Perpetuation of vaccine memory T cell responses against SIV/HIV

Results of the RV144 study of a primeboost regimen combining a canarypox vector-based candidate ALVAC-HIV (vCP1521) and AIDSVAX B/E gp120 human immunodeficiency virus (HIV) envelope showed a modest but statistically significant 31% reduction in the rate of HIV infection in healthy volunteers (Rerks-Ngarm et al, 2009). These promising results need to be confirmed in further clinical trials and researchers are hoping to gain more information about the correlates of protection against HIV and the mechanisms of action of these vaccines. In addition, from a clinical standpoint, the RV144 study provides two interesting pieces of information. First, at the end of the first year of the study the rate of protection was up to 60% in vaccinees compared to placebo recipients. Second, no differences in terms of peak of viral load were seen between vaccinated and placebo recipients who became infected. This suggests that the protective efficacy wanes overtime and that vaccines were unable to control viral replication once a systemic infection is established. The immune system controls pathogens through the generation of memory T cells, which can be divided in, at least,