Protection against Mucosal Simian Immunodeficiency Virus SIV(mac251) Challenge by Using Replicating Adenovirus-SIV Multigene Vaccine Priming and Subunit Boosting

Whereas several recent AIDS vaccine strategies have protected rhesus macaques against a pathogenic simian/human immunodeficiency virus (SHIV)(89.6P) challenge, similar approaches have provided only modest, transient reductions in viral burden after challenge with virulent, pathogenic SIV, which is more representative of HIV infection of people. We show here that priming with replicating adenovirus recombinants encoding SIV env/rev, gag, and/or nef genes, followed by boosting with SIV gp120 or an SIV polypeptide mimicking the CD4 binding region of the envelope, protects rhesus macaques from intrarectal infection with the highly pathogenic SIV(mac251). Using trend analysis, significant reductions in acute-phase and set point viremia were correlated with anti-gp120 antibody and cellular immune responses, respectively. Within immunization groups exhibiting significant protection, a subset (39%) of macaques have exhibited either no viremia, cleared viremia, or controlled viremia at the threshold of detection, now more than 40 weeks postchallenge. This combination prime-boost strategy, utilizing replication competent adenovirus, is a promising alternative for HIV vaccine development

Comparison of Vaccine Strategies Using Recombinant env–gag–pol MVA with or without an Oligomeric Env Protein Boost in the SHIV Rhesus Macaque Model

Rhesus macaques were immunized with a replication-deficient vaccinia virus (MVA) expressing human immunodeficiency virus type 1 89.6 envelope (env) and SIV gagpol (MVA/SHIV89.6) with or without a protein boost consisting of soluble 89.6 env (gp140). Immunization with MVA/SHIV89.6 alone elicited binding antibodies in all animals and neutralizing antibodies in 5 of 15 animals. Both types of antibodies were enhanced by protein boosting. In addition, CD8 cells exhibiting CM9 tetramer binding were detected in the subset of animals that were Mamu-A*01 positive. Animals were challenged intravenously with either SHIV-89.6 (Study 1) or the more pathogenic derivative SHIV-89.6P (Study 2). In Study 1, all control and vaccinated animals except one became infected. However, the levels of viremia were as follows: controls > rMVA alone > rMVA + protein. The differences were statistically significant between immunized and control groups but not between the two immunized groups. In Study 2, all animals became infected; however, the vaccinated group exhibited a 5-fold reduction in peak viremia and a 10-fold reduction in the postacute phase viremia in comparison to the controls. All of the controls required euthanasia by 10 months after challenge. A relationship between vaccine-induced antibody titers and reduction in virus burden was observed in both studies. Thus, immunization with MVA/SHIV89.6 alone or with a protein boost stimulated both arms of the immune system and resulted in significant control of viremia and delayed progression to disease after challenge with SHIV-89.6P

Rhesus Macaque Resistance to Mucosal Simian Immunodeficiency Virus Infection Is Associated with a Postentry Block in Viral Replication

Elucidation of the host factors which influence susceptibility to human immunodeficiency virus or simian immunodeficiency virus (SIV) infection and disease progression has important theoretical and practical implications. Rhesus macaque 359, a vaccine control animal, resisted two successive intravaginal challenges with SIV(mac251) and failed to seroconvert. Here, after an additional intrarectal SIVmac32H challenge, macaque 359 remained highly resistant to infection. Viral RNA (10(6) copies/ml) was observed in plasma only at week 2 postchallenge. Virus isolation and proviral DNA were positive only once at week eight postchallenge. The animal remained seronegative and cleared SIV in vivo. Its blood and lymph node cells obtained at 49 weeks after intrarectal challenge did not transmit SIV to a naive macaque. We found that the resistance of macaque 359 to SIV infection was not due to a high level of CD8(+) suppressor activity but to an inherent resistance of its CD4(+) T cells. To elucidate the basis for the unusually strong resistance of macaque 359 to SIV infection in vivo and in vitro, we investigated early events of viral infection and replication in CD4(+) cells of macaque 359, including expression and mutation screening of SIV coreceptors and analysis of viral entry and reverse transcription. Mutation screening revealed no genetic alteration in SIV coreceptors. PCR analysis revealed a significant delay in production of early in vitro reverse transcription intermediates in macaque 359 cells compared to susceptible controls, but cell fusion assays showed that SIV entered the CD4(+) CCR5(+) cells of macaque 359 as readily as cells of macaques susceptible to SIV infection. Our results suggest that the resistance of macaque 359 to SIV infection is due to a postentry block in viral replication and implicate a cellular inhibitory mechanism in its CD4(+) T cells. Identification of this host mechanism will help further elucidate the biochemistry of reverse transcription and may suggest therapeutic strategies. Determining the prevalence of this host resistance mechanism among macaques may lead to better design of SIV pathogenesis and vaccine studies

Improved Protection of Rhesus Macaques against Intrarectal Simian Immunodeficiency Virus SIV(mac251) Challenge by a Replication-Competent Ad5hr-SIVenv/rev and Ad5hr-SIVgag Recombinant Priming/gp120 Boosting Regimen

In this study we investigated the ability of a replication-competent Ad5hr-SIVenv/rev and Ad5hr-SIVgag recombinant priming/gp120 boosting regimen to induce protective immunity in rhesus macaques against pathogenic simian immunodeficiency virus(mac251). Immunization of macaques by two sequential administrations of the same recombinants by the same route resulted in boosting and persistence of SIV-specific cellular immune responses for 42 weeks past the initial immunization. Anti-SIV gp120 immunoglobulin G (IgG) and IgA antibodies were induced in secretory fluids, and all macaques exhibited serum neutralizing antibody activity. After intrarectal SIV(mac251) challenge, all of the macaques became infected. However, relative protection, as assessed by statistically significant lower SIV viral loads in plasma at both acute infection and set point, was observed in 8 out of 12 immunized non-Mamu-A∗01 animals. Elevated mean cellular immune responses to Gag and Env, neutralizing antibody activity, and IgG and IgA binding antibody levels were observed in the eight protected macaques. Statistically significant correlations with protective outcome were observed for cellular immune responses to SIV Env and Gag and for SIV gp120-specific IgG antibodies in nasal and vaginal fluids. Two macaques that exhibited the greatest and most persistent viremia control also exhibited strong CD8(+) T-cell antiviral activity. The results suggest that a spectrum of immune responses may be necessary for adequate control of viral replication and disease progression and highlight a potential role for nonneutralizing antibodies at mucosal sites