The HIV is used to modify white blood cells .. so I'd wager harmless as they are not putting the HIV into the patient.

This is why I changed the title after a little nudge, to avoid people getting the wrong end of the stick.

I haven't studied the details of the vector they used, but as a general comment HIV is a very well-understood virus, so removing its potential to infect a human should be easy to do in theory. Practice is another matter, since molecular biology is quite messy.