I think its been done a few times [1]. Crudely put: try to wipe out as much of the immune system then replace with stem cells from a donor. Previously they used donors who had a gene mutation that made them HIV resistant, but this was with 'normal' genes. But a stem cell transplant may have worse survivability than HIV for many people

[1] https://www.nbcnews.com/health/health-news/7th-person-hiv-cu...