Louis Picker from the Vaccine and Gene Therapy Institute at Oregon Health & Science University gave an update on results obtained in macaques with a CMV-based vaccine against SIV (abstract, webcast -- fourth in session). As Picker has shown in published work, the vaccine consistently facilitates strict control of a pathogenic SIVmac239 challenge in around 50% of immunized macaques. The remarkable news shared by Picker at CROI is that, over time, these protected animals appear to clear SIV infection. This claim is based on multiple criteria, including loss of detectable virus, waning of CD8 T-cell responses to viral antigens not included in the vaccine, and the failure to transmit infection to uninfected macaques despite transfer of over 50 million blood and/or tissue white blood cells (in contrast, similar transfers from elite controller animals or those on suppressive ART reliably transmitted infection). Picker noted that the CD8 T-cell responses in the vaccine recipients appear to "violate all the rules" in that they target very large numbers of different SIV epitopes and, in many cases, their ability to recognize the virus involves MHC class II molecules, which normally facilitate antigen recognition by CD4 T cells rather than CD8 T cells. Picker is now working to shed further light on these findings, as well as collaborating with the Vaccine and Gene Therapy Institute of Florida to try and develop a CMV vaccine vector that can safely be studied in humans.
Richard Jefferys is the coordinator of the Michael Palm HIV Basic Science, Vaccines & Prevention Project Weblog at the Treatment Action Group (TAG). The original blog post may be viewed here.