Some really fascinating work is being done to save leukemia patients who have reached the end of conventional therapy without a cure. Detailed in a NEJM article here, the treatment takes the patients own T cells and reprograms them, targeting the cells to attack the patients own B cells. The reprogramming is done using an HIV derived vector that integrates its DNA payload into the genome of the hosts T cells.
The New York Times has a couple of good writes-ups on this. At the time of this post, this is the most recent.