CAR-T Anti-aging
CAR-T technology was used to combat aging of cells in the lungs and liver
Polina Loseva, N+1
American scientists for the first time used T-lymphocytes to fight senescent cells, the appearance of which accompanies tissue aging. To do this, they used CAR-T technology: they modified immune cells so that they recognized the protein spread on the surface of the senescent cells. The method proved to be effective not only in vitro, but also in vivo, and improved the condition of mice with lung and liver fibrosis, as well as with steatohepatitis. In addition, in minimal doses, it did not cause any side effects. The study was published in the journal Nature (Amor et al., Senolytic CAR T cells reverse senescence-associated pathologies).
Senescent cells, which accumulate in tissues during aging, resemble tumor cells in many ways. They similarly do not perform their main functions in the tissue, but instead trigger the restructuring of the intercellular substance, and the mechanisms of cellular suicide – apoptosis are blocked in them in the same way.
Therefore, some antitumor drugs are being tested as senolytics – drugs that are designed to purify tissue from old cells, since they act selectively on cells with blocked apoptosis. In some experiments, senolytics have already shown their ability to prolong the life of mice and improve (albeit only slightly) the condition of people with different age-related diseases, for example, joint inflammation, lung fibrosis and diabetes.
Corina Amor together with colleagues from Memorial Sloan-Kettering Cancer Center in In New York, another weapon originally invented to fight cancer was proposed to be used against senescent cells – CAR-T technology (read more about this technology in our material "Chimera against Cancer"). These are genetically modified T-lymphocytes that express the chimeric receptor gene, that is, they are programmed to recognize a specific molecule on the cell surface and destroy its carrier.
In order to identify the protein by which it is most convenient to distinguish a senescent cell from any other, the authors of the work sequenced RNA in cell cultures aged in different ways – under the action of antitumor therapy, by oncogene expression or simply long-term cultivation. They identified a list of genes that began to work more intensively after the transformation of the cell into senescent, and compared it with a list of genes that should work normally in vital organs (according to the Atlas of Human Proteins).
As a result, the PLAUR gene was chosen as a distinctive feature, which encodes the uPAR protein, a surface receptor on cells. At a signal from him, the cells begin to destroy the intercellular substance, and in the tumor he transmits a signal about the beginning of movement. After binding to its ligand, the uPAR receptor is partially cleaved and ends up in the blood. It has been repeatedly found in the composition of SASP, a pro–inflammatory protein cocktail secreted by senescent cells, and it serves as a marker for certain diseases, such as kidney failure and diabetes. All this, according to the authors of the article, indicates that uPAR is a good target for CAR-T cells.
The researchers verified that uPAR is indeed expressed on the surface of senescent cells – not only in cultures, but also in the tissues of patients with age-related diseases, for example, atherosclerosis and liver fibrosis.
Then the authors of the work created CAR-T lymphocytes with a receptor for uPAR and tested on mouse cell cultures that they attack only those cells that carry uPAR on the surface. After that, the system was tested in vivo. To do this, the researchers took immunodeficient mice and injected them with senescent cells expressing luciferase into their blood. They are usually excreted from the body, but are delayed in the liver. After some time, CAR-T lymphocytes were injected into the liver of mice, and after that, there were significantly fewer senescent cells.
Liver fibrosis in mice after therapy. From left to right: normal T-lymphocytes, CAR-T cells against the tumor, CAR-T cells against uPAR in small and increased doses. Staining on extracellular substance proteins (upper row, red) and senescent cells (lower row, blue). Figure from the article by Amor et al.
Finally, the researchers tested how effectively CAR-T technology copes with age-related diseases in mice. As the first model, they used animals with lung adenocarcinoma, which were treated with chemotherapy – this method causes the accumulation of senescent cells in tissues. After the introduction of chimeric T-lymphocytes, such animals lived significantly longer than the control ones: on average, about 40 days versus the usual 30. The second model was liver fibrosis, a condition that precedes cirrhosis and tumors. In this case, CAR-T cells also worked: the number of senescent cells in the liver significantly decreased compared to the control (p<0.001). Finally, the therapy proved to be effective in steatohepatitis, a disease in which liver obesity is combined with inflammation. In this case, also after the action of CAR-T, the senescent cells became three times less, and the liver performance, measured in blood protein albumin, increased by one and a half times.
Most senolytics, like other anticancer drugs, cause side effects. And if they can be neglected in a critical condition of the patient, choosing the lesser of two evils, then this may be unacceptable to combat the aging of the body as a whole. Therefore, the authors of the work separately note that in minimal therapeutic doses, therapy did not reduce the viability of mice: they remained as active as ever, did not lose weight and retained the required amount of blood cells. In elevated doses, traces of a cytokine storm – an exaggerated inflammatory response – were noticed in mice, which, however, disappeared after a few days. Next, the scientists will have to check in what doses their method does not cause a cytokine storm, since this complication has already caused the death of patients during clinical trials of CAR-T against cancer.
Previously, GM lymphocytes have already been tried against fibrosis, but only in the heart. In addition, CAR-T cells were able to incite HIV-infected mouse cells. CAR-T lymphocytes can also be obtained using CRISPR/Cas9 technology, and in 2019 they were already tested on the first patients with sarcoma and myeloma.
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