Stanford Researchers Engineer Tissue-Resident NK Cells That Infiltrate and Slow Solid Tumors in Mice
核心洞察
Stanford Medicine researchers transformed donor natural killer cells (搜索) into a CD39 (搜索)+CD49a (搜索)+CD103 (搜索)+ cytotoxic tissue-resident phenotype that infiltrates solid tumors more effectively than conventional NK cells.
In mouse models, the enhanced cells slowed growth of multiple solid tumors, including melanoma (搜索) and head and neck squamous cell carcinoma (搜索), with stronger effects when combined with cetuximab.
Because NK cells do not trigger immune reactions between donors, the approach could yield an "off-the-shelf" cell therapy, with one donor generating roughly 20 cryopreserved doses in about two weeks.
Stanford Medicine researchers and their collaborators have found a way to make natural killer (NK) cells better at attacking cancer, transforming them into a specialized, tissue-resident form better suited to living and fighting inside solid tumors. In a new study published in Science Translational Medicine, the enhanced cells infiltrated solid tumors more effectively and slowed their growth in mice, pointing toward a potentially more accessible form of cell therapy for cancers that have been difficult to reach.
"We show that these tissue-resident natural killer cells (搜索) infiltrate into the solid tumors much better than conventional natural killer cells. It was very reproducible, very striking and very clear," said John Sunwoo, MD, the Edward C. and Amy H. Sewall Professor in the School of Medicine and senior author of the study. The co-lead authors are Nina Horowitz, PhD, a former doctoral student in otolaryngology; Imran Mohammad, PhD, a postdoctoral fellow in the Sunwoo lab; and June Ho Shin, PhD, a senior scientist in the Sunwoo lab.
A "Goldilocks" Recipe for Cytotoxic Tissue-Resident NK Cells
Natural killer cells (搜索) were first identified in the 1970s and earned their name because they can quickly detect and destroy abnormal cells, including cancer cells and virus-infected cells. Unlike B cells and T cells, these immune cells do not need to encounter a target before responding, making them fast-acting defenders. However, immunotherapy has historically worked far better against blood cancers than solid tumors, which can behave like fortified strongholds—keeping immune cells out while releasing signals that blunt the attack of those that get inside.
Tissue-resident NK cells are found in places such as the skin, mucous membranes, lungs, and liver, but their role has not always been clear. Some studies have described them as weak killers that may even suppress immune activity, while others have suggested they can be highly effective cancer fighters. "They may adopt different functions based on certain cues in the microenvironment and in the tissue, and differentiate into a certain kind of sub-population," Sunwoo said.
To resolve this contradiction, Sunwoo's team collected circulating NK cells from human blood donors and exposed them to different combinations of cellular signals. They found that TGF-beta (搜索) (transforming growth factor beta), a multifunctional signaling protein released by many cell types including tumor cells, was required to turn NK cells into tissue-resident cells—but the dose mattered greatly.
"It's a Goldilocks kind of thing where if you give just enough of a TGF-b signal, then the natural killer cells (搜索) become tissue resident with strong toxic activity against malignant cells. If you give too much TGF-b, they're still tissue resident, but they're inhibited and dysfunctional, and they don't kill," Sunwoo said. "You need it to be presented to the natural killer cells in just the right amount and in just the right manner."
The most powerful cancer-killing cells emerged when NK cells were briefly exposed to human epithelial tumor cells, which delivered a short burst of active TGF-beta (搜索). Direct contact with the tumor cells was also required, suggesting that other activation signals were involved. Using peripheral NK cells from human blood donors, the team found that sustained exposure to soluble TGF-beta produced tissue-resident-like NK cells with weaker activity, whereas short-lived contact with epithelial tumor cells in the presence of IL-15 generated cytotoxic cells expressing CD39 (搜索), CD49a (搜索), and CD103 (搜索).
"These two tissue-resident natural killer cell populations look very similar, and they have some of the same requirements, but their function seems to be on opposite ends of the spectrum," Sunwoo said.
The team then mapped the traits that made the two tissue-resident cell types similar and different. Both carried the surface proteins CD49a (搜索) and CD103 (搜索), but only the highly efficient killers carried CD39 (搜索). These more powerful cells also had more of the machinery needed to trigger cell death, including perforin, which opens holes in target cells, and granzyme A, a killing molecule delivered through those openings. The researchers describe these cells as cytotoxic tissue-resident NK cells, or ctrNK cells.
Controlling Tumor Growth in Mouse Models
Once the team had a dependable method for producing enhanced NK cells, they showed that the cells could move into tumor organoids grown in the lab. When injected into mice, the cells slowed the growth of multiple solid tumors over days and weeks, including tumors derived from human melanoma (搜索) and head and neck squamous cell carcinoma (搜索).
The strongest results appeared when the enhanced NK cells were combined with cetuximab, a monoclonal antibody treatment that helps mark certain tumor cells for destruction. Cetuximab is an EGFR-targeting antibody approved for metastatic colorectal cancer (搜索) and advanced head and neck squamous cell carcinoma (搜索), although it does not work well by itself, Sunwoo said.
Over one month, a single dose of the combined treatment suppressed tumors in mice more effectively than either therapy alone and did not appear to cause harmful effects. "Even at day 30, when the other mice were sick, the mice that received the combination seemed very healthy," Sunwoo said, though he cautioned against extrapolating too much from mice to humans, adding, "This was just proof of concept."
Toward an Off-the-Shelf Cell Therapy
Natural killer cells (搜索) offer an important advantage over many current immunotherapies: they do not trigger an immune reaction when transferred from one person to another. That means a treatment built from these enhanced cells could potentially be manufactured in large batches, frozen, and given to patients as needed, instead of being custom-made from each patient's own cells.
"It would be almost an off-the-shelf drug," Sunwoo said. "It could make cell therapy much more accessible to a wider variety of patients."
Sunwoo has developed and applied to patent the method for transforming and expanding these enhanced NK cells at scale. Natural killer cells (搜索) from one donor could produce about 20 therapy doses in roughly two weeks. "They'll be cryopreserved, so we can make a bunch of doses and give it to different patients," Sunwoo said. "There would be no delay."
Sunwoo and his colleagues are now preparing a Phase I clinical trial of the combination therapy for patients with advanced squamous cell carcinoma. Pending approval by the Food and Drug Administration, the trial could begin by the end of the year.
The study received funding from the National Institutes of Health (grants R35DE030054, K22CA282364 and R25DC020174), the Tai Tsun Wu Research Fund for Natural Killer Cell Immunotherapy, and the Stanford Bio-X Fellowship.