Considering that chemotherapy is basically feeding poison to your organism in the hope that cancer cells (which are more active) will ingest it in higher quantity, I'd say that we have a pretty high tolerance threshold in term of side-effects while we are looking for an alternative.

As I understand it, most chemotherapy targets only dividing cells. In adult humans there are relatively few of these: cancer cells (which you want to kill), bone marrow (produces blood cells, so you have to monitor blood cell counts during chemo), and reproductive organs (produce gametes, so you may want to freeze sperm/eggs before chemo).

all things considered, it's probably far more dangerous than chemo in the sense that it could kill you or seriously and permanently injure you with your first dose depending on your phenotype. at least chemo is a slower process.

but immunotherapies don't kill most people, thankfully. there are also many ways that you could assay the patient to see how they might react to immunotherapy, but i dont know whether these are done clinically or not.

I think the name for this is

https://en.wikipedia.org/wiki/Cytokine_storm