[Show abstract][Hide abstract] ABSTRACT: Nonhuman primate AIDS models are essential for the analysis of AIDS pathogenesis and the evaluation of vaccine efficacy. Multiple
studies on human immunodeficiency virus and simian immunodeficiency virus (SIV) infection have indicated the association of
major histocompatibility complex class I (MHC-I) genotypes with rapid or slow AIDS progression. The accumulation of macaque
groups that share not only a single MHC-I allele but also an MHC-I haplotype consisting of multiple polymorphic MHC-I loci
would greatly contribute to the progress of AIDS research. Here, we investigated SIVmac239 infections in four groups of Burmese
rhesus macaques sharing individual MHC-I haplotypes, referred to as A, E, B, and J. Out of 20 macaques belonging to A+ (n = 6), E+ (n = 6), B+ (n = 4), and J+ (n = 4) groups, 18 showed persistent viremia. Fifteen of them developed AIDS in 0.5 to 4 years, with the remaining three at
1 or 2 years under observation. A+ animals, including two controllers, showed slower disease progression, whereas J+ animals exhibited rapid progression. E+ and B+ animals showed intermediate plasma viral loads and survival periods. Gag-specific CD8+ T-cell responses were efficiently induced in A+ animals, while Nef-specific CD8+ T-cell responses were in A+, E+, and B+ animals. Multiple comparisons among these groups revealed significant differences in survival periods, peripheral CD4+ T-cell decline, and SIV-specific CD4+ T-cell polyfunctionality in the chronic phase. This study indicates the association of MHC-I haplotypes with AIDS progression
and presents an AIDS model facilitating the analysis of virus-host immune interaction.
Full-text · Article · Apr 2012 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Cytotoxic T lymphocyte (CTL) responses play a central role in viral suppression in human immunodeficiency virus (HIV) infections.
Prophylactic vaccination resulting in effective CTL responses after viral exposure would contribute to HIV control. It is
important to know how CTL memory induction by vaccination affects postexposure CTL responses. We previously showed vaccine-based
control of a simian immunodeficiency virus (SIV) challenge in a group of Burmese rhesus macaques sharing a major histocompatibility
complex class I haplotype. Gag206-216 and Gag241-249 epitope-specific CTL responses were responsible for this control. In the present study, we show the impact of individual
epitope-specific CTL induction by prophylactic vaccination on postexposure CTL responses. In the acute phase after SIV challenge,
dominant Gag206-216-specific CTL responses with delayed, naive-derived Gag241-249-specific CTL induction were observed in Gag206-216 epitope-vaccinated animals with prophylactic induction of single Gag206-216 epitope-specific CTL memory, and vice versa in Gag241-249 epitope-vaccinated animals with single Gag241-249 epitope-specific CTL induction. Animals with Gag206-216-specific CTL induction by vaccination selected for a Gag206-216-specific CTL escape mutation by week 5 and showed significantly less decline of plasma viral loads from week 3 to week 5
than in Gag241-249 epitope-vaccinated animals without escape mutations. Our results present evidence indicating significant influence of prophylactic
vaccination on postexposure CTL immunodominance and cooperation of vaccine antigen-specific and non-vaccine antigen-specific
CTL responses, which affects virus control. These findings provide great insights into antigen design for CTL-inducing AIDS
Full-text · Article · Nov 2011 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: In our prior study on a prophylactic T-cell-based vaccine, some vaccinated macaques controlled a simian immunodeficiency virus (SIV) challenge. These animals allowed viremia in the acute phase but showed persistent viral control after the setpoint. Here, we examined the breadth of postchallenge virus-specific cellular immune responses in these SIV controllers.
We previously reported that in a group of Burmese rhesus macaques possessing the MHC haplotype 90-120-Ia, immunization with a Gag-expressing vaccine results in nonsterile control of a challenge with SIVmac239 but not a mutant SIV carrying multiple cytotoxic T lymphocyte (CTL) escape gag mutations. In the present study, we investigated whether broader cellular immune responses effective against the mutant SIV replication are induced after challenge in those vaccinees that maintained wild-type SIVmac239 control.
We analyzed cellular immune responses in these SIV controllers (n = 8).
These controllers elicited CTL responses directed against SIV non-Gag antigens as well as Gag in the chronic phase. Postvaccinated, prechallenge CD8(+) cells obtained from these animals suppressed wild-type SIV replication in vitro, but mostly had no suppressive effect on the mutant SIV replication, whereas CD8(+) cells in the chronic phase after challenge showed efficient antimutant SIV efficacy. The levels of in-vitro antimutant SIV efficacy of CD8(+) cells correlated with Vif-specific CD8(+) T-cell frequencies. Plasma viremia was kept undetectable even after the mutant SIV superchallenge in the chronic phase.
These results suggest that vaccine-based wild-type SIV controllers can acquire CD8(+) cells with the potential to suppress replication of SIV variants carrying CTL escape mutations.
Full-text · Article · Nov 2010 · AIDS (London, England)
[Show abstract][Hide abstract] ABSTRACT: The Gag capsid (CA) is one of the most conserved proteins in highly-diversified human and simian immunodeficiency viruses (HIV and SIV). Understanding the limitations imposed on amino acid sequences in CA could provide valuable information for vaccine immunogen design or anti-HIV drug development. Here, by comparing two pathogenic SIV strains, SIVmac239 and SIVsmE543-3, we found critical amino acid residues for functional interaction between the N-terminal and the C-terminal domains in CA.
We first examined the impact of Gag residue 205, aspartate (Gag205D) in SIVmac239 and glutamate (Gag205E) in SIVsmE543-3, on viral replication; due to this difference, Gag206-216 (IINEEAADWDL) epitope-specific cytotoxic T lymphocytes (CTLs) were previously shown to respond to SIVmac239 but not SIVsmE543-3 infection. A mutant SIVmac239, SIVmac239Gag205E, whose Gag205D is replaced with Gag205E showed lower replicative ability. Interestingly, however, SIVmac239Gag205E passaged in macaque T cell culture often resulted in selection of an additional mutation at Gag residue 340, a change from SIVmac239 valine (Gag340V) to SIVsmE543-3 methionine (Gag340M), with recovery of viral fitness. Structural modeling analysis suggested possible intermolecular interaction between the Gag205 residue in the N-terminal domain and Gag340 in the C-terminal in CA hexamers. The Gag205D-to-Gag205E substitution in SIVmac239 resulted in loss of in vitro core stability, which was recovered by additional Gag340V-to-Gag340M substitution. Finally, selection of Gag205E plus Gag340M mutations, but not Gag205E alone was observed in a chronically SIVmac239-infected rhesus macaque eliciting Gag206-216-specific CTL responses.
These results present in vitro and in vivo evidence implicating the interaction between Gag residues 205 in CA NTD and 340 in CA CTD in SIV replication. Thus, this study indicates a structural constraint for functional interaction between SIV CA NTD and CTD, providing insight into immunogen design to limit viral escape options.
[Show abstract][Hide abstract] ABSTRACT: Despite many efforts to develop AIDS vaccines eliciting virus-specific T-cell responses, whether induction of these memory
T cells by vaccination before human immunodeficiency virus (HIV) exposure can actually contribute to effective T-cell responses
postinfection remains unclear. In particular, induction of HIV-specific memory CD4+ T cells may increase the target cell pool for HIV infection because the virus preferentially infects HIV-specific CD4+ T cells. However, virus-specific CD4+ helper T-cell responses are thought to be important for functional CD8+ cytotoxic-T-lymphocyte (CTL) induction in HIV infection, and it has remained unknown whether HIV-specific memory CD8+ T cells induced by vaccination without HIV-specific CD4+ T-cell help can exert effective responses after virus exposure. Here we show the impact of CD8+ T-cell memory induction without virus-specific CD4+ T-cell help on the control of a simian immunodeficiency virus (SIV) challenge in rhesus macaques. We developed a prophylactic
vaccine by using a Sendai virus (SeV) vector expressing a single SIV Gag241-249 CTL epitope fused with enhanced green fluorescent protein (EGFP). Vaccination resulted in induction of SeV-EGFP-specific
CD4+ T-cell and Gag241-249-specific CD8+ T-cell responses. After a SIV challenge, the vaccinees showed dominant Gag241-249-specific CD8+ T-cell responses with higher effector memory frequencies in the acute phase and exhibited significantly reduced viral loads.
These results demonstrate that virus-specific memory CD8+ T cells induced by vaccination without virus-specific CD4+ T-cell help could indeed facilitate SIV control after virus exposure, indicating the benefit of prophylactic vaccination
eliciting virus-specific CTL memory with non-virus-specific CD4+ T-cell responses for HIV control.
Full-text · Article · Aug 2009 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Rapid depletion of memory CD4+ T cells and delayed induction of neutralizing antibody (NAb) responses are characteristics of human immunodeficiency virus
(HIV) and simian immunodeficiency virus (SIV) infections. Although it was speculated that postinfection NAb induction could
have only a limited suppressive effect on primary HIV replication, a recent study has shown that a single passive NAb immunization
of rhesus macaques 1 week after SIV challenge can result in reduction of viral loads at the set point, indicating a possible
contribution of postinfection NAb responses to virus control. However, the mechanism accounting for this NAb-triggered SIV
control has remained unclear. Here, we report rapid induction of virus-specific polyfunctional T-cell responses after the
passive NAb immunization postinfection. Analysis of SIV Gag-specific responses of gamma interferon, tumor necrosis factor
alpha, interleukin-2, macrophage inflammatory protein 1β, and CD107a revealed that the polyfunctionality of Gag-specific CD4+ T cells, as defined by the multiplicity of these responses, was markedly elevated in the acute phase in NAb-immunized animals.
In the chronic phase, despite the absence of detectable NAbs, virus control was maintained, accompanied by polyfunctional
Gag-specific T-cell responses. These results implicate virus-specific polyfunctional CD4+ T-cell responses in this NAb-triggered virus control, suggesting possible synergism between NAbs and T cells for control
of HIV/SIV replication.
Full-text · Article · Apr 2009 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Viral vectors are promising vaccine tools for eliciting antigen-specific T-cell responses. We previously showed the potential of recombinant Sendai virus (SeV) vectors to induce virus-specific T-cell responses in macaque AIDS models. Here, we have evaluated the immunogenicity of replication-competent V-knocked-out and replication-defective F-deleted SeV vectors in macaques. Intranasal replication-competent and replication-defective SeV immunizations both elicited robust systemic antigen-specific T-cell responses, whereas the responses induced by the former were more durable than those by the latter. However, even the latter-induced T-cell responses remained detectable in a local, retropharyngeal lymph node two months after the immunization. These findings are useful for establishment of a vaccine protocol using SeV vectors.
[Show abstract][Hide abstract] ABSTRACT: Gag-specific cytotoxic T lymphocytes (CTLs) exert strong suppressive pressure on human immunodeficiency virus (HIV) and simian
immunodeficiency virus (SIV) replication. However, it has remained unclear whether they can actually contain primary viral
replication. Recent trials of prophylactic vaccines inducing virus-specific T-cell responses have indicated their potential
to confer resistance against primary SIV replication in rhesus macaques, while the immunological determinant for this vaccine-based
viral control has not been elucidated thus far. Here we present evidence implicating Gag-specific CTLs as responsible for
the vaccine-based primary SIV control. Prophylactic vaccination using a Gag-expressing Sendai virus vector resulted in containment
of SIVmac239 challenge in all rhesus macaques possessing the major histocompatibility complex (MHC) haplotype 90-120-Ia. In contrast, 90-120-Ia-positive vaccinees failed to contain SIVs carrying multiple gag CTL escape mutations that had been selected, at the cost of viral fitness, in SIVmac239-infected 90-120-Ia-positive macaques. These results show that Gag-specific CTL responses do play a crucial role in the control of wild-type
SIVmac239 replication in vaccinees. This study implies the possibility of Gag-specific CTL-based primary HIV containment by
prophylactic vaccination, although it also suggests that CTL-based AIDS vaccine efficacy may be abrogated in viral transmission
between MHC-matched individuals.
Full-text · Article · Aug 2008 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Cytotoxic T-lymphocyte (CTL) responses frequently select for immunodeficiency virus mutations that result in escape from CTL
recognition with viral fitness costs. The replication in vivo of such viruses carrying not single but multiple escape mutations
in the absence of the CTL pressure has remained undetermined. Here, we have examined the replication of simian immunodeficiency
virus (SIV) with five gag mutations selected in a macaque possessing the major histocompatibility complex haplotype 90-120-Ia after its transmission into 90-120-Ia-negative macaques. Our results showed that even such a “crippled” SIV infection can result in persistent viral replication,
multiple reversions, and AIDS progression.
Preview · Article · Jun 2008 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: A current promising AIDS vaccine strategy is to elicit CD8(+) cytotoxic T lymphocyte (CTL) responses that broadly recognize highly-diversified HIVs. In our previous vaccine trial eliciting simian immunodeficiency virus (SIV) mac239 Gag-specific CTL responses, a group of Burmese rhesus macaques possessing a major histocompatibility complex haplotype 90-120-Ia have shown vaccine-based viral control against a homologous SIVmac239 challenge. Vaccine-induced Gag(206-216) epitope-specific CTL responses exerted strong selective pressure on the virus in this control. Here, we have evaluated in vivo efficacy of vaccine-induced Gag(206-216)-specific CTL responses in two 90-120-Ia-positive macaques against challenge with a heterologous SIVsmE543-3 that has the same Gag(206-216) epitope sequence with SIVmac239. Despite efficient Gag(206-216)-specific CTL induction by vaccination, both vaccinees failed to control SIVsmE543-3 replication and neither of them showed mutations within the Gag(206-216) epitope. Further analysis indicated that Gag(206-216)-specific CTLs failed to show responses against SIVsmE543-3 infection due to a change from aspartate to glutamate at Gag residue 205 immediately preceding the amino terminus of Gag(206-216) epitope. Our results suggest that even vaccine-induced CTL efficacy can be abrogated by a single amino acid change in viral epitope flanking region, underlining the influence of viral epitope flanking sequences on CTL-based AIDS vaccine efficacy.
No preview · Article · Apr 2008 · Microbes and Infection
[Show abstract][Hide abstract] ABSTRACT: 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.
Full-text · Article · Dec 2007 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: Induction of virus-specific CD8+ cytotoxic T-lymphocyte (CTL) responses is a promising strategy for AIDS vaccine development. However, it has remained unclear
if or how long-term viral containment and disease control are attainable by CTL-based nonsterile protection. Here, we present
three rhesus macaques that successfully maintained Env-independent vaccine-based control of simian immunodeficiency virus
(SIV) mac239 replication without disease progression for more than 3 years. SIV-specific neutralizing antibody induction was
inefficient in these controllers. Vaccine-induced Gag-specific CTLs were crucial for the chronic as well as the primary viral
control in one of them, whereas those Gag-specific CTL responses became undetectable and CTLs specific for SIV antigens other
than Gag, instead, became predominant in the chronic phase in the other two controllers. A transient CD8+ cell depletion experiment 3 years postinfection resulted in transient reappearance of plasma viremia in these two animals,
suggesting involvement of the SIV non-Gag-specific CTLs in the chronic SIV control. This sustained, neutralizing antibody-independent
viral control was accompanied with preservation of central memory CD4+ T cells in the chronic phase. Our results suggest that prophylactic CTL vaccine-based nonsterile protection can result in
long-term viral containment by adapted CTL responses for AIDS prevention.
Full-text · Article · Jun 2007 · Journal of Virology
[Show abstract][Hide abstract] ABSTRACT: The X4-tropic simian/human immunodeficiency virus (SHIV) 89.6P (or 89.6PD) causes rapid CD4(+) T-cell depletion leading to an acute crash of the host immune system, whereas pathogenic R5-tropic simian immunodeficiency virus (SIV) infection, like HIV-1 infection in humans, results in chronic disease progression in macaques. Recent pre-clinical vaccine trials inducing cytotoxic T lymphocyte (CTL) responses have succeeded in controlling replication of the former but shown difficulty in control of the latter. Analysis of the immune responses involved in consistent control of SHIV would contribute to elucidation of the mechanism for consistent control of SIV replication. This study followed up rhesus macaques that showed vaccine-based control of primary SHIV89.6PD replication and found that all of these controllers maintained viraemia control for more than 2 years. SHIV89.6PD control was observed in vaccinees of diverse major histocompatibility complex (MHC) haplotypes and was maintained without rapid selection of CTL escape mutations, a sign of particular CTL pressure. Despite the vaccine regimen not targeting Env, all of the SHIV controllers showed efficient elicitation of de novo neutralizing antibodies by 6 weeks post-challenge. These results contrast with our previous observation of particular MHC-associated control of SIV replication without involvement of neutralizing antibodies and suggest that vaccine-based control of SHIV89.6PD replication can be stably maintained in the presence of multiple functional immune effectors.
Full-text · Article · Mar 2007 · Journal of General Virology
[Show abstract][Hide abstract] ABSTRACT: Unlike most acute viral infections controlled with the appearance of virus-specific neutralizing antibodies (NAbs), primary HIV infections are not met with such potent and early antibody responses. This brings into question if or how the presence of potent antibodies can contribute to primary HIV control, but protective efficacies of antiviral antibodies in primary HIV infections have remained elusive; and, it has been speculated that even NAb induction could have only a limited suppressive effect on primary HIV replication once infection is established. Here, in an attempt to answer this question, we examined the effect of passive NAb immunization post-infection on primary viral replication in a macaque AIDS model.
[Show abstract][Hide abstract] ABSTRACT: Cytotoxic T-lymphocyte (CTL) responses are crucial for the control of immunodeficiency virus replication. Possible involvement
of a dominant single epitope-specific CTL in control of viral replication has recently been indicated in preclinical AIDS
vaccine trials, but it has remained unclear if multiple epitope-specific CTLs can be involved in the vaccine-based control.
Here, by following up five rhesus macaques that showed vaccine-based control of primary replication of a simian immunodeficiency
virus, SIVmac239, we present evidence indicating involvement of multiple epitope-specific CTL responses in this control. Three
macaques maintained control for more than 2 years without additional mutations in the provirus. However, in the other two
that shared a major histocompatibility complex haplotype, viral mutations were accumulated in a similar order, leading to
viral evasion from three epitope-specific CTL responses with viral fitness costs. Accumulation of these multiple escape mutations
resulted in the reappearance of plasma viremia around week 60 after challenge. Our results implicate multiple epitope-specific
CTL responses in control of immunodeficiency virus replication and furthermore suggest that sequential accumulation of multiple
CTL escape mutations, if allowed, can result in viral evasion from this control.
Full-text · Article · Mar 2006 · Journal of Virology