Generation of macaque B lymphoblastoid cell lines with simian Epstein-Barr-like viruses: transformation procedure, characterization of the cell lines and occurrence of simian foamy virus

Identification and Characterization of Antigen-Specific CD8+ T Cells Using Surface-Trapped TNF-α and Single-Cell Sequencing

CD8+ T cells are key mediators of antiviral and antitumor immunity. The isolation and study of Ag-specific CD8+ T cells, as well as mapping of their MHC restriction, has practical importance to the study of disease and the development of therapeutics. Unfortunately, most experimental approaches are cumbersome, owing to the highly variable and donor-specific nature of MHC-bound peptide/TCR interactions. Here we present a novel system for rapid identification and characterization of Ag-specific CD8+ T cells, particularly well suited for samples with limited primary cells. Cells are stimulated ex vivo with Ag of interest, followed by live cell sorting based on surface-trapped TNF-α. We take advantage of major advances in single-cell sequencing to generate full-length sequence data from the paired TCR α- and β-chains from these Ag-specific cells. The paired TCR chains are cloned into retroviral vectors and used to transduce donor CD8+ T cells. These TCR transductants provide a virtually unlimited experimental reagent, which can be used for further characterization, such as minimal epitope mapping or identification of MHC restriction, without depleting primary cells. We validated this system using CMV-specific CD8+ T cells from rhesus macaques, characterizing an immunodominant Mamu-A1*002:01-restricted epitope. We further demonstrated the utility of this system by mapping a novel HLA-A*68:02-restricted HIV Gag epitope from an HIV-infected donor. Collectively, these data validate a new strategy to rapidly identify novel Ags and characterize Ag-specific CD8+ T cells, with applications ranging from the study of infectious disease to immunotherapeutics and precision medicine.

The Role of MHC-E in T Cell Immunity Is Conserved among Humans, Rhesus Macaques, and Cynomolgus Macaques

MHC-E is a highly conserved nonclassical MHC class Ib molecule that predominantly binds and presents MHC class Ia leader sequence-derived peptides for NK cell regulation. However, MHC-E also binds pathogen-derived peptide Ags for presentation to CD8+ T cells. Given this role in adaptive immunity and its highly monomorphic nature in the human population, HLA-E is an attractive target for novel vaccine and immunotherapeutic modalities. Development of HLA-E-targeted therapies will require a physiologically relevant animal model that recapitulates HLA-E-restricted T cell biology. In this study, we investigated MHC-E immunobiology in two common nonhuman primate species, Indian-origin rhesus macaques (RM) and Mauritian-origin cynomolgus macaques (MCM). Compared to humans and MCM, RM expressed a greater number of MHC-E alleles at both the population and individual level. Despite this difference, human, RM, and MCM MHC-E molecules were expressed at similar levels across immune cell subsets, equivalently upregulated by viral pathogens, and bound and presented identical peptides to CD8+ T cells. Indeed, SIV-specific, Mamu-E-restricted CD8+ T cells from RM recognized antigenic peptides presented by all MHC-E molecules tested, including cross-species recognition of human and MCM SIV-infected CD4+ T cells. Thus, MHC-E is functionally conserved among humans, RM, and MCM, and both RM and MCM represent physiologically relevant animal models of HLA-E-restricted T cell immunobiology.

Induction of encephalitis in rhesus monkeys infused with lymphocryptovirus-infected B-cells presenting MOG(34-56) peptide

The overlapping epidemiology of multiple sclerosis (MS) and Epstein-Barr virus (EBV), the increased risk to develop MS after infectious mononucleosis (IM) and the localization of EBV-infected B-cells within the MS brain suggest a causal link between EBV and MS. However, the underlying mechanism is unknown. We hypothesize that EBV-infected B-cells are capable of eliciting a central nervous system (CNS) targeting autoimmune reaction. To test this hypothesis we have developed a novel experimental model in rhesus monkeys of IM-like disease induced by infusing autologous B-lymphoblastoid cells (B-LCL). Herpesvirus papio (HVP) is a lymphocryptovirus related to EBV and was used to generate rhesus monkey B-LCL. Three groups of five animals were included; each group received three intravenous infusions of B-LCL that were either pulsed with the encephalitogenic self peptide MOG_34–56 (group A), a mimicry peptide (981–1003) of the major capsid protein of cytomegalovirus (CMVmcp_981–1003; group B) or the citrullinated MOG_34–56 (cMOG_34–56; group C). Groups A and B received on day 98 a single immunization with MOG_34–56 in incomplete Freund’s adjuvant (IFA). Group C monkeys were euthanized just prior to day 98 without booster immunization. We observed self-peptide-specific proliferation of T-cells, superimposed on similar strong proliferation of CD3⁺CD8⁺ T-cells against the B-LCL as observed in IM. The brains of several monkeys contained perivascular inflammatory lesions of variable size, comprising CD3⁺ and CD68⁺ cells. Moreover, clusters of CD3⁺ and CD20⁺ cells were detected in the meninges. The only evident clinical sign was substantial loss of bodyweight (>15%), a symptom observed both in early autoimmune encephalitis and IM. In conclusion, this model suggests that EBV-induced B-LCL can elicit a CNS targeting inflammatory (auto)immune reaction.

Cytomegalovirus vectors violate CD8+ T cell epitope recognition paradigms

CD8(+) T cell responses focus on a small fraction of pathogen- or vaccine-encoded peptides, and for some pathogens, these restricted recognition hierarchies limit the effectiveness of antipathogen immunity. We found that simian immunodeficiency virus (SIV) protein-expressing rhesus cytomegalovirus (RhCMV) vectors elicit SIV-specific CD8(+) T cells that recognize unusual, diverse, and highly promiscuous epitopes, including dominant responses to epitopes restricted by class II major histocompatibility complex (MHC) molecules. Induction of canonical SIV epitope-specific CD8(+) T cell responses is suppressed by the RhCMV-encoded Rh189 gene (corresponding to human CMV US11), and the promiscuous MHC class I- and class II-restricted CD8(+) T cell responses occur only in the absence of the Rh157.5, Rh157.4, and Rh157.6 (human CMV UL128, UL130, and UL131) genes. Thus, CMV vectors can be genetically programmed to achieve distinct patterns of CD8(+) T cell epitope recognition.

A novel protective MHC-I haplotype not associated with dominant Gag-specific CD8+ T-cell responses in SIVmac239 infection of Burmese rhesus macaques

Several major histocompatibility complex class I (MHC-I) alleles are associated with lower viral loads and slower disease progression in human immunodeficiency virus (HIV) and simian immunodeficiency virus (SIV) infections. Immune-correlates analyses in these MHC-I-related HIV/SIV controllers would lead to elucidation of the mechanism for viral control. Viral control associated with some protective MHC-I alleles is attributed to CD8+ T-cell responses targeting Gag epitopes. We have been trying to know the mechanism of SIV control in multiple groups of Burmese rhesus macaques sharing MHC-I genotypes at the haplotype level. Here, we found a protective MHC-I haplotype, 90-010-Id (D), which is not associated with dominant Gag-specific CD8+ T-cell responses. Viral loads in five D+ animals became significantly lower than those in our previous cohorts after 6 months. Most D+ animals showed predominant Nef-specific but not Gag-specific CD8+ T-cell responses after SIV challenge. Further analyses suggested two Nef-epitope-specific CD8+ T-cell responses exerting strong suppressive pressure on SIV replication. Another set of five D+ animals that received a prophylactic vaccine using a Gag-expressing Sendai virus vector showed significantly reduced viral loads compared to unvaccinated D+ animals at 3 months, suggesting rapid SIV control by Gag-specific CD8+ T-cell responses in addition to Nef-specific ones. These results present a pattern of SIV control with involvement of non-Gag antigen-specific CD8+ T-cell responses.

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

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

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.

Induction of Gag-specific T-cell responses by therapeutic immunization with a Gag-expressing Sendai virus vector in macaques chronically infected with simian-human immunodeficiency virus

Recent prophylactic vaccine trials inducing virus-specific CD8+ T-cell responses have shown control of primary infections of a pathogenic simian-human immunodeficiency virus (SHIV) in macaques. In the chronic phase, therapeutic immunization replenishing virus-specific CD8+ T-cells is likely to contribute to sustained control of virus replication. In this study, we have administered a recombinant Sendai virus (SeV) vector into five rhesus macaques that had received prophylactic vaccinations and had controlled SHIV replication for more than 1 year after challenge. Our results indicate that virus-specific CD8+ T-cell responses can be expanded and broadened by therapeutic immunization with SeV vectors in the chronic phase after prophylactic vaccine-based control of primary immunodeficiency virus infections.

Cytotoxic T lymphocyte-based control of simian immunodeficiency virus replication in a preclinical AIDS vaccine trial

Recently, encouraging AIDS vaccine trials in macaques have implicated cytotoxic T lymphocytes (CTLs) in the control of the simian human immunodeficiency virus SHIV89.6P that induces acute CD4⁺ T cell depletion. However, none of these vaccine regimens have been successful in the containment of replication of the pathogenic simian immunodeficiency viruses (SIVs) that induce chronic disease progression. Indeed, it has remained unclear if vaccine-induced CTL can control SIV replication. Here, we show evidence suggesting that vaccine-induced CTLs control SIVmac239 replication in rhesus macaques. Eight macaques vaccinated with DNA-prime/Gag-expressing Sendai virus vector boost were challenged intravenously with SIVmac239. Five of the vaccinees controlled viral replication and had undetectable plasma viremia after 5 wk of infection. CTLs from all of these five macaques rapidly selected for escape mutations in Gag, indicating that vaccine-induced CTLs successfully contained replication of the challenge virus. Interestingly, analysis of the escape variant selected in three vaccinees that share a major histocompatibility complex class I haplotype revealed that the escape variant virus was at a replicative disadvantage compared with SIVmac239. These findings suggested that the vaccine-induced CTLs had “crippled” the challenge virus. Our results indicate that vaccine induction of highly effective CTLs can result in the containment of replication of a highly pathogenic immunodeficiency virus.

Characterization of rhesus macaque natural killer activity against a rhesus-derived target cell line at the single-cell level

Natural killer (NK) cells and NK cell activities in the rhesus macaque have been incompletely characterized. Using a recently developed rhesus NK target cell line with down-regulated MHC-I (B116Lo) as stimulators and FACS-sorted cells as effectors in a 4-h [51Cr]-release assay we showed that the CD3-CD8lo subpopulation is the primary effector population for NK cell-mediated cytolysis. The majority of these cells co-express CD16, CD11b, NKG2D, and NKp46. To evaluate functional activity at the individual cell level, we employed intracellular cytokine staining and a flow cytometric assay for degranulation, based on cell surface CD107a expression. Flow cytometric analysis revealed that a greater proportion of NK cells degranulated than produced cytokines in response to B116Lo stimulation; the frequency of CD107a-expressing cells within the total NK cell population ranging from 5 to 39%. Somewhat surprisingly, we did not find a significant correlation between lysis, measured by [51Cr]-release assay, and the size of the degranulating NK cell population, implying that additional mechanisms may regulate lytic activity. Use of these approaches should facilitate an improved understanding of NK activity in the rhesus macaque.

Loss of virus-specific CD4(+) T cells with increases in viral loads in the chronic phase after vaccine-based partial control of primary simian immunodeficiency virus replication in macaques

Virus-specific cellular immune responses play an important role in the control of immunodeficiency virus replication. However, preclinical trials of vaccines that induce virus-specific cellular immune responses have failed to contain simian immunodeficiency virus (SIV) replication in macaques. A defective provirus DNA vaccine system that efficiently induces virus-specific CD8(+) T-cell responses has previously been developed. The vaccinated macaques showed reduced viral loads, but failed to contain SIVmac239 replication. In this study, macaques that showed partial control of SIV replication were followed up to see if or how they lost this control in the chronic phase. Two of them showed increased viral loads about 4 or 8 months after challenge and finally developed AIDS. Analysis of SIV-specific T-cell levels by detection of SIV-specific gamma interferon (IFN-gamma) production revealed that these two macaques maintained SIV-specific CD8(+) T cells, even after loss of control, but lost SIV-specific CD4(+) T cells when plasma viral loads increased. The remaining macaque kept viral loads at low levels and maintained SIV-specific CD4(+) T cells, as well as CD8(+) T cells, for more than 3 years. Additional analysis using macaques vaccinated with a Gag-expressing Sendai virus vector also found loss of viraemia control, with loss of SIV-specific CD4(+) T cells in the chronic phase of SIV infection. Thus, SIV-specific CD4(+) T cells that were able to produce IFN-gamma in response to SIV antigens were preserved by the vaccine-based partial control of primary SIV replication, but were lost with abrogation of control in the chronic phase.

Replication of primate foamy viruses in natural and experimental hosts

Foamy viruses (FVs) are common apathogenic retroviruses readily spread by horizontal transmission in nonhuman primate and some other mammalian host populations. Primate FV infections have been known for half a century, i.e., 15 years before the definition of retroviruses and another 15 years before the detection of primate immune deficiency viruses. The emerging interest in human retroviruses included primate FV, and although the role of human hosts for FV was greatly overestimated temporarily, enthusiastic researchers compiled invaluable data on molecular biology and classic as well as molecular epidemiology of these viruses. It has been shown that lytic FV infection in a wide range of cell cultures is in great contrast to the silent state of the infection in animals. Once transmitted by saliva via biting, FVs reside in all tissues as DNA copies, but their replication is untraceable except in oral submucosal cells, which are thought to supply the virus for transmission. FVs have not definitely been associated with any disease, regardless of viral phylogenetic differences. Various primate and nonprimate species have been used for studies on the natural carrier state and primary infection. Experimental infections have mostly proven to be inefficient in primates as well as lower laboratory animals. However, investigation of the immune response in FV-infected animals has only partly explained the control of FV replication in the animal host. Thus, the biological role of FV remains an enigma to be resolved in the future.

Protective efficacy of an AIDS vaccine, a single DNA priming followed by a single booster with a recombinant replication-defective Sendai virus vector, in a macaque AIDS model

We previously demonstrated the excellent protective efficacy of DNA priming followed by Gag-expressing Sendai virus (SeV) boosting (DNA prime/SeV-Gag boost vaccine) against a pathogenic simian-human immunodeficiency virus (SHIV89.6PD) infection in macaques. Here we show that we established a practical, safer AIDS vaccine protocol, a single DNA priming followed by a single booster with a recently developed replication-defective F deletion SeV-expressing Gag, and show its protective efficacy against SHIV89.6PD infections.

Primary replication of a recombinant Sendai virus vector in macaques

An efficient antigen expression system using a recombinant Sendai virus (SeV) has been established recently and its potential to induce resistance against immunodeficiency virus infections in macaques has been shown. SeV replication has been well characterized in mice, the natural host, but not in primates, including humans. Here, primary SeV replication was investigated in macaques. After intranasal immunization with a recombinant SeV expressing simian immunodeficiency virus Gag protein, SeV-Gag, robust gag expression was observed in the nasal mucosa and much lower but significant levels of gag expression were observed in the local retropharyngeal and submandibular lymph nodes (LN). Expression peaked within a week and lasted at least up to 13 days after immunization. SeV-Gag was isolated from nasal swabs consistently at day 4 but not at all at day 13. Gag expression was undetectable in the lung as well as in remote lymphoid tissues, such as the thymus, spleen and inguinal LN, indicating that the spread of the virus was more restricted in macaques than in mice. SeV-specific T cells were detectable in SeV-immunized macaques at day 7. Finally, no naive macaques showed significant levels of anti-SeV antibodies in the plasma, even after living in a cage together with an acutely SeV-infected macaque for 5 weeks, indicating that SeV transmission from SeV-infected macaques to naive ones was inefficient. None of the SeV-immunized macaques displayed appreciable clinical manifestations. These results support the idea that this system may be used safely in primates, including humans.

Rapid appearance of secondary immune responses and protection from acute CD4 depletion after a highly pathogenic immunodeficiency virus challenge in macaques vaccinated with a DNA prime/Sendai virus vector boost regimen

Heterologous prime/boost regimens are AIDS vaccine candidates because of their potential for inducing cellular immune responses. Here, we have developed a prime/boost regimen leading to rapid control of highly pathogenic immunodeficiency virus infection in macaques. The strategy, priming by an env and nef deletion-containing simian-human immunodeficiency virus (SHIV) proviral DNA followed by a single booster with a Gag-expressing Sendai virus (SeV-Gag), efficiently induced virus-specific T cells, which were maintained for more than 3 months until challenge. While all naive control macaques showed acute CD4(+) T-cell depletion at week 2 after an intravenous SHIV89.6PD challenge, all the macaques vaccinated with the prime/boost regimen were protected from depletion and showed greatly reduced peak viral loads compared with controls. Vaccination with the DNA alone or SeV-Gag alone was not enough to confer the consistent protection from the depletion, although it led to efficient secondary CD8(+) T-cell responses at week 2 after challenge. At week 1, a difference in the secondary responses between the protected and the unprotected macaques was clear; rapid augmentation of virus-specific CD8(+) T cells was detected in the former but not in the latter. Thus, our results indicate the importance of rapid secondary responses for reduction in the peak viral loads and protection from acute CD4(+) T-cell depletion.

Induction of protective immunity against pathogenic simian immunodeficiency virus by a foreign receptor-dependent replication of an engineered avirulent virus

In AIDS vaccine strategies, live attenuated vaccines can confer good resistance against pathogenic virus infections but have the potential risk of inducing disease, whereas safer replication-negative strategies such as DNA vaccinations have so far failed to prevent the disease onset. Here, we developed a novel DNA vaccine strategy to induce restricted replication of an avirulent virus and evaluated it in a simian immunodeficiency virus (SIV) infection model. We generated a chimeric SIV, FMSIV, by replacing SIV env with ecotropic Friend murine leukemia virus (FMLV) env to confine its replication to FMLV receptor (mCAT1)-expressing cells. In primate cells lacking mCAT1, FMSIV did not replicate unless mCAT1 was introduced exogenously. Vaccination to macaques with both the FMSIV DNA and the mCAT1-expression plasmid DNA induced SIV Gag-specific cellular immune responses and resistance against pathogenic SIV(mac239) challenge more efficiently than the replication-negative control vaccination with the FMSIV DNA alone. This strategy may be useful for development of safe and effective vaccines against various kinds of pathogenic viruses.

Prenatal stress and immune recognition of self and nonself in the primate neonate

The capacity of the neonate to respond to nonself antigens was evaluated in infant monkeys born after normal and disturbed pregnancies. Mixed lymphocyte cultures were used to test the infants' proliferative responses to mitomycin-treated stimulator cells, either from a genetically unrelated animal or from a virally transformed monkey cell line. Periods of daily stress for 6 weeks in mid-late pregnancy (months 3.0-4.5) resulted in a significant decrease in proliferative responses, whereas the same stressor early in pregnancy (months 1.5-3.0) increased responses by the neonate's cells. Similar to the late stress effect, an inhibition of proliferative responses by neonatal cells was induced by dexamethasone administered for 2 days late in pregnancy at 4.5 months after conception, 1 month before term. These findings demonstrate that certain immune responses at birth are extremely sensitive to prior prenatal events. Further, the bidirectional changes indicate that there may be critical periods in gestation when the same extrinsic events have radically different effects on the fetus.

Antigen-specific cytokine responses in vaccinated Macaca nemestrina

We describe a new surrogate assay for CD8 + T lymphocyte activity that has the capability of discriminating between cytotoxic T lymphocyte (CTL) activity and cytokine-mediated suppressive activity. We applied this approach to two groups of Macaca nemestrina vaccinated with a minimally pathogenic strain of human immunodeficiency virus type 2 [HIV-2 (HIV-2(KR))] as a model of an attenuated virus vaccine. Group 1 was then inoculated with a non-infectious stock of a pathogenic strain, HIV-2287. Both groups 1 and 2 were subsequently challenged with an infectious stock of HIV-2287. Five out of six group 1 animals were protected against CD4 decline, whereas three out of six animals in group 2 were protected. Analysis of CTL responses demonstrated strong activity against HIV-2(KR)-Gag in group 1. It was determined that strong CTL responses correlate with antigen-specific T-helper (Th) type 1 responses. This antigen-specific cytokine assay has the potential to better elucidate the functional mechanisms of CD8 + T-cell-mediated protection than traditional methods to date.

Sensitive assays for isolation and detection of simian foamy retroviruses

Simian foamy viruses (SFVs) are highly prevalent in a variety of nonhuman primate species ranging from prosimians to apes. SFVs possess a broad host range, and human infections can occur by cross-species transfer (W. Heneine et al., Nat. Med. 4:403-407, 1998). Retrovirus screening of potential sources of infection, such as laboratory research animals and simian-derived biological products, could minimize human exposure to SFVs by reducing the risk of potential retrovirus infection in humans. We describe a variety of sensitive assays for SFV isolation and detection which were developed with a prototype strain of SFV serotype 2. The Mus dunni cell line (M. R. Lander and S. K. Chattopadhyay, J. Virol. 52:695-698, 1984) was found to be highly sensitive for SFV production on the basis of various general and specific retrovirus detection assays such as reverse transcriptase assay, transmission electron microscopy, immunofluorescence assay, and Western blotting. A highly sensitive PCR assay was developed on the basis of the sequences in primary SFV isolates obtained from pig-tailed macaques (Macaca nemestrina) and rhesus macaques (Macaca mulatta). Analysis of naturally occurring SFV infection in macaques indicated that analysis by a combination of assays, including both highly sensitive, specific assays and less sensitive, broadly reactive assays, is important for evaluation of retrovirus infection.

Simultaneous induction of multiple antigen-specific cytotoxic T lymphocytes in nonhuman primates by immunization with a mixture of four Plasmodium falciparum DNA plasmids

CD8(+) T cells have been implicated as critical effector cells in protective immunity against malaria parasites developing within hepatocytes. A vaccine that protects against malaria by inducing CD8(+) T cells will probably have to include multiple epitopes on the same protein or different proteins, because of parasite polymorphism and genetic restriction of T-cell responses. To determine if CD8(+) T-cell responses against multiple P. falciparum proteins can be induced in primates by immunization with plasmid DNA, rhesus monkeys were immunized intramuscularly with a mixture of DNA plasmids encoding four P. falciparum proteins or with individual plasmids. All six monkeys immunized with PfCSP DNA, seven of nine immunized with PfSSP2 DNA, and five of six immunized with PfExp-1 or PfLSA-1 DNA had detectable antigen-specific cytotoxic T lymphocytes (CTL) after in vitro restimulation of peripheral blood mononuclear cells. CTL activity was genetically restricted and dependent on CD8(+) T cells. By providing the first evidence for primates that immunization with a mixture of DNA plasmids induces CD8(+) T-cell responses against all the components of the mixture, these studies provide the foundation for multigene immunization of humans.

Generation of herpes virus saimiri-transformed T-cell lines from macaques is restricted by reactivation of simian spuma viruses

Herpes virus saimiri (HVS) transforms human T-cells in vitro to stable growth. These T-cell lines retain their immunological characteristics of the parent cells and do not release infectious virus. Recently, lymphocytes of Old World monkeys were efficiently transformed by HVS. In parallel to these studies we initiated transformation experiments by infecting peripheral blood cell cultures of 45 monkeys, 35 rhesus and 10 cynomolgus macaques. In only three cases, we obtained transformed T-cell lines. The transformed T-cells were largely double-positive for CD4 and CD8. They responded with increased proliferation to mitogenic or IL-2 stimulation and transcribed mRNA for IL-2, IL-4, and IL-10. However, most initiated T-cell cultures from macaques developed giant cells. The cytopathic agent was identified as simian foamy virus (SFV) as confirmed by PCR, immunofluorescence, and coculture experiments. Treatment of the T-cell cultures with AZT- and SFV-specific sera did only shortly prolong the life-span of the cultures. Therefore, the reactivation of SFV caused remarkable difficulties in the establishment of macaque T-cell lines by HVS. This seems to be a general problem since most animals from several breeding colonies are SFV-positive.

Inhibition of the in vitro infectivity and cytopathic effect of human foamy virus by dideoxynucleosides

Human foamy virus (HFV) is a human retrovirus that has not been clearly associated with human disease. In this study, we tested the capacity of nucleoside derivatives to inhibit the infectivity and cytopathic effect of HFV in T-lymphoblastoid cells in vitro. H9 cells showed a dramatic cytopathic effect 3 weeks after exposure to HFV. At this time, viral infection was demonstrated by detection of viral antigens by immunofluorescence staining, release of reverse transcriptase activity (RT) in the supernatant, detection of typical viral particles by electron microscopy, and presence of proviral DNA by Southern blot analysis. H9 cells were pretreated with dideoxycytidine (ddC), dideoxyinosine (ddI), or azidothymidine (AZT) at various concentrations before HFV infection. ddC could not completely suppress viral replication at low concentrations, and inhibited cell proliferation at higher concentrations. ddI partially inhibited the formation of giant cells at 10 microM, with 95% inhibition of RT in the supernatant. AZT induced a complete inhibition of cytopathic effect at concentrations > or = 1 microM, with more than 95% inhibition of RT in the supernatant. Moreover, the synthesis of proviral DNA was completely suppressed by 10 microM AZT. These results show that AZT and ddI can inhibit HFV replication in vitro.

Definition of human immunodeficiency virus type 1 gp120 and gp41 cytotoxic T-lymphocyte epitopes and their restricting major histocompatibility complex class I alleles in simian-human immunodeficiency virus-infected rhesus monkeys

With the development of chimeric simian-human immunodeficiency virus (SHIV)-infected macaques as a model for assessing novel human immunodeficiency virus type I (HIV-1) envelope glycoprotein (Env)-based vaccine strategies for preventing HIV-1 infection in man, it will be important to determine HIV-1 Env-specific cytotoxic T-lymphocyte (CTL) responses in vaccinated and virus-infected monkeys. To facilitate performing such CTL studies, we have defined two HIV-1 Env CTL epitopes in SHIV-infected rhesus monkeys and characterized the major histocompatibility complex (MHC) class I alleles that bind these Env peptide fragments and present them to CTL. A 9-amino-acid (aa) fragment of HIV-1 gp4l (p6B, aa 553 to 561) is presented to CD8+ CTLs of SHIV-infected animals by the rhesus monkey HLA-B homolog molecule Mamu-B*12. An 8-aa HIV-1 gpl.20 peptide (p9CD, aa 117 to 124) represents a CTL epitope in rhesus monkeys restricted by the HLA-A homolog MHC allele Mamu-A*08. This gp120 CTL epitope is fully conserved in all simian immunodeficiency virus, HIV-1, and HIV-2 isolates that have been sequenced to date and exhibits functional cross-reactivity. Screening of 14 unselected rhesus monkeys for expression of the two novel MHC class I alleles revealed the presence of each of the alleles in more than 40% of the animals. The characterization of the two HIV-1 Env CTL epitopes and their restricting MHC class I alleles will provide a basis for studying vaccine- and virus-elicited cytotoxic effector cell responses in rhesus monkeys.

Cell-mediated immune response of macaques immunized with low doses of simian immunodeficiency virus (SIV)

Many uninfected people at high risk of HIV infection developed an HIV-specific cellular immune response despite their lack of seroconversion. Therefore, they must have been exposed to HIV without subsequent infection. It has been concluded from these data, that cell-mediated immunity (CMI) rather than humoral immunity might confer protection to HIV infection. Therefore, we tried to induce such a strong CMI in macaques by different immunization strategies. Five or seven animals were immunized with high or low doses of a whole SIV split vaccine. The lower dose of the vaccine provoked a stronger T-helper cell (TH) proliferation than the higher dose, which led to a pronounced humoral immune response. To induce a strong CMI without any specific antibody response, five macaques were inoculated with low doses of infectious SIV. None of these animals seroconverted but each animal developed a SIV-specific TH response. Interestingly, we could neither detect an SIV-specific CTL activity in the animals nor did we find typical TH1- or TH2-like cytokine profiles investigating stimulated bulk-cultures from SIV-exposed animals by RT-PCR. 24 weeks after the first low dose SIV exposure the animals were boosted by a second low dose of SIV followed by a subsequent intravenous challenge with a high dose of SIV 12 weeks later. Unexpectedly, none of the animals was found to be protected against infection and the development of AIDS-like symptoms.

Characterization of the natural immune response of rhesus monkey CD4+ve T cells to the bacterial antigen streptolysin O (SLO)

Rhesus monkeys show a high proliferative T cell response to the bacterial exotoxin SLO without prior immunization. The present study was undertaken to characterize this naturally present SLO-responsiveness with particular emphasis on CD4+ve reactive T cells. It is demonstrated that the frequency of SLO-reactive cells in the circulation.ranges between 1 in 75 and 1 in 610 CD4+ve T cells as determined with limiting dilution analysis. It is also shown that induction of a good proliferative response requires Mhc-DR matching between T cell and the antigen presenting cells (APC). Stable and DR-restricted SLO-specific CD4+ve T cell lines were generated from CD8 depleted peripheral blood mononuclear cells (PBMC). The SLO-reactive CD4+ve cell lines are tentatively characterized as Th1-like based on the predominant production of interferon-gamma (IFN-gamma) over IL-4, although this seems contradicted by the IL-4 dependent growth of the lines.