In the phase IIa study, in which meningoencephalitis reactions were more frequent than in the phase I study, T-cell responses to Aβ were Th1-biased, and it was hypothesized that the meningoencephalitis might be associated with Th1 CD4 T cells, which are known to be pro-inflammatory, or with CD8, cytotoxic T cells. Here, CD8A is linked to meningoencephalitis.