Persistent Low-Level Replication of SIVΔnef Drives Maturation of Antibody and CD8 T Cell Responses to Induce Protective Immunity against Vaginal SIV Infection

Defining the correlates of immune protection conferred by SIVΔnef, the most effective vaccine against SIV challenge, could enable the design of a protective vaccine against HIV infection. Here we provide a comprehensive assessment of immune responses that protect against SIV infection through detailed analyses of cellular and humoral immune responses in the blood and tissues of rhesus macaques vaccinated with SIVΔnef and then vaginally challenged with wild-type SIV. Despite the presence of robust cellular immune responses, animals at 5 weeks after vaccination displayed only transient viral suppression of challenge virus, whereas all macaques challenged at weeks 20 and 40 post-SIVΔnef vaccination were protected, as defined by either apparent sterile protection or significant suppression of viremia in infected animals. Multiple parameters of CD8 T cell function temporally correlated with maturation of protection, including polyfunctionality, phenotypic differentiation, and redistribution to gut and lymphoid tissues. Importantly, we also demonstrate the induction of a tissue-resident memory population of SIV-specific CD8 T cells in the vaginal mucosa, which was dependent on ongoing low-level antigenic stimulation. Moreover, we show that vaginal and serum antibody titers inversely correlated with post-challenge peak viral load, and we correlate the accumulation and affinity maturation of the antibody response to the duration of the vaccination period as well as to the SIVΔnef antigenic load. In conclusion, maturation of SIVΔnef-induced CD8 T cell and antibody responses, both propelled by viral persistence in the gut mucosa and secondary lymphoid tissues, results in protective immune responses that are able to interrupt viral transmission at mucosal portals of entry as well as potential sites of viral dissemination.

Annually, more than two million people worldwide are infected with HIV, the virus that causes AIDS. Rhesus macaques can be infected with SIV, a close relative and ancestor of HIV, resulting in simian AIDS, recapitulating key aspects of human HIV infection. SIVΔnef, a live attenuated form of SIV, protects rhesus macaques from subsequent challenge with pathogenic SIV and is widely viewed as the most effective SIV vaccine. Here we demonstrate that SIVΔnef persistence during the vaccination period drives both cell-mediated and humoral immune response maturation. During the vaccination period, cell-mediated immune responses elicited by SIVΔnef target more conserved regions of the virus rendering immune escape more difficult. Furthermore, the localization of the cell-mediated immune responses is shifted over time from peripheral blood to sites of viral production that are rich in uninfected SIV target cells, thereby positioning cell-mediated immune responses where they are most needed after wild-type SIV challenge. Similarly, SIVΔnef persistence during the vaccination period also leads to the accumulation and maturation of the humoral immune response. Our findings highlight the unique capacity of persistent vaccines to elicit durable and effective immune responses against wild-type SIV challenge.

Suppression of a Natural Killer Cell Response by Simian Immunodeficiency Virus Peptides

Natural killer (NK) cell responses in primates are regulated in part through interactions between two highly polymorphic molecules, the killer-cell immunoglobulin-like receptors (KIRs) on NK cells and their major histocompatibility complex (MHC) class I ligands on target cells. We previously reported that the binding of a common MHC class I molecule in the rhesus macaque, Mamu-A1*002, to the inhibitory receptor Mamu-KIR3DL05 is stabilized by certain simian immunodeficiency virus (SIV) peptides, but not by others. Here we investigated the functional implications of these interactions by testing SIV peptides bound by Mamu-A1*002 for the ability to modulate Mamu-KIR3DL05⁺ NK cell responses. Twenty-eight of 75 SIV peptides bound by Mamu-A1*002 suppressed the cytolytic activity of primary Mamu-KIR3DL05⁺ NK cells, including three immunodominant CD8⁺ T cell epitopes previously shown to stabilize Mamu-A1*002 tetramer binding to Mamu-KIR3DL05. Substitutions at C-terminal positions changed inhibitory peptides into disinhibitory peptides, and vice versa, without altering binding to Mamu-A1*002. The functional effects of these peptide variants on NK cell responses also corresponded to their effects on Mamu-A1*002 tetramer binding to Mamu-KIR3DL05. In assays with mixtures of inhibitory and disinhibitory peptides, low concentrations of inhibitory peptides dominated to suppress NK cell responses. Consistent with the inhibition of Mamu-KIR3DL05⁺ NK cells by viral epitopes presented by Mamu-A1*002, SIV replication was significantly higher in Mamu-A1*002⁺ CD4⁺ lymphocytes co-cultured with Mamu-KIR3DL05⁺ NK cells than with Mamu-KIR3DL05^- NK cells. These results demonstrate that viral peptides can differentially affect NK cell responses by modulating MHC class I interactions with inhibitory KIRs, and provide a mechanism by which immunodeficiency viruses may evade NK cell responses.

Natural killer (NK) cells recognize and kill infected cells without prior antigenic stimulation, and thus provide an important early defense against virus infection. NK cell responses in primates are regulated in part through interactions between two highly polymorphic molecules, the killer-cell immunoglobulin-like receptors (KIRs) on NK cells and their major histocompatibility complex (MHC) class I ligands on target cells. Inhibitory KIRs normally suppress NK cell responses through interactions with their MHC class I ligands on the surface of healthy cells. However, when these interactions are perturbed, this inhibition is lost resulting in NK cell activation and killing of the target cell. We investigated the functional implications of simian immunodeficiency virus (SIV) peptides bound by a common MHC class I molecule in the rhesus macaque that stabilize or disrupt binding to an inhibitory KIR. Whereas SIV peptides that stabilized KIR-MHC class I binding suppressed NK cell activation, peptides that disrupted this interaction did not and resulted in NK cell lysis. These findings demonstrate that viral peptides can modulate NK cell responses through KIR-MHC class I interactions, and are consistent with the possibility that human and simian immunodeficiency viruses may acquire changes in epitopes that increase the binding of MHC class I ligands to inhibitory KIRs as a mechanism to suppress NK cell responses.

Hypercytotoxicity and rapid loss of NKp44+ innate lymphoid cells during acute SIV infection

HIV/SIV infections break down the integrity of the gastrointestinal mucosa and lead to chronic immune activation and associated disease progression. Innate lymphoid cells (ILCs), distinguishable by high expression of NKp44 and RORγt, play key roles in mucosal defense and homeostasis, but are depleted from gastrointestinal (GI) tract large bowel during chronic SIV infection. However, less is known about the kinetics of ILC loss, or if it occurs systemically. In acute SIV infection, we found a massive, up to 8-fold, loss of NKp44⁺ILCs in all mucosae as early as day 6 post-infection, which was sustained through chronic disease. Interestingly, no loss of ILCs was observed in mucosa-draining lymph nodes. In contrast, classical NK cells were not depleted either from gut or draining lymph nodes. Both ILCs and NK cells exhibited significantly increased levels of apoptosis as measured by increased Annexin-V expression, but while classical NK cells also showed increased proliferation, ILCs did not. Interestingly, ILCs, which are normally noncytolytic, dramatically upregulated cytotoxic functions in acute and chronic infection and acquired a polyfunctional phenotype secreting IFN-γ, MIP1-β, and TNF-α, but decreased production of the prototypical cytokine, IL-17. Classical NK cells had less dramatic functional change, but upregulated perforin expression and increased cytotoxic potential. Finally, we show that numerical and functional loss of ILCs was due to increased apoptosis and ROR γt suppression induced by inflammatory cytokines in the gut milieu. Herein we demonstrate the first evidence for acute, systemic, and permanent loss of mucosal ILCs during SIV infection associated with reduction of IL-17. The massive reduction of ILCs involves apoptosis without compensatory de novo development/proliferation, but the full mechanism of depletion and the impact of functional change so early in infection remain unclear.

HIV-1 has long been shown to deplete CD4+ T cells and disrupt barrier integrity in the gastrointestinal tract, but effects on other subpopulations of lymphocytes are less well described. A recently identified subpopulation of mucosa-restricted cells, termed innate lymphoid cells (ILCs) is thought to play critical roles in maintaining homeostasis in the gastrointestinal tract and mucosal pathogen defense. Although previous work from our laboratory and others have shown SIV infection of rhesus macaques can deplete ILCs in some parts of the gastrointestinal tract, systemic as well as kinetic effects were unclear. In this report we show that ILCs, but not classical NK cells are systemically depleted during infection and also acquire cytotoxic capabilities. Furthermore, our data is the first to indicate that this important subset of innate cells is depleted acutely, permanently, and systemically during SIV infection of rhesus macaques as a model for HIV-1 infection. Given the important role of ILCs in maintaining gut homeostasis these findings could have significant implications for the understanding and treatment of HIV-induced disease.

Bone marrow-imprinted gut-homing of plasmacytoid dendritic cells (pDCs) in acute simian immunodeficiency virus infection results in massive accumulation of hyperfunctional CD4+ pDCs in the mucosae

Plasmacytoid dendritic cells (pDCs), a primary source of interferon α (IFN-α), provide a first line of innate immune defense against human immunodeficiency virus infection. However, their kinetics and functions during acute infection are poorly understood. In mucosal tissues of normal rhesus macaques, we found CD4(+) pDCs to be the subset responsible for most IFN-α and tumor necrosis factor α (TNF-α) production in response to Toll-like receptor (TLR) 7/8 stimulation, compared with relatively anergic CD4(-) pDCs. During acute simian immunodeficiency virus (SIV) infection, gut homing was imprinted on pDCs in the bone marrow, resulting in a decline in pDCs from circulation and secondary lymphoid tissues. Although the accumulated pDCs in the gut mucosae had robust cytokine responses to TLR7/8 stimulation in vitro, pDC gut migration occurred after infection and detection of SIV in plasma. Our data suggest that innate pDC responses do not control initial SIV seeding and dissemination but instead may contribute to ongoing immune activation in the gut.

Postnatal acquisition of primary rhesus cytomegalovirus infection is associated with prolonged virus shedding and impaired CD4+ T lymphocyte function

BACKGROUND

Although virus-specific CD4(+) T lymphocytes emerge rapidly during primary cytomegalovirus (CMV) infection in humans, they exhibit a state of prolonged functional exhaustion of unknown etiology. To investigate the suitability of rhesus macaques as a model of primary human CMV infection, we examined the virologic and immunologic features of naturally acquired primary CMV infection in rhesus macaques.

METHODS

CMV-specific CD4(+) T lymphocytes and CMV load in blood, saliva, and urine were evaluated in a cohort of simian immunodeficiency virus (SIV)-negative rhesus macaques stratified by age into infant, juvenile, and adult groups.

RESULTS

CMV infection was detected in juvenile and adult monkeys but not in infant monkeys. CMV loads and shedding frequency in urine and saliva were significantly higher in the 2-3-year old juvenile monkeys, compared with the adult monkeys. The increased CMV load in juvenile monkeys was associated with lower polyfunctionality, impaired proliferation, and increased expression of the inhibitory receptor PD-1 in CMV-specific CD4(+) T lymphocytes. The proliferative defect was partially reversible by exogenous PD-1 blockade or addition of interleukin 2.

CONCLUSIONS

Postnatal acquisition of primary CMV infection in rhesus macaques results in prolonged virus excretion and impaired CMV-specific CD4(+) T-lymphocyte function, findings that recapitulate key features of primary CMV infection in humans.

KIR3DL01 recognition of Bw4 ligands in the rhesus macaque: maintenance of Bw4 specificity since the divergence of apes and Old World monkeys

The identification of MHC class I ligands for rhesus macaque killer cell Ig-like receptors (KIRs) is fundamental to our basic understanding of KIR and MHC class I coevolution and to the study of NK cell responses in this nonhuman primate model for AIDS and other viral diseases. In this study, we show that Mamu-KIR3DL01, which is expressed by ∼90% of rhesus macaques, recognizes MHC class I molecules with a Bw4 motif. Primary NK cells expressing Mamu-KIR3DL01 were identified by staining with a mAb which, in this study, was shown to bind Mamu-KIR3DL01 allotypes with an aspartic acid at position 233. The cytolytic activity of Mamu-KIR3DL01(+) NK cells was suppressed by cell lines expressing the Bw4 molecules Mamu-B*007:01, -B*041:01, -B*058:02, and -B*065:01. The Bw4 motif was necessary for Mamu-KIR3DL01 recognition because substitutions in this region abrogated Mamu-KIR3DL01(+) NK cell inhibition. However, the presence of a Bw4 motif was not sufficient for recognition because another Bw4 molecule, Mamu-B*017:01, failed to suppress the cytolytic activity of these NK cells. Replacement of three residues in Mamu-B*017:01, predicted to be KIR contacts based on the three-dimensional structure of the human KIR3DL1-HLA-Bw4 complex, with the corresponding residues at these positions for the other Mamu-Bw4 ligands restored Mamu-KIR3DL01(+) NK cell inhibition. These results define the ligand specificity of one of the most polymorphic and commonly expressed KIRs in the rhesus macaque and reveal similarities in Bw4 recognition by Mamu-KIR3DL01 and human KIR3DL1, despite the absence of an orthologous relationship between these two KIRs or conservation of surface residues predicted to interact with MHC class I ligands.

Transcription factor expression profiling to characterize differentiation of antigen-specific CD8 T cells induced by a live attenuated viral vaccine. (113.18)

Live attenuated SIV (SIVΔnef) is the most effective approach to induce protection to pathogenic SIV challenge in macaques. Protective immunity, in part mediated by CD8 T cell responses, correlates with phenotypic maturation of SIV-specific T cells, but remains incompletely understood. Expression profiling of T cell transcription factors (TF) offers a novel approach to characterize antigen-specific T cell differentiation. Highly parallel qRT-PCR was used to characterize the expression of 21 TF in naïve, central, transitional, and effector memory T cell subsets, and in SIV-specific CD8 T cells obtained at times associated with lesser protection (wk 5) and greater protection (wk 20) following SIVΔnef vaccination. Unsupervised clustering organized samples from CD4 and CD8 T cells into groups concordant with cell surface phenotype. TF expression in SIV-specific CD8+ T cells segregated by time, with wk 20 cells exhibiting increased expression of TF associated with both maintenance of quiescence (TCF7, BAZF) and promotion of effector function (Eomes, T-Bet). Different expression profiles were observed in T cells specific for different SIV epitopes, consistent with different epitope escape kinetics. TF expression profiling suggests T cell responses correlated with protection may include characteristics of both memory and effector cells. TF expression profiling can provide data complementary to the analysis of memory cell differentiation based on classical phenotypic markers.

Gut inflammation and indoleamine deoxygenase inhibit IL-17 production and promote cytotoxic potential in NKp44+ mucosal NK cells during SIV infection

Natural killer (NK) cells are classically viewed as effector cells that kill virus-infected and neoplastic cells, but recent studies have identified a rare mucosal NK- cell subpopulation secreting the TH17 cytokine IL-22. Here, we report identification of 2 distinct lineages of mucosal NK cells characterized as NKG2A(+)NFIL3(+)RORC(-) and NKp44(+)NFIL3(+)RORC(+). NKG2A(+) NK cells were systemically distributed, cytotoxic, and secreted IFN-γ, whereas NKp44(+) NK cells were mucosae-restricted, noncytotoxic, and produced IL-22 and IL-17. During SIV infection, NKp44(+) NK cells became apoptotic, were depleted, and had an altered functional profile characterized by decreased IL-17 secretion; increased IFN-γ secretion; and, surprisingly, increased potential for cytotoxicity. NKp44(+) NK cells showed no evidence of direct SIV infection; rather, depletion and altered function were associated with SIV-induced up-regulation of inflammatory mediators in the gut, including indoleamine 2,3-dioxygenase 1. Furthermore, treatment of NKp44(+) NK cells with indoleamine 2,3-dioxygenase 1 catabolites in vitro ablated IL-17 production in a dose-dependent manner, whereas other NK-cell functions were unaffected. Thus lentiviral infection both depletes and modifies the functional repertoire of mucosal NK cells involved in the maintenance of gut integrity, a finding that highlights the plasticity of this rare mucosal NK-cell population.

Quantification of mucosal mononuclear cells in tissues with a fluorescent bead-based polychromatic flow cytometry assay

Since the vast majority of infections occur at mucosal surfaces, accurate characterization of mucosal immune cells is critically important for understanding transmission and control of infectious diseases. Standard flow cytometric analysis of cells obtained from mucosal tissues can provide valuable information on the phenotype of mucosal leukocytes and their relative abundance, but does not provide absolute cell counts of mucosal cell populations. We developed a bead-based flow cytometry assay to determine the absolute numbers of multiple mononuclear cell types in colorectal biopsies of rhesus macaques. Using 10-color flow cytometry panels and pan-fluorescent beads, cells were enumerated in biopsy specimens by adding a constant ratio of beads per mg of tissue and then calculating cell numbers/mg of tissue based on cell-to-bead ratios determined at the time of sample acquisition. Testing in duplicate specimens showed the assay to be highly reproducible (Spearman R=0.9476, P<0.0001). Using this assay, we report enumeration of total CD45(+) leukocytes, CD4(+) and CD8(+) T cells, B cells, NK cells, CD14(+) monocytes, and myeloid and plasmacytoid dendritic cells in colorectal biopsies, with cell numbers in normal rhesus macaques varying from medians of 4486 cells/mg (T cells) to 3 cells/mg (plasmacytoid dendritic cells). This assay represents a significant advancement in rapid, accurate quantification of mononuclear cell populations in mucosal tissues and could be applied to provide absolute counts of a variety of different cell populations in diverse tissues.

Heterogeneity in phenotype and function of CD8+ and CD4/CD8 double-negative Natural Killer T cell subsets in sooty mangabeys

BACKGROUND

We have recently reported the presence of CD8(+) and CD4/8 double-negative (DN) natural killer T (NKT) lymphocytes in sooty mangabeys. To investigate differences in the two NKT cell subsets, we compared the phenotype and function of sooty mangabey CD8(+) and DN NKT cells.

METHODS

Flow-sorted NKT lymphocytes from one SIV-negative sooty mangabey were subjected to limiting dilution cloning. Invariant NKT clones were characterized by flow cytometry and cytokine ELISA.

RESULTS

The majority of NKT clones displayed an effector memory phenotype and expressed CXCR3 and NKG2D. While CD8(+) NKT subsets expressed significantly higher levels of granzyme B and perforin and produced more IFN-gamma, the DN NKT subsets secreted significantly more IL-4, IL-13, and IL-10.

CONCLUSIONS

The Th1 and Th2 cytokine bias of CD8(+) and DN NKT cells, respectively, indicates the presence of functionally heterogeneous populations of NKT cells in sooty mangabeys.

Paucity of CD4+ natural killer T (NKT) lymphocytes in sooty mangabeys is associated with lack of NKT cell depletion after SIV infection

Lack of chronic immune activation in the presence of persistent viremia is a key feature that distinguishes nonpathogenic simian immunodeficiency virus (SIV) infection in natural hosts from pathogenic SIV and HIV infection. To elucidate novel mechanisms downmodulating immune activation in natural hosts of SIV infection, we investigated natural killer T (NKT) lymphocytes in sooty mangabeys. NKT lymphocytes are a potent immunoregulatory arm of the innate immune system that recognize glycolipid antigens presented on the nonpolymorphic MHC-class I-like CD1d molecules. In a cross-sectional analysis of 50 SIV-negative and 50 naturally SIV-infected sooty mangabeys, ligand alpha-galactosylceramide loaded CD1d tetramers co-staining with Valpha24-positive invariant NKT lymphocytes were detected at frequencies >or=0.002% of circulating T lymphocytes in approximately half of the animals. In contrast to published reports in Asian macaques, sooty mangabey NKT lymphocytes consisted of CD8(+) and CD4/CD8 double-negative T lymphocytes that were CXCR3-positive and CCR5-negative suggesting that they trafficked to sites of inflammation without being susceptible to SIV infection. Consistent with these findings, there was no difference in the frequency or phenotype of NKT lymphocytes between SIV-negative and SIV-infected sooty mangabeys. On stimulation with alpha-galactosylceramide loaded on human CD1d molecules, sooty mangabey NKT lymphocytes underwent degranulation and secreted IFN-gamma, TNF-alpha, IL-2, IL-13, and IL-10, indicating the presence of both effector and immunoregulatory functional capabilities. The unique absence of CD4(+) NKT lymphocytes in sooty mangabeys, combined with their IL-10 cytokine-secreting ability and preservation following SIV infection, raises the possibility that NKT lymphocytes might play a role in downmodulating immune activation in SIV-infected sooty mangabeys.

B cell antigen receptor signal strength and peripheral B cell development are regulated by a 9-O-acetyl sialic acid esterase

We show that the enzymatic acetylation and deacetylation of a cell surface carbohydrate controls B cell development, signaling, and immunological tolerance. Mice with a mutation in sialate:O-acetyl esterase, an enzyme that specifically removes acetyl moieties from the 9-OH position of α2–6-linked sialic acid, exhibit enhanced B cell receptor (BCR) activation, defects in peripheral B cell development, and spontaneously develop antichromatin autoantibodies and glomerular immune complex deposits. The 9-O-acetylation state of sialic acid regulates the function of CD22, a Siglec that functions in vivo as an inhibitor of BCR signaling. These results describe a novel catalytic regulator of B cell signaling and underscore the crucial role of inhibitory signaling in the maintenance of immunological tolerance in the B lineage.

Potent inhibition of simian immunodeficiency virus (SIV) replication by an SIV-based lentiviral vector expressing antisense Env

In light of findings demonstrating that the macaque TRIM5alpha protein inhibits infection of cells by human immunodeficiency virus (HIV)-1, simian immunodeficiency virus (SIV)-based lentiviral vectors may have distinct advantages over HIV-1 vectors for the transduction of macaque hematopoietic stem cells. We evaluated the ability of an SIV vector (VRX859) encoding an antisense SIV envelope sequence and enhanced green fluorescent protein (GFP) to inhibit viral replication and to transduce rhesus CD34(+) lymphoid progenitor cells. After infection with homologous SIV strains, CD4(+) cell lines transduced with VRX859 exhibited more than 600-fold inhibition of viral replication compared with control cells. Less inhibition was observed with the divergent SIV strain SIVsmE660. Partial inhibition of a chimeric simian-human immunodeficiency virus, which contains an HIV-1 envelope in an SIV backbone, was observed, suggesting that the SIV vector also contributes to viral inhibition independent of the antisense envelope inhibitor. Transduction of rhesus CD34(+) cells with VRX859 at various multiplicities of infection resulted in transduction efficiencies comparable to those obtained with the HIV vector VRX494. However, when we evaluated transduction of rhesus T lymphocyte progenitors by examining GFP expression in CD4(+) T cells derived from transduced CD34(+) cells, we observed more efficient transduction with the SIV-based vector. GFP(+)CD4(+) T cells derived from VRX859-transduced CD34(+) cells strongly inhibited SIVmac239 replication as compared with control CD4(+) T cells. The ability of this SIV-based vector to mediate potent inhibition of SIV replication, coupled with its efficient transduction of rhesus hematopoietic progenitor cells, make it an important candidate for proof-of-principle experiments of stem cell gene therapy in the SIV-macaque model.

Balancing selection and the evolution of functional polymorphism in Old World monkey TRIM5alpha

Retroviral restriction factor TRIM5alpha exhibits a high degree of sequence variation among primate species. It has been proposed that this diversity is the cumulative result of ancient, lineage-specific episodes of positive selection. Here, we describe the contribution of within-species variation to the evolution of TRIM5alpha. Sampling within two geographically distinct Old World monkey species revealed extensive polymorphism, including individual polymorphisms that predate speciation (shared polymorphism). In some instances, alleles were more closely related to orthologues of other species than to one another. Both silent and nonsynonymous changes clustered in two domains. Functional assays revealed consequences of polymorphism, including differential restriction of a small panel of retroviruses by very similar alleles. Together, these features indicate that the primate TRIM5alpha locus has evolved under balancing selection. Except for the MHC there are few, if any, examples of long-term balancing selection in primates. Our results suggest a complex evolutionary scenario, in which fixation of lineage-specific adaptations is superimposed on a subset of critical polymorphisms that predate speciation events and have been maintained by balancing selection for millions of years.

Inhibition of simian/human immunodeficiency virus replication in CD4+ T cells derived from lentiviral-transduced CD34+ hematopoietic cells

We examined the ability of a HIV-1-based vector (VRX494) encoding a 937-bp antisense HIV-1 envelope sequence to inhibit the replication of chimeric SIV/HIV-1 viruses encoding the HIV-1 envelope. Challenge of VRX494-transduced CEMx174 cells resulted in potent inhibition of HIV-1 and several SHIV strains. To evaluate the potential efficacy of the VRX494 vector for stem cell gene therapy, rhesus CD34(+) bone marrow cells were transduced with VRX494 and then cultured on thymus stroma to induce T cell differentiation. Transduction conditions for CD34(+) cells were optimized to yield high transduction efficiency with minimal effective multiplicity of infection. Purified CD4(+) GFP(+) T cells derived from VRX494-transduced CD34(+) cells strongly inhibited SHIV HXBC2P 3.2 and SHIV 89.6P replication compared to controls. Southern blot analysis of VRX494-transduced T cell clones revealed a subset of cells with multiple proviral copies per cell. Expression of GFP and the antisense inhibitor in VRX494-transduced cells was upregulated by Tat. Analysis of HIV-1 envelope sequences in VRX494-transduced cells revealed modifications consistent with those mediated by double-stranded RNA-dependent adenosine deaminase. These results indicate that the macaque/SHIV model should serve as a useful preclinical model to evaluate this lentiviral vector expressing an HIV-1 antisense inhibitor for stem cell gene therapy for AIDS.

Structural analysis of the Kaposi's sarcoma-associated herpesvirus K1 protein

The K1 protein of Kaposi's sarcoma-associated herpesvirus (KSHV) efficiently transduces extracellular signals to elicit cellular activation events through its cytoplasmic immunoreceptor tyrosine-based activation motif (ITAM). In addition, the extracellular domain of K1 demonstrates regional homology with the immunoglobulin (Ig) family and contains conserved regions (C1 and C2) and variable regions (V1 and V2). To generate mouse monoclonal antibodies directed against the KSHV K1 protein, BALB/c mice were primed and given boosters with K1 protein purified from mammalian cells. Twenty-eight hybridomas were tested for reactivity with K1 protein by enzyme-linked immunosorbent assay, immunofluorescence, flow cytometry, immunohistochemistry, and immunoblotting. Deletion mutants of the K1 extracellular domain were used to map the epitope of each antibody. All antibodies were directed to the Ig, C1, and C2 regions of K1. Furthermore, antibody recognition of a short sequence (amino acids 92 to 125) of the C2 region overlapping with the Ig region of K1 efficiently induced intracellular free calcium mobilization; antibody recognition of the other regions of K1 did not. The efficient signal transduction of K1 induced by antibody stimulation required both the ITAM sequence of the cytoplasmic domain and the normal structure of the extracellular domain. Finally, immunological assays showed that K1 was expressed during the early lytic cycle of viral replication in primary effusion lymphoma cells. K1 was readily detected in multicentric Castleman's disease tissues, whereas it was not detected in Kaposi's sarcoma lesions, suggesting that K1 is preferentially expressed in lymphoid cells. Thus, these results indicate that the conserved regions, particularly the Ig and C2 regions, of the K1 extracellular domain are exposed on the outer surface and play an important role in K1 structure and signal transduction, whereas the variable regions of K1 appear to be away from the surface.

Induction of cytotoxic T lymphocyte and antibody responses to enhanced green fluorescent protein following transplantation of transduced CD34(+) hematopoietic cells

Genetic modification of hematopoietic stem cells often results in the expression of foreign proteins in pluripotent progenitor cells and their progeny. However, the potential for products of foreign genes introduced into hematopoietic stem cells to induce host immune responses is not well understood. Gene marking and induction of immune responses to enhanced green fluorescent protein (eGFP) were examined in rhesus macaques that underwent nonmyeloablative irradiation followed by infusions of CD34(+) bone marrow cells transduced with a retroviral vector expressing eGFP. CD34(+) cells were obtained from untreated animals or from animals treated with recombinant human granulocyte colony-stimulating factor (G-CSF) alone or G-CSF and recombinant human stem cell factor. Levels of eGFP-expressing cells detected by flow cytometry peaked at 0.1% to 0.5% of all leukocytes 1 to 4 weeks after transplantation. Proviral DNA was detected in 0% to 17% of bone marrow--derived colony-forming units at periods of 5 to 18 weeks after transplantation. However, 5 of 6 animals studied demonstrated a vigorous eGFP-specific cytotoxic T lymphocyte (CTL) response that was associated with a loss of genetically modified cells in peripheral blood, as demonstrated by both flow cytometry and polymerase chain reaction. The eGFP-specific CTL responses were MHC-restricted, mediated by CD8(+) lymphocytes, and directed against multiple epitopes. eGFP-specific CTLs were able to efficiently lyse autologous CD34(+) cells expressing eGFP. Antibody responses to eGFP were detected in 3 of 6 animals. These data document the potential for foreign proteins expressed in CD34(+) hematopoietic cells and their progeny to induce antibody and CTL responses in the setting of a clinically applicable transplantation protocol. (Blood. 2001;97:1951-1959)

Identification of primitive hematopoietic progenitor cells in the rhesus macaque

The close phylogenetic relationship of macaques to humans has resulted in their widespread use as a preclinical model for bone marrow transplantation and stem cell gene therapy. To facilitate further use of this model, we undertook analysis of hematopoietic cells using multiparametric flow cytometric analysis. Rhesus CD34+CD38- cells displayed a number of characteristics of primitive hematopoietic cells, including low forward and orthogonal scatter and the lack of expression of lineage-specific markers or human lymphocyte antigen-DR. Four-color flow cytometric analysis demonstrated that rhesus CD34+CD38- cells were heterogenous with respect to Thy-1 expression and were CD59dim. Quantitative limiting dilution long-term culture-initiating cell (LTC-IC) analysis demonstrated that CD34+CD38- cells were approximately 150-fold enriched for LTC-IC as compared with unfractionated bone marrow, and occurred at a frequency similar to that previously reported in humans. Thus, as in humans, the CD34+38- population of rhesus macaque bone marrow is enriched for primitive, multipotent hematopoietic progenitor cells.

Mechanisms associated with thymocyte apoptosis induced by simian immunodeficiency virus

Despite considerable research, the mechanisms by which HIV disrupts thymic function remain controversial. We have described the phenotypic changes that occur in the thymus of SIV-infected macaques during acute SIV infection. In this study, we analyzed the effects of SIV infection on apoptotic pathways in thymic tissue from newborn macaques infected with SIV. Thymocyte apoptosis was accompanied by a modest increase in surface Fas expression, a profound decrease in the frequency of bcl-2-positive cells, as well as the amount of bcl-2 per cell. With control of viral replication, levels of bcl-2 and Fas returned to baseline together with a return to basal levels of apoptosis. In the thymus, SIV infection resulted in depletion of CD4+CD8+ thymocytes, an increase in apoptosis of thymocytes, and a down-regulation of MHC class I molecules. These changes peaked 14-21 days after infection at or just after peak viremia. This data further suggests disruption of the antiapoptotic pathway regulated by bcl-2 plays a critical role in SIV-induced apoptosis of thymocytes.