Most people have heard of cancer immunotherapy by now. These treatments help a patient’s own immune system recognize and attack cancer. The best-known examples are immune checkpoint inhibitors such as pembrolizumab (Keytruda) and nivolumab (Opdivo). These drugs release certain “brakes” that normally keep the immune system from becoming overactive. Another approach, called CAR-T therapy, is more involved. Doctors remove some of a patient’s T cells, a type of white blood cell, genetically engineer them in a laboratory so they can recognize a specific target on cancer cells, grow large numbers of those modified cells, and return them to the patient. A related form of cell therapy is tumor-infiltrating lymphocyte therapy, commonly called TIL therapy. In TIL therapy, doctors collect immune cells that have already found their way into a tumor, expand them outside the body, and send much larger numbers back in.
These strategies differ in important ways, but they share a common theme: Each tries to make the immune system’s cancer-fighting cells stronger, less inhibited, more numerous, or better able to recognize their targets. The therapy described here starts somewhere else. It focuses not on the cells trying to kill the cancer, but on one of the cell populations the cancer uses to protect itself, essentially turning the tumor’s own immune bodyguards into the therapeutic target.
The tumor’s bodyguards
That idea sits at the center of an investigational treatment called CRG-150, developed by CoRegen. In July 2026, the U.S. Food and Drug Administration (FDA) cleared the company’s Investigational New Drug (IND) application, allowing a first-in-human phase 1/2a trial to proceed. The study is registered as NCT07730125 and plans to enroll up to 67 adults with metastatic triple-negative breast cancer, metastatic hormone receptor-positive/HER2-negative breast cancer, or metastatic prostate cancer. Enrollment is expected to open late in 2026. As of this writing, no patient has yet received the therapy, and there is no evidence that it works in people. The biology behind it, however, raises a broader question about where cancer immunotherapy may be heading.
To understand why CRG-150 is unusual, it helps to understand a group of cells most people outside immunology rarely hear about: regulatory T cells, usually called Tregs. The immune system must walk a difficult line. It has to be aggressive enough to destroy viruses, bacteria, and abnormal cells, yet restrained enough not to attack healthy tissue. Tregs help maintain that balance. They act as a natural brake, suppressing excessive immune responses and helping prevent the immune system from turning against the body’s own tissues, a problem known as autoimmunity. In a healthy person, that function is essential. An immune system with no brakes would be dangerous.
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Cancer has become very good at exploiting those same brakes. Tumors are not just collections of malignant cells. They live inside a complicated neighborhood of blood vessels, connective tissue, signaling molecules, and immune cells that scientists call the tumor microenvironment. Some immune cells there try to attack the tumor. Others end up protecting it. Many cancers are skilled at drawing Tregs into that neighborhood, where their normal immunosuppressive function becomes an advantage for the cancer. A Treg that keeps an immune response from becoming excessive in healthy tissue may perform essentially the same job inside a tumor, except now the cells being protected are cancer cells. A patient may therefore have immune cells capable of damaging a tumor, but those cells are operating inside an environment shaped to suppress them. The bodyguards are doing their job. They are simply guarding the wrong thing.
Changing the bodyguards’ instructions
The obvious solution might seem to be getting rid of Tregs altogether. Biology is rarely that cooperative. Tregs exist for a reason, and eliminating their function throughout the body risks removing an important safeguard against autoimmunity and uncontrolled inflammation.
CRG-150 approaches the problem differently. Researchers collect immune cells from the patient’s blood through apheresis, a procedure that separates specific cell types from circulating blood, and isolate the patient’s own Tregs. They then use the gene-editing system CRISPR-Cas9 to disrupt a gene called NCOA3, which produces a protein known as steroid receptor coactivator-3, or SRC-3. The manufacturing process is expected to take approximately 28 days from apheresis to delivery of the product back to the patient, after which the edited cells are infused. CRG-150 is the name of that specific product, which consists of a patient’s own SRC-3-edited Tregs. The broader strategy can be described as Treg reprogramming: altering regulatory T cells so that instead of shielding a tumor, they help organize an attack on it.
SRC-3 is what scientists call a transcriptional coactivator. In plain language, it helps regulate broad programs of gene activity inside a cell rather than acting as a single on-or-off switch. Researchers at Baylor College of Medicine, including the late Bert W. O’Malley, MD, spent decades studying steroid receptor coactivators, including SRC-3, before uncovering its role in regulatory T-cell biology. Work published in 2021 showed that when SRC-3 is depleted or pharmacologically inhibited in human Tregs, the cells lose characteristic features of their identity and much of their ability to suppress the proliferation of other T cells. Disrupting SRC-3, in other words, does not simply dial down one signal. It begins to erode the cell’s regulatory identity.
In mouse experiments, removing SRC-3 specifically from Tregs produced a striking change in how those cells behaved. The altered Tregs no longer acted like conventional immunosuppressive Tregs within the tumor. They proliferated extensively, moved into tumors, and released inflammatory signals that helped cancer-fighting T cells and natural killer cells enter the tumor and function there. Investigators also reported that the altered Tregs could interfere with the suppressive activity of the animal’s own unedited Tregs, meaning a relatively small number of modified cells might influence a much larger immune population. Whether that dominant effect occurs in humans is unknown.
The results in mice were dramatic. In a breast cancer model, a single transfer of SRC-3-deficient Tregs eliminated already-established tumors, and animals that cleared the cancer resisted later tumor challenge, suggesting durable antitumor immunity. The same 2023 study also reported tumor eradication in a prostate cancer model. In 2026, researchers extended the work to mouse models of glioblastoma, melanoma, and lung cancer, again finding substantial antitumor effects. Much of that broader work, however, tested the underlying biology in genetically engineered animals rather than in animals treated with a manufactured cell product. These remain animal experiments, not evidence that CRG-150 will work in humans.
Still, the fact that altering the same Treg program produced antitumor effects across several types of solid cancer is one reason Treg reprogramming is intriguing. It suggests a strategy that may not depend on identifying one particular mutation or marker on the cancer cell, but instead on changing the immune environment surrounding it.
A different strategy from existing cell therapies
This is where the strategy begins to look fundamentally different from better-known forms of cell therapy. In CAR-T therapy, a patient’s cells are given a new targeting system so they can recognize a specific molecule on a cancer cell and attack it. That approach has transformed treatment for several blood cancers, but most solid tumors have proved far more difficult. Not every cancer cell necessarily carries the same target, and solid tumors are often surrounded by physical and immune barriers that make it hard for engineered killer cells to reach them and work effectively.
A regulatory T cell presents an almost opposite opportunity. Tumors are already very good at drawing Tregs in. Ordinarily, that is part of the problem. But if the cell’s instructions can be changed before it is returned to the body, a cell type the tumor already accommodates could theoretically become useful. Rather than forcing another killer cell into a hostile environment, researchers may be able to work with a cell population already well adapted to entering and functioning within the tumor microenvironment.
For years, Tregs in cancer have largely been viewed as cells we need to overcome, suppress, or remove. Treg reprogramming starts from a different proposition. The cell itself may not be the problem. Its programming is.
That distinction becomes clearer when compared with checkpoint inhibitors, which interfere with individual molecular signals used to restrain immune responses. Those drugs produce remarkable results for some patients, but many people do not respond, and some tumors remain immunologically “cold,” meaning few active cancer-fighting cells enter them at all. Disrupting SRC-3 aims at something broader: the overall state of the regulatory T cell rather than a single receptor on its surface. In its IND-clearance announcement, CoRegen states that CRG-150 affects multiple immune checkpoint-related targets, including PD-1, PD-L1, CTLA-4, LAG3, and CCR4. That does not mean CRG-150 blocks all five checkpoints the way drugs directed against those individual molecules would. Rather, the claim is that changing an upstream transcriptional regulator alters several parts of the Treg’s immunosuppressive program at once.
A familiar protein in an unfamiliar role
SRC-3 is better known to many breast cancer researchers by another name: AIB1, for “amplified in breast cancer 1.” It was identified in the 1990s as a gene amplified in breast tumors and as a coactivator of the estrogen receptor. It has long been studied for its role in hormone-dependent cancer growth inside malignant cells.
That history can make the target confusing, because the same protein can support cancer through two entirely different cellular compartments. Inside a cancer cell, SRC-3 can enhance estrogen receptor signaling and other growth-promoting pathways. Inside a regulatory T cell, it helps maintain the suppressive program that tumors can exploit to evade immune attack. CRG-150 acts only on the second of these, which is especially worth noting because the trial includes patients with hormone receptor-positive, HER2-negative breast cancer, a setting in which SRC-3/AIB1 has long been studied within the malignant cells themselves. CRG-150 is not an attempt to knock out a cancer-driving gene inside the tumor. It edits the patient’s Tregs. It does not edit the cancer.
That distinction is easy to lose. CoRegen’s own announcement of its FDA clearance describes SRC-3 as a gene enabling cancer cell immune evasion and states that it is overexpressed in most human cancers before explaining that the therapy disrupts the tumor-protective function of regulatory T cells. Placed together, those statements can invite a reader to conclude that CRG-150 attacks SRC-3 in the tumor. It does not. The target is SRC-3, but the therapeutic target cell is the regulatory T cell. For patients and physicians encountering headlines about “targeting SRC-3 in cancer,” that is the distinction that matters most.
Important open questions
The breadth of what SRC-3 does is both the appeal and the concern. Changing an upstream regulator that influences broad programs of gene activity could create a deeper and more durable effect than blocking a single receptor. It could also produce consequences that are harder to predict. The same concern applies to the Treg itself. These cells help keep our immune systems from attacking our own tissues. The goal is not simply to remove immune suppression. It is to remove the right kind of immune suppression, in the right place, while preserving the body’s tolerance of healthy tissue everywhere else.
That may be the most important question CRG-150 has to answer: Can immune tolerance be turned down inside a tumor without turning it down throughout the body?
The animal studies are encouraging on this point because researchers did not observe the widespread autoimmune disease one might fear from wholesale elimination of Treg function. But humans are not laboratory mice, and genome-edited living cells introduce uncertainties that ordinary drugs do not. A medication can be stopped. The genetic edit itself cannot simply be reversed after the cells have been infused. Reflecting that uncertainty, the clinical protocol includes long-term safety follow-up extending as long as fifteen years, consistent with the FDA’s framework for genome-edited therapies.
Manufacturing is its own challenge. Tregs are a relatively scarce population in blood, and isolating, editing, and expanding them while maintaining a viable, consistent cell population is technically difficult. Researchers working on this program published a study in 2025 developing a process to isolate, edit, and expand SRC-3-knockout human Tregs that could be adapted for current good manufacturing practice (cGMP) clinical-scale production. CoRegen has partnered with Lonza to manufacture CRG-150 for the first-in-human study. Producing consistent, well-characterized batches across patients will be an important practical test of the platform.
There is another unusual feature of CRG-150 worth noting. Many existing cell therapies require patients to first receive chemotherapy that temporarily depletes large parts of the immune system, a process called lymphodepletion. The goal is to create space and a more favorable environment for the engineered cells. CRG-150 takes a different route. No lymphodepleting chemotherapy is planned. The edited Tregs are not meant to be the main cancer killers. Their role, based on the preclinical model, is to reshape the tumor environment and recruit the patient’s existing effector immune cells into the fight. At least in theory, depleting a large portion of those lymphocytes beforehand could work against the mechanism the therapy is designed to use.
That is a real potential advantage. It is also a real potential weakness. To enroll, patients must have metastatic disease that has progressed after multiple prior classes of systemic therapy. Their immune responses may already be compromised or substantially altered by advanced disease and prior treatment. A strategy that depends on mobilizing the patient’s remaining immune response will therefore be tested first in exactly the population where that response may be most depleted.
What the first trial will and will not tell us
Expectations should be set accordingly. The first phase is designed primarily to establish safety and identify a dose. The expansion phase plans roughly ten patients per tumor type. Ten patients can reveal a signal worth pursuing. Ten patients cannot establish that a therapy works. Investigators will also track how long the edited cells persist in the body, which may prove as informative as any early response data. If the cells fail to expand or persist without lymphodepletion, that would raise a real question about whether the strategy can work as intended.
Tumors disappearing in mice make compelling headlines. They do not constitute a cancer cure, and many approaches that looked powerful in preclinical studies have failed when confronted with the complexity of human disease. CRG-150 may fail too.
But the significance of an experimental therapy sometimes lies less in whether that particular product succeeds than in the question it forces the field to ask. CAR-T changed our idea of what a medicine could be: a patient’s own living cells, modified and returned as treatment. Checkpoint inhibitors showed that cancer could be attacked not by poisoning the malignant cell directly, but by interfering with the conversations it was having with the immune system. Treg reprogramming raises a further possibility. Cells we have classified as part of the tumor’s defenses may not always need to be eliminated. Perhaps they can be reinstructed.
Cancer is extraordinarily adaptive. It hijacks normal biological processes such as blood vessel formation, metabolism, wound healing, and immune tolerance, then turns them toward its own survival. Regulatory T cells are part of that story. Their purpose is protective. Cancer simply learned to make that protection work in its favor.
Whether that relationship can be reversed in a patient rather than a mouse is now, finally, a question with a trial attached to it.
Laurel A. Coons is a scientist with a background in genomics and biomedical research. She completed her doctoral training in pharmacology and cancer biology at Duke University and conducted research at the National Institute of Environmental Health Sciences. Her work has focused on genomic regulation, endocrine signaling, and translating complex scientific data into insights relevant to medicine and patient care.
She shares professional updates on X at laurelcoons.
