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A Sette

Publications and source records attributed to A Sette.

At least 37 records · Page 2Linked to original sources
PubMed2001

Spreading of HIV-specific CD8+ T-cell repertoire in long-term nonprogressors and its role in the control of viral load and disease activity.

Long-term non-progressors (LTNP) represent a minority of human immunodeficiency virus (HIV) infected individuals characterized by stable or even increasing CD4+ T-cell count and by stronger immune responses against HIV than progressors. In this study, HIV-specific effector CD8+ T cells, as detected by both a sensitive ex vivo enzyme-linked immunospot (ELISPOT) assay and specific major histocompatibility complex (MHC) peptide tetramers, were at a low frequency in the peripheral blood of LTNP, and recognized a lower number of HIV peptides than their memory resting cell counterparts. Both factors may account for the lack of complete HIV clearance by LTNP, who could control the viral spread, and displayed a higher magnitude of cytotoxic T lymphocyte (CTL) responses than progressors. By combining cell purification and ELISPOT assays this study demonstrates that both effector and memory resting cells were confined to a CD8+ population with memory CD45RO+ phenotype, with the former being CD28- and the latter CD28+. Longitudinal studies highlighted a relatively stable HIV-specific effector repertoire, viremia, and CD4+ T-cell counts, which were all correlated with maintenance of nonprogressor status. In conclusion, the analysis of HIV-specific cellular responses in these individuals may help define clear correlates of protective immunity in HIV infection.

Adult↗
PubMed2001

Majority of peptides binding HLA-A*0201 with high affinity crossreact with other A2-supertype molecules.

The A*0201, A *0202, A*0203, A*0206, and A*6802 binding capacity of single amino acid substitution analogs of known A2-supertype binding peptides and of large nonredundant peptide libraries was measured. The results were utilized to rigorously define the peptide binding specificities of these A2-supertype molecules. Although each molecule was noted to have unique preferences, large overlaps in specificity were found. The presence of L, I, V, M, A, T, and Q residues in position 2, and L, I, V, M, A, and T residues at the C-terminus of peptide ligands were tolerated by all molecules. Likewise, whereas examination of secondary influences on peptide binding revealed allele specific preferences, shared features could also be identified. These shared features were utilized to define an A2-supermotif and were noted to correlate with crossreactivity. Over 70% of the peptides that bound A *0201 with high affinity were found to bind at least two other A2-supertype molecules. Because the A2-supertype molecules studied herein cover the variants most common in different major ethnicities, these findings have important implications for epitope-based approaches to vaccination, immunotherapy, and the monitoring of immune responses.

Alleles↗
PubMed2001

The outcome of hepatitis C virus infection is predicted by escape mutations in epitopes targeted by cytotoxic T lymphocytes.

CD8(+) cytotoxic T lymphocytes (CTL) are thought to control hepatitis C virus (HCV) replication and so we investigated why this response fails in persistently infected individuals. The HCV quasispecies in three persistently infected chimpanzees acquired mutations in multiple epitopes that impaired class I MHC binding and/or CTL recognition. Most escape mutations appeared during acute infection and remained fixed in the quasispecies for years without further diversification. A statistically significant increase in the amino acid replacement rate was observed in epitopes versus adjacent regions of HCV proteins. In contrast, most epitopes were intact when hepatitis C resolved spontaneously. We conclude that CTL exert positive selection pressure against the HCV quasispecies and the outcome of infection is predicted by mutations in class I MHC restricted epitopes.

Acute Disease↗
PubMed2001

Mucosal AIDS vaccine reduces disease and viral load in gut reservoir and blood after mucosal infection of macaques.

Given the mucosal transmission of HIV-1, we compared whether a mucosal vaccine could induce mucosal cytotoxic T lymphocytes (CTLs) and protect rhesus macaques against mucosal infection with simian/human immunodeficiency virus (SHIV) more effectively than the same vaccine given subcutaneously. Here we show that mucosal CTLs specific for simian immunodeficiency virus can be induced by intrarectal immunization of macaques with a synthetic-peptide vaccine incorporating the LT(R192G) adjuvant. This response correlated with the level of T-helper response. After intrarectal challenge with pathogenic SHIV-Ku2, viral titers were eliminated more completely (to undetectable levels) both in blood and intestine, a major reservoir for virus replication, in intrarectally immunized animals than in subcutaneously immunized or control macaques. Moreover, CD4+ T cells were better preserved. Thus, induction of CTLs in the intestinal mucosa, a key site of virus replication, with a mucosal AIDS vaccine ameliorates infection by SHIV in non-human primates.

AIDS Vaccines↗
PubMed2001

T-cell reactivity against streptococcal antigens in the periphery mirrors reactivity of heart-infiltrating T lymphocytes in rheumatic heart disease patients.

T-cell molecular mimicry between streptococcal and heart proteins has been proposed as the triggering factor leading to autoimmunity in rheumatic heart disease (RHD). We searched for immunodominant T-cell M5 epitopes among RHD patients with defined clinical outcomes and compared the T-cell reactivities of peripheral blood and intralesional T cells from patients with severe RHD. The role of HLA class II molecules in the presentation of M5 peptides was also evaluated. We studied the T-cell reactivity against M5 peptides and heart proteins on peripheral blood mononuclear cells (PBMC) from 74 RHD patients grouped according to the severity of disease, along with intralesional and peripheral T-cell clones from RHD patients. Peptides encompassing residues 1 to 25, 81 to 103, 125 to 139, and 163 to 177 were more frequently recognized by PBMC from RHD patients than by those from controls. The M5 peptide encompassing residues 81 to 96 [M5(81-96) peptide] was most frequently recognized by PBMC from HLA-DR7+ DR53+ patients with severe RHD, and 46.9% (15 of 32) and 43% (3 of 7) of heart-infiltrating and PBMC-derived peptide-reactive T-cell clones, respectively, recognized the M5(81-103) region. Heart proteins were recognized more frequently by PBMC from patients with severe RHD than by those from patients with mild RHD. The similar pattern of T-cell reactivity found with both peripheral blood and heart-infiltrating T cells is consistent with the migration of M-protein-sensitized T cells to the heart tissue. Conversely, the presence of heart-reactive T cells in the PBMC of patients with severe RHD also suggests a spillover of sensitized T cells from the heart lesion.

Antigen Presentation↗
PubMed2001

In vivo selection of a lymphocytic choriomeningitis virus variant that affects recognition of the GP33-43 epitope by H-2Db but not H-2Kb.

CD8 T cells drive the protective immune response to lymphocytic choriomeningitis virus (LCMV) infection and are thus a determining force in the selection of viral variants. To examine how escape mutations affect the presentation and recognition of overlapping T-cell epitopes, we isolated an LCMV variant that is not recognized by T-cell receptor (TCR)-transgenic H-2Db-restricted LCMV GP33-41-specific cytotoxic T lymphocytes (CTL). The variant virus carried a single-amino-acid substitution (valine to alanine) at position 35 of the viral glycoprotein. This region of the LCMV glycoprotein encodes both the Db-restricted GP33-43 epitope and a second epitope (GP34-42) presented by the Kb molecule. We determined that the V-to-A CTL escape mutant failed to induce a Db GP33-43-specific CTL response and that Db-restricted GP33-43-specific CTL induced by the wild-type LCMV strain were unable to kill target cells infected with the variant LCMV strain. In contrast, the Kb-restricted response was much less affected. We found that the V-to-A substitution severely impaired peptide binding to Db but not to Kb molecules. Strikingly, the V-to-A mutation did not change any of the anchor residues, and the dramatic effect on binding was therefore unexpected. The strong decrease in Db binding explains why the variant virus escapes the Db GP33-43-specific response but still elicits the Kb-restricted response. These findings also illustrate that mutations within regions encoding overlapping T-cell epitopes can differentially affect the presentation and recognition of individual epitopes.

Amino Acid Substitution↗
PubMed2001

CD8(+) lymphocytes from simian immunodeficiency virus-infected rhesus macaques recognize 14 different epitopes bound by the major histocompatibility complex class I molecule mamu-A*01: implications for vaccine design and testing.

It is becoming increasingly clear that any human immunodeficiency virus (HIV) vaccine should induce a strong CD8(+) response. Additional desirable elements are multispecificity and a focus on conserved epitopes. The use of multiple conserved epitopes arranged in an artificial gene (or EpiGene) is a potential means to achieve these goals. To test this concept in a relevant disease model we sought to identify multiple simian immunodeficiency virus (SIV)-derived CD8(+) epitopes bound by a single nonhuman primate major histocompatibility complex (MHC) class I molecule. We had previously identified the peptide binding motif of Mamu-A*01(2), a common rhesus macaque MHC class I molecule that presents the immunodominant SIV gag-derived cytotoxic T lymphocyte (CTL) epitope Gag_CM9 (CTPYDINQM). Herein, we scanned SIV proteins for the presence of Mamu-A*01 motifs. The binding capacity of 221 motif-positive peptides was determined using purified Mamu-A*01 molecules. Thirty-seven peptides bound with apparent K(d) values of 500 nM or lower, with 21 peptides binding better than the Gag_CM9 peptide. Peripheral blood mononuclear cells from SIV-infected Mamu-A*01(+) macaques recognized 14 of these peptides in ELISPOT, CTL, or tetramer analyses. This study reveals an unprecedented complexity and diversity of anti-SIV CTL responses. Furthermore, it represents an important step toward the design of a multiepitope vaccine for SIV and HIV.

AIDS Vaccines↗
PubMed2001

Molecular determinants of peptide binding to two common rhesus macaque major histocompatibility complex class II molecules.

Major histocompatibility complex class II molecules encoded by two common rhesus macaque alleles Mamu-DRB1*0406 and Mamu-DRB*w201 have been purified, and quantitative binding assays have been established. The structural requirements for peptide binding to each molecule were characterized by testing panels of single-substitution analogs of the two previously defined epitopes HIV Env242 (Mamu-DRB1*0406 restricted) and HIV Env482 (Mamu-DRB*w201 restricted). Anchor positions of both macaque DR molecules were spaced following a position 1 (P1), P4, P6, P7, and P9 pattern. The specific binding motif associated with each molecule was distinct, but largely overlapping, and was based on crucial roles of aromatic and/or hydrophobic residues at P1, P6, and P9. Based on these results, a tentative Mamu class II DR supermotif was defined. This pattern is remarkably similar to a previously defined human HLA-DR supermotif. Similarities in binding motifs between human HLA and macaque Mamu-DR molecules were further illustrated by testing a panel of more than 60 different single-substitution analogs of the HLA-DR-restricted HA 307-319 epitope for binding to Mamu-DRB*w201 and HLA-DRB1*0101. The Mamu-DRB1*0406 and -DRB*w201 binding capacity of a set of 311 overlapping peptides spanning the entire simian immunodeficiency virus (SIV) genome was also evaluated. Ten peptides capable of binding both molecules were identified, together with 19 DRB1*0406 and 43 DRB*w201 selective binders. The Mamu-DR supermotif was found to be present in about 75% of the good binders and in 50% of peptides binding with intermediate affinity but only in approximately 25% of the peptides which did not bind either Mamu class II molecule. Finally, using flow cytometric detection of antigen-induced intracellular gamma interferon, we identify a new CD4(+) T-lymphocyte epitope encoded within the Rev protein of SIV.

Amino Acid Sequence↗
PubMed2001

Identification of novel HLA-A2-restricted human immunodeficiency virus type 1-specific cytotoxic T-lymphocyte epitopes predicted by the HLA-A2 supertype peptide-binding motif.

Virus-specific cytotoxic T-lymphocyte (CTL) responses are critical in the control of human immunodeficiency virus type 1 (HIV-1) infection and will play an important part in therapeutic and prophylactic HIV-1 vaccines. The identification of virus-specific epitopes that are efficiently recognized by CTL is the first step in the development of future vaccines. Here we describe the immunological characterization of a number of novel HIV-1-specific, HLA-A2-restricted CTL epitopes that share a high degree of conservation within HIV-1 and a strong binding to different alleles of the HLA-A2 superfamily. These novel epitopes include the first reported CTL epitope in the Vpr protein. Two of the novel epitopes were immunodominant among the HLA-A2-restricted CTL responses of individuals with acute and chronic HIV-1 infection. The novel CTL epitopes identified here should be included in future vaccines designed to induce HIV-1-specific CTL responses restricted by the HLA-A2 superfamily and will be important to assess in immunogenicity studies in infected persons and in uninfected recipients of candidate HIV-1 vaccines.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Degenerate immunogenicity of an HLA-A2-restricted hepatitis B virus nucleocapsid cytotoxic T-lymphocyte epitope that is also presented by HLA-B51.

The recent identification of hepatitis B virus (HBV) epitopes restricted by multiple HLA alleles has greatly expanded the epitope repertoire available for T-cell-mediated therapeutic vaccine development. The HLA-B51-restricted peptide HBc19-27 is particularly interesting because it is located entirely within the HLA-A2-restricted HBc18-27 epitope. Here we show that HLA-B51-restricted cytotoxic T lymphocytes specific for HBc19-27 from a patient with acute HBV infection were also able to lyse HLA-B51-positive target cells pulsed with HBc18-27 and to produce gamma interferon when stimulated by that peptide, implying that HBc18-27 can be presented by HLA-B51 as well as by HLA-A2. These results demonstrate the concept of degenerate immunogenicity across HLA class supertype boundaries in a human viral disease setting. In addition, they could facilitate the development of an epitope-based therapeutic vaccine to terminate chronic HBV infection that could provide a broad and diverse population coverage with a single peptide.

Acute Disease↗
PubMed2001

Identification and antigenicity of broadly cross-reactive and conserved human immunodeficiency virus type 1-derived helper T-lymphocyte epitopes.

Human immunodeficiency virus (HIV)-specific helper T lymphocytes (HTL) play a key role in the immune control of HIV type 1 (HIV-1) infection, and as such are an important target of potential HIV-1 vaccines. In order to identify HTL epitopes in HIV-1 that might serve as vaccine targets, conserved HIV-1-derived peptides bearing an HLA-DR binding supermotif were tested for binding to a panel of the most representative HLA-DR molecules. Eleven highly cross-reactive binding peptides were identified: three in Gag and eight in Pol. Lymphoproliferative responses to this panel of peptides, as well as to the HIV-1 p24 and p66 proteins, were evaluated with a cohort of 31 HIV-1-infected patients. All 11 peptides were recognized by peripheral blood mononuclear cells from multiple HIV-infected donors. Many of the responsive HIV-infected subjects showed recognition of multiple peptides, indicating that HIV-1-specific T-helper responses may be broadly directed in certain individuals. A strong association existed between recognition of the parental recombinant HIV-1 protein and the corresponding HTL peptides, suggesting that these peptides represent epitopes that are processed and presented during the course of HIV-1 infection. Lastly, responses to the supermotif peptides were mediated by CD4(+) T cells and were restricted by major histocompatibility complex class II molecules. The epitopes described herein are potentially important components of HIV-1 therapeutic and prophylactic vaccines.

Amino Acid Sequence↗
PubMed2001

Role for HLA class II molecules in HIV-1 suppression and cellular immunity following antiretroviral treatment.

HIV-1-infected patients treated early with combination antiretrovirals respond favorably, but not all maintain viral suppression and improved HIV-specific Th function. To understand if genetic factors contribute to this variation, we prospectively evaluated over 18 months 21 early-treated patients stratified by alleles of class II haplotypes. All seven subjects with the DRB1*13-DQB1*06 haplotype, but only 21% of other subjects, maintained virus suppression at every posttreatment measurement. Following HIV-1 p24 antigen stimulation, PBMCs from patients with this haplotype demonstrated higher mean lymphoproliferation and IFN-gamma secretion than did cells from patients with other haplotypes. Two DRB1*13-restricted Gag epitope regions were identified, a promiscuous one that bound its putative restriction element with nanomolar affinity, and another that mapped to a highly conserved region. These findings suggest that class II molecules, particularly the DRB1*13 haplotype, have an important impact on virologic and immunologic responses. The advantage of the haplotype may relate to selection of key HIV-1 Th1 epitopes in highly conserved regions with avid binding to class II molecules. Eliciting responses to the promiscuous epitope region may be beneficial in vaccine strategies.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Human T-cell responses to HLA-A-restricted high binding affinity peptides of human papillomavirus type 18 proteins E6 and E7.

Human Papillomaviruses (HPVs) are sexually transmitted pathogens, which are implicated in the etiology of cervical cancer. The early proteins E6 and E7 of HPV have transforming capacity and interfere with the cell cycle control of infected host cells and are essential for the maintenance of the transformed state. Identification of MHC class I-restricted, immunogenic peptides derived from either the E6 or the E7 protein is essential for the design of vaccines as well as the monitoring of clinical trials and immunotherapeutic approaches for the treatment of HPV-18-induced carcinomas. We have determined the binding affinities for all possible 9-mer peptides spanning the entire E6 and E7 amino acid sequence for the HLA-A*0101, HLA-A*0201, HLA-A*0302, HLA-A*1102, and HLA-A*2402101 molecules by a competition assay with reference peptides, thereby establishing the binding peptides as potential cytotoxic T-cell epitopes. From the HLA-A*0201 binding peptides, we selected five E6-derived and one E7-derived peptide with high affinities for HLA-A*0201. These six peptides were tested for their immunogenicity by in vitro immunization assays with purified human CD8+ T cells. We identified three HPV-18 E6-derived peptides (ELTEVFEFA, KTVLELTEV, and KLPDLCTEL) and the E7-derived peptide TLQDIVLHL to be highly immunogenic. Overall, these results will help to design vaccines for the prevention or treatment of HPV-18-induced cervical cancer.

Amino Acids↗
PubMed2000

Definition of the Mamu A*01 peptide binding specificity: application to the identification of wild-type and optimized ligands from simian immunodeficiency virus regulatory proteins.

Single amino acid substitution analogs of the known Mamu A*01 binding peptide gag 181-190 and libraries of naturally occurring sequences of viral or bacterial origin were used to rigorously define the peptide binding motif associated with Mamu A*01 molecules. The presence of S or T in position 2, P in position 3, and hydrophobic or aromatic residues at the C terminus is associated with optimal binding capacity. At each of these positions, additional residues are also tolerated but associated with significant decreases in binding capacity. The presence of at least two preferred and one tolerated residues at the three anchor positions is necessary for good Mamu A*01 binding; optimal ligand size is 8-9 residues. This detailed motif has been used to map potential epitopes from SIVmac239 regulatory proteins and to engineer peptides with increased binding capacity. A total of 13 wild type and 17 analog candidate epitopes were identified. Furthermore, our analysis reveals a significantly lower than expected frequency of epitopes in early regulatory proteins, suggesting a possible evolutionary- and/or immunoselection directed against variants of viral products that contain CTL epitopes.

Algorithms↗
PubMed2000

Antimicrobial activity of MHC class I-restricted CD8+ T cells in human tuberculosis.

Studies of mouse models of tuberculosis (TB) infection have indicated a central role for MHC class I-restricted CD8+ T cells in protective immunity. To define antigens and epitopes of Mycobacterium tuberculosis (MTB) proteins that are presented by infected cells to CD8+ T cells, we screened 40 MTB proteins for HLA class I A*0201-binding motifs. Peptides that bound with high affinity to purified HLA molecules were subsequently analyzed for recognition by CD8+ cytotoxic T lymphocytes. We identified three epitopes recognized by CD8+ T cells from patients recovering from TB infection. Those three epitopes were derived from three different antigens: thymidylate synthase (ThyA(30-38)), RNA polymerase beta-subunit (RpoB(127-135)), and a putative phosphate transport system permease protein A-1 (PstA1(75-83)). In addition, CD8+ T cell lines specific for three peptides (ThyA(30-38), PstA1(75-83), and 85B(15-23)) were generated from peripheral blood mononuclear cells of normal HLA-A*0201 donors. These CD8+ T cell lines specifically recognized MTB-infected macrophages, as demonstrated by production of IFN-gamma and lysis of the infected target cells. Finally, CD8+ cytotoxic T lymphocytes reduced the viability of the intracellular MTB, providing evidence that CD8+ T cell recognition of MHC class I-restricted epitopes of these MTB antigens can contribute to effective immunity against the pathogen.

Animals↗
PubMed2000

Identification of HLA-A*03, A*11 and B*07-restricted melanoma-associated peptides that are immunogenic in vivo by vaccine-induced immune response (VIIR) analysis.

With the discovery of increasing numbers of tumor antigens, there is a need to rapidly determine whether these antigens and the individual peptides they express are able to stimulate immune responses in vivo and thus, can be used to construct cancer vaccines. In this study we used the method of vaccine-induced immune response (VIIR) analysis to identify multiple immunogenic peptide epitopes derived from several melanoma associated antigens and presented by HLA-A*03, A*11 and B*07. Thirty-one patients with melanoma were immunized to a polyvalent vaccine containing multiple antigens, including MAGE-3, Melan A/MART-1, gp100 and tyrosinase. Their peripheral blood was tested for peptide-specific, vaccine-induced CD8+ T cell responses before and after immunization using an enzyme-linked immune spot (ELISPOT) assay with panels of peptides restricted by these three alleles. The peptides were selected for immunogenic potential based on their strong binding affinity in vitro to HLA-A*03, A*11 or B*07. Overall, 60% of the 20 peptides studied were recognized by at least one patient and 50% of the patients showed a vaccine-induced CD8+ T cell response to at least one peptide that matched their HLA specificity. We conclude that VIIR analysis is an effective strategy to directly identify immunogenic peptides that are good candidates for vaccine construction.

Alleles↗