From what I remember, these blood cancer have an antigen, CD13 or something, which is unique to them - no other body part has it, making it easy to target them.
Otherwise, you get the side effect of destroying your own body, the case of a woman a few years ago, who died having her lungs destroyed by immunotherapy. Lungs had the same antigen.
This morning I read something hopeful in this direction - UCSF researchers designed an AND gate, so now they could trigger a T cell attack only when 2 specific antigens are present, making it much more reliable. And I could imagine these can be chained, further narrowing it down. It needs genetic sequencing to isolate.