Terry Fry spent the 2016 winter holiday in the hospital – not as a patient but as a doctor.
That winter, he was trying something that had never been done before, using a new drug built from his patient’s own immune cells to treat a boy whose acute lymphoblastic leukemia (ALL) had shrugged off chemotherapy, radiation, bone marrow transplant and even a targeted treatment that was a cousin of Fry’s new drug. Fry, now a recent arrival to University of Colorado Cancer Center, had overseen much of the basic science behind the new drug while leading the Hematologic Malignancies Section in the Pediatric Oncology Branch of the National Cancer Institute, but that winter, he took a break from the lab.
“I intentionally put myself in the clinical service because I wasn’t exactly sure what was going to happen. I wanted to be there in person for my patient,” he says.
The boy was beyond the reach of traditional treatments. This new drug was his last real hope. In the next few pages, we’ll try to understand this new drug that Terry Fry hoped would save his young patient’s life. But to do that, we need to go back a little further than the winter of 2016. Actually, we need to go back much further.
Curing Cancer Starts with HIV Research
Two billion years ago (give or take a few years), viruses learned something that would take schoolyard bullies another 1.999998 billion years to discover: It’s much easier to force someone else to do your homework than it is to do it yourself. Viruses force cells to do their homework. But instead of threatening cells with their viral little fists, viruses are much more devious – they insert their “work” alongside a cell’s own assignments so that when the cell goes through its pile of homework, it accidentally does the virus’s work, too.
A virus’s “homework” is to make more viruses. And certain viruses are specialized to bully certain types of cells into doing it for them. For example, HIV is a “lentivirus,” which is specialized to latch onto and infect immune system T cells (which is why HIV infection undermines the immune system). Basically, the HIV lentivirus grabs a T cell and inserts its own genetic material into the T cell’s DNA, so that when the T cell replicates its DNA, it also replicates the HIV virus.
But it only takes a PhD in genetics and molecular biology to see that lentiviruses like HIV could be used insert other genetic material into T cells – whatever genetic code is inserted, the T cells will manufacture. In other words, and in a twist that perhaps rights the wrongs of so many molecular biologists’ childhoods, these scientists are now bullying lentiviruses, which bully T cells into making whatever the researchers want them to make.
So now the question becomes what should researchers have T cells make?
It would be neat to have T cells grow tiny moustaches. But perhaps even more useful is to use lentiviruses make T cells manufacture new antibodies. If it’s been a while since you took Bio 101, you can think of an antibody like the flashlight that a T cell holds to illuminate a specific antigen. When an antibody recognizes its antigen, T cells attack. And by giving T cells new antibodies, researchers could “point” them at new antigens.
If you don’t want to remember the word “antibody,” just remember they’re the things that catch antigens – call them “antigen receptors.” Actually, because these new antigen receptors are built from a little bit of this and a little bit of that, let’s call them “chimeric antigen receptors.” And because that’s a mouthful of rocks, we can shorten it to CARs. Finally, because we’re talking about CARs built into T cells, let’s just call the whole system a CAR-T.
By using HIV-like lentiviruses to make CAR-Ts, scientists could theoretically program T cells to attack cells marked by pretty much any antigen. You wouldn’t want to set CAR-Ts loose against antigens found on healthy cells because they would eat these healthy cells leading to side effects such as death. But Terry Fry is the anchor of a cutting-edge team that is making Colorado a worldwide leader in the use of CAR-Ts to attack cells marked by antigens associated with cancer.
Unlike UB40, CD19 betters human life. Specifically, the gene aids the early development of B cells, one of our immune system’s flavors of white blood cell. Then, when B cells are mature and have finished their period of rapid growth, CD19 goes silent…at least, it should. When mature B cells restart CD19, the result can be the out-of-control growth of lymphoma or leukemia.
But just as CD19 helps to cause these cancers, it may also help to cure them. That’s because CD19 marks these cancerous cells as different than healthy cells – it is an “antigen” that is present on the surfaces of cancerous but not healthy cells.
In February of 2018, just as Broncos fans were experiencing deep schadenfreude at Tom Brady’s last second Super Bowl failure,
CU Cancer Center investigator Enkhtsetseg Purev, MD, PhD, was infusing a patient with CD19-targeted CAR-T cells as part of a phase I/
II clinical trial against relapsed and refractory B-cell lymphoma.
Purev earned her MD at the Mongolian National Medical University before going on to a PhD at Temple University and a residency and fellowship at the National Heart, Lung, and Blood Institute at the National Institutes of Health, working in part in the laboratory of Terry Fry. Now also in Colorado, Purev will manage CAR-T therapies in adult patients at UCHealth University of Colorado Hospital while Terry Fry oversees CAR-Ts in pediatric patients at Children’s Hospital Colorado. An essential third member of this all-star team is Ryan Crisman, PhD, formerly of Seattle-based biotech Juno Therapeutics, who will oversee the manufacture of CAR-T cell therapies at the nearby Gates Center for Regenerative Medicine Biomanufacturing Facility.
Earlier that winter, Purev drew blood from her lymphoma patient and sent it in a bag across the street to Crisman at the Gates Biomanufacturing Facility. From there, Crisman isolated the T cells and introduced the lentivirus that inserted genetic code that made T cells manufacture CARs directed at CD19. (“Now the T cells are genetically modified to treat cancer,” Crisman says.) The next step was expanding these T cells until there were enough to be therapeutic. Then Crisman and his team used a specially designed “analytics package” to ensure the CAR-Ts were safe. And then, “the CAR-Ts were frozen to deliver back to the clinic,” he says.
The ability to manufacture CAR-Ts literally within walking distance of where blood cells are drawn from patients and the living drug is eventually reinfused may seem like a little thing, but in fact is hugely important. “These patients are really sick. The ability to cut out two days of shipping to get a patient’s cells here and two days to get CAR-Ts back is really helpful. The fact that we walk cells across the street both ways lets us work closely with our doctors and researchers and decreases the downtime for the patient,” Crisman says. The fact that
CU now has the capability to explore the science of CAR-Ts, manufacture them, deliver CAR-T treatments to pediatric and adult patients, and learn from the results of these treatments positions Colorado as a leader in this new paradigm of cell-based medicines.
Twenty-nine days after Purev’s patient received the infusion of CD19-targeted CAR-T cells, he was back for a scan and Purev wrote in an email, “Complete response at day 29 after treatment with CAR-T cells. Aggressive lymphoma is all gone!”
What seems like a miracle cure is becoming the norm. In fact, CD19-targeted CAR-T therapy leads to remission in almost 90 percent of ALL patients and about 60 percent of lymphoma patients. And remember, CAR-T therapies have only been used with the most aggressive forms of leukemia and lymphoma, those that have resisted previous therapies – those that you would think are impossible to control.
“CAR-T therapy has helped so many patients to achieve remission, even after other therapies have failed,” Purev says. “Now our big question is how long this remission will last.”
The problem is that remissions created by CD19-targeted CAR-T cell therapy don’t always last. One reason for relapse may be that CD19-targeted CAR-Ts die off before the cancer does, leaving enough cancer cells to eventually restart growth.
“Some patients lose CAR-T cells and this is associated with relapse,” Purev says. This is called CD19-positive relapse – cancer cells marked with CD19 still exist, only there are no more CD19-targeted CAR-T cells to attack them. But there is also “CD19-negative” relapse in which the CAR-Ts wipe out all traces of CD19- marked cells, and yet the cancer returns.
One theory goes like this: Imagine you are one in a crowd of people wearing red hats and suddenly find yourself running down the streets of Pamplona closely pursued by a herd of large, angry bulls. You might choose to take off that red hat. Instead, you might choose to put on a blue one. Eventually, the bulls trample and gore everyone stupid enough to insist on wearing a red hat, leaving a population of intelligent people like you that switched to blue. In other words, a smart cancer cell may ditch CD19 like a red hat, and instead put on another one that serves a similar purpose.
Another theory is that the crowd of people running down the streets of Pamplona is made up of some wearing red hats and others wearing blue. Like before, the bulls trample and gore the people in red hats, leaving the population of people in blue hats, but this time individuals have not changed – the evolution of the population from “red” to “blue” is accomplished by selecting for blue. In cancer, this would be like some cells wearing CD19 and others wearing another “hat” from the start, and when CD19-targeted CAR-T cell therapy eradicates the CD19 cells, it leaves these other cells wearing other hats to drive CD19-negative relapse.
A third theory is that everyone starts out wearing both red and blue hats, and some people are smart enough to take off the red one. But no matter how a population of cancer cells loses CD19, we know the color of the other hat. The hat is colored CD22.
Do you remember the patient that Terry Fry treated over the 2016 winter holiday? The new drug that Fry was using for the first time
was a CD22-targeted CAR-T cell therapy. The patient he treated was the first of 21 patients ranging from seven to 30 years old treated with CD22-targeted CAR-T cell drug known as JCAR018. Twelve of these 21 patients achieved complete remission, including 11 of 15 who were treated with the trial’s highest dose. Here’s a very important point: Almost all of these patients had relapsed after CD19-targeted CAR-T cell therapy, meaning that doctors may be able to use first one drug and then when it fails, switch to the other. Even better, they may even be able to use both at the same time.
CD19 and CD22
As we’ve seen, CD19 and CD22 are parallel roads that cancer can take to the same destination. Barricade CD19 and cancer cells can take CD22; barricade CD22 and cancer cells may take CD19. But what happens when you barricade both roads at once?
“Now that we have CAR 19s and CAR 22s, we’re starting to see trials that treat them both at the same time,” Fry says (for example clinicaltrials.gov #NCT03233854). And he sees Colorado as the place where this will happen.
“I’ve been in this long enough to know that the programs that are successful ensure that developing treatments is always a two-way street – you do your lab work, take it to the clinic, and then take your clinical observations back to the lab,” Fry says. “What we’re seeing with CAR-T cells emphasizes that it’s always bench-to-bedside and back again. Colorado has a long history of strong immunology research, both at CU and at National Jewish and that’s what it’s going to take to improve these therapies. The next generation of this field is going to take what we’ve learned back to the laboratory to understand it.”
Back to the Laboratory
Combining CD19 with CD22 CAR-Ts is just the start. Fry also plans to open a trial of CD33 CAR-Ts against pediatric ALL. Then, of course, with three CAR-Ts on the table, there will be opportunity to sequence and combine these treatments, and to find the best strategies against specific kinds of cancer, both in the blood and perhaps even against solid tumors. And Fry points out that “CD’s” are only one possible target for CAR-Ts. For example, CU Cancer Center investigator Nick Foreman, MD, is exploring CAR-Ts aimed at the well-known breast cancer gene HER2.
“The success with CAR 19 creates the opportunity to think about doing the same thing with other antigens and other cancers,” Fry says.
Futuristic strategies may even include gene editing on the tumor side of the equation – using lentiviruses or even the gene- editing technology CRISPR (see next page), researchers may be able to force cancers to express certain antigens. For example, instead of being forced to discover targets like CD19 and CD22 that happen to already exist on cancer cells, doctors could insert a new genetic target into cancer cells that makes them naturally visible to the immune system.
“I think that one of the perceptions has been that, okay, now with CAR-Ts, we pretty much have at least the B cell malignancies locked up,” Fry says. “But having 50 percent of our patients in remission at one year is not enough. It’s already a paradigm- changing treatment, but as our experience matures it tells me that we really have a long way to go.”