Cytotoxic T lymphocyte recognition of the influenza hemagglutinin gene product expressed by DNA-mediated gene transfer

A chimeric haemagglutinin-based universal influenza virus vaccine boosts human cellular immune responses directed towards the conserved haemagglutinin stalk domain and the viral nucleoprotein

BACKGROUND

The development of a universal influenza virus vaccine, to protect against both seasonal and pandemic influenza A viruses, is a long-standing public health goal. The conserved stalk domain of haemagglutinin (HA) is a promising vaccine target. However, the stalk is immunosubdominant. As such, innovative approaches are required to elicit robust immunity against this domain. In a previously reported observer-blind, randomised placebo-controlled phase I trial (NCT03300050), immunisation regimens using chimeric HA (cHA)-based immunogens formulated as inactivated influenza vaccines (IIV) -/+ AS03 adjuvant, or live attenuated influenza vaccines (LAIV), elicited durable HA stalk-specific antibodies with broad reactivity. In this study, we sought to determine if these vaccines could also boost T cell responses against HA stalk, and nucleoprotein (NP).

METHODS

We measured interferon-γ (IFN-γ) responses by Enzyme-Linked ImmunoSpot (ELISpot) assay at baseline, seven days post-prime, pre-boost and seven days post-boost following heterologous prime:boost regimens of LAIV and/or adjuvanted/unadjuvanted IIV-cHA vaccines.

FINDINGS

Our findings demonstrate that immunisation with adjuvanted cHA-based IIVs boost HA stalk-specific and NP-specific T cell responses in humans. To date, it has been unclear if HA stalk-specific T cells can be boosted in humans by HA-stalk focused universal vaccines. Therefore, our study will provide valuable insights for the design of future studies to determine the precise role of HA stalk-specific T cells in broad protection.

INTERPRETATION

Considering that cHA-based vaccines also elicit stalk-specific antibodies, these data support the further clinical advancement of cHA-based universal influenza vaccine candidates.

FUNDING

This study was funded in part by the Bill and Melinda Gates Foundation (BMGF).

The DRiP hypothesis decennial: support, controversy, refinement and extension

In 1996, to explain the rapid presentation of viral proteins to CD8+ T cells, it was proposed that peptides presented by MHC class I molecules derive from defective ribosomal products (DRiPs), presumed to be polypeptides arising from in-frame translation that fail to achieve native structure owing to inevitable imperfections in transcription, translation, post-translational modifications or protein folding. Here, we consider findings that address the DRiP hypothesis, and extend the hypothesis by proposing that cells possess specialized machinery, possibly in the form of "immunoribosomes", to couple protein synthesis to antigen presentation.

Cross-reactive, cell-mediated immunity and protection of chickens from lethal H5N1 influenza virus infection in Hong Kong poultry markets

In 1997, avian H5N1 influenza virus transmitted from chickens to humans resulted in 18 confirmed infections. Despite harboring lethal H5N1 influenza viruses, most chickens in the Hong Kong poultry markets showed no disease signs. At this time, H9N2 influenza viruses were cocirculating in the markets. We investigated the role of H9N2 influenza viruses in protecting chickens from lethal H5N1 influenza virus infections. Sera from chickens infected with an H9N2 influenza virus did not cross-react with an H5N1 influenza virus in neutralization or hemagglutination inhibition assays. Most chickens primed with an H9N2 influenza virus 3 to 70 days earlier survived the lethal challenge of an H5N1 influenza virus, but infected birds shed H5N1 influenza virus in their feces. Adoptive transfer of T lymphocytes or CD8(+) T cells from inbred chickens (B(2)/B(2)) infected with an H9N2 influenza virus to naive inbred chickens (B(2)/B(2)) protected them from lethal H5N1 influenza virus. In vitro cytotoxicity assays showed that T lymphocytes or CD8(+) T cells from chickens infected with an H9N2 influenza virus recognized target cells infected with either an H5N1 or H9N2 influenza virus in a dose-dependent manner. Our findings indicate that cross-reactive cellular immunity induced by H9N2 influenza viruses protected chickens from lethal infection with H5N1 influenza viruses in the Hong Kong markets in 1997 but permitted virus shedding in the feces. Our findings are the first to suggest that cross-reactive cellular immunity can change the outcome of avian influenza virus infection in birds in live markets and create a situation for the perpetuation of H5N1 influenza viruses.

Incomplete CD8(+) T lymphocyte differentiation as a mechanism for subdominant cytotoxic T lymphocyte responses to a viral antigen

CD8(+) cytotoxic T lymphocytes (CTLs) recognize antigen in the context of major histocompatibility complex (MHC) class I molecules. Class I epitopes have been classified as dominant or subdominant depending on the magnitude of the CTL response to the epitope. In this report, we have examined the in vitro memory CTL response of H-2(d) haplotype murine CD8(+) T lymphocytes specific for a dominant and subdominant epitope of influenza hemagglutinin using activation marker expression and staining with soluble tetrameric MHC-peptide complexes. Immune CD8(+) T lymphocytes specific for the dominant HA204-210 epitope give rise to CTL effectors that display activation markers, stain with the HA204 tetramer, and exhibit effector functions (i.e., cytolytic activity and cytokine synthesis). In contrast, stimulation of memory CD8(+) T lymphocytes directed to the subdominant HA210-219 epitope results in the generation of a large population of activated CD8(+) T cells that exhibit weak cytolytic activity and fail to stain with the HA210 tetramer. After additional rounds of restimulation with antigen, the HA210-219-specific subdominant CD8(+) T lymphocytes give rise to daughter cells that acquire antigen-specific CTL effector activity and transition from a HA210 tetramer-negative to a tetramer-positive phenotype. These results suggest a novel mechanism to account for weak CD8(+) CTL responses to subdominant epitopes at the level of CD8(+) T lymphocyte differentiation into effector CTL. The implications of these findings for CD8(+) T lymphocyte activation are discussed.

Db-binding peptides from influenza virus: effect of non-anchor residues on stability and immunodominance

Relative affinities were determined for the interaction of H-2Db with all the peptides from the A/PR/8/34 strain of influenza virus that contained the Db-binding motif. The results indicated that, even though 23 peptides with the appropriate motif were identified and analysed, binding of only five of them could be detected at peptide concentrations lower than 10(-7) M. Of these five, only one, TGICNQNII, bound with better affinity than the nucleoprotein-derived natural epitope, ASNENMETM. The origin of the higher binding peptide was the influenza neuraminidase, a protein for which little cytosolic processing would be expected since it is a surface glycoprotein. To establish why many of the influenza-derived peptides did not bind, the role of non-anchor residues on Db-peptide interactions was analysed, using a scheme where QDIENEEKI, a non-binding peptide from the influenza virus polymerase 1, was sequentially converted to ASNENMETI, which binds to Db with an affinity similar to that of ASNENMETM. Although all positions examined influenced peptide binding, peptide residue no. 2 (P2) was of particular importance. Therefore, each of the 20 naturally occurring amino acids were inserted at this position to investigate their effects on peptide-MHC interaction. The results indicated that amino acids having side chains with charged or ring structures were deleterious, while non-polar and polar residues were either neutral or facilitated binding to different degrees. Our data also indicated that every residue of the peptide contributes to the stability of the MHC-peptide complex, and the final affinity is dependent on the nature of the amino acids at each position, not just on those at a small number of anchor positions. The results also suggested that increased stability, as indicated by the half-life of the peptide-MHC class I complex, might play an important role in selecting the immunodominant epitope.

Characteristics of cytotoxic T lymphocytes directed to influenza virus haemagglutinin elicited by immunization with muramyldipeptide-influenza liposome vaccine

We examined the characterization of the antiviral T lymphocytes elicited by immunization with a novel liposome vaccine (MDP-virosome) constructed with synthetic muramyldipeptide; [6-0-(2-tetradecylhexadecanoyl)-N-acetylmuramyl-L-alanyl-D-isoglutamine] , cholesterol, influenza virus haemagglutinin and neuraminidase. The haemagglutinin glycoprotein first appeared to induce a significant subtype-specific cytotoxic activity through its arrangement on the inner and outer surfaces of the MDP-virosome. Splenocytes of BALB/c mice immunized with the virosome vaccine containing H3 haemagglutinin and N2 neuraminidase from human Hong Kong virus markedly lysed H3N2 virus-infected target cells, but not those infected with virus possessing a different subtype such as H1N1 surface antigens. Exposure of these splenic lymphocytes to virus antigen in vitro further enhanced their cytotoxic activity. The cytotoxic lymphocytes generated by the MDP-virosome vaccine expressed Thy 1 and CD4 antigens on their cell surface, and these activities were restricted by class II histocompatibility gene products. The marked reduction of pulmonary virus titres in infected mice caused by transferred immune spleen cells suggested that the MDP-virosome vaccination is able to protect against influenza virus infection through enhanced cellular immune responses.

Protective cross-reactive epitope on the nonstructural protein NS1 of influenza A virus

We reported previously that adoptive immunization with an influenza A virus NS1-specific H-2Ld-restricted, cross-reactive, CTL clone A-11 established by stimulation with A/PR/8/34 virus (H1N1) reduced lung virus titers in mice challenged with virus in vivo (Virology 178:174-179, 1990). Using a set of recombinant vaccinia virus constructs containing truncated portions of the NS gene we have localized this cross-protective CTL epitope to the N-terminal region of the NS1 protein. This region of NS1 is active in inducing CD8+ CTL in vivo because virus-stimulated BALB/c immune spleen cells in bulk cultures also recognized the N-terminal region of the NS1 protein.

Characterization of two distinct major histocompatibility complex class I Kk-restricted T-cell epitopes within the influenza A/PR/8/34 virus hemagglutinin

Cytotoxic T-lymphocyte (CTL) clones specific for the influenza A/PR/8/34 virus hemagglutinin (HA) were isolated by priming CBA mice with a recombinant vaccinia virus expressing the HA molecule. The epitopes recognized by two of these clones, which were CD8+, Kk restricted, and HA subtype specific, were defined by using a combination of recombinant vaccinia viruses expressing HA fragments and synthetic peptides. One epitope is in the HA1 subunit at residues 259 to 266 (numbering from the initiator methionine), amino acid sequence FEANGNLI, and the other epitope is in the HA2 subunit at residues 10 to 18 (numbering from the amino terminus of the HA2 subunit), sequence IEGGWTGMI. These two peptides are good candidates for naturally processed HA epitopes presented during influenza infection, as they are the same length (eight and nine residues) as other naturally processed viral peptides presented to CTL. A comparison of the sequences of these two new epitopes with those of the three previously published Kk-restricted T-cell epitopes showed some homology among all of the epitopes, suggesting a binding motif. In particular, an isoleucine residue at the carboxy-terminal end is present in all of the epitopes. On the basis of this homology, we predicted that the Kk-restricted epitope in influenza virus nucleoprotein, previously defined as residues 50 to 63, was contained within residues 50 to 57, sequence SDYEGRLI. This shorter peptide was found to sensitize target cells at a 200-fold lower concentration than did nucleoprotein residues 50 to 63 when tested with a CTL clone, confirming the alignment of Kk-restricted epitopes.

Identification of an epitope encoded in the env gene of Friend murine leukemia virus recognized by anti-Friend virus cytotoxic T lymphocytes

We have previously shown that strong epitopes recognized by anti-Friend virus (FV) cytotoxic T lymphocytes (CTL) in H-2b mice are encoded in both the env and gag/pol regions of the helper friend leukemia virus genome. Two approaches have been used to identify these epitopes. At the nucleic acid level, we have constructed env genes with either of two in-frame deletions: pKR2, an env gene with a 681-bp deletion in the gp70 region and inserted into the pSV2-gpt-1 expression vector; and pKR1, an env gene with an 81-bp deletion in the p15E region and inserted into pSV2-gpt-1. Cell clones were established by transfecting Fisher rat embryo cells with pDb (the H-2Db restriction element), pNEO (for G418 selection) and either pKR1 or pKR2. Db and env gene expression was monitored by immunoprecipitation with polyclonal antibodies or by detection of viral RNA on Northern blots. Expressor cell clones were tested for susceptibility to lysis by polyclonal anti-FV/Db CTL in 51Cr-release assays. Whereas cells expressing pKR1 were lysed to the same extent as cells expressing the intact env gene, cells expressing pKR2 were resistant to lysis, suggesting that all detectable env epitopes are encoded within the 681-bp deletion. Polypeptides representing the two most likely candidate epitopes encoded in this segment were synthesized and tested for their abilities to sensitize FRE cells expressing Db alone for lysis by the CTL. One 17-mer polypeptide, AGTGDRLLNLVQGAYQA [corrected], functioned as a strong CTL epitope in this assay, but the other 18-mer polypeptide was inactive. Studies of the role of this epitope in the immune response to candidate viral vaccines are in progress.

Class I major histocompatibility complex-restricted T lymphocyte recognition of the influenza hemagglutinin. Overlap between class I cytotoxic T lymphocytes and antibody sites

The influenza hemagglutinin is a critical regulator of disease expression during influenza virus infection and serves as a major target for the host immune response to this pathogen. In this report, we have analyzed an immunodominant site on the hemagglutinin (residues 202-221) recognized by murine class I MHC-restricted T lymphocytes. This analysis has revealed evidence for the duplication of a T cell recognition site within the region 202-221. We have also identified critical amino acids necessary for class I-restricted T cell recognition within these two epitopes. In addition, we provide evidence that a site on the influenza hemagglutinin recognized by neutralizing antibody directly overlaps with an epitope recognized by class I MHC-restricted CTL.

A 15 amino acid fragment of influenza nucleoprotein synthesized in the cytoplasm is presented to class I-restricted cytotoxic T lymphocytes

A recombinant vaccinia has been designed to express amino acids 366-379 of influenza nucleoprotein, previously shown to be the minimal epitope recognized by a class I-restricted cytotoxic T cell clone. Target cells infected with the recombinant vaccinia virus expressing this peptide are recognized by CTL as efficiently as target cells expressing the complete nucleoprotein. The results imply the existence of a peptide transport system that constitutively passes the products of degraded proteins from the cytoplasm into a membrane-bound compartment of the cell.

Recognition of the PB1, neuraminidase, and matrix proteins of influenza virus A/NT/60/68 by cytotoxic T lymphocytes

We have investigated the recognition of the PB1, neuraminidase, and matrix (M1) proteins of influenza virus A/NT/60/68 (H3N2 subtype) by secondary in vitro stimulated polyclonal cytotoxic T lymphocyte (CTL) populations. While these three proteins have different functions and cellular locations, they can all be recognized as target antigens. However, the immunogenicity of these proteins for CTLs is under strict genetic control. Thus, PB1 protein is recognized as a cross-reactive target antigen by CTLs raised in CBA (H-2k) but not BALB/c (H-2d) mice. CBA, but not BALB/c mice, also generate a low-level CTL response to the neuraminidase. This latter response was only detectable following in vivo priming of CBA mice with a recombinant vaccinia virus expressing neuraminidase (N2-VACC). The matrix protein, expressed from recombinant vaccinia virus M-VACC, was not recognized as an antigen by CTL generated from either CBA or BALB/c strains of mice. By contrast, human HLA-A2-restricted influenza virus-specific CTLs were shown to recognize this matrix protein as a target antigen. Endogenous expression of as little as 90 amino acids of the matrix protein was sufficient to render target cells susceptible to lysis by such CTLs.

Active immunization against virus infections due to antigenic drift by induction of crossreactive cytotoxic T lymphocytes

We have examined whether active immunization with c13 protein, a hybrid protein of the first 81 amino acids of the viral NS1 nonstructural protein and the HA2 subunit of A/PR/8 (H1N1) hemagglutinin, could protect BALB/c mice from challenge with A/PR/8 H1 subtype virus. Mice immunized with the c13 protein had a significant reduction of pulmonary virus titers with A/PR/8 (H1) virus, but failed to limit the replication of A/PC (H3) virus, which reflects the in vitro CTL activity of c13 immune spleen cells. We observed that the epitope recognized by HA2 specific CTL, which are induced by a derivative of c13 protein, is highly conserved among H1 and H2 subtype virus strains. This led us to test whether active immunization with c13 protein would also limit pulmonary virus replication in mice infected with the A/TW virus, a virus of the H1 subtype, which was isolated in 1986, and with a virus of the H2 subtype, A/Japan/305/57. Immunized mice had significantly lower lung virus titers than did control mice, and did not possess any neutralizing antibodies to the challenger viruses. These results indicate that active immunization with a fusion protein containing the cross-reactive CTL epitope protects mice from influenza infection by inducing CTL against influenza A H1 and H2 subtype virus strains, which markedly vary in their antibody binding sites on the HA1. The ability to induce active cross-reactive immunization with a fusion protein which contains a highly conserved CTL epitope offers a model for vaccine approaches against viruses which undergo significant variations in their antibody binding sites.

Class I major histocompatibility complex-restricted cytolytic T lymphocytes recognize a limited number of sites on the influenza hemagglutinin

Two distinct regions of the influenza A/JAP/305/57 hemagglutinin molecule are identifiable as sites recognized by murine class I major histocompatibility complex (MHC) (H-2d)-restricted cytolytic T lymphocytes (CTL) generated in response to immunization with infectious type A influenza virus. Each of these sites can be mimicked by a synthetic oligopeptide of approximately 20 amino acids. Data presented herein indicate that these two sites define the dominant immunogenic epitopes on the hemagglutinin recognized by H-2Kd-restricted CTL. These same sites are not efficiently recognized by hemagglutinin-specific class I MHC-restricted CTL of several unrelated MHC haplotypes. These observations show that even for a large complex glycoprotein molecule like the influenza hemagglutinin, only a limited number of class I CTL recognition sites are generated in the infected cell and that the subset of immunogenic epitopes is dependent on the MHC haplotype of the responding individual. These parameters need to be considered in the design of synthetic and recombinant vaccines.

Class I MHC-restricted cytotoxic T cells efficiently recognize haemagglutinin that is defective in protein folding and cell surface expressions

Cytotoxic T-cell recognition of an engineered variant of the influenza viral haemagglutinin (HA), expressed in vaccinia virus, was investigated. We show that the insertion of a Foot-and-Mouth Disease virus (FMDV) immunogenic peptide into the HA results in major disruption of its higher order structure with intracellular rather than cell surface localization accompanying the loss of conformational epitopes detected by antibody. In contradistinction to antibody, recognition of the chimaeric molecule by HA-specific class I-restricted cytotoxic T-cells was unimpaired, demonstrating that class I-specific T-cells recognize, in majority, continuous epitopes rather than conformational epitopes in the HA.

Effect of mutations and variations of HLA-A2 on recognition of a virus peptide epitope by cytotoxic T lymphocytes

Cytotoxic T lymphocytes (CTL) specific for influenza A virus were prepared from 15 donors. Those with HLA-A2 recognized autologous or HLA-A2-matched B-lymphoblastoid cells in the presence of synthetic peptide representing residues 55-73 or 56-68 of the virus matrix protein sequence. Influenza A virus-specific CTL from donors without HLA-A2 or with an HLA-A2 variant type failed to respond to this peptide. CTL lines specific for HLA-A2 plus peptide did not lyse peptide-treated target cells from HLA-A2 variant donors. They also failed to lyse peptide-treated cells with point mutations that had been inserted into HLA-A2 at positions 62-63, 66, 152, and 156 and, in some instances, mutations at positions 9 and 70. CTL lysed peptide-treated target cells with mutations in HLA-A2 at positions 43, 74, and 107. The results imply that this defined peptide epitope therefore interacts with HLA-A2 in the binding groove so that the long alpha-helices of HLA-A2 make important contact with the peptide at positions 66, 152, and 156. Different amino acids at position 9, which is in the floor of the peptide binding groove of HLA-A2 and the closely related position 70, modulate the peptide interaction so that some T-cell clones react and some do not.

A region of the influenza A/NT/60/68 PB2 protein containing an antigenic determinant recognized by murine H-2Dd restricted cytotoxic T lymphocytes

We have used a recombinant vaccinia virus to investigate the recognition of the PB2 protein of influenza A/NT/60/68 (H3N2) by murine polyclonal CTL populations. PB2 is recognized as a major cross-reactive target antigen. Recognition of PB2 is under strict genetic control, since BALB/c (H-2d) but not CBA (H-2k) mice are responders. We also demonstrate, by use of cell lines transfected with individual genes encoding class I molecules of the H-2d haplotype, that recognition of PB2 occurs in conjunction with the H-2Dd but not the H-2Kd or H-2Ld molecules. In contrast, recognition of the nucleoprotein of A/PR/8/34 by BALB/c-derived polyclonal CTL is restricted via the H-2Kd molecule. By using three recombinant vaccinia viruses expressing deleted forms of the PB2 protein we show that at least one epitope of the PB2 protein resides within the amino-terminal 256 amino acids. This approach offers an effective method to map the regions of large proteins containing epitopes recognized by CTL.

Development and testing of AIDS vaccines

Recent advances in delineating the molecular biology of human immunodeficiency virus type 1 (HIV-1) have led to innovative approaches to development of a vaccine for acquired immunodeficiency syndrome (AIDS). However, the lack of understanding of mechanisms of protective immunity against HIV-1, the magnitude of genetic variation of the virus, and the lack of effective animal models for HIV-1 infection and AIDS have impeded progress. The testing of AIDS vaccines also presents challenges. These include liability concerns over vaccine-related injuries; identification of suitable populations for phase 3 efficacy studies; balancing the ethical obligation to counsel research subjects to avoid high-risk behavior with the necessity to obtain vaccine efficacy data; and the effect of vaccine-induced seroconversion on the recruiting and welfare of trial volunteers. Several candidate AIDS vaccines are nevertheless currently under development, and some are undergoing phase 1 clinical trials. Rapid progress will depend on continued scientific advancement in conjunction with maximum use of resources, open information and reagent exchange, and a spirit of international collaboration.

New approaches to animal vaccines utilizing genetic engineering

Control of infectious diseases in livestock is an important determinant in the success of a nation's effort to efficiently meet its need for animal products. Genetic engineering offers many new options in the design of animal vaccines. Monoclonal antibodies, DNA cloning, recombination, and transfection are examples of techniques that facilitate innovative strategies in antigen identification, production, and delivery. This article reviews the use of genetic engineering in the production of vaccines directed against foot-and-mouth disease virus and other important pathogens of animals. The advantages and disadvantages of vaccines produced through the use of genetic engineering are discussed.

Synthesis and cellular location of the ten influenza polypeptides individually expressed by recombinant vaccinia viruses

A complete set of recombinant vaccinia viruses that express each of the influenza virus polypeptides has been constructed. PB1, PB2, PA, HA, NP, M1, and NS1 genes were derived from influenza virus A/PR/8/34, NA from influenza virus A/Cam/46, and M2 and NS2 genes from influenza virus A/Udorn/72. Cells infected with these recombinant viruses synthesize influenza polypeptides that are precipitable with specific antisera and that have electrophoretic mobilities similar to the corresponding influenza virus polypeptides. Indirect immunofluorescence studies have shown that HA, NA, and MS2 proteins migrate to the cell surface; PB2, PB1, PA, NP, and NS1 proteins migrate to the cell nucleus; and M1 and NS2 are distributed throughout the cell, although NS2 accumulates preferentially in nuclei. These transport processes occurred independently of other influenza polypeptides and are therefore attributable to the intrinsic properties of the influenza polypeptides themselves.

On the role of the transmembrane anchor sequence of influenza hemagglutinin in target cell recognition by class I MHC-restricted, hemagglutinin-specific cytolytic T lymphocytes

We have examined the requirement for the transmembrane hydrophobic anchor sequence of the influenza hemagglutinin (HA) in the formation of the antigenic moiety on the surface of target cells recognized by class I MHC-restricted murine CTL. For this analysis we have used a line of CV-1 monkey epithelial cells that express the transfected murine H-2Kd gene product as target cells and have used recombinant SV40-based late replacement vectors to achieve expression of genes encoding wild-type and mutant forms of HA. We have found that the majority of Kd-restricted HA-specific CTL clones recognize target cells that express a secreted HA molecule that lacks the transmembrane and cytoplasmic domains of the parent glycoprotein. Several Kd-restricted CTL clones that recognize subtype-specific and crossreactive epitopes on HA fail to recognize the anchor-negative, secreted HA or chimeric HA molecules containing the transmembrane and cytoplasmic domains of unrelated glycoproteins. These CTL clones appear to be directed to antigenic epitopes located within the transmembrane domain of HA, as defined by their capacity to recognize target cells sensitized with a synthetic 23-amino-acid peptide corresponding to sequences within this domain. The implications of these results for class I MHC-restricted CTL recognition are discussed.

Specific recognition of influenza virus polymerase protein (PB1) by a murine cytotoxic T-cell clone

Cytotoxic T-cell clones were raised in CBA mice that recognised both A/X31 and A/JAP/305/1957 influenza virus. Here, we describe one CTL clone that recognises target cells infected with a recombinant vaccinia virus expressing influenza PB1.

Mouse H-2k-restricted cytotoxic T cells recognize antigenic determinants in both the HA1 and HA2 subunits of the influenza A/PR/8/34 hemagglutinin

We have constructed two chimeric influenza hemagglutinin (HA) genes in which the HA1 and HA2 subunits of the HA molecule have been interchanged between influenza A/PR/8/34 (H1 subtype) and A/NT/60/68 (H3 subtype). These genes were used to construct recombinant vaccinia viruses that expressed intact chimeric HA. These recombinant viruses were used to test whether murine CTL recognize antigenic determinants in either the HA1, HA2, or both subunits. We found that both subunits of the HA molecule contain determinants for CTL. This implies that CTL have, at least in part, separate antigenic determinants from B lymphocytes, which recognize mainly epitopes within the HA1 subunit.

Anti-influenza virus cytotoxic T lymphocytes recognize the three viral polymerases and a nonstructural protein: responsiveness to individual viral antigens is major histocompatibility complex controlled

It has recently been shown that antiviral major histocompatibility complex class I-restricted cytotoxic T lymphocytes can recognize proteins that serve as internal viral structural components (influenza A virus nucleoprotein, vesicular stomatitis virus nucleocapsid protein). To further examine the role of internal viral proteins in cytotoxic T-lymphocyte recognition, we constructed recombinant vaccinia viruses containing individual influenza A virus genes encoding three viral polymerases (PB1, PB2, PA) and a protein not incorporated into virions (NS1). We found that cells infected with each of these recombinant vaccinia viruses could be lysed by anti-influenza cytotoxic T lymphocytes. Cytotoxic T-lymphocyte responsiveness to the individual viral antigens varied greatly between mouse strains. By using congenic mouse strains, responsiveness to PB1 and PB2 was found to cosegregate with major histocompatibility complex haplotype. These findings provide further evidence that internal antigens play a critical role in cytotoxic T-lymphocyte recognition of virus-infected cells. Additionally, they suggest that the cytotoxic T-lymphocyte response to viral antigens may often be restricted to only a fraction of the major histocompatibility complex class I repertoire.

Identification of viral molecules recognized by influenza-specific human cytotoxic T lymphocytes

Human cytotoxic T cells specific for influenza A virus were tested for recognition of each of the ten influenza A virus proteins expressed in target cells using recombinant vaccinia viruses. They recognized the matrix M1, polymerase PB2, and nucleoproteins of influenza virus in association with MHC class I antigens. These internal viral proteins were seen by CTL in conjunction with one or more of the available dependent HLA gene products. There was no detectable recognition of influenza virus surface glycoproteins in target cells.

Cytotoxic T lymphocytes recognize influenza haemagglutinin that lacks a signal sequence

A surprising feature of most cytotoxic T lymphocytes (CTL) responding to influenza infection is that they recognize the unglycosylated (non-transmembrane) proteins of the virus, including the nucleoprotein. Recognition of cells that express nucleoprotein by CTL does not depend on a definite signal sequence within the protein, and the epitopes recognized can be defined with short synthetic peptides in vitro. Haemagglutinin (HA), the major transmembrane protein of the virus, is recognized by a minor population of CTL from infected mice. We have deleted the sequence coding for the N-terminal signal peptide from a complementary DNA encoding HA of the H1 subtype. The signal-deleted HA is detected with antibodies as a short-lived, unglycosylated, intracellular protein. However, CTL raised to the complete molecule recognize cells expressing the signal-deleted HA and vice versa. These results cast doubts on the assumption that CTL recognize the HA molecule only after its insertion into the plasma membrane.

HLA B37 determines an influenza A virus nucleoprotein epitope recognized by cytotoxic T lymphocytes

Human influenza A virus-specific, cytotoxic T cells have been shown previously to recognize the virus nucleoprotein on infected cells. CTL preparations from four HLA B37-positive donors were shown to recognize a synthetic peptide that corresponded to amino acids 335-349 of the nucleoprotein sequence. Influenza-specific CTL from 10 donors of other HLA types failed to recognize this epitope. CD8+ CTL lines were derived from lymphocytes of two HLA B37-positive donors and used to show that the peptide was represented on virus-infected cells and to determine the probable boundaries of the epitope.

Influenza virus-specific cytotoxic T-cell recognition: stimulation of nucleoprotein-specific clones with intact antigen

The present study was undertaken to investigate the role of 'antigen processing' in influenza virus-specific cytotoxic T (Tc)-cell recognition. H-2 Db-restricted Tc-cell clones specific for the 1934 influenza nucleoprotein (NP) were tested in an in vitro proliferation assay for the recognition of intact virus, purified protein or peptide antigen. Inactivated virus required further 'processing', which was inhibited by either NH4Cl treatment or paraformaldehyde fixation of antigen-presenting cells (APC). Purified NP, by contrast, was readily presented by both normal peritoneal exudate cells and H-2 Db gene 'transfected' L cells. The response was not inhibited by either NH4Cl or prior paraformaldehyde treatment of APC. Peptone-induced peritoneal exudate cells presented ineffectively unless treated with NH4Cl or prefixed with paraformaldehyde. Comparison of the responses to either purified protein or a synthetic peptide implies that the epitope recognized by the three NP specific clones is not 'cryptic' and, therefore, that the purified protein, in this case, does not require 'processing'.

Herpes simplex virus (HSV)-specific human T-cell clones recognize HSV glycoprotein D expressed by a recombinant vaccinia virus

Human cytotoxic T-cell (CTL) clones that lyse autologous cells infected with herpes simplex virus (HSV) type 1 or 2 were generated by stimulating lymphocytes with a recombinant vaccinia virus (recombinant vaccinia-gD-1 virus) that expresses HSV type 1 glycoprotein D (gD-1). Furthermore, CTL clones generated with HSV type 1 or with cloned gD-1 lysed autologous cells infected with the recombinant vaccinia-gD-1 virus. Our findings thus showed that gD serves as a target antigen for human CTLs and that a recombinant vaccinia-gD virus activates HSV-specific human CTL.

VSV G protein induces murine cytolytic T lymphocytes

Mice immunized with vesicular stomatitis virus (VSV), with its glycoprotein (G) in lipid vesicles or with a truncated, soluble form of G called Gs, developed an expanded population of virus specific cytolytic T lymphocyte (CTL) precursors and also led to the production of neutralizing serum antibody. The CTL precursors could be restimulated in vitro with either the virus or its glycoprotein components. Thus the glycoprotein of VSV, either associated with lipids or in soluble form, induced both cellular and humoral immune responses that might be sufficient to result in protective immunity.

Low responder MHC alleles for Tc recognition of influenza nucleoprotein

Since virus nucleoprotein is an important target antigen for anti-influenza cytotoxic T cells (Tc), we examined the genetics of Tc responses to this single viral protein to find three nonresponder alleles (Dd, Dk, and Kb) in three haplotypes and their recombinants so far tested. B10.A(5R) mice bearing nonresponder MHC class I antigen in the D and K regions show no anti-NP Tc responses, however they do show a strong A-virus cross-reactive anti-influenza cytotoxicity. The high frequency of nonresponsiveness to a single viral component, as compared with the entire virus, has implications for the development of simple vaccines.

Recognition of cloned vesicular stomatitis virus internal and external gene products by cytotoxic T lymphocytes

It has generally been assumed that most if not all CTL specific for vesicular stomatitis virus (VSV)-infected cells recognize the viral glycoprotein (G), an integral membrane protein abundantly expressed on infected cell surfaces. Using recombinant vaccinia viruses containing copies of cloned VSV genes to examine CTL recognition of VSV, we have confirmed that G is recognized by VSV-specific CTL. More interestingly, however, we have also found that nucleocapsid protein (N), an internal virion protein, can be detected on infected cell surfaces using mAb, and serves as a major target antigen for VSV-specific CTL. In contrast to the highly serotype-specific recognition of G, N is recognized by a major population of CTL able to lyse cells infected with either the Indiana or New Jersey VSV serotypes. Using target cells expressing a cloned MHC class I gene, we could directly show that CTL recognition of N occurs in the context of the MHC Ld molecule.

Viral-restricted cytolytic T lymphocyte recognition of hybrid human-murine class I histocompatibility antigens

Hybrid human-murine major histocompatibility antigens have been constructed and expressed on the surface of both human RD and murine L cell lines after DNA mediated gene transfer. These antigens linked the polymorphic domains (alpha 1 and alpha 2) of H-2Kb and the carboxy-terminal domains (alpha 3, transmembrane, and intracellular) of HLA-A2. Previously we demonstrated that these antigens were serologically intact and were recognized by allospecific cytolytic T lymphocytes. However, the cell lines expressing the hybrid antigen were less well lysed than the native H-2Kb expressing cell lines. In this study, we extend these observations and demonstrate that virally restricted cytolytic T lymphocytes specific for vesicular stomatitis virus and for Sendai virus can recognize cell lines expressing the hybrid antigen, whether expressed on murine (L cell) or human (RD cell) lines. Furthermore, the data show a profound influence by the carboxy-terminal domains upon the polymorphic T-cell restricting epitopes.

Differences in antigen presentation to MHC class I-and class II-restricted influenza virus-specific cytolytic T lymphocyte clones

We have examined requirements for antigen presentation to a panel of MHC class I-and class II-restricted, influenza virus-specific CTL clones by controlling the form of virus presented on the target cell surface. Both H-2K/D- and I region-restricted CTL recognize target cells exposed to infectious virus, but only the I region-restricted clones efficiently lysed histocompatible target cells pulsed with inactivated virus preparations. The isolated influenza hemagglutinin (HA) polypeptide also could sensitize target cells for recognition by class II-restricted, HA-specific CTL, but not by class I-restricted, HA-specific CTL. Inhibition of nascent viral protein synthesis abrogated the ability of target cells to present viral antigen relevant for class I-restricted CTL recognition. Significantly, presentation for class II-restricted recognition was unaffected in target cells exposed to preparations of either inactivated or infectious virus. This differential sensitivity suggested that these H-2I region-restricted CTL recognized viral polypeptides derived from the exogenously introduced virions, rather than viral polypeptides newly synthesized in the infected cell. In support of this contention, treatment of the target cells with the lysosomotropic agent chloroquine abolished recognition of infected target cells by class II-restricted CTL without diminishing class I-restricted recognition of infected target cells. Furthermore, when the influenza HA gene was introduced into target cells without exogenous HA polypeptide, the target cells that expressed the newly synthesized protein product of the HA gene were recognized only by H-2K/D-restricted CTL. These observations suggest that important differences may exist in requirements for antigen presentation between H-2K/D and H-2I region-restricted CTL. These differences may reflect the nature of the antigenic epitopes recognized by these two CTL subsets.

Recognition of cloned influenza virus hemagglutinin gene products by cytotoxic T lymphocytes

The influenza A virus hemagglutinin (HA) is an integral membrane glycoprotein expressed in large quantities on infected cell surfaces and is known to serve as a target antigen for influenza virus-specific cytotoxic T lymphocytes (CTL). Despite the fact that HAs derived from different influenza A virus subtypes are serologically non-cross-reactive, the HA has been implicated by previous experiments to be a target antigen for the subset of T cells capable of lysing cells infected with any human influenza A subtype (cross-reactive CTL). To directly determine whether the HA is recognized by cross-reactive CTL, we used vaccinia virus recombinants containing DNA copies of the PR8 (A/Puerto Rico/8/34) (H1N1) or JAP (A/JAP/305) (H2N2) HA genes. When these viruses were used to stimulate HA-specific CTL and to sensitize target cells for lysis by HA-specific CTL, we found no evidence for HA recognition by cross-reactive CTL aside from a relatively small degree of cross-reactivity between H1 and H2 HAs. Results of unlabeled target inhibition studies were consistent with the conclusion that the HA is, at most, only a minor target antigen for cross-reactive CTL.