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PubMed2001

Accelerated HER-2 degradation enhances ovarian tumor recognition by CTL. Implications for tumor immunogenicity.

We investigated the ubiquitination and degradation of a tumor antigen, the HER-2/neu (HER-2) protooncogene product which is overexpressed in epithelial cancers. HER-2 degradation was investigated in the ovarian tumor line, SKOV3.A2, that constitutively overexpressed long-life HER-2. We used as agonist geldanamycin (GA), which initiated downmodulation of HER-2 from the cell surface. HER-2 was polyubiquitinated and degraded faster in the presence than in the absence of GA. GA did not decrease HLA-A2 expression. Presentation of the immunodominant cytotoxic T lymphocyte (CTL) epitope, E75 (369-377) from SKOV.A2 was inhibited by proteasome inhibitors, such as LLnL but was enhanced by cysteine protease inhibitors such as E64, indicating that both the proteasome and cysteine proteases are involved in epitope formation but have different effects. Enhanced tumor recognition was not an immediate or early effect of GA treatment, but was evident after 20 h of GA treatment. In contrast, 20 h GA treatment did not increase tumor sensitivity to LAK cell lysis. Twenty hour GA-treated SKOV3.A2 cells expressed an unstable HER-2 protein synthesized in the presence of GA, of faster electrophoretic mobility than control HER-2. This suggested that the newly synthesized HER-2 in the presence of GA was the main source of epitopes recognized by CTL. Twenty hour GA-treated SKOV3.A2 cells were better inducers of CTL activity directed to a number of HER-2 CTL epitopes, in peripheral blood mononuclear cells compared with control untreated SKOV3.A2 cells. Thus, induction of HER-2 protein instability enhanced the sensitivity of tumor for CTL lysis. Increased HER-2 CTL epitopes presentation may have implications for overcoming the poor immuno-genicity of human tumors, and design of epitope precursors for cancer vaccination.

Antigen Presentation↗
PubMed2003

Measurement of CTL-induced cytotoxicity: the caspase 3 assay.

Cytotoxic T lymphocytes (CTL) are critical effector cells of the immune system. Measurement of target cell damage has historically been an important measure of CTL function. CTL kill their target cells predominantly by inducing programmed cell death, or apoptosis. The gold standard for CTL-mediated cytotoxicity has been the (51)Cr release assay. However, measurement of target cell lysis by (51)Cr release does not provide mechanistic information on the fate of target cells, especially at the single cell level. Given the recent advances in our understanding of programmed cell death, newer assays are required which evaluate the status of the apoptotic pathways in target cells. We have developed a flow cytometry-based assay for CTL-mediated cytotoxicity based on specific binding of antibody to activated caspase 3 in target cells. Our assay is convenient and more sensitive than the (51)Cr release assay. The use of this assay should allow mechanistic studies of the intracellular events resulting from CTL attack.

Animals↗
PubMed1993

Tumour-specific CTL response requiring interactions of four different cell types and recognition of MHC class I and class II restricted tumour antigens.

This study demonstrates that a syngeneic specific cytotoxic T lymphocyte (CTL) response to a class I major histocompatibility complex (MHC) positive tumour requires dual processing and recognition of tumour antigens. One type of antigen is processed and expressed in association with class I MHC at the surface of intact tumour cells. It is recognized by CD8 alpha, beta TCR CTL in vitro and by protective immune T cells in vivo and thus functions as a tumour-associated transplantation antigen (TATA). The other type of antigen is processed and expressed by distinct host APC in association with class II MHC. This is recognized by immune CD4 T cells which function as essential helper cells in the generation of the CD8 CTL response. These conclusions are supported by cell depletion and reconstitution experiments as well as by blocking experiments with monoclonal antibodies using the highly metastatic class II negative murine lymphoma ESb as a model system. The existence of two types of cognate T cell responses in a syngeneic anti-tumour response was directly proved by the establishment of two types of tumour specific T cell lines which required as co-stimulator either MHC class II positive APC or IL-2. In suboptimal mixed lymphocyte tumour cell cultures either of these co-stimulator functions was found to be limiting the overall anti-tumour CTL response. The generation of the tumour specific CTL response could be blocked by monoclonal antibodies against all the molecules involved in the cognate interactions (i.e. class I MHC, CD8, class II MHC, CD4 and TCR) but not by anti-CD2 or anti-IgG. The strict requirement for helper cells and APC could be bypassed by the addition of recombinant IL-2 but optimal triggering of CD8 CTL-precursor required viable tumour stimulator cells. This well characterized in vitro assay may be useful (i) for monitoring the immune status of CD4 and CD8 immune T cells separately, for instance of tumour bearing and/or treated animals and (ii) for the development and testing of potent tumour cell vaccines with T cell stimulatory and/or co-stimulatory activities.

Animals↗
PubMed1996

Endogenous presentation of a nascent antigenic epitope to CD8+ CTL is more efficient than exogenous presentation.

Cytotoxic T lymphocytes (CTL) recognize short antigenic peptides in association with class I MHC molecules at the cell surface. Newly synthesized viral polypeptides are processed in the cytoplasm and the fragments of antigen are transported into the endoplasmic reticulum (ER) via a peptide transporter where they complex with nascent class I molecules. The peptide-MHC complex is transported to the cell surface and presented to CTL. Sequence analysis of endogenously expressed, MHC-associated self or viral antigens indicates that the naturally processed peptides bound to class I MHC molecules are in general 9 +/- 1 residues long. Peptides bound to specific class I MHC molecules have in common allele-specific motifs of conserved residues. The motif for the class I Kd molecules has been shown to be nine or 10 residues with the sequence X-Tyr-(X)6-I/L or X-Tyr-(X)7-I/L. The Tyr residue at the second position and the I/L residue at the ninth position are allele-specific anchor residues which appear to be required for binding of the peptide to Kd. To examine the stringency of the requirement for Tyr at the second position, we have performed saturation mutagenesis of a minigene encoding the class I Kd-restricted influenza HA210-219 site at the Tyr residue 211. A series of 10 mutants was tested for effects on target-cell sensitization. Most amino acid substitutions for the Tyr residue resulted in a loss of endogenous peptide recognition by HA210-219 reactive CTL, consistent with the critical role of the Tyr at the second position for interaction with Kd molecules. One mutant gene-product encoding a His substitution for the Tyr residue was recognized by CTL. However, the corresponding synthetic peptide containing a His substitution at the dominant anchor position bound only weakly to Kd, and target cells treated with the peptide were poorly recognized by CTL. The endogenous His-containing peptide was also less stably associated with class I MHC Kd molecules at the cell surface than the wild-type Tyr peptide. These data indicate that endogenous antigenic peptides may bind newly-synthesized class I MHC molecules in the ER more efficiently than fully formed class I molecules at the cell surface and that endogenous peptides may dissociate from class I MHC molecules at different rates. The implication of these findings for CTL recognition and epitope mapping are discussed.

Amino Acid Sequence↗
PubMed1997

Antiviral pressure exerted by HIV-1-specific cytotoxic T lymphocytes (CTLs) during primary infection demonstrated by rapid selection of CTL escape virus.

The HIV-1-specific cytotoxic T lymphocyte (CTL) response is temporally associated with the decline in viremia during primary HIV-1 infection, but definitive evidence that it is of importance in virus containment has been lacking. Here we show that in a patient whose early CTL response was focused on a highly immunodominant epitope in gp 160, there was rapid elimination of the transmitted virus strain and selection for a virus population bearing amino acid changes at a single residue within this epitope, which conferred escape from recognition by epitope-specific CTL. The magnitude (> 100-fold), kinetics (30-72 days from onset of symptoms) and genetic pathways of virus escape from CTL pressure were comparable to virus escape from antiretroviral therapy, indicating the biological significance of the CTL response in vivo. One aim of HIV-1 vaccines should thus be to elicit strong CTL responses against multiple codominant viral epitopes.

Acquired Immunodeficiency Syndrome↗
PubMed1997

IFN-gamma gene transfer restores HLA-class I expression and MAGE-3 antigen presentation to CTL in HLA-deficient small cell lung cancer.

In this study, we have analyzed the possibility of inducing T cell responses against small cell lung cancer (SCLC), a still incurable tumor, by cytokine gene transfer approaches. By RT-PCR analysis most SCLC expressed the CTL-defined tumor antigens MAGE-3 (10/11), MAGE-1 (7/11) and less frequently BAGE (4/11) and GAGE1,2 (4/11). Although the surface expression of HLA class I molecules was low on most SCLC, thus preventing CTL recognition, treatment of the cells with IFN-gamma enhanced HLA-class I levels in all cases. Two MAGE3+ SCLC cell lines displaying the A2 HLA-class I allele, involved in MAGE-3 antigen presentation to CTL, were stably transfected with the IFN-gamma gene (alone or co-transfected with IL-2). IFN-gamma-transfected cells displayed a clearcut increase in expression of HLA-class I and beta 2-microglobulin at both protein and mRNA level, and of TAP-1 and TAP-2 mRNA. Perhaps more importantly, IFN-gamma transfected cells were recognized by the MAGE-3-specific A2-restricted antimelanoma CTL clone 297/22, while unmodified cells or cells transfected with the IL-2 gene alone were not. These data indicate that IFN-gamma gene transfection into HLA-deficient SCLC cells is able to restore their ability to present endogenous tumor antigens to CTL and that IFN-gamma gene transfer approaches may be attempted to induce specific CTL responses in SCLC.

Antigen Presentation↗
PubMed1996

Peptide immunization in humans: a combined CD8+/CD4+ T cell-targeted vaccine restimulates the memory CD4 T cell response but fails to induce cytotoxic T lymphocytes (CTL).

Immunization with short antigenic peptides represents a potential strategy to induce peptide-specific CTL in vivo. In this study, a synthetic vaccine consisting of an HIV-derived, HLA-A2.1-binding CTL epitope and a tetanus toxin-derived T helper epitope was evaluated for its capacity to induce peptide-specific CTL in humans. Thirteen volunteers were immunized and boosted twice with 100 micrograms of the CTL epitope plus 300 micrograms of the T helper peptide (p30). Peripheral blood mononuclear cells (PBMC) were regularly analysed for cytotoxic and proliferative responses before, between and after the immunizations, and the serum was tested for anti-peptide antibodies. No unequivocal induction of HIV peptide-specific CTL in any of the volunteers was observed. However, a wide pattern of mild and transient side reactions was observed, ranging from local redness at the injection site to generalized exanthema, myalgias, arthralgias and fever. The side-effects were related to the T helper epitope, as they were similar to the side-effects experienced after tetanus immunization, correlated to the magnitude of the p30-specific in vitro proliferative response, and occurred only if p30 was co-injected. No antibodies against the HIV-derived peptides nor against p30 were detectable in the serum after repeated immunizations. The data suggest that the CTL peptide, at the concentration used in this study, failed to induce a cytotoxic immune response in vivo, although the T helper peptide seems to be capable of restimulating the specific memory T cells.

Animals↗
PubMed2004

Apoptotic pathways are selectively activated by granzyme A and/or granzyme B in CTL-mediated target cell lysis.

Purified cytolytic T lymphocyte (CTL) proteases granzyme (gzm)A and gzmB with sublytic dose of perforin (perf) initiate distinct proapoptotic pathways. Their physiological relevance in CTL-mediated target cell apoptosis is elusive. Using ex vivo virus-immune CD8(+) T cells from mice deficient in perf, gzmA and/or gzmB, and the Fas-resistant EL4.F15 tumor target cell, we show that (a) CTL from gzmA(-/-) or gzmB(-/-) mice similarly induced early proapoptotic features, such as phosphatidyl serine (PS) exposure on plasma membrane, Delta Psi(m) loss, and reactive oxygen radical generation, though with distinct kinetics; (b) CTL from gzmA(-/-) but not from gzmB(-/-) mice activate caspase 3 and 9; (c) PS exposure induced by CTL from gzmA(-/-) or gzmB(-/-) mice is prevented, respectively, by caspase inhibitors or by reactive oxygen scavengers without interfering with target cell death; and (d) all gzm-induced apoptotic features analyzed depend critically on perf. Thus, perf is the principal regulator in CTL-mediated and gzm-facilitated intracellular processes. The ability of gzmA and gzmB to induce multiple independent cell death pathways may be the hosts response to circumvent evasion strategies of pathogens and tumors.

Animals↗
PubMed1997

Evasion of cytotoxic T lymphocyte (CTL) responses by nef-dependent induction of Fas ligand (CD95L) expression on simian immunodeficiency virus-infected cells.

Inoculation of macaques with live attenuated SIV strains has been shown to protect against subsequent challenge with wild-type SIV. The protective mechanism(s) remain obscure. To study the effect in more detail, we have investigated the role of virus-specific CTL responses in macaques infected with an attenuated SIV strain (pC8), which has a four-amino acid deletion in the nef gene, as compared with the wild-type SIVmac32H clone (pJ5). Cynomolgus macaques infected with pC8 were protected against subsequent challenge with pJ5 and did not develop any AIDS-like symptoms in the 12 months after infection. The pC8-induced protection was associated with high levels of virus-specific CTL responses to a variety of viral antigens. In contrast, pJ5-infected macaques had little, if any, detectable CTL response to the viral proteins after three months. The latter group of macaques also showed increased Fas expression and apoptotic cell death in both the CD4(+) and CD8(+) populations. In vitro, pJ5 but not pC8 leads to an increase in FasL expression on infected cells. Thus the expression of FasL may protect infected cells from CTL attack, killing viral-specific CTLs in the process, and providing a route for escaping the immune response, leading to the increased pathogenicity of pJ5. pC8, on the other hand does not induce FasL expression, allowing the development of a protective CTL response. Furthermore, interruption of the Fas-FasL interaction allows the regeneration of viral-specific CTL responses in pJ5-infected animals. This observation suggests an additional therapeutic approach to the treatment of AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed2001

In vitro HIV-specific CTL activity from HIV-seropositive individuals is augmented by interleukin-12 (IL-12).

IL-12 production is reduced in HIV infection, and recombinant human IL-12 (rhIL-12) augments in vitro HIV-specific proliferative responses in PBMC from HIV-seropositive individuals. To determine whether rhIL12 could also augment HIV-specific CTL responses we studied 41 HIV-seropositive individuals. Recombinant hIL-12 increased the detectable in vitro HIV-specific CD8 CTL activity of PBMC taken from HIV-seropositive individuals with CD4 counts >500 cells/microl and from some individuals with lower CD4 counts. IL-12 increased cell recovery in cultures of PBMC from HIV-seropositive individuals with CD4 counts >500 cells/microl and also increased the precursor CTL frequency. However, the increase in HIV-specific CTL activity was not due to IL-2 or IFN-gamma production or an increase in the number of cells with surface markers characteristic of CTL effector cells. This study demonstrates that rhIL-12 augments in vitro HIV-specific CTL activity and provides evidence to justify further investigation within clinical trials of this cytokine in HIV infection.

Adult↗
PubMed2002

Cytotoxic T-lymphocyte (CTL) responses directed against regulatory and accessory proteins in HIV-1 infection.

The HIV-1 regulatory proteins Tat and Rev and the accessory proteins Vpr, Vpu, and Vif are essential for viral replication, and their cytoplasmic production suggests that they should be processed for recognition by cytotoxic T lymphocytes. However, only limited data is available evaluating to which extent these proteins are targeted in natural infection and optimal cytotoxic T lymphocyte (CTL) epitopes within these proteins have not been defined. In this study, CTL responses against HIV-1 Tat, Rev, Vpr, Vpu, and Vif were analyzed in 70 HIV-1 infected individuals and 10 HIV-1 negative controls using overlapping peptides spanning the entire proteins. Peptide-specific interferon-gamma (IFN-gamma) production was measured by Elispot assay and flow-based intracellular cytokine quantification. HLA class I restriction and cytotoxic activity were confirmed after isolation of peptide-specific CD8+ T-cell lines. All regulatory and accessory proteins served as targets for HIV-1- specific CTL and multiple CTL epitopes were identified in functionally important regions of these proteins. In certain individuals HIV-1-specific CD8+ T-cell responses to these accessory and regulatory proteins contributed up to a third to the magnitude of the total HIV-1-specific CTL response. These data indicate that despite the small size of these proteins regulatory and accessory proteins are targeted by CTL in natural HIV-1 infection, and contribute importantly to the total HIV-1-specific CD8+ T-cell responses. These findings are relevant for the evaluation of the specificity and breadth of immune responses during acute and chronic#10; infection, and will be useful for the design and testing of candidate human immunodeficiency virus (HIV) vaccines.

CD8-Positive T-Lymphocytes↗
PubMed1992

Decline in CTL and antibody responses to HIV-1 p17 and p24 antigens in HIV-1-infected hemophiliacs irrespective of disease progression. A 5-year follow-up study.

CTL and antibody responses to HIV-1 p17 and p24 antigens were monitored from 1986-1991, in 4 hemophiliacs. The patients had been infected with HIV-1 between 1980 and 1984. Two patients have remained asymptomatic while two progressed to AIDS in 1990. CTL were boosted by culturing with peptides from p17 aa 86-115, or p24 aa 265-279; and aa 270-373 or PHA. Lysis was measured on autologous or allogeneic targets pulsed with peptides or infected with recombinant vaccinia virus carrying HIV-1 gag or influenza A matrix genes. Antibodies to p17 and p24 were tested by ELISA using peptides and by Western blotting. High levels of CTL activity to p17 and p24 antigens could be generated only with lymphocytes from the two asymptomatic patients between 1986 and 1989, but these responses were absent in 1990 and 1991. Antibodies to p17 peptides disappeared in parallel with CTL activity. Antibodies to some p24 peptides also declined but most patients retained activity to others. In all patients a > or = 3-fold increase in CD8+ cell numbers occurred over time and accompanied the decline of CTL and antibody responses. The loss of CTL and p17 antibodies occurred irrespective of whether patients remained asymptomatic or progressed to AIDS in the intervening two years.

Cell Line, Transformed↗
PubMed1998

Conservation of cytotoxic T lymphocyte (CTL) epitopes as a host strategy to constrain parasite adaptation: evidence from the nef gene of human immunodeficiency virus 1 (HIV-1).

Host cytotoxic T lymphocytes (CTLs) that recognize specific viral peptides (epitopes) are thought to provide the most effective control of viral replication and spread. However, viruses may escape this recognition through mutations in CTL epitopes. We tested the hypothesis that, as an adaptation on the part of the host to constrain parasite escape from immune control, class I major histocompatibility complex (MHC) molecules present peptides that are derived from conserved regions of foreign proteins to CTLs. We did this by estimating the relative conservation of CTL epitopes of the functionally important Nef protein of human immunodeficiency virus 1 (HIV-1) and relating this to the structure and function of the protein. In comparisons among sequences from several HIV-1 subtypes and both major groups, CTL epitopes had lower rates of nonsynonymous nucleotide substitution per site than did the remainder of the protein, indicating the relative conservation of these epitopes. In contrast, helper T-cell epitopes were as conserved as, and monoclonal antibody epitopes less conserved than, the remainder of the protein. The conservation of CTL epitopes is apparently due to their derivation from functionally important domains of Nef, since CTL epitopes coincide with these domains and these domains are conserved relative to the remainder of the protein, in contrast to secondary structural elements, which are not. Recent studies provide evidence of CTL selection on HIV-1 epitopes, but the variational range of viral escape mutants appears to be limited by functional constraints on the protein regions from which epitopes are derived. The presentation of conserved foreign peptides to CTLs by class I MHC molecules may be a general adaptation of vertebrate hosts to constrain the adaptation of their intracellular parasites.

Adaptation, Physiological↗
PubMed1997

Transfection of IL-2 augments CTL response to human melanoma cells in vitro: immunological characterization of a melanoma vaccine.

We have transfected human melanoma cell line 518A2 with the cDNA encoding interleukin-2 (IL-2) or granulocyte-macrophage colony-stimulating factor (GM-CSF), and compared cytokine-producing clones for their ability to induce melanoma-specific cytotoxic T lymphocytes (CTL) from autologous peripheral blood mononuclear cells (PBMC) in vitro. The parental cell line expressed HLA-A1, HLA-A2, ICAM-1, LFA-3, in addition to the common CTL antigens MAGE-1, MAGE-3, tyrosinase, gp100, and Melan-A/MART-1. Stimulation of autologous PBMC responders with the IL-2-transfected clone 518/IL2.14 specifically induced CTL lines reactive with all cell lines derived from the autologous patient. Strikingly, GM-CSF-transfected 518A2 cells did not induce anti-tumor CTL reactivity. CTL induction against 518/IL2.14 was independent of HLA class II expression or CD4 help. The parental cell line 518A2 gained immunogenic properties when high concentrations of IL-2 were supplied exogenously, indicating that IL-2 produced and present at high levels locally by itself enhanced immunogenicity. From the autologous CTL line reactive with 518/IL2.14, clones were generated against an as yet unknown antigen, which was present in all autologous melanoma cell lines as well as in 7 of 15 HLA-A2+ melanoma cell lines tested, but not in melanocytes. These results will be discussed with respect to the possibility of using IL-2-transfected melanoma cells as a vaccine for treatment of patients with melanoma.

Cancer Vaccines↗
PubMed1990

Discrimination of HLA-B5 crossreactive group antigens by human allospecific CTL clones.

Human CTL clones discriminating serologically closely related HLA-Bw52, B51, and B35, which belong to HLA-B5 crossreacting group (CREG), were established from peripheral blood lymphocytes by repeated in vitro stimulations. Five HLA-Bw52-specific CTL clones from an individual with HLA-B5 CREG antigens and four CTL clones from another individual with HLA-B51 were generated. The specificity of these CTL clones was ascertained by their lysis of EBV-transformed B cells with HLA-Bw52, but not those with HLA-B51 or B35, and Bw52-transfected Hmy2CIR cells but not HLA-B51 or B35 transfectants. Conversely HLA-B51-specific clones were generated from the HLA-B5 CREG-negative individual, as well as another individual with HLA-Bw52. Their specificity was determined in a similar fashion. Since HLA-B51 differed from HLA-Bw52 only by two amino acid substitutions on the alpha helical region of the alpha 1 domain, these results demonstrated that allospecific CTLs can be produced and discriminate the epitopes formed by the subtle difference in the structure of these HLA class I molecules. Furthermore, three HLA-B35-specific CTL clones were generated from the HLA-B5 CREG-negative individual that discriminated HLA-B35 from HLA-Bw52 and B51. Taken together these results demonstrated that human CTL clones could definitively discriminate the three serologically related HLA-B5 CREG specificities.

Clone Cells↗
PubMed1999

Replication-deficient recombinant adenoviruses expressing the human immunodeficiency virus Env antigen can induce both humoral and CTL immune responses in mice.

An effective vaccine against infection with human immunodeficiency virus type 1 (HIV-1) is thought likely to require both a humoral and a CTL immune response. A non-replicating adenovirus vector system has been developed that can induce both a humoral and CTL response to HIV-1 envelope in mice. It is demonstrated that the stimulatory tat/rev 5' splice-donor site sequence is required for efficient expression of HIV-1 env by this adenovirus vector system. rev can be provided bicistronically or in trans to result in good expression of env in vitro. A humoral immune response was detected after two immunizations with a bicistronic recombinant adenovirus (RAd142). The response was dose dependent, 5x10(7) p.f.u. inducing a response in some, but not all, animals and 1x10(8) p.f.u. giving a consistent antibody response. However, CTLs were induced by the lower dose of virus and after only one immunization with the higher dose. A positive CTL response was also seen consistently when the two monocistronic adenoviruses (RAd501 expressing env and RAd46 expressing rev) were given together, although two immunizations were required to give approximately the same level of response as seen with the bicistronic virus. RAd501 on its own also gave a low CTL response when two immunizations were given. It is suggested that a lower level of env expression is required to produce a CTL response than a humoral response and that this nonreplicating adenovirus vector is a good system for inducing CTL.

AIDS Vaccines↗
PubMed2003

Optimization and immune recognition of multiple novel conserved HLA-A2, human immunodeficiency virus type 1-specific CTL epitopes.

MHC-I-restricted cytotoxic responses are considered a critical component of protective immunity against viruses, including human immunodeficiency virus type 1 (HIV-1). CTLs directed against accessory and early regulatory HIV-1 proteins might be particularly effective; however, CTL epitopes in these proteins are rarely found. Novel artificial neural networks (ANNs) were used to quantitatively predict HLA-A2-binding CTL epitope peptides from publicly available full-length HIV-1 protein sequences. Epitopes were selected based on their novelty, predicted HLA-A2-binding affinity and conservation among HIV-1 strains. HLA-A2 binding was validated experimentally and binders were tested for their ability to induce CTL and IFN-gamma responses. About 69 % were immunogenic in HLA-A2 transgenic mice and 61 % were recognized by CD8(+) T-cells from 17 HLA-A2 HIV-1-positive patients. Thus, 31 novel conserved CTL epitopes were identified in eight HIV-1 proteins, including the first HLA-A2 minimal epitopes ever reported in the accessory and regulatory proteins Vif, Vpu and Rev. Interestingly, intermediate-binding peptides of low or no immunogenicity (i.e. subdominant epitopes) were found to be antigenic and more conserved. Such epitope peptides were anchor-optimized to improve immunogenicity and further increase the number of potential vaccine epitopes. About 67 % of anchor-optimized vaccine epitopes induced immune responses against the corresponding non-immunogenic naturally occurring epitopes. This study demonstrates the potency of ANNs for identifying putative virus CTL epitopes, and the new HIV-1 CTL epitopes identified should have significant implications for HIV-1 vaccine development. As a novel vaccine approach, it is proposed to increase the coverage of HIV variants by including multiple anchor-optimized variants of the more conserved subdominant epitopes.

Adult↗
PubMed2001

Role of furin in delivery of a CTL epitope of an anthrax toxin-fusion protein.

Anthrax toxin lethal factor (LF) in combination with anthrax toxin protective antigen (PA) was endocytosed and translocated to the cytosol of mammalian cells. Residues 1-255 of anthrax toxin lethal factor (LFn) was fused to a cytotoxic T lymphocyte (CTL) epitope of an influenza virus. For processing the toxins, PA must be cleaved into a 63-kDa fragment (PA63) by furin, which is a subtilisin-like processing endo-protease expressed by many eukaryotic cells. To test the ability of cells treated with the LFn fusion protein plus PA to deliver the epitope, CTL assay was performed. Two types of cell lines were identified, one was able to deliver CTL epitope while the other failed to efficiently deliver the epitope. To further elucidate the differences between these cells, the role of furin in these cells was examined. Disruption of the furin gene reduced its ability to deliver the CTL epitope. Furin expression in cells capable of efficiently delivering CTL epitope was quantitatively higher than in cells unable to deliver the epitope. The results suggest that furin plays a critical role in delivery of the CTL epitope of LFn fusion protein.

Animals↗