Genetically modified immune cells taken from patients and then reintroduced called chimeric antigen receptor (CAR) T cells have gained notoriety for treating blood cancers. But could these re-engineered immune cells be used to treat other conditions like aging? 

Lowe and colleagues from the Sloan Kettering Institute in New York published a study in Nature where they deployed CAR T cells against other diseased tissues. These diseased tissues were adversely impacted by senescence—an age-associated state of arrested cell proliferation and elevated inflammation. Doctors may one day use this potential therapy to treat a wide array of senescence-associated ailments, such as fibrotic liver disease, atherosclerosis, and diabetes.

CAR T Cells Need Targets to Locate and Destroy Diseased Cells

When used in cancer treatment, doctors remove immune cells called T cells from a patient and engineer them so that they can target cancer cells before returning them to the body. When they are reintroduced into the patient, the CAR T cells locate and destroy cancer cells with precision and accuracy.

But for CAR T cell therapy to be successful, the cells must have a good target. Accordingly, the first FDA-approved CAR T cells target a cell-surface molecule on blood cancer cells called CD19 that presents on cancer cells but few normal cells. Taking this prior work into account, Lowe and colleagues sought to identify a molecular target on senescent cells.

“Senescence is a double-edge sword,” said Scott Lowe, Ph.D., a senior author on the paper in a press release. “Cells in this state play an important role in wound healing and cancer deterrence. But if they linger for too long, they can cause chronic inflammation, which itself is a cause of many diseases. Finding a way to safely eliminate these cells would be a major therapeutic breakthrough in the treatment of these diseases.”

As for the role of senescent cells in disease, the authors wrote, “the aberrant accumulation of senescent cells generates an inflammatory milieu that leads to chronic tissue damage and contributes to diseases such as liver and lung fibrosis, atherosclerosis, diabetes, and osteoarthritis.” They added that eliminating senescent cells from damaged mouse tissue “ameliorates the symptoms of these pathologies and even promotes longevity.”

Senescent Cells Exclusively Present the Receptor uPAR

The researchers compared molecules on the surface of senescent cells to other cell types to identify a molecular characteristic that distinguishes senescent cells from other cell types. In doing so, they identified a molecule called urokinase plasminogen activator receptor (uPAR) enriched on these cells. uPAR molecules are mostly absent on other cell types. The scientists examined cells in which they induced senescence to identify this cell surface marker. They compared protein levels between senescent cells and other cell types by measuring the presence of molecules indicative of protein expression called ribonucleic acid (RNA). In this way, they specifically identified uPAR on the cell surface of senescent cells.

The team then designed CAR T cells that recognize uPAR so that the re-engineered immune cells could target senescent cells presenting uPAR. To test whether the re-engineered CAR T cells actually destroy senescent cells, they examined whether these CAR T cells would engulf and dispose of liver cells with genetically-induced senescence (oncogene-induced senescence). They found effective clearance of senescent liver cells within 10 days of treatment. They concluded that their designed CAR T cells can eliminate senescent cells in laboratory dishes.

(Amor et al., 2020 | Nature) CAR T cells specifically targeting the molecule uPAR engulf and dispose of senescent cells. The figure on the left shows cells stained blue that were genetically-induced to become senescent. The right image shows that following the addition of CAR T cells directed toward uPAR, clearance of senescent cells occurs. The graph to the right of the two images shows that the percentage of genetically-induced senescent cells in untreated (UT) cells was around 40%, and this percentage significantly decreased well below 10% with CAR T cells directed toward uPAR treatment.

To see if this treatment scheme was effective in live animals, the research team treated live mice with different diseases that cause senescence using these CAR T cells. In a disease mouse model of lung cancer, they found that the CAR T cell treatment prolonged the survival and reduced the presence of lung tumor cells.

(Amor et al., 2020 | Nature) CAR T cell therapy targeting uPAR significantly increased the percentage of surviving mice with lung cancer over time. The red and dark red lines represent the survival percentages of mice treated with CAR T cells that targeted the molecule uPAR on senescent cells. The results indicate the CAR T cell therapy targeting uPAR significantly improved survival in mice with lung cancer.

They also examined the effectiveness of the CAR T therapy on a couple of models of liver fibrosis, which causes cell senescence. They found that CAR T cell treatment also reduced the presence of senescent cells in mice given a molecule that induced liver fibrosis called carbon tetrachloride. CAR T cell treatment targeting uPAR also significantly reduced senescent cell concentrations in another form of diet-induced liver fibrosis called non-alcoholic steatohepatitis. 

These results indicated that CAR T cell treatment works to clear senescent cells not only in cells of laboratory dishes but also in live mice. “This study demonstrates that T cell engineering and CAR therapy can be effective beyond cancer immunotherapy,” said Michael Sadelain, MD, Ph.D., an author of the study in the press release.

(Amor et al., 2020 | Nature) Senolytic CAR T cells reduce liver fibrosis in mice. The top figure shows liver fibrosis accumulation as represented with red staining (Sirius Red). In untreated livers on the far left and non-specific CAR T cell treated livers on the middle left, red staining is more intense compared to uPAR targeting CAR T cell staining on the middle and far right.  The figures on the top indicate that CAR T cells targeting uPAR significantly reduce liver fibrosis in mice. The bottom images show the color blue staining senescent cells in mice with liver fibrosis. The middle right image and image on the far right indicate a significantly reduced concentration of senescent cells with CAR T cell therapy targeting uPAR molecules as shown by reduced blue staining. The graph on the bottom left shows marked reductions in liver fibrosis with CAR T cell therapy targeting uPAR molecules, and the bottom right graph shows a similar effect for senescent cell concentrations.

Applying CAR T Cells to Other Age-Related Diseases

The next steps will be to find out whether uPAR targeting CAR T cells can combat other senescence-related diseases like atherosclerosis, diabetes, and osteoarthritis. This research team hopes to eventually develop this CAR T therapy for use in people.

“We think this approach has the potential to tackle a number of senescence-related diseases for which new treatments are badly needed,” added senior author Scott Lowe, Ph.D.