In vitro immortalization of Old World monkey T lymphocytes with Herpesvirus saimiri: its susceptibility to infection with simian immunodeficiency viruses

Translational regulation and protein-coding capacity of the 5' untranslated region of human TREM2

TREM2 is a transmembrane receptor expressed in microglia and macrophages. Elevated TREM2 levels in these cells are associated with age-related pathological conditions, including Alzheimer's disease. However, the regulatory mechanism underlying the protein expression of TREM2 remains unclear. In this study, we uncover the role of the 5' untranslated region (5'-UTR) of human TREM2 in translation. An upstream start codon (uAUG) in the 5'-UTR of TREM2 is specific to some primates, including humans. The expression of the conventional TREM2 protein, starting from the downstream AUG (dTREM2), is repressed by the 5'-UTR in a uAUG-mediated manner. We also detect a TREM2 protein isoform starting from uAUG (uTREM2) that is largely degraded by proteasomes. Finally, the 5'-UTR is essential for the downregulation of dTREM2 expression in response to amino acid starvation. Collectively, our study identifies a species-specific regulatory role of the 5'-UTR in TREM2 translation.

In vivo virulence of MHC-adapted AIDS virus serially-passaged through MHC-mismatched hosts

CD8⁺ T-cell responses exert strong suppressive pressure on HIV replication and select for viral escape mutations. Some of these major histocompatibility complex class I (MHC-I)-associated mutations result in reduction of in vitro viral replicative capacity. While these mutations can revert after viral transmission to MHC-I-disparate hosts, recent studies have suggested that these MHC-I-associated mutations accumulate in populations and make viruses less pathogenic in vitro. Here, we directly show an increase in the in vivo virulence of an MHC-I-adapted virus serially-passaged through MHC-I-mismatched hosts in a macaque AIDS model despite a reduction in in vitro viral fitness. The first passage simian immunodeficiency virus (1pSIV) obtained 1 year after SIVmac239 infection in a macaque possessing a protective MHC-I haplotype 90-120-Ia was transmitted into 90-120-Ia^- macaques, whose plasma 1 year post-infection was transmitted into other 90-120-Ia^- macaques to obtain the third passage SIV (3pSIV). Most of the 90-120-Ia-associated mutations selected in 1pSIV did not revert even in 3pSIV. 3pSIV showed lower in vitro viral fitness but induced persistent viremia in 90-120-Ia^- macaques. Remarkably, 3pSIV infection in 90-120-Ia⁺ macaques resulted in significantly higher viral loads and reduced survival compared to wild-type SIVmac239. These results indicate that MHC-I-adapted SIVs serially-transmitted through MHC-I-mismatched hosts can have higher virulence in MHC-I-matched hosts despite their lower in vitro viral fitness. This study suggests that multiply-passaged HIVs could result in loss of HIV-specific CD8⁺ T cell responses in human populations and the in vivo pathogenic potential of these escaped viruses may be enhanced.

CD8⁺ T-cell responses exert considerable control over replication of HIV and select for viral escape mutations. Recent studies have suggested that these major histocompatibility complex class I (MHC-I)-associated mutations accumulate in populations and make viruses less pathogenic in vitro. Other studies have shown that some of these escape mutations can revert after passage to MHC-I-disparate hosts. In an attempt to reconcile these apparently conflicting results, we serially passaged a virus isolate through MHC-I-mismatched hosts in the macaque AIDS model of simian immunodeficiency virus (SIV) infection. Here we show an increase in the in vivo virulence of an MHC-I-adapted virus despite a reduction in in vitro viral replication capacity. Only a few of the selected escape mutations reverted after transmission to MHC-I-disparate recipients. Results clearly showed that MHC-I-adapted SIVs that have been serially-transmitted through MHC-I-mismatched hosts can have higher in vivo virulence in MHC-I-matched hosts despite their lower in vitro viral fitness. This study suggests that HIVs may become less sensitive to CD8⁺ T cell responses and could have increased in vivo virulence by adaptation to MHC-I in human populations.

A highly pathogenic simian/human immunodeficiency virus effectively produces infectious virions compared with a less pathogenic virus in cell culture

BACKGROUND

The host range of human immunodeficiency virus (HIV) is quite narrow. Therefore, analyzing HIV-1 pathogenesis in vivo has been limited owing to lack of appropriate animal model systems. To overcome this, chimeric simian and human immunodeficiency viruses (SHIVs) that encode HIV-1 Env and are infectious to macaques have been developed and used to investigate the pathogenicity of HIV-1 in vivo. So far, we have many SHIV strains that show different pathogenesis in macaque experiments. However, dynamic aspects of SHIV infection have not been well understood. To fully understand the dynamic properties of SHIVs, we focused on two representative strains-the highly pathogenic SHIV, SHIV-KS661, and the less pathogenic SHIV, SHIV-#64-and measured the time-course of experimental data in cell culture.

METHODS

We infected HSC-F with SHIV-KS661 and -#64 and measured the concentration of Nef-negative (target) and Nef-positive (infected) HSC-F cells, the total viral load, and the infectious viral load daily for 9 days. The experiments were repeated at two different multiplicities of infection, and a previously developed mathematical model incorporating the infectious and non-infectious viruses was fitted to the full dataset of each strain simultaneously to characterize the infection dynamics of these two strains.

RESULTS AND CONCLUSIONS

We quantified virological indices including virus burst sizes and basic reproduction number of both SHIV-KS661 and -#64. Comparing the burst size of total and infectious viruses (viral RNA copies and TCID₅₀, respectively), we found that there was a statistically significant difference between the infectious virus burst size of SHIV-KS661 and -#64, while there was no significant difference between the total virus burst size. Furthermore, our analyses showed that the fraction of infectious virus among the produced SHIV-KS661 viruses, which is defined as the infectious viral load (TCID₅₀/ml) divided by the total viral load (RNA copies/ml), is more than 10-fold higher than that of SHIV-#64 during overall infection (i.e., for 9 days). Taken together, we conclude that the highly pathogenic SHIV produces infectious virions more effectively than the less pathogenic SHIV in cell culture.

Impact of TRIM5α in vivo

HIV type 1 (HIV-1) has a very narrow host range that is limited to humans and chimpanzees. HIV-1 cannot replicate well in Old World monkey cells such as rhesus and cynomolgus monkeys. Tripartite motif (TRIM)5α is a key molecule that confers potent resistance against HIV-1 infection and is composed of really interesting new gene, B-box2, coiled-coil and PRYSPRY domains. Interaction between TRIM5α PRYSPRY domains and HIV-1 capsid core triggers the anti-HIV-1 activity of TRIM5α. Analysis of natural HIV variants and extensive mutational experiments has revealed the presence of critical amino acid residues in both the PRYSPRY domain and HIV capsid for potent HIV suppression by TRIM5α. Genetic manipulation of the human TRIM5 gene could establish human cells totally resistant to HIV-1, which may lead to a cure for HIV-1 infection in the future.

A method to determine the duration of the eclipse phase for in vitro infection with a highly pathogenic SHIV strain

The time elapsed between successful cell infection and the start of virus production is called the eclipse phase. Its duration is specific to each virus strain and, along with an effective virus production rate, plays a key role in infection kinetics. How the eclipse phase varies amongst cells infected with the same virus strain and therefore how best to mathematically represent its duration is not clear. Most mathematical models either neglect this phase or assume it is exponentially distributed, such that at least some if not all cells can produce virus immediately upon infection. Biologically, this is unrealistic (one must allow for the translation, transcription, export, etc. to take place), but could be appropriate if the duration of the eclipse phase is negligible on the time-scale of the infection. If it is not, however, ignoring this delay affects the accuracy of the mathematical model, its parameter estimates, and predictions. Here, we introduce a new approach, consisting in a carefully designed experiment and simple analytical expressions, to determine the duration and distribution of the eclipse phase in vitro. We find that the eclipse phase of SHIV-KS661 lasts on average one day and is consistent with an Erlang distribution.

A conservation law for virus infection kinetics in vitro

Conservation laws are among the most important properties of a physical system, but are not commonplace in biology. We derived a conservation law from the basic model for viral infections which consists in a small set of ordinary differential equations. We challenged the conservation law experimentally for the case of a virus infection in a cell culture. We found that the derived, conserved quantity remained almost constant throughout the infection period, implying that the derived conservation law holds in this biological system. We also suggest a potential use for the conservation law in evaluating the accuracy of experimental measurements.

Complement-mediated virus infectivity neutralisation by HLA antibodies is associated with sterilising immunity to SIV challenge in the macaque model for HIV/AIDS

Sterilising immunity is a desired outcome for vaccination against human immunodeficiency virus (HIV) and has been observed in the macaque model using inactivated simian immunodeficiency virus (SIV). This protection was attributed to antibodies specific for cell proteins including human leucocyte antigens (HLA) class I and II incorporated into virions during vaccine and challenge virus preparation. We show here, using HLA bead arrays, that vaccinated macaques protected from virus challenge had higher serum antibody reactivity compared with non-protected animals. Moreover, reactivity was shown to be directed against HLA framework determinants. Previous studies failed to correlate serum antibody mediated virus neutralisation with protection and were confounded by cytotoxic effects. Using a virus entry assay based on TZM-bl cells we now report that, in the presence of complement, serum antibody titres that neutralise virus infectivity were higher in protected animals. We propose that complement-augmented virus neutralisation is a key factor in inducing sterilising immunity and may be difficult to achieve with HIV/SIV Env-based vaccines. Understanding how to overcome the apparent block of inactivated SIV vaccines to elicit anti-envelope protein antibodies that effectively engage the complement system could enable novel anti-HIV antibody vaccines that induce potent, virolytic serological response to be developed.

Nonhuman primate models for HIV/AIDS vaccine development

The development of HIV vaccines has been hampered by the lack of an animal model that can accurately predict vaccine efficacy. Chimpanzees can be infected with HIV-1 but are not practical for research. However, several species of macaques are susceptible to the simian immunodeficiency viruses (SIVs) that cause disease in macaques, which also closely mimic HIV in humans. Thus, macaque-SIV models of HIV infection have become a critical foundation for AIDS vaccine development. Here we examine the multiple variables and considerations that must be taken into account in order to use this nonhuman primate (NHP) model effectively. These include the species and subspecies of macaques, virus strain, dose and route of administration, and macaque genetics, including the major histocompatibility complex molecules that affect immune responses, and other virus restriction factors. We illustrate how these NHP models can be used to carry out studies of immune responses in mucosal and other tissues that could not easily be performed on human volunteers. Furthermore, macaques are an ideal model system to optimize adjuvants, test vaccine platforms, and identify correlates of protection that can advance the HIV vaccine field. We also illustrate techniques used to identify different macaque lymphocyte populations and review some poxvirus vaccine candidates that are in various stages of clinical trials. Understanding how to effectively use this valuable model will greatly increase the likelihood of finding a successful vaccine for HIV.

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 SIV_mac239-infected, NAb-negative rhesus macaques, respectively. Their binding capacity to whole SIV_mac239 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-SIV_mac239 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.

TRIM5α polymorphism identification in cynomolgus macaques of Vietnamese origin and Chinese rhesus macaques

TRIM5α is a retroviral restriction factor, in which the B30.2 (SPRY) and coiled-coil domains cooperate to determine the specificity of TRIM5α-mediated capture of retroviral capsids. Here, all exons of TRIM5α were analyzed in 39 Vietnamese cynomolgus macaques (VCE) and 29 Chinese rhesus macaques (CR). Our results revealed the presence of 22 alleles using the PHASE 2.0 software package (PHylogenetics And Sequence Evolution), including two novel species-specific alleles with a low frequency in VCE in exons 4 and 8, which encoded the coiled-coil and B30.2 (SPRY) domains, respectively. Nine alleles were detected in both VCE and CR, while four alleles were likely shared between the species. Of these alleles, the highest frequencies of 38% and 26% occurred in VCE and CR, respectively. Importantly, we found that some alleles encoded the same coiled-coil domain, but not the SPRY domain. In contrast, other alleles encoded the same SPRY domain, but not the coiled-coil domain. Our findings will contribute to the understanding of the interaction between the two domains and the determination of the specificity of TRIM5α-mediated capture of retroviral capsids. Our results from the phylogenetic trees constructed for VCE and CR suggested that the macaques' ability to inhibit SIV replication became gradually stronger if they carried corresponding alleles in four clades (clades4-7). More interesting, in clade3, both novel allele pairs (4E100a, 10E147a) and allele pairs (7R17b and 13R11b), which had the strong ability to inhibit SIV replication, originated from the same ancestral allele, suggesting that the novel alleles might play a key role to determine an animal's ability to inhibit SIV/HIV replication. However, further studies are needed to increase our understanding of the genetic background of TRIM5α in these two macaque species.

Establishment of an immortal cynomolgus macaque fibroblast cell line for propagation of cynomolgus macaque cytomegalovirus (CyCMV)

Cynomolgus macaques are widely used as an animal model in biomedical research. We have established an immortalized cynomolgus macaque fibroblast cell line (MSF-T) by transducing primary dermal fibroblasts isolated from a 13-year-old male cynomolgus macaque with a retrovirus vector expressing human telomerase reverse transcriptase (hTERT). The MSF-T cells showed increased telomerase enzyme activity and reached over 200 in vitro passages compared to the non-transduced dermal fibroblasts, which reached senescence after 43 passages. The MSF-T cell line is free of mycoplasma contamination and is permissive to the newly identified cynomolgus macaque cytomegalovirus (CyCMV). CyCMV productively infects MSF-T cells and induces down-regulation of MHC class I expression. The MSF-T cell line will be extremely useful for the propagation of CyCMV and other cynomolgus herspesviruses in host-derived fibroblast cells, allowing for the retention of host-specific viral genes. Moreover, this cell line will be beneficial for many in vitro experiments related to this animal model.

Identifying viral parameters from in vitro cell cultures

Current in vitro cell culture studies of viral replication deliver detailed time courses of several virological variables, like the amount of virions and the number of target cells, measured over several days of the experiment. Each of these time points solely provides a snap-shot of the virus infection kinetics and is brought about by the complex interplay of target cell infection, and viral production and cell death. It remains a challenge to interpret these data quantitatively and to reveal the kinetics of these underlying processes to understand how the viral infection depends on these kinetic properties. In order to decompose the kinetics of virus infection, we introduce a method to “quantitatively” describe the virus infection in in vitro cell cultures, and discuss the potential of the mathematical based analyses for experimental virology.

Electrostatic potential of human immunodeficiency virus type 2 and rhesus macaque simian immunodeficiency virus capsid proteins

Human immunodeficiency virus type 2 (HIV-2) and simian immunodeficiency virus isolated from a macaque monkey (SIVmac) are assumed to have originated from simian immunodeficiency virus isolated from sooty mangabey (SIVsm). Despite their close similarity in genome structure, HIV-2 and SIVmac show different sensitivities to TRIM5α, a host restriction factor against retroviruses. The replication of HIV-2 strains is potently restricted by rhesus (Rh) monkey TRIM5α, while that of SIVmac strain 239 (SIVmac239) is not. Viral capsid protein is the determinant of this differential sensitivity to TRIM5α, as the HIV-2 mutant carrying SIVmac239 capsid protein evaded Rh TRIM5α-mediated restriction. However, the molecular determinants of this restriction mechanism are unknown. Electrostatic potential on the protein-binding site is one of the properties regulating protein-protein interactions. In this study, we investigated the electrostatic potential on the interaction surface of capsid protein of HIV-2 strain GH123 and SIVmac239. Although HIV-2 GH123 and SIVmac239 capsid proteins share more than 87% amino acid identity, we observed a large difference between the two molecules with the HIV-2 GH123 molecule having predominantly positive and SIVmac239 predominantly negative electrostatic potential on the surface of the loop between α-helices 4 and 5 (L4/5). As L4/5 is one of the major determinants of Rh TRIM5α sensitivity of these viruses, the present results suggest that the binding site of the Rh TRIM5α may show complementarity to the HIV-2 GH123 capsid surface charge distribution.

Quantification system for the viral dynamics of a highly pathogenic simian/human immunodeficiency virus based on an in vitro experiment and a mathematical model

Background

Developing a quantitative understanding of viral kinetics is useful for determining the pathogenesis and transmissibility of the virus, predicting the course of disease, and evaluating the effects of antiviral therapy. The availability of data in clinical, animal, and cell culture studies, however, has been quite limited. Many studies of virus infection kinetics have been based solely on measures of total or infectious virus count. Here, we introduce a new mathematical model which tracks both infectious and total viral load, as well as the fraction of infected and uninfected cells within a cell culture, and apply it to analyze time-course data of an SHIV infection in vitro.

Results

We infected HSC-F cells with SHIV-KS661 and measured the concentration of Nef-negative (target) and Nef-positive (infected) HSC-F cells, the total viral load, and the infectious viral load daily for nine days. The experiments were repeated at four different MOIs, and the model was fitted to the full dataset simultaneously. Our analysis allowed us to extract an infected cell half-life of 14.1 h, a half-life of SHIV-KS661 infectiousness of 17.9 h, a virus burst size of 22.1 thousand RNA copies or 0.19 TCID₅₀, and a basic reproductive number of 62.8. Furthermore, we calculated that SHIV-KS661 virus-infected cells produce at least 1 infectious virion for every 350 virions produced.

Conclusions

Our method, combining in vitro experiments and a mathematical model, provides detailed quantitative insights into the kinetics of the SHIV infection which could be used to significantly improve the understanding of SHIV and HIV-1 pathogenesis. The method could also be applied to other viral infections and used to improve the in vitro determination of the effect and efficacy of antiviral compounds.

TRIM5α and Species Tropism of HIV/SIV

Human immunodeficiency virus type 1 (HIV-1) infects humans and chimpanzees but not old world monkeys (OWMs) such as the rhesus monkey (Rh) and cynomolgus monkey (CM). HIV-1 efficiently enters cells of OWMs but encounters a block before reverse transcription. This narrow host range is attributed to a barrier in the host cell. In 2004, the screening of a Rh cDNA library identified tripartite motif 5α (TRIM5α) as a cellular antiviral factor. TRIM5α is one of splicing variants produced by TRIM5 gene and TRIM5 proteins are members of the TRIM family containing RING, B-box 2, and coiled-coil domains. The RING domain is frequently found in E3 ubiquitin ligase and TRIM5α is degraded via the ubiquitin–proteasome-dependent pathway. Among TRIM5 splicing variants, TRIM5α alone has an additional C-terminal PRYSPRY (B30.2) domain. Previous studies have shown that sequence variation in variable regions of the PRYSPRY domain among different monkey species affects species-specific retrovirus infection, while amino acid sequence differences in the viral capsid protein determine viral sensitivity to restriction. TRIM5α recognizes the multimerized capsid proteins (viral core) of an incoming virus by its PRYSPRY domain and is thus believed to control retroviral infection. There are significant intraspecies variations in the Rh-TRIM5 gene. It has also been reported that some Rh and CM individuals have retrotransposed cyclophilin A open reading frame in the TRIM5 gene, which produces TRIM5–cyclophilin A fusion protein (TRIMCyp). TRIMCyp, which was originally identified as an anti-HIV-1 factor of New World owl monkeys, is an interesting example of the gain of a new function by retrotransposition. As different TRIM5 genotypes of Rh showed different levels of simian immunodeficiency virus replication in vivo, the TRIM5 genotyping is thought to be important in acquired immunodeficiency syndrome monkey models.

Host cell species-specific effect of cyclosporine A on simian immunodeficiency virus replication

Background

An understanding of host cell factors that affect viral replication contributes to elucidation of the mechanism for determination of viral tropism. Cyclophilin A (CypA), a peptidyl-prolyl cis-trans isomerase (PPIase), is a host factor essential for efficient replication of human immunodeficiency virus type 1 (HIV-1) in human cells. However, the role of cyclophilins in simian immunodeficiency virus (SIV) replication has not been determined. In the present study, we examined the effect of cyclosporine A (CsA), a PPIase inhibitor, on SIV replication.

Results

SIV replication in human CEM-SS T cells was not inhibited but rather enhanced by treatment with CsA, which inhibited HIV-1 replication. CsA treatment of target human cells enhanced an early step of SIV replication. CypA overexpression enhanced the early phase of HIV-1 but not SIV replication, while CypA knock-down resulted in suppression of HIV-1 but not SIV replication in CEM-SS cells, partially explaining different sensitivities of HIV-1 and SIV replication to CsA treatment. In contrast, CsA treatment inhibited SIV replication in macaque T cells; CsA treatment of either virus producer or target cells resulted in suppression of SIV replication. SIV infection was enhanced by CypA overexpression in macaque target cells.

Conclusions

CsA treatment enhanced SIV replication in human T cells but abrogated SIV replication in macaque T cells, implying a host cell species-specific effect of CsA on SIV replication. Further analyses indicated a positive effect of CypA on SIV infection into macaque but not into human T cells. These results suggest possible contribution of CypA to the determination of SIV tropism.

Immortalization of human and rhesus macaque primary antigen-specific T cells by retrovirally transduced telomerase reverse transcriptase

Human and rhesus macaque primary antigen-specific T cells derived from infected or immunized individuals or animals are a valuable material with which to study cellular immune responses against pathogens and tumors. Antigen-specific T cells can be expanded in vitro but have a finite proliferative life span. After a limited period in culture, primary T cells undergo replicative senescence and stop dividing. This restricts their applicability to short-term experiments and complicates their use in adoptive immunotherapy. The proliferative life span of primary human and rhesus macaque T cells can be considerably extended by ectopically expressed human telomerase reverse transcriptase (TERT). Antigen-specific T cells transduced with TERT-expressing retroviral vectors can proliferate and expand in culture for long periods of time while maintaining their primary T cell characteristics, including antigen-specific responses. Thus, TERT-immortalized T cells are an important and valuable resource for studying T cell-mediated immune responses and, potentially, for adoptive immunotherapy.

Herpesvirus saimiri infection of rhesus macaques: a model for acute rhadinovirus-induced t-cell transformation and oncogenesis

Herpesvirus saimiri (HVS) causes acute lymphoma and leukemia upon experimental infection of various monkey species. HVS strain C488 is also capable of transforming human T-lymphocytes to stable growth in culture. The most susceptible species for oncogenesis are New World primates, in particular the cottontop tamarin (Saguinus oedipus). However, Old World monkeys such as macaques are the most used animal model for the close-to-human situation. The limited data on HVS infection in Old World monkeys prompted us to investigate susceptibility to infection and disease induction by HVS in macaques. After having established that rhesus macaques can be infected productively, and that rhesus T-cells can be transformed in vivo by HVS, we observed induction of lymphoma in all inoculated animals. Pre-existing humoral immunity in part of the rhesus colony capable of blocking HVS infection could be overcome by preselecting rhesus macaques for lack of this immunity of unknown origin. HVS infection of rhesus macaques as compared to that of New World monkeys has the advantages that disease progression is more prolonged, and larger blood volumes can be collected, which allows more extended analyses. Also, rhesus monkeys are the best immunologically and immunogenetically characterized primate species next to humans. This model could be useful for the evaluation of candidate tumor vaccines and to test novel approaches for cancer immunotherapy. In addition, HVS infection of macaques could eventually be useful as a surrogate model to address certain questions in rhadinovirus-induced human cancer such as effusion lymphoma or Kaposi's sarcoma.

Broadening of CD8+ cell responses in vaccine-based simian immunodeficiency virus controllers

OBJECTIVE

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.

DESIGN

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.

METHODS

We analyzed cellular immune responses in these SIV controllers (n = 8).

RESULTS

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.

CONCLUSION

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.

A structural constraint for functional interaction between N-terminal and C-terminal domains in simian immunodeficiency virus capsid proteins

BACKGROUND

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.

RESULTS

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.

CONCLUSIONS

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.

Multiple sites in the N-terminal half of simian immunodeficiency virus capsid protein contribute to evasion from rhesus monkey TRIM5α-mediated restriction

BACKGROUND

We previously reported that cynomolgus monkey (CM) TRIM5α could restrict human immunodeficiency virus type 2 (HIV-2) strains carrying a proline at the 120th position of the capsid protein (CA), but it failed to restrict those with a glutamine or an alanine. In contrast, rhesus monkey (Rh) TRIM5α could restrict all HIV-2 strains tested but not simian immunodeficiency virus isolated from macaque (SIVmac), despite its genetic similarity to HIV-2.

RESULTS

We attempted to identify the viral determinant of SIVmac evasion from Rh TRIM5α-mediated restriction using chimeric viruses formed between SIVmac239 and HIV-2 GH123 strains. Consistent with a previous study, chimeric viruses carrying the loop between α-helices 4 and 5 (L4/5) (from the 82nd to 99th amino acid residues) of HIV-2 CA were efficiently restricted by Rh TRIM5α. However, the corresponding loop of SIVmac239 CA alone (from the 81st to 97th amino acid residues) was not sufficient to evade Rh TRIM5α restriction in the HIV-2 background. A single glutamine-to-proline substitution at the 118th amino acid of SIVmac239 CA, corresponding to the 120th amino acid of HIV-2 GH123, also increased susceptibility to Rh TRIM5α, indicating that glutamine at the 118th of SIVmac239 CA is necessary to evade Rh TRIM5α. In addition, the N-terminal portion (from the 5th to 12th amino acid residues) and the 107th and 109th amino acid residues in α-helix 6 of SIVmac CA are necessary for complete evasion from Rh TRIM5α-mediated restriction. A three-dimensional model of hexameric GH123 CA showed that these multiple regions are located on the CA surface, suggesting their direct interaction with TRIM5α.

CONCLUSION

We found that multiple regions of the SIVmac CA are necessary for complete evasion from Rh TRIM5α restriction.

Contribution of Cyclophilin A to determination of simian immunodeficiency virus tropism: a progress update

An understanding of cellular factors that affect viral replication contributes to elucidation of the mechanism for the determination of viral tropism. Cyclophilin A (CypA), a peptidyl-prolyl cis-trans isomerase (PPIase), is an essential host factor for the efficient replication of human immunodeficiency virus type 1 (HIV-1) in human cells. However, its role in simian immunodeficiency virus (SIV) replication has not been determined. In the 2008 US-Japan AIDS panel meeting, I have presented the effect of cyclosporine A (CsA), a PPIase inhibitor, on replication of wild-type SIV. Interestingly, CsA treatment enhanced SIV replication in human cells but abrogated SIV replication in macaque cells, implying a species-specific effect of CsA on SIV replication. After this meeting, analysis using CypA knocked-down human cells indicated that CypA was considered inhibitory for SIV replication. These results suggest possible involvement of CypA in the determination of SIV tropism.

Anti-retroviral activity of TRIM5 alpha

Human immunodeficiency virus type 1 (HIV-1) shows a very narrow host range limited to humans and chimpanzees. Experimentally, HIV-1 does not infect Old World monkeys, such as rhesus (Rh) and cynomolgus (CM) monkeys, and fails to replicate in activated CD4 positive T lymphocytes obtained from these monkeys. In contrast, simian immunodeficiency virus isolated from a macaque monkey (SIVmac) can replicate well in both Rh and CM. In 2004, tripartite motif 5 alpha (TRIM5 alpha) was identified as a host factor which plays an important role in the restricted host range of HIV-1. Rh and CM TRIM5 alpha restrict HIV-1 infection but not SIVmac, while in comparison, anti-viral activity of human TRIM5 alpha against those viruses is very weak. TRIM5 alpha consists of the RING, B-box 2, coiled-coil and SPRY (B30.2) domains. The RING domain is frequently found in E3 ubiquitin ligase and TRIM5 alpha is degraded via the ubiquitin-proteasome pathway during HIV-1 restriction. TRIM5 alpha recognises the multimerised capsid (viral core) of an incoming virus by its alpha-isoform specific SPRY domain and is believed to be involved in innate immunity to control retroviral infection. Differences in amino acid sequences in the SPRY domain of TRIM5 alpha of different monkey species were found to affect species-specific restriction of retrovirus infection, while differences in amino acid sequences in the viral capsid protein determine viral sensitivity to restriction. Accurate structural analysis of the binding surface between the viral capsid protein and TRIM5 alpha SPRY is thus required for the development of new antiretroviral drugs that enhance anti-HIV-1 activity of human TRIM5 alpha.

Analysis of humoral immune responses in rhesus macaques vaccinated with attenuated SIVmac239Deltanef and challenged with pathogenic SIVmac251

BACKGROUND

To determine the correlation between protection and humoral immune response against simian immunodeficiency virus (SIVmac251), 11 macaques were immunized with live-attenuated SIVmac239Deltanef either intravenously or via the tonsils and exposed to SIVmac251 after either 6 or 15 months along with unvaccinated controls.

RESULTS

Independent of the route of vaccine application, viremia was significantly reduced in vaccinees compared with controls 2 weeks post-challenge. Concomitantly, viremia correlated inversely with SIV-specific IgG, complement-mediated lysis and neutralizing antibodies and these parameters seemed to contribute to reduced viremia. During chronic infection, six monkeys controlled viremia in the circulation (two or fewer infectious units per 10(6) PBMCs) and showed no signs of trapping in lymphatic tissues (Appendix S1).

CONCLUSIONS

As no significant differences were observed throughout the study, with respect to the humoral immune response and viremia control, between the two vaccinated cohorts, mucosal immunization strategies are recommended due to more simplified application.

Modification of a loop sequence between alpha-helices 6 and 7 of virus capsid (CA) protein in a human immunodeficiency virus type 1 (HIV-1) derivative that has simian immunodeficiency virus (SIVmac239) vif and CA alpha-helices 4 and 5 loop improves replication in cynomolgus monkey cells

Background

Human immunodeficiency virus type 1 (HIV-1) productively infects only humans and chimpanzees but not cynomolgus or rhesus monkeys while simian immunodeficiency virus isolated from macaque (SIVmac) readily establishes infection in those monkeys. Several HIV-1 and SIVmac chimeric viruses have been constructed in order to develop an animal model for HIV-1 infection. Construction of an HIV-1 derivative which contains sequences of a SIVmac239 loop between α-helices 4 and 5 (L4/5) of capsid protein (CA) and the entire SIVmac239 vif gene was previously reported. Although this chimeric virus could grow in cynomolgus monkey cells, it did so much more slowly than did SIVmac. It was also reported that intrinsic TRIM5α restricts the post-entry step of HIV-1 replication in rhesus and cynomolgus monkey cells, and we previously demonstrated that a single amino acid in a loop between α-helices 6 and 7 (L6/7) of HIV type 2 (HIV-2) CA determines the susceptibility of HIV-2 to cynomolgus monkey TRIM5α.

Results

In the study presented here, we replaced L6/7 of HIV-1 CA in addition to L4/5 and vif with the corresponding segments of SIVmac. The resultant HIV-1 derivatives showed enhanced replication capability in established T cell lines as well as in CD8+ cell-depleted primary peripheral blood mononuclear cells from cynomolgus monkey. Compared with the wild type HIV-1 particles, the viral particles produced from a chimeric HIV-1 genome with those two SIVmac loops were less able to saturate the intrinsic restriction in rhesus monkey cells.

Conclusion

We have succeeded in making the replication of simian-tropic HIV-1 in cynomolgus monkey cells more efficient by introducing into HIV-1 the L6/7 CA loop from SIVmac. It would be of interest to determine whether HIV-1 derivatives with SIVmac CA L4/5 and L6/7 can establish infection of cynomolgus monkeys in vivo.

Role of complement and antibodies in controlling infection with pathogenic simian immunodeficiency virus (SIV) in macaques vaccinated with replication-deficient viral vectors

Background

We investigated the interplay between complement and antibodies upon priming with single-cycle replicating viral vectors (SCIV) encoding SIV antigens combined with Adeno5-SIV or SCIV pseudotyped with murine leukemia virus envelope boosting strategies. The vaccine was applied via spray-immunization to the tonsils of rhesus macaques and compared with systemic regimens.

Results

Independent of the application regimen or route, viral loads were significantly reduced after challenge with SIVmac239 (p < 0.03) compared to controls. Considerable amounts of neutralizing antibodies were induced in systemic immunized monkeys. Most of the sera harvested during peak viremia exhibited a trend with an inverse correlation between complement C3-deposition on viral particles and plasma viral load within the different vaccination groups. In contrast, the amount of the observed complement-mediated lysis did not correlate with the reduction of SIV titres.

Conclusion

The heterologous prime-boost strategy with replication-deficient viral vectors administered exclusively via the tonsils did not induce any neutralizing antibodies before challenge. However, after challenge, comparable SIV-specific humoral immune responses were observed in all vaccinated animals. Immunization with single cycle immunodeficiency viruses mounts humoral immune responses comparable to live-attenuated immunodeficiency virus vaccines.

Molecular cloning and characterization of the common marmoset huntingtin gene

We report here for the first time the isolation and identification of the common marmoset (Callithrix jacchus) huntingtin (Htt) gene, whose ortholog in humans is known to be related to Huntington's disease (HD). A 9396 nucleotide complementary DNA (cDNA) carrying the putative full-length open reading frame of the marmoset Htt gene was identified, and highly conserved nucleotide and amino acid sequences among primates were observed. Based on this data and using tools evaluated for the detection of the marmoset Htt gene, we have demonstrated gene silencing against the expression of endogenous Htt gene in immortalized common marmoset mononuclear cells by means of RNA interference (RNAi). Taken together, the data presented here may assist us in realizing a non-human primate HD model with the common marmoset.

Gag-specific cytotoxic T-lymphocyte-based control of primary simian immunodeficiency virus replication in a vaccine trial

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.

Construction and infection of a new simian/human immunodeficiency chimeric virus (SHIV) containing the integrase gene of the human immunodeficiency virus type 1 genome and analysis of its adaptation to monkey cells

Expanding the HIV-1-derived regions in the SHIV genome may help to clarify the viral restriction factors determining the host range. In this study, we constructed a new SHIV having the reverse transcriptase and integrase-encoding regions of HIV-1 in addition to the 3' half genomic region of HIV-1. This SHIV, termed SHIVrti/3rn, could replicate in a monkey CD4+ T cell line, HSC-F, although its replication in monkey PBMCs was very weak. After SHIVrti/3rn was passaged in HSC-F cells for 26weeks, it gradually began to replicate in monkey PBMCs. This monkey-cell-adapted virus, termed SHIVrti/3rnP, could replicate in rhesus macaques. The whole genome of SHIVrti/3rnP was sequenced and was found to differ from SHIVrti/3rn at eleven positions. We constructed a series of mutants having some or all of these mutations and investigated their replication kinetics. The mutational analysis revealed that all of the mutations, but mainly the mutations in env, were responsible for the adaptation in HSC-F cells and were enough to replicate in rhesus PBMCs. Of all the SHIVs reported so far that can infect rhesus monkeys in vivo, SHIVrti/3rnP is the one that is genetically the closest to HIV-1.

Construction of a novel SHIV having an HIV-1-derived protease gene and its infection to rhesus macaques: a useful tool for in vivo efficacy tests of protease inhibitors

We generated a novel SHIV (termed SHIV-pr) that possesses the HIV-1-derived protease (PR) gene in the corresponding position in the SIVmac genome. SHIV-pr is replication-competent in human and monkey CD4(+) T lymphoid cell lines as well as rhesus macaque PBMCs. The viral growth of SHIV-pr was completely blocked in the presence of a peptide-analog PR inhibitor at the tissue culture level. When SHIV-pr was intravenously inoculated into two rhesus macaques, it resulted in a weak but long-lasting persistent infection in one monkey, whereas the infection of another was only temporary. To enhance the viral growth competence by adaptation, we then passaged the virus in vivo from a monkey up to the fourth generation. The initial peak values of plasma viral loads as well as the setpoint values increased generation by generation and reached those of a parental virus SIVmac. When a medication using the content of Kaletra capsule (a mixture of two PR inhibitors, lopinavir and ritonavir) was orally given to three SHIV-pr-infected monkeys for 4 weeks, plasma viral loads dropped to near or below the detection limit and quickly rebounded after the cessation of medication. The results suggest that SHIV-pr can be used to evaluate PR inhibitors using monkeys.

Involvement of multiple epitope-specific cytotoxic T-lymphocyte responses in vaccine-based control of simian immunodeficiency virus replication in rhesus macaques

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.

Construction and in vitro characterization of a chimeric simian and human immunodeficiency virus with the RANTES gene

Chimeric simian-human immunodeficiency virus (SHIV) containing the env gene of HIV-1 infects macaque monkeys and provides basic information that is useful for the development of HIV-1 vaccines. Regulated-on-activation-normal-T-cell-expressed-and-secreted (RANTES), a CC-chemokine, enhances antigen-specific T helper type-1 responses against HIV-1. With the final goal of testing the adjuvant effects of RANTES in SHIV-macaque models, we constructed a SHIV having the RANTES gene (SHIV-RANTES) and characterized its properties in vitro. SHIV-RANTES replicated both in human and monkey T cell lines. Along with SHIV-RANTES replication, RANTES was detected in the supernatant of human and monkey cell cultures, at maximal levels of 98.5 and 4.1 ng/ml, respectively. A flow cytometric analysis showed that the expressed RANTES down-modulated CC-chemokine receptor 5 (CCR5) on PM1 cells, which was restored by adding anti-RANTES antibody. UV-irradiated culture supernatants from the SHIV-RANTES-infected cells suppressed replication of CCR5-tropic HIV-1 BaL in PM-1 cells. Differentiating real-time RT-PCR showed that pre-infection of SHIV-RANTES in C8166 cells expressing CCR5 suppressed the replication of HIV-1 BaL. Biological activity of the expressed RANTES and the inserted RANTES gene in SHIV-RANTES remained stable after 10 passages. These results suggest that SHIV-RANTES is worth testing in macaque models.

A specific region of 37 amino acid residues in the SPRY (B30.2) domain of African green monkey TRIM5alpha determines species-specific restriction of simian immunodeficiency virus SIVmac infection

Human immunodeficiency virus type 1 (HIV-1) efficiently enters cells of Old World monkeys but encounters a block before reverse transcription. This restriction is mediated by a dominant repressive factor. Recently, a member of the tripartite motif (TRIM) family proteins, TRIM5alpha, was identified as a blocking factor in a rhesus macaque cDNA library. Among Old World monkey cell lines, the African green monkey kidney cell line CV1 is highly resistant to not only HIV-1 but also simian immunodeficiency virus SIVmac infection. We analyzed TRIM5alpha of CV1 cells and HSC-F cells, a T-cell line from a cynomolgus monkey, and found that both CV1- and HSC-F-TRIM5alphas could inhibit CD4-dependent HIV-1 infection, as well as vesicular stomatitis virus glycoprotein-mediated infection. CV1-TRIM5alpha could also inhibit SIVmac infection, whereas HSC-F-TRIM5alpha could not. In the SPRY (B30.2) domain of CV1-TRIM5alpha, there was a 20-amino-acid duplication that was not present in HSC-F-TRIM5alpha. A chimeric TRIM5alpha containing 37 amino acid residues from CV1-TRIM5alpha, which spanned the 20-amino-acid duplication, in the background of HSC-F-TRIM5alpha fully gained the ability to inhibit SIVmac infection. Conversely, the mutant CV1-TRIM5alpha lacking the 20-amino-acid duplication completely lost the ability to restrict SIVmac infection. These findings clearly indicated that a specific region of 37 amino acid residues in the SPRY domain of CV1-TRIM5alpha contained a determinant of species-specific restriction of SIVmac.

T-cell transformation and oncogenesis by gamma2-herpesviruses

gamma2-Herpesviruses, also termed rhadinoviruses, have long been known as animal pathogens causing lymphoproliferative diseases such as malignant catarrhal fever in cattle or T-cell lymphoma in certain Neotropical primates. The rhadinovirus prototype is Herpesvirus saimiri (HVS), a T-lymphotropic agent of squirrel monkeys (Saimiri sciureus); Herpesvirus ateles (HVA) is closely related to HVS. The first human rhadinovirus, human herpesvirus type 8 (HHV-8), was discovered a decade ago in Kaposi's sarcoma (KS) biopsies. It was found to be strongly associated with all forms of KS, as well as with multicentric Castleman's disease and primary effusion lymphoma (PEL). Since DNA of this virus is regularly found in all KS forms, and specifically in the spindle cells of KS, it was also termed KS-associated herpesvirus (KSHV). Several simian rhadinoviruses related to KSHV have been discovered in various Old World primates, though they seem only loosely associated with pathogenicity or tumor induction. In contrast, HVS and HVA cause T-cell lymphoma in numerous non-natural primate hosts; HVS strains of the subgroup C are capable of transforming human and simian T-lymphocytes to continuous growth in cell culture and can provide useful tools for T-cell immunology or gene transfer. Here, we describe their natural history, genome structure, biology, and pathogenesis in T-cell transformation and oncogenesis.

Herpesvirus saimiri transformation of human T lymphocytes

Viral transformation of T cells is an effective method for obtaining large numbers of T cells that are easily maintained in the laboratory. This unit describes a method for generating antigen-independent, virally-transformed T cells using a T-lymphotropic primate gamma-2 herpesvirus, Herpesvirus saimiri (HVS; strain C488). Support protocols for preparing and titrating HSV C488 stocks and testing the functional status of transformed T cells are also included.

The genome of herpesvirus saimiri C488 which is capable of transforming human T cells

Herpesvirus saimiri (HVS), the rhadinovirus prototype, is apathogenic in the persistently infected natural host, the squirrel monkey, but causes acute T cell leukemia in other New World primate species. In contrast to subgroups A and B, only strains of HVS subgroup C such as C488 are capable of transforming primary human T cells to stable antigen-independent growth in culture. Here, we report the complete 155-kb genome sequence of the transformation-competent HVS strain C488. The A+T-rich unique L-DNA of 113,027 bp encodes at least 77 open reading frames and 5 URNAs. In addition to the viral oncogenes stp and tip, only a few genes including the transactivator orf50 and the glycoprotein orf51 are highly divergent. In a series of new primary HVS isolates, the subgroup-specific divergence of the orf50/orf51 alleles was studied. In these new isolates, the orf50/orf51 alleles of the respective subgroup segregate with the stp and/or tip oncogene alleles, which are essential for transformation.

Molecular cloning, functional characterization, and enzyme-linked immunosorbent assay of cynomolgus monkey Fas ligand

Fas ligand (FasL) cDNAs were cloned and sequenced from cynomolgus, rhesus, and pig-tailed monkeys. The 840-bp cDNAs were identical among these three species of monkeys except for one nucleotide. The deduced 280 amino acids were completely identical and displayed 97% homology with human FasL (hFasL). Recombinant soluble FasL obtained from COS cells transfected with cynomolgus monkey FasL (cm-FasL) cDNA induced apoptosis in cells displaying human or cynomolgus monkey Fas-expressing cells. Several anti-human FasL monoclonal antibodies (mAbs) were able to neutralize the cytotoxic activity of monkey FasL, and a combination of mAbs was selected to obtain the most sensitive detection of monkey soluble FasL (sFasL) under sandwich enzyme-linked immunosorbent assay (ELISA). Plasma from normal monkey did not contain detectable levels of sFasL, whereas plasma from monkeys acutely infected with simian immunodeficiency virus (SIV) displayed increased levels of sFasL.

Construction and in vivo infection of a new simian/human immunodeficiency virus chimera containing the reverse transcriptase gene and the 3' half of the genomic region of human immunodeficiency virus type 1

A new simian/human immunodeficiency virus (SHIV) chimera with the reverse transcriptase (RT)-encoding region of pol, in addition to the 3' region encoding vpr, vpu, tat, rev, env and nef of HIV-1, on an SIV(mac) (SIV from a macaque monkey) background was constructed. This new SHIV chimera, named SHIVrt/3rn, could replicate in monkey peripheral blood mononuclear cells (PBMCs) as well as in the human and monkey CD4(+) T-cell lines M8166 and HSC-F. Since SHIVrt/3rn contains the RT gene of HIV-1, replication of the virus in M8166 cells was inhibited by an HIV-1-specific non-nucleoside RT inhibitor, MKC-442, with a sensitivity similar to that of HIV-1. To investigate the replication competence of SHIVrt/3rn in vivo, two rhesus monkeys were inoculated intravenously with the virus. At 2 to 4 weeks post-inoculation (p.i.), plasma viral RNA loads of both monkeys showed a peak value of more than 10(4) copies ml(-1). Infectious virus was isolated from the PBMCs of one monkey at 2 and 3 weeks p.i. and from the other at 4 weeks p.i. Moreover, proviral DNA was detected constantly throughout the observation period, starting from 3 weeks p.i. An antibody response, detected first at 3 weeks p.i., was maintained at high titres. These results indicate that SHIVrt/3rn can infect and replicate in vivo. SHIVrt/3rn, having part of HIV-1 pol in addition to the 3' part of the HIV-1 genome is genetically more close to HIV-1 than any of the other monkey-infecting SHIVs reported previously.

Vpx and Vpr proteins of HIV-2 up-regulate the viral infectivity by a distinct mechanism in lymphocytic cells

Mutants of human immunodeficiency virus type 2 (HIV-2) carrying a frame-shift mutation in vpx, vpr, and in both genes were monitored for their growth potentials in a newly established lymphocytic cell line, HSC-F. Worthy of note, the replication of a vpx single mutant, but not vpr, was severely impaired in these cells, and that of a vpx-vpr double mutant was more damaged. Defective replication sites of the vpx single and vpx-vpr double mutants were demonstrated to be mapped, respectively, to the nuclear import of viral genome, and to both, this process and the virus assembly/release stage. While the mutational effect of vpr was small, the replication efficiency in one cycle of the vpx mutant relative to that of wild-type virus was estimated to be 10%. The growth phenotypes of the vpx, vpr, and vpx-vpr mutant viruses in HSC-F cells were essentially repeated in primary human lymphocytes. In primary human macrophages, whereas the vpx and vpx-vpr mutants did not grow at all, the vpr mutant grew equally as well as the wild-type virus. These results strongly suggested that Vpx is critical for up-regulation of HIV-2 replication in natural target cells by enhancing the genome nuclear import, and that Vpr promotes HIV-2 replication somewhat, at least in lymphocytic cells, at a very late replication phase.

Peripheral T-cell lymphoma in herpesvirus saimiri-infected tamarins: tumor cell lines reveal subgroup-specific differences

Efficiency of lymphoma induction by herpesvirus saimiri (HVS) isolates correlates with the genetically defined viral subgroups A, B, and C. To compare subgroup-specific effects, highly susceptible tamarins were infected with HVS strain A-11, B-SMHI, or C-488. All animals developed T-cell lymphomas indistinguishable with respect to clinical, pathological, and virological parameters. Ex vivo T-cell lines were established readily from the HVS C-488 animal, less efficiently in the presence of HVS A-11, and from only a single HVS B-SMHI sample. These cultivated cells revealed strain-specific biochemical characteristics. HVS A-11 strongly induced the expression of tyrosine kinase Lyn. HVS C-488 led to the activation of STAT3, which is most likely linked to the association of virus-encoded Tip with tyrosine kinase Lck. The lack of these activities in HVS B-SMHI-transformed cells may correlate with the reduced oncogenic phenotype of this virus in species other than tamarins.

Herpesvirus saimiri

Herpesvirus saimiri (saimiriine herpesvirus 2) is the classical prototype of the gamma(2)-herpesviruses or rhadinoviruses, which also contains a human member, the Kaposi's sarcoma-associated herpesvirus. The T-lymphotropic Herpesvirus saimiri establishes specific replicative and persistent conditions in different primate host species. Virtually all squirrel monkeys (Saimiri sciureus) are persistently infected with this virus. In its natural host, the virus does not cause disease, whereas it induces fatal acute T-cell lymphoma in other monkey species after experimental infection. The virus can be isolated by cocultivation of permissive epithelial cells with peripheral blood cells from naturally infected squirrel monkeys and from susceptible New World monkeys during the virus-induced disease. Tumour-derived and in vitro-transformed T-cell lines from New World monkeys release virus particles. Herpesvirus ateles is a closely related virus of spider monkeys (Ateles spp.) and has similar pathogenic properties to Herpesvirus saimiri in other New World primate species. Similar to other rhadinoviruses, the genome of Herpesvirus saimiri harbours a series of virus genes with pronounced homology to cellular counterparts including a D-type cyclin, a G-protein-coupled receptor, an interleukin-17, a superantigen homologue, and several inhibitors of the complement cascade and of different apoptosis pathways. Preserved function has been demonstrated for most of the homologues of cellular proteins. These viral functions are mostly dispensable for the transforming and pathogenic capability of the virus. However, they are considered relevant for the apathogenic persistence of Herpesvirus saimiri in its natural host. A terminal region of the non-repetitive coding part of the virus genome is essential for pathogenicity and T-cell transformation. Based on the pathogenic phenotypes and the different alleles of this variable region, the virus strains have been assigned to three subgroups, termed A, B and C. In the highly oncogenic subgroup C strains, the two virus genes stpC and tip are transcribed from one bicistronic mRNA and are essential for transformation and leukaemia induction. stpC fulfils the typical criteria of an oncogene; its product interacts with Ras and tumour necrosis factor-associated factors and induces mitogen-activated protein kinase and nuclear factor kappa B activation. Tip interacts with the RNA transport factor Tap, with signal transduction and activation of transcription factors, and with the T-cellular tyrosine kinase Lck, which is activated by this interaction and phosphorylates Tip as a substrate. It is of particular interest that certain subgroup C virus strains such as C488 are capable of transforming human T lymphocytes to stable growth in culture. The transformed human T cells harbour multiple copies of the viral genome in the form of stable, non-integrated episomes. The cells express only a few virus genes and do not produce virus particles. The transformed cells maintain the antigen specificity and many other essential functions of their parental T-cell clones. Based on the preserved functional phenotype of the transformed T cells, Herpesvirus saimiri provides useful tools for T-cell immunology, for gene transfer and possibly also for experimental adoptive immunotherapy.

Characterization of less pathogenic infectious molecular clones derived from acute-pathogenic SHIV-89.6p stock virus

For a better understanding of the acute pathogenicity of SHIV-89.6P stock virus, which induces prominent CD4 cell loss within a month after inoculation in monkeys, we have constructed four infectious molecular clones (cl 18, cl 64, cl 69, and cl 71). Cl 64, cl 69, and cl 71, like the parental virus, showed a high in vitro replication ability and a pathogenic-like effect (CD4 downmodulation) in a monkey CD4(+) cell line, whereas cl 18 showed a lower replication ability and could not downmodulate CD4. Cl 64, which has characteristics similar to those of the parental virus in vitro, was inoculated into four rhesus monkeys. All monkeys showed a plasma viral load similar to that of the parental virus with a peak at 2 weeks after inoculation. However, the viral load gradually decreased and the virus failed to cause an AIDS-like disease in infected monkeys, but it induced a strong antiviral antibody response. These results demonstrate the polyclonal nature of the parental SHIV-89.6P virus stock and demonstrate that cl 64, aside from its high replicability, may differ qualitatively from the parental virus.

Detection of viral RNA in CD4(-)CD8(-) and CD4(-)CD8(+) lymphocytes in vivo in rhesus monkeys infected with simian immunodeficiency virus of macaques

A definition of the specific cell types that support HIV replication early in the course of infection will be important for understanding AIDS pathogenesis and designing strategies for preventing infection. Observations have indicated that the population of lymphocytes susceptible to productive infection extends beyond activated CD4(+) T cells. To explore this issue, we have employed laser scanning cytometry technology and the techniques of lymphocyte surface immunophenotyping followed by fluorescent in situ hybridization to detect simian immunodeficiency virus of macaques (SIVmac) RNA in phenotypically defined rhesus monkey lymphocytes. The immunophenotype of productively infected cells in either a rhesus monkey T cell line or in PBMCs infected in vitro with SIVmac was remarkably similar to that observed in productively infected PBMCs obtained from monkeys during primary infection. We observed low levels or no detectable expression of CD4 on cells infected in vitro or on PBMCs of infected monkeys. However, a substantial number of SIVmac-infected PBMCs both in cultured lymphocytes and sampled directly from infected monkeys expressed CD8 but not CD4. These observations are consistent with the possibility that the CD4 molecule may be modulated off the surface of CD4(+)CD8(-) or CD4(+)CD8(+) lymphocytes after infection or that infection occurred via a CD4-independent mechanism. Moreover, there was no preferential expression of CD25 on cells positive for SIVmac RNA, which might have been predicted if replication of the virus was occurring selectively in activated lymphocytes. These results broaden the range of lymphocytes that support productive SIVmac infection to include CD4(-)CD8(-) and CD4(-)CD8(+) subsets, and are consistent with virus replication occurring in nonactivated cells.

Response differences between human CD4(+) and CD8(+) T-cells during CD28 costimulation: implications for immune cell-based therapies and studies related to the expansion of double-positive T-cells during aging

Since CD28 costimulation is critical for T-cell activation, there is great interest in CD28 as a target for immuntherapeutic approaches. We show that stimulation of human CD4(+) and CD8(+) T-cells differs in their responsiveness to stimulation with anti-CD3/CD28-coated beads, as surrogate antigen-presenting cells. While the CD4(+) subset responded with sustained proliferation, CD8(+) T-cells grew for a limited period only and failed to produce IL-2 beyond the first few days in culture. This decrease is accompanied with an increased rate of apoptosis in CD8(+) T-cells despite Bcl-x(L) expression. The CD8(+) but not the CD4(+) subset developed a reversible double-positive phenotype during CD28 costimulation. This finding may have some bearing on the appearance of double-positive T-cells in human peripheral blood. This double-positive subset was shown to undergo a statistically significantly increase during aging in humans. Taken together, the above data have important implications for immunotherapy and immune senescence.

Suppression of acute viremia by short-term postexposure prophylaxis of simian/human immunodeficiency virus SHIV-RT-infected monkeys with a novel reverse transcriptase inhibitor (GW420867) allows for development of potent antiviral immune responses resulting in efficient containment of infection

A nonnucleoside reverse transcriptase (RT) inhibitor, GW420867, was tested for postexposure prophylaxis (PEP) in rhesus macaques experimentally infected with 100 50% tissue culture infective doses of a chimeric simian/human immunodeficiency virus (SHIV) containing the RT gene of HIV-1 (SHIV-RT). Animals were either mock treated, or treated for 4 weeks starting at 8 or 24 h postinfection (p.i.) with GW420867. While such therapy led to undetectable plasma viremia in three of six monkeys, a transient plasma viremia was noted in the other three treated animals at 2 to 4 weeks following cessation of therapy. Following this transient viremia all drug-treated animals showed low or undetectable levels of plasma viremia up to the last sample examined at 90 weeks p.i. Despite low and/or undetectable viremia, virus-specific cytotoxic T lymphocyte and viral Env-specific proliferative responses were seen in the peripheral blood mononuclear cells of both mock- and drug-treated animals as early as 3 weeks p.i. Such virus-specific cellular responses, however, were better maintained in the drug-treated animals than the mock-treated animals. In contrast to the virus-specific cellular response, the magnitude and kinetics of virus specific humoral responses appeared to correlate with the detection of viremia. These data support the view that a short-term PEP with GW420867 permits the generation and maintenance of long-lasting virus-specific cell-mediated immune responses while markedly reducing viral loads to undetectable levels for a prolonged period of time (90 weeks) and leads to long-term disease protection. This model provides a unique means to define mechanisms and correlates of disease protection.

Peripheral blood extrathymic CD4(+)CD8(+) T cells with high cytotoxic activity are from the same lineage as CD4(+)CD8(-) T cells in cynomolgus monkeys

We have previously reported that CD4/CD8 double-positive (DP) T cells with the resting memory phenotype are present in the periphery of healthy cynomolgus monkeys. In the present study, we performed functional studies on the T cells. The expression of CD4 and CD8 on DP, CD4 single-positive (SP) or CD8 SP T cells was stable in cultures with either mitogen or anti-CD3 antibody stimulation. In spite of lacking CD28 expression, DP T cells showed similar proliferative ability and apoptosis sensitivity to CD4 SP and CD8 SP T cells. DP T cells showed both helper and cytotoxic activities. Although the helper activity of DP T cells was lower than that of CD4 SP T cells, cytotoxic activity was comparable to that of CD8 SP T cells. Fresh DP T cells killed target cells mainly by the perforin-granzyme pathway. In addition, fresh DP T cells expressed a high level of mRNA for IFN-gamma and produced a high level of IFN-gamma when they were activated by anti-CD3 antibody ligation. On the other hand, several expanded DP T cell clones shared TCR V(beta) with expanded CD4 SP T cell clones, strongly suggesting that those two corresponding clones with DP and CD4 SP phenotypes might be derived from the same ancestor T cell. These results showed that the DP T cells are a novel T cell subset with functions overlapping with those of CD4 SP and CD8 SP T cells, and that they might play protective and regulatory roles in secondary immune response in cynomolgus monkeys.

Herpesvirus saimiri–transformed macaque T cells are tolerated and do not cause lymphoma after autologous reinfusion

Human T cells are transformed in vitro to stable growth after infection with herpesvirus saimiri subgroup C strain C488, and they retain their antigen-specific reactivity and other important functional features of mature activated T lymphocytes. The virus persists as nonintegrating episomes in human T cells under restricted viral gene expression and without production of virus particles. This study analyzes the behavior of herpesvirus-transformed autologous T cells after reinfusion into the donor under close-to-human experimental conditions. T cells of 5 macaque monkeys were transformed to stable interleukin-2 dependent growth and were intravenously infused into the respective donor. The animals remained healthy, without occurrence of lymphoma or leukemia for an observation period of more than 1 year. Over several months virus genomes were detectable in peripheral blood cells and in cultured T cells by polymerase chain reaction. In naive control animals, a high-dose intravenous infection rapidly induced pleomorphic peripheral T-cell lymphoma. In contrast, monkeys were protected from lymphoma after challenge infection if they had previously received autologous T-cell transfusions. High levels of antibodies against virus antigens were detectable after challenge infection only. Taken together, herpesvirus-transformed T cells are well tolerated after autologous reinfusion. This may allow us to develop a novel concept for adoptive T-cell mediated immunotherapy.