So I had my CD57 retested a few weeks ago. I do not place a ton of value in this test based on the research that was presented at the ILADS presentation in 2012. Apparently the number can fluctuate by as much as 60% in a day and it is questionable whether other conditions can also lower this specific subset of NK cells.
Although I don't think that it's a clear-cut measure of remission, I do think that those who have tested with a low number can use it to guide treatment somewhat. In my case, I had a CD57 of under 20 before treatment. Now, after two years of aggressive treatment, it's even lower. In my situation it does coincide with how I feel. I feel severely ill 90% of the time.