Nav: Home

Platelets suppress T cell immunity against cancer

May 05, 2017

Blood platelets help disguise cancer from the immune system by suppressing T cells, report scientists at the Medical University of South Carolina (MUSC) in the May 5, 2017 issue of Science Immunology. In extensive preclinical tests, a promising T cell therapy more successfully boosted immunity against melanoma when common antiplatelet drugs such as aspirin were added.

Zihai Li, M.D., Ph.D., senior author on the article, is chair of the MUSC Department of Microbiology and Immunology, the program leader for the Cancer Immunology Research Program at MUSC Hollings Cancer Center, and the SmartState® Sally Abney Rose Chair in Stem Cell Biology & Therapy. Li studies how tumors hide themselves from the immune system.

Li's team found that platelets release a molecule that suppresses the activity of cancer-fighting T cells. That molecule, unsurprisingly, was TGF-beta, which has been recognized for decades for its role in cancer growth.

Yet this study is the first of its kind. Most TGF-beta is inactive. Li and his group found that the surface of platelets has a protein called GARP, a molecular hook that is uniquely able to trap and activate TGF-beta. Platelets, which are small cell fragments that circulate throughout the blood and are normally involved in clotting, become the major source of activated TGF-beta that invading tumor cells use to suppress T cells. In other words, platelets help give tumors their invisibility cloak from the immune system.

Scientists have known for several years that certain cancers suppress T cells to avoid the immune system. That is why adoptive T cell therapy is one of the most promising advances in modern cancer treatment. It is a type of immunotherapy that awakens the immune system by retraining a patient's T cells to recognize their cancer. T cells are isolated from a patient's blood and retrained, or "primed," to recognize tumor cells. They are then injected back into the patient's bloodstream where they can now hunt and fight cancer.

There was some evidence that platelets might make cancer worse. For example, patients who have excessive clotting related to their cancer almost always have a worse prognosis, according to Li.

"Over the years, it has become appreciated that platelets are doing more than just clotting," says Li.

The first clue that cancer-fighting T cells might be suppressed by the body's own clotting system came when the researchers gave melanoma to mice with genetically defective platelets. Melanoma tumors grew much more slowly and primed T cells were much more active than in mice with normal platelets.

Next, the team isolated platelets and T cells from blood drawn from humans and mice. In both cases, platelets with activated clotting activity suppressed T cell response. It then used mass spectrometry to thoroughly identify the molecules released by activated platelets that most suppressed T cell activity. The molecule with the most T cell suppression was TGF-beta.

Li and his team then studied how platelets activate TGF-beta. In genetically modified mice without GARP, the molecular hook on the surface of platelets, adoptive T cell therapy was more successful at controlling melanoma. This meant that platelets without the ability to grab and activate TGF-beta were not able to suppress cancer-fighting T cells. Similar experiments confirmed this result in mice with colon carcinoma.

Finally, mice with normal platelets that were given melanoma and then adoptive T cell therapy survived longer and relapsed less when aspirin and clopidogrel, two antiplatelet drugs, were added. The researchers noted that antiplatelet drugs by themselves were not successful in combating melanoma in their experiments.

This study could inform future treatment of melanoma and other cancers and offers a sound reason to test antiplatelet drugs in clinical trials of adoptive T cell therapy. In patients with melanoma or other cancers, adoptive T cell therapy may be successful if highly available platelet-blocking drugs such as aspirin are added to the treatment. However, the current standard of care for melanoma is not adoptive T cell therapy, but so-called checkpoint inhibitors.

Li and his group want to know if combination therapy with antiplatelet drugs could improve existing cancer treatment. They are waiting for approval to begin a clinical trial that will test certain checkpoint inhibitors in combination with aspirin and clopidogrel for the treatment of patients with advanced cancers. Li's trial will complement clinical trials that are already testing adoptive T cell therapy as a single treatment for cancer.

"I'm very excited about this," says Li. "We can test simple, over-the-counter antiplatelet agents to really improve immunity and make a difference in how to treat people with cancer."
-end-
About MUSC

Founded in 1824 in Charleston, The Medical University of South Carolina is the oldest medical school in the South. Today, MUSC continues the tradition of excellence in education, research, and patient care. MUSC educates and trains more than 3,000 students and residents in six colleges (Dental Medicine, Graduate Studies, Health Professions, Medicine, Nursing, and Pharmacy), and has nearly 13,000 employees, including approximately 1,500 faculty members. As the largest non-federal employer in Charleston, the university and its affiliates have collective annual budgets in excess of $2.2 billion, with an annual economic impact of more than $3.8 billion and annual research funding in excess of $250 million. MUSC operates a 700-bed medical center, which includes a nationally recognized children's hospital, the Ashley River Tower (cardiovascular, digestive disease, and surgical oncology), Hollings Cancer Center (a National Cancer Institute-designated center), Level I Trauma Center, Institute of Psychiatry, and the state's only transplant center. In 2016, U.S. News & World Report named MUSC Health the number one hospital in South Carolina. For more information on academic programs or clinical services, visit musc.edu. For more information on hospital patient services, visit muschealth.org.

Medical University of South Carolina

Related Cancer Articles:

Cancer mortality continues steady decline, driven by progress against lung cancer
The cancer death rate declined by 29% from 1991 to 2017, including a 2.2% drop from 2016 to 2017, the largest single-year drop in cancer mortality ever reported.
Stress in cervical cancer patients associated with higher risk of cancer-specific mortality
Psychological stress was associated with a higher risk of cancer-specific mortality in women diagnosed with cervical cancer.
Cancer-sniffing dogs 97% accurate in identifying lung cancer, according to study in JAOA
The next step will be to further fractionate the samples based on chemical and physical properties, presenting them back to the dogs until the specific biomarkers for each cancer are identified.
Moffitt Cancer Center researchers identify one way T cell function may fail in cancer
Moffitt Cancer Center researchers have discovered a mechanism by which one type of immune cell, CD8+ T cells, can become dysfunctional, impeding its ability to seek and kill cancer cells.
More cancer survivors, fewer cancer specialists point to challenge in meeting care needs
An aging population, a growing number of cancer survivors, and a projected shortage of cancer care providers will result in a challenge in delivering the care for cancer survivors in the United States if systemic changes are not made.
New cancer vaccine platform a potential tool for efficacious targeted cancer therapy
Researchers at the University of Helsinki have discovered a solution in the form of a cancer vaccine platform for improving the efficacy of oncolytic viruses used in cancer treatment.
American Cancer Society outlines blueprint for cancer control in the 21st century
The American Cancer Society is outlining its vision for cancer control in the decades ahead in a series of articles that forms the basis of a national cancer control plan.
Oncotarget: Cancer pioneer employs physics to approach cancer in last research article
In the cover article of Tuesday's issue of Oncotarget, James Frost, MD, PhD, Kenneth Pienta, MD, and the late Donald Coffey, Ph.D., use a theory of physical and biophysical symmetry to derive a new conceptualization of cancer.
Health indicators for newborns of breast cancer survivors may vary by cancer type
In a study published in the International Journal of Cancer, researchers from the UNC Lineberger Comprehensive Cancer Center analyzed health indicators for children born to young breast cancer survivors in North Carolina.
Few women with history of breast cancer and ovarian cancer take a recommended genetic test
More than 80 percent of women living with a history of breast or ovarian cancer at high-risk of having a gene mutation have never taken the test that can detect it.
More Cancer News and Cancer Current Events

Trending Science News

Current Coronavirus (COVID-19) News

Top Science Podcasts

We have hand picked the top science podcasts of 2020.
Now Playing: TED Radio Hour

Uncharted
There's so much we've yet to explore–from outer space to the deep ocean to our own brains. This hour, Manoush goes on a journey through those uncharted places, led by TED Science Curator David Biello.
Now Playing: Science for the People

#555 Coronavirus
It's everywhere, and it felt disingenuous for us here at Science for the People to avoid it, so here is our episode on Coronavirus. It's ok to give this one a skip if this isn't what you want to listen to right now. Check out the links below for other great podcasts mentioned in the intro. Host Rachelle Saunders gets us up to date on what the Coronavirus is, how it spreads, and what we know and don't know with Dr Jason Kindrachuk, Assistant Professor in the Department of Medical Microbiology and infectious diseases at the University of Manitoba. And...
Now Playing: Radiolab

Dispatch 1: Numbers
In a recent Radiolab group huddle, with coronavirus unraveling around us, the team found themselves grappling with all the numbers connected to COVID-19. Our new found 6 foot bubbles of personal space. Three percent mortality rate (or 1, or 2, or 4). 7,000 cases (now, much much more). So in the wake of that meeting, we reflect on the onslaught of numbers - what they reveal, and what they hide.  Support Radiolab today at Radiolab.org/donate.