N protein is the predominant antigen recognized by vesicular stomatitis virus-specific cytotoxic T cells

Cellular and humoral immunity to Ebola Zaire glycoprotein and viral vector proteins following immunization with recombinant vesicular stomatitis virus-based Ebola vaccine (rVSVΔG-ZEBOV-GP)

While effective at preventing Zaire ebolavirus (ZEBOV) disease, cellular immunity to ZEBOV and vector-directed immunity elicited by the recombinant vesicular stomatitis virus expressing ZEBOV glycoprotein (rVSVΔG-ZEBOV-GP) vaccine remain poorly understood. Sera and peripheral blood mononuclear cells were collected from 32 participants enrolled in a prospective multicenter study [ClinicalTrials.gov NCT02788227] before vaccination and up to six months post-vaccination. IgM and IgG antibodies, IgG-producing memory B cells (MBCs), and T cell reactivity to ZEBOV glycoprotein (ZEBOV-GP), vesicular stomatitis virus-Indiana strain (VSV-I) matrix (M) protein, and VSV-I nucleoprotein (NP) were measured using ELISA, ELISpot, and flow cytometry, respectively. 11/32 (34.4%) participants previously received a different investigational ZEBOV vaccine prior to enrollment and 21/32 (65.6%) participants were ZEBOV vaccine naïve. Both ZEBOV vaccine naïve and experienced participants had increased ZEBOV-GP IgG optical densities (ODs) post-rVSVΔG-ZEBOV-GP vaccination while only ZEBOV vaccine naïve participants had increased ZEBOV-GP IgM ODs. Transient IgM and IgG antibody responses to VSV-I M protein and NP were observed in a minority of participants. All participants had detectable ZEBOV-GP specific IgG-producing MBCs by 6 months post-vaccination while no changes were observed in the median IgG-producing MBCs to VSV-I proteins. T cell responses to ZEBOV-GP differed between ZEBOV vaccine experienced and ZEBOV vaccine naïve participants. T cell responses to both VSV-I M protein and VSV-I NP were observed, but were of a low magnitude. The rVSVΔG-ZEBOV-GP vaccine elicits robust humoral and memory B cell responses to ZEBOV glycoprotein in both ZEBOV vaccine naïve and experienced individuals and can generate vector-directed T cell immunity. Further research is needed to understand the significance of pre-existing vector and target antigen immunity on responses to booster doses of rVSVΔG-ZEBOV-GP and other rVSV-vectored vaccines.

Creation of matrix protein gene variants of two serotypes of vesicular stomatitis virus as prime-boost vaccine vectors

To take advantage of live recombinant vesicular stomatitis viruses (rVSVs) as vaccine vectors for their high yield and for their induction of strong and long-lasting immune responses, it is necessary to make live vaccine vectors safe for use without losing their immunogenicity. We have generated safer and highly efficient recombinant VSV vaccine vectors by combining the M51R mutation in the M gene of serotype VSV-Indiana (VSVInd) with a temperature-sensitive mutation (tsO23) of the VSVInd Orsay strain. In addition, we have generated two new serotype VSV-New Jersey (VSVNJ) vaccine vectors by combining M48R and M51R mutations with G22E and L110F mutations in the M gene, rVSVNJ(G22E M48R M51R) [rVSVNJ(GMM)] and VSVNJ(G22E M48R M51R L110F) [rVSVNJ(GMML)]. The combined mutations G21E, M51R, and L111F in the M protein of VSVInd significantly reduced the burst size of the virus by up to 10,000-fold at 37°C without affecting the level of protein expression. BHK21 cells and SH-SY5Y human neuroblastoma cells infected with rVSVInd(GML), rVSVNJ(GMM), and rVSVNJ(GMML) showed significantly reduced cytopathic effects in vitro at 37°C, and mice injected with 1 million infectious virus particles of these mutants into the brain showed no neurological dysfunctions or any other adverse effects. In order to increase the stability of the temperature-sensitive mutant, we have replaced the phenylalanine with alanine. This will change all three nucleotides from UUG (leucine) to GCA (alanine). The resulting L111A mutant showed the temperature-sensitive phenotype of rVSVInd(GML) and increased stability. Twenty consecutive passages of rVSVInd(GML) with an L111A mutation did not convert back to leucine (UUG) at position 111 in the M protein gene.

IMPORTANCE

Recombinant vesicular stomatitis viruses as live vaccine vectors are very effective in expressing foreign genes and inducing adaptive T cell and B cell immune responses. As with any other live viruses in humans or animals, the use of live rVSVs as vaccine vectors demands the utmost safety. Our strategy to attenuate rVSVInd by utilizing a temperature-sensitive assembly-defective mutation of L111A and combining it with an M51R mutation in the M protein of rVSVInd significantly reduced the pathogenicity of the virus while maintaining highly effective virus production. We believe our new temperature-sensitive M gene mutant of rVSVInd(GML) and M gene mutants of rVSVNJ(GMM) and rVSVNJ(GMML) add excellent vaccine vectors to the pool of live viral vectors.

Attenuation of recombinant vesicular stomatitis virus-human immunodeficiency virus type 1 vaccine vectors by gene translocations and g gene truncation reduces neurovirulence and enhances immunogenicity in mice

Recombinant vesicular stomatitis virus (rVSV) has shown great potential as a new viral vector for vaccination. However, the prototypic rVSV vector described previously was found to be insufficiently attenuated for clinical evaluation when assessed for neurovirulence in nonhuman primates. Here, we describe the attenuation, neurovirulence, and immunogenicity of rVSV vectors expressing human immunodeficiency virus type 1 Gag. These rVSV vectors were attenuated by combinations of the following manipulations: N gene translocations (N4), G gene truncations (CT1 or CT9), noncytopathic M gene mutations (Mncp), and positioning of the gag gene into the first position of the viral genome (gag1). The resulting N4CT1-gag1, N4CT9-gag1, and MncpCT1-gag1 vectors demonstrated dramatically reduced neurovirulence in mice following direct intracranial inoculation. Surprisingly, in spite of a very high level of attenuation, the N4CT1-gag1 and N4CT9-gag1 vectors generated robust Gag-specific immune responses following intramuscular immunization that were equivalent to or greater than immune responses generated by the more virulent prototypic vectors. MncpCT1-gag1 also induced Gag-specific immune responses following intramuscular immunization that were equivalent to immune responses generated by the prototypic rVSV vector. Placement of the gag gene in the first position of the VSV genome was associated with increased in vitro expression of Gag protein, in vivo expression of Gag mRNA, and enhanced immunogenicity of the vector. These findings demonstrate that through directed manipulation of the rVSV genome, vectors that have reduced neurovirulence and enhanced immunogenicity can be made.

Matrix protein of VSV New Jersey serotype containing methionine to arginine substitutions at positions 48 and 51 allows near-normal host cell gene expression

The matrix (M) protein of vesicular stomatitis virus (VSV) plays significant roles in the replication of VSV through its involvement in the assembly of virus particles as well as by facilitating the evasion of innate host cell defense mechanisms. The presence of methionine at position 51 (M51) of the matrix (M) protein of the VSV Indiana serotype (VSV(Ind)) has been proven to be crucial for cell rounding and inhibition of host cell gene expression. The M protein of VSV(Ind) with the substitution of M51 with arginine (R:M51R) results in the loss of inhibitory effects on host cell gene expression. The VSV(Ind) expressing the M(M51R) protein became the attractive oncolytic virus which is safer and more tumor-specific because the normal cells can clear the mutant VSV(Ind) easily but tumor cells are susceptible to the virus because a variety of tumor cells lack innate antiviral activities. We have studied the role of the methionines at positions 48 and 51 of the M protein of the New Jersey serotype of VSV (VSV(NJ)) in the induction of cytopathic effects (CPE) and host cell gene expression. We have generated human embryonic kidney 293 cell lines inducibly expressing M proteins with M to R mutations at positions 48 and 51, either separately or together as a double mutant, and examined expression of heat shock protein 70 (HSP70) as an indicator of host cell gene expression. We have also generated recombinant VSV(NJ) encoding the mutant M proteins M(M48R) or M(M48R+M51R) for the first time and tested for the expression of HSP70 in infected cells. Our results demonstrated that the M51 of VSV(NJ) M proteins has a major role in cell rounding and in suppressing the host cell gene expression either when the M protein was expressed alone in inducible cell lines or when expressed together with other VSV proteins by the recombinant VSV(NJ). Amino acid residue M48 may also have some role in cell rounding and in the inhibitory effects of VSV(NJ) M, which was demonstrated by the fact that the cell line expressing the double substitution mutant M(M48R+M51R) exhibited the least cytopathic effects and the least inhibitory effect on host cell gene expression.

Evaluation of immunological paradigms in a virus model: are dendritic cells critical for antiviral immunity and viral clearance?

We have examined the role of dendritic cells (DCs) in the antiviral immune response and viral clearance using a transgenic mouse model (CD11c-diphtheria toxin (DT) receptor GFP) that allows for their conditional ablation in vivo. DT administration systemically ablated conventional and IFN-producing plasmacytoid DCs (pDCs) in transgenic, but not nontransgenic littermates, without elimination of splenic macrophages. Unexpectedly, early (12 and 48 h postinfection) viral clearance of vesicular stomatitis virus was normal in DC-depleted mice despite markedly reduced serum titers of type I IFN. DC-depleted mice remained virus-free with the exception of a subset (approximately 30%) that developed overwhelming and fatal brain infections 6 days postinfection. However, DT treatment profoundly inhibited clonal expansion of naive CD8+ vesicular stomatitis virus-specific T cells without altering the primary Th1 and Th2 cytokine response. Optimal clonal expansion required pDCs because selective elimination of these cells in vivo with a depleting Ab also suppressed expansion of tetramer+ cells, although Th1/Th2 cytokine production remained unaltered. Collectively, these data indicate that conventional DCs and to a lesser extent pDCs are critical for proliferation of naive antiviral T cells. However, other components of the primary adaptive immune response (Th1/Th2 cytokines) are essentially normal in the absence of DCs, which may account for the efficient viral clearance seen in DC-depleted mice. Thus, sufficient redundancy exists in the immune system to sustain efficient viral clearance despite loss of an APC considered essential for induction of a primary antiviral immune response.

Propanil exposure induces delayed but sustained abrogation of cell-mediated immunity through direct interference with cytotoxic T-lymphocyte effectors

The postemergent herbicide propanil (PRN ; also known as 3,4-dichloropropionanilide) is used on rice and wheat crops and has well-known immunotoxic effects on various compartments of the immune system, including T-helper lymphocytes, B lymphocytes, and macrophages. It is unclear, however, whether PRN also adversely affects cytotoxic T lymphocytes (CTLs) , the primary (1 degrees ) effectors of cell-mediated immunity. In this study we examined both the direct and indirect effects of PRN exposure on CTL activation and effector cell function to gauge its likely impact on cell-mediated immunity. Initial experiments addressed whether PRN alters the class I major histocompatibility complex (MHC) pathway for antigen processing and presentation by antigen-presenting cells (APCs) , thereby indirectly affecting effector function. These experiments demonstrated that PRN does not impair the activation of CTLs by PRN-treated APCs. Subsequent experiments addressed whether PRN treatment of CTLs directly inhibits their activation and revealed that 1 degrees alloreactive CTLs exposed to PRN are unimpaired in their proliferative response and only marginally inhibited in their lytic activity. Surprisingly, secondary stimulation of these alloreactive CTL effectors, however, even in the absence of further PRN exposure, resulted in complete abrogation of CTL lytic function and a delayed but significant long-term effect on CTL responsiveness. These findings may have important implications for the diagnosis and clinical management of anomalies of cell-mediated immunity resulting from environmental exposure to various herbicides and other pesticides.

Direct intralymphatic injection of peptide vaccines enhances immunogenicity

Research to enhance the efficiency of vaccines focuses mainly on improving either the adjuvant or the type and form of the antigen. This study evaluates the influence of the administration route on the efficiency of a peptide-based vaccine. Peptide vaccines are generally administered subcutaneously or intradermally, from where they must reach secondary lymphatic organs to induce an immune response. We analyzed the efficacy of peptide vaccines administered directly into a lymph node. Using a MHC class I-binding peptide from lymphocytic choriomeningitis virus, we found that intralymphatic injection enhanced immunogenicity by as much as 10(6) times when compared to subcutaneous and intradermal vaccination. Intralymphatic administration induced CD8 T cell responses with strong cytotoxic activity and IFN-gamma production that conferred long-term protection against viral infections and tumors. These results should have immediate implications for clinical immunotherapy of infectious disease and cancer.

CD8 T cell responses to viral infections in sequence

Our current understanding of virus-specific T cell responses has been shaped by model systems with mice, where naive animals are infected with a single viral pathogen. Paradigms derived from such models, however, may not always be applicable to a natural setting, where a host is exposed to numerous pathogens over its lifetime. Accumulating data in animal models and with some human diseases indicate that a host's prior history of infections can impact the specificity of future CD8 T cell responses, even to unrelated viruses. This can have both beneficial and detrimental consequences for the host, including altered clearance of virus, distinct forms of immunopathology, and substantial changes in the pool of memory T cells. Here we will describe the characteristics of CD8 T cells and the dynamics of their response to heterologous viral infections in sequence.

Uncertainties - discrepancies in immunology

The many immunological observations and results from in-vitro or in-vivo experiments vary, and their interpretations differ enormously. A major problem is that within a normal distribution of biological phenomena, which are measurable with many methods, virtually anything is possible. Within a coevolutionary context, the definition of biologically relevant thresholds is an important key to improve our understanding of weaknesses and strengths of the immune system. This review is a personal view, comparing textbook rules and experiments using model antigens with observations on immunity against infections or tumors to critically evaluate our perception and understanding of specificity, affinity maturation, antigen presentation, selection of the class of the immune response, immunological memory and protective immunity, positive selection of T cells and self/nonself discrimination.

Fucosyltransferase VII-deficient mice with defective E-, P-, and L-selectin ligands show impaired CD4+ and CD8+ T cell migration into the skin, but normal extravasation into visceral organs

The first step of leukocyte extravasation, leukocyte rolling, is mediated by E-, P-, and L-selectins. Mice deficient for alpha-1,3-fucosyltransferase VII (FucTVII)(-/-) are characterized by deficiency of E-, P-, and L-selectin ligand activity. This model system was used to evaluate the role of the interactions of selectins with their ligands in T and B cell responses. In the present study, FucTVII(-/-) mice showed reduced CD4+ T cell-mediated contact hypersensitivity reactions of the ears to FITC as well as reduced CD8+ T cell-mediated delayed-type hypersensitivity reactions of the footpads against lymphocytic choriomeningitis virus infection. As Langerhans cell migration to local lymph nodes as well as CD4+ and CD8+ T cell induction were found to be normal, the afferent arm of these reactions was not impaired. The reduced inflammatory reactions of the skin were due to inefficient lymphocyte extravasation into the skin. In contrast, extravasation of CD4+ and CD8+ T cells into visceral organs, such as the ovaries or the brain, was not impaired in FucTVII(-/-) mice. Elimination of vaccinia virus and of lymphocytic choriomeningitis virus from ovaries and brain, as well as elimination of tumor cells from several visceral organs was normal. Thus, interactions of selectins with their ligands are important for lymphocyte homing into the skin, but not for lymphocyte extravasation into visceral organs.

High-level primary CD8(+) T-cell response to human immunodeficiency virus type 1 gag and env generated by vaccination with recombinant vesicular stomatitis viruses

We investigated the primary cellular immune responses to human immunodeficiency virus type 1 (HIV-1) Env and Gag proteins elicited by recombinant vesicular stomatitis viruses (rVSVs). The primary response to Env peaked 5 to 7 days after intraperitoneal vaccination, at which time 40% of CD8(+) cells were Env tetramer positive and activated (CD62L(Lo)). These freshly isolated cells actively lysed target cells pulsed with the p18-I10 peptide and secreted gamma interferon and tumor necrosis factor alpha after stimulation with the Env p18-I10 peptide. The primary response to Env elicited by rVSVs was sixfold higher than that elicited by recombinant vaccinia viruses (rVVs) at 5 days postvaccination. An intranasal route of vaccination with VSV-Env also elicited a strong primary response to Env. The primary immune response to Gag elicited by rVSV peaked 7 days after vaccination, at which time 3% of CD8(+) cells were Gag tetramer positive and CD62L(Lo) and functional by intracellular cytokine staining. This response was eightfold higher than that elicited by rVV expressing Gag. VSV-GagEnv, which expresses both Gag and Env from a single recombinant, also induced strong cytotoxic T-lymphocyte (CTL) responses to both Env and Gag. Our quantitative analyses illustrate the potency of the VSV vector system in CTL induction.

Heat shock protein-chaperoned peptides but not free peptides introduced into the cytosol are presented efficiently by major histocompatibility complex I molecules

The studies reported here bear on the events in the cytosol that lead to trafficking of peptides during antigen processing and presentation by major histocompatibility complex (MHC) I molecules. We have introduced free antigenic peptides or antigenic peptides bound to serum albumin or to cytosolic heat shock proteins hsp90 (and its endoplasmic reticular homologue gp96) or hsp70 into the cytosol of living cells and have monitored the presentation of the peptides by appropriate MHC I molecules. The experiments show that (i) free peptides or serum albumin-bound peptides, introduced into the cytosol, become ligands of MHC I molecules at a far lower efficiency than peptides chaperoned by any of the heat shock proteins tested and (ii) treatment of cells with deoxyspergualin, a drug that binds hsp70 and hsp90 with apparent specificity, abrogates the ability of cells to present antigenic peptides through MHC I molecules, and introduction of additional hsp70 into the cytosol overcomes this abrogation. These results suggest for the first time a functional role for cytosolic chaperones in antigen processing.

Preferential localization of effector memory cells in nonlymphoid tissue

Many intracellular pathogens infect a broad range of host tissues, but the importance of T cells for immunity in these sites is unclear because most of our understanding of antimicrobial T cell responses comes from analyses of lymphoid tissue. Here, we show that in response to viral or bacterial infection, antigen-specific CD8 T cells migrated to nonlymphoid tissues and were present as long-lived memory cells. Strikingly, CD8 memory T cells isolated from nonlymphoid tissues exhibited effector levels of lytic activity directly ex vivo, in contrast to their splenic counterparts. These results point to the existence of a population of extralymphoid effector memory T cells poised for immediate response to infection.

Direct analysis of the dynamics of the intestinal mucosa CD8 T cell response to systemic virus infection

The CD8 T cell response to vesicular stomatitis virus infection was characterized in the spleen and intestinal mucosa using MHC tetramers. Surprisingly, the primary response persisted in the lamina propria long after the splenic response had declined. Furthermore, the response was characterized by a protracted effector phase in which cytolytic activity in the lamina propria, but not in the spleen, was maintained. The appearance of Ag-specific cells in the intestinal mucosa was largely, though not exclusively, a result of beta(7) integrin-mediated migration. Infection with Listeria monocytogenes or with vaccinia virus also led to sustained mucosal responses. After reinfection of vesicular stomatitis virus-primed mice with a serotypically distinct virus, a sustained recall response was detected in all tissues. In CD40(-/-) mice, the mucosal, but not the splenic, response was compromised, resulting in diminished mucosal memory. The recall response was CD40 independent and correlated with memory levels, indicating that the mucosal and systemic responses operated independently. These findings illustrated the integrated yet distinct nature of systemic vs mucosal immune responses.

Recognition of an MHC Class I-Restricted Antigenic Peptide Can Be Modulated by para-Substitution of Its Buried Tyrosine Residues in a TCR-Specific Manner

Conformational dependence of TCR contact residues of the H-2Kb molecule on the two buried tyrosine side chains of the vesicular stomatitis virus (VSV)-8 peptide was investigated by systematic substitutions of the tyrosines with phenylalanine, p-fluorophenylalanine (pFF), or p-bromophenylalanine (pBrF). The results of peptide competition CTL assays revealed that all of the peptide variants, except for the pBrF analogues, had near-native binding to the H-2Kb molecule. Epitope-mapped anti-H-2Kb mAbs detected conformational differences among H-2Kb molecules stabilized with these VSV-8 variants on RMA-S cells. Selective recognition of the VSV-8 analogues was displayed by a panel of three H-2Kb-restricted, anti-VSV-8 TCRs. Thus, these substitutions result in an antigenically significant conformational change of the MHC molecular surface structure at both C and D pockets, and the effect of this change on cognate T cell recognition is dependent on the TCR structure. Our results confirm that the structure of buried peptide side chains can determine the surface conformation of the MHC molecule and demonstrate that even a very subtle structural nuance of the buried side chain can be incorporated into the surface conformation of the MHC molecule. The ability of buried residues to modulate this molecular surface augments the number of residues on the MHC-peptide complex that can be recognized as “foreign” by the CD8+ T cell repertoire and allows for a higher level of antigenic discrimination. This may be an important mechanism to expand the total number of TCR specificities that can respond to a single peptide determinant.

Generation of mucosal cytotoxic T cells against soluble protein by tissue-specific environmental and costimulatory signals

We compared peripheral and mucosal primary CD8 T cell responses to inflammatory and noninflammatory forms of antigen in a T cell-adoptive transfer system. Immunization with the soluble antigen, ovalbumin (ova), administered i.p. or orally without adjuvant, activated nonmucosal CD8 T cells but did not induce cytotoxic activity. However, after activation, the transferred cells entered the intestinal mucosa and became potent antigen-specific killers. Thus, exogenous intact soluble protein entered the major histocompatibility complex class I antigen presentation pathway and induced mucosal cytotoxic T lymphocytes. Moreover, distinct costimulatory requirements for activation of peripheral versus mucosal T cells were noted in that the CD28 ligand, B7-1, was critical for activated mucosal T cell generation but not for activation of peripheral CD8 T cells. The costimulator, B7-2, was required for optimum activation of both populations. Infection with a new recombinant vesicular stomatitis virus encoding ovalbumin induced lytic activity in mucosal as well as peripheral sites, demonstrating an adjuvant effect of inflammatory mediators produced during virus infection. Generation of antiviral cytotoxic T lymphocytes was also costimulation-dependent. The results indicated that induction of peripheral tolerance via antigen administration may not extend to mucosal sites because of distinct costimulatory and inflammatory signals in the mucosa.

Contribution of peptide backbone atoms to binding of an antigenic peptide to class I major histocompatibility complex molecule

Antigenic peptides are thought to bind to class I major histocompatibility complex (MHC) molecules through three modes of interaction: van der Waals interaction and, to a lesser extent, hydrogen bonding of anchor side chain atoms to residues comprising the binding pockets of the MHC molecule; hydrogen bonding of N- and C-termini to residues at the ends of the binding groove; and hydrogen bonding of peptide backbone atoms to residues lining the binding groove. To dissect the relative contribution of each of these interactions to class I MHC-peptide stability, a retro inverso (RI) analog of VSV-8. an H-2Kb restricted cytotoxic T lymphocyte (CTL) epitope and terminally modified variants of both VSV-8 and RI VSV-8 were synthesized and their ability to target H-2Kb bearing cells for CTL mediated lysis was compared. None of RI VSV-8 analogs elicited lysis of target cells by CTL specific for VSV-8 nor did they appear to compete with the native peptide for binding to H-2Kb. In contrast, terminally modified VSV-8 peptides elicited target lysis. These findings suggest that side chain topochemistry of the peptide is insufficient for stable peptide binding to H-2Kb; rather, hydrogen bonding of the peptide backbone atoms to H-2Kb side chain atoms appears to play a major role in the stability of the complex. Computer modeling confirmed that none of the RI analogs participate in the extensive hydrogen bonding network between the peptide backbone and the MHC molecule seen in the native structure.

Heat shock protein-peptide complexes, reconstituted in vitro, elicit peptide-specific cytotoxic T lymphocyte response and tumor immunity

Heat shock protein (HSP) preparations derived from cancer cells and virus-infected cells have been shown previously to elicit cancer-specific or virus-specific immunity. The immunogenicity of HSP preparations has been attributed to peptides associated with the HSPs. The studies reported here demonstrate that immunogenic HSP-peptide complexes can also be reconstituted in vitro. The studies show that (a) complexes of hsp70 or gp96 HSP molecules with a variety of synthetic peptides can be generated in vitro; (b) the binding of HSPs with peptides is specific in that a number of other proteins tested do not bind synthetic peptides under the conditions in which gp96 molecules do; (c) HSP-peptide complexes reconstituted in vitro are immunologically active, as tested by their ability to elicit antitumor immunity and specific CD8+ cytolytic T lymphocyte response; and (d) synthetic peptides reconstituted in vitro with gp96 are capable of being taken up and re-presented by macrophage in the same manner as gp96- peptides complexes generated in vivo. These observations demonstrate that HSPs are CD8+ T cell response-eliciting adjuvants.

The carboxyl-terminal 120-residue polypeptide of infectious bronchitis virus nucleocapsid induces cytotoxic T lymphocytes and protects chickens from acute infection

Specific cytotoxic T-lymphocyte (CTL) responses to nucleocapsid of infectious bronchitis virus (IBV) were identified by using target cells infected with a Semliki Forest virus (SFV) vector. Effector cells for CTL assays were collected from chickens infected with the Gray strain of IBV or inoculated with a DNA plasmid encoding nucleocapsid proteins. IBV-specific CTL epitopes were mapped within the carboxyl-terminal 120 amino acids of the nucleocapsid protein. CTL lysis of target cells infected with SFV encoding nucleocapsid was major histocompatibility complex restricted and mediated by CD8+ T cells. In addition, splenic T cells collected from chickens inoculated in the breast muscle with a DNA plasmid encoding this CTL epitope(s) recognized target cells infected with wild-type virus or an SFV vector encoding nucleocapsid proteins. CTL activity of splenic T cells collected from chicks immunized with a DNA plasmid encoding CTL epitopes was cross-reactive, in that lysis of target cells infected with serologically distinct strains of IBV was dose responsive in a manner similar to that for lysis of target cells infected with the homologous strain of IBV. Furthermore, chickens immunized with a DNA plasmid encoding a CTL epitope(s) were protected from acute viral infection.

Antiviral immune responses in Itk-deficient mice

Mice lacking Itk, a T-cell-specific protein tyrosine kinase, have reduced numbers of T cells and reduced responses to allogeneic major histocompatibility molecules. This study analyzed antiviral immune responses in mice deficient for Itk. Primary cytotoxic T-lymphocyte (CTL) responses were analyzed after infection with lymphocytic choriomeningitis virus (LCMV), vaccinia virus (VV), and vesicular stomatitis virus (VSV). Ex vivo CTL activity was consistently reduced by a factor of two to six for the different viruses. CTL responses after restimulation in vitro were similarly reduced unless exogenous cytokines were added. In the presence of interleukin-2 or concanavalin A supernatant, Itk-deficient and control mice responded similarly. Interestingly, while LCMV was completely eliminated by day 8 in both Itk-deficient and control mice, VV cleared from itk-/- mice with delayed kinetics. Antibody responses were evaluated after VSV infection. Both the T-cell-independent neutralizing immunoglobulin M (IgM) and the T-cell-dependent IgG responses were similar in Itk-deficient and control mice. Taken together, the results show that CTL responses are reduced in the absence of Itk whereas antiviral B-cell responses are not affected.

Peptide antigen treatment of naive and virus-immune mice: antigen-specific tolerance versus immunopathology

Peptide-specific down-regulation of T cell responses may represent a powerful tool to intervene in autoimmune diseases or graft rejections. It is therefore important to know whether peptide treatment tolerizes both naive and antigen-experienced memory T lymphocytes. Here we show that a major histocompatibility complex class I binding peptide, derived from the glycoprotein (GP33 peptide) of lymphocytic choriomeningitis virus (LCMV), specifically tolerized naive cytotoxic T lymphocytes (CTL) when administered three times intraperitoneally in incomplete Freund's adjuvants. However, in the presence of GP33-specific memory CTL in LCMV-primed mice, the same treatment had a general immunosuppressive effect on unrelated third-party antigen-specific T cell responses and caused severe immunopathological damage to the spleen.

Antiviral immune responses in CTLA4 transgenic mice

The role of B7 binding CD28 in the regulation of T- and B-cell responses against viral antigens was assessed in transgenic mice expressing soluble CTLA4-Hgamma1 (CTLA4-Ig tg mice) that blocks B7-CD28 interactions. The results indicate that transgenic soluble CTLA4 does not significantly alter cytotoxic T-cell responses against replicating lymphocytic choriomeningitis virus (LCMV) or vaccinia virus but drastically impairs the induction of cytotoxic T-cell responses against abortively replicating vesicular stomatitis virus (VSV). While the T-independent neutralizing immunoglobulin M (IgM) responses were within normal ranges, the switch to IgG was reduced 4- to 16-fold after immunization with abortively replicating VSV and more than 30-fold after immunization with an inert VSV glycoprotein antigen in transgenic mice. IgG antibody responses to LCMV, as detected by enzyme-linked immunosorbent assay and by neutralizing action, were reduced about 3- to 20-fold and more than 50-fold, respectively. These results suggest that responses in CTLA4-Ig tg mice are mounted according to their independence of T help. While immune responses to nonreplicating or poorly replicating antigens are in general most dependent on T help and B7-CD28 interactions, they are most impaired in CTLA4-Ig tg mice. The results of the present experiments also indicate that highly replicating viruses, because of greater quantities of available antigens and by inducing as-yet-undefined factors and/or cell surface changes, are capable of compensating for the decrease in T help caused by the blocking effects of soluble CTLA4.

Decreased tumor surveillance in perforin-deficient mice

Immune surveillance against tumors usually depends on T cell recognition of tumor antigens presented by major histocompatibility complex (MHC) molecules, whereas MHC class I- tumors may be controlled by natural killer (NK) cells. Perforin-dependent cytotoxicity is a major effector function of CD8+ MHC class I-restricted T cells and of NK cells. Here, we used perforin-deficient C57BL/6 (PKO) mice to study involvement of perforin and Fas ligand in tumor surveillance in vivo. We induced tumors in PKO and normal C57BL/6 mice by (a) injection of different syngeneic tumor cell lines of different tissue origin in naive and primed mice; (b) administration of the chemical carcinogens methylcholanthrene (MCA) or 12-O-tetradecanoylphorbol-13-acetate (TPA) plus 7,12-dimethylbenzanthracene (DMBA), or (c) by injection of acutely oncogenic Moloney sarcoma virus. The first set of models analyzes the defense against a tumor load given at once, whereas the last two sets give information on immune defense against tumors at the very moment of their generation. Most of the tumor cell lines tested were eliminated 10-100-fold better by C57BL/6 mice in an unprimed situation; after priming, the differences were more pronounced. Lymphoma cells transfected with Fas were controlled 10-fold better by PKO and C57BL/6 mice when compared to untransfected control cells, indicating some role for FasL in tumor control. MCA-induced tumors arose more rapidly and with a higher incidence in PKO mice compared to C57BL/6 or CD8-deficient mice. DMBA+TPA-induced skin papillomas arose with similar high incidence and comparable kinetics in both mouse strains. C57BL/6 and PKO mice have a similar incidence of Moloney murine sarcoma and leukemia virus-induced sarcomas, but tumors are larger and regression is retarded in PKO mice. Thus, perforin-dependent cytotoxicity is not only a crucial mechanism of both cytotoxic T lymphocyte- and NK-dependent resistance to injected tumor cell lines, but also operates during viral and chemical carcinogenesis in vivo. Experiments addressing the role of Fas-dependent cytotoxicity by studying resistance to tumor cell lines that were stably transfected with Fas neither provided evidence for a major role of Fas nor excluded a minor contribution of Fas in tumor surveillance.

Constitutive phosphorylation of the vesicular stomatitis virus P protein modulates polymerase complex formation but is not essential for transcription or replication

As a subunit of both the P-L polymerase complex and the P-N assembly complex, the vesicular stomatitis virus (VSV) P protein plays a pivotal role in transcription and replication of the viral genome. Constitutive phosphorylation of this protein is currently thought to be essential for formation of the P-L complex. We recently identified the three relevant phosphate acceptor sites in the VSV Indiana serotype P protein (R. L. Jackson, D. Spadafora, and J. Perrault, Virology 214:189-197, 1995). We now report the effects of substituting Ala at these acceptor sites on transcription reconstitution in vitro and replication of defective interfering virus (DI) templates in vivo. The singly substituted S60A, T62A, and S64A mutants and the doubly substituted S60A/T62A and T62A/S64A mutants, all of which retain some constitutive phosphorylation, were nearly as active as the wild type in both assays. Surprisingly, the nonphosphorylated S60A/S64A protein was also active in transcription (> or = 28%)) and replication (> or = 50%) under optimal conditions. However, this mutant was much less active in in vitro transcription (< or = 5% of wild type) at low P concentrations (<27 nM). In addition, S60A/S64A required higher concentrations of L protein than did the wild type for optimal DI replication in vivo. DI replication efficiency and intracellular accumulation of L, P, and N proteins in the transfected system were very similar to those in VSV-infected cells. We conclude that P protein constitutive phosphorylation is not essential for VSV RNA synthesis per se but likely plays an important role in vivo in facilitating P multimerization and possibly P-L complex formation.

Duration of TCR stimulation determines costimulatory requirement of T cells

Current models suggest that T cells that receive only signal-1 through antigenic stimulation of the T cell receptor (TCR) become anergic, but will mount an immune response when a costimulatory signal-2 is provided. Using mice deficient for an important costimulatory molecule, CD28, we show that a transient signal-1 alone, either through infection with an abortively replicating virus, or through injection of viral peptide, anergizes CD8+ T cells, demonstrating the biological relevance of T cell anergy in vivo. However, in the absence of CD28, continued presence of signal-1 alone, either through prolonged viral replication or repeated injection of peptide, prevents the induction of anergy and generates a functional T cell response in vivo.

Identification of a murine CD4+ T-lymphocyte response site in hepatitis C virus core protein

The T cell response to a recombinant HCV truncated core protein (cp1-10) was measured in a proliferation assay. Based on a 10-fold greater response to this truncated core protein than to its shorter form (cp1-8), a predominant epitope was mapped to the carboxyl quarter of this sequence. This epitope was further mapped to a synthetic peptide corresponding to amino acids 121-140 of the core protein. The peptide was antigenic for T cells of all three H-2 types tested, H-2 r, b and d, and the proliferating T cells were CD4+. Besides inducing specific proliferation in vitro, peptide aa121-140 can prime helper T cells in vivo. When boosted with core protein, mice primed with peptide produced 64-fold higher antibody titer than without priming in 1 week. The identification of a broadly immunogenic T cell helper epitope on core protein may be important for vaccine design against HCV.

On T cell memory: arguments for antigen dependence

Memory is a hallmark of the immune system. Considerable progress has been made towards understanding B cell memory, but T cell memory remains poorly understood and its nature is controversial. There is good evidence that B cell memory is driven by antigen, but the antigen dependence of T cell memory is still being debated. For several years we have investigated the nature, duration and antigen dependence of different aspects of CD8+ T cell memory and this review will discuss our findings as well as how and why they differ from some other results. As others, we find that antigen, due to proliferation of antigen-specific T cell clones, induces a shift in the T cell repertoire which remains detectable for years as an elevated cytotoxic T cell precursor frequency (CTLp) in lymphoid organs. Also in the absence of antigen, in vitro assays for T cell memory which invariably isolate memory T cells from these lymphoid organs therefore remain positive. In contrast, immunity against reinfection with a pathogen requires more than just elevated numbers of CTLp in lymphoid organs. Since reinfection usually takes place via peripheral nonlymphoid tissue, these CTLp have to a) efficiently extravasate and patrol through such tissues, and b) be immediately able to exert effector function in case of reinfection. Both functions, require a certain level of activation which critically depends on T cell stimulation by persisting antigen.

Impaired negative selection of T cells in Hodgkin's disease antigen CD30-deficient mice

CD30 is found on Reed-Sternberg cells of Hodgkin's disease and on a variety of non-Hodgkin's lymphoma cells and is up-regulated on cells after Epstein-Barr virus, human T cell leukemia virus, and HIV infections. We report here that the thymus in CD30-deficient mice contains elevated numbers of thymocytes. Activation-induced death of thymocytes after CD3 cross-linking is impaired both in vitro and in vivo. Breeding the CD30 mutation separately into alpha beta TCR-or gamma delta TCR-transgenic mice revealed a gross defect in negative but not positive selection. Thus, like TNF-receptors and Fas/Apo-1, the CD30 receptor is involved in cell death signaling. It is also an important coreceptor that participates in thymic deletion.

A mechanism for the specific immunogenicity of heat shock protein-chaperoned peptides

Endogenously synthesized antigenic determinants are generally presented on major histocompatibility complex (MHC) class I molecules, whereas exogenous determinants are presented by MHC class II molecules. Here, it is shown that exogenous antigens chaperoned by a heat shock protein can be channeled into the endogenous pathway, presented by MHC class I molecules, and recognized by CD8+ T lymphocytes. This pathway is functional only in a subset of macrophages among the cell types tested. These observations provide a basis for the tumor-specific and virus-specific immunogenicity of cognate heat shock protein preparations and offer a mechanism for the classical phenomenon of cross-priming.

T cell development and repertoire of mice expressing a single T cell receptor alpha chain

We examined T cell development and T cell repertoire in transgenic mice expressing a single T cell receptor (TCR) alpha chain derived from the H-2Db-lymphocytic choriomeningitis virus (LCMV)-specific cytolytic T lymphocyte (CTL) clone P14. To generate these alpha P14 mice, mice transgenic for the P14 TCR alpha chain were backcrossed to TCR alpha-deficient mice. Thymi from alpha P14 mice exhibited a marked decrease of mature CD4+8- and CD8+4- single-positive thymocytes comparable to thymi from TCR alpha-deficient mice. Correspondingly, the number of peripheral T cells was reduced in the CD4 (tenfold) and in the CD8 (twofold) subsets when compared to normal mice. T cells from alpha P14 mice generated a primary anti-LCMV CTL response when stimulated in vitro with LCMV in contrast to normal mice which require priming in vivo; elimination of LCMV in vivo was, however, not improved. Flow cytometric analysis of T cells with V beta-specific antibodies showed a diverse endogenous TCR V beta repertoire. Functional analysis of the T cell repertoire, however, revealed a strongly reduced (30-fold) allogeneic and the absence of a vesicular stomatitis virus-specific CTL response and an impaired ability to provide T cell help for antibody isotype switching. Thus, T cell selection in the thymus was impaired and the T cell repertoire was limited in mice expressing only one type of TCR alpha chain.

Antiviral defense in mice lacking both alpha/beta and gamma interferon receptors

Alpha/beta interferon (IFN) and gamma IFN exert widely overlapping biological effects. Still, mice with individually inactivated alpha/beta or gamma receptors exhibit variably severely reduced resistance to infection and altered immune responses. To investigate to what extent the two IFN systems are functionally redundant, we generated mice with a combined receptor defect (AG129 mice). Like mice with individual mutations, AG129 mice had no apparent anomalies, confirming that in the mouse the IFN system is not essential for normal development. These mice showed an additive phenotype with respect to antiviral defense and exhibited an increased susceptibility to lymphocytic choriomeningitis virus (LCMV) and notably vaccinia virus infection. Because of unlimited replication and subsequent rapid exhaustion of cytotoxic T lymphocyte (CTL) precursors, these mice were unable to mount a CTL response to LCMV. CD8(+)-mediated immunopathology was absent in LCMV-infected mice, and virus persisted. Vaccinia virus replicated much faster in AG129 mice, and a 10(4)-fold lower dose of vaccinia virus was sufficient to prime these mice. With the normal priming dose of 10(6) PFU, cytopathic effects and overwhelming infection possibly causing partial exhaustion of CTL interfered with the anti-vaccinia virus response. Even though global antiviral immunoglobulin G (IgG) titers were within normal ranges, the IgG subclass distribution was heavily biased toward IgG1.

Phagocyte-induced antigen-specific activation of unprimed CD8+ T cells in vitro

The strict segregation of the major histocompatibility complex (MHC) class I and class II loading pathways has been challenged by recent reports indicating that MHC class I molecules can acquire antigen in the phagocytic pathway. We now show that this alternative peptide loading pathway can be used efficiently to generate macrophages able to activate unprimed antigen-specific cytotoxic T cells in vitro. Short peptides (8-11 residues), administered in the phagocytic pathway at nanomolar concentrations, were found to be effective in specifically activating naïve cytotoxic T lymphocytes (CTL) in vitro, but longer peptides or whole protein antigen were not. Whole protein antigen coated on beads did, however, render macrophages susceptible to lysis by an antigen-specific CTL clone. This indicates that proteolysis in the phagocytic pathway has limited capability for class I-restricted presentation. We propose a model for class I loading in the phagocytic pathway consisting of direct trafficking of nascent MHC class I from the trans-Golgi network to the phagosome, prior to appearance at the cell surface, and the use of the narrow cavity between bead and phagosomal membrane as a peptide exchange/loading compartment. Targeting immunogenic class I-binding peptide to the phagocytic pathway of macrophages facilitates presentation in association with class I. This is a useful tool for CTL response induction in vitro.

Diversity of T cell receptors specific for the VSV antigenic peptide (N52-59) bound by the H-2Kb class I molecule

As an approach to determine the structural basis of interactions between T cell receptors (TCRs) and MHC class I/peptide complexes, the fine specificities of a panel of vesicular stomatitis virus (VSV)-specific CTL clones recognizing the antigenic peptide (nucleoprotein 52-59) and the class I (Kb) molecule were correlated with the TCR primary structure. Each TCR showed a distinct interaction pattern with N52-59 and the Kb molecule. The large majority of the TCRs expressed by the panel of CTL clones used V beta 13 gene segments that had randomly recombined with D beta and J beta gene segments. The alpha chains were from randomly assorted V alpha and J alpha gene segments. Thus, the panel was found to be a highly heterogeneous set of TCRs, each member of which appeared to have an unique surface interface area, the recognition site, that interacted with a complementary surface formed by the single peptide bound in the class I antigenic groove.

Immunization with recombinant protein: conditions for cytotoxic T cell and/or antibody induction

Safe vaccines should optimally induce both cell-mediated and humoral immunity. Recently, it has been shown that protective cytotoxic T cells (CTLs) can be induced not only with live vaccines, but also with recombinant viral proteins. This report shows in C57BL/6 (H-2b) mice that the recombinant nucleoprotein (N) of vesicular stomatitis virus (VSV) induced protective CTLs but no neutralizing antibodies in mice, whereas the recombinant glycoprotein (G) of VSV alone induced neutralizing antibodies but no CTLs. If the N and G of VSV were coinjected, both CTLs and a long-lasting neutralizing IgG response was measurable, demonstrating that mixed vaccines can be used to induce protective CTLs and antibodies with an efficiency comparable to live virus. In an attempt to define optimal conditions for CTL priming, the intravenous, intraperitoneal and subcutaneous route of injection were compared. Intravenous injection of recombinant VSV-N induced up to 30 times higher responses than the latter two routes. Finally, we tried to define conditions inducing only CTLs and no antibodies binding to the native protein form, or vice versa, only antibodies and no CTLs. Intravenous injection of boiled VSV-N induced a CTL response but no antibodies specific for the native VSV-N, whereas VSV-N injected subcutaneously in incomplete Freund's adjuvant induced high amounts of anti-VSV-N antibodies but virtually no CTLs. The conditions defined here permit vaccines to be designed which would function along selected and defined immunological effector pathways.

Induction of protective cytotoxic T cells with viral proteins

Induction of CD8+, class I-restricted T cells by non-infectious, exogenous antigens has been documented for model protein antigens such as ovalbumin and for major histocompatibility complex restricted short peptides in viral and tumor systems. However, the protective capacity of cytotoxic T cells induced by conventional proteins has not been tested in vivo so far. We, therefore, evaluated the induction of protective cytotoxic T cells against three different full-length recombinant viral proteins derived from a baculovirus expression system, i.e. the glycoprotein and nucleoprotein of lymphocytic choriomeningitis virus (LCMV) and the nucleoprotein of vesicular stomatitis virus (VSV). These viral proteins induced cytotoxic T cells in a T helper cell-independent fashion which lysed infected target cells in vitro and protected mice from viral replication, immunopathological disease and growth of a tumor expressing the same antigen as a tumor antigen. These results are surprising, since it had been shown earlier for completely inactivated nonreplicating viral vaccines and again here for beta-propiolactone-inactivated VSV or UV-light inactivated LCMV that nonreplicating viral vaccines were incapable of inducing protective cytotoxic T cells. Our data show that immunization of mice with as little as 10 micrograms of non-infectious viral proteins triggered long-lasting CD8+ T cell-mediated antiviral immunity. It was found that the protein alone was only weakly able to induce cytotoxic T cells, and that association with cellular debris functioned as an adjuvant. These findings may be relevant for our understanding of the phenomenon of cross-priming and have obvious implications for vaccine strategies.

Vesicular stomatitis virus Indiana glycoprotein as a T-cell-dependent and -independent antigen

The neutralizing immunoglobulin M (IgM) response to vesicular stomatitis virus (VSV) has been shown to be largely T-cell independent in several T-cell-deficient models of mice. By using different antigen froms of VSV, VSV antigen doses could be graded in vivo (infectious > > UV inactivated > formalin inactivated). The present study reveals a T-cell-dependent component of the neutralizing IgM response in nude mice given intravenous injections of low doses of noninfectious UV-inactivated VSV serotype Indiana (VSV-IND) only if the mice are transfused with VSV-IND-specific helper T cells. Instead, nude mice immunized with infectious VSV, which leads to greater antigen doses in vivo, were able to mount an IgM response in the absence of T cells. These results indicate that the IgM response to low doses of VSV-IND glycoprotein (G) is T-cell dependent. Nude mice immunized with infectious VSV also made a variable but low VSV-IND-neutralizing IgG response. A VSV-IND matrix (M)-specific helper T-cell line rendered this response more consistent, much higher, and longer lasting. Thus (i) VSV-G induces a mostly T-cell-independent but partially T-cell-dependent IgM (the latter can be visualized best at low doses of antigen) and (ii) the antibody response to VSV in nude mice proceeds through steps, i.e., IgM and IgG, that are dose dependent. The results suggest that the predominant role of helper T cells may be to expand and maintain the individual steps of differentiating B cells.

Immunogenicity of a viral model vaccine after different inactivation procedures

Various strategies for the production of safe vaccines have been used. This study compared three different inactivation procedures, i.e. treatment with formaldehyde, beta-propiolactone or UV-light using vesicular stomatitis virus (VSV) as a model antigen. All three inactivation procedures drastically impaired induction of neutralizing IgG responses, confirming previous observations [Bachmann et al. (1993) J Virol 67:3917-3922]. This reduction could be overcome using higher doses for all three preparations. Both formaldehyde and beta-propiolactone completely abrogated the induction of VSV-specific cytotoxic T cells (CTLs), whereas UV-inactivated virus was able to induce significant and long-lasting CTL responses. These results may be of practical relevance since induction of neutralizing antibodies alone is often not sufficient for protection and sometimes may even enhance immunopathological responses of vaccinees.

Peptide variants reveal how antibodies recognize major histocompatibility complex class I

The T cell receptor (TcR) on CD8+ T lymphocytes recognizes a complex which consists of a major histocompatibility complex (MHC) heavy chain, beta 2-microglobulin (beta 2M), and peptide on the surface of antigen-presenting cells. Mutational analyses have suggested that the TcR recognizes both the alpha 1 and alpha 2 domains of the heavy chain as well as the peptide. In light of this, it is of interest to know to what extent the heavy chain domains take on distinct conformations when bound to individual peptides. It has recently been shown that antibodies which recognize the Kb MHC complex are sensitive to which peptides are bound in the groove. We have extended this analysis to include eight Kb-specific antibodies, seven of which are peptide sensitive. These antibodies, all of which are allo-antibodies, recognize Kb-bearing cells which, it is now appreciated, have a highly heterogeneous mix of self peptides presented in their grooves. We show that these self peptides also can affect antibody binding. It has been suggested that peptides alter the conformation of the alpha 1 and alpha 2 domains of the heavy chain and that this in turn affects the recognition of Kb by antibody. An alternative hypothesis is that solvent-exposed peptide side chains may prevent the antibody from binding the complex. Using a panel of 128 single-amino acid variants of a Kb-binding antigenic peptide from ovalbumin we show that for most Kb-specific antibodies, the second idea is more likely. Those variants which prevent antibody binding are at solvent exposed positions, and in general, the bulkier the side chain, the greater the inhibition of antibody binding. However, in the case of two antibodies, 100.30 and 34.4.20, the peptide residues which affect antibody recognition are buried, suggesting that these antibodies see an alternate conformation of the peptide/MHC complex.

Formalin inactivation of vesicular stomatitis virus impairs T-cell- but not T-help-independent B-cell responses

The effects of formalin on the infectivity and immunogenicity of vesicular stomatitis virus (VSV) serotype Indiana were investigated. We found that formalin inactivation of VSV prevents infection of Vero cells in a concentration- and time-dependent manner, as shown by fluorometric cell analysis and inhibition of plaque formation. Inactivated VSV failed to induce significant cytotoxic T-lymphocyte responses in vivo or after restimulation in vitro. In contrast, the early immunoglobulin M (IgM) response, which is T help independent in the VSV system, was unaltered, suggesting normal antigenicity for and induction of B cells. However, no switch to IgG occurred, demonstrating failure of induction of T help. If cross-reactive T help was provided by previous infection with a second serotype of VSV (New Jersey), the IgG response was almost completely restored, confirming that the absence of IgG was due to lack of T help. A formalin-treated preparation of glycoprotein of VSV led to a delayed but otherwise normal IgG response, whereas treatment of VSV with UV light or beta-propiolactone reduced IgG titers to the same extent as did formalin. These results suggest that loss of infectivity and the ensuing lack of amplification of viral antigens of formaldehyde-inactivated VSV is the major factor impairing induction of specific T-helper cell responses.

Positive selection of the T-cell repertoire is affected by mutations in the peptide-binding site of MHC class I molecules

H-2Kb mutant molecules (H-2Kbm) and the H-2Kb-restricted response to OVA and VSV N peptides were used to investigate the influence of polymorphism of structurally defined regions of the MHC class I molecules on intrathymic positive selection of the T-cell repertoire. We show that the positive selection of the T-cell repertoire in the thymus requires the self-peptide to be present in the MHC antigen-binding site. A correlation between the ability of four MHC molecules to present antigenic peptide and to positively select T cells specific for it was noted. The self-peptides involved in positive selection may therefore mimic the foreign peptide during intrathymic selection. A structural correlate of this mimicry may be a similar or identical binding requirement for the antigen-binding pocket(s)/residues of the MHC peptide-binding site.

Fewer protective cytotoxic T-cell epitopes than T-helper-cell epitopes on vesicular stomatitis virus

Cytotoxic T-lymphocyte (CTL) and T-helper-cell responses in various mouse strains were monitored. Protective CTL responsiveness against three proteins of vesicular stomatitis virus was H-2 linked and inducible only in half of the 15 combinations tested (each of five H-2 haplotypes combined with each of three viral proteins), whereas biologically relevant T-helper-cell responses were inducible in all. This suggests that vesicular stomatitis virus exhibits more T-helper-cell than CTL epitopes.

The proportion of herpes simplex virus-specific cytotoxic T lymphocytes (Tc) that recognize glycoprotein C varies between individual mice and is dependent on the form of immunization

In mice the immune response to HSV-1 includes a brisk Tc response that is intimately associated with the control of infection. This report evaluated the Tc response to gC, one of the envelope glycoproteins of HSV-1. This protein was recognized as a target antigen for Tc from HSV-1 immune mice only if they expressed the H-2Kb MHC allele. However, even within these "responder" strains of mice the proportion of gC specific Tc was highly variable. The failure of HSV-induced Tc to recognize gC in the context of other class 1 MHC haplotypes (H-2d and H-2k) was demonstrable at the clonal level and could not be attributed to peculiarities of the recombinant constructs. Surprisingly, despite the inability of H-2k-restricted, HSV-1-induced Tc to recognize gC, when a vaccinia gC virus construct was used to immunize H-2k strains of mice it showed a variable ability to induce memory Tc populations capable of lysing HSV-1-infected autologous cells. Of added importance was the correlation of this induced Tc response with optimum protection against subsequent challenge with HSV-1. This demonstrated that despite the presence of suitable epitopes, the context of the immunogen would also influence its ability to induce Tc. Consequently, the potential repertoire of available HSV-1-specific Tc specificities is larger than indicated by studying animals immunized with HSV.

Susceptibility to measles virus-induced encephalitis in mice correlates with impaired antigen presentation to cytotoxic T lymphocytes

In measles virus (MV) infection in humans, meningitis and encephalitis are important complications. However, little is known of the pathogenesis of MV encephalitis, in particular about the role of the immune response. We have examined the role of cytotoxic T lymphocytes (CTL) in a mouse model of MV-induced encephalitis. We report here that the resistance of inbred strains of mice to MV-induced encephalitis correlated with the major histocompatibility complex (MHC) haplotype and that only resistant mouse strains mounted an effective CTL response to MV. Mice with low susceptibility to MV infection, such as the BALB/c strain (H-2d), generated CTL, whereas the highly susceptible strains, C3H (H-2k) and C57BL/6 (H-2b), revealed very poor CTL responses. MV-induced CTL were usually CD8+, and the generation of these cells was independent of the route of inoculation or the time postinfection. CD4+ T cells were generally only weakly lytic. The nucleocapsid protein was the major target antigen for CTL in BALB/c mice, although in some experiments the hemagglutinin was also recognized. CTL from C3H and C57BL/6 mice did not lyse MV-infected target cells. However, targets infected with vaccinia virus recombinants expressing the nucleocapsid protein or hemagglutinin were lysed, but levels of cytotoxicity were still low. Experiments using target cells transfected with single MHC class I genes suggested inefficient antigen presentation of MV proteins by the MHC molecules of the H-2k and H-2b haplotypes.

Skin test to assess virus-specific cytotoxic T-cell activity

A way to assess specific CD8+ T-cell activity in a skin test analogous to the conventional delayed-type hypersensitivity (DTH) reaction for CD4+ T cells is presented. Local injection of viral class I binding peptides caused a specific CD8+ T-cell-mediated DTH in footpads of virally infected mice. The DTH was inducible only during the acute phase of the infection. Apparently because of the short half-life of locally available peptide, only activated CD8+ effector T cells could mediate the reaction. This skin test may prove to be particularly interesting for use in humans to evaluate the activation status of CD8+ T cells during acute viral infections and of memory CD8+ T cells, for example, in chronically active immunopathological disease or infection.

Induction of cytotoxic T cells to a cross-reactive epitope in the hepatitis C virus nonstructural RNA polymerase-like protein

Cytotoxic T lymphocytes (CTL) have been found to mediate protection in vivo against certain virus infections. CTL also may play an important role in control of infection by hepatitis C virus (HCV), but no CTL epitopes have yet been defined in any HCV protein. The nonstructural protein with homology to RNA polymerase should be a relatively conserved target protein for CTL. To investigate the epitope specificity of CTL specific for this protein, we used 28 peptides from this sequence to study murine CTL. Mice were immunized with a recombinant vaccinia virus expressing the HCV nonstructural region corresponding to the flavivirus NS5 gene (RNA polymerase), and the primed spleen cells were restimulated in vitro with peptides. CTL from H-2d mice responded to a single 16-residue synthetic peptide (HCV 2422 to 2437). This relatively conserved epitope was presented by H-2d class I major histocompatibility complex (MHC) molecules to conventional CD4- CD8+ CTL but was not recognized by CTL restricted by H-2b. Moreover, exon shuffle experiments using several transfectants expressing recombinant Dd/Ld and Kd demonstrated that this peptide is seen in association with alpha 1 and alpha 2 domains of the Dd class I MHC molecule. This peptide differs from the homologous segments of this nonstructural region from three other HCV isolates by one residue each. Variant peptides with single amino acid substitutions were made to test the effect of each residue on the ability to sensitize targets. Neither substitution affected recognition. Therefore, these conservative mutations affected peptide interaction neither with the Dd class I MHC molecule nor with the T-cell receptor. Because these CTL cross-react with all four sequenced isolates of HCV in the United States and Japan, if human CTL display similar cross-reactivity, this peptide may be valuable for studies of HCV diagnosis and vaccine development. Our study provides the first evidence that CD8+ CTL can recognize an epitope from the HCV sequence in association with a class I MHC molecule.

Immune response to the nominal phosphoprotein of rabies virus

The immune response to the nominal phosphoprotein (NS protein) of rabies virus was investigated with the use of a vaccinia recombinant virus that expressed the NS protein of a fixed rabies virus strain. Mice of the H-2k haplotype that were injected with either live rabies virus or the vaccinia recombinant virus developed a strong cytolytic T-cell response specific for the NS protein. This response was under immune response (Ir) gene control. The NS protein as presented by the vaccinia recombinant virus was a poor inducer of rabies virus-specific T-helper (Th) cells and B cells in the H-2k background. Furthermore, mice of the H-2k haplotype could not be protected by vaccination with the vaccinia recombinant virus expressing the NS protein, although protection in outbred mice was partial and incomplete. These data indicate that cytolytic T cells to the NS protein of rabies virus are insufficient to protect mice against a challenge with rabies virus.

Vesicular stomatitis virus antigenic octapeptide N52-59 is anchored into the groove of the H-2Kb molecule by the side chains of three amino acids and the main-chain atoms of the amino terminus

This study describes an analysis of the interaction of individual amino acid residues of the vesicular stomatitis virus (VSV) nucleocapsid antigenic octapeptide (N52-59; Arg-Gly-Tyr-Val-Tyr-Gln-Gly-Leu) with the H-2Kb molecule and T-cell receptors (TCRs). Tyr-3, Tyr-5, and Leu-8 were the positions in the peptide found to be H-2Kb contact residues by analyzing single alanine-substituted peptides in a competition assay with a Kb-restricted antigenic nonapeptide of Sendai virus. Arg-1, Gly-2, Val-4, Gln-6, and Gly-7 of the peptide were identified as putative TCR contact residues by testing the peptide analogs for their capacity to sensitize targets for VSV-specific cytolytic T-lymphocyte clones. The octamer N52-59 was the optimal length of the peptide required for binding to Kb. This peptide length requirement and the finding of an irregular interspersing of major histocompatibility complex and TCR contact residues are most consistent with the conclusion that the peptide is in an extended conformation in the antigen binding groove. Furthermore, data on binding of truncated peptides show that, although the Arg-1 side chain has been assigned as a TCR contact residue, the main-chain atoms of the N-terminal amino group are most likely involved in interacting with the major histocompatibility complex molecule. A panel of H-2Kb point mutants was constructed to explore the effect of altered amino acid residues on the binding of N52-59. Mutants with amino acid substitutions along the floor of the groove all bound the VSV peptide but modulated its interaction with Kb, apparently causing subtle changes in the spatial arrangement of some specific TCR contact residues in the peptide.

An endogenous antigenic peptide bypasses the class I antigen presentation defect in RMA-S

The RMA-S cell line was derived from the Raucher virus-induced murine cell line RBL-5 by ethylmethane sulfonate mutagenesis and anti-H-2 antibody plus complement selection (Ljunggren, H.-G., and K. Karre. 1985. J. Exp. Med. 162:1745). RMA-S is defective in the ability to present endogenously synthesized antigens to class I major histocompatibility complex (MHC)-restricted cytotoxic T lymphocytes (CTL) (Townsend, A., C. Ohlen, J. Bastin, H.-G. Ljunggren, L. Foster, and K. Karre. 1989. Nature [Lond.]. 340:443; Ohlen, C., J. Bastin, H.-G. Ljunggren, L. Foster, E. Wolpert, G. Klein, A. R. M. Townsend, and K. Karre. 1990. J. Immunol. 145:52). This defect has been attributed to the inability of RMA-S to deliver antigenic peptides derived from antigens in the cytosol into the endoplasmic reticulum (ER), where they can associate with class I MHC molecules (Townsend, A., C. Ohlen, J. Bastin, H.-G. Ljunggren, L. Foster, and K. Karre. 1989. Nature [Lond.]. 340:443). We show that RMA-S can present at least one endogenous antigen, vesicular stomatitis virus nucleoprotein (VSV-N), to class I MHC-restricted CTL. RMA-S presents VSV-N to CTL both when infected with VSV or transfected with the VSV nucleoprotein gene. The natural antigenic VSV nucleoprotein peptides purified from either RMA or RMA-S are indistinguishable when analyzed by high performance liquid chromatography. We also show that the genetic defect responsible for the RMA-S phenotype maps to the murine chromosome 17. This chromosome encodes the murine class I MHC genes as well as two genes, HAM-1 and -2, with homology to the adenosine triphosphate-dependent transporter superfamily (Monaco, J. J., S. Cho, and M. Attaya. 1990. Science [Wash. DC]. 250:1723). These results suggest that the system that delivers antigenic peptides from the cytosol to the ER in RMA-S may still be present and retain partial function.