If we're controlling the cells' genomes (which we are), we can add any sort of killswitch (see another comment https://news.ycombinator.com/item?id=45220068 ) that we would like, and this would function better than relying on host immune surveillance. The opposite could be done, making insulin release dependent on the presence of a harmless drug, e.g., insulin release can only happen if a designer steroid molecule is present in the blood.
There are already cell therapies that envisage permanent implantation of modified cells, so I am not sure why a long delay for 'any type of usable treatment' would occur. The structure of this need not be analogous to a stem cell transplant; you could imagine injecting new cells intramuscularly every few months.
The costs to develop this are incurred during development (unlike the autologous therapies that require extensive, expert-level analysis for each new patient). I'm not sure that we can compare the current levels of investment in autologous gene editing to this product.
You are correct that current cell transplant therapies exist, but I don't believe any before have contained these immune escaping edits and I believe all of those treatments are cancer treatments which allow for a different level of risk. Diabetes is a very serious disease but a quality of life treatment does exist and having cells result in a potential cancer in patients would not be acceptable as an outcome.
> once you start adding more than one item to a cell it doesn't always work out.
Very true, but the amounts of money at stake would justify the relatively inexpensive cost of hooking cells up to the already-available ER/TR-responsive gene elements.
> but I don't believe any before have contained these immune escaping edits
Hard to say, I'm not an expert on immune escape. It's an old idea, however, so I imagine it's been used in other pre-clinical or Phase 1 settings.
> I believe all of those treatments are cancer treatments which allow for a different level of risk
I imagine you're speaking about allogeneic treatment? Either way, this isn't true at all - here's a list of current treatments for diabetes alone:
https://pmc.ncbi.nlm.nih.gov/articles/PMC12401705/#s4