A helper T-cell antigen enhances generation of hepatitis C virus-specific cytotoxic T lymphocytes in vitro

A T-cell help for generation of hepatitis C virus-specific cytotoxic T lymphocytes was studied in three patients with chronic hepatitis C. In all three, human leukocyte antigen B44-restricted cytotoxic T lymphocytes recognizing an epitope in hepatitis C virus nucleocapsid protein residues 81–100 were generated from the peripheral blood lymphocytes by repeated stimulation with a synthetic hepatitis C virus nucleocapsid pep-tide. The proliferative response of peripheral blood lymphocytes to hepatitis C virus nucleocapsid protein residues 1–120 was observed in one patient, and was ascribed to CD4⁺ T cells. The helper T cells recognized a major epitope in residues 21–40 and a minor epitope(s) in residues 81–110. They produced interferon γ, but interleukin 4 was not detectable in the T-helper cell culture supernatants. The hepatitis C virus nucleocapsid protein residues 1–120 and the major helper T-cell epitope enhanced generation of hepatitis C virus-specific cytotoxic T lymphocytes in vitro, although the protein alone did not generate them. In the other two patients, the protein did not enhance generation of hepatitis C virus-specific cytotoxic T lymphocytes in vitro. The results suggest that a hepatitis C virus-specific helper T-cell epitope is helpful for inducing a strong specific cytotoxic T-lymphocyte response. © 1995 Wiley-Liss, Inc.     

Generation of virus-specific cytotoxic T cells in vitro. I. Induction conditions of primary and secondary Sendai virus-specific cytotoxic T cells.

H-2-restricted cytotoxic T cells specific for Sendai virus were generated in vitro in a primary response from normal mouse lymphocytes cultured in the presence of infective as well as inactivated Sendai virus. Antigen-presenting cells of different origin, including T cells, were found to be effective stimulators. Antibodies to Sendai virus were shown to inhibit the activation of specific precursor killer cells when added to cultures before, but not after, the addition of viral antigen. Data obtained by Lyt phenotyping, revealed that precursor killer cells specific for Sendai virus reside in the Lyt-2,3+ T cell population and that Lyt-1,2,3+ T cells are not required for the generation of cytotoxic lymphocytes. Different activation kinetics were demonstrated for primary and secondary antiviral cytotoxic responses, and the analysis of the proliferation and stimulation requirements suggests qualitative differences.     

In vivo efficacy of virus-derived peptides and virus-specific cytotoxic T lymphocytes.

The in vivo efficacy of virus- and tumor-specific cytotoxic T lymphocytes (CTL) is discussed as well as ways to activate these cells in vivo with lymphokines, monoclonal antibodies and immunization. In vivo and in vitro peptide immunization can induce such virus- and tumor-specific CTL but several questions have to be answered before peptide vaccination can be implemented as a novel immunotherapeutic or preventive approach in man.     

Control of primary and secondary antibody responses by cytotoxic T lymphocytes specific for a soluble antigen

BALB/c mice immunized with keyhole limpet hemocyanin (KLH) develop Thy-1+ and CD8+, KLH-specific cytotoxic T cells (Tc). Such Tc cells can lyse TNP-specific B cells activated with TNP-KLH, but not with TNP-ovalbumin. Cytotoxicity was inhibited by anti-H-2K/D antibodies, but not by anti-Ia antibodies, suggesting a major histocompatibility complex class I-restricted killing. Selective enrichment for virgin and memory TNP-specific B cells revealed that the latter cells were relatively resistant to lysis by KLH-specific Tc cells. Depletion of CD8+ T cells from cultures of TNP-specific virgin B cells activated with TNP-KLH and KLH-primed T cells, increased the titer of anti-TNP antibodies in the culture supernatants. This increase was reduced if KLH-primed CD8+ T cells were added to the culture 1 day before its termination. Anti-TNP antibody secretion by memory B cells activated in the same manner was not affected by depletion or addition of CD8+ cells. These results suggest that Tc cells are generated following immunization with a soluble antigen which may participate in the down-regulation of primary B cell responses.     

Proliferation and MHC-unrestricted bystander lysis by virus-specific cytotoxic T cells following antigen self-presentation

Cytotoxic T cells (CTL) not only act as effector cells, but can also serve as antigen-presenting cells (APC) for other CTL due to their expression of major histocompatibility complex (MHC) class I molecules. In the present study we show that independently derived CTL lines (CTLL) with specificity for an L^d-presented nonapeptide corresponding to amino acids 168–176 of the immediate-early 1 (IE1) protein of murine cytomegalovirus not only lyse syngeneic but also allogeneic target cells, if the peptide is present during the cytolytic assay. Whereas a short peptide pulse is sufficient to render syngeneic cells susceptible to lysis, continued presence of soluble peptide is mandatory for the lysis of allogeneic target cells. This indicates a difference in the mechanisms involved. Syngeneic BALB/c B cell blasts (K^dD^dL^d) and mutant BALB/ c-H-2^dm2 B cell blasts lacking the restricting L^d molecules (K^dD^d0) were lysed to a similar extent in the absence of the IE1 nonapeptide, provided that the IE1-specific CTL had been pre-incubated with the peptide before the cytolytic assay. Since the mutant cells cannot present the IE1 peptide, their lysis indicates an MHC-unrestricted, peptide-independent mode of recognition by the CTLL. In addition, proliferation of the CTLL takes place after incubation with the cognate peptide, even in the absence of professional APC. These data indicate inter-CTL antigen self-presentation, resulting in activation of the lytic machinery leading to peptide-independent bystander lysis of allogeneic as well as syngeneic target cells. Received: 13 February 1998     

The lysis of cytotoxic T lymphocytes and their blasts by cytotoxic T lymphocytes.

After binding to their targets, cytotoxic T lymphocytes (CTL) deliver a lethal hit signal, ultimately leading to target cell lysis, and then can recycle to lyse additional targets, without themselves being destroyed. If non-specific secreted lytic mediators are involved in such lysis. CTL survival would not be expected unless the effectors are immune to CTL-mediated lysis. Therefore the lytic susceptibilities of alloimmune peritoneal exudate lymphocytes (PEL), containing up to 50% CTL, and of the cytolytic PEL blasts (PEB), obtained by culturing with interleukin-2 (IL-2), were examined. 51Cr-labelled BALB/c (H-2d) anti-EL4 (H-2b) (d alpha b) PEL were lysed 88%, 78%, and 48% by C3H/eb (H-2k) anti-P815 (H-2d) (k alpha d) PEL, C57BL/6 (H-2b) anti-P815 (b alpha d) PEL and b alpha d PEB, respectively. Similarly, b alpha d PEL were lysed 82% and 21% by d alpha b PEL and PEB, respectively. b alpha d PEB were lysed 82%, 28-39% and 39-51% by k alpha d PEL, b alpha d PEL and b alpha d PEB, respectively, b alpha d PEB were lysed 29-55% by d alpha b PEL. Furthermore, the CTL-containing populations were no less susceptible to lysis than normal lymphocytes. Since the majority (80-90%) of cells in these two types of CTL-containing populations can be directly and specifically lysed by appropriately immunized PEL CTL, we conclude that both the lytic granule and perforin lacking (PEL) and containing (PEB) CTL are not a priori immune to CTL-mediated lysis. These findings are in accord with theories proposing lysis to be induced by receptor-mediated contact between effector CTL and target cells, and challenge those suggesting the involvement of secreted lytic mediators.     

Feline leukaemia virus: protective immunity is mediated by virus-specific cytotoxic T lymphocytes

Feline leukaemia virus (FeLV) nucleic acid vaccination of domestic cats affords protection against viraemia and the development of latency without inducing antiviral antibodies.1 To determine the contribution of cell-mediated immunity to the control of virus replication and clearance from the host, FeLV-specific cytotoxic T lymphocyte (CTL) responses were compared in vaccine-protected, transiently viraemic, and persistently viraemic cats. Vaccinal immunity was associated with the detection of higher levels of virus-specific effector CTL in the peripheral blood and lymphoid organs to FeLV Gag/Pro and Env antigens than those observed in unvaccinated control, persistently viraemic cats (P<0.001). Likewise, higher levels of virus-specific CTLs were also observed in transiently viraemic cats which recovered following exposure to FeLV. In cats that controlled their infection, recognition of Gag/Pro antigens was significantly higher than the recognition of Env antigens. This is the first report highlighting the very significant role that virus-specific CTL have in determining the outcome of FeLV infection in either vaccinated cats or cats recovering naturally from FeLV exposure.     

Suppression of the generation of secondary virus-specific proliferative and cytotoxic T lymphocytes by suppressor cells induced during primary anti-viral sensitization in vitro

Murine spleen cells first primed with syngeneic vaccinia virus-infected peritoneal exudate cells (PEC) in vitro and then restimulated with the virus failed to give a typical virus-specific secondary cytotoxic T lymphocyte (CTL) response. In contrast, "memory' spleen cells from mice primed with the virus in vivo produced CTL after the same challenge with virus-infected PEC in vitro. In the former situation, the lack of a virus-specific secondary CTL response by in vitro primed and restimulated spleen cells seemed to be associated with the generation of suppressor cells in cultures; these cells inhibited the cytotoxic as well as proliferative secondary and tertiary responses of spleen presensitized with virus in vitro alone, or in vivo plus in vitro. Weak suppressor activity was also induced in control spleen-cell cultures from normal unprimed or virus-primed mice that were not stimulated with virus-infected cells, suggesting either a quantitative difference in the generation of suppression or, alternatively, the co-existence of virus-dependent and independent suppressor cells in the virus-stimulated cultures. Our experiments cannot conclusively establish that suppression is T-cell mediated and/or possibly natural-killer-(NK)-cell dependent. The suppressor phenomena were exerted by irradiation resistant (850 rad) lymphocytes that passed through nylon wool columns and were sensitive to treatment with anti-Thy-1 antibody plus C; but the suppressor cells were partially reactive across allogeneic barriers.     

EB病毒潜伏膜蛋白2 DNA疫苗的构建及其初步免疫效果观察

目的：以EB病毒潜伏膜蛋白2（latent membrane protein 2,LMP2)为靶基因,构建EBV－LMP2的侯选DNA疫苗,并初步探讨其在小鼠体内诱导特异性细胞毒方面的作用,为研制鼻咽癌（nasopharyngeal carcinoma,NPC)等EB病毒相关肿瘤的治疗性疫苗提供有益资料。方法：将EB病毒LMP2全cDNA片段克隆至含CMV早期启动子的真核表达载体pCDNAⅢ,构建CMV启动子EB病毒LMP2DNA疫苗,在体外将重组质粒转染COS细胞,以RT－PCR和间接免疫荧光法检测重组质粒在转染的COS细胞中的转录和表达,采用50μg,100μg,200μg3种质粒剂量进行初步的小鼠后可诱发机体产生会对LMP2蛋白的特异性体液免疫和细胞免疫,50μg,100μg,200μg 3种免疫剂量产生的抗体水平差异不大。在免疫接种6周后,重组质粒免疫的小鼠产生针对LMP2的特异性CTL均明显高于空载体免疫小鼠,3种剂量的CTL结果显示：在100μg,200μg免疫组,小鼠诱导产生的CTL水平要略高于50μg免疫组。结论：EB病毒重组质粒LMP2免疫小鼠可以诱发小鼠产生特异的体液和细胞免疫应答,这些结果为研制鼻咽癌DNA疫苗提供有益的资料。     

Recognition of distinct epitopes on the HLA-A2 antigen by cytotoxic T lymphocytes

Alloimmune CTLs specifically recognizing the HLA-A2.3 subtype could be made besides the previously described HLA-A2.1 and A2.2 subtype-specific CTLs. Examination of the fine specificity of 15 different CTLs directed against distinct HLA-A2 subtypes demonstrated further complexity of antigenic epitopes present on the A2 molecule. First, epitopes could be defined which are unique for the HLA-A2.1, A2.2, A2.3, and A2.4 subtypes. Second, epitopes could be defined which are shared between the HLA-A2.1, A2.2 and A2.4 subtypes, but which are not shared by the A2.3 subtype. Analysis of the reactivity patterns of CTLs directed against the HLA-A2.2 and A2.4 subtypes indicated that the observed cytotoxic response was dependent on the HLA type of the responder cell. Biochemical analysis demonstrated the existence of isoelectric point variation in A2 heavy chains which deviated from the expected pIs for the A2 subtypes as described previously. Individuals were identified who possessed A2 heavy chains typical for the A2.3 subtype antigen although the CTL analysis demonstrated the presence of an A2.1 subtype antigen.     

Minor histocompatibility antigen-specific cytotoxic T lymphocytes generated with dendritic cells from DLA-identical littermates.

Donor cytotoxic T lymphocytes (CTL) specific for minor histocompatibility antigens (mHA) mediate the graft-versus-host effect whereas host mHA-specific CTL mediate graft rejection in the setting of major histocompatibility complex identical allogeneic hematopoietic stem cell transplantation. Development of a large animal model from which mHA-specific CTL can be isolated would accelerate translation in clinical studies to improve control of the graft-versus-host effect as well as prevention of graft rejection in sensitized hosts. The aims of the current study were to isolate mHA-specific CTL from dog leukocyte antigen-identical littermate nonsensitized recipients before transplantation, from stable mixed hematopoietic chimeras, and from dogs sensitized to mHA after graft rejection. Donor dendritic cells (DCs) were cultured from bone marrow-derived CD34(+) cells and were used to stimulate recipient T lymphocytes on days 1, 10, and 20 of CTL culture. We reliably generated and expanded mHA-specific CTL ex vivo from sensitized dogs that were given a donor-specific blood transfusion to boost immune recall after graft rejection after a nonmyeloablative transplantation. The mHA-specific cytotoxicity measured by (51)Cr release assay was enriched from less than 5% in the starting population of sensitized peripheral blood mononuclear cells to a median of 63% after 4 weeks in CTL culture. The expanded mHA-specific CTLs were not tissue-specific: hematopoietic cells, fibroblast, and stromal cell lines were lysed in an mHA-specific manner. Allogeneic DCs, but not peripheral blood mononuclear cells, were necessary for stimulating ex vivo expansion of mHA-specific CTL. We were unable to generate mHA-specific CTL from nonsensitized dogs before transplantation, from previously sensitized dogs but without recent recall immunization, or from stable mixed hematopoietic chimeras. We conclude that after recent in vivo sensitization, large-scale ex vivo expansion of mHA-specific CTL was feasible using allogeneic DCs.     

Activation of secondary cytotoxic lymphocytes by cell-free factors from I-region-primed and D-region-primed lymphocytes.

Cell co-operation in the generation of secondary cytotoxic responses was studied by selectively sensitizing lymphocytes in mixed lymphocyte culture (MLC) across I or D region difference and by combining the primed lymphocytes in the secondary MLC. Secondary cytotoxic responses were induced in D-region-primed lymphocytes by restimulation with the original priming D-region antigens, by co-culturing with the I-region-primed lymphocytes in the presence of the priming I-region antigens, or by cell-free supernatants obtained 24 h after the restimulation of D-region-primed lymphocytes and I-region-primed lymphocytes, The active MLC supernatants produced by both I-region-primed and D-region-primed cells also induced accelerated proliferative responses in D-region-primed lymphocytes. Heat-treatment or ultraviolet irradiation of the stimulator cells eliminated the capacity of the cells to induce the production of CTL-helper factor in I-region-primed and D-region-primed lymphocytes. It was concluded that both I-region-primed and D-region-primed lymphocytes produce a cell-free factor which induces proliferation and secondary cytotoxicity in D-region-primed lymphocytes. The possible participation of D-region reactive helper T cells and D-region reactive cytotoxic T cells in the cytotoxic responses to D-region antigens in the absence of I-region difference is discussed.     

The telomerase catalytic subunit is a widely expressed tumor-associated antigen recognized by cytotoxic T lymphocytes.

The discovery of tumor-associated antigens (TAA) in certain human malignancies has prompted renewed efforts to develop antigen-specific immunotherapy of cancer. However, most TAA described thus far are expressed in one or a few tumor types, and, among patients with these types of tumors, TAA expression is not universal. Here, we characterize the telomerase catalytic subunit (hTERT) as a widely expressed TAA capable of triggering antitumor cytotoxic T lymphocyte (CTL) responses. More than 85% of human cancers exhibit strong telomerase activity, but normal adult tissues, with few exceptions, do not. In a human system, CD8+ CTL specific for an hTERT peptide and restricted to MHC HLA-A2 lysed hTERT+ tumors from multiple histologies. These findings identify hTERT as a potentially important and widely applicable target for anticancer immunotherapeutic strategies.     

In vivo activation of melanoma-specific CD8(+) T cells by endogenous tumor antigen and peptide vaccines. A comparison to virus-specific T cells

Many new types of vaccines against infectious or malignant diseases are currently being proposed. Careful characterization of the induced immune response is required in assessing their efficiency. While in most studies human tumor antigen-specific T cells are analyzed after in vitro re-stimulation, we investigated these T cells directly ex vivo using fluorescent tetramers. In peripheral blood lymphocytes from untreated melanoma patients with advanced disease, a fraction of tumor antigen (Melan-A/MART-1)-specific T cells were non-naive, thus revealing tumor-driven immune activation. After immunotherapy with synthetic peptides plus adjuvant, we detected tumor antigen-specific T cells that proliferated and differentiated to memory cells in vivo in some melanoma patients. However, these cells did not present the features of effector cells as found in cytomegalovirus specific T cells analyzed in parallel. Thus, peptide plus adjuvant vaccines can lead to activation and expansion of antigen specific CD8(+) T cells in PBL. Differentiation to protective CD8(+) effector cells may, however, require additional vaccine components that stimulate T cells more efficiently, a major challenge for the development of future immunotherapy.     

Cultured T lymphocytes cytotoxic for a syngeneic lymphoma: derivation in Con A-conditioned medium and in vivo activity.

Cultures of murine T lymphocytes with cytotoxic activity towards syngeneic RBL-5 lymphoma cells were obtained from spleen cells of immunized animals after co-culture in vivo with irradiated RBL-5 cells. At different times after initiation, these mixed tumour-lymphocyte cultures (MTLC) were multiplied by transfer to conditioned medium (CM) containing T cell growth factor (TCGF) activity, produced by the stimulation of rat spleen cells with Con A. The effect of residual Con A was investigated by the addition of specific blocking sugar, alpha-methyl mannoside (alpha MM), to the CM in some experiments. This procedure did not reduce the growth potential of the cells, and resulted in a dramatic increase in the cytotoxic activity of the cultures as measured by a 4-hr 51Cr-release assay. The cultures multiplied 1 X 10(3)-fold over a 3-week period with retention of cytotoxicity for RBL-5 cells at levels up to 70-fold greater than those of the MTLCs from which they were derived. The cultured cells, when injected i.p. together with RBL-5 cells into normal mice, were shown to mediate a significant prolongation of the survival of the treated animals. This effect was, however, less dramatic than had been expected from the in vitro results. It would therefore appear that, while cells grown in tissue culture using Con A-conditioned medium may fulfill some theoretical requirements for the immunotherapy of experimental tumours, other factor(s) are required for full protection.     

Influenza virus-specific cytotoxic T cells in man; induction and properties of the cytotoxic cell.

Human peripheral blood lymphocytes have been sensitized in vitro to influenza virus antigen. After an induction period of 4--14 days, cytotoxic cells which lyse autologous influenza virus-infected lymphoid cells could be demonstrated. The cytotoxic cell is a T lymphocyte which shows specificity for sensitizing influenza virus type A or B. It cannot distinguish between major subtypes of influenza A virus. The use of virus-infected normal lymphoid cells as target cells overcame the difficulties of nonspecific killing encountered with some transformed cells.     

Bi-directional allelic recognition of the human minor histocompatibility antigen HB-1 by cytotoxic T lymphocytes

Human minor histocompatibility antigens (mHag) are target antigens of the graft-versus-leukemia response observed after allogeneic HLA-identical stem cell transplantation. We previously defined the molecular nature of the B cell lineage-specific mHag HB-1. The CTL epitope was identified as the decamer peptide EEKRGSLHVW presented in the context of HLA-B44. The HB-1 antigen is encoded by a locus of yet unknown function on chromosome 5q32. A single nucleotide polymorphism within this locus results in an amino acid change from histidine (H) to tyrosine (Y) at position P8 within the CTL epitope. Based on genomic information, we have developed a PCR-RFLP assay to perform HB-1 typing at the DNA level. We determined that the allelic frequency for the H and Y variant is 0.79 and 0.21, respectively. From these data, we calculated that the expected recipient disparity between HLA-B44-matched sibling pairs for HB-1H is 2.8%, whereas recipient disparity for HB-1Y is expected to be 12.4%. Therefore, we addressed whether the HB-1Y peptide is reciprocally immunogenic. We revealed that both peptide variants bind equally efficient to HLA-B44 molecules and that the H/Y substitution has no influence on formation of epitope precursor peptides by 20 S proteasome-mediated degradation. More directly, CTL recognizing the naturally presented HB-1Y peptide could be generated from a HB-1H homozygous donor using peptide-pulsed dendritic cells. Using a set of synthetic structurally related peptide variants, we found that the H/Y substitution has a major impact on TCR recognition by CTL specific for either of the HB-1 allelic homologues. HB-1 is the first human mHag described that induces bi-directional allogeneic CTL responses that may contribute to a specific graft-versus-leukemia response following allogeneic stem cell transplantation.     

Induction of Lyt-2+ cytotoxic T lymphocytes following primary and secondary Salmonella infection.

Investigations of the cytotoxic activity of T cells induced following one or two intraperitoneal doses of live Salmonella revealed that cytotoxicity was restricted to the Lyt-2+ T-cell subset and was enhanced following secondary infection with Salmonella. Initial studies using the lectin-dependent cellular cytotoxicity (LDCC) assay detected Lyt-2+ cytotoxic T cells in peritoneal cell suspensions of S. enteritidis 11RX (11RX)-infected mice, with the peak of activity occurring 5 days after infection. This did not correlate with the proliferative activity of these cells, which peaked 10-12 days after infection. Secondary challenge with 11RX or S. typhimurium C5 (C5) induced a rapid increase in the cytotoxic activity of Lyt-2+ peritoneal T cells and was detected even 21 days later. The antigen specificity of some of these cells was confirmed in cytotoxicity assays using P815 tumour cells infected with 11RX organisms as targets. No cytotoxic activity was detected in the spleen cell suspensions of infected (and normal) mice unless the cells were first activated by in vitro culture with concanavalin A (Con A). Both types of activated spleen cells showed LDCC but Salmonella-specific cytotoxic Lyt-2+ T cells were detected only in spleen cell (SC) cultures prepared from mice challenged with a second dose of Salmonella.     

Induction of cytotoxic T lymphocytes specific for paraneoplastic cerebellar degeneration-associated antigen in vivo by DNA immunization.

Paraneoplastic cerebellar degeneration associated with gynecological and breast malignancies (PCD) is known to develop autoantibodies and autoreactive cytotoxic T lymphocytes (CTLs) specific for a cytoplasmic protein of Purkinje cells PCD17/cdr2, in the blood of patients. The functional roles of these antibodies and CTLs in the pathogenesis of PCD are unknown. Induction of immune response to this antigen in experimental animals should be useful to clarify the immune mechanisms in PCD patients. We immunized Balb/c mice with naked DNA, which is encoded human PCD17 neural protein in an eukaryotic expression plasmid under control of CMV promoter, and explored whether or not humoral and cell-mediated immune responses against PCD17 could be induced in vivo. We show that DNA immunization with naked pcd17 cDNA could induce autoantibodies against the cytoplasmic protein of Purkinje cells and CTLs could lyse syngenic myeloma cells pulsed with H-2K-restricted PCD17 peptide. In spite of the generation of anti-Purkinje cell antibodies and PCD17-specific CTLs in vivo, neither clinical nor pathological changes consistent with significant cerebellar degeneration have been detected.