In mice with Duchenne muscular dystrophy, immune cells with an engineered receptor cleared most uPAR-bearing cells that sustained muscle inflammation and scarring: tissue regeneration resumed, and lower-leg muscle strength reached 1,8 times that of controls
In mice with Duchenne muscular dystrophy, immune cells with an engineered receptor cleared most uPAR-bearing cells that sustained muscle inflammation and scarring: tissue regeneration resumed, and lower-leg muscle strength reached 1,8 times that of controls
On October 29, Cell Stem Cell published a study by Yarui Diao and Charles Gersbach of Duke University. The researchers identified a small population of cells bearing the protein uPAR in mouse muscle and reduced it using CAR-T cells, T lymphocytes with an engineered receptor that enables them to kill cells bearing a specific protein.
In Duchenne muscular dystrophy, a mutation deprives muscle fibers of dystrophin, leaving them vulnerable to repeated damage. Muscle stem cells repair these fibers with help from neighboring cells: immune cells called macrophages and fibro-adipogenic progenitors (FAP), which give rise to connective tissue and fat cells. With persistent damage, some of these neighboring cells fail to resume their normal functions. Macrophages release inflammatory signals, FAP deposit excess collagen, scar tissue accumulates in the muscle, and the muscle stem cell pool becomes depleted.
Gene therapies restore dystrophin in muscle fibers but leave inflammation and scarring unaddressed. Macrophages and FAP are needed for repair, so treatment must selectively remove the harmful subsets. To identify a shared marker, the researchers ranked macrophages from diseased mice by inflammatory gene activity and FAP by the activity of genes involved in scarring, then compared the top and bottom quarters. In the top quarter, 599 genes were more active in macrophages and 521 in FAP, with 86 genes shared between the two groups. Six of these encode cell-surface proteins accessible to CAR-T cells, including uPAR.
Three findings supported the choice of uPAR. In mice lacking the uPAR gene, otherwise healthy muscle regenerates normally after injury, and muscular dystrophy remains unchanged, indicating that repair can proceed without this protein. CAR-T cells targeting uPAR had already killed senescent cells, improved intestinal regeneration in old mice, and caused no severe adverse effects over 12–15 months. In muscle samples from three patients, uPAR gene activity in macrophages and FAP was higher than in samples from two healthy individuals.
Two-month-old male mice with the disease received a single dose of CAR-T cells, while controls received T cells without the engineered receptor. After one day, mean body temperature in the CAR-T group fell to 32,8 °C, returning to 37,4 °C by day four. After three weeks, the proportion of muscle cells with high uPAR levels had fallen to 0,55%, compared with 3,1% in controls, and areas positive for scarring markers were 3,2–3,5 times smaller. According to the authors, cells without uPAR were preserved, while collagen gene activity decreased in the remaining FAP and inflammatory gene activity decreased in macrophages.
Mice treated with CAR-T cells had 1,5 times as many muscle stem cells and 2,9 times as many new muscle fibers as controls. Their lower-leg muscle strength was 1,8 times that of controls, and their grip strength was 1,3 times that of controls. In the diaphragm, whose impairment is a leading cause of death in patients, the number of scar-forming cells fell by 87%, and breathing under low-oxygen, high-carbon-dioxide conditions approached that of healthy mice.
In mice treated at two months of age, the grip-strength benefit disappeared after eight weeks. The authors suggest two possible reasons: muscle fibers lacking dystrophin continue to sustain damage, and CAR-T cells lose activity. When treatment began earlier, in four-week-old mice, grip strength had increased by 48% by week 11, compared with 24% in controls. The CAR-T-treated mice then received a second dose, and three weeks later their grip strength reached approximately 92% of that of healthy mice.
The authors suggest that a lasting effect may require combining these cells with therapies that restore dystrophin: a temporary change in the surrounding cell populations could give those therapies time to establish a sustained benefit.