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Biomedical subjects

B D Walker

Publications and source records attributed to B D Walker.

At least 127 records · Page 7Linked to original sources
PubMed1995

An epitope-selective, transporter associated with antigen presentation (TAP)-1/2-independent pathway and a more general TAP-1/2-dependent antigen-processing pathway allow recognition of the HIV-1 envelope glycoprotein by CD8+ CTL.

The lysis of virally infected cells by CTLs requires the recognition of processed fragments of viral proteins presented in association with class I MHC molecules on the surfaces of infected cells. Processing begins in the cytosol with the degradation of viral proteins into peptides that are then transported into the endoplasmic reticulum (ER) for association with newly synthesized class I molecules. Transport is mediated by a heterodimer of the MHC-encoded proteins, transporter associated with Ag presentation (TAP)-1 and TAP-2. Uncertainty exists over the site of processing of viral envelope (env) proteins. The extracellular domains of env proteins are not present in the cytosol, the site in which the class I-restricted Ag-processing pathway begins. Rather, the ecto-domains of env proteins are cotranslationally translocated into the ER during biosynthesis. We have analyzed the processing of the HIV-1 env protein by using a large series of env-specific human CD8+ CTL clones. These studies have led to the delineation of two distinct processing pathways. The first pathway permits a subset of class I-restricted epitopes in the ecto-domain of the env protein to be generated efficiently by a TAP-1/2-independent mechanism localized to the ER or a premedial Golgi compartment. A second, more general pathway that is capable of generating all env epitopes uses as a substrate env protein mislocalized to the cytosol and produces peptides that are transported from the cytoplasm to the ER in a TAP-1/2-dependent fashion.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Cytotoxic CD8+ T lymphocytes reactive with human immunodeficiency virus-1 produce granulocyte/macrophage colony-stimulating factor and variable amounts of interleukins 2, 3, and 4 following stimulation with the cognate epitope.

Infection with human immunodeficiency virus type 1 (HIV-1) induces vigorous and persistent cytotoxic CD8+ T cell responses. CTL clones were derived from peripheral blood or cerebrospinal fluid of three HIV-1 patients, with depressed CD4+ T cell counts. When stimulated with HLA-compatible target cells (B-LCL) presensitized with cognate HIV-1 peptides, all clones produced GM-CSF, TNF-alpha, and IFN-gamma and most produced low amounts of IL2, IL3, and IL4. After nonspecific stimulation with a phorbol ester and calcium ionophore, the clones secreted cytokines at levels similar to those from CD4+ lines from an HIV-1 infected donor. The ability of supernatants from the stimulated CTL clones to support the formation of granulocyte-macrophage colonies in normal bone marrow suggests that the GM-CSF was biologically active. Release of cytokines by activated CTL may influence the immunopathogenesis of HIV disease.

CD4-Positive T-Lymphocytes↗
PubMed1995

Cytotoxic T lymphocytes and HIV-1 related neurologic disorders.

In summary, one can conclude that infected persons exhibit an extremely vigorous, virus-specific CTL response, and in at least some individuals this response is broadly directed at multiple epitopes. These cells are present at the time or initial control of viremia and can also be detected after more than a decade of asymptomatic infection. These cells can also be found in the central nervous system in persons with ADC, and one can envision pathways in which the inflammatory cytokines released by these cells upon activation could contribute to the neurologic sequelae of infection. However, the precise role of these cells as a protective host defense and the possible contribution of these cells, or products released by these cells, to tissue damage at sites such as the lung and brain remain to be determined. Further delineation of the role played by CTLs in the pathogenesis of disease should be extremely useful in helping to understand the disease itself and to guide intervention strategies.

AIDS Dementia Complex↗
PubMed1995

Persistence of attenuated rev genes in a human immunodeficiency virus type 1-infected asymptomatic individual.

With the goal of examining the functional diversity of human immunodeficiency virus type 1 (HIV-1) env genes within the peripheral blood mononuclear cells of an asymptomatic individual, we substituted four complete env genes into the replication-competent NL4-3 provirus. Despite encoding full-length open reading frames for gp120 and gp41 and the second coding exon of tat and rev, each chimera was replication defective. Site-directed mutagenesis of codon 78 in the Rev activation domain (from a hitherto unique Ile to the subtype B consensus Leu) partially restored infectivity for two of three chimeras tested. Similarly, mutagenesis of rev codon 78 of NL4-3 from Leu to Ile partially attenuated this virus. Ile-78 was found in all 13 clones examined from samples taken from this asymptomatic subject 4.5 years after infection, including 9 from peripheral blood mononuclear cells and 4 from a virus isolate, as well as 4 additional clones each from peripheral blood mononuclear cells sampled 37 and 51 months later. We next examined conservation of the Rev activation domain within and among long-term survivors (LTS) and patients with AIDS, as well as T-cell-line-adapted strains of HIV-1. Putative attenuating mutations were found in a minority of sequences from all five LTS and two of four patients with AIDS. Of the 11 T-cell-line-adapted viruses examined, none had these changes. Among and within LTS virus population had marginally higher levels of diversity in Rev than in Env; patients with AIDS had similar levels of diversity in the two reading frames; and T-cell-line-adapted viruses had higher levels of diversity in Env. These results are consistent with the hypothesis that asymptomatic individuals harbor attenuated variants of HIV-1 which correlate with and contribute to their lack of disease progression.

Acquired Immunodeficiency Syndrome↗
PubMed1995

HLA class I-restricted cytotoxic T lymphocytes specific for hepatitis C virus. Identification of multiple epitopes and characterization of patterns of cytokine release.

Cytotoxic T lymphocytes (CTL) are important to the control of viral replication and their presence may be important to disease outcome. An understanding of the spectrum of proteins recognized by hepatitis C virus (HCV)-specific CTL and the functional properties of these cells is an important step in understanding the disease process and the mechanisms of persistent infection, which occurs in the majority of HCV-infected individuals. In this report we identify HCV-specific CTL responses restricted by the HLA class I molecules A2, A3, A11, A23, B7, B8, and B53. The epitopes recognized by these intrahepatic CTL conform to published motifs for binding to HLA class I molecules, although in some cases we have identified CTL epitopes for which no published motif exists. The use of vectors expressing two different strains of HCV, HCV-1 and HCV-H, revealed both strain-specific and cross-reactive CTL. These HCV-specific CTL were shown to produce cytokines including IFN-gamma, TNF-alpha, GM-CSF, IL-8, and IL-10 in an antigen- and HLA class I-specific manner. These studies indicate that the CTL response to HCV is broadly directed and that as many as five different epitopes may be targeted in a single individual. The identification of minimal epitopes may facilitate peptide-specific immunization strategies. In addition, the release of proinflammatory cytokines by these cells may contribute to the pathogenesis of HCV-induced liver damage.

Amino Acid Sequence↗
PubMed1995

T lymphocytes and their cytokines in human immunodeficiency virus (HIV) infection: implications for associated neoplasias.

Infection with the human immunodeficiency virus (HIV) results in gradual immunosuppression due to the loss of CD4+ T cells. In the wake of immune system breakdown, infected individuals may acquire multiple opportunistic infections and develop certain malignancies which ultimately account for the vast majority of deaths in these persons. A limited number of malignancies are directly associated with HIV infection and suggest a common tie between these tumors. Inappropriate immune surveillance resulting in insufficient inhibition of virus replication and inadequate control of the growth of transformed cells may contribute to the development of malignancies in HIV-infected individuals. Alternatively, malignancies in HIV infection may be the consequence of immune dysregulation. Cellular immune responses mediated by antigen-specific cytotoxic T lymphocytes (CTL) are of particular importance for immunologic control of viral infections and substantial information has been gathered about theses cells in HIV infection. The goal of this review is therefore to summarize recent findings regarding the cellular immune response to HIV with a particular focus on cytokines released by HIV-specific CTL.

Cytokines↗
PubMed1994

Naturally processed viral peptides recognized by cytotoxic T lymphocytes on cells chronically infected by human immunodeficiency virus type 1.

We have established long-term cultures of several cell lines stably and uniformly expressing human immunodeficiency virus type 1 (HIV-1) in order to (a) identify naturally processed HIV-1 peptides recognized by cytotoxic T lymphocytes (CTL) from HIV-1-seropositive individuals and (b) consider the hypothesis that naturally occurring epitope densities on HIV-infected cells may limit their lysis by CTL. Each of two A2-restricted CD8+ CTL specific for HIV-1 gag or reverse transcriptase (RT) recognized a single naturally processed HIV-1 peptide in trifluoroacetic acid (TFA) extracts of infected cells: gag 77-85 (SLYNTVATL) or RT 476-484 (ILKEPVHGV). Both processed peptides match the synthetic peptides that are optimally active in cytotoxicity assays and have the consensus motif described for A2-associated peptides. Their abundances were approximately 400 and approximately 12 molecules per infected Jurkat-A2 cell, respectively. Other synthetic HIV-1 peptides active at subnanomolar concentrations were not present in infected cells. Except for the antigen processing mutant line T2, HIV-infected HLA-A2+ cell lines were specifically lysed by both A2-restricted CTL, although infected Jurkat-A2 cells were lysed more poorly by RT-specific CTL than by gag-specific CTL, suggesting that low cell surface density of a natural peptide may limit the effectiveness of some HIV-specific CTL despite their vigorous activity against synthetic peptide-treated target cells.

Amino Acid Sequence↗
PubMed1994

Longitudinal analysis of T cell receptor (TCR) gene usage by human immunodeficiency virus 1 envelope-specific cytotoxic T lymphocyte clones reveals a limited TCR repertoire.

Human immunodeficiency virus 1 (HIV-1) infection is associated with a vigorous cellular immune response that allows detection of cytotoxic T lymphocyte (CTL) activity using freshly isolated peripheral blood mononuclear cells (PBMC). Although restricting class I antigens and epitopes recognized by HIV-1-specific CTL have been defined, the effector cells mediating this vigorous response have been characterized less well. Specifically, no studies have addressed the breadth and duration of response to a defined epitope. In the present study, a longitudinal analysis of T cell receptor (TCR) gene usage by CTL clones was performed in a seropositive person using TCR gene sequences as a means of tracking responses to a well-defined epitope in the glycoprotein 41 transmembrane protein. 10 CTL clones specific for this human histocompatibility leukocyte antigen-B14-restricted epitope were isolated at multiple time points over a 31-mo period. All clones were derived from a single asymptomatic HIV-1-infected individual with a vigorous response to this epitope that was detectable using unstimulated PBMC. Polymerase chain reaction amplification using V alpha and V beta family-specific primers was performed on each clone, followed by DNA sequencing of the V-D-J regions. All 10 clones utilized V alpha 14 and V beta 4 genes. Sequence analysis of the TCR revealed the first nine clones isolated to also be identical at the nucleotide level. The TCR-alpha junctional region sequence of the tenth clone was identical to the junctional region sequences of the other nine, but this clone utilized distinct D beta and J beta gene segments. This study provides evidence that the observed high degree of HIV-1-specific CTL activity may be due to monoclonal or oligoclonal expansion of specific effector cells, and that progeny of a particular CTL clone may persist for prolonged periods in vivo in the presence of a chronic productive viral infection. The observed limited TCR diversity against an immunodominant epitope may limit recognition of virus variants with mutations in regions interacting with the TCR, thereby facilitating immune escape.

Amino Acid Sequence↗
PubMed1994

HIV type 1-specific cytotoxic T lymphocytes stimulate HLA class I and intercellular adhesion molecule type 1 expression and increase beta 2-microglobulin levels in vitro.

Besides acting in a direct manner, cytolytic HIV-1-specific CTLs release a variety of cytokines. To assess the potential role of cytokines released by these CTLs we tested the ability of soluble products secreted by HIV-1-specific CTLs to induce HLA class I and ICAM-1 expression and to raise beta 2-microglobulin (beta 2M) concentrations in cell culture. To this end, supernatants were derived from HIV-1-specific CTLs incubated with autologous B lymphoblasts presenting either the cognate HIV-1 epitope or a control peptide. Cell lines and peripheral blood mononuclear cells (PBMCs) were incubated with these supernatants for 24-48 hr. Similarly, cells were cocultured with CTLs and their targets. This study demonstrates that in parallel with lysis of their cognate target, HIV-1-specific CTLs secreted products that stimulated HLA class I and ICAM-1 expression on cell lines and PBMCs. As few as 1000 CTLs significantly induced the expression of these molecules. In addition, secreted products of HIV-specific CTLs enhanced beta 2M release by PBMCs and Jurkat cells. These effects were mediated primarily by IFN-gamma and suggest that HIV-specific CTLs may contribute to increased HLA class I expression in infected tissue and elevated ICAM-1 and beta 2M concentrations in serum and cerebrospinal fluid of infected individuals.

B-Lymphocytes↗
PubMed1994

Human immunodeficiency virus type 1 evolution in vivo tracked by DNA heteroduplex mobility assays.

High mutation rates and strong selective pressures imposed on human immunodeficiency viruses in vivo result in the formation of pools of genetic variants known as quasispecies. DNA heteroduplex mobility and tracking analyses were used to monitor the generation of HIV sequence diversity, to estimate quasispecies complexity, and to assess the turnover of genetic variants to approach an understanding of the relationship between viral quasispecies evolution in vivo and disease progression. Proviral DNA pools were nearly homogeneous soon after sexual transmission. The emergence and clearance of individual variants then occurred at different rates in different individuals. High quasispecies complexity was found in long-term-infected, asymptomatic individuals, while rapid CD4+ cell decline and AIDS were often, but not always, associated with lower quasispecies complexity. Proviral genetic variation was often low following in vitro culture, because of the outgrowth of one or a few variants that often became more abundant only later as proviruses in peripheral blood mononuclear cells. These studies provide insight into the dynamics of human immunodeficiency virus sequence changes in vivo and illustrate the utility of heteroduplex analysis for the study of phenomena associated with rapid genetic changes.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Induction of a major histocompatibility complex class I-restricted cytotoxic T-lymphocyte response to a highly conserved region of human immunodeficiency virus type 1 (HIV-1) gp120 in seronegative humans immunized with a candidate HIV-1 vaccine.

Efforts to induce broadly reactive immunity against human immunodeficiency virus type 1 (HIV-1) have been impaired by the extent of sequence variation exhibited by this lentivirus. Cytotoxic T lymphocytes (CTL) specific for other viruses such as influenza virus have been shown to mediate immunity against divergent viral strains, a property that is related to the ability of CTL to recognize processed antigen derived from conserved viral proteins. A recent candidate HIV-1 vaccine regimen has been described in which subjects receive a primary immunization with a recombinant vaccinia virus expressing gp160 and then a booster immunization with recombinant gp160. Volunteers immunized with this regimen have exhibited augmented humoral responses and have also developed CD4+ and CD8+ CTL specific for gp160. In this report, we have identified the epitopes recognized by CD4+ and CD8+ CTL obtained from two vaccines. An immunodominant CD8+ CTL response was HLA-A3.1 restricted and recognized a 10-amino-acid epitope (gp120/38-47) in a highly conserved region of gp120. CTL specific for the epitope gp120/38-47 were able to lyse targets sensitized with peptides corresponding to all known natural sequence variants in this region. In addition, other HLA class I-restricted CTL epitopes were identified in relatively conserved regions of gp120 and gp41, and CD4+ CTL were shown to recognize two different regions of gp120. Thus, in these two volunteers, immunization with a single strain of HIV-1 induced CD4+ and CD8+ CTL that are specific for multiple conserved regions of HIV-1 and would be expected to recognize a broad range of viral isolates.

AIDS Vaccines↗
PubMed1994

The cytotoxic T-lymphocyte response in HIV-1 infection.

HIV infection is associated with an extremely vigorous virus-specific cytotoxic T-lymphocyte (CTL) response. This CTL activity is of sufficient magnitude to be detected using freshly isolated peripheral blood mononuclear cells, but despite this vigorous immune response, HIV-1 disease ultimately progresses. This article describes methods used to detect CTL responses and epitopes recognized by HIV-1 specific CTL. The potential role of CTL in the control of viral replication, disease pathogenesis, and possible mechanisms that allow HIV-1 to ultimately evade the host's immune response is discussed. Finally, efforts to induce CTL responses through vaccines are summarized.

AIDS Vaccines↗
PubMed1994

The rationale for immunotherapy in HIV-1 infection.

Human immunodeficiency virus type 1 (HIV-1) infection causes progressive and ultimately profound immunosuppression. Initially, however, infection is associated with vigorous virus-specific immune responses, including both neutralizing antibodies and cytotoxic T lymphocytes (CTLs). Although the host immune response is ultimately unable to eliminate the virus, experimental data suggest that these immune responses help to inhibit virus replication during the prolonged asymptomatic phase of illness. A number of mechanisms have been proposed to contribute to viral persistence in infected persons, among them direct immunosuppressive effects of the virus; defects in antigen presentation; down-modulation of human leukocyte antigens (HLA); clonal deletion of existing immune responses; sequence variation leading to immune escape; and decreased T-helper cell function. The rationale supporting the use of vaccine therapy in HIV-1 infection is based on the hypothesis that viral persistence is due to an inadequate immune response generated by natural infection and that the immune system can be induced to generate more effective immunoregulatory responses by vaccination. Potential mechanisms by which this might occur include enhanced clearance of circulating virus, enhanced recognition of virus variants, enhanced presentation of viral antigens to the immune system, and increased regional T-cell help. A number of protocols evaluating vaccine therapy in HIV-1 infection are presently under way, the results of which should facilitate rational decisions regarding the use of this approach in HIV-1-infected persons.

AIDS Vaccines↗