International
Antibody-based drugs are among the most powerful treatments available today, used across diseases ranging from cancer to infectious illness. These proteins recognize specific structures on the surface of cells, viruses and bacteria, enabling highly precise targeting of disease. Yet their reach has been limited to the outside of cells. A longstanding goal has been to bring that precision inside the cell. A new study introduces a method enabling cells to produce compact antibody fragments internally, using highly compact antibody fragments known as nanobodies to carry that precision into the intracellular environment, opening the door to therapies for conditions such as Alzheimer’s and Parkinson’s.
Antibodies are built from combinations of protein components that form a structure capable of recognizing specific targets. They are produced inside cells and transported out, where they bind to structures on the surface of pathogens or affected cells. This natural design makes them highly effective at targeting threats in the bloodstream or surrounding tissues, but not within the cell itself. This is like delivering a package to the correct house but leaving it outside the front door. The delivery is accurate, but the contents never reach the room where they are needed. Many disease-driving processes take place inside cells, including the buildup of harmful proteins in neurodegenerative disease. Efforts to shrink antibodies into smaller fragments that could function inside cells have faced a major obstacle: once inside, these fragments often clump together or break down before they can act.
"Heavy chain antibodies occur naturally in the blood serum of camelids (camels, dromedaries, llamas, alpacas, and vicuñas)."
Antibody Design Labs
A solution comes from reengineering antibodies to use only the target-binding portion, creating intrabodies, or fragments that function inside cells. These fragments exclude parts of the antibody structure that make the molecule poorly suited for the intracellular environment. Instead of delivering the antibody directly, cells are given genetic instructions for producing these fragments. Standard fragments often carry an electrical charge that causes them to stick together, but by redesigning them for the environment, more than 600 stable intracellular antibody fragments were created from existing antibodies. These redesigned molecules retain their ability to recognize disease-related targets while operating inside cells, providing a foundation for therapies that can directly engage the proteins driving neurodegenerative disease. In this work, nanobody-like fragments are tuned so that their surface charge favors free movement and proper folding inside the cell, rather than aggregation.
Antibodies are naturally engineered to work outside cells. Inside a cell, the environment is chemically different, which causes antibody fragments to aggregate or degrade before binding their target. A major challenge is electrical charge imbalance, which promotes clumping rather than mobility inside cells.
Adjusting charge distribution allows redesigned fragments to remain functional. Starting from existing antibodies, artificial intelligence was used to modify structures while preserving target recognition. Instead of altering the antibody targets, the redesign focuses on their behavior inside cells. This creates a modular platform that can be applied across many antibodies, allowing the conversion of hundreds of existing antibodies into intracellular versions for new uses.
The strongest immediate impact may be in diseases driven by protein misfolding and toxic protein buildup. In conditions such as Alzheimer’s, Parkinson’s, Huntington’s, and motor neuron disease, abnormal proteins disrupt normal cellular function. These changes often occur within the cell, making them difficult to address with traditional antibody therapies.
Intracellular antibody fragments offer a way to recognize and bind these harmful proteins at the site where damage begins. Because the platform preserves the recognition properties of the original antibodies, it can distinguish between normal and abnormal proteins with high precision. This level of selectivity is especially important in neurodegenerative disease, where targeting the wrong protein form could impact healthy cells.
The approach also aligns with emerging gene-based delivery technologies, in particular RNA-based delivery systems, where cells can be directed to produce the antibody fragment themselves. The RNA enters the cell and directs the cell to make the nanobody, which then becomes active within the cell. This RNA-driven strategy contrasts with DNA-based delivery and focuses on transiently instructing cells to produce functional nanobodies exactly where they are needed. This opens a path toward highly targeted intracellular treatments for diseases that currently have few options.
Artificial intelligence plays a central role in making this possible on a larger scale. After identifying the key design rule around charge, AI-based protein redesign improved stability while preserving target recognition, allowing the rapid conversion of hundreds of antibody sequences into intracellular-ready formats.
This modular approach is particularly valuable in biotechnology, where platforms that apply across multiple disease areas carry strong long-term potential. A system that converts existing antibodies into intracellular tools could have applications far beyond neurodegenerative disease, including cancer biology, inflammatory disorders and rare genetic conditions.
Changing where antibodies can operate expands the range of biological processes that can be targeted. Existing molecules that were previously limited by their inability to enter cells may now be repurposed into intracellular therapeutics and research tools. In a field where time, specificity and scalability are critical, this shift could have profound implications.
The next wave of biologic therapies may no longer stop at the cell surface. With AI-guided intracellular redesign, antibodies are now positioned to reach the molecular events that lie at the heart of some of the world’s most devastating diseases.
This is the first article in a series of nanobodies for medical applications.
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