Use of synthetic peptides of influenza nucleoprotein to define epitopes recognized by class I-restricted cytotoxic T lymphocytes

A Host-Restricted Self-Attenuated Influenza Virus Provides Broad Pan-Influenza A Protection in a Mouse Model

Influenza virus infections can cause a broad range of symptoms, form mild respiratory problems to severe and fatal complications. While influenza virus poses a global health threat, the frequent antigenic change often significantly compromises the protective efficacy of seasonal vaccines, further increasing the vulnerability to viral infection. Therefore, it is in great need to employ strategies for the development of universal influenza vaccines (UIVs) which can elicit broad protection against diverse influenza viruses. Using a mouse infection model, we examined the breadth of protection of the caspase-triggered live attenuated influenza vaccine (ctLAIV), which was self-attenuated by the host caspase-dependent cleavage of internal viral proteins. A single vaccination in mice induced a broad reactive antibody response against four different influenza viruses, H1 and rH5 (HA group 1) and H3 and rH7 subtypes (HA group 2). Notably, despite the lack of detectable neutralizing antibodies, the vaccination provided heterosubtypic protection against the lethal challenge with the viruses. Sterile protection was confirmed by the complete absence of viral titers in the lungs and nasal turbinates after the challenge. Antibody-dependent cellular cytotoxicity (ADCC) activities of non-neutralizing antibodies contributed to cross-protection. The cross-protection remained robust even after in vivo depletion of T cells or NK cells, reflecting the strength and breadth of the antibody-dependent effector function. The robust mucosal secretion of sIgA reflects an additional level of cross-protection. Our data show that the host-restricted designer vaccine serves an option for developing a UIV, providing pan-influenza A protection against both group 1 and 2 influenza viruses. The present results of potency and breadth of protection from wild type and reassortant viruses addressed in the mouse model by single immunization merits further confirmation and validation, preferably in clinically relevant ferret models with wild type challenges.

Molecular genetic characteristics of influenza A virus clinically isolated during 2011-2016 influenza seasons in Korea

BACKGROUND

The influenza virus is reportedly associated with 3-5 million cases of severe illness and 250 000-500 000 deaths annually worldwide.

OBJECTIVES

We investigated the variation of influenza A virus in Korea and examined the association with death.

METHODS

A total of 13 620 cases were enrolled in the Hospital-based Influenza Morbidity & Mortality surveillance system in Korea during 2011-2016. Among these cases, a total of 4725 were diagnosed with influenza using RT-PCR (influenza A; n = 3696, influenza B; n = 928, co-infection; n = 101). We used 254 viral sequences from the 3696 influenza A cases for phylogenetic analysis using the BioEdit and MEGA 6.06 programs.

RESULTS

We found that the sequences of A/H3N2 in the 2011-2012 season belong to subgroup 3C.1, whereas the sequences in the 2012-2013 season pertain to subgroup 3C.2. The sequences in the 2013-2014 and 2014-2015 seasons involve subgroups 3C.3a and 3C.2a. The A/H1N1pdm09 subtype belongs to subgroup 6 and contains two clusters. In addition, sequence analysis confirmed the several substitutions of internal genes and gene substitutions associated with drug resistance (I222V in NA and S31N in M2) in the fatal cases. While statistical analysis found no significant associations between genetic differences in the viruses and mortality, mortality was associated with certain host factors, such as chronic lung disease.

CONCLUSIONS

In conclusion, influenza A virus clade changes occurred in Korea during the 2011-2016 seasons. These data, along with antigenic analysis, can aid in selecting effective vaccine strains. We confirmed that fatality in influenza A cases was related to underlying patient diseases, such as chronic lung disease, and further studies are needed to confirm associations between mortality and viral genetic substitutions.

Division of labor between subsets of lymph node dendritic cells determines the specificity of the CD8⁺ T-cell recall response to influenza infection

Cytotoxic T lymphocytes (CTLs) are important targets for vaccines against a wide variety of infections that enter the body via mucosal tissues. To induce effective immunity these vaccines must include the most protective epitopes and elicit rapid recall responses at the site of infection. Although live attenuated viruses are sometimes used to induce cellular immunity against recurrent influenza infections, the mechanisms that determine the magnitude of the response to individual viral components are very poorly defined. Heterosubtypic infections in C57BL/6 mice illustrate an additional level of complexity, when the antigen specificity of the response shifts dramatically between primary and secondary challenge. This model provides a unique opportunity to identify the mechanisms that regulate memory CD8(+) T-cell reactivation in vivo and control the specificity of the recall response by pathogen-specific CTL. We show that multiple factors contribute to the changing pattern of immunodominance during secondary infection, including the location of the memory CD8(+) T cells at the time of reinfection and their ability to directly recognize migratory CD103(+) DCs as they arrive in the lung draining LN.

Effect of MHC class I diversification on influenza epitope-specific CD8+ T cell precursor frequency and subsequent effector function

Earlier studies of influenza-specific CD8(+) T cell immunodominance hierarchies indicated that expression of the H2K(k) MHC class I allele greatly diminishes responses to the H2D(b)-restriced D(b)PA(224) epitope (acid polymerase, residues 224-233 complexed with H2D(b)). The results suggested that the presence of H2K(k) during thymic differentiation led to the deletion of a prominent Vβ7(+) subset of D(b)PA(224)-specific TCRs. The more recent definition of D(b)PA(224)-specific TCR CDR3β repertoires in H2(b) mice provides a new baseline for looking again at this possible H2K(k) effect on D(b)PA(224)-specific TCR selection. We found that immune responses to several H2D(b)- and H2K(b)-restricted influenza epitopes were indeed diminished in H2(bxk) F(1) versus homozygous mice. In the case of D(b)PA(224), lower numbers of naive precursors were part of the explanation, though a similar decrease in those specific for the D(b)NP(366) epitope did not affect response magnitude. Changes in precursor frequency were not associated with any major loss of TCR diversity and could not fully account for the diminished D(b)PA(224)-specific response. Further functional and phenotypic characterization of influenza-specific CD8(+) T cells suggested that the expansion and differentiation of the D(b)PA(224)-specific set is impaired in the H2(bxk) F(1) environment. Thus, the D(b)PA(224) response in H2(bxk) F(1) mice is modulated by factors that affect the generation of naive epitope-specific precursors and the expansion and differentiation of these T cells during infection, rather than clonal deletion of a prominent Vβ7(+) subset. Such findings illustrate the difficulties of predicting and defining the effects of MHC class I diversification on epitope-specific responses.

Revival of the identification of cytotoxic T-lymphocyte epitopes for immunological diagnosis, therapy and vaccine development

Immunogenic T-cell epitopes have a central role in the cellular immunity against pathogens and tumors. However, in the early stage of cellular immunity studies, it was complicated and time-consuming to identify and characterize T-cell epitopes. Currently, the epitope screening is experiencing renewed enthusiasm due to advances in novel techniques and theories. Moreover, the application of T-cell epitope-based diagnoses for tuberculosis and new data on epitope-based vaccine development have also revived the field. There is a growing knowledge on the emphasis of epitope-stimulated T-cell immune responses in the elimination of pathogens and tumors. In this review, we outline the significance of the identification and characterization of T-cell epitopes. We also summarize the methods and strategies for epitope definition and, more importantly, address the relevance of cytotoxic T-lymphocyte epitopes to clinical diagnoses, therapy and vaccine development.

Principles of memory CD8 T-cells generation in relation to protective immunity

Memory T-cell responses are of vital importance in understanding the host's response against pathogens and cancer cells and to begin establishing the correlation of protection against disease. In this review, we discuss our own data in the general context of current knowledge to sketch tentative working principles for the induction of protective T-cell responses by vaccination. We draw attention to quantitative and qualitative aspects of the initial contact with antigen, as well as to the kinetics of events leading to the generation of memory T cells thereafter. Our arguments are based on the current distinction of memory T cells into two lineages: effector memory T cells (T(EM)) and central memory T cells (T(CM)). Our provisional conclusion is that protective T-cell responses correlate positively with the T cells of the central memory phenotype. In proposing a set of working principles to enable protective memory T cells by vaccination we address vaccination both in the context of the immunologically-inexperienced and immunologically-experienced individual, respectively. Finally, we draw attention to the interplay between systemic and local immunity as important factors in determining the success of memory T-cell responses in protecting the individual. We believe that considerations on the immunodynamics of memory induction and maintenance, memory lineage differentiation and their relation to protection may help design strategies to control disease caused by pathogens and cancer.

Respiratory Vaccination of Mice Against Influenza Virus: Dissection of T- and B-Cell Priming Functions

We find that a single respiratory administration of replicationally inactivated influenza A viral particles most often elicits a waning serum antibody response, as the long-sustained bone marrow antiviral plasma cell populations characteristically induced by viral infection are lacking, though antiviral plasma cells at other sites may occasionally persist for a long time. To determine whether this alteration in the pattern of the B-cell response is a reflection of the nature of T-helper (Th) priming, we simultaneously primed B cells with inactivated influenza A/PR8(H1N1) and Th cells with infectious A/x31(H3N2). We show that Th cells cross-react extensively between these two viruses, although the antibody response to viral envelope glycoproteins is completely non-cross-reactive. Th cells primed by infectious A/x31 have little impact on the antibody response specifically elicted from naïve B cells by inactivated A/PR8 viruses, suggesting that the characteristic vigour of the antibody response to influenza viral infection depends on the direct interaction of antiviral B cells with virally infected dendritic cells. Memory B cells primed by inactivated influenza viral particles however, respond rapidly to secondary challenge with live or inactivated viruses, promptly populating bone marrow with antiviral plasma cells. Moreover, Th cells primed by previous live A/x31 viral challenge alter the pattern of the response of naïve B cells to live A/PR8 challenge by accelerating the appearance of anti-H1/N1 plasma cells in bone marrow, eliminating the early spike of anti-H1/N1 plasma cells in the mediastinal node, and generally diminishing the magnitude of the lymph node response. Inactivated A/PR8 and infectious A/x31 are both effective vaccines against A/PR8 infection, as mice preimmunized with either vaccine exhibit much more rapid viral clearance from the lung after infectious A/PR8 challenge. In fact, even when given during a course of anti-CD8 treatment to preempt cross-reactive cytotoxic T cells, live A/x31 is a more effective vaccine against A/PR8 infection than is inactivated A/PR8 itself.

High resolution structures of highly bulged viral epitopes bound to major histocompatibility complex class I. Implications for T-cell receptor engagement and T-cell immunodominance

Although HLA class I alleles can bind epitopes up to 14 amino acids in length, little is known about the immunogenicity or the responding T-cell repertoire against such determinants. Here, we describe an HLA-B*3508-restricted cytotoxic T lymphocyte response to a 13-mer viral epitope (LPEPLPQGQLTAY). The rigid, centrally bulged epitope generated a biased T-cell response. Only the N-terminal face of the peptide bulge was critical for recognition by the dominant clonotype SB27. The SB27 public T-cell receptor (TcR) associated slowly onto the complex between the bulged peptide and the major histocompatibility complex, suggesting significant remodeling upon engagement. The broad antigen-binding cleft of HLA-B*3508 represents a critical feature for engagement of the public TcR, as the narrower binding cleft of HLA-B*3501(LPEPLPQGQLTAY), which differs from HLA-B*3508 by a single amino acid polymorphism (Arg156 --> Leu), interacted poorly with the dominant TcR. Biased TcR usage in this cytotoxic T lymphocyte response appears to reflect a dominant role of the prominent peptide x major histocompatibility complex class I surface.

Analysis of immunodominance among minor histocompatibility antigens in allogeneic hematopoietic stem cell transplantation

In major histocompatibility complex (MHC)-matched allogeneic hematopoietic stem cell transplantation (HSCT), donor responses are directed against multiple host minor histocompatibility antigens (mHAgs), producing graft-versus-host disease (GVHD) and graft-versus-tumor (GVT) effects. We studied MHC-matched, mHAg-mismatched C3H.SW>C57BL/6 HSCT in which three mHAg are molecularly defined (B6dom1, H3, H13) to determine if there is a hierarchy of immunodominance among the mHAgs and to learn the contribution of each to GVHD. We found that B6dom1 was the immunodominant mHAg. B6dom1 did not block responses to the subdominant mHAgs H3 and H13. The mechanism of immunodominance was not mHAg avidity or affinity for class I. B6dom1 elicited a broader variety of Vbeta clonotypes than either H3 or H13. Severe GVHD could occur in the absence of a strong B6dom1 response. Alloreactivity to isolated B6dom1, H3 or H13 differences did not produce severe GVHD. We concluded that immunodominance is explained by both mHAg density on host cells and the repertoire of donor T cells capable of responding to the mHAgs. Clinically significant GVHD requires donor responses to multiple mHAgs. Modulation of responses to a single immunodominant mHAg is insufficient for the prevention of GVHD, while immunotherapies directed against isolated mHAgs may not provoke severe GVHD.

Influence of tumor vaccines on graft versus tumor activity and graft versus host disease in allogeneic bone marrow transplantation

Powerful immunologically-mediated antitumor efforts can be observed in allogeneic hematopoietic stem cell transplantation. In the absence of specific immune interventions, this graft versus tumor effect is closely associated with graft versus host disease. In the work summarized here, the influence of cellular tumor vaccines on graft versus tumor activity and graft versus host disease is examined in a murine model of MHC-matched, minor histocompatibility antigen-mismatched bone marrow transplantation. The experiments have generated the following conclusions. First, complex cellular vaccines, which include recipient minor histocompatibility antigens, when administered to allogeneic donors generate powerful graft versus tumor effects but also induce unacceptable exacerbations of graft versus host disease. Second, cellular tumor vaccines, which contain recipient minor histocompatibility antigens, can be administered to transplant recipients after transplant without significant exacerbation of GVHD and with retention of clinically significant graft versus tumor effects. Third, immunization of donors with molecularly defined tumor-associated antigens, which are not recipient minor histocompatibility antigens, can be coupled with post-transplant immunization of recipients with cellular vaccines without exacerbation of GVHD.

Local IL-4 expression in the lung reduces pulmonary influenza-virus-specific secondary cytotoxic T cell responses

We studied the effect of lung-specific IL-4 expression on the T cell response during primary and secondary heterologous infection with influenza virus by using transgenic mice that express IL-4 under a lung-specific promoter. Subsequent to primary infection with a type A/H1N1 influenza virus these transgenic mice exhibited similar local recruitment of CD4(+) and CD8(+) T cells and only slightly decreased virus-specific CTL activity. However, during secondary challenge with a heterologous influenza virus, the local infiltration with virus-specific, MHC class I-restricted CD8(+) T cells was significantly decreased compared to that of nontransgenic littermates. The ability of IL-4 transgenic mice to clear the heterologous infection was delayed but not abrogated. This was associated with a faster virus-neutralizing antibody response in IL-4 transgenic mice and with their ability to mount significant Th1 responses even in the presence of increased local IL-4 expression. Our observations demonstrate a negative regulatory effect of IL-4 on memory Tc1/CD8(+) T cells, but are also consistent with complementary mechanisms important for virus clearance such as virus-neutralizing antibodies. The reduction of memory CTL in the presence of IL-4 might have consequences for understanding the course of influenza infection in situations where T(H)2 immunity is increased.

Functional conservation of HTLV-1 rex balances the immune pressure for sequence variation in the rex gene

Naturally occurring mutations in Human T-cell Leukemia Virus Type 1 (HTLV-1) Tax protein lead to loss of recognition by cytotoxic T-lymphocytes. Most of these mutations also abolish or severely impair the transactivation function of Tax. Ninety percent of the rex gene, which encodes the viral regulator of mRNA splicing (Rex), overlaps with the tax gene. In this paper, we report that four previously described point mutations in tax that abolished CTL recognition and activity did not alter either the dimerisation function or the ability to export viral mRNA of the corresponding Rex proteins. Rex proteins containing two other amino acid changes were likewise functional. However, five Rex deletion mutants, predominantly but not exclusively found in HAM/TSP patients, had all lost these functions. We conclude that, although the Tax protein is subject to strong CTL-mediated selection, there are stronger functional constraints on amino acid variation in Rex. This may limit the variation in the tax/rex nucleotide sequence which results in immune evasion.

Pathogenic and protective correlates of T cell proliferation in AIDS. HNRC Group. HIV Neurobehavioral Research Center

To investigate the association of antigen specific CD4 T cell activation with HIV disease progression and AIDS-related central nervous system damage, T cell proliferation responses to HIV, CMV, and HSV were evaluated in infected individuals. CD4 T cell loss and neurocognitive impairment were assessed at 6-mo intervals. Individuals with known times of seroconversion who responded to more HIV peptides were at greater risk of progressing to < 200 CD4 T cells (P = 0.04) and dying (P = 0.03) than those with responses to fewer peptides. A positive correlation (0.52) was seen between the breadth of the HIV proliferation response and HIV plasma RNA levels. Higher proliferation responses to CMV and HSV were also associated with more rapid CD4 loss (P = 0.05). HLA phenotyped individuals (n = 150) with two HLA-DR alleles associated with response to more HIV peptides and CMV (DR-2,5,w6,10) were less likely to develop neurocognitive (P = 0.002) and neurologic impairment (P = 0.04), but were not protected from CD4 loss and death. Thus, the ability to generate a greater T cell proliferation response to HIV and opportunistic herpes viruses may lead to resistance to central nervous system damage, but also risk of more rapid HIV disease progression.

Specificity of the H-2 L(d)-restricted cytotoxic T-lymphocyte response to the mouse hepatitis virus nucleocapsid protein

Cytotoxic T lymphocytes provide protection against persistent infection of the central nervous system by the JHM strain of mouse hepatitis virus. In BALB/c (H-2d) mice, the dominant response is directed against an Ld-restricted peptide in the nucleocapsid protein (APTAGAFFF). Characterization of the fine specificity of this response revealed that the predicted anchor residues at positions 2 and 9 were the most critical for class I binding. Amino acids at positions 7 and 8 were identified as T-cell receptor contact residues. Virus-induced cytotoxic T lymphocytes to other Ld motif-containing nucleocapsid peptides were not detected, despite the identification of two epitopes with reduced Ld affinity. These data suggest that mutations within four residues of the dominant epitope could contribute to the persistence of the JHM strain of mouse hepatitis virus.

Recognition of out-of-frame major histocompatibility complex class I-restricted epitopes in vivo

In the course of constructing a recombinant vaccinia virus encoding the influenza A nucleoprotein (NP) gene preceded by the hemagglutinin leader sequence, we isolated a single base-pair deletion mutant which gave rise to L+NP(1-159) in which only the first 159 amino acids were in frame. Despite this, when we infected target cells, we found that the point mutant was able to sensitize them for lysis not only by cytotoxic T cells recognizing residues 50-58 (the in-frame portion), but also by CTL to epitopes which are downstream of the mutation (366-374 and 378-386). Furthermore, normal C57BL/6 mice can be primed with the frameshift NP to recognize the immunodominant Db-restricted epitope 366-374 (which is out of frame). Experiments in which the mutant gene product was processed in the endoplasmic reticulum of target cells suggested that the apparent suppression occurred during polypeptide extension.

Peptide-pulsed dendritic cells induce antigen-specific CTL-mediated protective tumor immunity

Cytotoxic T lymphocytes (CTLs) are a critical component of the immune response to tumors. Tumor-derived peptide antigens targeted by CTLs are being defined for several human tumors and are potential immunogens for the induction of specific antitumor immunity. Dendritic cells (DC) are potent antigen-presenting cells (APCs) capable of priming CTL responses in vivo. Here we show that major histocompatibility complex class I-presented peptide antigen pulsed onto dendritic APCs induces protective immunity to lethal challenge by a tumor transfected with the antigen gene. The immunity is antigen specific, requiring expression of the antigen gene by the tumor target, and is eliminated by in vivo depletion of CD8+ T cells. Furthermore, mice that have rejected the transfected tumor are protected from subsequent challenge with the untransfected parent tumor. These results suggest that immunization strategies using antigen-pulsed DC may be useful for inducing tumor-specific immune responses.

Long-lasting anti-viral cytotoxic T lymphocytes induced in vivo with chimeric-multirestricted lipopeptides

Cytotoxic T lymphocytes (CTL) play a major role in protective immunity against viral diseases. However, the antigenic formulations that can be used in vaccinations able to generate virus-specific CTL responses in vivo have yet to be defined. We have previously shown that HIV-1-specific CTL can be elicited in mice by injecting without adjuvant a synthetic peptide of the envelope glycoprotein that has been modified by the addition of a simple lipid tail to the end of the sequence (lipopeptide). The present study set out to address the question of whether such immunogens may be appropriate for preparing a human synthetic vaccine. We first showed that CTL were effectively induced by lipopeptides when given s.c. or i.p. We evidenced that the in vivo induction required stimulation of a concomitant specific T helper cell response, implying the presence of at least one CD4 epitope in the synthetic sequence used. Bearing in mind the particular properties that would be required in a prospective human peptide vaccine, we conceived a strategy in which a virus-specific CTL response could be generated in mice of different haplotypes using a single lipopeptide. We therefore tested a lipopeptide construct that integrated a synthetic sequence having three colinear epitopes of the influenza virus nucleoprotein, each restricted to a different H-2 haplotype. We found that a CTL response could be elicited to all three epitopes of this chimeric multirestricted lipopeptide construct. Finally, we have attempted to estimate the duration of the responses; strong CTL activities were still present up to six months after the last injection. These findings indicate that this approach may be suitable for developing a synthetic vaccine for human use.

Immune regulation in Epstein-Barr virus-associated diseases

Epstein-Barr virus (EBV) is a member of the human herpesvirus family and, like many other herpesviruses, maintains a lifelong latent association with B lymphocytes and a permissive association with stratified epithelium in the oropharynx. Clinical manifestations of primary EBV infection range from acute infectious mononucleosis to an asymptomatic persistent infection. EBV is also associated with a number of malignancies in humans. This review discusses features of the biology of the virus, both in cell culture systems and in the natural host, before turning to the role of the immune system in controlling EBV infection in healthy individuals and in individuals with EBV-associated diseases. Cytotoxic T cells that recognize virally determined epitopes on infected cells make up the major effector arm and control the persistent infection. In contrast, the options for immune control of EBV-associated malignancies are more restricted. Not only is antigen expression restricted to a single nuclear antigen, EBNA1, but also these tumor cells are unable to process EBV latent antigens, presumably because of a transcriptional defect in antigen-processing genes (such as TAP1 and TAP2). The likelihood of producing a vaccine capable of controlling the acute viral infection and EBV-associated malignancies is also discussed.

Identification of Kk-restricted T-cell epitope within influenza virus nucleoprotein

In order to determine the epitope structure in peptide NP50-63, which has been reported to be the only Kk-restricted T-cell antigen within the influenza virus (A/PR/8/34) nucleoprotein, a series of 13 peptides truncated from C- and N-termini of NP50-63 were synthesized and their sensitizing activities against Kk-restricted nucleoprotein-specific cytotoxic T lymphocytes (CTLs) were examined. One of the 13 peptides, NP50-57, sensitized L929 cells at the nM level, which was 100-1000 times lower in concentration than that at which the other peptides sensitized these cells. The presence of NP50-57 in A/PR/8/34-infected L929 cells was also investigated. Acid extracts of virus-infected cells were separated on a reverse-phase HPLC column and then anion-exchange column. By both separations, only one peak of sensitizing activity against nucleoprotein-specific CTLs was observed. The position of the peak coincided with that of the elution of NP50-57. These results strongly suggest that NP50-57 is the natural epitope in the antigenic structure, NP50-63.

Periodic variation in side-chain polarities of T-cell antigenic peptides correlates with their structure and activity

We present an analysis that synthesizes information on the sequence, structure, and motifs of antigenic peptides, which previously appeared to be in conflict. Fourier analysis of T-cell antigenic peptides indicates a periodic variation in amino acid polarities of 3-3.6 residues per period, suggesting an amphipathic alpha-helical structure. However, the diffraction patterns of major histocompatibility complex (MHC) molecules indicate that their ligands are in an extended non-alpha-helical conformation. We present two mutually consistent structural explanations for the source of the alpha-helical periodicity, based on an observation that the side chains of MHC-bound peptides generally partition with hydrophobic (hydrophilic) side chains pointing into (out of) the cleft. First, an analysis of haplotype-dependent peptide motifs indicates that the locations of their defining residues tend to force a period 3-4 variation in hydrophobicity along the peptide sequence, in a manner consistent with the spacing of pockets in the MHC. Second, recent crystallographic determination of the structure of a peptide bound to a class II MHC molecule reveals an extended but regularly twisted peptide with a rotation angle of about 130 degrees. We show that similar structures with rotation angles of 100-130 degrees are energetically acceptable and also span the length of the MHC cleft. These results provide a sound physical chemical and structural basis for the existence of a haplotype-independent antigenic motif which can be particularly important in limiting the search time for antigenic peptides.

LMP2+ proteasomes are required for the presentation of specific antigens to cytotoxic T lymphocytes

BACKGROUND

Major histocompatibility complex (MHC) class I molecules present short peptides generated by intracellular protein degradation to cytotoxic T lymphocytes (CTL). The multisubunit, non-lysosomal proteinases known as proteasomes have been implicated in the generation of these peptides. Two interferon-gamma (IFN-gamma)-inducible proteasome subunits, LMP2 and LMP7, are encoded within the MHC gene cluster in a region associated with antigen presentation. The incorporation of these LMP subunits into proteasomes may alter their activity so as to favour the generation of peptides able to bind to MHC class I molecules. It has been difficult, however, to demonstrate a specific requirement for LMP2 or LMP7 in the presentation of peptide epitopes to CTL.

RESULTS

We describe a T-cell lymphoma, termed SP3, that displays a novel selective defect in MHC class I-restricted presentation of influenza virus antigens. Of the MHC-encoded genes implicated in the class I pathway, only LMP2 is underexpressed in SP3 cells. Expression of IFN-gamma in transfected SP3 cells simultaneously restores LMP2 expression and antigen presentation to CTL. Expression of antisense-LMP2 mRNA in these IFN-gamma-transfected cells selectively represses antigen recognition and the induction of surface class I MHC expression. Moreover, the expression of this antisense-LMP2 mRNA in L929 fibroblast cells, which constitutively express LMP2 and have no presentation defect, blocks the presentation of the same influenza virus antigens that SP3 cells are defective in presenting.

CONCLUSIONS

Our results show that the LMP2 proteasome subunit can directly influence both MHC class I-restricted antigen presentation and class I surface expression.

Bone marrow-generated dendritic cells pulsed with a class I-restricted peptide are potent inducers of cytotoxic T lymphocytes

It has previously been shown that bone marrow-generated dendritic cells (DC) are potent stimulators in allogeneic mixed leukocyte reactions and are capable of activating naive CD4+ T cells in situ in an antigen-specific manner. In this study we have investigated whether bone marrow-generated DC are capable of inducing antigen-specific CD8+ T cell responses in vivo. Initial attempts to induce specific cytotoxic T lymphocyte (CTL) responses in mice injected with bone marrow-generated DC pulsed with ovalbumin (OVA) peptide were frustrated by the presence of high levels of nonspecific lytic activity, which obscured, though not completely, the presence of Ag-specific CTL. Using conditions that effectively differentiate between antigen-specific and nonspecific lytic activity, we have shown that bone marrow-generated DC pulsed with OVA peptide are potent inducers of OVA-specific CTL responses in vivo, compared with splenocytes or RMA-S cells pulsed with OVA peptide, or compared with immunization with free OVA peptide mixed with adjuvant. Antibody-mediated depletion experiments have shown that the cytotoxic effector cells consist primarily of CD8+ cells, and that induction of CTL in vivo is dependent on CD4+ as well as on CD8+ T cells. These results provide the basis for exploring the role of bone marrow-generated DC in major histocompatibility class I-restricted immune responses, and they provide the rationale for using bone marrow-generated DC in CTL-mediated immunotherapy of cancer and infectious diseases.

Functional analysis of amino acid residues encompassing and surrounding two neighboring H-2Db-restricted cytotoxic T-lymphocyte epitopes in simian virus 40 tumor antigen

Simian virus 40 tumor (T) antigen contains three H-2Db-and one H-2Kb-restricted cytotoxic T lymphocyte (CTL) epitopes (sites). Two of the H-2Db-restricted CTL epitopes, I and II/III, are separated by 7 amino acids in the amino-terminal one third of T antigen. In this study, we determine if the amino acids separating these two H-2Db-restricted CTL epitopes are dispensable for efficient processing and presentation. In addition, the importance of amino acid residues lying within and flanking the H-2Db-restricted epitopes I and II/III for efficient processing, presentation, and recognition by site-specific CTL clones was determined by using T-antigen mutants containing single-amino-acid substitutions between residues 200 and 239. Using synthetic peptides in CTL lysis and major histocompatibility complex class I stabilization assays, CTL recognition site I has been redefined to include residues 206 to 215. Substitutions in amino acids flanking either site I or site II/III did not affect recognition by any of the T-antigen-specific CTL clones. Additionally, the removal of the 7 residues separating site I and site II/III did not affect CTL recognition, thus demonstrating that these two epitopes when arranged in tandem in the native T antigen can be efficiently processed and presented to CTL clones. Differences in fine specificities of two CTL clones which recognize the same epitope (Y-1 and K-11 for site I and Y-2 and Y-3 for site II/III) have been used in conjunction with synthetic peptide variants to assign roles for residues within epitopes I and II/III with respect to TCR recognition and/or peptide-major histocompatibility complex association.

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.

Processing of major histocompatibility class I-restricted antigens in the endoplasmic reticulum

We have introduced long precursor peptides directly into the endoplasmic reticulum (ER) of a mutant cell line (T2-Db) that lacks the ability to transport peptides from the cytosol to the ER in a transporter associated with antigen processing (TAP) dependent way. This was done by expressing various influenza A-derived peptides containing the naturally processed epitope ASNENMDAM (366-374) preceded by the influenza hemagglutinin ER translocation sequence. Peptides derived from these minigenes that became associated with Db were isolated and identified by combined reversed phase liquid chromatography and detection by cytotoxic T lymphocytes. Our results establish that NH2-terminal extensions of at least 40 residues can be trimmed from peptides entering the ER, but that proteolysis of larger proteins may be limited.

Linear epitopes of the replication-activator protein of Epstein-Barr virus recognised by specific serum IgG in nasopharyngeal carcinoma

The linear antigenic epitopes of the Epstein-Barr virus replication activator protein (ZEBRA), recognised by specific serum IgG in nasopharyngeal carcinoma (NPC), were determined. This was achieved by synthesizing the entire amino acid sequence of ZEBRA as a set of 29, 22-residue peptides with an overlap of 14 amino acids. The ZEBRA peptides were tested in enzyme-linked immunosorbent assay (ELISA) for IgG binding in sera from 37 selected NPC patients who had IgG antibodies to the native ZEBRA protein. The most immunogenic epitope was peptide 1 at the amino-terminal end with 36 of the sera reactive against it. Further analysis of peptide 1, using the multipin peptide-scanning technique, defined a 10-amino-acid sequence FTPDPYQVPF, which was strongly bound by IgG. Two other regions of ZEBRA were also identified as immunodominant IgG epitopes, namely peptide 11 (amino acids 82-103) and peptide 19/20 (amino acids 146-175) with 8-13 of the NPC sera reactive against the peptides. The number of peptides reactive with individual NPC serum varies from 1 to 6 or more and there is some correlation between a greater number of peptide (at least 4) bound and a higher (at least 1:40) titre of serum IgA to viral capsid antigen. The immunodominant ZEBRA peptide 1 could be utilised in IgG ELISA for the detection of NPC.

Major histocompatibility complex class I-restricted presentation of influenza virus nucleoprotein peptide by B lymphoma cells harboring an antibody gene antigenized with the virus peptide

We analyzed the capacity of B cells to process and present a peptide from the variable region of an endogenous immunoglobulin heavy (H) chain to a major histocompatibility complex (MHC) class I-restricted cytotoxic T lymphocyte (CTL) clone. The H-chain gene was engineered to express 14-amino acid peptide from the sequence of the influenza virus nucleoprotein (NP) antigen in the third complementarity-determining region (CDR3). This NP peptide is presented in association with the Db allele in H-2b mice. We demonstrate that B lymphoma cells (H-2b) harboring the antigenized H-chain gene process and present the NP peptide in association with the Db molecule and are lysed by a CTL clone specific for that peptide in an MHC-restricted way. In contrast, the soluble antigenized antibody failed to mediate lysis of H-2b target cells. The endogenously processed immunoglobulin CDR3 peptide could be eluted from surface Db molecules in transfected cells. This study formally demonstrates that peptides from the hypervariable loops of endogenous immunoglobulin are processed through the endogenous degradative pathway and are presented to CD8+ T cells in the context of MHC class I molecules. The implication of these findings for processing and presentation of endogenous immunoglobulin peptides in B cells and network regulation by idiopeptides is discussed.

Presentation by a major histocompatibility complex class I molecule of nucleoprotein peptide expressed in two different genes of an influenza virus transfectant

Major histocompatibility (MHC) class I glycoproteins are specialized to present to CD8+ T cells, peptides that originate from proteins synthesized within the cytoplasm. Conventional killed vaccines are unable to get into the cell cytoplasm and therefore fail to expand the CD8+ T cell population. We have created a novel influenza transfectant virus, R10, which carries an immunogenic peptide from the nucleoprotein (NP) of PR8 influenza virus in its hemagglutinin (HA) and another similar peptide in its HK influenza virus NP. The two peptides are both presented by H-2Db and bind with approximately equal affinity. They can compete with one another for binding to H-2Db. Yet in cells infected with R10, both peptides are presented efficiently enough to expand the respective cytotoxic T lymphocyte (CTL) precursors in vivo and to serve as targets for CTL lysis in vitro. It has been proposed that proteins bearing signal sequences may be processed by a transporter-independent pathway. To investigate this, we infected the transporter-deficient cell line RMA-S with the R10 virus to see if the NP peptide expressed by the HA would be presented. The result shows that even the presence of a signal peptide in the HA does not overcome the lack of a transporter function, suggesting that the presentation of both peptides is dependent on functional transporter proteins. Our data also suggest the feasibility of creating by genetic engineering, recombinant vaccines expressing multiple epitopes that can effectively stimulate a cellular immune response.

Identification of functional domains of adenovirus tumor-specific transplantation antigen in types 5 and 12 by viable viruses carrying chimeric E1A genes

The adenovirus (Ad) E1A gene induces in immunized animals a strong tumor transplantation (TSTA) immunity against Ad tumors. Such immunity with group-A and group-C viruses is highly group-specific and no cross-protection is detected between serotypes 5 and 12. This fact was used to map the domains of the Ad5 and Ad12 E1A gene products, respectively, which control the TSTA. We constructed a library of 8 recombinant viruses (H5sub1101 through H5sub1108) which carry chimeric Ad5/Ad12 E1A genes in the background of Ad5. The chimeric genes are functional and these viruses are viable. Some of these constructs induce strong and highly specific tumor syngraft immunity in immunized rats. The viruses carrying the 5' terminus of the first E1A exon derived from Ad12 (viruses H5sub1101, H5sub1102 and H5sub1103) induce strong protection against Ad12 tumors irrespective of the rest of their E1A sequence. The viruses which carry the second exon of the Ad5 E1A gene (viruses H5sub1101, H5sub1102 and H5sub1106) protect against group-C tumors, regardless of the origin of the rest of their E1A gene. The 2 viruses that carry the 5' E1A terminus of the first exon of Ad12 and the second exon of Ad5 (H5sub1101 and H5sub1102) are thus effective in inducing immunity against Ad12 tumors as well as against Ad2 tumors. The viruses which carry the 5' terminus of the first exon derived from Ad5 and the second exon of Ad12 (H5sub1107 and H5sub 1108) fail to induce immunity against either tumor. Expression of only the truncated 5' terminus of the Ad12 E1A gene (viruses H5sub1104 and H5sub1105) is sufficient for induction of Ad12 TSTA. Our results provide direct and unequivocal in vivo evidence that TSTA activities of adenovirus groups A and C are controlled by different domains of their respective E1A genes. The Ad12 TSTA is a function of the 5' terminus of the first E1A exon, while the Ad5 TSTA is coded for by the 3' exon of its E1A gene.

The three-dimensional structure of H-2Db at 2.4 A resolution: implications for antigen-determinant selection

Solution at 2.4 A resolution of the structure of H-2Db with the influenza virus peptide NP366-374 (ASNEN-METM) and comparison with the H-2Kb-VSV (RGY-VYQGL) structure allow description of the molecular details of MHC class I peptide binding interactions for mice of the H-2b haplotype, revealing a strategy that maximizes the repertoire of peptides than can be presented. The H-2Db cleft has a mouse-specific hydrophobic ridge that causes a compensatory arch in the backbone of the peptide, exposing the arch residues to TCR contact and requiring the peptide to be at least 9 residues. This ridge occurs in about 40% of the known murine D and L allelic molecules, classifying them as a structural subgroup.

Characterization of the Ld-restricted cytotoxic T-lymphocyte epitope in the mouse hepatitis virus nucleocapsid protein

The mouse hepatitis virus (MHV) JHM strain (JHMV) produces primary demyelination in the central nervous system associated with acute encephalomyelitis. Humoral and cellular immune responses both participate in controlling the development of chronic MHV-induced demyelination. A subset of the CD8+ cytotoxic T lymphocytes (CTL) induced by immunization of BALB/c (H-2d) mice with JHMV is specific for the viral nucleocapsid protein. This CTL population recognizes an epitope located within the carboxy-terminal 149 amino acids in association with the Ld class I molecule (S. A. Stohlman, S. Kyuwa, M. Cohen, C. Bergmann, J. P. Polo, J. Yeh, R. Anthony, and J. G. Keck, Virology 189:217-224, 1992). Using a panel of vaccinia virus recombinants expressing truncated forms of the nucleocapsid protein and a series of overlapping synthetic peptides, we mapped the response to 15 amino acids. This sequence, encompassing the MHV epitope, contains the Ld-specific binding motif. The predicted 9-mer peptide (residues 318 to 326: APTAGAFFF) was sufficient and highly active in sensitizing target cells for CTL recognition when either added exogenously or synthesized intracellularly. Cross-reactivity of JHMV nucleocapsid protein-specific CTL with six other MHV strains indicated that natural sequence variations within the 9-mer epitope are tolerated in positions 4 and 5, whereas all other amino acids are conserved. These data define a novel 9-mer Ld-restricted CTL epitope which represents the first MHV CTL epitope. Characterization of this epitope provides a molecular basis to study the role of nucleocapsid protein-specific CTL in the clearance of JHMV from the central nervous system.

Response to influenza infection in mice with a targeted disruption in the interferon gamma gene

Interferon gamma (IFN-gamma) is a pleiotropic cytokine secreted by T lymphocytes and natural killer (NK) cells and has been noted to be a first line of host defense in the control of viral infections. To examine further the role of this cytokine in the control of viral infections, mice with a targeted mutation in the IFN-gamma gene were infected with influenza virus, and the in vivo antibody and cell-mediated immune response to viral infection were examined. In addition, cell lines and clones were derived from the immunized animals and the in vitro cytokine production and cytotoxic T lymphocyte (CTL) response were analyzed. The absence of IFN-gamma led to increased production of influenza-specific IgG1, IL-4, and IL-5 as compared to wild-type littermate control animals. In contrast, there was no difference noted in the development of an effective CTL response between IFN-gamma-deficient and wild-type animals. In this model of experimental influenza infection, IFN-gamma is not necessary for the development of an effective humoral or cellular immune response to challenge with this respiratory virus.

Viral hemagglutinin augments peptide-specific cytotoxic T cell responses

In attempt to increase the induction of peptide-specific cytolytic T cells (CTL) we investigated the effect of the Newcastle disease virus (NDV) hemagglutinin-neuraminidase (HN) gene product on the activation of peptide-specific CTL. Spleen cells of CH3 mice immunized against the influenza nucleoprotein peptide 50-63 (NP 50-63) were restimulated in vitro (i) with peptide-pulsed syngeneic fibroblast cells (Ltk-) as antigen-presenting cells, which were in addition (ii) infected with NDV or (iii) stably transfected with the HN cDNA of NDV. A greater than sixfold increase in peptide-specific CTL responses was observed in cultures restimulated with peptide-pulsed Ltk- cells which co-expressed viral hemagglutinin due to either infection or transfection. A similar augmentation was seen in CTL responses against other types of antigen (major histocompatibility complex alloantigens, minor histocompatibility antigens or tumor antigens) when suboptimal cultures were stimulated with the respective antigen-presenting cells modified by NDV infection. These findings suggest that NDV or viral HN expressed on antigen-presenting cells or tumor cells can exert a T cell co-stimulatory function.

Induction of virus-specific cytotoxic T lymphocytes in vivo by liposome-entrapped mRNA

The induction of anti-influenza cytotoxic T lymphocytes (CTL) in vivo by immunizing mice with liposomes containing messenger RNA (mRNA) encoding the influenza virus nucleoprotein (NP) is described. NP mRNA, obtained by in vitro transcription, was encapsulated into simple cholesterol/phosphatidylcholine/phosphatidylserine liposomes by the detergent removal technique. The dependence of the route of mRNA-liposomes delivery on CTL induction was studied. The CTL induced were identical to those obtained in vivo with infectious virus in terms of specificity, lysing both peptide-sensitized and virus-infected targets. Furthermore, with the same mRNA-liposome preparation, virus-specific CTL responses could be also elicited in mice of three different haplotypes each of them known to present a distinct NP peptide in an MHC-restricted fashion. The relevance of these results in the context of vaccine development is discussed.

In vivo priming effect during various stages of ontogeny of an influenza A virus nucleoprotein peptide

In vivo priming of cytotoxic T lymphocytes (CTL) by an influenza virus nucleoprotein (NP) peptide was studied at various stages of development. Adult mice immunized twice with the NP peptide in complete Freund's adjuvant and incomplete Freund's adjuvant, respectively, produce significant CTL responses. Neonates immunized at birth with large amounts of NP peptide and boosted twice with the peptide during adulthood, also mount a weak but significant CTL response. By contrast, offspring from mothers immunized with the NP peptide at days 15, 17, and 19 of pregnancy showed unresponsiveness to the peptide subsequent to a similar regimen of peptide immunization at the age of 1 month. The data indicate that the contact of T cell precursors with antigen during fetal life induces CTL tolerance, whereas, after birth the precursors are not susceptible to tolerogenic signals.

Heterologous protection against influenza by injection of DNA encoding a viral protein

Cytotoxic T lymphocytes (CTLs) specific for conserved viral antigens can respond to different strains of virus, in contrast to antibodies, which are generally strain-specific. The generation of such CTLs in vivo usually requires endogenous expression of the antigen, as occurs in the case of virus infection. To generate a viral antigen for presentation to the immune system without the limitations of direct peptide delivery or viral vectors, plasmid DNA encoding influenza A nucleoprotein was injected into the quadriceps of BALB/c mice. This resulted in the generation of nucleoprotein-specific CTLs and protection from a subsequent challenge with a heterologous strain of influenza A virus, as measured by decreased viral lung titers, inhibition of mass loss, and increased survival.

Antigenicity and immunogenicity of antigenized antibodies. Studies on B and T cells

This laboratory has been testing the possibility of using the complementarity-determining region (CDR) loops of the antibody molecule to express oligopeptide epitopes in an immunologically-accessible and conformationally-suitable way. The new process consists in grafting peptides epitopes derived from antigens other than immunoglobulins into antibody CDR loops. This process, "antibody antigenization," utilizes the immunoglobulin fold as a scaffold to immobilize and present oligopeptide epitopes to the immune system as the integral part of the immunoglobulin molecule. Here we describe some of the initial results with antigenized antibodies (AgAbs).

Short peptides assist the folding of free class I heavy chains in solution

Previous experiments have shown that short peptides coresponding to naturally processed epitopes of viral antigens can induce a conformational change in the class I heavy chain (HC) to which they bind in the fully assembled molecule. Here, we present evidence that the mechanism for this conformational change may involve binding of peptide to a partially unfolded form of free HC, followed by its subsequent folding. These results may be important for understanding the way in which class I molecules are assembled in vivo, and how certain epitopes are selected for presentation to T cells.

Structural requirements for the peptide-induced conformational change of free major histocompatibility complex class I heavy chains

In an attempt to define the structural features of peptides which are important for inducing the folding of free class I heavy chains in the absence of beta 2-microglobulin, and to determine whether they are the same as those required to form stable major histocompatibility complex (MHC): peptide adducts, we have used a panel of peptides related to the Db-binding nonamer ASNENMDAM (influenza nucleoprotein residues 366-374) with altered primary structures, and a number of other peptides which have the Db-binding "motif". In this way, we have shown that in addition to the "anchor" residues which define this motif, the alpha amino and carboxyl groups at the N and C termini also play a major role in both inducing the conformational change in free heavy chain (HC) and formation of a stable Db:peptide complex. We also show that the importance of the key residues is affected by the primary sequence "context" in which they appear. In addition, we have extended our original finding that naturally processed epitopes induce a conformational change in free HC to the H2Kb HC, and show that the effect does not require the presence of the class I alpha 3 domain.

Mouse hepatitis virus nucleocapsid protein-specific cytotoxic T lymphocytes are Ld restricted and specific for the carboxy terminus

Infection of mice with the JHM strain of mouse hepatitis virus (MHV) results in an acute encephalomyelitis associated with primary demyelination of the central nervous system. Efforts at understanding the components of the immune response in the development of chronic MHV-induced demyelination have implicated the antibody response and both the CD4+ and CD8+ T cell responses. In this report, we demonstrate that Balb/c (H-2d) mice immunized with the JHM (JHMV) strain of MHV develop a CD8+ cytotoxic T lymphocyte (CTL) response. One population of these virus-specific CTL recognize the nucleocapsid (N) protein. Recombinant vaccinia viruses expressing either the entire N protein or carboxy-terminal deletions were used to determine the number and location of the epitope(s) recognized. The CTLs were found to recognize a peptide contained within the carboxy-terminal 149 amino acids of the N protein. Analysis of infected cell lines expressing transfected major histocompatibility genes demonstrated that the anti-N protein CTLs were restricted exclusively to the Ld molecule. These data provide the first definition of a MHV-specific CTL response directed to a viral protein and suggest that the anti-N protein CTL response is one potential mechanism used by the host to clear JHMV from the central nervous system.

Measles virus transmembrane fusion protein synthesized de novo or presented in immunostimulating complexes is endogenously processed for HLA class I- and class II-restricted cytotoxic T cell recognition

The routes used by antigen-presenting cells (APC) to convert the transmembrane fusion glycoprotein (F) of measles virus (MV) to HLA class I and class II presentable peptides have been examined, using cloned cytotoxic T lymphocytes in functional assays. Presentation by Epstein-Barr virus-transformed B lymphoblastoid cell lines was achieved using live virus, ultraviolet light-inactivated virus, and purified MV-F delivered either as such or incorporated in immunostimulating complexes (MV-F-ISCOM). Only live virus and MV-F-ISCOM allow presentation by class I molecules, while all antigen preparations permit class II-restricted presentation. We observe presentation of MV-F from live virus and as MV-F-ISCOM by class II molecules in a fashion that is not perturbed by chloroquine. Our studies visualize novel presentation pathways of type I transmembrane proteins.