Targeting Cardiac Fibrosis with Chimeric Antigen Receptor Neutrophils Derived from Human Pluripotent Stem Cells
This study demonstrates that human pluripotent stem cell-derived neutrophils engineered with chimeric antigen receptors targeting fibroblast activation protein can selectively eliminate activated fibroblasts and improve cardiac function in a murine myocardial infarction model, offering a promising immunotherapeutic strategy for treating cardiac fibrosis.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
When the heart suffers a severe injury, such as a heart attack, it does not simply heal like a cut on the skin. Instead, it attempts to patch the damaged area with a thick, stiff scar made of fibrous tissue. This process, known as cardiac fibrosis, is a natural response to injury, but when it goes on too long or becomes too extensive, it turns the heart muscle into a rigid, unyielding wall. This stiffness prevents the heart from pumping blood effectively, leading to heart failure, a condition that remains a leading cause of death worldwide. For decades, doctors have treated this problem by trying to calm the chemical signals that tell the heart to scar, but these medicines cannot remove the scar tissue that has already formed or stop the specific cells building it. The challenge has been finding a way to target and eliminate these overactive scar-building cells without harming the healthy heart muscle that needs to keep beating.
A team of researchers has explored a new approach to this problem by turning to the body's own immune system, specifically a type of white blood cell called a neutrophil. Neutrophils are the immune system's first responders; they rush to sites of injury to fight infection and clean up debris, but they are short-lived and usually disappear quickly once their job is done. The scientists wanted to see if they could engineer these cells to act as precise, temporary cleaners for the heart. They took human stem cells, which have the potential to become any type of cell in the body, and guided them to become neutrophils. Then, they gave these new cells a special set of instructions, or a targeting device, that allowed them to recognize and attack a specific marker found on the surface of the scar-building cells, known as fibroblasts. This marker is called fibroblast activation protein, or FAP, and it is like a bright red flag that only appears on the cells causing the damage, not on the healthy heart muscle.
To make this work, the researchers first had to solve a practical problem: neutrophils are very difficult to grow and store in a lab because they die quickly. Instead of trying to keep the finished cells alive, the team developed a method to freeze the cells at an earlier stage of development, like a middle step in their growth, and then thaw them later to finish becoming neutrophils. This allowed them to create a reliable supply of these cells. They then genetically modified the stem cells to carry the instructions for the FAP-targeting device. When these cells matured, they carried this device on their surface, ready to seek out the fibroblast activation protein. The researchers tested whether these engineered cells could still perform their normal duties, such as moving toward chemical signals and releasing bursts of oxygen to kill bacteria. They found that the cells worked just as well as normal neutrophils, proving that adding the targeting device did not break their natural abilities.
The next step was to see if these cells could actually find and destroy the scar-building cells without hurting the heart muscle. The team grew tiny, three-dimensional models of heart tissue in the lab, which contained both heart muscle cells and the activated fibroblasts that build scars. When they introduced the engineered neutrophils to these models, the cells swarmed the fibroblasts and reduced their numbers significantly. Crucially, the heart muscle cells in the same models remained healthy and showed no signs of damage. In contrast, when they used normal, unmodified neutrophils, the heart muscle cells did suffer some harm. This suggested that the engineered cells were precise enough to target the bad cells while leaving the good ones alone. The researchers also observed that the engineered cells formed a tight connection with the fibroblasts, similar to a handshake, before delivering their attack, which helped explain how they avoided hitting the wrong targets.
To understand when this treatment would work best in a real heart, the researchers looked at large collections of genetic data from mice that had suffered heart injuries. They wanted to know exactly when the scar-building cells appeared and when they were most active. The data showed that while the immune system rushes to the heart immediately after an injury, the specific cells that build the scar become most active a few days later. Based on this timing, the researchers decided to test their treatment in mice four days after a heart attack, a moment when the scar-building cells were present but the heart was still vulnerable. They injected the engineered neutrophils into the mice and monitored their heart function over the following week.
The results were promising. The mice that received the engineered neutrophils maintained a much stronger ability to pump blood compared to those that received a harmless saltwater solution or unmodified neutrophils. By the end of the first week, the hearts of the treated mice were functioning significantly better. When the researchers examined the hearts two weeks later, they saw that the treated mice had less scar tissue and thicker heart walls than the control group, though the difference in scar size was not statistically definitive in this early trial. The study also confirmed that the human cells successfully traveled from the bloodstream into the injured heart tissue of the mice. While the researchers caution that more work is needed to fully understand the long-term safety and effectiveness, the study provides strong evidence that using engineered, short-lived immune cells to target and remove scar-building cells is a viable strategy. It offers a new path forward for treating heart failure by directly addressing the root cause of the stiffening heart, rather than just managing the symptoms.
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