Just glancing at the literature I can see a number of areas where I should make corrections on my recent posts, but most of it doesn't matter much and is a fair bit of work to rectify but: the first CAR type effort was as long ago as 1989 is seems. Toxicity may more frequently be referring to off-target CAR-T response, and not the Tregs depletion (I don't know about the Treg depletion effects), what got the ball rolling for CAR-T in the first place was expt using the TILs in breast cancer (go in and grab some T cells from the tumor itself, grow in test tube, re-introduce) but the costs and complexity and having solid tumor to grab cells out of all pointed towards a more generic approach .. enter CAR-T , as I understand it. Considerable effort is being mad eon the matter of persistence, much of it hinging around second and third generation chimeras that use co-receptor inside portions. etc.
By now I hope it is clear I am no expert on this, more familiar than many, but it'd take some effort to get up to speed.