Cancer immunotherapy gets assist from micro-scale engineering

Today’s cancer treatments can sometimes feel like yesterday’s science fiction. In 2017, the Food and Drug Administration approved two therapies that manipulate immune cells’ DNA to give them the power to hunt down and kill certain blood cancers. Scientists are working to extend this treatment strategy to as many cancer types as possible, including solid tumors like breast and pancreatic cancers. But solid tumors pose new challenges even to empowered immune cells, such as the sheer number of cancer cells found in one solid-tumor mass.

Dr. Matthias Stephan at Fred Hutchinson Cancer Research Center developed a patented strategy to deliver active, genetically engineered anti-cancer immune cells to solid tumors, dramatically improving their efficacy in mouse models of cancer. Now, he’s combined this science-fiction cancer treatment with a science-fiction material to improve it even further.

In a study published Dec. 9 in the journal Nature Biomedical Engineering, Stephan showed that loading genetically engineered immune cells onto a metal micromesh-based tumor stent can keep tumors from growing into and blocking the stent in a preclinical model of pancreatic cancer. He and his team also demonstrated that the micromesh can also deliver curative, standardized doses of anti-cancer immune cells to mice with inoperable ovarian cancer.

The micromesh is made from Nitinol, the same nickel-titanium alloy as many biomedical implants, and it is just a few microns — one-thousandth of a millimeter — thick. The micromesh thin-film technology is being commercialized by Monarch Biosciences for several biomedical applications. Formed into thin films, it maximizes T-cell delivery while minimizing the size of the delivery device, explained Stephan, a bioengineer who develops strategies to bring cell-based immunotherapy to solid tumors.

"What we have is a super high density [of anti-cancer immune cells] locally because the thin film stays where it is. You get the highest possible densities of T cells with minimal implant backbone," he said.

A flexible immunotherapy-delivering strategy

CAR T cells are genetically engineered to produce a new molecule, called a chimeric antigen receptor, or CAR, that allows them to recognize and attack cancer cells. Two CAR T-cell therapies, delivered via infusion into the bloodstream, have been FDA-approved to treat certain blood cancers.

But CAR T cells infused into the bloodstream can’t gang up on solid tumors in the numbers necessary to overcome cancer. Stephan developed a strategy to deliver a concentrated, cancer-killing dose of immune cells directly to solid tumors. In 2017, he showed in mice with pancreatic cancer that CAR T cells delivered directly into tumors via an algae-derived dissolving sponge implant shrank tumors while CAR T cells infused into the bloodstream did not.

Just having a CAR isn’t enough to turn a T cell into a cancer killer, even if it’s sitting in an implant directly on a tumor. T cells need help getting out of the implant, plus they need a strong attack signal. Stephan’s patented strategy includes molecular “handles” within the implant that immune cells can grab onto to crawl along, as well as molecular cues that turn on their killer instincts.

In the current study, Stephan adapted this strategy to Nitinol thin films fabricated by MonarchBio. When formed into micron-sized (one-thousandth of a millimeter) patterns, these micromesh films are flexible yet strong. MonarchBio entered an exclusive licensing agreement to combine Stephan’s strategy with its thin films.

A key benefit of the micromesh scaffold was the ability to create a precise shape, Stephan said.

“It was always important that we generate a pattern where the T cells really feel at home,” he said. “So it shouldn't be too big, so that they don't just fall through the cracks, but it shouldn't be too small, because we also want them to migrate from one side to the other.”

The team settled on a grid-like pattern that allowed a precise number of T cells to be loaded to the top and bottom sides of the films. This made for a standardized delivery system in which the exact same T-cell dose could be delivered to every patient.

It’s so precise, “You can almost count [the T cells] and say, ‘OK, everybody present,’” Stephan said.

T cells loaded onto naked Nitinol don’t do much: “They’re like on slippery ice,” he explained.

To give T cells a handhold and an activating boost, the team coated the Nitinol thin films with fibrin, a fibrous protein found in the blood that gives the T cells the handles they need to crawl, and stimulatory molecules that mimic the signals T cells receive during an infection.

The fibrin allows the T cells to cling to the top and bottom surfaces of the thin film. “It’s like a piece of bread spread with marmalade on both sides,” Stephan said. “The metal film is the bread, and then we put CAR T cells on both sides of it and then they soak into the middle, too.”

New and improved applications

Stephan tested his T cell-boosting strategy in two different applications of MonarchBio’s thin film: as stents designed to be used in cancer treatment and an implant that could be used to deliver treatment to an inoperable cancer.

Tumor stents are different than heart stents. They are currently used in lung cancer treatment to keep the airway open, in esophageal cancer treatment to keep the esophagus open and allow the patient to eat, and in pancreatic cancer treatment to allow bile to pass from the liver to the intestine.

But stents inserted into a tumor may in turn become blocked as the tumor grows. First, Stephan tested whether CAR T cells could help keep thin-film stents open in pancreatic tumors growing in a lab dish.  After 10 days, all stents without T cells were obstructed with tumor cells. Of the stents loaded with T cells, 53% were completely clear and the rest had only minor tumor-cell ingrowth.

Then, the team also tested the CAR T cell-enhanced stents in mice implanted with pancreatic tumor cells. After three weeks, all stents without T cells were over 99% blocked; T cell-loaded stents only showed an average of 30% tumor-cell ingrowth.

The team also examined how Stephan’s T-cell delivery strategy worked with the Nitinol  thin films in mice with inoperable ovarian cancer. In about 40% of patients with advanced ovarian cancer whose cancer has spread to their abdominal cavity, tumors grow into the diaphragm and can’t be removed, which impairs patients’ breathing. Patients often undergo what’s known as a debulking procedure, in which as much of the tumor surface is scraped away, though the tumor itself is not cut out.

Stephan and his team tested whether CAR T cell-loaded thin films could be used to shrink tumor tissue that remains after debulking. They compared the efficacy of four different treatment types: IV-infused anti-cancer CAR T cells, anti-cancer CAR T cells injected directly into tumors, thin films loaded with anti-cancer CAR T cells, and thin films loaded with T cells that had no cancer specificity.

Untreated mice survived an average of 30 days. IV-infused anti-cancer CAR T cells extended average survival to 40 days but didn’t shrink tumors. Anti-cancer CAR T cells injected directly into the tumors extended survival to 50 days but also did not shrink tumors. Thin film-delivered non-specific T cells extended survival to 38 days.

In contrast, thin film-delivered anti-cancer CAR T cells cleared tumors in seven of 10 mice and slowed tumor growth in the other three. This treatment extended average survival to 80 days.

A vision for off-the-shelf immunotherapy

Stephan envisions using immune-cell delivering implants in a variety of applications: to prevent recurrence after tumor-removal surgery, on inoperable tumors to shrink or even clear them, and to improve current treatment strategies, such as the CAR-loaded tumor stents tested in this study.

“Ideally, these implants would be functionalized with T cells ahead of time so that they would be off-the-shelf products,” he said.

The strategy also has potential beyond T cells, he said. Researchers are experimenting with other immune cells, including macrophages and natural killer cells, which could be delivered to tumors in a similar fashion.

Stephan’s work shows how the micromesh’s characteristics can improve on the sponge-based delivery strategy he first tested. The ability to load a precise dose of T cells onto thin films would make for a more standardized off-the-shelf product, and T cells sitting on the surface of the Nitinol thin films move into the tumor more easily than those within the sponge. The thin films are also less fragile and therefore easier for a surgeon to place than the sponge, he said.

Stephan’s previous work showed that implant-delivered, activated CAR T cells spread deep into tumor tissue and even throughout the body. Because of this, he believes that adding CAR T cells to stents could theoretically do more than keep the stents open.

A CAR T cell-loaded stent could be “a potentially curative therapy,” he said. Chemotherapy delivered by stent only penetrates a few millimeters into the surrounding tumor, Stephan noted. “In our case we're sending out the troops [in the form of CAR T cells] and they actively penetrate deep, deep into the tissue.”

As long as cutting-edge ideas remain in the lab, they remain fiction. CAR T cells that never reach tumors will never fulfill their cancer-killing potential. With his science, Stephan hopes to turn ideas into effective, real-life cancer therapies.

Fred Hutch, Monarch Biosciences and the Bezos family funded this work.