This study's pretty wild -- but this approach has a major downside that they only mentioned in passing in the actual report in the New England Journal of Medicine (paywalled, unfortunately).

To gene-edit these cells, they had to use a lentivirus vector -- a (limited form of a) class of viruses that notably includes HIV. These viral vectors work by splicing themselves into random places in the host cell's DNA. Which is fine, except that there's a non-zero chance that in the process, the virus will initiate a cancer.

When you combine that with a cell deliberately engineered to hide from the immune system, you have the ticket to a very bad time.

One would probably engineer these cells with a killswitch, such as doxycycline induced Caspase9 https://pmc.ncbi.nlm.nih.gov/articles/PMC1895037/.

The transgene engineering is totally possible without a viral vector. We engineer cells all the time with recombinase based editing methods for targeted safe harbor insertion of transgenes https://www.nature.com/articles/s41551-024-01227-1. This stuff just permeates through the community slowly.