MxA test reflects IFN-beta bioactivity (or lack thereof) in people with MS

In a disease like MS that goes into relapse and remission unpredictably, it's hard to know whether a treatment is working or not, particularly during times when there is no noticeable activity. Even when someone on a treatment does have clinical activity, it's impossible to say that their treatment is not working, because the activity might have been worse without it. If there was a way to tell whether an MS drug was actively working in an individual, that would be very helpful for that person in deciding whether to stay on it or perhaps switch to something else.

In the case of interferon beta, scientists have known for a while that some people develop antibodies to the drug that appear to block its activity in the body. A blood test for levels of a protein called MxA was developed that gives one indication of IFN-b's activity. Normally, administering IFN-b results in increased MxA levels, but in people with antibodies to IFN-b, this response can be absent. However, perhaps IFN-b is still having other useful effects even if it's no longer affecting MxA.

A group of scientists decided to explore whether the MxA test reflects general IFN-b activity through comparing 12 subjects who had IFN-b antibodies and no MxA response and 12 subjects with no antibodies and an MxA response. They analyzed blood samples taken before and after an IFN-b injection to see how expression levels for over 8,000 genes were affected. The team found that over 1,000 genes were significantly affected by IFN-b in the antibody-negative, MxA-positive group. However, no genes had altered expression in the antibody-positive, MxA-negative group -- in other words, IFN-b had no significant biological effect in this group. If these results are validated in larger studies, then perhaps the MxA test will prove to be useful in determining who isn't responding to IFN-b and therefore might benefit from trying something else.