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B D Walker

Publications and source records attributed to B D Walker.

At least 145 records · Page 8Linked to original sources
PubMed1993

Presentation of endogenous peptides to MHC class I-restricted cytotoxic T lymphocytes in transport deletion mutant T2 cells.

The ability of minigene-encoded viral peptide epitopes to be presented by class I molecules in the absence of MHC-encoded transporters has been evaluated in mutant T2 cells. These cells have a large deletion in the class II MHC region that includes the known transporter protein for antigenic peptides and proteasome genes and they are defective in presenting viral epitopes to CTL. T2 cells that express minigenes encoding the influenza virus matrix peptide 58-66 (GILGFVFTL) and two HTLV 1 Tax peptides 11-19 (LLFGYPVYV) and 12-19 were lysed by HLA-A2-restricted peptide-specific CTL. Minigene expression of a HLA-A2-restricted HIV reverse transcriptase peptide 476-484 (ILKEPVHGV) with three charged residues sensitized T2 cells poorly for lysis by HIV-specific CTL unless the peptide was preceded by an endoplasmic reticulum translocation signal sequence. Expression of an influenza virus nucleoprotein peptide 383-391 (SRYWAIRTR) with three charged arginine residues did sensitize HLA-B27+ T2 cells for lysis by peptide-specific CTL. These and other results with endogenously expressed peptide analogs in which hydrophobic and charged amino acids were interchanged demonstrate that antigenic peptides can be translocated from the cytoplasm into the class I Ag presentation pathway independent of MHC-encoded transporters; and that peptide hydrophobicity appears not to be a major determinant in selecting peptides for this alternate pathway.

Amino Acid Sequence↗
PubMed1993

CD4+ human immunodeficiency virus type 1 (HIV-1) envelope-specific cytotoxic T lymphocytes derived from the peripheral blood cells of an HIV-1-infected individual.

Virus-specific cytotoxic T lymphocytes (CTL) are frequently of the CD8+ surface phenotype, although CTL of the CD4+ surface phenotype have also been described. Published reports of CTL derived from peripheral blood mononuclear cells (PBMC) of individuals infected with human immunodeficiency virus type 1 (HIV-1) have described primarily cells of the CD8+ surface phenotype. However, CD4+ HIV-1 envelope-specific CTL have been reported after in vitro stimulation with HIV-1 envelope protein of peripheral blood cells obtained from HIV-1-seronegative donors, in peripheral blood cells after vaccination of HIV-1-seronegative persons with HIV-1 envelope proteins, and in cerebrospinal fluid cells of HIV-1-infected individuals. Recently, CD4+ HIV-1 gag-specific CTL were also reported. We now report a patient from whom we derived HIV-1 envelope-specific CTL cell lines of the CD4+ surface phenotype. Our cell culture technique did not employ exogenous viral antigenic stimulation, and may therefore yield cells that more closely reflect those in the underlying populations from which they were derived. These CTL did not appear to have the clear human leukocyte antigen (HLA) class II restriction pattern typically seen in CD4-expressing cells and were not functionally inhibited by anti-CD3 antibody. Further work will be required to define the role of CD4+ CTL in the pathogenesis of HIV-1 disease.

CD4 Antigens↗
PubMed1993

Recognition of a highly conserved region of human immunodeficiency virus type 1 gp120 by an HLA-Cw4-restricted cytotoxic T-lymphocyte clone.

Human immunodeficiency virus type 1 (HIV-1) isolates exhibit extensive sequence variation, particularly in the gp120 subunit of the envelope glycoprotein, and the degree of this variation has raised questions as to whether conserved regions of the HIV-1 envelope can be recognized by the host immune response. A CD8+ cytotoxic T-lymphocyte (CTL) clone specific for the HIV-1 envelope was derived by culturing peripheral blood mononuclear cells from an HIV-1 seropositive subject in the presence of a CD3-specific monoclonal antibody, interleukin-2, and irradiated allogeneic peripheral blood mononuclear cells. Lysis of target cells was restricted by an HLA-C molecule, Cw4, which has not been previously shown to present viral antigen to CTL. Mapping of the specificity of this CTL clone by using synthetic HIV-1 peptides localized the epitope to an 8-amino-acid region of gp120 (amino acids 376 to 383) which is conserved among approximately 90% of sequenced viral isolates. Examination of the recognition of variant peptides by this CTL clone demonstrated that a single, nonconservative amino acid substitution within the 8-amino-acid minimal epitope could abrogate lysis of targets incubated with the variant peptide. The identification of a CTL epitope in a highly conserved region of gp120 documents the ability of cellular immune responses of infected persons to respond to relatively invariant portions of this highly variable envelope glycoprotein. However, the ability of even a single-amino-acid change in gp120 to abolish lysis by CTL supports the hypothesis that sequence variation in HIV-1 may serve as a mechanism of immune escape. In addition, the identification of an HLA-C molecule presenting viral antigen to CTL supports a functional role for these molecules.

Amino Acid Sequence↗
PubMed1993

Hepatitis C virus (HCV)-specific cytotoxic T lymphocytes recognize epitopes in the core and envelope proteins of HCV.

Hepatitis C virus (HCV) is a major cause of posttransfusion and community-acquired hepatitis, and a majority of individuals infected with this virus will subsequently develop chronic hepatitis. Characterization of the host immune response to this infection is an important first step that should facilitate the development of immunomodulatory agents and vaccines. Cellular immune responses, especially those mediated by cytotoxic T lymphocytes (CTL), are important in the control of many viral diseases. In this study, liver-infiltrating lymphocytes from persons with chronic HCV hepatitis were examined for evidence of HCV-specific CTL by using target cells infected with recombinant vaccinia viruses expressing the HCV core, E1, E2, and part of the NS2 proteins. Bulk expansion of liver-derived CD8+ lymphocytes resulted in the detection of HCV-specific CTL activity, whereas activity could not be found in CD8+ lymphocytes expanded from peripheral blood. Epitopes recognized by these CTL were defined by using CTL clones obtained by limiting dilution and target cells sensitized with synthetic HCV peptides. Four distinct HLA class I-restricted epitopes were identified, including two epitopes in the amino-terminal portion of the core protein. These studies provide evidence that the highly conserved core protein is a target for HCV-specific CTL and identify CTL epitopes within the more highly variable E2 envelope protein. Our studies also suggest that HCV-specific CTL are localized at the site of tissue injury in infected persons with chronic hepatitis. Identification of the epitopes recognized by HCV-specific CTL will facilitate exploration of their role in disease pathogenesis and may provide information useful in development of therapeutic interventions or vaccines.

Amino Acid Sequence↗
PubMed1993

Human immunodeficiency virus type 1-specific cytotoxic T lymphocytes release gamma interferon, tumor necrosis factor alpha (TNF-alpha), and TNF-beta when they encounter their target antigens.

Human immunodeficiency virus type 1 (HIV-1) infection is associated with elevated levels of inflammatory cytokines in the serum and cerebrospinal fluid of infected persons, but the sources of these proteins as well as the specific stimuli which trigger their production and release have not been fully defined. In this study, we evaluated the ability of HIV-1-specific cytotoxic T-lymphocyte (CTL) clones derived from seropositive persons to release gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), and TNF-beta upon contact with target cells presenting viral antigen. Peripheral blood- and cerebrospinal fluid-derived HIV-1-specific CD3+ CD4- CD8+ CTL clones as well as freshly isolated peripheral blood mononuclear cells from infected persons were tested in parallel for HIV-1-specific cytotoxicity and cytokine release. Target cells consisted of autologous and allogeneic B-lymphoblastoid cell lines sensitized with synthetic HIV-1 peptides containing the epitopes recognized by these CTL. Cytokine production was measured by specific enzyme-linked immunosorbent assay of culture supernatant fluid. HIV-1-specific CTL clones directed at envelope, Gag, reverse transcriptase, and Nef epitopes specifically released IFN-gamma, TNF-alpha, and TNF-beta upon contact with their relevant target epitopes but not following contact with irrelevant epitopes. These cytokines were released in an HLA class I-restricted fashion, and release was detectable as early as 4 to 6 h of incubation and remained elevated at 48 h. Fresh peripheral blood mononuclear cells from a seropositive person likewise released IFN-gamma in an antigen-specific and HLA class I-restricted manner when incubated with target cells presenting a peptide containing a CTL epitope, paralleling the HIV-specific cytolytic activity of these cells. These studies indicate that in addition to mediating direct cytotoxicity, HIV-1-specific CTL may affect other immune responses by releasing IFN-gamma, TNF-alpha, and TNF-beta. Elevated levels of these cytokines which have been detected in serum and cerebrospinal fluid of infected persons may be due at least in part to the persistent HIV-1-specific CTL response.

Amino Acid Sequence↗
PubMed1993

Induction of HIV-1 replication in a chronically infected T-cell line by cytotoxic T lymphocytes.

CD8-positive cytotoxic T cells (CTLs) are activated by recognition of peptide bound to MHC class I molecules on target cells. This human leukocyte antigen-restricted process induces not only lysis of target cells but also secretion of lymphokines by the CTLs, including TNF-alpha, TNF-beta, and IFN-gamma. In this study we show that activation of HIV-1-specific CTL clones by their cognate peptide epitopes induces HIV-1 replication in the chronically HIV-1-infected T-cell line ACH-2. The HIV-1-inducing activity correlates with increased levels of TNF-alpha produced by these CTLs, and can be inhibited by anti-TNF-alpha antibodies, indicating that the effect is mediated by this cytokine. These studies suggest that activation of CTL in vivo could lead to enhanced viral replication. Although HIV-1-specific CTLs may serve as a host defense to inhibit virus replication, the induction of TNF-alpha production by these cells may facilitate viral replication in infected bystander cells, contributing to viral persistence and disease pathogenesis.

Cell Line↗
PubMed1992

Intrahepatic cytotoxic T lymphocytes specific for hepatitis C virus in persons with chronic hepatitis.

Hepatitis C virus (HCV) is a major cause of post-transfusion and sporadic hepatitis worldwide, leading to chronic liver disease in at least 50% of infected individuals. The pathogenic mechanisms that result in chronic hepatitis are unknown. Lymphocytes are typically observed within the hepatic parenchyma, but the functional characteristics of these cells have not been defined. In this study, liver-infiltrating lymphocytes from two subjects with chronic HCV hepatitis were cloned at limiting dilution and tested for HCV-specific cytolytic activity using autologous target cells infected with vaccinia viruses expressing recombinant HCV Ag or sensitized with synthetic HCV peptides. In both subjects, HCV-specific, HLA class I-restricted CTL were identified that recognized epitopes in variable regions of either the envelope or nonstructural proteins. These results demonstrate the presence of HCV-specific CTL at the site of tissue damage in persons with chronic HCV hepatitis, and provide a means to evaluate the possible pathogenic role of these cells in HCV infection.

Amino Acid Sequence↗
PubMed1992

Detection of a vigorous HIV-1-specific cytotoxic T lymphocyte response in cerebrospinal fluid from infected persons with AIDS dementia complex.

AIDS dementia complex is a common neurologic disorder in later stages of HIV-1 infection. Because virus-specific CTL have been shown to contribute to neurologic disease in certain viral illnesses, we examined the cerebrospinal fluid of HIV-1-infected persons with various stages of AIDS dementia complex for the presence of HIV-1-specific CTL. In five of six subjects studied, HIV-1-specific CTL were identified in the cerebrospinal fluid. These CTL were directed at epitopes within the gag, reverse transcriptase, envelope, and nef proteins and restricted by HLA class I Ag. In four of these subjects, virus-specific CTL were detected in higher numbers in the cerebrospinal fluid compared to the peripheral blood, suggesting a specific recruitment to or local induction within the nervous system. These studies demonstrate the presence of a vigorous and broadly directed CTL response to HIV-1 in the central nervous system of infected persons with AIDS dementia complex, and provide immunologic evidence of localized intrathecal infection. Although HIV-1-specific CTL may serve to inhibit viral replication in the central nervous system, the presence of a persistent CTL response in the central nervous system may also contribute to the neurologic disorders characteristic of HIV-1 infection.

AIDS Dementia Complex↗
PubMed1992

Identification of overlapping HLA class I-restricted cytotoxic T cell epitopes in a conserved region of the human immunodeficiency virus type 1 envelope glycoprotein: definition of minimum epitopes and analysis of the effects of sequence variation.

Although the immunologic basis of protective immunity in human immunodeficiency virus type 1 (HIV-1) infection has not yet been defined, virus-specific cytotoxic T lymphocytes (CTL) are likely to be an important host defense and may be a critical feature of an effective vaccine. These observations, along with the inclusion of the HIV-1 envelope in the majority of vaccine candidates presently in clinical trials, underscore the importance of the precise characterization of the cellular immune responses to this protein. Although humoral immune responses to the envelope protein have been extensively characterized, relatively little information is available regarding the envelope epitopes recognized by virus-specific CTL and the effects of sequence variation within these epitopes. Here we report the identification of two overlapping CTL epitopes in a highly conserved region of the HIV-1 transmembrane envelope protein, gp41, using CTL clones derived from two seropositive subjects. An eight-amino acid peptide was defined as the minimum epitope recognized by HLA-B8-restricted CTL derived from one subject, and in a second subject, an overlapping nine-amino acid peptide was identified as the minimal epitope for HLA-B14-restricted CTL clones. Selected single amino acid substitutions representing those found in naturally occurring HIV-1 isolates resulted in partial to complete loss of recognition of these epitopes. These data indicate the presence of a highly conserved region in the HIV-1 envelope glycoprotein that is immunogenic for CTL responses. In addition, they suggest that natural sequence variation may lead to escape from immune detection by HIV-1-specific CTL. Since the region containing these epitopes has been previously shown to contain an immunodominant B cell epitope and also overlaps with a major histocompatibility complex class II T cell epitope recognized by CD4+ CTL from HIV-1 rgp160 vaccine recipients, it may be particularly important for HIV-1 vaccine development. Finally, the identification of minimal CTL epitopes presented by class I HLA molecules should facilitate the definition of allele-specific motifs.

Amino Acid Sequence↗
PubMed1992

Viruses, chemotherapy and immunity.

An increasing number of antiviral agents are presently in various stages of development and testing, and an increasing number have recently been licensed for use in humans. These drugs have been used extensively to treat viral infections in immunocompromised individuals, and these studies indicate that for many antiviral agents the response to therapy is highly dependent on the integrity of the underlying host immune response. In particular, the response to zidovudine, acyclovir and ganciclovir in persons with HIV-1 infection is highly dependent upon CD4 number, which can be considered a surrogate marker for the state of host immune function in these subjects. Responses to interferons likewise can be shown to depend on the host immune response, with responses due to both direct antiviral effects of this agent as well as immunomodulatory effects mediated through interferon-induced upregulation of HLA molecule expression. The interdependence of host immunity with antiviral efficacy is underscored by the increased antiviral drug resistance in persons with advanced degrees of chronic immunosuppression, related to the higher level of viral replication and viraemia which occurs in the absence of an effective host immune response. Further definition of the precise mechanisms of these interactions should facilitate the rational design of antiviral agents and immunomodulatory therapies to improve treatment of viral infections.

AIDS-Related Opportunistic Infections↗
PubMed1991

An optimal viral peptide recognized by CD8+ T cells binds very tightly to the restricting class I major histocompatibility complex protein on intact cells but not to the purified class I protein.

CD8+ cytotoxic T lymphocytes recognize cell surface complexes formed by class I major histocompatibility complex (MHC-I) glycoproteins and antigenic peptides. We have identified a peptide nonamer (termed IV9) derived from the human immunodeficiency virus that is over a millionfold more active (at subpicomolar concentrations) than peptide analogues longer or shorter by one or two amino acid residues. Although IV9 does not detectably bind to isolated MHC-I molecules as measured by equilibrium dialysis, we quantitated its specific binding in unaltered form to MHC-I on intact cells. Less than 1% of cell surface MHC-I forms complexes with IV9, which suffices to trigger maximal cytotoxic T-lymphocyte activity. By contrast, a peptide dodecamer that includes the IV9 sequence and is active at micromolar concentrations does not bind to MHC-I on intact cells, raising the possibility that this longer peptide undergoes processing. Using stoichiometrically iodinated IV9 to obviate the ambiguities associated with trace labeling methods, we measured the dissociation kinetics of purified peptide/MHC-I complexes isolated by affinity chromatography and found these complexes to be exceedingly stable (t1/2 = 200-600 hr).

Amino Acid Sequence↗
PubMed1991

HIV-1 gag-specific cytotoxic T lymphocytes recognize multiple highly conserved epitopes. Fine specificity of the gag-specific response defined by using unstimulated peripheral blood mononuclear cells and cloned effector cells.

CTL directed at the highly conserved HIV-1 gag protein have been described in HIV-1 seropositive persons and may be an important host defense against this retrovirus. Presently only limited data are available regarding the specific epitopes recognized by these CTL. In this study, we have performed a detailed examination of the gag-specific CTL response in three HIV-1 seropositive subjects, using both unstimulated PBMC and cloned CTL. Lysis of gag-expressing targets was found to be mediated by CD3+CD8+ lymphocytes and restricted by class I Ag. Multiple class I Ag were found to restrict gag epitopes in each subject studied, with as many as three of these Ag involved in presenting gag CTL epitopes in a single subject. The majority of gag-specific CTL activity was found to be directed against epitopes in the p24 subunit of the gag protein, with at least seven different HLA class I-restricted CTL p24 epitopes identified in these three subjects. Less CTL activity was directed against p17 subunit of gag and two CTL epitopes were identified in this protein. Although as many as four different epitopes in gag were recognized using CTL from a single subject, none of the epitopes was recognized by CTL from more than one subject. Analysis of gag epitope recognition using cloned CTL demonstrated heterogeneity and specificity not appreciated using unstimulated PBMC. The identification of multiple relatively conserved epitopes in the HIV-1 gag protein and the heterogeneity of CTL responses to this protein may have important implications for vaccine development and our understanding of AIDS pathogenesis.

Amino Acid Sequence↗
PubMed1991

HIV-1 infection does not induce tumor necrosis factor-alpha or interferon-beta gene transcription.

An early host defense against infection by RNA or DNA viruses is the induction, within infected cells, of tumor necrosis factor-alpha (TNF-alpha) gene transcription. The protein product of the TNF-alpha gene alone, or together with different types of interferons, inhibits viral propagation in diverse cell types. In this study, the effect of acute and chronic human immunodeficiency virus type 1 (HIV-1) infection on the transcription of the TNF-alpha and interferon-beta (IFN-beta) genes was examined in susceptible monocyte and T-cell lines as well as in primary human mononuclear phagocytes. Although Sendai virus, a prototypic inducer of TNF-alpha and IFN-beta mRNA, induced the transcription of both genes in the monocyte cell lines and TNF-alpha in the T-cell line and in primary mononuclear phagocytes, transcription of these genes was not inducible by HIV-1. Therefore, HIV-1 was able to infect these cells without triggering the transcription of genes encoding proteins important in immediate antiviral cellular defenses. These results may explain in part how HIV-1 is able to establish persistent intracellular infections and escape acute host responses that have evolved to combat viral infection.

Cell Line↗
PubMed1990

Cytotoxic T lymphocytes against HIV.

HIV-1 infection has clearly been shown to induce a vigorous CTL response in infected people, and this response is present at a time when immune function otherwise is globally impaired. HIV-1-specific CTL are detectable both in peripheral blood and tissues of infected people, and are aimed at multiple viral proteins. The precise epitopes recognized by these CTL are now being defined, and the establishment of CTL clones should facilitate further functional analysis of these cells. However, the central question as to the clinical relevance of HIV-1-specific CTL remains. By analogy with animal model systems of virus infection, it is reasonable to postulate that HIV-1-specific CTL serve a protective role as a host defense. In this regard, in vitro data indicate that HIV-1-specific CTL can suppress viral replication, and longitudinal clinical studies indicate that the vigorous CTL activity seen in the early stages of infection declines with disease progression. Alternatively, the presence of HIV-1-specific CTL in tissues such as the lung and brain have to at least raise the possibility that these cells may be contributing to the pathologic consequences of infection. In addition, the relative protective effects of virus-specific CTL compared to other effector mechanisms such as ADCC and neutralizing antibodies remain to be determined. Nevertheless, recent data in the SIV vaccine model give reason for encouragement that a state of protective immunity can be achieved in AIDS-like illness caused by retroviruses. The search continues presently not only for the parameters which define protective immunity in HIV-1 infection, but also for the ideal HIV-1 immunogens to be used for vaccination of human populations.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Long-term culture and fine specificity of human cytotoxic T-lymphocyte clones reactive with human immunodeficiency virus type 1.

The definition of human immunodeficiency virus type 1 (HIV-1) immunogenic epitopes is central to the rational design of AIDS vaccine strategies. In this study, we have generated seven HIV-1 reverse transcriptase-specific cytotoxic T-lymphocyte (CTL) clones from the peripheral blood of two seropositive subjects. Epitopes recognized by these CTL clones were identified by using target cells infected with recombinant HIV-1-vaccinia virus vectors expressing truncated reverse transcriptase proteins and further defined by using target cells incubated with overlapping 25-amino acid synthetic reverse transcriptase peptides. Five different CTL epitopes were identified, and in each case recognition was restricted by class I human leukocyte antigens (HLA). Clones maintained specific cytolytic function in continuous culture for up to 11 months, requiring only periodic restimulation with a CD3-specific monoclonal antibody. These results indicate that HIV-1-specific, major histocompatibility class I-restricted CTL recognize multiple epitopes of a single viral gene product in conjunction with different host HLA antigens. In addition, they demonstrate that human virus-specific CTL can be grown in long-term culture without the need for reexposure to viral antigen.

Cell Line↗
PubMed1989

Synergistic inhibition of human immunodeficiency virus type 1 (HIV-1) replication in vitro by recombinant soluble CD4 and 3'-azido-3'-deoxythymidine.

A combination of antiviral therapies that target different sites in the human immunodeficiency virus type 1 (HIV-1) replicative cycle may be necessary for optimal treatment of HIV-1 infections. We evaluated the interactions of a soluble virus receptor (recombinant soluble CD4 or rsT4) and a reverse transcriptase inhibitor (azidothymidine, AZT) against HIV-1 replication in vitro. A variety of cell types was studied including peripheral blood mononuclear cells, a CD4-positive T-cell line, and a CD4-positive human monocyte cell line. The combination of rsT4 and AZT inhibited HIV-1 synergistically over a broad range of drug concentrations and multiplicities of infection in several different HIV-1 replication assays. Drug interactions were evaluated by the median-effect principle and the isobologram technique using a computer analysis. In all of the cell types tested, combinations of rsT4 and AZT were synergistic in vitro, without additive cytotoxicity.

Antigens, Differentiation, T-Lymphocyte↗