The AIDS-causing lentiviruses HIV and SIV effectively evade host immunity, and once established, infections with these viruses are only rarely controlled by immunologic mechanisms1-3. However, the initial establishment of infection in the first few days after mucosal exposure, prior to viral dissemination and massive replication, may be more vulnerable to immune control4. Here, we report that SIV vaccines that include rhesus cytomegalovirus (RhCMV) vectors5 establish indefinitely persistent, high frequency, SIV-specific effector-memory T cell (TEM) responses at potential sites of SIV replication in rhesus macaques (RM) and stringently control highly pathogenic SIVmac239 infection early after mucosal challenge. Thirteen of 24 RM receiving either RhCMV vectors alone or RhCMV vectors followed by adenovirus 5 (Ad5) vectors (vs. 0 of 9 DNA/Ad5-vaccinated RM) manifested early complete control of SIV (undetectable plasma virus), and in 12/13 of these RM, we observed long-term (≥1 year) protection characterized by: 1) occasional blips of plasma viremia that ultimately waned; 2) predominantly undetectable cell-associated viral load in blood and lymph node mononuclear cells; 3) no depletion of effector site CD4+ memory T cells; 4) no induction or boosting of SIVenv-specific antibodies (Abs); and 5) induction and then loss of T cell responses to an SIV protein (vif) not included in the RhCMV vectors. Protection correlated with the magnitude of the peak SIV-specific CD8+ T cell responses in the vaccine phase, and occurred without anamnestic T cell responses. Remarkably, long-term RhCMV vector-associated SIV control was insensitive to either CD8+ or CD4+ lymphocyte depletion, and at necropsy, cell-associated SIV was only occasionally measurable at the limit of detection with ultrasensitive assays, observations suggesting the possibility of eventual viral clearance. Thus, persistent vectors such as CMV and their associated TEM responses might significantly contribute to an efficacious HIV/AIDS vaccine.

The rapid onset of massive, systemic viral replication during primary HIV/SIV infection and the immune evasion capabilities of these viruses pose fundamental problems for vaccines that depend upon initial viral replication to stimulate effector T cell expansion and differentiation1–5. We hypothesized that vaccines designed to maintain differentiated “effector memory” T cell (TEM) responses5,6 at viral entry sites might improve efficacy by impairing viral replication at its earliest stage2, and have therefore developed SIV protein-encoding vectors based on rhesus cytomegalovirus (RhCMV), the prototypical inducer of life-long TEM responses7–9. RhCMV vectors expressing SIV Gag, Rev/Nef/Tat, and Env persistently infected rhesus macaques (RM), regardless of pre-existing RhCMV immunity, and primed and maintained robust SIV-specific, CD4+ and CD8+ TEM responses (characterized by coordinate TNF, IFN-γ and MIP-1β expression, cytotoxic degranulation, and accumulation at extra-lymphoid sites) in the absence of neutralizing antibodies. Compared to control RM, these vaccinated RM showed increased resistance to acquisition of progressive SIVmac239 infection upon repeated, limiting dose, intra-rectal challenge, including four animals that controlled rectal mucosal infection without progressive systemic dissemination. These data suggest a new paradigm for AIDS vaccine development: that vaccines capable of generating and maintaining HIV-specific TEM might decrease the incidence of HIV acquisition after sexual exposure.

Six strains of human cytomegalovirus have been sequenced, including two laboratory strains (AD169 and Towne) that have been extensively passaged in fibroblasts and four clinical isolates that have been passaged to a limited extent in the laboratory (Toledo, FIX, PH, and TR). All of the sequenced viral genomes have been cloned as infectious bacterial artificial chromosomes. A total of 252 ORFs with the potential to encode proteins have been identified that are conserved in all four clinical isolates of the virus. Multiple sequence alignments revealed substantial variation in the amino acid sequences encoded by many of the conserved ORFs