Building a CAR-T cell is one thing, getting it into a tumour and preventing the tumour from growing back is a whole other thing.

Leukemia doesn't really form tumours which is why CAR-T's work so well with it. B-cell becomes cancerous, all B-cells have a receptor called cd-19 on them, so if you target all cells with cd-19 on them, you kill the cancer.

What happens when a tumour doesn't have a receptor like that? Or when access to the tumour is difficult to get to for the car-t? Even worse - what happens when the tumour has co-opted immune cells that suppress T-cells? This happens in many tumour types - most notably (in my opinion) glioblastoma.

We have lots of newer, better, car-t's always coming out, and some of them can even clear the initial disease, but recurrent disease returns and it's either less receptive to the car-t, or you just continue to get relapse.