Extensively deleted simian immunodeficiency virus (SIV) DNA in macaques inoculated with supercoiled plasmid DNA encoding full-length SIVmac239

Immunotherapy with DNA vaccine and live attenuated rubella/SIV gag vectors plus early ART can prevent SIVmac251 viral rebound in acutely infected rhesus macaques

Anti-retroviral therapy (ART) has been highly successful in controlling HIV replication, reducing viral burden, and preventing both progression to AIDS and viral transmission. Yet, ART alone cannot cure the infection. Even after years of successful therapy, ART withdrawal leads inevitably to viral rebound within a few weeks or months. Our hypothesis: effective therapy must control both the replicating virus pool and the reactivatable latent viral reservoir. To do this, we have combined ART and immunotherapy to attack both viral pools simultaneously. The vaccine regimen consisted of DNA vaccine expressing SIV Gag, followed by a boost with live attenuated rubella/gag vectors. The vectors grow well in rhesus macaques, and they are potent immunogens when used in a prime and boost strategy. We infected rhesus macaques by high dose mucosal challenge with virulent SIVmac251 and waited three days to allow viral dissemination and establishment of a reactivatable viral reservoir before starting ART. While on ART, the control group received control DNA and empty rubella vaccine, while the immunotherapy group received DNA/gag prime, followed by boosts with rubella vectors expressing SIV gag over 27 weeks. Both groups had a vaccine "take" to rubella, and the vaccine group developed antibodies and T cells specific for Gag. Five weeks after the last immunization, we stopped ART and monitored virus rebound. All four control animals eventually had a viral rebound, and two were euthanized for AIDS. One control macaque did not rebound until 2 years after ART release. In contrast, there was only one viral rebound in the vaccine group. Three out of four vaccinees had no viral rebound, even after CD8 depletion, and they remain in drug-free viral remission more than 2.5 years later. The strategy of early ART combined with immunotherapy can produce a sustained SIV remission in macaques and may be relevant for immunotherapy of HIV in humans.

Efficacy of a SHIV 89.6 proviral DNA vaccine against mucosal SIVmac239 challenge

Sixty percent of rhesus macaques infected with virulence attenuated virus SHIV 89.6 are protected from subsequent intravaginal challenge with pathogenic SIVmac239 [Abel K, Compton L, Rourke T, Montefiori D, Lu D, Rothaeusler K, et al. Simian-human immunodeficiency virus SHIV89.6-induced protection against intravaginal challenge with pathogenic SIVmac239 is independent of the route of immunization and is associated with a combination of cytotoxic T-lymphocyte and alpha interferon responses. J Virol 2003;77(5):3099-118; Miller CJ, McChesney MB, Lu X, Dailey PJ, Chutkowski C, Lu D, et al. Rhesus macaques previously infected with simian/human immunodeficiency virus (HIV) are protected from vaginal challenge with pathogenic SIVmac239. J Virol 1997;71(3):1911-21]. Previously, we have shown that inoculation with a proviral plasmid encoding SHIV 89.6 (pMA SHIV-89.6) results in systemic infection that is delayed compared to SHIV 89.6 virus inoculation [Busch M, Lu D, Fritts L, Lifson JD, Miller CJ. Comparison of virology and immunology in SHIV 89.6 proviral DNA and virus-inoculated rhesus macaques. J Med Primatol 2003;32(4-5):240-6]. We now report that, although monkeys inoculated with pMA SHIV-89.6 or SHIV 89.6 virus had similar plasma anti-SIV binding antibody titers and number of anti-SIV IFN-gamma secreting cells on the day of mucosal SIVmac239 challenge, a smaller proportion of monkeys immunized with pMA SHIV-89.6 were protected from vaginal SIVmac239 challenge compared to monkeys immunized using SHIV 89.6 virus. Protected DNA immunized monkeys had stronger anti-SIV IFN-gamma ELISPOT responses in the acute stage post-challenge than unprotected monkeys. Plasma anti-SIV binding antibody titers and PBMC cytokine responses in the acute stages post-challenge were similar in DNA vaccinated-protected and DNA vaccinated-unprotected monkeys. These results suggest that the delay in systemic infection resulting from delivery of SHIV 89.6 as a plasmid decreased the effectiveness of this live attenuated vaccine.

Dual role of prostratin in inhibition of infection and reactivation of human immunodeficiency virus from latency in primary blood lymphocytes and lymphoid tissue

To design strategies to purge latent reservoirs of human immunodeficiency virus type 1 (HIV-1), we investigated mechanisms by which a non-tumor-promoting phorbol ester, prostratin, inhibits infection of CD4(+) T lymphocytes and at the same time reactivates virus from latency. CD4(+) T lymphocytes from primary blood mononuclear cells (PBMC) and in blocks of human lymphoid tissue were stimulated with prostratin and infected with HIV-1 to investigate the effects of prostratin on cellular susceptibility to the virus. The capacity of prostratin to reactivate HIV from latency was tested in CD4(+) T cells harboring preintegrated and integrated latent provirus. Prostratin stimulated CD4(+) T cells in an aberrant way. It induced expression of the activation markers CD25 and CD69 but inhibited cell cycling. HIV-1 uptake was reduced in prostratin-stimulated CD4(+) T PBMC and tissues in a manner consistent with a downregulation of CD4 and CXCR4 receptors in these systems. At the postentry level, prostratin inhibited completion of reverse transcription of the viral genome in lymphoid tissue. However, prostratin facilitated integration of the reverse-transcribed HIV-1 genome in nondividing CD4(+) T cells and facilitated expression of already integrated HIV-1, including latent forms. Thus, while stimulation with prostratin restricts susceptibility of primary resting CD4(+) T cells to HIV infection at the virus cell-entry level and at the reverse transcription level, it efficiently reactivates HIV-1 from pre- and postintegration latency in resting CD4(+) T cells.

Comparison of virology and immunology in SHIV 89.6 proviral DNA and virus-inoculated rhesus macaques

Inoculation of cats, goats and monkeys with plasmids encoding full-length proviral genomes results in persistent lentiviral infections. This system could be used as a method for administration of an attenuated human immunodeficiency virus (HIV) vaccine. Here, we compare the virology and immunology in rhesus macaques inoculated with either simian/human immunodeficiency virus 89.6 (SHIV 89.6) virus or a plasmid containing the SHIV 89.6 proviral genome. There was a delay in appearance of systemic infection in DNA-inoculated animals compared with virus-inoculated animals, but otherwise the pattern of infection was similar. The serum immunoglobulin G anti-simian immunodeficiency virus (SIV) binding antibody response in DNA-inoculated animals was also delayed compared with virus-inoculated animals, but ultimately there was no difference between live virus and DNA-inoculation in the ability to induce the anti-SIV immune responses that were measured. Thus, the data support the concept that plasmid DNA encoding an attenuated virus could be used instead live virus for vaccination.

Truncated forms of human and simian immunodeficiency virus in infected individuals and rhesus macaques are unique or rare quasispecies

Truncated proviruses of variable sizes are present in peripheral blood mononuclear cells (PBMC) of human immunodeficiency virus type 1 (HIV-1)-infected persons and simian immunodeficiency virus (SIV)-infected rhesus macaques. Here, we investigated whether the highly deleted HIV and SIV proviruses are present in infected organisms as multiple copies or whether each truncated provirus is unique. Using end-point dilution, multiple long-distance (LD) DNA PCR assays were run in parallel using DNA extracted from PBMC of seropositive, treatment-naive persons and from lymph nodes of a rhesus monkey inoculated with cloned, full-length SIVmac239 DNA. The PCR products were titrated and mapped. Most truncated proviruses were present in the DNA samples tested as single, nonintegrated molecules that differed from one another in size and/or nucleotide sequence. These results indicate that truncated primate lentiviral sequences found in infected tissues are unique or rare quasispecies that do not replicate significantly.