More on the Alemtuzumab trial

The previous post is simply the headline results; we need to wait for the full results that will be presented at the ECTRIMS/ACTRIMS meeting from the 19 – 22 October 2011, in Amsterdam, The Netherlands.

The important differences between the phase 2 and 3 studies are:
  1. The patients in the phase 2 study the diagnosis of MS had to be within 3 years of symptom onset and subjects had to have at least two relapses in the 2 years prior to study entry (i.e., the initial event if within 2 years of study entry plus ≥1 relapse, or ≥2 relapses if the initial event was between 2 and 3 years prior to study entry).
  2. In the phase 3 study the diagnosis of MS had to be within 5 years of symptom onset and subjects had to have two or more MS attacks within 24 months, with at least one attack within the last 12 months.
This means that the subjects in the phase 2 study had earlier disease (<3 years) and their relapses were more likely to occur within the first 2 years of disease onset.

We don't know why but relapses occurring within the first 2 years of symptom onset are much more meaningful with regard to prognosis (more on that later in another post). Therefore selecting MS'ers for treatment based on high-activity with in this period selects for subjects with more active and aggressive MS. 

Recovery from attacks is greater the earlier you are in the disease course; this may explain why subjects recovered more from disability in the phase 2 or earlier study compared to what has been reported in the press release yesterday.

The population of MS'ers from which these studies recruited are also different; the populations for more recent or later studies tend to have less active disease. This makes it more difficult to see differences between the treatment arms.

Finally, the phase 2 study tested two doses of Alemtuzumab (low and a high dose), where as the phase 3 study only tested the low dose. This is important as the high dose was more effective than the low dose; this will explain why the results in the phase 3 study in relation to relapse reduction is not as good as that seen in the phase 2 study. 

"These results are still very impressive, particularly as Alemtuzumab is only given as a course of infusions once a year for 2 years."

CoI: Multiple