CAR T-cells are cytotoxic T-cells modified so they do not cooperate with the rest of your immune system (they do reproduce inside your body, they just don't car

CAR T-cells are cytotoxic T-cells modified so they do not cooperate with the rest of your immune system (they do reproduce inside your body, they just don't care what your "normal" immune system thinks on the matter). They do not listen to instructions from your immune system. They are modified from your own immune system so they don't get attacked, your immune system can't tell the difference between its own cells and CAR T-cells. They are then further modified to go looking for specific targets (they go through your body, randomly, and check for specific molecules on cell membranes), and become "cytotoxic" towards them (they fire exploding acidic "bubbles" that digest a target cell). Needless to say, this is a very dangerous treatment (uncontrolled killer T-cells roaming around inside your body multiplying ... not hard to imagine what happens if they target normal cells) and small mistakes will kill patients. In addition to directly killing off important cells, they may can also make the immune system overactive (which in fact happened in this study to three of the patients). They have a bad reputation in research for killing off entire batches of test animals when making a small mistake in less time than you'll need to diagnose the problem and, uh, "fix" it (you're supposed to kill test animals when a treatment doesn't work so they don't suffer). This is not allowed, and has to be explained to the authorities when it does happen and has ended research careers. Normally, or should I say ideally, after multiplying a more-or-less set number of times, they die off and are removed by the body. So no, this does not modify the bone marrow of the patient. Not at all. It just attacks and digests specific cells inside your body and dies off.