have suppressed the effectiveness of vaccination and also may have enhanced the risk of HIV infection in some clinical trial populations [1], [2] and [3]. The finding that the adenovirus subtype 5 used in the Merck STEP trial was associated with a higher incidence of HIV infection in uncircumcised males, who were seropositive for Ad5 has been linked by some investigators to the recruitment of activated CD4 T cells to the site of infection.