Prior infection with a nonpathogenic chimeric simian-human immunodeficiency virus does not efficiently protect macaques against challenge with simian immunodeficiency virus.

Prior infection with a nef-deleted simian immunodeficiency virus (SIV) protects macaques not only against a homologous pathogenic SIV challenge but also against challenge with a chimeric SIV expressing a human immunodeficiency virus type 1 env gene (SHIV). Since this SHIV is itself nonpathogenic, we sought to explore the use of a nonpathogenic SHIV as a live, attenuated AIDS virus vaccine. Four cynomolgus monkeys infected for greater than 600 days with a chimeric virus composed of SIVmac 239 expressing the human immunodeficiency virus type 1 HXBc2 env, tat, and rev genes were challenged intravenously with 100 animal infectious doses of the J5 clone of SIVmac 32H, an isolate derived by in vivo passage of SIVmac 251. Three of the four monkeys became infected with SIVmac. This observation underlines the difficulty, even with a live virus vaccine, in protecting against an AIDS virus infection.     

Depo-Provera abrogates attenuated lentivirus-induced protection in male rhesus macaques challenged intravenously with pathogenic SIVmac239

BACKGROUND: Progesterone administration prior to intravaginal challenge with pathogenic SIVmac239 decreases the protective efficacy of live attenuated vaccines in rhesus macaques. METHODS: To determine if progesterone alters the efficacy of live attenuated vaccines through local or systemic effects, seven male rhesus macaques were immunized with SHIV89.6 and then challenged intravenously with SIVmac239. Three of these animals were treated with Depo-Provera 30 days prior to the SIV challenge. RESULTS: The SHIV animals had significantly lower plasma viral RNA levels than the unimmunized control monkeys, but the Depo-Provera treated, SHIV-immunized animals did not. Despite the lack of protection, the Depo-Provera SHIV animals had strong SIV specific T-cell responses. However, altered patterns of NK frequency and CD38 T-cell expression prior to SIV challenge were observed in Depo-Provera SHIV animals. CONCLUSIONS: Depo-Provera eliminates live-attenuated lentivirus vaccine efficacy in male rhesus monkeys through systemic effects on antiviral immunity and/or viral replication.     

Immune mechanisms associated with protection from vaginal SIV challenge in rhesus monkeys infected with virulence-attenuated SHIV 89.6

Although live-attenuated human immunodeficiency virus-1 (HIV) vaccines may never be used clinically, these vaccines have provided the most durable protection from intravenous (IV) challenge in the simian immunodeficiency virus (SIV)/rhesus macaque model. Systemic infection with virulence attenuated-simian-human immunodeficiency virus (SHIV) 89.6 provides protection against vaginal SIV challenge. This paper reviews the findings related to the innate and adaptive immune responses and the role of inflammation associated with protection in the SHIV 89.6/SIVmac239 model. By an as yet undefined mechanism, most monkeys vaccinated with live-attenuated SHIV 89.6 mounted effective anti-viral CD8+ T cell responses while avoiding the self-destructive inflammatory cycle found in the lymphoid tissues of unprotected and unvaccinated monkeys.     

Early potent protection against heterologous SIVsmE660 challenge following live attenuated SIV vaccination in Mauritian cynomolgus macaques

Background

Live attenuated simian immunodeficiency virus (SIV) vaccines represent the most effective means of vaccinating macaques against pathogenic SIV challenge. However, thus far, protection has been demonstrated to be more effective against homologous than heterologous strains. Immune correlates of vaccine-induced protection have also been difficult to identify, particularly those measurable in the peripheral circulation.

Methodology/Principal Findings

Here we describe potent protection in 6 out of 8 Mauritian-derived cynomolgus macaques (MCM) against heterologous virus challenge with the pathogenic, uncloned SIVsmE660 viral stock following vaccination with live attenuated SIVmac251/C8. MCM provided a characterised host genetic background with limited Major Histocompatibility Complex (MHC) and TRIM5α allelic diversity. Early protection, observed as soon as 3 weeks post-vaccination, was comparable to that of 20 weeks vaccination. Recrudescence of vaccine virus was most pronounced in breakthrough cases where simultaneous identification of vaccine and challenge viruses by virus-specific PCR was indicative of active co-infection. Persistence of the vaccine virus in a range of lymphoid tissues was typified by a consistent level of SIV RNA positive cells in protected vaccinates. However, no association between MHC class I /II haplotype or TRIM5α polymorphism and study outcome was identified.

Conclusion/Significance

This SIV vaccine study, conducted in MHC-characterised MCM, demonstrated potent protection against the pathogenic, heterologous SIVsmE660 challenge stock after only 3 weeks vaccination. This level of protection against this viral stock by intravenous challenge has not been hitherto observed. The mechanism(s) of protection by vaccination with live attenuated SIV must account for the heterologous and early protection data described in this study, including those which relate to the innate immune system.     

Highly attenuated vaccine strains of simian immunodeficiency virus protect against vaginal challenge: inverse relationship of degree of protection with level of attenuation

Three different deletion mutants of simian immunodeficiency virus (SIV) that vary in their levels of attenuation were tested for the ability to protect against mucosal challenge with pathogenic SIV. Four female rhesus monkeys were vaccinated by intravenous inoculation with SIVmac239Delta3, four with SIVmac239Delta3X, and four with SIVmac239Delta4. These three vaccine strains exhibit increasing levels of attenuation: Delta3 < Delta3X 相似文献   

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

Attenuated primate lentivirus vaccines provide the most consistent protection against challenge with pathogenic simian immunodeficiency virus (SIV). Thus, they provide an excellent model to examine the influence of the route of immunization on challenge outcome and to study vaccine-induced protective anti-SIV immune responses. In the present study, rhesus macaques were immunized with live nonpathogenic simian-human immunodeficiency virus (SHIV) 89.6 either intravenously or mucosally (intranasally or intravaginally) and then challenged intravaginally with pathogenic SIVmac239. The route of immunization did not affect mucosal challenge outcome after a prolonged period of systemic infection with the nonpathogenic vaccine virus. Further, protection from the SIV challenge was associated with the induction of multiple host immune effector mechanisms. A comparison of immune responses in vaccinated-protected and vaccinated-unprotected animals revealed that vaccinated-protected animals had higher frequencies of SIV Gag-specific cytotoxic T lymphocytes and gamma interferon (IFN-gamma)-secreting cells during the acute phase postchallenge. Vaccinated-protected animals also had a more pronounced increase in peripheral blood mononuclear cell IFN-alpha mRNA levels than did the vaccinated-unprotected animals in the first few weeks after challenge. Thus, innate as well as cellular anti-SIV immune responses appeared to contribute to the SHIV89.6-induced protection against intravaginal challenge with pathogenic SIVmac239.     

Vaccine protection by a triple deletion mutant of simian immunodeficiency virus.

Twelve rhesus monkeys were vaccinated with SIVmac316 delta nef (lacking nef sequences), and 12 were vaccinated with SIVmac239 delta3 (lacking nef, vpr, and upstream sequences in U3). SIVmac316 and SIVmac239 differ by only eight amino acids in the envelope; these changes render SIVmac316 highly competent for replication in macrophages. Seventeen of the animals developed persistent infections with the vaccine viruses. Seven of the 24 vaccinated animals, however, developed infections that were apparently transient in nature. Six of these seven yielded virus from peripheral blood when tested at weeks 2 and/or 3, three of the seven had transient antibody responses, but none of the seven had persisting antibody responses. The 24 monkeys were challenged in groups of four with 10 rhesus monkey infectious doses of wild-type, pathogenic SIVmac251 at weeks 8, 20, and 79 following receipt of vaccine. None of the seven with apparently transient infections with vaccine virus were protected upon subsequent challenge. Analysis of cell-associated viral loads, CD4+ cell counts, and viral gene sequences present in peripheral blood in the remainder of the monkeys following challenge allowed a number of conclusions. (i) There was a trend toward increased protection with length of time of vaccination. (ii) Solid vaccine protection was achieved by 79 weeks with the highly attenuated SIV239 delta3. (iii) Solid long-term protection was achieved in at least two animals in the absence of complete sterilizing immunity. (iv) Genetic backbone appeared to influence protective capacity; animals vaccinated with SIV239 delta3 were better protected than animals receiving SIV316 delta nef. This better protection correlated with increased levels of the replicating vaccine strain. (v) The titer of virus-neutralizing activity in serum on the day of challenge correlated with protection when measured against a primary stock of SIVmac251 but not when measured against a laboratory-passaged stock. The level of binding antibodies to whole virus by enzyme-linked immunosorbent assay also correlated with protection.     

A combination DNA and attenuated simian immunodeficiency virus vaccine strategy provides enhanced protection from simian/human immunodeficiency virus-induced disease

Among the most effective vaccine candidates tested in the simian immunodeficiency virus (SIV)/macaque system, live attenuated viruses have been shown to provide the best protection from challenge. To investigate if preimmunization would increase the level of protection afforded by live attenuated SIVmac239Deltanef (Deltanef), macaques were given two priming immunizations of DNA encoding SIV Gag and Pol proteins, with control macaques receiving vector DNA immunizations. In macaques receiving the SIV DNA inoculation, SIV-specific cellular but not humoral responses were readily detectable 2 weeks after the second DNA inoculation. Following boosting with live attenuated virus, control of Deltanef replication was superior in SIV-DNA-primed macaques versus vector-DNA-primed macaques and was correlated with higher levels of CD8+/gamma-interferon-positive and/or interleukin-2-positive cells. Challenge with an intravenous inoculation of simian/human immunodeficiency virus (SHIV) strain SHIV89.6p resulted in infection of all animals. However, macaques receiving SIV DNA as the priming immunizations had statistically lower viral loads than control animals and did not develop signs of disease, whereas three of seven macaques receiving vector DNA showed severe CD4+ T-cell decline, with development of AIDS in one of these animals. No correlation of immune responses to protection from disease could be derived from our analyses. These results demonstrate that addition of a DNA prime to a live attenuated virus provided better protection from disease following challenge than live attenuated virus alone.     

Induction of CD8+ cells able to suppress CCR5-tropic simian immunodeficiency virus SIVmac239 replication by controlled infection of CXCR4-tropic simian-human immunodeficiency virus in vaccinated rhesus macaques

Recent recombinant viral vector-based AIDS vaccine trials inducing cellular immune responses have shown control of CXCR4-tropic simian-human immunodeficiency virus (SHIV) replication but difficulty in containment of pathogenic CCR5-tropic simian immunodeficiency virus (SIV) in rhesus macaques. In contrast, controlled infection of live attenuated SIV/SHIV can confer the ability to contain SIV superchallenge in macaques. The specific immune responses responsible for this control may be induced by live virus infection but not consistently by viral vector vaccination, although those responses have not been determined. Here, we have examined in vitro anti-SIV efficacy of CD8+ cells in rhesus macaques that showed prophylactic viral vector vaccine-based control of CXCR4-tropic SHIV89.6PD replication. Analysis of the effect of CD8+ cells obtained at several time points from these macaques on CCR5-tropic SIVmac239 replication in vitro revealed that CD8+ cells in the chronic phase after SHIV challenge suppressed SIV replication more efficiently than those before challenge. SIVmac239 superchallenge of two of these macaques at 3 or 4 years post-SHIV challenge was contained, and the following anti-CD8 antibody administration resulted in transient CD8+ T-cell depletion and appearance of plasma SIVmac239 viremia in both of them. Our results indicate that CD8+ cells acquired the ability to efficiently suppress SIV replication by controlled SHIV infection, suggesting the contribution of CD8+ cell responses induced by controlled live virus infection to containment of HIV/SIV superinfection.     

Influence of Mismatch of Env Sequences on Vaccine Protection by Live Attenuated Simian Immunodeficiency Virus

Vaccine/challenge experiments that utilize live attenuated strains of simian immunodeficiency virus (SIV) in monkeys may be useful for elucidating what is needed from a vaccine in order to achieve protective immunity. Derivatives of SIVmac239 and SIVmac239Δnef were constructed in which env sequences were replaced with those of the heterologous strain E543; these were then used in vaccine/challenge experiments. When challenge occurred at 22 weeks, 10 of 12 monkeys exhibited apparent sterilizing immunity despite a mismatch of Env sequences, compared to 12 of 12 monkeys with apparent sterilizing immunity when challenge virus was matched in its Env sequence. However, when challenge occurred at 6 weeks, 6 of 6 SIV239Δnef-immunized monkeys became superinfected by challenge virus mismatched in its Env sequence (SIV239/EnvE543). These results contrast markedly not only with the results of the week 22 challenge but also with the sterilizing immunity observed in 5 of 5 SIV239Δnef-immunized rhesus monkeys challenged at 5 weeks with SIV239, i.e., with no mismatch of Env sequences. We conclude from these studies that a mismatch of Env sequences in the challenge virus can have a dramatic effect on the extent of apparent sterilizing immunity when challenge occurs relatively early, 5 to 6 weeks after the nef-deleted SIV administration. However, by 22 weeks, mismatch of Env sequences has little or no influence on the degree of protection against challenge virus. Our findings suggest that anti-Env immune responses are a key component of the protective immunity elicited by live attenuated, nef-deleted SIV.     

A formalin inactivated whole SIVmac vaccine in Ribi adjuvant protects against homologous and heterologous SIV challenge.

Eight monkeys were immunized at 0, 4, 9, and 18 weeks with a total of 2 mg of formalin inactivated SIVmac vaccine with Ribi adjuvant. Two weeks after the last booster four immunized monkeys and two controls were challenged with 10 MID50 of live homologous virus SIVmac, and the remaining four vaccinated animals along with two controls were challenged with the heterologous SIVsm strain. All eight vaccinated monkeys resisted the virus challenge, whereas all controls became infected. Three months after the first challenge the monkeys were rechallenged with the same virus strain, without further boosting. Two of four vaccinated monkeys were still resistant to the homologous SIV strain, and three of four monkeys were resistant to the heterologous SIVsm strain. This study demonstrates vaccine induced cross-protection between SIV strains.     

Protection of Macaques with Diverse MHC Genotypes against a Heterologous SIV by Vaccination with a Deglycosylated Live-Attenuated SIV

HIV vaccine development has been hampered by issues such as undefined correlates of protection and extensive diversity of HIV. We addressed these issues using a previously established SIV-macaque model in which SIV mutants with deletions of multiple gp120 N-glycans function as potent live attenuated vaccines to induce near-sterile immunity against the parental pathogenic SIVmac239. In this study, we investigated the protective efficacy of these mutants against a highly pathogenic heterologous SIVsmE543-3 delivered intravenously to rhesus macaques with diverse MHC genotypes. All 11 vaccinated macaques contained the acute-phase infection with blood viral loads below the level of detection between 4 and 10 weeks postchallenge (pc), following a transient but marginal peak of viral replication at 2 weeks in only half of the challenged animals. In the chronic phase, seven vaccinees contained viral replication for over 80 weeks pc, while four did not. Neutralizing antibodies against challenge virus were not detected. Although overall levels of SIV specific T cell responses did not correlate with containment of acute and chronic viral replication, a critical role of cellular responses in the containment of viral replication was suggested. Emergence of viruses with altered fitness due to recombination between the vaccine and challenge viruses and increased gp120 glycosylation was linked to the failure to control SIV. These results demonstrate the induction of effective protective immune responses in a significant number of animals against heterologous virus by infection with deglycosylated attenuated SIV mutants in macaques with highly diverse MHC background. These findings suggest that broad HIV cross clade protection is possible, even in hosts with diverse genetic backgrounds. In summary, results of this study indicate that deglycosylated live-attenuated vaccines may provide a platform for the elucidation of correlates of protection needed for a successful HIV vaccine against diverse isolates.     

Live attenuated lentivirus infection elicits polyfunctional simian immunodeficiency virus Gag-specific CD8+ T cells with reduced apoptotic susceptibility in rhesus macaques that control virus replication after challenge with pathogenic SIVmac239

HIV-specific CD8+ T cells that secrete multiple cytokines in response to Ag stimulation are associated with the control of virus replication during chronic HIV infection. To determine whether the presence of polyfunctional CD8+ T cell responses distinguishes protected and unprotected monkeys in a live attenuated lentivirus model, SIV Gag peptide-specific CD8+ T cell responses of simian HIV (SHIV) 89.6-vaccinated, SIVmac239-challenged rhesus macaques were compared in two monkeys that controlled challenge virus replication and two that did not. The ratio of Bcl-2+ Gag-specific CD8+ T cells to caspase-3+ Gag-specific CD8+ T cells was higher in the vaccinated-protected animals compared with unprotected monkeys. In addition, polyfunctional SIV-specific CD8+ T cells were consistently detected through 12 wk postchallenge in the protected animals but not in the unprotected animals. In the unprotected monkeys, there was an increased frequency of CD8+ T cells expressing markers associated with effector memory T cells. Further, there was increased annexin V expression in central memory T cells of the unprotected animals before challenge. Thus, monkeys that control viral replication after live attenuated SHIV infection have polyfunctional SIV-specific CD8+ T cells with an increased survival potential. Importantly, the differences in the nature of the SIV-specific CD8+ T cell response in the protected and unprotected animals are present during acute stages postchallenge, before different antigenic levels are established. Thus, the polyfunctional capacity and increased survival potential of CD8+ SIV-specific T cells may account for live attenuated, SHIV89.6-mediated protection from uncontrolled SIV replication.     

Role of CD8(+) lymphocytes in control of simian immunodeficiency virus infection and resistance to rechallenge after transient early antiretroviral treatment

Transient antiretroviral treatment with tenofovir, (R)-9-(2-phosphonylmethoxypropyl)adenine, begun shortly after inoculation of rhesus macaques with the highly pathogenic simian immunodeficiency virus (SIV) isolate SIVsmE660, facilitated the development of SIV-specific lymphoproliferative responses and sustained effective control of the infection following drug discontinuation. Animals that controlled plasma viremia following transient postinoculation treatment showed substantial resistance to subsequent intravenous rechallenge with homologous (SIVsmE660) and highly heterologous (SIVmac239) SIV isolates, up to more than 1 year later, despite the absence of measurable neutralizing antibody. In some instances, resistance to rechallenge was observed despite the absence of detectable SIV-specific binding antibody and in the face of SIV lymphoproliferative responses that were low or undetectable at the time of challenge. In vivo monoclonal antibody depletion experiments demonstrated a critical role for CD8(+) lymphocytes in the control of viral replication; plasma viremia rose by as much as five log units after depletion of CD8(+) cells and returned to predepletion levels (as low as <100 copy Eq/ml) as circulating CD8(+) cells were restored. The extent of host control of replication of highly pathogenic SIV strains and the level of resistance to heterologous rechallenge achieved following transient postinoculation treatment compared favorably to the results seen after SIVsmE660 and SIVmac239 challenge with many vaccine strategies. This impressive control of viral replication was observed despite comparatively modest measured immune responses, less than those often achieved with vaccination regimens. The results help establish the underlying feasibility of efforts to develop vaccines for the prevention of AIDS, although the exact nature of the protective host responses involved remains to be elucidated.     

Significant protection against high-dose simian immunodeficiency virus challenge conferred by a new prime-boost vaccine regimen

We constructed vaccine vectors based on live recombinant vesicular stomatitis virus (VSV) and a Semliki Forest virus (SFV) replicon (SFVG) that propagates through expression of the VSV glycoprotein (G). These vectors expressing simian immunodeficiency virus (SIV) Gag and Env proteins were used to vaccinate rhesus macaques with a new heterologous prime-boost regimen designed to optimize induction of antibody. Six vaccinated animals and six controls were then given a high-dose mucosal challenge with the diverse SIVsmE660 quasispecies. All control animals became infected and had peak viral RNA loads of 10(6) to 10(8) copies/ml. In contrast, four of the vaccinees showed significant (P = 0.03) apparent sterilizing immunity and no detectable viral loads. Subsequent CD8(+) T cell depletion confirmed the absence of SIV infection in these animals. The two other vaccinees had peak viral loads of 7 × 10(5) and 8 × 10(3) copies/ml, levels below those of all of the controls, and showed undetectable virus loads by day 42 postchallenge. The vaccine regimen induced high-titer prechallenge serum neutralizing antibodies (nAbs) to some cloned SIVsmE660 Env proteins, but antibodies able to neutralize the challenge virus swarm were not detected. The cellular immune responses induced by the vaccine were generally weak and did not correlate with protection. Although the immune correlates of protection are not yet clear, the heterologous VSV/SFVG prime-boost is clearly a potent vaccine regimen for inducing virus nAbs and protection against a heterogeneous viral swarm.     

High beta-chemokine expression levels in lymphoid tissues of simian/human immunodeficiency virus 89.6-vaccinated rhesus macaques are associated with uncontrolled replication of simian immunodeficiency virus challenge inoculum

Viral suppression by noncytolytic CD8+ T cells, in addition to that by classic antiviral CD8+ cytotoxic T lymphocytes, has been described for human immunodeficiency virus and simian immunodeficiency virus (SIV) infections. However, the role of soluble effector molecules, especially beta-chemokines, in antiviral immunity is still controversial. In an attenuated vaccine model, approximately 60% of animals immunized with simian/human immunodeficiency virus (SHIV) 89.6 and then challenged intravaginally with SIVmac239 controlled viral replication (viral RNA level in plasma, <10(4) copies/ml) and were considered protected (K. Abel, L. Compton, T. Rourke, D. Montefiori, D. Lu, K. Rothaeusler, L. Fritts, K. Bost, and C. J. Miller, J. Virol. 77:3099-3118, 2003). To determine the in vivo importance of beta-chemokine secretion and CD8+-T-cell proliferation in the control of viral replication in this vaccine model, we examined the relationship between viral RNA levels in the axillary and genital lymph nodes of vaccinated, protected (n = 20) and vaccinated, unprotected (n = 11) monkeys by measuring beta-chemokine mRNA levels and protein expression, the frequency of CD8+ T cells expressing beta-chemokines, and the extent of CD8+-T-cell proliferation. Tissues from uninfected (n = 3) and unvaccinated, SIVmac239-infected (n = 9) monkeys served as controls. Axillary and genital lymph nodes from unvaccinated and vaccinated, unprotected monkeys had significantly higher beta-chemokine mRNA expression levels and increased numbers of beta-chemokine-positive cells than did vaccinated, protected animals. Furthermore, the lymph nodes of vaccinated, unprotected monkeys had significantly higher numbers of beta-chemokine(+) CD8+ T cells than did vaccinated, protected monkeys. Lymph nodes from vaccinated, unprotected animals also had significantly more CD8+-T-cell proliferation and marked lymph node hyperplasia than the lymph nodes of vaccinated, protected monkeys. Thus, higher levels of virus replication were associated with increased beta-chemokine secretion and there is no evidence that beta-chemokines contributed to the SHIV89.6-mediated control of viral replication after intravaginal challenge with SIVmac239.     

Temporal Analyses of Virus Replication, Immune Responses, and Efficacy in Rhesus Macaques Immunized with a Live, Attenuated Simian Immunodeficiency Virus Vaccine

Despite evidence that live, attenuated simian immunodeficiency virus (SIV) vaccines can elicit potent protection against pathogenic SIV infection, detailed information on the replication kinetics of attenuated SIV in vivo is lacking. In this study, we measured SIV RNA in the plasma of 16 adult rhesus macaques immunized with a live, attenuated strain of SIV (SIVmac239Δnef). To evaluate the relationship between replication of the vaccine virus and the onset of protection, four animals per group were challenged with pathogenic SIVmac251 at either 5, 10, 15, or 25 weeks after immunization. SIVmac239Δnef replicated efficiently in the immunized macaques in the first few weeks after inoculation. SIV RNA was detected in the plasma of all animals by day 7 after inoculation, and peak levels of viremia (10⁵ to 10⁷ RNA copies/ml) occurred by 7 to 12 days. Following challenge, SIVmac251 was detected in all of the four animals challenged at 5 weeks, in two of four challenged at 10 weeks, in none of four challenged at 15 weeks, and one of four challenged at 25 weeks. One animal immunized with SIVmac239Δnef and challenged at 10 weeks had evidence of disease progression in the absence of detectable SIVmac251. Although complete protection was not achieved at 5 weeks, a transient reduction in viremia (approximately 100-fold) occurred in the immunized macaques early after challenge compared to the nonimmunized controls. Two weeks after challenge, SIV RNA was also reduced in the lymph nodes of all immunized macaques compared with control animals. Taken together, these results indicate that host responses capable of reducing the viral load in plasma and lymph nodes were induced as early as 5 weeks after immunization with SIVmac239Δnef, while more potent protection developed between 10 and 15 weeks. In further experiments, we found that resistance to SIVmac251 infection did not correlate with the presence of antibodies to SIV gp130 and p27 antigens and was achieved in the absence of significant neutralizing activity against the primary SIVmac251 challenge stock.     

Macaques Vaccinated with Simian Immunodeficiency Virus SIVmac239Δnef Delay Acquisition and Control Replication after Repeated Low-Dose Heterologous SIV Challenge

An effective human immunodeficiency virus (HIV) vaccine will likely need to reduce mucosal transmission and, if infection occurs, control virus replication. To determine whether our best simian immunodeficiency virus (SIV) vaccine can achieve these lofty goals, we vaccinated eight Indian rhesus macaques with SIVmac239Δnef and challenged them intrarectally (i.r.) with repeated low doses of the pathogenic heterologous swarm isolate SIVsmE660. We detected a significant reduction in acquisition of SIVsmE660 in comparison to that for naïve controls (log rank test; P = 0.023). After 10 mucosal challenges, we detected replication of the challenge strain in only five of the eight vaccinated animals. In contrast, seven of the eight control animals became infected with SIVsmE660 after these 10 challenges. Additionally, the SIVsmE660-infected vaccinated animals controlled peak acute virus replication significantly better than did the naïve controls (Mann-Whitney U test; P = 0.038). Four of the five SIVsmE660 vaccinees rapidly brought virus replication under control by week 4 postinfection. Unfortunately, two of these four vaccinated animals lost control of virus replication during the chronic phase of infection. Bulk sequence analysis of the circulating viruses in these animals indicated that recombination had occurred between the vaccine and challenge strains and likely contributed to the increased virus replication in these animals. Overall, our results suggest that a well-designed HIV vaccine might both reduce the rate of acquisition and control viral replication.The goals of any human immunodeficiency virus (HIV) vaccine are both to prevent infection and, if infection occurs, to control virus replication. If vaccinated individuals who become infected are able to reduce virus replication to extremely low or undetectable levels, they will live longer, healthier lives and will be less likely to transmit the virus to others (7, 16, 41). An HIV vaccine that successfully meets these two goals will therefore have a significant impact on slowing the spread of HIV (3).Live-attenuated simian immunodeficiency virus (SIV) vaccines have proven to be universally effective at protecting macaques against homologous virus challenges, regardless of the route of transmission (10, 21, 33, 36, 50, 51). For this reason, live-attenuated SIV vaccines are considered the “gold standard” of protection in the SIV/rhesus macaque model of HIV infection (25). Previously, we and others showed that SIVmac239Δnef-vaccinated animals can reduce plasma virus replication after intravenous (i.v.) inoculation with the uncloned heterologous swarm virus SIVsmE660 (43, 50). This vaccine-induced effect was most pronounced, particularly during acute infection, in animals expressing major histocompatibility complex (MHC) class I alleles (Mamu-A*01, -B*08, and -B*17) previously associated with control of pathogenic SIVmac239 replication (29, 38, 43, 52, 54). Despite these encouraging results for this subset of animals, and in contrast to previous studies using homologous virus challenges, most of the vaccinated animals failed to maintain control of virus replication of the challenge strain during the chronic phase of infection.There are several potential explanations for why SIVmac239Δnef vaccination was not as effective against i.v. exposure to the heterologous challenge virus (1, 43, 50). First, sequence variation between the vaccine and infecting strains may have rendered the vaccine-induced immune responses ineffective at controlling chronic-phase virus replication. Second, unlike the case in homologous SIVmac239 challenge studies using cloned viral stocks, the heterologous SIVsmE660 isolate contains many quasispecies within the inoculum (23, 49). Third, the heterologous challenges were administered i.v., thereby bypassing any potentially protective vaccine-induced immune responses at mucosal surfaces. All of the SIVsmE660 quasispecies in the inoculum therefore had the potential to infect cells and to establish a reservoir of viral diversity. This broad spectrum of viral diversity may have contributed to the decreased efficacy of SIVmac239Δnef-induced immune responses in protecting against heterologous virus replication after a high-dose i.v. challenge.Since a large i.v. dose of multiple quasispecies of heterologous virus might overwhelm any potentially protective vaccine-induced immune responses, we tested the possibility that SIVmac239Δnef vaccination may be more efficacious against a more physiologically relevant low-dose challenge. In the SIV/rhesus macaque model of HIV infection, repeated low doses of pathogenic SIV more accurately reflect human sexual transmission than a single high-dose i.v. challenge does (32). Keele et al. recently established that one to three virus strains typically cross mucosal barriers to establish HIV infections (22). We and others observed similar results using repeated-dose mucosal challenge of macaques (23, 49). This model therefore facilitates the testing of vaccines in a more physiologically relevant manner.     

Live-Attenuated Lentivirus Immunization Modulates Innate Immunity and Inflammation while Protecting Rhesus Macaques from Vaginal Simian Immunodeficiency Virus Challenge

Immunization with attenuated lentiviruses is the only reliable method of protecting rhesus macaques (RM) from vaginal challenge with pathogenic simian immunodeficiency virus (SIV). CD8(+) lymphocyte depletion prior to SIVmac239 vaginal challenge demonstrated that a modest, Gag-specific CD8(+) T cell response induced by immunization with simian-human immunodeficiency virus 89.6 (SHIV89.6) protects RM. Although CD8(+) T cells are required for protection, there is no anamnestic expansion of SIV-specific CD8(+) T cells in any tissues except the vagina after challenge. Further, SHIV immunization increased the number of viral target cells in the vagina and cervix, suggesting that the ratio of target cells to antiviral CD8(+) T cells was not a determinant of protection. We hypothesized that persistent replication of the attenuated vaccine virus modulates inflammatory responses and limits T cell activation and expansion by inducing immunoregulatory T cell populations. We found that attenuated SHIV infection decreased the number of circulating plasmacytoid dendritic cells, suppressed T cell activation, decreased mRNA levels of proinflammatory mediators, and increased mRNA levels of immunoregulatory molecules. Three days after SIV vaginal challenge, SHIV-immunized RM had significantly more T regulatory cells in the vagina than the unimmunized RM. By day 14 postchallenge, immune activation and inflammation were characteristic of unimmunized RM but were minimal in SHIV-immunized RM. Thus, a modest vaccine-induced CD8(+) T cell response in the context of immunoregulatory suppression of T cell activation may protect against vaginal HIV transmission.     

Depo-Provera? Treatment Does Not Abrogate Protection from Intravenous SIV Challenge in Female Macaques Immunized with an Attenuated AIDS Virus

Background

In a previous study, progesterone treatment of female monkeys immunized with live, attenuated SHIV89.6 abrogated the generally consistent protection from vaginal simian immunodeficiency virus (SIV) challenge. The mechanisms responsible for the loss of protection remain to be defined. The objective of the present study was to determine whether Depo-Provera® administration alters protection from intravenous SIV challenge in SHIV-immunized female macaques.

Methods and Findings

Two groups of female macaques were immunized with attenuated SHIV89.6 and then challenged intravenously with SIVmac239. Four weeks before challenge, one animal group was treated with Depo-Provera®, a commonly used injectable contraceptive progestin. As expected, SHIV-immunized monkeys had significantly lower peak and set-point plasma viral RNA levels compared to naïve controls, but in contrast to previously published findings with vaginal SIV challenge, the Depo-Provera® SHIV-immunized animals controlled SIV replication to a similar, or even slightly greater, degree than did the untreated SHIV-immunized animals. Control of viral replication from week 4 to week 20 after challenge was more consistent in the progesterone-treated, SHIV-immunized animals than in untreated, SHIV-immunized animals. Although levels of interferon-γ production were similar, the SIV-specific CD8⁺ T cells of progesterone-treated animals expressed more functions than the anti-viral CD8⁺ T cells from untreated animals.

Conclusions

Depo-Provera® did not diminish the control of viral replication after intravenous SIV challenge in female macaques immunized with a live-attenuated lentivirus. This result contrasts with the previously reported effect of Depo-Provera® on protection from vaginal SIV challenge and strongly implies that the decreased protection from vaginal challenge is due to effects of progesterone on the genital tract rather than to systemic effects. Further, these results demonstrate that the effects of hormonal contraceptives on vaccine efficacy need to be considered in the context of testing and use of an AIDS vaccine.