Antigenic stimulation by BCG vaccine as an in vivo driving force for SIV replication and dissemination.

The impact of antigenic stimulation on the dynamics of simian immunodeficiency virus (SIV) replication was studied following repeated intravenous BCG inoculation of a SIV infected macaque. At the site of a delayed type hypersensitivity reaction to purified protein derivative of M. tuberculosis, a distinctive SIV variant was noted, probably as a result of the infiltration of activated antigen-specific T cell clones as opposed to infection by blood borne virus in situ. The dynamics of SIV quasispecies in peripheral blood suggests sequential waves of viral replication, illustrating the role of antigenic stimulation as a driving force in viral dissemination and pathogenesis.

Herpesvirus saimiri strain 11 immortalizes a restricted marmoset T8 lymphocyte subpopulation in vitro.

Herpesvirus saimiri induces a fatal lymphoproliferative syndrome in a variety of New World primate species. We now show that cell lines derived from PBL of the common marmoset by in vitro-immortalization with H. saimiri strain 11 represent a remarkably restricted lymphocyte population. These cell lines have NK cell function, phenotypically express both suppressor/cytotoxic (T8) and NK cell (NKH1)-associated antigens, and express a T cell receptor. This subpopulation of lymphocytes is a very minor population of cells in the peripheral blood of common marmosets (less than or equal to 3%). The specificity in the interaction between H. saimiri strain 11 and a subpopulation of common marmoset lymphocytes represents an example of a restricted viral lymphotropism and may have important implications for the disease induced by this virus in New World monkeys.

A naturally occurring bone marrow-chimeric primate. II. Environment dictates restriction on cytolytic T lymphocyte-target cell interactions.

Restriction on cytolytic T lymphocyte (CTL)-target cell-interactions are studied in the primate S. oedipus, a naturally occurring A + B----A bone marrow-chimeric species. We show that the T cell, B cell, and myelomonocytic progenitor cell populations are chimeric in this species. We selected animals for study that are populated by fully major histocompatibility complex (MHC)-disparate hematopoietic cell populations, using a functional assay system. We then developed an in vitro system for analyzing at the clonal level the genetic restrictions on the trinitrophenyl-specific CTL-target cell interactions of this species. In this system, we have shown that tolerance to foreign MHC determinants was not, of itself, sufficient to facilitate the generation of CTL specific for target cells expressing those foreign MHC determinants. Rather, a marked preference for the expansion of CTL clones with a restriction for target cells bearing the host animals' MHC determinants was seen. Hematopoietically derived cells did not affect the repertoire of these T lymphocytes. These studies represent the first demonstration of the phenomenon of an environment dictating interactional restrictions on CTL in a naturally occurring bone marrow-chimeric animal. This is also the first demonstration of the profound influence of the environment on the repertoire of the T lymphocyte in a primate species.

A cytotoxic T lymphocyte inhibits acquired immunodeficiency syndrome virus replication in peripheral blood lymphocytes.

CD8+ (suppressor/cytotoxic) lymphocytes block replication of HIV-1 or the simian immunodeficiency virus of macaques (SIVmac) in PBL of infected individuals. We now show that these CD8+ lymphocytes undergo clonal expansion in vivo after AIDS virus infection of the individual, suggesting they may be antigen-specific T cells. These CD8+ cells block replication of virus in autologous but not MHC class I-mismatched PBL. The inhibitory lymphocytes express the integrin family molecule 4B4 and the CTL-associated S6F1 epitope of LFA-1. Finally, physical contact is required for the CD8+ lymphocyte-mediated inhibition of AIDS virus replication, since this inhibitory function is blocked by anti-LFA-1 and anti-CD8 mAbs. These studies suggest that the cell that inhibits AIDS virus replication in PBL of infected individuals is a CTL.

Vaccination of rhesus monkeys with synthetic peptide in a fusogenic proteoliposome elicits simian immunodeficiency virus-specific CD8+ cytotoxic T lymphocytes.

An effective vaccine against the human immunodeficiency virus should be capable of eliciting both an antibody and a cytotoxic T lymphocyte (CTL) response. However, when viral proteins and peptides are formulated with traditional immunological adjuvants and inoculated via a route acceptable for use in humans, they have not been successful at eliciting virus-specific, major histocompatibility complex (MHC) class I-restricted CTL. We have designed a novel viral subunit vaccine by encapsulating a previously defined synthetic peptide CTL epitope of the simian immunodeficiency virus (SIV) gag protein within a proteoliposome capable of attaching to and fusing with plasma membranes. Upon fusing, the encapsulated contents of this proteoliposome can enter the MHC class I processing pathway through the cytoplasm. In this report, we show that after a single intramuscular vaccination, rhesus monkeys develop a CD8+ cell-mediated, MHC class I-restricted CTL response that recognizes the synthetic peptide immunogen. The induced CTL also demonstrate antiviral immunity by recognizing SIV gag protein endogenously processed by target cells infected with SIV/vaccinia recombinant virus. These results demonstrate that virus-specific, MHC class I-restricted, CD8+ CTL can be elicited by a safe, nonreplicating viral subunit vaccine in a primate model for acquired immune deficiency syndrome. Moreover, the proteoliposome vaccine formation described can include multiple synthetic peptide epitopes, and, thus, offers a simple means of generating antiviral cell-mediated immunity in a genetically heterogeneous population.

Analysis of Gag-specific cytotoxic T lymphocytes in simian immunodeficiency virus-infected rhesus monkeys by cell staining with a tetrameric major histocompatibility complex class I-peptide complex.

A tetrameric recombinant major histocompatibility complex (MHC) class I-peptide complex was used as a staining reagent in flow cytometric analyses to quantitate and define the phenotype of Gag-specific cytotoxic T lymphocytes (CTLs) in the peripheral blood of simian immunodeficiency virus macaque (SIVmac)-infected rhesus monkeys. The heavy chain of the rhesus monkey MHC class I molecule Mamu-A*01 and beta2-microglobulin were refolded in the presence of an SIVmac Gag synthetic peptide (p11C, C-M) representing the optimal nine-amino acid peptide of Mamu-A*01-restricted predominant CTL epitope to create a tetrameric Mamu-A*01/p11C, C-M complex. Tetrameric Mamu-A*01/p11C, C-M complex bound to T cells of SIVmac-infected, Mamu-A*01(+), but not uninfected, Mamu-A*01(+), or infected, Mamu-A*01(-) rhesus monkeys. Specific staining of peripheral blood mononuclear cells (PBMC) from SIVmac-infected, Mamu-A*01(+) rhesus monkeys was only found in the cluster of differentiation (CD)8alpha/beta+ T lymphocyte subset and the percentage of CD8alpha/beta+ T cells in the peripheral blood of four SIVmac-infected, Mamu-A*01+ rhesus monkeys staining with this complex ranged from 0.7 to 10.3%. Importantly, functional SIVmac Gag p11C-specific CTL activity was seen in sorted and expanded tetrameric Mamu-A*01/p11C, C-M complex-binding, but not nonbinding, CD8alpha/beta+ T cells. Furthermore, the percentage of CD8alpha/beta+ T cells binding this tetrameric Mamu-A*01/p11C, C-M complex correlated well with p11C-specific cytotoxic activity as measured in both bulk and limiting dilution effector frequency assays. Finally, phenotypic characterization of the cells binding this tetrameric complex indicated that this lymphocyte population is heterogeneous. These studies indicate the power of this approach for examining virus-specific CTLs in in vivo settings.

T cell receptor V beta repertoire in an acute infection of rhesus monkeys with simian immunodeficiency viruses and a chimeric simian-human immunodeficiency virus.

Changes in T cell receptor (TCR) V beta repertoire and their correlation with virologic events were investigated in rhesus monkeys after acute infection with the simian immunodeficiency virus (SIV). 11 genetically defined rhesus monkeys were experimentally infected with SIVmac or a chimeric simian-human immunodeficiency virus (SHIV), and their peripheral blood lymphocytes (PBL) and lymph nodes were prospectively assessed for TCR V beta gene expression. PBL and lymph nodes of the acutely infected monkeys demonstrated an expansion of selected V beta-expressing T lymphocyte subpopulations as early as 3 d after infection. These expanded V beta-expressing lymphocyte subpopulations were comprised predominantly of CD8+ cells. Six of seven infected monkeys sharing a single electrophoretically defined major histocompatibility complex class I allele exhibited a similar expansion of V beta 14-expressing PBL. Sequence analyses of V-D-J segments of TCR-beta cDNA indicated that the V beta-expressing T cell subpopulation expansion can be oligoclonal. SIVmac-specific CD8+ cytotoxic T lymphocytes were demonstrated in both PBL and lymph nodes of the infected monkeys at the time expansion of the selected V beta-expressing cell subpopulations was seen. Finally, the expansion of the selected V beta-expressing lymphocytes in PBL coincided with the emergence and clearance of SIV p27 from the plasma of the infected monkeys. These results demonstrate that acute infection of rhesus monkeys with SIVmac or SHIV results in an expansion of CD8+ lymphocyte subpopulations expressing selected V beta gene families. The selectively expanded T lymphocytes may contribute to early viral clearance after acute SIVmac or SHIV infection.

The envelope glycoprotein ectodomains determine the efficiency of CD4+ T lymphocyte depletion in simian-human immunodeficiency virus-infected macaques.

CD4+ T lymphocyte depletion in human immunodeficiency virus type 1 (HIV-1)-infected humans underlies the development of acquired immune deficiency syndrome. Using a model in which rhesus macaques were infected with chimeric simian-human immunodeficiency viruses (SHIVs), we show that both the level of viremia and the structure of the HIV-1 envelope glycoprotein ectodomains individually contributed to the efficiency with which CD4(+) T lymphocytes were depleted. The envelope glycoproteins of recombinant SHIVs that efficiently caused loss of CD4(+) T lymphocytes exhibited increased chemokine receptor binding and membrane-fusing capacity compared with those of less pathogenic viruses. These studies identify the HIV-1 envelope glycoprotein ectodomains as determinants of CD4(+) T lymphocyte loss in vivo and provide a foundation for studying pathogenic mechanisms.

Progress in the development of an HIV-1 vaccine.

Containment of the acquired immunodeficiency syndrome (AIDS) epidemic will require an effective human immunodeficiency virus type 1 (HIV-1) vaccine. Accumulating evidence suggests that such a vaccine must efficiently elicit an HIV-1-specific cytotoxic T lymphocyte (CTL) response. Nonhuman primate models will continue to provide an important tool for assessing the extent of protective immunity induced by various immunization strategies. Although replication-competent AIDS viruses attenuated for pathogenicity by selective gene deletions have provided protective immunity in nonhuman primate models, the long-term safety of such vaccines in human populations is suspect. Inactivated virus and subunit vaccines have elicited neither CTLs nor antibodies capable of neutralizing a wide array of patient HIV-1 isolates. Considerable effort is now being focused on evaluating live vector-based vaccine and plasmid DNA vaccine approaches for preventing HIV-1 infection both in animal model and human studies. Our growing understanding of the biology of HIV-1 and immune responses to this virus will continue to suggest improved vaccination approaches for exploration.

A new type D retrovirus isolated from macaques with an immunodeficiency syndrome.

Macaque monkeys with the recently described acquired immunodeficiency syndrome show a marked defect in T-lymphocyte function and die with opportunistic infections and lymphoproliferative abnormalities. In the study described here a new type D retrovirus was isolated from two Macaca cyclopis with this syndrome. This virus is related to, but distinct from, Mason-Pfizer monkey virus, a type D retrovirus previously isolated from a mammary tumor of a rhesus monkey (Macaca mulatta).

Recombinant virus vaccine-induced SIV-specific CD8+ cytotoxic T lymphocytes.

Evidence indicates that cytotoxic T lymphocytes (CTLs) may be important in containing the spread of the human immunodeficiency virus (HIV) in the infected host. Although the use of recombinant viruses has been proposed as an approach to elicit protective immunity against HIV, the ability of recombinant viral constructs to elicit CD8+ CTL responses in higher primates has never been demonstrated. A live recombinant virus, vaccinia-simian immunodeficiency virus of macaques (SIVmac), was used to determine whether such a genetically restricted, T lymphocyte-mediated antiviral response could be generated in a primate. Vaccinia-SIVmac vaccination elicited an SIVmac Gag-specific, CD8+ CTL response in rhesus monkeys. These CTLs recognized a peptide fragment that spans residues 171 to 195 of the Gag protein. The rhesus monkey major histocompatibility complex (MHC) class I gene product restricting this CTL response was defined. Both the vaccinated and SIVmac-infected monkeys that shared this MHC class I gene product developed CTLs with the same Gag epitope specificity. These findings support the use of recombinant virus vaccines for the prevention of HIV infections in humans.

Induction of AIDS-like disease in macaque monkeys with T-cell tropic retrovirus STLV-III.

The T-cell tropic retrovirus of macaque monkeys STLV-III has morphologic, growth, and antigenic properties indicating that it is related to HTLV-III/LAV, the etiologic agent of the acquired immune deficiency syndrome (AIDS) in humans. Four of six rhesus monkeys died within 160 days of STLV-III inoculation with a wasting syndrome, opportunistic infections, a primary retroviral encephalitis, and immunologic abnormalities including a decrease in T4+ peripheral blood lymphocytes. These data show that an immunodeficiency syndrome can be produced experimentally in a nonhuman primate by an agent from the HTLV-III/LAV group of retroviruses. The STLV-III-macaque system will thus provide a useful model for the study of antiviral agents and vaccine development for human AIDS.

Isolation of T-cell tropic HTLV-III-like retrovirus from macaques.

The isolation of a T-cell tropic retrovirus from three immunodeficient macaques and one macaque with lymphoma is described. The morphology, growth characteristics, and antigenic properties of this virus indicate that it is related to the causative agent of acquired immune deficiency syndrome in humans (HTLV-III or LAV). This virus is referred to as simian T-lymphotropic virus type III (STLV-III) of macaques. The existence of a cytopathic, T-cell tropic virus resembling HTLV-III in monkeys may facilitate study of disease induction and vaccine development in an animal model.

Serologic identification and characterization of a macaque T-lymphotropic retrovirus closely related to HTLV-III.

Human T-lymphotropic virus type III (HTLV-III) is thought to play an etiologic role in the development of the acquired immune deficiency syndrome (AIDS). In this study the serologic characterization of a new simian retrovirus that is related to HTLV-III is described. This new virus, here referred to as STLV-III, was isolated from sick macaques at the New England Regional Primate Research Center. Radioimmunoprecipitation analysis revealed STLV-III-specific proteins of 160, 120, 55, and 24 kilodaltons, all similar in size to the major gag and env proteins of HTLV-III. These antigens were recognized by representative macaque serum samples and human reference serum samples positive for HTLV-III antibodies. Monoclonal antibodies directed to p24, the major core protein of HTLV-III, also immunoprecipitated a 24-kilodalton species in lysates of cells infected with the macaque virus. This HTLV-III-related virus, which naturally infects a nonhuman primate species, may provide a useful model for the study of HTLV-III and the pathogenesis of AIDS.

Lymphoma in macaques: association with virus of human T lymphotrophic family.

Human T-cell leukemia virus has been linked with adult T-cell leukemia-lymphoma (ATLL), a tumor of mature T cells that occurs at elevated rates in southwestern Japan and in the Caribbean Basin. Human T-cell leukemia virus (HTLV) or a closely related virus, has also been found in varying proportions of healthy individuals of several species of Old World monkeys. In the present study, conducted with macaques from Taiwan and the New England Regional Primate Research Center, antibodies to membrane antigens of HTLV-infected cells (HTLV-MA) were found in 11 of 13 macaques with malignant lymphoma or lymphoproliferative disease but in only 7 of 95 of healthy macaques. This indicates that antibodies to HTLV are significantly associated with the development of naturally occurring lymphoid neoplasms in at least some species of nonhuman primates.

Control of viremia in simian immunodeficiency virus infection by CD8+ lymphocytes.

Clinical evidence suggests that cellular immunity is involved in controlling human immunodeficiency virus-1 (HIV-1) replication. An animal model of acquired immune deficiency syndrome (AIDS), the simian immunodeficiency virus (SIV)-infected rhesus monkey, was used to show that virus replication is not controlled in monkeys depleted of CD8+ lymphocytes during primary SIV infection. Eliminating CD8+ lymphocytes from monkeys during chronic SIV infection resulted in a rapid and marked increase in viremia that was again suppressed coincident with the reappearance of SIV-specific CD8+ T cells. These results confirm the importance of cell-mediated immunity in controlling HIV-1 infection and support the exploration of vaccination approaches for preventing infection that will elicit these immune responses.

Sexual transmission and propagation of SIV and HIV in resting and activated CD4+ T cells.

In sexual transmission of simian immunodeficiency virus, and early and later stages of human immunodeficiency virus-type 1 (HIV-1) infection, both viruses were found to replicate predominantly in CD4(+) T cells at the portal of entry and in lymphoid tissues. Infection was propagated not only in activated and proliferating T cells but also, surprisingly, in resting T cells. The infected proliferating cells correspond to the short-lived population that produces the bulk of HIV-1. Most of the HIV-1-infected resting T cells persisted after antiretroviral therapy. Latently and chronically infected cells that may be derived from this population pose challenges to eradicating infection and developing an effective vaccine.

Control of viremia and prevention of clinical AIDS in rhesus monkeys by cytokine-augmented DNA vaccination.

With accumulating evidence indicating the importance of cytotoxic T lymphocytes (CTLs) in containing human immunodeficiency virus-1 (HIV-1) replication in infected individuals, strategies are being pursued to elicit virus-specific CTLs with prototype HIV-1 vaccines. Here, we report the protective efficacy of vaccine-elicited immune responses against a pathogenic SHIV-89.6P challenge in rhesus monkeys. Immune responses were elicited by DNA vaccines expressing SIVmac239 Gag and HIV-1 89.6P Env, augmented by the administration of the purified fusion protein IL-2/Ig, consisting of interleukin-2 (IL-2) and the Fc portion of immunoglobulin G (IgG), or a plasmid encoding IL-2/Ig. After SHIV-89.6P infection, sham-vaccinated monkeys developed weak CTL responses, rapid loss of CD4+ T cells, no virus-specific CD4+ T cell responses, high setpoint viral loads, significant clinical disease progression, and death in half of the animals by day 140 after challenge. In contrast, all monkeys that received the DNA vaccines augmented with IL-2/Ig were infected, but demonstrated potent secondary CTL responses, stable CD4+ T cell counts, preserved virus-specific CD4+ T cell responses, low to undetectable setpoint viral loads, and no evidence of clinical disease or mortality by day 140 after challenge.

A defect of immunoregulatory T cell subsets in systemic lupus erythematosus patients demonstrated with anti-2H4 antibody.

The cell surface phenotype of peripheral blood lymphocytes (PBL) of systemic lupus erythematosus (SLE) patients was characterized with the anti-2H4 monoclonal antibody that defines the human suppressor inducer subset. The T4+2H4+ population of cells has been shown to be critical for the activation of T8+ suppressor cells. Patients with SLE has a markedly decreased percentage of T4+2H4+ cells (13 +/- 2%) in their PBL compared with normal controls (21 +/- 1%) (P less than 0.001). This reduction was greatest in patients with active SLE, especially those with renal disease. Serial analysis of patients with SLE and renal disease showed a correlation between percent positive circulating T4+2H4+ cells and disease activity. Moreover, there was a significant correlation between a low percentage of T4+2H4+ cells and decreased suppressor-inducer function in autologous mixed lymphocyte reaction-activated T4+ cells from SLE patients. Thus, a deficiency exists in SLE patients with active renal disease in the T4+2H4+ suppressor-inducer T cell subset.

Influence of cell cycle phase-specific agents on simian fetal hemoglobin synthesis.

To determine the influence of cell cycle-specific agents on primate hematopoiesis and fetal hemoglobin production, two juvenile cynomolgus monkeys (Macaca fascicularis) were repeatedly bled to maintain their hemoglobins at approximately 6.5 g/dl and fetal hemoglobin levels at 3-5%. Six separate 5-d courses of hydroxyurea at 100 mg/kg per d were then administered over the next 200 d while phlebotomy was continued. These courses of hydroxyurea progressively raised the fetal hemoglobin levels to 17 and 18%, respectively. The drug had very little effect on the frequency of immature erythroid progenitors (BFU-E) in the bone marrow, but caused a marked reduction in the frequency of later progenitors (CFU-E) and a transient fall in the reticulocyte count. Following the courses of hydroxyurea, the number of F cells and the fetal hemoglobin level fell to base line over a period of 4 wk. Two control animals which were not phlebotomized showed no detectable increase in F cells or fetal hemoglobin when treated with the same regimen of hydroxyurea. A 5-d course of 5-azacytidine at 8 mg/kg per d was then given to each of the phlebotomized animals. This produced a more profound, albeit transient, reticulocytopenia, a fall in the CFU-E/BFU-E ratio, and a prompt increase in the fetal hemoglobin to levels even higher than were seen following a single 5-d course of hydroxyurea at 100 mg/kg/d. Subsequently, the animals were given a single dose of vinblastine at 0.4 mg/kg which reduced reticulocytes and CFU-E to the same extent as hydroxyurea; however, vinblastine at this dose had no effect on hemoglobin F (HbF) production. In contrast, when vinblastine was administered to the phlebotomized monkeys as a 5-d course at 0.2 mg/kg/d, prolonged reticulocytopenia followed by dramatic F cell and HbF responses were seen. Combinations of single dose vinblastine and a 5-d course of hydroxyurea were subsequently administered using two different schedules. When the animals received vinblastine on the first day of a 5-d course of hydroxyurea, the F cell response was double that seen following hydroxyurea treatment alone. In contrast, when vinblastine was administered on the final day of hydroxyurea treatment, the magnitude of the F cell response was the same as that which occurred following hydroxyurea treatment alone, but the onset of the rise was delayed for 4 d and HbF/F cell response was much higher. These results establish several important features of the fetal hemoglobin response to cytotoxic agents in the primate model. The response requires accelerated erythropoiesis and is preceded by transient reticulocytopenia. The response is produced by S phase- and M phase-specific agents when given in sufficient doses and at appropriate schedules. Passage of erythrocyte progenitors through M phase appears to be necessary for expression of the effect produced by S phase agents. The fetal hemoglobin response induced by cytotoxic drug administration occurs during the recovery of erythropoiesis following marrow suppression.