They have never isolated it. HIV is not a virus, but an artifact of cellular stress. See the Perth Group's papers on this matter. It looks like HIV is produced from within the cell as a repair mechanism. Thus, HIV is the effect of immune system imbalance, not the cause. Of course, the mainstream media never talks about this. Google Perth Group and read their papers. Their claims are fully referenced and supported in the literature. The Perth Group is a group of several Australian scientists.