Adjuvanted HIV-1 vaccine promotes antibody-dependent phagocytic responses and protects against heterologous SHIV challenge.

To augment HIV-1 pox-protein vaccine immunogenicity using a next generation adjuvant, a prime-boost strategy of recombinant modified vaccinia virus Ankara and multimeric Env gp145 was evaluated in macaques with either aluminum (alum) or a novel liposomal monophosphoryl lipid A (MPLA) formulation adsorbed to alum, ALFA. Binding antibody responses were robust and comparable between arms, while antibody-dependent neutrophil and monocyte phagocytotic responses were greatly enhanced by ALFA. Per-exposure vaccine efficacy against heterologous tier 2 SHIV mucosal challenge was 90% in ALFA-adjuvanted males (P = 0.002), while alum conferred no protection. Half of the ALFA-adjuvanted males remained uninfected after the full challenge series, which spanned seven months after the last vaccination. Antibody-dependent monocyte and neutrophil phagocytic responses both strongly correlated with protection. Significant sex differences in infection risk were observed, with much lower infection rates in females than males. In humans, MPLA-liposome-alum adjuvanted gp120 also increased HIV-1-specific phagocytic responses relative to alum. Thus, next-generation liposome-based adjuvants can drive vaccine elicited antibody effector activity towards potent phagocytic responses in both macaques and humans and these responses correlate with protection. Future protein vaccination strategies aiming to improve functional humoral responses may benefit from such adjuvants.

Reduction of peak viremia by an integration-defective SIV proviral DNA vaccine in rhesus macaques.

An integrase-defective SIV (idSIV) vaccine delivered by a DNA prime and viral particle boost approach can suppress viral loads (VLs) during the acute infection stage after intravenous SIVmac239 challenge. This study investigated how idSIV DNA and viral particle immunization alone contributed to the suppression of VLs in Chinese rhesus macaques after SIV challenge. Two macaques were immunized with idSIV DNA five times and two macaques were immunized with idSIV viral particles three times. Cellular and humoral immune responses were measured in the vaccinated macaques after immunization. The VLs and CD4+ T cell counts were monitored for 28 weeks after the intravenous SIVmac239 challenge. The SIV-specific T cell responses were only detected in the DNA-vaccinated macaques. However, binding and neutralizing antibodies against autologous and heterologous viruses were moderately better in macaques immunized with viral particles than in macaques immunized with DNA. After the challenge, the mean peak viremia in the DNA group was 2.3 logs lower than that in the control group, while they were similar between the viral particle immunization and control groups. Similar CD4+ T cell counts were observed among all groups. These results suggest that idSIV DNA immunization alone reduces VLs during acute infection after SIV challenge in macaques and may serve as a key component in combination with other immunogens as prophylactic vaccines.

Oral Coadministration of an Intramuscular DNA/Modified Vaccinia Ankara Vaccine for Simian Immunodeficiency Virus Is Associated with Better Control of Infection in Orally Exposed Infant Macaques.

The majority of human immunodeficiency virus (HIV) type 1 infections in infants are acquired orally through breastfeeding. Toward development of a pediatric HIV vaccine to prevent breastmilk transmission, we tested the efficacy of a simultaneous oral and intramuscular (IM) vaccination regimen for preventing oral simian immunodeficiency virus (SIV) transmission in infant rhesus macaques. Two groups of neonatal macaques were immunized with DNA encoding SIV virus-like particles (DNA-SIV) on weeks 0 and 3, then boosted with modified vaccinia Ankara (MVA) virus expressing SIV antigens (MVA-SIV) on weeks 6 and 9. One group was prime/boosted by the IM route only. Another group was immunized with DNA by both the IM and topical oral (O) buccal routes, and boosted with MVA-SIV by both the IM and sublingual (SL) routes. A third group of control animals received saline by O + IM routes on weeks 0 and 3, and empty MVA by SL + IM routes on weeks 6 and 9. On week 12, infants were orally challenged once weekly with SIVmac251 until infected. The vaccine regimen that included oral routes resulted in reduced peak viremia. The rate of infection acquisition in vaccinated infants was found to be associated with prechallenge intestinal immunoglobulin G (IgG) responses to SIV gp120 and V1V2. Peak viremia was inversely correlated with postinfection intestinal IgG responses to gp120, gp41, and V1V2. These results suggest that codelivery of a pediatric HIV vaccine by an oral route may be superior to IM-only regimens for generating mucosal antibodies and preventing HIV breastmilk transmission in neonates.

Adjuvant-dependent innate and adaptive immune signatures of risk of SIVmac251 acquisition.

A recombinant vaccine containing Aventis Pasteur's canarypox vector (ALVAC)-HIV and gp120 alum decreased the risk of HIV acquisition in the RV144 vaccine trial. The substitution of alum with the more immunogenic MF59 adjuvant is under consideration for the next efficacy human trial. We found here that an ALVAC-simian immunodeficiency virus (SIV) and gp120 alum (ALVAC-SIV + gp120) equivalent vaccine, but not an ALVAC-SIV + gp120 MF59 vaccine, was efficacious in delaying the onset of SIVmac251 in rhesus macaques, despite the higher immunogenicity of the latter adjuvant. Vaccine efficacy was associated with alum-induced, but not with MF59-induced, envelope (Env)-dependent mucosal innate lymphoid cells (ILCs) that produce interleukin (IL)-17, as well as with mucosal IgG to the gp120 variable region 2 (V2) and the expression of 12 genes, ten of which are part of the RAS pathway. The association between RAS activation and vaccine efficacy was also observed in an independent efficacious SIV-vaccine approach. Whether RAS activation, mucosal ILCs and antibodies to V2 are also important hallmarks of HIV-vaccine efficacy in humans will require further studies.

Limited impact of passive non-neutralizing antibody immunization in acute SIV infection on viremia control in rhesus macaques.

BACKGROUND: Antiviral antibodies, especially those with neutralizing activity against the incoming strain, are potentially important immunological effectors to control human immunodeficiency virus (HIV) infection. While neutralizing activity appears to be central in sterile protection against HIV infection, the entity of inhibitory mechanisms via HIV and simian immunodeficiency virus (SIV)-specific antibodies remains elusive. The recent HIV vaccine trial RV144 and studies in nonhuman primate models have indicated controversial protective efficacy of HIV/SIV-specific non-neutralizing binding antibodies (non-NAbs). While reports on HIV-specific non-NAbs have demonstrated virus inhibitory activity in vitro, whether non-NAbs could also alter the pathogenic course of established SIV replication in vivo, likewise via neutralizing antibody (NAb) administration, has been unclear. Here, we performed post-infection passive immunization of SIV-infected rhesus macaques with polyclonal SIV-specific, antibody-dependent cell-mediated viral inhibition (ADCVI)-competent non-NAbs. METHODS AND FINDINGS: Ten lots of polyclonal immunoglobulin G (IgG) were prepared from plasma of ten chronically SIVmac239-infected, NAb-negative rhesus macaques, respectively. Their binding capacity to whole SIVmac239 virions showed a propensity similar to ADCVI activity. A cocktail of three non-NAb lots showing high virion-binding capacity and ADCVI activity was administered to rhesus macaques at day 7 post-SIVmac239 challenge. This resulted in an infection course comparable with control animals, with no significant difference in set point plasma viral loads or immune parameters. CONCLUSIONS: Despite virus-specific suppressive activity of the non-NAbs having been observed in vitro, their passive immunization post-infection did not result in SIV control in vivo. Virion binding and ADCVI activity with lack of virus neutralizing activity were indicated to be insufficient for antibody-triggered non-sterile SIV control. More diverse effector functions or sophisticated localization may be required for non-NAbs to impact HIV/SIV replication in vivo.

Working group consultation: alloimmunity as a vaccine approach against HIV/AIDS: National Institutes of Health Meeting Report, May 24, 2012.

Alloimmunization vaccine strategies propose to avoid the problem of the extreme antigenic variability of human immunodeficiency virus (HIV) by instead focusing on the cellular antigens incorporated into HIV virions as they bud from infected cells. This report summarizes a Consultation meeting convened by the National Institute of Allergy and Infectious Diseases, National Institutes of Health on May 24, 2012. The objectives of the meeting were to (1) reach a consensus on the essential questions surrounding alloimmunization as a strategy for vaccine design against HIV, and (2) determine the experimental elements that might be needed for addressing these questions in an optimized pilot framework nonhuman primate (NHP) protocol for allogeneic immunization. The Consultation revisited the rationale and concerns of vaccination to induce allogeneic immunity, one of the most potent natural immune responses. The panelists' consensus was that a carefully designed skin graft transplant pilot experiment, in major histocompatibility complex (MHC) disparate male Mauritian cynomolgus macaques (MCM; Macaca fascicularis), would be useful for initially evaluating if alloimmunization results in an effective or even a partially effective safe AIDS vaccine. A successful NHP study for allogeneic immunization would provide further opportunities to explore vaccine-elicited immune and genetic correlates of protection against the acquisition of viral infection.

Lessons in nonhuman primate models for AIDS vaccine research: from minefields to milestones.

Nonhuman primate (NHP) disease models for AIDS have made important contributions to the search for effective vaccines for AIDS. Viral diversity, persistence, capacity for immune evasion, and safety considerations have limited development of conventional approaches using killed or attenuated vaccines, necessitating the development of novel approaches. Here we highlight the knowledge gained and lessons learned in testing vaccine concepts in different virus/NHP host combinations.

Dominant induction of vaccine antigen-specific cytotoxic T lymphocyte responses after simian immunodeficiency virus challenge.

Cytotoxic T lymphocyte (CTL) responses are crucial for the control of human and simian immunodeficiency virus (HIV and SIV) replication. A promising AIDS vaccine strategy is to induce CTL memory resulting in more effective CTL responses post-viral exposure compared to those in natural HIV infections. We previously developed a CTL-inducing vaccine and showed SIV control in some vaccinated rhesus macaques. These vaccine-based SIV controllers elicited vaccine antigen-specific CTL responses dominantly in the acute phase post-challenge. Here, we examined CTL responses post-challenge in those vaccinated animals that failed to control SIV replication. Unvaccinated rhesus macaques possessing the major histocompatibility complex class I haplotype 90-088-Ij dominantly elicited SIV non-Gag antigen-specific CTL responses after SIV challenge, while those induced with Gag-specific CTL memory by prophylactic vaccination failed to control SIV replication with dominant Gag-specific CTL responses in the acute phase, indicating dominant induction of vaccine antigen-specific CTL responses post-challenge even in non-controllers. Further analysis suggested that prophylactic vaccination results in dominant induction of vaccine antigen-specific CTL responses post-viral exposure but delays SIV non-vaccine antigen-specific CTL responses. These results imply a significant influence of prophylactic vaccination on CTL immunodominance post-viral exposure, providing insights into antigen design in development of a CTL-inducing AIDS vaccine.

Estrategias de inmunización en niños VIH positivos / Immunizing HIV-infected children after immune reconstitution with antiretroviral therapy

Introducción: La inmunización de los niños VIH positivos es un campo de rápida evolución ya que la terapia antirretroviral(TAR) se encuentra más fácilmente disponible en los países en vías de desarrollo. Se ha descrito adecuadamente que los pacientes infectados por el VIH presentan respuestas inmunogénicas subóptimas frente a las vacunas pediátricas de rutina. Métodos: Este artículo es una revisión de la bibliografía publicada en los últimos 10 años acerca de la inmunización de los niños que reciben TAR, con énfasis específico en las reinmunizaciones. Resultados y discusión: La revacunación es claramente necesaria, pero no se han establecido con claridad los métodos óptimos. Existen también dos grupos diferentes de niños a considerar: los que iniciaron la TAR durante la primera infancia, cuando se administran las primeras series de vacunas, y aquellos que inician la TAR después del primer año de vida. Las investigaciones recientes sugieren que el inicio temprano de la TAR durante la infancia preserva la función de los linfocitos B y la memoria de la respuesta a las vacunas, lo que resulta en protección prolongada. No se definió la necesidad de las dosis de refuerzo después de la inmunización primaria en estos niños. Aquellos que iniciaron la TAR después del primer año de vida requieren repetir las series de vacunas iniciales o múltiples dosis de refuerzo debido a deficiencias inmunitarias funcionales. Conclusiones: La reinmunización dirigida sobre la base de la cuantificación de los títulos de anticuerpos, de los análisis de la proliferación de linfocitos, o ambos, no es posible en países con recursos limitados. En estos contextos, deberían proponerse normativas de reinmunización de rutina sin una pesquisa de laboratorio previa.

Early events in sexual transmission of HIV and SIV and opportunities for interventions.

To constrain the growth of the HIV/AIDS pandemic and ultimately end it, effective measures must be developed to prevent sexual mucosal transmission, the major route by which new infections are acquired. I review sexual mucosal transmission of HIV and SIV, with a focus on vaginal transmission in the SIV rhesus macaque animal model, and the evidence for small founder populations of infected cells and the local expansion at the portal of entry necessary to establish systemic infection. These early events represent windows of maximum opportunity for interventions to prevent systemic infection. I highlight the paradoxical role the innate immune response plays in actually facilitating transmission, and a novel microbicide strategy that targets this innate response to prevent systemic infection, and I conclude with an agenda for future research that emphasizes mucosal immunology, virology and pathogenesis studies at each anatomic site of entry.

Vaccination reduces simian-human immunodeficiency virus sequence reversion through enhanced viral control.

It has been suggested that vaccination prior to infection may direct the mutational evolution of human immunodeficiency virus type 1 (HIV-1) to a less fit virus, resulting in an attenuated course of disease. The present study was initiated to explore whether prior immunization might prevent the reversion of the virus to the wild-type form. Mamu-A*01 monkeys were vaccinated to generate a cytotoxic T-lymphocyte response to the immunodominant Gag p11C epitope and were then challenged with a cloned pathogenic CXCR4-tropic simian-human immunodeficiency virus (SHIV) expressing a mutant Gag p11C sequence (Δp11C SHIV). The epitopic and extraepitopic compensatory mutations introduced into gag of Δp11C SHIV resulted in attenuated replicative capacity and eventual reversions to the wild-type Gag p11C sequence in naïve rhesus monkeys. However, in vaccinated rhesus monkeys, no reversions of the challenge virus were observed, an effect that may have been a consequence of significantly decreased viral replication rather than a redirection of the mutational evolution of the virus. These findings highlight the multifactorial pressures that affect the evolution of primate immunodeficiency viruses.

Partial protection against SIV challenge by vaccination of adenovirus and MVA vectors in rhesus monkeys.

This study explores the effect of priming rhesus monkeys with an Ad5/35 vector expressing simian immunodeficiency virus (SIV) gag and gp120, and then boosting the animals with an modified vaccinia virus Ankara (MVA) vector encoding the same antigens after a 2-month interval. The animals were intravenously challenged with 100 TCID50 of highly pathogenic SIVmac239 virus 2 months after the booster vaccination. The priming vaccination induced robust SIV-specific cell-mediated and humoral immune responses, and boosting further enhanced the cellular immunity. Vaccination reduced peak and long-term viral loads by 1-2 logs for a period of >6 months, as reflected by a reduction in both the SIV RNA and DNA levels. Of considerable interest, the immunized monkeys did not suffer from loss of CD4 T cells, particularly central memory CD4 T cells. These results demonstrate that prophylactic vaccination with Ad5/35 followed by MVA reduces viral replication and prevents CD4 T-cell loss, and that these effects may decrease the likelihood of disease progression.

Adenovirus 5- and 35-based immunotherapy enhances the strength but not breadth or quality of immunity during chronic SIV infection.

Heterologous adenovirus-based vectors hold promise as preventative HIV vaccines but their capacity to induce effective T-cell immunity in established infection has not been explored. We vaccinated rhesus macaques chronically infected with SIVmac251 and undergoing antiretroviral therapy (ART) with human adenovirus serotype 5-based vectors expressing SIV Gag, Env, and Nef with and without IL-15 and evaluated vaccine immunogenicity. Vaccination increased Ag-specific T cells 20-fold but did not expand the breadth of epitopes recognized or the quality of response, as the majority of CD8(+) and CD4(+) T cells produced only one cytokine irrespective of vaccination. Immunization transiently restored blood CD4(+) central memory T cells (Tcm) and boosted CD4(+) and CD8(+) Tcm and effector cell responses but did not prevent virus rebound upon cessation of ART. Boosting with human adenovirus serotype 35-based vectors during a second ART cycle increased Ag-specific T cells to 50-fold above pre-vaccination levels and boosted CD4(+) Tcm numbers but did not expand the breadth or quality of immunity or control virus levels following drug discontinuation. The number of blood CD4(+) Tcm correlated positively with complexity of T-cell responses and negatively with virus load, suggesting that more complete restoration of this subset through vaccination would be beneficial.

Vector-mediated gene transfer engenders long-lived neutralizing activity and protection against SIV infection in monkeys.

The key to an effective HIV vaccine is development of an immunogen that elicits persisting antibodies with broad neutralizing activity against field strains of the virus. Unfortunately, very little progress has been made in finding or designing such immunogens. Using the simian immunodeficiency virus (SIV) model, we have taken a markedly different approach: delivery to muscle of an adeno-associated virus gene transfer vector expressing antibodies or antibody-like immunoadhesins having predetermined SIV specificity. With this approach, SIV-specific molecules are endogenously synthesized in myofibers and passively distributed to the circulatory system. Using such an approach in monkeys, we have now generated long-lasting neutralizing activity in serum and have observed complete protection against intravenous challenge with virulent SIV. In essence, this strategy bypasses the adaptive immune system and holds considerable promise as a unique approach to an effective HIV vaccine.

Effect of therapeutic immunization using Ad5/35 and MVA vectors on SIV infection of rhesus monkeys undergoing antiretroviral therapy.

Antiretroviral therapy (ART) effectively slows the progression of AIDS. However, drug resistance and/or toxicity can limit the utility of ART in many patients. In this study, we assessed whether a viral vector-based vaccine can be used as a therapeutic vaccine in simian immunodeficiency virus (SIV)-infected monkeys. The effect of vaccinating SIVmac239-infected rhesus monkeys with an SIV gag and gp120-expressing adenovirus (Ad) vector vaccine and a modified vaccinia Ankara (MVA) vaccine was explored while being treated with ART. Rhesus monkeys were intravenously infected with 10 and 1000 TCID(50) (50% tissue culture infectious dose) of SIVmac239. Two months after SIV infection, the monkeys received a 4-month treatment with ART. Some of the monkeys were immunized with adenovirus-based vaccine and MVA-based vaccine with 2 months interval during ART. Viral load, CD4 count and SIV-specific immune responses were observed for 7 months after interruption of ART. The vaccinated animals had higher (i) CD4 counts, (ii) SIV-specific cell-mediated immune responses and (iii) anti-SIV-neutralizing antibody (Ab) titers than monkeys treated with ART alone. More importantly, the vaccination significantly reduced the SIV RNA load from animals infected with a low dose of SIV (10 TCID(50)). The anti-SIV cell-mediated and humoral responses induced by the vaccination was inversely correlated with a reduction in SIV viral load and positively correlated with an increase in CD4(+) T cell counts. These results suggest that vaccination can improve antiviral cell-mediated and humoral immunity, which may contribute to controlling viral replication.

Immunity in natural SIV infections.

In stark contrast to human immunodeficiency virus (HIV)-infected individuals who, if left untreated, almost invariably progress to acquired immunodeficiency syndrome (AIDS), natural hosts for the simian immunodeficiency viruses (SIV) remain asymptomatic throughout the course of infection. This observation represents one of the main unresolved puzzles of AIDS research, particularly if one considers that natural SIV infections are characterized by chronically high levels of viraemia as well as intrinsic virus cytopathicity comparable with that of HIV. In this review, I discuss the basic immunological features of natural, nonpathogenic SIV infections, the evidence suggesting that attenuated, rather than extraordinarily strong, immune responses to the virus may favour their benign course, and the implications of these findings in terms of HIV therapy and vaccines.

Therapeutic vaccination with simian immunodeficiency virus (SIV)-DNA + IL-12 or IL-15 induces distinct CD8 memory subsets in SIV-infected macaques.

DNA vaccination is an invaluable approach for immune therapy in that it lacks vector interference and thus permits repeated vaccination boosts. However, by themselves, DNA-based vaccines are typically poor inducers of Ag-specific immunity in humans and non-human primates. Cytokines, such as IL-12 and IL-15, have been shown to be potent adjuvants for the induction and maintenance of cellular immune responses, in particular during HIV infection. In this study, we examined the ability of therapeutic vaccination with SIV-DNA+IL-12 or IL-15 as molecular adjuvants to improve DNA vaccine potency and to enhance memory immune responses in SIV-infected macaques. Our results demonstrate that incorporating IL-12 into the vaccine induces SIV-specific CD8 effector memory T cell (T(EM)) functional responses and enhances the capacity of IFN-gamma-producing CD8 T(EM) cells to produce TNF. Lower levels of PD-1 were expressed on T cells acquiring dual function upon vaccination as compared with mono-functional CD8 T(EM) cells. Finally, a boost with SIV-DNA+IL-15 triggered most T cell memory subsets in macaques primed with either DNA-SIV or placebo but only CD8 T(EM) in macaques primed with SIV-DNA+IL-12. These results indicate that plasmid IL-12 and IL-15 cytokines represent a significant addition to enhance the ability of therapeutic DNA vaccines to induce better immunity.

Selective induction of cell-mediated immunity and protection of rhesus macaques from chronic SHIV(KU2) infection by prophylactic vaccination with a conserved HIV-1 envelope peptide-cocktail.

Infection of Indian-origin rhesus macaques by the simian human immunodeficiency virus (SHIV) is considered to be a suitable preclinical model for directly testing efficacy of vaccine candidates based on the HIV-1 envelope. We used this model for prophylactic vaccination with a peptide-cocktail comprised of highly conserved HIV-1 envelope sequences immunogenic/antigenic in macaques and humans. Separate groups of macaques were immunized with the peptide-cocktail by intravenous and subcutaneous routes using autologous dendritic cells (DC) and Freund's adjuvant, respectively. The vaccine elicited antigen specific IFN-gamma-producing cells and T-cell proliferation, but not HIV-neutralizing antibodies. The vaccinated animals also exhibited efficient cross-clade cytolytic activity against target cells expressing envelope proteins corresponding to HIV-1 strains representative of multiple clades that increased after intravenous challenge with pathogenic SHIV(KU2). Virus-neutralizing antibodies were either undetectable or present only transiently at low levels in the control as well as vaccinated monkeys after infection. Significant control of plasma viremia leading to undetectable levels was achieved in majority of vaccinated monkeys compared to mock-vaccinated controls. Monkeys vaccinated with the peptide-cocktail using autologous DC, compared to Freund's adjuvant, and the mock-vaccinated animals, showed significantly higher IFN-gamma production, higher levels of vaccine-specific IFN-gamma producing CD4(+) cells and significant control of plasma viremia. These results support DC-based vaccine delivery and the utility of the conserved HIV-1 envelope peptide-cocktail, capable of priming strong cell-mediated immunity, for potential inclusion in HIV vaccination strategies.

Therapeutic immunization with Modified Vaccinia Virus Ankara (MVA) vaccines in SIV-infected rhesus monkeys undergoing antiretroviral therapy.

BACKGROUND: The long-term benefits of highly active antiretroviral therapy in HIV-infected patients are limited by emergence of drug-resistant variants and side effects. Therefore, we studied the concept of therapeutic immunization in 18 rhesus monkeys infected with a highly pathogenic simian immunodeficiency virus (SIV) swarm. METHODS: Monkeys were treated with the reverse transcriptase inhibitor (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA) for 19 weeks starting 10 days after infection. After suppression of viremia, one group of monkeys was immunized with recombinant modified vaccinia virus Ankara (MVA) vectors expressing gag-pol and env. A second group received MVA vectors expressing the regulatory genes tat, rev and nef, while a third group was not immunized. RESULTS: Immunization with gag-pol and env expressing MVA enhanced SIV antibody titers. Following discontinuation of PMPA treatment, a rebound in viral load was observed. However, in three of six monkeys immunized with MVA gag-pol and MVA env, and two of six monkeys immunized MVA expressing regulatory genes set point RNA levels were below or close to a threshold level of 10(4) RNA copies/ml, while only one of six unvaccinated monkeys maintained such low RNA levels. CONCLUSIONS: Although a subset of animals seem to benefit from therapeutic immunization with MVA vectors, the difference in set point RNA levels between the groups did not reach statistical significance.