Relkin said that the original analysis of the MRI data, conducted by his collaborator Jim Brewer at University of California, San Diego, were so impressive that he found it hard to believe. But independent analysis of the data by Dana Moore at Weill Cornell, using different software, essentially told the same story: that patients on IVIg had rates of brain atrophy consistent with those of age-matched normal individuals.

That atrophy was normal in treated patients would be suggestive of a disease-modifying (DM) effect. In fact, as luck would have it, this Phase 2 trial of IVIg used a delayed start design, which is one potential way of demonstrating disease modification. By comparing the rate of progression of disease in groups of patients starting the therapy at different times, DM effects can be revealed, the theory goes. In this case, however, the delayed start was not designed from the outset to prove disease modification. It was more a case of how the study evolved—funding agencies initially required a six-month proof-of-concept trial, said Relkin, and the trial was later extended to 18 months. As a result, eight patients received placebo for six months and then IVIg for 12 months (the delayed start), while 16 patients received the treatment from the beginning of the trial. “The hope of having something which is disease modifying has eluded us in so many clinical trials. I’m reluctant to say that we found something that is disease modifying, but in terms of trajectory and biological changes, things seem to point in that direction,” said Relkin. The patients who received the optimal dose of IVIg had an initial symptomatic improvement that was maintained over the 18 months of the study. MR measurements showed that they also had less atrophy than patients who had the delayed start.

Patients received 0.2 g IVIg per kg body weight twice a month, 0.4 g/Kg twice a month, or 0.8 g/Kg once a month. The trial was blinded during the first six months and open-label afterwards. Patients knew they were receiving treatment, though not which dose; raters stayed blinded to who had initially been on placebo. Overall, the MRIs measured 46 percent reduction in annual brain atrophy in patients who received continuous treatment compared to those who initially received placebo, said Relkin. There was significantly less ventricular enlargement in the continuous treatment group as well (6.7 percent a year versus 12.7 percent a year). There appears to have been a dose-dependent effect, whereby patients on the optimal dose (0.4 g/Kg biweekly) had annual rates of atrophy similar to those seen in normal patients in the ADNI cohort, according to Relkin. “What makes the data exciting is a tight correlation between brain volumetric data and primary outcome measures of cognition (ADAS-cog) and global change (ADCS-CGIC),” said Relkin. At baseline no correlation was apparent between brain volumes and the primary measures, but the changes over the course of 18 months were highly correlated.

IVIg is a mixture of immunoglobulins, some of which Relkin believes target Aβ. He told ARF that these antibodies may differ from others currently being tested in that they recognize epitopes formed when Aβ aggregates. IVIg also has documented immunomodulatory effects, Relkin added, noting that this may convert pro-inflammatory microglia into phagocytic, non-inflammatory cell types that can mop up Aβ. Amyloid imaging with PIB-PET may be able to address the question of Aβ removal. Half the patients in this Phase 2 trial were scanned for PIB at six months and again at 18 to 24 months. Those data are currently being analyzed, Relkin said.

A Phase 3, multicenter trial of IVIg enrolling 360 AD patients is underway. It is sponsored by an NIA grant through the Alzheimer’s Disease Cooperative Study (ADCS) and is jointly funded by Baxter BioScience, who make the IVIg preparations. This non-patentable therapy is FDA approved and has been used for decades for certain life-threatening immunodeficiency disorders, including congenital pediatric immunodeficiency. The rising interest in an Alzheimer’s indication has certain patient groups worried that a successful Phase 3 trial could result in intense demand for the immunoglobulin mix, noted Relkin. He stressed that IVIg should not be used off-label and mentioned that there is an industry initiative afoot to guarantee IVIg to those patients who cannot live without it. Ultimately, if the ADCS Phase 3 trial is successful, then an analysis of the mixture could identify specific components that could be used to make more targeted immunotherapies, said Relkin.—Tom Fagan.