INTRODUCTION
A new generation of cancer treatment has been rapidly evolving: CAR Cell Therapy. Cell therapy is a type of treatment where cells are given to a patient to help fight disease. In the context of cancer, the goal is to use these cells to directly attack cancer cells more effectively. For cancer treatment, Chimeric Antigen Receptors (CARs) are specially engineered molecules that give immune cells the ability to recognize and attack specific targets on the surface of cancer cells. They essentially activate the immune system to find and kill cells it might otherwise ignore. A CAR is a man-made protein inserted into the membrane (surface) of an immune cell. It functions as a “a sensor and switch”, detecting a cancer cell and ‘turning on’ the immune cell. A CAR is made of different parts (chimeric). A CAR typically has three parts that are joined together:
- An antigen-binding section = the “eyes” (what the CAR sees, and attaches to), located on the outside of the immune cell.
- A linker/transmembrane section = the “neck/bridge” (holds the parts together, stabilizes), that passes through the cell membrane.
- A signaling section = the “engine” (decides what action the cell takes: kill, suppress, eat/phagocytose), which is on the inside of the cell.
Each immune cell type (T, NK, macrophage, iNKT, Treg, γδ T) has its own “personality,” so scientists design the CAR parts differently to make sure the cell responds in the best way.
CAR-T cells are T cells (a type of white blood cell that fights infections) taken from a patient’s blood and genetically modified in a lab to recognize and attack cancer cells. Scientists equip these T cells with special CARs, which act like a GPS that specifically targets proteins on cancer cells. CAR-T cells have changed how we treat certain blood cancers, but they don’t always work in solid tumors and can sometimes cause serious side effects. To overcome toxicity issues with CAR-T cells, researchers are now developing different kinds of CAR cells using different types of immune cells. This review goes beyond T cells expressing CARS into new cutting-edge approaches exploring different types of immune cells using similar technology.
Each type of immune cell used has different characteristics. For example, CAR-NK cells can be made in advance and used in many patients, offering strong cancer-fighting effects with fewer safety risks. CAR-macrophages can “eat” cancer cells and wake up the immune system residing in solid tumors. CAR-invariant NKT cells can attack tumors directly while lowering the risk of immune rejection and helping immune cells get inside tumors. CAR-Treg cells are designed for autoimmune diseases and transplants, where they help down-regulate (calm) the immune system instead of attacking it. Finally, CAR-gamma-delta T cells can recognize a wider range of tumor markers and may work especially well against solid and metastasizing cancers. Altogether, these new CAR cell types show how the field is growing, with each one bringing unique strengths that go beyond the original CAR-T approach.
CAR-NK cells: Ready-made cancer fighters for many patients with fewer safety risks.
CAR-iNKT cells: Kill tumors and help immune cells get inside tumors, lowering the risk of rejection.
CAR-Macrophages: “Eat” cancer cells in solid tumors and alert the immune system.
CAR-Treg cells: Down-regulate the immune system; useful for autoimmune diseases and transplants.
CAR-γδ T cells: Recognize many tumor types and may work well against solid or metastasizing cancers.
CAR-NK cells
Natural Killer (NK) cells are a type of white blood cell that play a crucial role in your immune system. Think of them as the body’s rapid-response security team. NK cells can quickly detect and destroy abnormal cells without prior exposure. CAR-NK cells are genetically engineered to improve their cancer killing effect and have some advantages. For example, unlike other immune cells that need to recognize a specific “ID badge” (like a unique protein on a virus or cancer cell) before attacking, they tend to be safer, with fewer dangerous side effects like severe inflammation. CAR-NK cells can be made in labs as “off-the-shelf” treatments that don’t have to come from each individual patient.
Recently, a wave of important studies has pushed this field forward. Scientists have designed chimeric antigen receptors (CARS) better suited for NK cells, found new ways to produce CAR-NK therapies at scale, tested them against more types of cancers, and uncovered how these cells actually work once they encounter tumors. Instead of competing with CAR-T cells, CAR-NK therapies are now seen as a powerful complementary option, particularly in cases where CAR-T therapies don’t perform well.
When scientists design CAR-NK cells to fight cancer, they give these immune cells a “target,” which is usually a protein found on the surface of cancer cells but not on most healthy cells. By recognizing that target, the CAR-NK cell can latch onto the tumor and destroy it, much like a guided missile homing in on its mark. One well-studied target is CD19, a protein commonly found on leukemias and lymphomas. When CAR-NK cells bind to a cell surface protein called CD19, they release toxic molecules that directly poke holes and deliver toxins to the leukemia cells while sparing most normal tissues. Another promising target is CD70, which shows up on both blood cancers like certain leukemias and lymphomas, as well as some solid tumors such as kidney cancer. In this case, CAR-NK cells use their built-in ability to trigger cell death and activate the broader immune system, leading to a more powerful and lasting attack against the tumor. By choosing the right target, researchers can make CAR-NK cells highly selective and effective cancer killers.
CAR-NK therapy has gone from being mostly experimental to showing real success in both research and early clinical use. Scientists have redesigned these immune cells to better fit the natural biology of NK cells, making them stronger. New ways of producing them make it possible to create ready-to-use treatments that could be shipped worldwide. CAR-NKs are now being tested not only for blood cancers, but also for solid tumors and even inflammation related diseases. Research shows they work by combining the precision of engineered ability to find cancer cells, with the natural strength of NK cells, giving them a unique advantage compared to other cell therapies.
Looking ahead, there are still hurdles, such as helping CAR-NKs survive longer in the body, making sure they can reach solid tumors effectively, and preventing cancer from finding ways to hide. Even so, their safety and flexibility make them strong competitors, and useful partners to other therapies. As larger clinical trials continue, CAR-NKs could help shape the next generation of immune- cell based treatments, expanding their use not just in cancer but also in other immune-related conditions.
CAR iNKT Cells
Invariant Natural Killer T (iNKT) cells are a rare type of immune cell that can recognize certain fat-like molecules on other cells. They are unique because they act like both first-line defenders (innate immunity) and specialized soldiers (adaptive immunity), responding quickly, killing harmful cells, and helping guide other immune cells. iNKT cells are a special type of T cell that all use the same sensor to detect fat-like molecules on other cells, while NK cells don’t use that sensor but instead act like security guards, attacking cells that look stressed or lack their normal ID badge. Unlike regular T cells, iNKTs are less likely to attack a patient’s healthy cells, making them attractive for “off-the-shelf” cancer therapies.
With the development of CAR technology, scientists can now boost iNKT cells’ ability to fight cancer. By genetic engineering, iNKTs can better find and destroy tumor cells while keeping their natural advantages, such as moving toward tumors, controlling immune responses, and reducing the risk of serious side effects seen in other cell therapies. Recently, research has made CAR-iNKT cells more effective by improving how they are made, identifying new cancer targets, and understanding how they work at the molecular level.
In cancer therapy, CAR-iNKT cells are designed to recognize and attack cancer cells by homing in on specific “targets”, molecules that appear on the surface of tumor cells but are rare or absent on healthy cells. These targets act like a flag, letting the CAR-iNKT cells know which cells to destroy. One example is GD2, a molecule commonly found on neuroblastoma cells, a type of childhood cancer. When CAR-iNKT cells bind to GD2, they release toxic molecules that directly kill the tumor cell and signal other immune cells to join the attack. Another target is HER2, which is often found on breast and ovarian cancer cells. By recognizing HER2, CAR-iNKT cells can attach to the tumor, destroy it, and stimulate a broader immune response to help eliminate the cancer more effectively. Essentially, these molecular targets guide CAR-iNKT cells to the cancer and give them instructions to destroy it safely and efficiently.
CAR-iNKT cells main weapon is killing cancer cells directly, using proteins called perforin (pokes holes in the membrane) and granzyme (a toxin). They also send out strong chemical signals, called cytokines, which help rally other immune cells. Some enhanced versions can even keep this response going longer with extra cytokine signals.
These cells move into tumors differently depending on the type of cancer. Blood cancers are easier for them to control, but solid tumors are tougher because the dense tissue and suppressive microenvironment block them. Studies have shown that CAR-iNKT cells sometimes struggle to move efficiently inside solid tumors, so scientists are working on ways to improve their mobility. Researchers are also focusing on helping these cells live longer and “remember” cancer, using tools like cytokines or tweaking survival pathways. Importantly, clinical tests so far show that CAR-iNKT cells cause fewer serious side effects than traditional CAR-T cells, making them safer for patients.
Combining CAR technology with iNKT cells has created a promising new approach to cancer therapy. Researchers have learned the best ways to design these cells, grow them at scale, and target the right cancer markers. Early patient trials show that CAR-iNKTs might avoid some of the safety problems of other therapies and could even be used from donor cells without major risks. However, challenges remain. Getting these cells into solid tumors and keeping them active is still difficult, and picking the right targets is critical to make sure they kill cancer without harming healthy tissue. Scientists are exploring ways to add extra helpful signals, block inhibitory checkpoints, and use synthetic biology to fully unlock CAR-iNKT potential. Overall, these cells are on the verge of broader clinical use. Their unique combination of natural immune power, safety, and adaptability makes them a promising new tool in the fight against cancer, both in children and adults.
CAR Macrophages
Macrophages are a type of immune cell that normally help keep our tissues healthy, fight infections, and watch for anything harmful. Unlike T cells, which need to recognize very specific targets before multiplying, macrophages are much more flexible and can easily move into different parts of the body, including tumors. Recently, scientists have started using CAR technology to reprogram macrophages so they can fight cancer. These CAR-macrophages are designed to better recognize and eat cancer cells, activate other immune responses, and change the tumor environment to make it less friendly for cancer growth.
Like all CAR-immune cells, CAR-macrophages are specially engineered to recognize and attack cancer. They do this by focusing on “targets,” which are unique markers found on the surface of cancer cells. These targets act like flags that tell the immune system which cells to attack. For example, one important target is HER2, a protein often found in high amounts on breast and gastric cancer cells. When CAR-macrophages latch onto HER2, they not only phagocytose (eat) and destroy the cancer cell but also send out signals that recruit other immune cells to join the fight. Another target is mesothelin, which is commonly present on ovarian, pancreatic, and mesothelioma tumor cells but not on most healthy tissues. By binding to mesothelin, CAR-macrophages can directly digest cancer cells and activate an immune response in the tumor environment, making the cancer easier to eliminate. Through these mechanisms, CAR-macrophages act both as killers and as recruiters, helping the body’s defenses better recognize and destroy cancer.
When CAR-macrophages find a cancer cell, they spring into action. They rearrange their structure to “swallow” the tumor cell and trigger signals that cause inflammation. This leads to the release of molecules called cytokines, which act like alarms that call in other immune cells, including T cells, to join the fight. CAR-macrophages also act like “teachers” for the immune system. After eating tumor cells, they show pieces of the cancer to T cells on the cell surface, helping the body recognize and attack the tumor more effectively. Some studies even show that CAR-macrophages can turn a tumor environment into one that is more active and hostile to cancer.
CAR-macrophages offer an exciting new approach to cancer treatment. Unlike CAR-T cells, which often struggle to work inside solid tumors, CAR-macrophages naturally move into these tumors and help reshape the environment to boost immune responses. With improvements in their design, targeting, and understanding of how they work, CAR-macrophages are emerging as a strong candidate for next-generation cancer therapies. As research moves from the lab to clinical trials, CAR-macrophage therapy could tackle some of the main challenges that limit the effectiveness of drugs to treat cancer.
CAR Regulatory T Cells (CAR-Treg)
Chimeric antigen receptor regulatory T cells, or CAR-Tregs, are a new type of engineered cell therapy designed to down-regulate the immune system in conditions like organ transplants, autoimmune diseases, and chronic inflammation. Unlike regular CAR-T cells, which are made to kill harmful cells, CAR-Tregs use the natural “brakes” of regulatory T cells to specifically control immune responses in targeted areas. Recently, several important studies have explored how to best modify these cells, how to produce them efficiently, which diseases they should go after, and exactly how they work inside the body.
Regulatory T cells, or Tregs, are a special type of immune cell that keep the immune system in balance. They stop it from overreacting and help the body tolerate its own tissues or transplanted organs. They do this by secreting inhibitory signals which tell nearby immune cells to quiet down. They also directly bind and shut off overactive cells. Scientists have long recognized their therapeutic potential but using them effectively has been tricky because it’s hard to control where they go, how strong they are, and how long they last. CAR technology, which has already been used to make cancer-killing T cells, now gives us a way to redirect Tregs to specific targets.
While other CAR cells are programmed to destroy dangerous cells, CAR-Tregs are programmed to go to specific areas, like inflamed tissues or a rejected organ, and apply their calming effect. This new approach has sparked a lot of research into how to optimize CAR-Tregs for therapy. Recent high-profile studies have made major progress in understanding how to design these cells, produce them efficiently, pick the right targets, and understand how they behave when they reach their destination.
The “targets” for CAR-Tregs are specific molecules or proteins found on the cells or tissues that are being attacked by the immune system. By recognizing these targets, CAR-Tregs can home in on the problem area and release signals that suppress immune overactivity, preventing tissue damage. For example, one target is HLA-A2, a molecule found on the surface of donor cells in organ transplants; CAR-Tregs directed against HLA-A2 can prevent the recipient’s immune system from attacking the transplanted organ. Another example is insulin-producing beta cells in the pancreas, targeted via molecules like GAD65 in type 1 diabetes; CAR-Tregs recognizing these molecules can reduce the immune attack on the pancreas and help preserve insulin production. In both cases, the cells act like peacekeepers, shutting down harmful immune reactions while leaving the rest of the immune system intact.
Even with big scientific advances, using CAR-Tregs in patients still has hurdles. These cells can sometimes lose their “identity” when exposed to inflammation, partly turning into more aggressive immune cells. Scientists are working on ways to make them safer, like adding “kill switches” that can remove the cells if needed. Choosing the right targets for CAR-Tregs is tricky too, they need to be specific enough to work where needed without harming the rest of the immune system. Plus, differences in people’s natural Treg cells may make the therapy work better for some than others, so reliable tests are needed to measure their effectiveness.
Future approaches might involve more complex engineering, combining CARs with extra receptors or metabolic tweaks to make the cells stay suppressive. CAR-Tregs could also work together with other treatments that promote tolerance, like special immune cells or gut microbiome therapies. Ultimately, large clinical trials will show how well they work for organ transplants, autoimmune diseases, and chronic inflammation. If successful, CAR-Tregs could change the way we treat immune-related conditions, moving from broad immunosuppressive drugs to precise, lasting immune control.
CAR-γδ T Cells
γδ (Gamma-Delta) T cells are a rare type of immune cell with unique features. Unlike conventional T cells, they can detect stressed or abnormal cells without relying on the usual recognition system, which lets them respond quickly to tumors or infections. They also naturally fight tumors, travel to affected tissues, and are less likely to cause immune complications, making them suitable for ready-to-use CAR therapies. Recent studies have explored many ways to improve CAR γδ T cells: refining their design, developing ways to produce them at scale, broadening the range of targets they can recognize, and understanding how they kill cancer cells. The evidence so far suggests that CAR γδ T cells could offer advantages over conventional CAR-T cells and even other immune therapies like NK cells. CAR-T cells precisely kill only the cells their CAR recognizes, while CAR- γδ T cells can attack both CAR-targeted cells and stressed or abnormal cells using their natural sensors, giving them a broader, faster response.
CAR γδ T cells are designed to recognize and attack disease in a very precise way. The “targets” they look for specific proteins or markers found on the surface of harmful cells, like cancer cells, which tell the CAR γδ T cells where to act. CAR γδ T cells still keep their natural ability to sense general signs of stress or danger in tumor cells. This means they can attack cancer both through the CAR “flag recognition” and through their built-in stress detection, making them more flexible killers. These cells can be used to treat diseases such as blood cancers, like leukemia, and solid tumors, including certain types of breast or lung cancer. For example, one target is BCMA, a protein found on malignant plasma cells in multiple myeloma; CAR γδ T cells recognize BCMA and directly kill the cancerous cells. Another target is HER2, which is often present on breast and gastric cancer cells; by binding to HER2, CAR γδ T cells trigger the cancer cells to self-destruct while also calling in other parts of the immune system to help clear the tumor. By focusing on these specific markers, CAR γδ T cells can attack disease without harming healthy cells as much, offering a more precise and potentially safer treatment.
CAR γδ T cells combine smart design, scalable production, and the ability to target a wide range of disease markers. Because they have features of both the body’s rapid-response (innate) and long-term (adaptive) immune systems, they may be able to tackle challenges that traditional CAR-T cells struggle with, especially in hard-to-treat solid tumors. However, there are still important hurdles. Making these cells safely and consistently on a large scale requires standardized manufacturing processes. Safety is a big concern, particularly when using donor cells, because uncontrolled cell growth could be dangerous. So far, most studies have been in the lab or early clinical trials, and it’s still unclear how well these results will hold up in patients. The coming years will be crucial to see if these promising findings translate into real, lasting benefits for people. New developments suggest CAR γδ T cells could overcome some of the limits of current CAR therapies and expand the range of diseases that immune cells can treat effectively.
CONCLUSION
In conclusion, there has been remarkable progress across multiple types of CAR-based immune therapies, each harnessing the unique strengths of different immune cells. CAR-NK cells offer rapid, safe, and versatile cancer-killing potential with “off-the-shelf” availability. CAR-macrophages excel in solid tumors by directly consuming cancer cells and reshaping the tumor environment to boost immunity. CAR-iNKT cells combine fast-acting innate responses with adaptive precision, providing targeted attacks with fewer side effects. CAR-Tregs shift the focus from destruction to regulation, controlling harmful immune reactions in autoimmune diseases and transplantation. Finally, CAR γδ T cells merge innate and adaptive features, targeting a wide range of cancers with precision and speed. Together, these emerging therapies highlight a new era in immunotherapy, one that is more personalized, flexible, and capable of addressing diseases that have resisted traditional treatments. While challenges remain, ongoing research and clinical trials suggest that these diverse CAR strategies will expand the reach and effectiveness of immune-based medicine in the coming years.
