Molecular analyses of a five-amino-acid cytotoxic T-lymphocyte (CTL) epitope: an immunodominant region which induces nonreciprocal CTL cross-reactivity

Vaccination or tolerance to prevent diabetes

Experiments with transgenic mice expressing the glycoprotein (GP) of lymphocytic choriomeningitis virus (LCMV) under the control of the rat insulin promoter (RIP) have demonstrated that potentially self-reactive T cells that normally ignore self peptides may nevertheless be induced by self peptides or "cross-reactive" foreign (e.g. viral) peptides that arise in the host in an immunogenic form; once activated these potentially self-reactive T cells may cause autoaggressive diseases (e.g. diabetes). The possibility of vaccinating against such T cell-mediated immunopathological diseases was evaluated in the RIP-GP transgenic mouse line Bln. Any attempt to vaccinate with the self antigen itself (e.g. recombinant vaccinia virus expressing LCMV-GP) failed to protect mice from disease. However, immunization with a recombinant vaccinia virus expressing LCMV-nucleoprotein (vacc-NP) as a non-GP LCMV vaccine was able to modulate the immune response and prevented autoaggressive disease in a MHC-dependent fashion. In contrast, tolerance induction neonatally or, more generally applicable, by lethal irradiation and reconstitution with neo-self antigen-expressing bone marrow cells always resulted in prevention of virally induced diabetes in this model situation.

Design of high-affinity major histocompatibility complex-specific antagonist peptides that inhibit cytotoxic T-lymphocyte activity: implications for control of viral disease

Cytotoxic T lymphocytes (CTLs) recognize viral antigens presented by infected cells in the context of their major histocompatibility complex glycoproteins. The irreversible killing of virus-infected cells by virus-specific CTLs can be the cause of serious disease, particularly in the central nervous, hepatic, and cardiovascular systems. Design of molecules controlling (blocking) interaction between CTLs and infected cells, and their further use to inhibit (or antagonize) T-lymphocyte activity, is an important pharmacologic goal. In this report, we describe the design of a new family of peptides which selectively inhibit activity of lymphocytic choriomeningitis virus-specific CD8+ T lymphocytes, which recognize endogenously processed viral epitopes presented by major histocompatibility complex class I molecules.

Novel LCMV-specific H-2k restricted CTL clones recognize internal viral gene products and cause CNS disease

H-2k (C3H/Hej) cytotoxic T lymphocytes (CTL) specific for lymphocytic choriomeningitis virus (LCMV) were cloned. Three clones recognizing internal viral antigens were studied. One such CTL clone recognized neither the glycoprotein nor nucleoprotein encoded by the viral short RNA segment, but reacted with a protein encoded by the long RNA segment, either the viral polymerase, or the Z protein. This one clone, in addition to primary CTL harvested from immunized C3H mice, failed to lyse target cells expressing the Z protein, suggesting recognition was to the viral polymerase. Two other clones recognized the viral nucleoprotein, amino acids 93-100, as determined by protein deletion and peptide mapping studies. When introduced directly into the central nervous systems of LCMV-infected histocompatible mice, all clones were active in vivo and capable of causing immunopathologically mediated death.

T-cell epitopes on the human acetylcholine receptor alpha-subunit residues 10-84 in myasthenia gravis

In myasthenia gravis the production of anti-acetylcholine receptor antibodies is modulated by acetylcholine receptor-specific T cells. Most B- and T-cell epitopes are located on the alpha-subunit of the receptor. In order to map the fine specificity of the antigen-specific T cells in myasthenia gravis, T-cell stimulation in response to 70 hexapeptides was studied in 24 patients and 24 healthy individuals. The hexapeptides overlapped with one amino acid and represented residues 10-84 of the NH2-terminal part of the alpha-subunit of the receptor. The IFN-gamma secretion from single T cells was used to detect T-cell stimulation. A significant difference in the T-cell response to several of the peptides was found between patients and healthy controls. The majority of the hexapeptides induced T-cell stimulation in at least one of the patients. Peptide-induced T-cell stimulation was evident in all but one of the patients. The results indicate that different epitopes and multiple T-cell clones are involved in the T-cell recognition of the acetylcholine receptor.

A common antiviral cytotoxic T-lymphocyte epitope for diverse major histocompatibility complex haplotypes: implications for vaccination

Of nine established murine haplotypes, mice of three types (H-2d, H-2u, and H-2q) possess major histocompatibility complex class I glycoproteins able to present an identical viral peptide for recognition and lysis by virus-specific cytotoxic T lymphocytes. Incorporation of this viral epitope into a recombinant vaccinia vaccine and administration of a single dose protects mice with these three haplotypes from an ordinarily lethal challenge of virus. Hence, a common epitope can exist. The sharing of the ability to bind such epitopes among different MHC haplotypes underscores the feasibility of developing an effective cytotoxic T-lymphocyte vaccine for outbred populations like humans.

Diversity of T-cell receptors in virus-specific cytotoxic T lymphocytes recognizing three distinct viral epitopes restricted by a single major histocompatibility complex molecule

Cytotoxic T lymphocytes (CTL) recognize virus peptide fragments complexed with class I major histocompatibility complex (MHC) molecules on the surface of virus-infected cells. Recognition is mediated by a membrane-bound T-cell receptor (TCR) composed of alpha and beta chains. Studies of the CTL response to lymphocytic choriomeningitis virus (LCMV) in H-2b mice have revealed that three distinct viral epitopes are recognized by CTL of the H-2b haplotype and that all of the three epitopes are restricted by the Db MHC molecule. The immunodominant Db-restricted CTL epitope, located at LCMV glycoprotein amino acids 278 to 286, was earlier noted to be recognized by TCRs that consistently contained V alpha 4 segments but had heterogeneous V beta segments. Here we show that CTL clones recognizing the other two H-2Db-restricted epitopes, LCMV glycoprotein amino acids 34 to 40 and nucleoprotein amino acids 397 to 407 (defined in this study), utilize TCR alpha chains which do not belong to the V alpha 4 subfamily. Hence, usage of V alpha and V beta in the TCRs recognizing peptide fragments from one virus restricted by a single MHC molecule is not sufficiently homogeneous to allow manipulation of the anti-viral CTL response at the level of TCRs. The diversity of anti-viral CTL likely provides the host with a wider option for attacking virus-infected cells and prevents the emergence of virus escape mutants that might arise if TCRs specific for the virus were homogeneous.

Comoviruses and enteroviruses share a T cell epitope

An in vitro murine T cell proliferation assay was used to determine whether an antigenic epitope(s) recognized by enterovirus-immune T cells is held in common between plant comoviruses and human enteroviruses. Splenocytes isolated from C3H/HeJ mice infected with coxsackievirus B3 (CVB3) proliferated in vitro not only against a variety of enterovirus (CVB2, CVB3, CVB6, CVA16, PV1) antigens, but against comovirus (CPMV, BPMV) antigens as well. Splenocytes from mice inoculated with bean pod mottle virus (BPMV) also proliferated in response to comoviral and enteroviral antigens in vitro. However, if the viral inocula were highly purified prior to inoculation, then the splenocyte response was generated only against the group used to inoculate, suggesting that the epitope shared between the comoviruses and the enteroviruses resided in the nonstructural region. B (nonstructural) and M (structural) genomic segments of CPMV were translated in rabbit reticulocyte lysates and used as in vitro antigens. Splenocytes from mice inoculated with live CVB3 proliferated in response to the B-RNA-encoded but not the M-RNA-encoded polypeptides, confirming the nonstructural coding region location of the common epitope. Comparison of predicted amino acid sequences in the nonstructural coding regions of the comoviruses and picornaviruses suggested a potentially immunogenic linear epitope in protein 2C. The consensus peptide LEEKGI was synthezized and shown to be immunogenic for both BPMV- and CVB3-immune splenocytes.

Molecular anatomy of viral persistence

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Viral persistence in neurons explained by lack of major histocompatibility class I expression

Viruses frequently persist in neurons, suggesting that these cells can evade immune surveillance. In a mouse model, 5 x 10(6) cytotoxic T lymphocytes (CTLs), specific for lymphocytic choriomeningitis virus (LCMV), did not lyse infected neurons or cause immunopathologic injury. In contrast, intracerebral injection of less than 10(3) CTL caused disease and death when viral antigens were expressed on leptomeningeal and choroid plexus cells of the nervous system. The neuronal cell line OBL21 expresses little or no major histocompatibility (MHC) class I surface glycoproteins and when infected with LCMV, resisted lysis by virus-specific CTLs. Expression of MHC heavy chain messenger RNA was limited, but beta 2-microglobulin messenger RNA and protein was made normally. OBL21 cells were made sensitive to CTL lysis by transfection with a fusion gene encoding another MHC class I molecule. Hence, neuronal cells probably evade immune surveillance by failing to express MHC class I molecules.

Infection of lymphocytes by a virus that aborts cytotoxic T lymphocyte activity and establishes persistent infection

For viruses to establish persistent infections in their hosts, they must possess some mechanism for evading clearance by the immune system. When inoculated into adult immunocompetent mice, wild-type lymphocytic choriomeningitis virus (LCMV ARM) induces a CD8(+)-mediated cytotoxic T lymphocyte (CTL) response that clears the infection within 7-14 d (CTL+ [P-]). By contrast, variant viruses isolated from lymphoid tissues of persistently infected mice fail to induce a CTL response and are thus able to establish a persistent infection in adult mice (CTL- [P+]). This report compares the interaction of CTL+ (P-) and CTL- (P+) viruses with cells of the immune system. Both types of virus initially bind to 2-4% of CD4+ and CD8+ T lymphocytes and replicate within cells of both subsets. The replication of CTL- (P+) and CTL+ (P-) viruses in lymphocytes in vivo is similar for the first 5 d after initiating infection. Thereafter, in mice infected with CTL- (P+) variants, lymphocytes retain viral genetic information, and infectious virus can be recovered throughout the animals' lives. In contrast, when adult mice are infected with wild-type CTL+ (P-) LCMV ARM, virus is not recovered from lymphocytes for greater than 7 d after infection. A CD8(+)-mediated anti-LCMV CTL response is induced in such mice. Clearance of infected lymphocytes is produced by these LCMV-specific CTLs, as shown by their ability to lyse lymphocytes expressing LCMV determinants in vitro and the fact that depletion of CD8+ lymphocytes before infection with CTL+ (P-) viruses results in levels of infected lymphocytes similar to those found in undepleted CTL- (P+)-infected mice. Hence, CTL-mediated lysis of T lymphocytes carrying infectious virus is a critical factor determining whether virus persists or the infection is terminated.

Major histocompatibility complex binding and T cell recognition of a viral nonapeptide containing a minimal tetrapeptide

The primary immune response of cytotoxic T lymphocytes in H-2d and H-2q mice to infection with lymphocytic choriomeningitis virus is directed mostly towards the common major T cell epitope of amino acids 112-132 on the viral nucleoprotein (NP). The molecules responsible for presentation of the T cell epitope NP112-132 are in both haplotypes the MHC class I L antigens (Ld, Lq). Truncations of the amino and carboxy termini of the NP 112-132 sequence revealed the nonapeptide RPQASGVYM (NP118-126) as a most effective peptide antigen, but even the tetrapeptide GVYM was recognized by CTL of both haplotypes in a class I antigen-restricted specificity. When tyrosine (Y) or methionine (M) were substituted with alanine, CTL recognition of the altered nonamer required 10(6) to 10(8) times higher peptide concentrations and in one case (Y----A on Ld) the peptide was not recognized at all. Up-modulation of the expression of Ld and Lq class I antigens as measured by flow cytometry correlated with the ability to present the peptide antigens. The only exception was peptide NP118-126 (M----A), which was recognized by T cells on L-Ld and L-Lq target cells but failed to up-regulate Ld and Lq antigens.

Virus infection triggers insulin-dependent diabetes mellitus in a transgenic model: role of anti-self (virus) immune response

We investigated the potential association between viruses and insulin-dependent (type 1) diabetes (IDDM) by developing a transgenic mouse model. By inserting into these mice a unique viral protein that was then expressed as a self-antigen in the pancreatic islets of Langerhans, we could study the effect on that expressed antigen alone, or in concert with an induced antiviral (i.e., autoimmune) response manifested later in life in causing IDDM. Our results indicate that a viral gene introduced as early as an animal's egg stage, incorporated into the germline, and expressed in islet cells does not produce tolerance when the host is exposed to the same virus later in life. We observed that the induced anti-self (viral) CTL response leads to selective and progressive damage of beta cells, resulting in IDDM.

Identification of an immunodominant cytotoxic T-lymphocyte recognition site in glycoprotein B of herpes simplex virus by using recombinant adenovirus vectors and synthetic peptides

Cytotoxic T-lymphocyte (CTL) responses to herpes simplex virus (HSV) polypeptides play an important role in recovery from infection and in preventing latency. We have previously shown that glycoprotein B (gB) is a major target recognized by HSV-specific CTLs in C57BL/6 (H-2b) and BALB/c (H-2d) mice but not in CBA/J (H-2k) mice (L. A. Witmer, K. L. Rosenthal, F. L. Graham, H. M. Friedman, A. Yee, and D. C. Johnson, J. Gen. Virol. 71:387-396, 1990). In this report, we utilize adenovirus vectors expressing gB with various deletions to localize an immunodominant site in gB, recognized by H-2b-restricted anti-HSV CTLs, to a region between residues 462 and 594. Overlapping peptides spanning this region were synthesized and used to further localize the immunodominant site to residues 489 to 515, a region highly conserved in HSV type 1 (HSV-1) and HSV-2 strains. The 11-amino-acid peptide was apparently associated exclusively with the Kb major histocompatibility complex gene product and not the Db gene product. In contrast, H-2d-restricted CTLs recognized an immunodominant site between residues 233 and 379.

Sequence analysis of the S RNA of the African arenavirus Mopeia: an unusual secondary structure feature in the intergenic region

Mopeia virus is an apparently nonpathogenic African arenavirus which can protect animals from subsequent challenge by the closely related Lassa virus. As a step toward understanding these differences in pathogenicity and the means by which Mopeia virus infection can protect against subsequent Lassa virus infection, cDNA clones corresponding to 3419 nucleotides of Mopeia virus S RNA were isolated and sequenced. Two open reading frames, encoding the glycoprotein precursor (GPC) and nucleocapsid (N) proteins, were located in the ambisense arrangement characteristic of the arenaviruses. Comparison of the amino acid sequences of the translation products with those of two Lassa virus strains showed considerable conservation, with 74 and 80% identity for the two glycoproteins G1 and G2, and 74% identity for the N protein. The putative dibasic site of GPC cleavage (R-R) was conserved, as were the potential N-linked glycosylation sites. A striking difference between Mopeia virus and Lassa virus was identified in the noncoding intergenic region. Instead of the single hairpin structure formed by base-pairing of complementary sequences which is usually found, the Mopeia virus S RNA has the potential to form two hairpins. These hairpins were similar in sequence and may have been formed in a duplication event during RNA replication. The possible contribution of this secondary structure feature to differences in pathogenicity between Mopeia and Lassa viruses is discussed.

Generation of a functional cDNA encoding the LdH2 class-I molecule by using a single-LTR retroviral shuttle vector

The use of a new single long-terminal-repeat retroviral shuttle vector has allowed us to obtain copies of the Ld gene with the first seven exons spliced correctly, as well as many other partially spliced or aberrantly recombined copies. Nucleotide sequencing performed on double-stranded DNA with primers specific for the vector and for the coding region of the gene, allowed rapid screening of the recovered plasmids. Synthetic oligodeoxyribonucleotides were then used to link the 5 nt of the last exon, and the functionality of the cDNA copy was verified by expression in transfected L(TK-) cells. Cells that produced the Ld antigen were detected by immunofluorescence and were shown to synthesize an immunoprecipitable molecule of the expected size. In addition, Ld-producing cells were susceptible to killing by Ld-restricted cytotoxic T-lymphocytes. This material should prove useful for mutagenesis and for expression in cell types in which expression of the genes of the major histocompatibility complex appears to be highly regulated.

Restricted V-segment usage in T-cell receptors from cytotoxic T lymphocytes specific for a major epitope of lymphocytic choriomeningitis virus

Cytotoxic T lymphocytes (CTL) play an important role in recovery from a number of viral infections. They are also implicated in virus-induced immunopathology as best demonstrated in lymphocytic choriomeningitis virus (LCMV) infection of adult immunocompetent mice. In the present study, the structure of the T-cell receptor (TCR) in LCMV-specific CTL in C57BL/6 (B6) mice was investigated. Spleen T cells obtained from LCMV-infected mice were cultured in vitro with virus-infected stimulator cells and then stained with anti-TCR V beta antibodies. A skewing of V beta usage was noticeable in T cells enriched for their reactivity to LCMV, suggesting that particular V segments are important for the recognition of LCMV T-cell epitopes in B6 mice. To gain more detailed information on the structure of the TCR specific for LCMV epitopes, we studied CTL clones. It has been shown that approximately 90% of LCMV-reactive CTL clones generated in H-2b mice are specific for a short peptide fragment of the LCMV glycoprotein, residues 278 to 286, recognized in the context of the class I major histocompatibility complex molecule, Db. Four CTL clones possessing the specificity were randomly selected from a collection of clones, and their TCR genes were isolated by cDNA cloning or by the anchored polymerase chain reaction. All four clones were found to use V alpha gene segments belonging to the V alpha 4 subfamily. By RNA blot analysis, two more clones with the same specificity were also shown to express the V alpha 4 mRNA. In contrast, three different V beta gene segments were used among the four clones examined. J beta 2.1 was used by three of the clones. Although amino acid sequences in the V(D)J junctional regions were dissimilar, aspartic acid was found in the V alpha J alpha and/or V beta D beta J beta junctions of all four of these clones, suggesting that this residue is involved in binding the LCMV fragment. Restricted usage of V alpha and possibly J beta segments in the CTL response to a major T-cell epitope of LCMV raises the possibility that immunopathology in LCMV infection can be treated with antibodies directed against such TCR segments. Thus, similar analysis of the TCR in other virus infections is warranted and may lead to therapeutic strategies for immunopathology due to virus infections.

Vaccination and protection from a lethal viral infection: identification, incorporation, and use of a cytotoxic T lymphocyte glycoprotein epitope

The outcome of infection by lymphocytic choriomeningitis virus (LCMV) is determined largely by the cytotoxic T lymphocyte (CTL) response of the host. In H-2b mice, the anti-glycoprotein (GP) response is directed to at least two epitopes, one located at GP aa 272-286 and a second in GP-1. Here we show that the second epitope can be minimally identified by amino acid residues GP 34-40 (AVYNFAT). The epitope is restricted by the Db class I glycoprotein. Characterization of these CTL epitopes allowed us to address the role(s) played by each epitope when expressed singly in the control of a lethal challenge with LCMV. Here we show that a single immunization with a recombinant vaccinia virus (VV) vaccine expressing LCMV GP aa 1-59 confers protection to H-2b mice from lethal LCMV infection. In contrast, a VV expressing LCMV GP aa 272-293, although recognized by CTL, does not protect. We show that the success or failure of protective immunization is determined by the ability of the immunizing sequences to prime for CTL in vivo. Although the GP 278-286 epitope when contained as a "minigene" fails to induce CTL, when incorporated in the normal GP "backbone" it successfully elicits CTL. These observations suggest that the "minimal" recognition sequence alone may not be sufficient to induce a protective CTL response in vivo. Thus a single CTL epitope can protect against a lethal virus infection, but to achieve an effective vaccine, the immunizing sequences must be carefully selected.

Assessment of the specificity of cytotoxic T lymphocytes for the nucleoprotein of Pichinde virus using recombinant vaccinia viruses

Pichinde virus (PV) infection of mice results in induction of a strong H-2 restricted, virus-specific cytotoxic T lymphocyte (CTL) response and rapid clearance of the virus. To define the specificities of CTL induced by PV infection, we constructed vaccinia virus recombinants containing cloned cDNAs corresponding to full-length (VVNP) and a truncated form (VVNP 51-561) of the nucleoprotein (NP) gene of PV. Radioimmunoprecipitation analysis of infected cell lysates indicated that VVNP expressed a PV-specific product identical in size to that of authentic NP, while vaccinia virus recombinants containing truncated NP produced a polypeptide consistent with the synthesis of amino acids 51-561 of Pichinde virus NP. Interestingly, cells infected with VVNP synthesized easily detectable, but much lower levels of nucleoprotein relative to both PV and VVNP51-561. Primary virus-specific CTL induced in three different strains of inbred mice following intravenous infection with PV were able to lyse syngeneic target cells infected with PV but did not markedly lyse syngeneic targets expressing full-length or truncated NP following recombinant vaccinia virus infection. Similarly, secondary anti-PV specific CTL generated following in vitro restimulation by PV or selectively restimulated with vaccinia recombinants did not significantly lyse target cells expressing NP. Further, infection of mice with VVNP and VVNP51-561 did not induce CTLs specific for PV and did not prime mice for the generation of memory anti-PV CTL in vivo. These results suggest that PV gene products other than NP, such as the GPC or L protein, contain the major target epitope(s) recognized by PV-specific CTL.

Antiviral cytotoxic T cell response induced by in vivo priming with a free synthetic peptide

Induction in vivo of antiviral cytotoxic T cell response was achieved in a MHC class I-dependent fashion by immunizing mice three times with a free unmodified 15-mer peptide derived from the nucleoprotein of lymphocytic choriomeningitis virus in IFA. The effector T cells are CD8+, restricted to the class I Ld allele of the analyzed mouse strain, and are specific both at the level of secondary restimulation in vitro and at the effector T cell level. These results suggest that cocktails of viral peptides may be used as antiviral T cell vaccines.

Molecularly engineered vaccine which expresses an immunodominant T-cell epitope induces cytotoxic T lymphocytes that confer protection from lethal virus infection

Identification of a single viral T-cell epitope, associated with greater than 95% of the virus-specific cytotoxic T-lymphocyte (CTL) activity in BALB/c (H-2d) mice (J. L. Whitton, A. Tishon, H. Lewicki, J. Gebhard, T. Cook, M. Salvato, E. Joly, and M. B. A. Oldstone, J. Virol. 63:4303-4310, 1989), permitted us to design a CTL vaccine and test its ability to protect against a lethal virus challenge. Here we show that a single immunization with a recombinant vaccinia virus-lymphocytic choriomeningitis virus (LCMV) vaccine (VVNPaa1-201) expressing the immunodominant epitope completely protected H-2d mice from lethal infection with LCMV but did not protect H-2b mice. Furthermore, we show that the success or failure of immunization was determined entirely by the host class I major histocompatibility glycoproteins. The difference in outcome between mice of these two haplotypes was consistent with the presence or absence in the immunizing sequences of an epitope for CTL recognition and is correlated with the induction of LCMV-specific H-2-restricted CTL in H-2d mice. Protection is not conferred by a humoral immune response, since LCMV-specific antibodies were not detectable in sera from VVNPaa1-201-immunized mice. In addition, passive transfer of sera from vaccinated mice did not confer protection upon naive recipients challenged with LCMV. Hence, the molecular dissection of viral proteins can uncover immunodominant CTL epitope(s) that can be engineered into vaccines that elicit CTL. A single CTL epitope can protect against a lethal virus infection, but the efficacy of the vaccine varies in a major histocompatibility complex-dependent manner.