> Very interesting! It didn't work for everyone, but it did work for a majority it looks like.

Given that they didn't know what caused CFS (and without further study they still don't know for sure), they don't necessarily have a reliable test that distinguishes CFS from other things that present with similar symptoms. So it's entirely possible that CFS is an immune disorder, this treatment worked on people with CFS, and the remaining cases didn't actually have CFS. It's also possible that some fraction of those it didn't work on have CFS and the drug is not entirely effective, or that some fraction of those it did "work" on are experiencing a placebo effect or a treatment for a different disease that responds to the same treatment.

CFS, like most "syndromes", isn't really a well understood disease but rather a cluster of related symptoms that might indicate a currently unknown disease should a cause or mechanism be discovered. Are you chronically fatigued and the doctors can't diagnose an understood cause? Must be Chronic Fatigue Syndrome. Did your infant suddenly die and the doctors can't figure out how? Must be Sudden Infant Death Syndrome.

What this indicates is that, for a subset of people who are chronically fatigued for no reason that the doctors can figure out, there might be some kind of underlying autoimmune reaction that responds to this kind of treatment. If the mechanism is better understood and can be diagnosed, tested, and treated, then it's not Chronic Fatigue Syndrome anymore, but rather an actual disease.

The study was uncontrolled, so we don't know how much of that is the placebo effect (which typically is anywhere between 11 and 46% for CFS treatments). It will be interesting to see the results of the upcoming controlled study. A previous controlled study did show positive results, but it was quite small.