Developmental Biology - Brain Cancer|
Human Immune T Cells Vanquish Brain Tumor
A fatal pediatric brainstem tumor was cleared by injecting it with engineered T cells...
In 2018, a mouse with a fatal brainstem tumor was cleared by injecting it with engineered T cells that recognized the cancer and targeted it for destruction. This Stanford discovery is moving to human trials in the latter half of 2019.
Engineered human immune cells can vanquish a deadly pediatric brain tumor in a mouse model, a study from the Stanford University School of Medicine has demonstrated.
The study, which was published online April 16 in Nature Medicine, represents the first time a severe human brainstem tumor, diffuse intrinsic pontine glioma, has been eradicated in mice. DIPG affects a few hundred school-age children across the country each year and has a median survival time of only 10 months; there is no cure. In mice whose brainstems were implanted with human DIPG, engineered immune cells known as chimeric antigen receptor T cells — or CAR-T cells — were able to eliminate tumors, leaving very few residual cancer cells.
“I was pleasantly surprised with how well this worked. We gave CAR-T cells intravenously, and they tracked to the brain and cleared the tumor. It was a dramatically more marked response than I would have anticipated,” explained Michelle Monje MD PhD, assistant professor in Neurology, and senior author of the study.
When the brains of the mice were examined via immunostaining after treatment, the animals had, on average, a few dozen cancer cells left, compared with tens of thousands of cancer cells in animals that received a control treatment.
“As a cancer immunotherapist, what gets me really excited is when you take an established tumor and you make it disappear,” said Crystal Mackall, MD, professor of pediatrics and of medicine and the study’s other senior author. “In animal studies, we can often slow the growth of a tumor, shrink a tumor or prevent tumors from forming. But it isn’t so often that we take a tumor that’s established and eradicate it — and that’s what you want in the clinic.”
However, some mice experienced dangerous levels of brain swelling, a side effect of the immune response triggered by the engineered cells, according to researchers, adding that extreme caution will be needed to introduce the approach in human clinical trials.
‘Hiding in plain sight’
To begin the research, the scientists screened human DIPG tumor cultures for surface molecules that could act as targets for CAR-T cells. In CAR-T therapies now used in humans, some of the patient’s own immune cells are removed, engineered to attack a surface antigen on the cancer cells, and returned to the patient’s body, where they target the cancer cells for destruction. Cell surface antigens are large molecules sticking out from a cell that help the immune system determine whether the cell is harmless or harmful.
Monje’s team identified a sugar molecule, GD2, which is abundant on the surface of DIPG tumors in 80 percent of cases. Excess expression of the sugar is caused by the same mutation, known as the H3K27M mutation, that drives the growth of most DIPG tumors, the team found. Scientists have known for decades that GD2 levels on some other forms of cancer are very high, but its discovery on this tumor came as a surprise, Mackall said, adding, “It was hiding in plain sight, and we didn’t know.”
Mackall’s team had already designed a way to make CAR-T cells that attack the GD2 sugar; similar anti-GD2 CAR-T cells are now being tested in clinical trials in a few other cancers. In a dish, Mackall’s CAR-T cells killed cultured DIPG cells that carry the H3K27M mutation. If the cultured cells were genetically modified to stop expressing the target sugar, the CAR-T cells no longer worked. Other CAR-T cells that were tuned to different molecular targets also did not kill the DIPG cancer cells.
Next, the team tested the GD2 CAR-T cells in mice whose brainstem was implanted with human DIPG tumors, an experimental system that Monje’s lab pioneered. Seven to eight weeks after the tumor was established, each mouse received one intravenous injection of GD2 CAR-T cells or, as a control treatment, an injection of CAR-T cells that react to a different target. The cells are able to cross the blood-brain barrier. In the mice that received GD2 CAR-T cells, the DIPG tumors were undetectable after 14 days, while mice receiving the control treatment had no tumor regression. After 50 days, the animals were euthanized and their brains examined. Using immunostaining, the researchers counted the remaining tumor cells; the mice treated with GD2 CAR-T cells had a few dozen remaining cancer cells per animal, while each control mouse had tens of thousands of cancer cells. In the GD2 CAR-T treated animals, the residual cancer cells did not express GD2, suggesting that these remaining cells were not vulnerable to the immune therapy and might be able to cause the cancer to recur.
Risky to use near thalamus
Gliomas occurring in the spinal cord and thalamus of children also exhibit the H3K27M mutation and were found to similarly express very high levels of GD2. The research team also tried the GD2 CAR-T therapy in mice with human spinal cord and thalamic tumors implanted in their respective anatomical locations. Spinal cord tumors were effectively cleared by the GD2 CAR-T cells. However, some animals with thalamic tumors died from the CAR-T treatment. The inflammatory response generated by the immune cells caused brain swelling, which is particularly risky near the thalamus, a structure buried deep inside the brain, the researchers reported.
“While this strategy is very promising for a disease with few therapeutic options, it’s crucially important to keep in mind that these tumors are located in precarious neuroanatomical sites that just do not tolerate much swelling — and those regions are already expanded by tumors. With any effective clearing of a tumor by the immune system, by definition there is inflammation, which means there will be some degree of swelling. It’s a dangerous situation.”
Michelle Monje MD PhD, assistant professor in Neurology, and senior author of the study.
I don’t think one strategy is going to cure this extremely aggressive and deadly cancer.
The team plans to move the CAR-T treatment into human clinical trials, but will build as many safeguards as possible into the trial to minimize risks to people who participate, Monje said. “I think this is something we can bring to the clinic soon, but it needs to be done very carefully,” she said.
“These CAR-T cells are extremely potent,” Mackall said, noting that a therapy that uses CAR-T cells to treat pediatric leukemia was approved by the Food and Drug Administration in 2017. “In leukemia, that potency is the reason this has been a transformative therapy, but it is also the major cause for toxicity. It’s very difficult to find a cancer medicine that works but doesn’t have a down side.”
Because the CAR-T cells do not eradicate all cancer cells, the researchers think the immune therapy will need to be combined with other treatments. Monje’s team is also studying chemotherapy drugs to treat DIPG.
“I don’t think one strategy is going to cure this extremely aggressive and deadly cancer,” Monje said. “However, I think CAR-T immunotherapy is part of the puzzle of DIPG treatment in a way that I’m quite hopeful about.”
Diffuse intrinsic pontine glioma (DIPG) and other diffuse midline gliomas (DMGs) with mutated histone H3 K27M (H3-K27M)1,2,3,4,5 are aggressive and universally fatal pediatric brain cancers6. Chimeric antigen receptor (CAR)-expressing T cells have mediated impressive clinical activity in B cell malignancies7,8,9,10, and recent results suggest benefit in central nervous system malignancies11,12,13. Here, we report that patient-derived H3-K27M-mutant glioma cell cultures exhibit uniform, high expression of the disialoganglioside GD2. Anti-GD2 CAR T cells incorporating a 4-1BBz costimulatory domain14 demonstrated robust antigen-dependent cytokine generation and killing of DMG cells in vitro. In five independent patient-derived H3-K27M+ DMG orthotopic xenograft models, systemic administration of GD2-targeted CAR T cells cleared engrafted tumors except for a small number of residual GD2lo glioma cells. To date, GD2-targeted CAR T cells have been well tolerated in clinical trials15,16,17. Although GD2-targeted CAR T cell administration was tolerated in the majority of mice bearing orthotopic xenografts, peritumoral neuroinflammation during the acute phase of antitumor activity resulted in hydrocephalus that was lethal in a fraction of animals. Given the precarious neuroanatomical location of midline gliomas, careful monitoring and aggressive neurointensive care management will be required for human translation. With a cautious multidisciplinary clinical approach, GD2-targeted CAR T cell therapy for H3-K27M+ diffuse gliomas of pons, thalamus and spinal cord could prove transformative for these lethal childhood cancers.
Christopher W. Mount, Robbie G. Majzner, Shree Sundaresh, Evan P. Arnold, Meena Kadapakkam, Samuel Haile, Louai Labanieh, Esther Hulleman, Pamelyn J. Woo, Skyler P. Rietberg, Hannes Vogel, Michelle Monje and Crystal L. Mackall.
thank the following for generously providing cell cultures: A. Moore (University of Queensland) and C. Jones (Institute of Cancer Research) for QCTB R059, R. Seeger (Children's Hospital Los Angeles) for CHLA136, 255, C. Khanna (National Cancer Institute) for MG63-3 and L. Helman (Children's Hospital Los Angeles) for EW8 and TC32.
This work was supported by a Stand Up To Cancer–St. Baldrick’s–National Cancer Institute Pediatric Dream Team Translational Cancer Research Grant (C.L.M.). Stand Up To Cancer is a program of the Entertainment Industry Foundation administered by the American Association for Cancer Research. C.L.M is a member of the Parker Institute for Cancer Immunotherapy, which supports the Stanford University Cancer Immunotherapy Program. The authors gratefully acknowledge support from the National Institute of Neurological Disorders and Stroke (F31NS098554 to C.W.M. and R01NS092597 to M.M.), Abbie’s Army Foundation (M.M.), Unravel Pediatric Cancer (M.M.), Maiy’s Miracle Foundation (E.P.A.), Stella S. Jones Foundation (M.M.), McKenna Claire Foundation (M.M.), Alex’s Lemonade Stand Foundation (M.M.), Izzy's Infantry Foundation (M.M.), The Cure Starts Now Foundation and DIPG Collaborative (M.M.), Lyla Nsouli Foundation (M.M.), Declan Gloster Memorial Fund (M.M.), N8 Foundation (M.M.), Fly a Kite Foundation (M.M.), Liwei Wang Research Fund (M.M.), Virginia and D.K. Ludwig Fund for Cancer Research (M.M. and C.L.M.), Sam Jeffers Foundation (M.M.), Michael Mosier DEFEAT DIPG Foundation (M.M.), ChadTough Foundation (M.M.), Reller Family Research Fund, Child Health Research Institute at Stanford and SPARK program (M.M.) and the Anne T. and Robert M. Bass Endowed Faculty Scholarship in Pediatric Cancer and Blood Diseases (M.M.).
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To evaluate in vivo efficacy of GD2-CAR T cells against Diffuse intrinsic pontine glioma (DIPG), the team implanted human DIPG tumors in the brainstem of mice. Seven to eight weeks after the tumor was established, the mice received one intravenous injection of the anti-GD2 CAR T cells. The cells were able to cross the blood-brain barrier, a hurdle that monoclonal antibody therapies struggle to over-come. Within 40 days post-treatment, marked reductions in tumor burden were observed and all mice treated with anti-GD2 CAR T cells demonstrated complete tumor clearance as assessed through bio-luminescence imaging. CREDIT Crystal L. Mackall, Department of Medicine, Stanford University, USA