Researchers at the Vaccine and Gene Therapy Institute and Oregon National Primate Research Center in Beaverton, Oregon have reported in the journal Nature, that they have developed an effective vaccine against simian immunodeficiency virus (SIV). SIV is the monkey version of the human immunodeficiency virus (HIV), which infects humans and causes acquired immunodeficiency syndrome (AIDS) by depletion of helper CD4 T-lymphocytes. In the study, the researchers used a second virus called cytomegalovirus (CMV) as a vector to carry genes from SIV into the vaccinated Rhesus macaque monkeys. CMV is a common virus that infects many people but usually does not cause illness in healthy individuals. Of the 24 Rhesus macaque monkeys that were immunized with the SIV vaccine, 12 had survived for one year with undetectable levels of the SIV virus and no signs of immune compromise. Another group of 24 Rhesus macaque monkeys, which were not immunized with the SIV vaccine, all had detectable levels of the SIV virus and exhibited signs and symptoms of the monkey version of AIDS. The researchers postulate that the effectiveness of the vaccine stems from the CMV viral vector that is used to transfer the SIV genes to the Rhesus macaque monkeys. CMV usually maintains a low level of replication in the host body and thus provides lifelong stimulation of the immune system. This allows the immune system to be on constant alert for invading SIV viruses in order to attack the virus as soon as they enter into the body. Previous attempts at development of a vaccine against SIV have failed partly because they utilized an adenovirus vector. Adenovirus, in contrast to CMV, replicate a few times after infection and then vanishes from the body. As a result, previous vaccines utilizing adenovirus as a vector were ineffective due to the lack of persistent immune stimulation. The researchers stated that ongoing studies would examine why the vaccine was only effective in half of the Rhesus macaque monkeys. Dr. Louis Picker, who headed the research group, stated that a human version of the vaccine could be ready in three years for clinical trials in humans. The study gives new hope that a vaccine can someday be developed to prevent infection by the HIV virus and eventually eliminating AIDS from the human population.
Scott G. Hansen et al. “Profound early control of highly pathogenic SIV by an effector memory T-cell vaccine” Nature (11 May 2011) doi:10.1038/nature10003 Letter