Biology of cloned cytotoxic T lymphocytes specific for lymphocytic choriomeningitis virus: clearance of virus in vivo

Host Combats IBDV Infection at Both Protein and RNA Levels

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by infectious bursal disease virus (IBDV). In recent years, with the emergence of IBDV variants and recombinant strains, IBDV still threatens the poultry industry worldwide. It seems that the battle between host and IBDV will never end. Thus, it is urgent to develop a more comprehensive and effective strategy for the control of this disease. A better understanding of the mechanisms underlying virus-host interactions would be of help in the development of novel vaccines. Recently, much progress has been made in the understanding of the host response against IBDV infection. If the battle between host and IBDV at the protein level is considered the front line, at the RNA level, it can be taken as a hidden line. The host combats IBDV infection at both the front and hidden lines. Therefore, this review focuses on our current understanding of the host response to IBDV infection at both the protein and RNA levels.

Comparison of Neutralizing Dengue Virus B Cell Epitopes and Protective T Cell Epitopes With Those in Three Main Dengue Virus Vaccines

The four serotypes of Dengue virus (DENV1-4) are arboviruses (arthropod-borne viruses) that belong to the Flavivirus genus, Flaviviridae family. They are the causative agents of an infectious disease called dengue, an important global public health problem with significant social-economic impact. Thus, the development of safe and effective dengue vaccines is a priority according to the World Health Organization. Only one anti-dengue vaccine has already been licensed in endemic countries and two formulations are under phase III clinical trials. In this study, we aimed to compare the main anti-dengue virus vaccines, DENGVAXIA®, LAV-TDV, and TAK-003, regarding their antigens and potential to protect. We studied the conservation of both, B and T cell epitopes involved in immunological control of DENV infection along with vaccine viruses and viral isolates. In addition, we assessed the population coverage of epitope sets contained in each vaccine formulation with regard to different human populations. As main results, we found that all three vaccines contain the main B cell epitopes involved in viral neutralization. Similarly, LAV-TDV and TAK-003 contain most of T cell epitopes involved in immunological protection, a finding not observed in DENGVAXIA®, which explains main limitations of the only licensed dengue vaccine. In summary, the levels of presence and absence of epitopes that are target for protective immune response in the three main anti-dengue virus vaccines are shown in this study. Our results suggest that investing in vaccines that contain the majority of epitopes involved in protective immunity (cellular and humoral arms) is an important issue to be considered.

Complexities of Type I Interferon Biology: Lessons from LCMV

Over the past decades, infection of mice with lymphocytic choriomeningitis virus (LCMV) has provided an invaluable insight into our understanding of immune responses to viruses. In particular, this model has clarified the central roles that type I interferons play in initiating and regulating host responses. The use of different strains of LCMV and routes of infection has allowed us to understand how type I interferons are critical in controlling virus replication and fostering effective antiviral immunity, but also how they promote virus persistence and functional exhaustion of the immune response. Accordingly, these discoveries have formed the foundation for the development of novel treatments for acute and chronic viral infections and even extend into the management of malignant tumors. Here we review the fundamental insights into type I interferon biology gained using LCMV as a model and how the diversity of LCMV strains, dose, and route of administration have been used to dissect the molecular mechanisms underpinning acute versus persistent infection. We also identify gaps in the knowledge regarding LCMV regulation of antiviral immunity. Due to its unique properties, LCMV will continue to remain a vital part of the immunologists' toolbox.

Smyd1C Mediates CD8 T Cell Death via Regulation of Bcl2-Mediated Restriction of outer Mitochondrial Membrane Integrity

The SET and Mynd domain 1 (Smyd1) locus encodes three tissue-restricted isoforms. Two previously characterized isoforms, Smyd1A and Smyd1B, are heart and skeletal muscle-restricted histone methyl transferases. Here we report that a third, non-catalytic isoform, Smyd1C, is expressed predominantly in activated CD8 T cells. While Smyd1C- deficient CD8 T cells undergo activation-induced apoptosis, neither of two classical mechanisms activation-induced cell death nor activated cell autonomous death are utilized. Instead, Smyd1C accumulates within both mitochondria and the immunological synapse where it associates with Bcl-2, FK506-Binding Protein 8/38 (FKBP38) and Calcineurin. This complex maintains Bcl-2 phosphorylation, enhanced mitochondrial localization, and restricted apoptosis of activated CD8 T cells. We suggest that CD8 T cell death is governed, in part, by Smyd1C regulation of Bcl2-mediated restriction of outer mitochondrial membrane integrity.

Human Immunodeficiency Virus: Scientific Challenges Impeding Candidate Vaccines

Most initial work with HIV vaccines was directed at developing vaccines that elicited neutralizing antibodies. These neutralizing antibodies have been narrow in the focus of their action and specific almost entirely to the strain of the innoculating virus. Additionally, controversy has been reported about both the design of assay systems to measure the neutralization of such isolates and interpretation of the results. Researchers are now looking for a "broad-spectrum" vaccine; however, the high variability of the HIV envelope glycoprotein and its rapid rate of mutation creates an elusive target. Safety concerns have reduced interest in live attenuated virus or whole killed virus vaccines. Some novel approaches being taken include increasing cytotoxic T-lymphocyte responses, induction of immune responses in mucosal tissue surfaces, peptide-based vaccines, oligomeric envelope protein-based vaccine regimens, recombinant Tat protein vaccines, natural killer T-cell (NKT) ligand serving as adjuvant, and fusion of SIV gag with the extracellular domain of CTLA-4 as adjuvant. Most of the HIV vaccines currently in development are the products of recombinant DNA technology.

Chemokine guidance of central memory T cells is critical for antiviral recall responses in lymph nodes

A defining feature of vertebrate immunity is the acquisition of immunological memory, which confers enhanced protection against pathogens by mechanisms that are incompletely understood. Here, we compared responses by virus-specific naive T cells (T(N)) and central memory T cells (T(CM)) to viral antigen challenge in lymph nodes (LNs). In steady-state LNs, both T cell subsets localized in the deep T cell area and interacted similarly with antigen-presenting dendritic cells. However, upon entry of lymph-borne virus, only T(CM) relocalized rapidly and efficiently toward the outermost LN regions in the medullary, interfollicular, and subcapsular areas where viral infection was initially confined. This rapid peripheralization was coordinated by a cascade of cytokines and chemokines, particularly ligands for T(CM)-expressed CXCR3. Consequently, in vivo recall responses to viral infection by CXCR3-deficient T(CM) were markedly compromised, indicating that early antigen detection afforded by intranodal chemokine guidance of T(CM) is essential for efficient antiviral memory.

Mice deficient in STAT1 but not STAT2 or IRF9 develop a lethal CD4+ T-cell-mediated disease following infection with lymphocytic choriomeningitis virus

Interferon (IFN) signaling is crucial for antiviral immunity. While type I IFN signaling is mediated by STAT1, STAT2, and IRF9, type II IFN signaling requires only STAT1. Here, we studied the roles of these signaling factors in the host response to systemic infection with lymphocytic choriomeningitis virus (LCMV). In wild-type (WT) mice and mice lacking either STAT2 or IRF9, LCMV infection was nonlethal, and the virus either was cleared (WT) or established persistence (STAT2 knockout [KO] and IRF9 KO). However, in the case of STAT1 KO mice, LCMV infection was lethal and accompanied by severe multiorgan immune pathology, elevated expression of various cytokine genes in tissues, and cytokines in the serum. This lethal phenotype was unaltered by the coabsence of the gamma interferon (IFN-γ) receptor and hence was not dependent on IFN-γ. Equally, the disease was not due to a combined defect in type I and type II IFN signaling, as IRF9 KO mice lacking the IFN-γ receptor survived infection with LCMV. Clearance of LCMV is mediated normally by CD8(+) T cells. However, the depletion of these cells in LCMV-infected STAT1 KO mice was delayed, but did not prevent, lethality. In contrast, depletion of CD4(+) T cells prevented lethality in LCMV-infected STAT1 KO mice and was associated with a reduction in tissue immune pathology. These studies highlight a fundamental difference in the role of STAT1 versus STAT2 and IRF9. While all three factors are required to limit viral replication and spread, only STAT1 has the unique function of preventing the emergence of a lethal antiviral CD4(+) T-cell response.

Point mutation in the glycoprotein of lymphocytic choriomeningitis virus is necessary for receptor binding, dendritic cell infection, and long-term persistence

Arenaviruses are a major cause of hemorrhagic fevers endemic to Sub-Saharan Africa and South America, and thus a major public health and medical concern. The prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is widely used as a model system for studying persistent and acute infections, as well as for gaining an understanding of mammalian immune function. When originally characterized three decades ago, the LCMV isolate, Armstrong, which causes an acute infection in adult mice, was found to differ from the LCMV Clone 13 strain that causes a persistent infection by two amino acid changes, one within the virus surface glycoprotein (GP1: F260L) and the other within the virus L polymerase (K1076Q). Mutation F260L was considered solely responsible for the exceptionally strong binding affinity of Clone 13 (L at GP1 260) to its cellular receptor, α-dystroglycan, which among cells of the immune system is preferentially expressed on dendritic cells, and consequently, alters dendritic cell function leading to viral persistence. Recently, we noted a previously overlooked nucleotide difference between these two strains that results in an additional amino acid change in GP1, N176D. To investigate the potential contribution of this newly identified mutation to the Clone 13 phenotype, we used reverse-genetics approaches to generate recombinant LCM viruses with each of these individual mutations. Phenotypic characterization of these rLCMV showed that mutation F260L, but not N176D, in the GP1 of LCMV is essential for mediating the long-term persistence of Clone 13 infections. This work emphasizes the importance of subtle differences in viral strains that determine disease outcomes.

Arenavirus genetic diversity and its biological implications

The Arenaviridae family currently comprises 22 viral species, each of them associated with a rodent species. This viral family is important both as tractable experimental model systems to study acute and persistent infections and as clinically important human pathogens. Arenaviruses are enveloped viruses with a bi-segmented negative-strand RNA genome. The interaction with the cellular receptor and subsequent entry into the host cell differs between Old World and New World arenavirus that use α-dystoglycan or human transferring receptor 1, respectively, as main receptors. The recent development of reverse genetic systems for several arenaviruses has facilitated progress in understanding the molecular biology and cell biology of this viral family, as well as opening new approaches for the development of novel strategies to combat human pathogenic arenaviruses. On the other hand, increased availability of genetic data has allowed more detailed studies on the phylogeny and evolution of arenaviruses. As with other riboviruses, arenaviruses exist as viral quasispecies, which allow virus adaptation to rapidly changing environments. The large number of different arenavirus host reservoirs and great genetic diversity among virus species provide the bases for the emergence of new arenaviruses potentially pathogenic for humans.

Novel plant virus-based vaccine induces protective cytotoxic T-lymphocyte-mediated antiviral immunity through dendritic cell maturation

Currently used vaccines protect mainly through the production of neutralizing antibodies. However, antibodies confer little or no protection for a majority of chronic viral infections that require active involvement of cytotoxic T lymphocytes (CTLs). Virus-like particles (VLPs) have been shown to be efficient inducers of cell-mediated immune responses, but administration of an adjuvant is generally required. We recently reported the generation of a novel VLP system exploiting the self-assembly property of the papaya mosaic virus (PapMV) coat protein. We show here that uptake of PapMV-like particles by murine splenic dendritic cells (DCs) in vivo leads to their maturation, suggesting that they possess intrinsic adjuvant-like properties. DCs pulsed with PapMV-like particles displaying the lymphocytic choriomeningitis virus (LCMV) p33 immunodominant CTL epitope (PapMV-p33) efficiently process and cross-present the viral epitope to p33-specific transgenic T cells. Importantly, the CTL epitope is also properly processed and presented in vivo, since immunization of p33-specific T-cell receptor transgenic mice with PapMV-p33 induces the activation of large numbers of specific CTLs. C57BL/6 mice immunized with PapMV-p33 VLPs in the absence of adjuvant develop p33-specific effector CTLs that rapidly expand following LCMV challenge and protect vaccinated mice against LCMV infection in a dose-dependent manner. These results demonstrate the efficiency of this novel plant virus-based vaccination platform in inducing DC maturation leading to protective CTL responses.

Development and validation of a fluorescence polarization-based competitive peptide-binding assay for HLA-A*0201--a new tool for epitope discovery

Various approaches are currently proposed to successfully develop therapies for the prevention and treatment of infectious diseases and cancer. One of the most promising approaches is the development of vaccines that elicit cytotoxic T lymphocyte (CTL) responses. Consequently, identification and exact definition of molecular parameters involved in peptide-MHC class-I interactions of putative CTL epitopes are of prime importance for the development of immunomodulating compounds. To better facilitate epitope discovery, we developed and validated a novel state-of-the-art biochemical HLA-A0201 assay, which is comprised of technologically advanced cutting edge reagents. The technique is based on competition and uses a FITC-labeled reference peptide and highly purified soluble HLA-A0201 molecules to quantitatively measure the binding capacity of nonlabeled peptide candidates. Detection by fluorescence polarization allows real-time measurement of binding ratios without separation steps. During standardization, the problem of assay parameter variation is discussed, showing the dramatic influence of HLA and reference peptide concentrations as well as the choice of the reference peptide itself on IC(50) determinations. For validation, a panel of 15 well-defined HLA-A0201 ligands from various sources covering a broad range of binding affinities was tested. Binding data were used to compare against pre-existing quantitative assay systems. The results obtained demonstrated significant correlation among assay procedures, suggesting that the application of fluorescence polarization in combination with recombinant sHLA molecules is highly advantageous for the accurate assessment of peptide binding. Furthermore, the assay also features high-throughput screening capacity, providing uniquely efficient means of identifying and evaluating immune target molecules.

Equine infectious anemia virus-infected dendritic cells retain antigen presentation capability

To determine if equine monocyte-derived dendritic cells (DC) were susceptible to equine infectious anemia virus (EIAV) infection, ex vivo-generated DC were infected with virus in vitro. EIAV antigen was detected by immunofluorescence 3 days post-infection with maximum antigen being detected on day 4, whereas there was no antigen detected in DC incubated with the same amount of heat-inactivated EIAV. No cytolytic activity was observed after EIAV(WSU5) infection of DC. These monocyte-derived DC were more effective than macrophages and B cells in stimulating allogenic T lymphocytes. Both infected macrophages and DC stimulated similar levels of memory CTL responses in mixtures of CD8+ and CD4+ cells as detected with (51)Cr-release assays indicating that EIAV infection of DC did not alter antigen presentation. However, EIAV-infected DC were more effective than infected macrophages when used to stimulate memory CTL in isolated CD8+ cells. The maintenance of antigen processing and presenting function by EIAV-infected DC in vitro suggests that this function is maintained during in vivo infection.

Upregulation of RANTES gene expression in neuroglia by Japanese encephalitis virus infection

Infection with Japanese encephalitis virus (JEV) causes cerebral inflammation and stimulates inflammatory cytokine expression. Glial cells orchestrate immunocyte recruitment to focal sites of viral infection within the central nervous system (CNS) and synchronize immune cell functions through a regulated network of cytokines and chemokines. Since immune cell infiltration is prominent, we investigated the production of a responding chemoattractant, RANTES (regulated upon activation, normal T-cell expressed and secreted), in response to JEV infection of glial cells. Infection with JEV was found to elicit the production of RANTES from primary neurons/glia, mixed glia, microglia, and astrocytes but not from neuron cultures. The production of RANTES did not seem to be directly responsible for JEV-induced neuronal death but instead contributed to the recruitment of immune cells. RANTES expression required viral replication and the activation of extracellular signal-regulated kinase (ERK) as well as transcription factors, including nuclear factor kappa B (NF-kappaB) and nuclear factor IL-6 (NF-IL-6). The induction of RANTES expression by JEV infection in glial cells needed the coordinate activation of NF-kappaB and NF-IL-6. Using enzymatic inhibitors, we demonstrated a strong correlation between the ERK signaling pathway and RANTES expression. However, JEV replication was not dependent on the activation of ERK, NF-kappaB, and NF-IL-6. Altogether, these results demonstrated that infection of glial cells by JEV provided the early ERK-, NF-kappaB-, and NF-IL-6-mediated signals that directly activated RANTES expression, which might be involved in the initiation and amplification of inflammatory responses in the CNS.

Murine viral hepatitis involves NK cell depletion associated with virus-induced apoptosis

Mouse hepatitis virus type 3 (MHV3), a coronavirus, is an excellent animal model for the study of immunological disorders related to acute and chronic hepatitis. In this study, we have verified if the fulminant hepatitis induced by MHV3 could be related to an impairment of innate immunity. Groups of three C57BL/6 mice were infected with the pathogenic L2-MHV3 or attenuated YAC-MHV3 viruses, and the natural killer (NK) cell populations from liver, spleen and bone marrow were analysed. The percentage of intrahepatic NK1.1(+)T cell receptor (TCR)- cells did not increase while NK1.1(+)TCR(inter) cells decreased in both L2-MHV3- and YAC-MHV3-infected mice. Concurrently, splenic and myeloid NK1.1+ cells decreased in L2-MHV3-infected mice. However, the cytotoxic activity of NK cells increased in liver and decreased in bone marrow from pathogenic L2-MHV3-infected mice while no modification was detected in YAC-MHV3-infected mice. Flow cytometric analysis revealed that both normal and larger splenic or myeloid NK cells decreased more in pathogenic L2-MHV3-infected mice than in attenuated YAC-MHV3-infected mice. In vitro viral infections of interleukin (IL)-15-stimulated lymphoid cells from liver and bone marrow revealed that L2-MHV3 induced higher decreases in cell viability of NK1.1+ cells than the YAC-MHV3 variant. The NK cell decreases were due to the viral permissivity leading to cytopathic effects characterized by cell rounding, syncytia formation and apoptosis. Larger NK+ syncytia were observed in L2-MHV3-infected cells than in YAC-MHV3-infected cells. These results suggest that NK cell production is impaired by viral infection favouring fulminant hepatitis.

HIV type 1 antigen-responsive CD4+ T-lymphocytes in exposed yet HIV Type 1 seronegative Ugandans

CD4(+) T cell help is important for the functionality of CD8(+) cytotoxic T-lymphocytes (CTLs) in limiting viral replication and may contribute to mediation of apparent resistance to HIV-1 infection in exposed seronegative (ESN) individuals. Using five HIV-1 antigens in an intracellular cytokine assay, the presence of specific antigen-responsive interferon- gamma-positive (IFN-gamma(+)) CD69(+) CD4(+) T-lymphocytes was evaluated in ESNs, their seropositive partners, and unexposed seronegative controls. Ten ESNs (five females, five uncircumcised males) were identified from 10 HIV-1 serodiscordant couples with a history of frequent unprotected sexual intercourse. All ESNs and controls were negative on two EIAs and for HIV-1 proviral DNA. The frequency of ESNs with antigen-responsive IFN-gamma(+) CD69(+) CD4(+) T-lymphocytes ranged from three to five of eight for the different HIV-1 antigens. Six of eight ESNs tested had a positive response to at least one of the five antigens. Responses were on average 3.5 times higher among seropositives compared to ESNs and absent in the five unexposed controls. A negative correlation was noted between responses in ESNs and the plasma viral load of their seropositive spouse. Clade-specific and cross-clade reactivity were noted in both ESNs and seropositive partners tested. The findings confirm that ESNs are in a state of HIV-1-specific immune activation and suggest that HIV-1-specific IFN-gamma(+) CD69(+) CD4(+) T-lymphocytes in addition to HIV-1-specific CD8(+) CTLs already described by others are potential immunological correlates of protection from persistent HIV-1 infection.

Do thymically and strictly extrathymically developing T cells generate similar immune responses?

If present in sufficient numbers, could extrathymic T cells substitute for thymus-derived T cells? To address this issue, we studied extrathymic T cells that develop in athymic mice under the influence of oncostatin M (OM). In this model, extensive T-cell development is probably due to amplification of a minor pathway of T-cell differentiation taking place only in the lymph nodes. Extrathymic CD4 T cells expanded poorly and were deficient in providing B-cell help after infection with vesicular stomatitis virus (VSV) and lymphocytic choriomeningitis virus (LCMV). Compared with classic T cells, stimulated extrathymic CD8 T cells produced copious amounts of interferon gamma (IFN-gamma), and their expansion was precocious but of limited amplitude because of a high apoptosis rate. Consequently, although extrathymic cytotoxic T lymphocytes (CTLs) responded to LCMV infection, as evidenced by the expansion of GP33-41 tetramer-positive CD8 T cells, they were unable to eradicate the virus. Our data indicate that the site of development impinges on T-cell quality and function and that extrathymic T cells functionally cannot substitute for classical thymic T cells.

Antigen-driven effector CD8 T cell function regulated by T-bet

Type 1 immunity relies on the differentiation of two major subsets of T lymphocytes, the CD4+ T helper (Th) cell and the CD8+ cytotoxic T cell, that direct inflammatory and cytotoxic responses essential for the destruction of intracellular and extracellular pathogens. In contrast to CD4 cells, little is known about transcription factors that control the transition from the CD8 naïve to effector cell stage. Here, we report that the transcription factor T-bet, known to regulate Th cell differentiation, also controls the generation of the CD8+ cytotoxic effector cell. Antigen-driven generation of effector CD8+ cells was impaired in OT-I T cell receptor transgenic mice lacking T-bet, resulting in diminished cytotoxicity and a marked shift in cytokine secretion profiles. Furthermore, mice lacking T-bet responded poorly to infection with lymphocytic choriomeningitis virus. T-bet is a key player in the generation of type 1 immunity, in both Th and T cytotoxic cells.

The influence of macrophage inflammatory protein-1alpha on protective immunity mediated by antiviral cytotoxic T cells

Macrophage inflammatory protein 1alpha (MIP-1alpha), a member of the CC-chemokine subfamily, is known to induce chemotaxis of a variety of cell types in vivo. Although the role of MIP-1alpha in inflammatory responses generated following primary infection of mice with many different pathogens has been characterized, the influence of this chemokine on the generation of antigen-specific T-cell responses in vivo is less well understood. This is important, as virus-specific CD8+ T lymphocytes (CTL) play a crucial role in defence against viral infections, both acutely and in the long term. In this study, we compared the ability of wild-type and MIP-1alpha-deficient (MIP-1alpha-/-) mice to mount CTL responses specific for the immunodominant epitope derived from influenza nucleoprotein (NP366-374). Influenza-specific CTL responses were compared with respect to frequency, cytotoxic activity and ability to clear subsequent infections with recombinant vaccinia viruses expressing the influenza NP. The results indicate that antiviral CTL generated in MIP-1alpha-/- mice are slightly impaired in their ability to protect against a subsequent infection. However, impaired in vivo CTL-mediated antiviral protection was found to be associated with reduced cytotoxicity rather than with a failure of the CTL to migrate to peripheral sites of infection.

Identification of a novel human leucocyte antigen-A*01-restricted cytotoxic T-lymphocyte epitope in the respiratory syncytial virus fusion protein

Virus-specific cytotoxic T lymphocytes (CTL) play a major role in the clearance of respiratory syncytial virus (RSV) infection. To begin monitoring the immunological response to infection, especially in infants, it is important to identify human leucocyte antigen (HLA)-restricted CTL epitopes. Herein, we used a novel, comprehensive peptide panel containing all possible 8-, 9- and 10-mer peptides spanning the RSV fusion protein to screen for novel HLA-restricted T-cell epitopes. These peptide sets were synthesized as 10-mer peptides overlapping by nine amino acids and contained corresponding 8- and 9-mer peptides generated by C-terminal truncation. Unselected and uncultured peripheral blood mononuclear cells from healthy adult subjects were screened by interferon-gamma (IFN-gamma) Elispot assays against the peptide panel. Seven of 19 subjects displayed positive responses against 10 of the 565 peptides analysed. An HLA-A*01-restricted CTL epitope detected in three healthy adult subjects is characterized. This is the first RSV-specific memory CTL response identified in the fusion protein of RSV.

c-Jun NH(2)-terminal kinase (JNK)1 and JNK2 signaling pathways have divergent roles in CD8(+) T cell-mediated antiviral immunity

c-Jun NH(2)-terminal kinases (JNK) play important roles in T helper cell (Th) proliferation, differentiation, and maintenance of Th1/Th2 polarization. To determine whether JNKs are involved in antiviral T cell immunity, and whether JNK1 and JNK2 bear biological differences, we investigated the immune responses of JNK1-deficient and JNK2-deficient mice to lymphocytic choriomeningitis virus (LCMV). After LCMV infection, wild-type (JNK(+/+)) mice had a 5- to 10-fold increase in splenic CD8(+) T cells. In contrast, infected JNK1(-/-) mice showed a significantly lower virus-specific CD8(+) T cell expansion. However, JNK1(-/-) mice cleared LCMV infection with similar kinetics as JNK(+/+) mice. Splenic T cells from LCMV-infected JNK1(-/-) animals produced interferon gamma after stimulation with viral peptides. However, fewer JNK1(-/-) T cells acquired an activated phenotype (CD44(hi)) and more JNK1(-/-)CD8(+)CD44(hi) cells underwent apoptosis than JNK(+/+) cells at the peak of the primary response. In contrast, LCMV-infected JNK2(-/-) mice generated more virus-specific CD8(+) T cells than JNK(+/+) mice. These results indicate that JNK1 and JNK2 signal pathways have distinct roles in T cell responses during a viral infection. JNK1 is involved in survival of activated T cells during immune responses, and JNK2 plays a role in control of CD8(+) T cell expansion in vivo.

Peptide vaccines against hepatitis B virus: from animal model to human studies

An estimated 400 million people are chronically infected with the hepatitis B virus (HBV). Chronic viral hepatitis infection incurs serious sequelae such as liver cirrhosis and hepatocellular carcinoma. Prevention and treatment, thus, represent an important target for public health. Preventive vaccines using HBsAg alone or combined with other antigens allow for the generation of neutralizing antibodies which effectively prevent infection in immunocompetent individuals. Cell-mediated immunological mechanisms are thought to be crucial in determining viral persistence or viral elimination. Therapeutic approaches aiming to shift cellular immunity towards viral elimination have been on the research agenda for many years. This paper summarizes pre-clinical and clinical results obtained with the use of immunogenic peptides formulated as vaccines to selectively boost cellular immune responses. Such vaccines are capable of generating cellular immune responses in animal models as well as in humans and represent an important step towards the development of a therapeutic vaccine against chronic hepatitis.

Recovery from mouse hepatitis virus infection depends on recruitment of CD8(+) cells rather than activation of intrahepatic CD4(+)alphabeta(-)TCR(inter) or NK-T cells

Mouse hepatitis virus (MHV) provides an excellent animal model for the study of the immunopathological mechanisms involved in hepatic viral diseases. We previously generated an attenuated viral variant, YAC-MHV3, which induces a subclinical disease and recovery within 15 days. In contrast, the L2-MHV3 strain induces the development of a fulminant hepatitis, leading to death within 3 days. In this paper, we document intrahepatic and splenic T cell subpopulations involved in the hepatitis process and viral elimination identified in attenuated or pathogenic MHV3-infected C57BL/6 mice. Percentages of intrahepatic CD4(+) cells decreased in attenuated YAC-MHV3-infected mice, while they increased in mice infected with pathogenic L2-MHV3, compared with uninfected animals. Moreover, in YAC-MHV3-infected mice, the percentages of intrahepatic CD8(+) cells slightly decreased at 24 h pi, then increased until 15 days pi. In contrast, the CD4/CD8 ratios of splenic lymphoid subpopulations increased in the first days of infection and returned to normal values at 15 days pi. Intrahepatic NK1.1(+)alphabeta - TCR(inter) cells decreased in both virally infected groups of mice, while CD4(+)alphabeta - TCR(inter) LFA-1(high) cells increased in L2-MHV3-infected mice, in contrast with what was seen in YAC-MHV3-infected mice. However, these cells became anergic following Con A or PHA stimulation. Ex vivo studies showed that only the intrahepatic CD8(+) cells that were increased in YAC-MHV3-infected mice could be stimulated by lectins. In addition, in vitro viral infections revealed that L2-MHV3 viral infection led to an increase of intrahepatic CD4(+)alphabeta - TCR(inter) cells in the absence of CD8(+) cells only. These results indicate that the attenuated phenotype of the YAC-MHV3 virus is related to two different mechanisms: the first involves no increase of intrahepatic CD4(+)alphabeta - TCR(inter) or NK-T cells, while the second favors the recruitment and activation of CD8(+) cells in liver. The results are discussed in relation to the integrity of intrahepatic immune tolerance mechanisms and immune-mediated viral elimination.

The immunopathogenesis of hepatitis C virus infection

The outcome of HCV infection is determined by the interaction between the virus and the host immune system. The persistence of infection in most HCV-infected individuals, despite the presence of HCV-directed antibodies, suggests that such antibodies fail to induce viral clearance. Patients with self-limited hepatitis C have evidence of a polyclonal, multispecific CD8+ T-cell response along with a coordinated CD4+ T-cell response that is associated with eradication of HCV infection. Cytokines are produced both locally within the liver and systemically and may play an important role in controlling viral replication and contributing to hepatocellular damage through amplification of a nonspecific immune response. In most patients, the humoral, cellular immune, and cytokine response seem insufficient to eradicate infection. In its attempt to clear the virus from the liver, the immune system contributes to the hepatocellular injury seem in most chronically infected patients. A better understanding of the host's immune response may provide further insight on the pathogenetic mechanisms involved in development of chronic hepatitis and aid the development of better therapeutic strategies.

Structural and functional identification of major histocompatibility complex class I-restricted self-peptides as naturally occurring molecular mimics of viral antigens. Possible role in CD8+ T cell-mediated, virus-induced autoimmune disease

Structural similarity (molecular mimicry) between viral epitopes and self-peptides can lead to the induction of autoaggressive CD4(+) as well as CD8(+) T cell responses. Based on the flexibility of T cell receptor/antigen/major histocompatibility complex recognition, it has been proposed that a self-peptide could replace a viral epitope for T cell recognition and therefore participate in pathophysiological processes in which T cells are involved. To address this issue, we used, as a molecular model of viral antigen, the H-2D(b)-restricted immunodominant epitope nucleoprotein (NP)-(396-404) (FQPQNGQFI) of lymphocytic choriomeningitis virus (LCMV). We identified peptide sequences from murine self-proteins that share structural and functional homology with LCMV NP-(396-404) and that bound to H-2D(b) with high affinity. One of these self-peptides, derived from tumor necrosis factor receptor I (FGPSNWHFM, amino acids 302-310), maintained LCMV-specific CD8(+) T cells in an active state as observed both in vitro in cytotoxic assays and in vivo in a model of virus-induced autoimmune diabetes, the rat insulin promoter-LCMV NP transgenic mouse. The natural occurrence and molecular concentration at the surface of H-2(b) spleen cells of tumor necrosis factor receptor I-(302-310) were determined by on-line micro-high pressure liquid chromatography/mass spectrometry and supported its biological relevance.

Equine infectious anaemia virus proteins with epitopes most frequently recognized by cytotoxic T lymphocytes from infected horses

Efficacious lentiviral vaccines designed to induce cytotoxic T lymphocytes (CTL) in outbred populations with a diverse repertoire of MHC class I molecules should contain or express multiple viral proteins. To determine the equine infectious anaemia virus (EIAV) proteins with epitopes most frequently recognized by CTL from seven horses infected for 0.5 to 7 years, retroviral vector-transduced target cells expressing viral proteins were used in CTL assays. Gag p15 was recognized by CTL from 100% of these infected horses. p26 was recognized by CTL from 86%, SU and the middle third of Pol protein were each recognized by 43%, TM by 29%, and S2 by 14%. Based on these results, it is likely that a construct expressing the 359 amino acids constituting p15 and p26 would contain epitopes capable of stimulating CTL in most horses.

Cellular immune responses in neonates

Reduced numbers of lymphocytes and antigen presenting cells have been described as some of the main factors responsible for antigenic tolerance or low responsiveness in neonates. However, by changing the parameters of immunization, such as dose of antigen and frequency of antigen presenting cells we and others have shown that neonates have the option of developing the same variety of immune responses seen in adults. Several aspects of the development of cellular immunity in human and murine neonates are reviewed in this article, with a special focus on the development of T cell mediated responses, from ontogeny to effector function.

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.

Protection of CD3 delta knockout mice from lymphocytic choriomeningitis virus-induced immunopathology: implications for viral neuroinvasion

For a virus to establish a neuronal infection, it must spread from its primary site of infection to the central nervous system (CNS) before immune-mediated clearance occurs. Lymphocytic choriomeningitis virus (LCMV) is a murine pathogen that can result in persistent neuronal infection in newborn mice and in adults that lack CD8(+) T cells. To determine the neuroinvasive capacity of LCMV in the presence of an existent, but compromised, cytotoxic T lymphocyte response, the course of LCMV infection was examined in mice that possess 10% of the normal complement of T lymphocytes, due to the lack of the CD3 delta (delta) subunit of the T cell receptor complex (CD3 delta KO mice). Unlike immunocompetent mice that produced a massive immune response that caused death by 6-7 days postinfection, CD3 delta KO mice mounted a weak response and survived. The presence of viral antigen gradually shifted from the class I MHC-positive meninges and ependyma to class I MHC-deficient CNS neurons 10-30 days postinoculation. The infected CD3 delta KO mice developed a delayed T cell response that suppressed virus replication in peripheral tissues but not in the CNS; subsequent adoptive transfer experiments supported the hypothesis that the lack of clearance from neurons was due to sequestration of LCMV in an immune-privileged cell type. Based on these results, we propose that a critical parameter in the pathogenesis of neurotropic viruses is the rate of immune activation; individuals with impaired T cell responses may be more vulnerable to persisting CNS infections.

Immune responses following neonatal DNA vaccination are long-lived, abundant, and qualitatively similar to those induced by conventional immunization

Virus infections are devastating to neonates, and the induction of active antiviral immunity in this age group is an important goal. Here, we show that a single neonatal DNA vaccination induces cellular and humoral immune responses which are maintained for a significant part of the animal's life span. We employ a sensitive technique which permits the first demonstration and quantitation, directly ex vivo, of virus-specific CD8(+) T cells induced by DNA immunization. One year postvaccination, antigen-specific CD8(+) T cells were readily detectable and constituted 0.5 to 1% of all CD8(+) T cells. By several criteria-including cytokine production, perforin content, development of lytic ability, and protective capacity-DNA vaccine-induced CD8(+) memory T cells were indistinguishable from memory cells induced by immunization with a conventional (live-virus) vaccine. Analyses of long-term humoral immune responses revealed that, in contrast to the strong immunoglobulin G2a (IgG2a) skewing of the humoral response seen after conventional vaccination, IgG1 and IgG2a levels were similar in DNA-vaccinated neonatal and adult animals, indicating a balanced T helper response. Collectively, these results show that a single DNA vaccination within hours or days of birth can induce long-lasting CD8(+) T- and B-cell responses; there is no need for secondary immunization (boosting). Furthermore, the observed immune responses induced in neonates and in adults are indistinguishable by several criteria, including protection against virus challenge.

NK markers are expressed on a high percentage of virus-specific CD8+ and CD4+ T cells

NK cells have been phenotypically defined by the expression of specific markers such as NK1.1, DX5, and asialo-GM1 (ASGM1). In addition to NK cells, a small population of CD3+ T cells has been shown to express these markers, and a unique subpopulation of NK1. 1+CD3+ T cells that expresses an invariant TCR has been named "NKT cells." Here, we describe NK marker expression on a broad spectrum of MHC class I- and MHC class II-restricted T cells that are induced after acute viral infection. From 5 to >500 days post lymphocytic choriomeningitis virus (LCMV) infection, more than 90% of virus-specific CD8+ and CD4+ T cells coexpress one or more of these three prototypical NK markers. Furthermore, in vivo depletion of NK cells with anti-ASGM1 Ab resulted in the removal of 90% of virus-specific CD8+ T cells and 50-80% of virus-specific CD4+ T cells. This indicates that studies using in vivo depletion to determine the role of NK cells in immune defense could potentially be misinterpreted because of the unintended depletion of Ag-specific T cells. These results demonstrate that NK Ags are widely expressed on the majority of virus-specific T cells and indicate that the NK and T cell lineages may not be as distinct as previously believed. Moreover, the current nomenclature defining NKT cells will require comprehensive modification to include Ag-specific CD8+ and CD4+ T cells that express prototypical NK Ags.

Activated and memory CD8+ T cells can be distinguished by their cytokine profiles and phenotypic markers

Dissecting the mechanisms of T cell-mediated immunity requires the identification of functional characteristics and surface markers that distinguish between activated and memory T lymphocytes. In this study, we compared the rates of cytokine production by virus-specific primary and memory CD8+ T cells directly ex vivo. Ag-specific IFN-gamma and TNF-alpha production by both primary and long-term memory T cells was observed in </=60 min after peptide stimulation. Although the on-rate kinetics of cytokine production were nearly identical, activated T cells produced more IFN-gamma, but less TNF-alpha, than memory T cells. Ag-specific cytokine synthesis was not a constitutive process and terminated immediately following disruption of contact with peptide-coated cells, demonstrating that continuous antigenic stimulation was required by both T cell populations to maintain steady-state cytokine production. Upon re-exposure to Ag, activated T cells resumed cytokine production whereas only a subpopulation of memory T cells reinitiated cytokine synthesis. Analysis of cytokine profiles and levels of CD8, LFA-1, and CTLA-4 together revealed a pattern of expression that clearly distinguished in vivo-activated T cells from memory T cells. Surprisingly, CTLA-4 expression was highest at the early stages of the immune response but fell to background levels soon after viral clearance. This study is the first to show that memory T cells have the same Ag-specific on/off regulation of cytokine production as activated T cells and demonstrates that memory T cells can be clearly discriminated from activated T cells directly ex vivo by their cytokine profiles and the differential expression of three well-characterized T cell markers.

Vaccine-induced cytotoxic T lymphocytes against human immunodeficiency virus type 1 using two complementary in vitro stimulation strategies

CD8+ cytotoxic T lymphocytes (CTL) against human immunodeficiency virus type 1 (HIV-1) induced by candidate HIV-1 vaccines may be a mechanism of immune protection against HIV-1 infection. We measured in vitro inducible CD8+ and CD4+ CTL using two in vitro effector cell stimulation strategies. Peripheral blood mononuclear cells (PBMC) for CTL assay were obtained after the third and/or fourth immunization timepoints from 23 healthy, uninfected adult volunteers, of whom 19 received a canarypox virus vaccine expressing HIV-1 env, gag, pol, nef and protease gene products (vCP300) with or without injections of HIV-1(SF-2) rgp120 subunit vaccine and four subjects received only control injections. CD8+ CTL activity was detected employing the two in vitro stimulation strategies against one or more HIV-1 antigens in 15 (79%) of 19 HIV-1 vaccine recipients on at least one occasion and repeatedly against the same antigen in 8 (42%). Canarypox virus-based HIV-1 vaccines represent a step forward in HIV-1 vaccine development.

T(h)1 but not T(h)0 cell help is efficient to induce cytotoxic T lymphocytes by immunization with short synthetic peptides

Immunization of BALB/c mice with peptide HVSGHRMAWDMMMNWA, encompassing residues 121-135 from hepatitis C virus E1 protein, induced CD4(+) T(h)1 cells as well as a long-lasting CD8(+) cytotoxic T lymphocyte (CTL) response in vivo when the peptide was administered s.c. with or without incomplete Freund's adjuvant. Using truncated peptides from this sequence it was shown that the determinant recognized by cytotoxic T cells was encompassed by residues SGHRMAWDM. Deletion of residues from the N-terminus or the C-terminus of the wild-type peptide abrogated its helper character. When Val122 of the wild peptide was replaced by Ala, the ability to induce a cytotoxic response was lost concomitantly with the loss of the T(h)1 pattern of cytokine production. Interestingly, the Ala-modified peptide, when co-immunized with a peptide encompassing residues 323-329 from ovalbumin (OVA), which is able to induce a T(h)1 response in BALB/c mice, restored the capacity of the modified peptide to induce CTL. However, co-immunization of the Ala-modified peptide with a peptide encompassing residues 106-118 from sperm whale myoglobin, which induces a T(h)0 cytokine profile in BALB/c mice, was much less efficient than the OVA peptide to restore CTL induction. These results demonstrate that CTL induction with a short synthetic peptide requires that this peptide contains domains recognized by T(c) cells as well as by T(h)1 cells. For those peptides that do not contain this type of T(h) domain, competent T cell help can be provided by co-immunization with a distinct peptide that is able to stimulate a T(h)1 response.

Detection of simian immunodeficiency virus (SIV)-specific T-cell-mediated cytotoxicity in the peripheral blood from infected cynomolgus monkeys

We have previously demonstrated that peptide immunization restimulates the memory CD4 T-cell response, but fails to induce cytotoxic T lymphocyte (CTL) in cynomolgus macaques. To examine the nature of protective immunity to simian immunodeficiency virus (SIV) in this study, freshly isolated peripheral blood mononuclear cells (PBMC) from four infected juvenile cynomolgus macaques and from three uninfected control macaques were assessed for CTL activity monthly for 9 consecutive months, beginning 1 month after detection of infection. Target cells consisted of major histocompatibility (MHC) haploidentical parental PBMC which were stimulated with mitogen and then pulsed with heat-killed SIVcyn. CTL activity was demonstrated in PBMCs from all four infected animals. The effector cells are T cells which mediate cytotoxicity against SIVcyn-pulsed target cells in an MHC-restricted manner. Furthermore, the cytotoxicity is virus specific and predominantly, if not exclusively, mediated by CD8+ T cells; it is also MHC class I restricted. Incubation of target cells with pepstatin A during antigen pulsing prior to the cytotoxic assay inhibited target cell generation, suggesting that viral antigens are processed via an endocytic pathway.

4-1BB Ligand, a Member of the TNF Family, Is Important for the Generation of Antiviral CD8 T Cell Responses

4-1BB (CD137) is a costimulatory molecule expressed on activated T cells and interacts with 4-1BB ligand (4-1BBL) on APCs. To investigate the role of 4-1BB costimulation for the development of primary immune responses, 4-1BBL-deficient (4-1BBL−/−) mice were infected with lymphocytic choriomeningitis virus (LCMV). 4-1BBL−/− mice were able to generate CTL and eliminate acute LCMV infection with normal kinetics, but CD8 T cell expansion was 2- to 3-fold lower than in wild-type (+/+) mice. In the same mice, virus-specific CD4 Th and B cell responses were minimally affected, indicating that 4-1BB costimulation preferentially affects CD8 T cell responses. This result contrasts with our earlier work with CD40L-deficient (CD40L−/−) mice, in which the CD8 T cell response was unaffected and the CD4 T cell response was markedly impaired. When both 4-1BBL- and B7-dependent signals were absent, CD8 T cell expansion was further reduced, resulting in lower CTL activity and impairing their ability to clear LCMV. Altogether, these results indicate that T cells have distinct costimulatory requirements: optimal CD8 responses require 4-1BBL-dependent interactions, whereas CD4 responses are minimally affected by 4-1BB costimulation, but require CD40-CD40L and B7-dependent interactions.

Rapid on/off cycling of cytokine production by virus-specific CD8+ T cells

CD8-positive T cells protect the body against viral pathogens by two important mechanisms: production of antiviral cytokines and lysis of infected cells. Cytokine production can have both local and systemic consequences, whereas cytolytic activity is limited to infected cells that are in direct contact with T cells. Here we analyse activated CD8-positive T cells from mice infected with lymphocytic choriomeningitis virus and find that cytokines are not produced ex vivo in the absence of peptide stimulation, but that they are rapidly generated after T cells encounter viral peptides bound to the major histocompatibility complex. Remarkably, cytokine production ceases immediately upon dissociation of the T cells from their targets and resumes when antigenic contact is restored. In contrast to the 'on/off/on' cycling of cytokines, the pore-forming cytotoxic protein perforin is constitutively maintained. Our results indicate that there is differential expression of effector molecules according to whether the antiviral product is secreted (like cytokines) or stored inside the cell (like perforin). The ability to turn cytokines on and off while maintaining intracellular stores of perforin shows the versatility of the cellular immune response and provides a mechanism for maintaining effective immune surveillance while reducing systemic immunopathology.

Induction of cytotoxic and helper T cell responses by modified simian immunodeficiency virus hypervariable epitope constructs

We previously reported the broad humoral immunogenicity of peptides synthesized according to the cumulative variability of an epitope (1,16). These peptides, hypervariable epitope constructs (HECs), are designed to represent the envelope glycoproteins of several isolates of the simian immunodeficiency virus (SIV). When HEC peptides were conjugated to palmitic acid and palmitic acid ester (lipoHECs), they promoted the induction of cellular immune responses. SIV envelope lipoHEC immunization of BALB/c and ICR mice resulted in up to 80% cytotoxic T lymphocyte (CTL) lysis of SIV envelope-expressing target cells and SIV envelope-specific delayed type hypersensitivity (DTH). This DTH response was significantly higher than that of single peptide controls, and the response peaked at 24 hours. Strong SIV envelope-specific T-cell proliferative responses were also induced in mice with stimulation indexes higher than 20 for spleen cells and higher than 10 for lymph node cells. Overall, our results demonstrate that conjugation of these variable synthetic peptides to a lipid moiety results in an immunogen capable of inducing strong and cross-reactive cellular immune responses.

Lymphotoxin-beta-deficient mice show defective antiviral immunity

Lymphotoxin beta (LTbeta), a member of the tumor necrosis factor family, plays an important role in lymphoid organogenesis. In order to determine whether LTbeta is involved in cellular immunity, we investigated the antiviral immune response of LTbeta-deficient (LTbeta -/-) mice to lymphocytic choriomeningitis virus (LCMV). Cytotoxic T lymphocyte (CTL) responses to LCMV were severely diminished, leading to viral persistence in brain and kidney. However, major functions of LTbeta-deficient T lymphocytes and dendritic cells were intact. Reconstitution of irradiated LTbeta +/+ mice with LTbeta -/- bone marrow induced a disorganized splenic structure, accompanied by impairment of the LCMV-specific CTL response. These data indicate that the absence of LTbeta does not affect the intrinsic function of T lymphocytes or of dendritic cells but that the structural integrity of the spleen is strongly associated with generation of antiviral immunity.

Type 1 CD4(+) T-cell help is required for induction of antipeptide multispecific cytotoxic T lymphocytes by a lipopeptidic vaccine in rhesus macaques

We have optimized the induction of antiviral cytotoxic T lymphocytes (CTL) in rhesus macaques by a lipopeptide vaccine containing seven peptides from simian immunodeficiency virus (SIV) Nef and Gag proteins and a strong T-helper peptide from tetanus toxoid (TT) that is promiscuous in humans (peptide TT 830-846). Two of the eight immunized macaques showed T-helper (Th) cell proliferation and a specific synthesis of gamma interferon in response to TT 830-846 peptide. They also showed multispecific cytotoxic activity against three to five of the immunizing SIV peptides. These results show the importance of a strong specific type 1 Th response for inducing a multispecific CTL response in vivo, which is essential for the development of an anti-human immunodeficiency virus vaccine.

Utilization of MHC Class I Transgenic Mice for Development of Minigene DNA Vaccines Encoding Multiple HLA-Restricted CTL Epitopes

We engineered a multiepitope DNA minigene encoding nine dominant HLA-A2.1- and A11-restricted epitopes from the polymerase, envelope, and core proteins of hepatitis B virus and HIV, together with the PADRE (pan-DR epitope) universal Th cell epitope and an endoplasmic reticulum-translocating signal sequence. Immunization of HLA transgenic mice with this construct resulted in: 1) simultaneous CTL induction against all nine CTL epitopes despite their varying MHC binding affinities; 2) CTL responses that were equivalent in magnitude to those induced against a lipopeptide known be immunogenic in humans; 3) induction of memory CTLs up to 4 mo after a single DNA injection; 4) higher epitope-specific CTL responses than immunization with DNA encoding whole protein; and 5) a correlation between the immunogenicity of DNA-encoded epitopes in vivo and the in vitro responses of specific CTL lines against minigene DNA-transfected target cells. Examination of potential variables in minigene construct design revealed that removal of the PADRE Th cell epitope or the signal sequence, and changing the position of selected epitopes, affected the magnitude and frequency of CTL responses. Our results demonstrate the simultaneous induction of broad CTL responses in vivo against multiple dominant HLA-restricted epitopes using a minigene DNA vaccine and underline the utility of HLA transgenic mice in development and optimization of vaccine constructs for human use.

Lipopeptide particles as the immunologically active component of CTL inducing vaccines

Using a bipalmitoylated lipopeptide consisting of an ovalbumin helper T-cell epitope covalently linked to an influenza virus cytotoxic T-lymphocyte (CTL) epitope, we addressed possible factors that may be critical for CTL induction. Antigen processing of lipopeptide appears to be required for T-cell induction since there was virtually no in vitro binding of lipopeptide to purified MHC molecules. A major portion of lipopeptide immunogenicity was due to its particulate nature inasmuch as CTL induction in mice correlated with insoluble lipopeptide constructs, whereas more soluble analogs were significantly less immunogenic. Immunohistological analysis of tissue from immunized animals revealed that lipopeptide migration from the s.c. injection site to the spleen could be detected as early as 1 h after immunization and cell-associated lipopeptide was observed on macrophages and dendritic cells, implicating both cell populations in the processing and presentation of lipopeptide particles to CTLs.

CD40 ligand-mediated interactions are involved in the generation of memory CD8(+) cytotoxic T lymphocytes (CTL) but are not required for the maintenance of CTL memory following virus infection

CD8(+) cytotoxic T lymphocytes (CTL) play a key role in the control of many virus infections, and the need for vaccines to elicit strong CD8(+) T-cell responses in order to provide optimal protection in such infections is increasingly apparent. However, the mechanisms involved in the induction and maintenance of CD8(+) CTL memory are currently poorly understood. In this study, we investigated the involvement of CD40 ligand (CD40L)-mediated interactions in these processes by analyzing the memory CTL response of CD40L-deficient mice following infection with lymphocytic choriomeningitis virus (LCMV). The maintenance of memory CD8(+) CTL precursors (CTLp) at stable frequencies over time was not impaired in CD40L-deficient mice. By contrast, the initial generation of memory CTLp was affected. CD40L-deficient mice produced lower levels of CD8(+) CTLp during the primary immune response to LCMV than did wild-type controls, despite the fact that the LCMV-specific effector CTL response of CD40L-deficient mice was indistinguishable from that of control animals. The differentiation of naïve CD8(+) T cells into effector and memory CTL thus involves pathways that can be discriminated from each other by their requirement for CD40L-mediated interactions. Expression of CD40L by CTLp themselves was not an essential step during their expansion and differentiation from naïve CD8(+) cells into memory CTLp; instead, the reduction in memory CTLp generation in CD40L-deficient mice was likely a consequence of defects in the CD4(+) T-cell response mounted by these animals. These results thus suggest a previously unappreciated role for CD40L in the generation of CD8(+) memory CTLp, the probable nature of which is discussed.

Intestinal intraepithelial lymphocytes are primed for gamma interferon and MIP-1beta expression and display antiviral cytotoxic activity despite severe CD4(+) T-cell depletion in primary simian immunodeficiency virus infection

Intraepithelial lymphocytes (IEL) are a critical effector component of the gut-associated lymphoid tissue (GALT) and play an important role in mucosal immunity as well as in the maintenance of the epithelial cell integrity and barrier function. The objective of this study was to determine whether simian immunodeficiency virus (SIV) infection of rhesus macaques would cause alterations in the immunophenotypic profiles of IEL and their mitogen-specific cytokine (gamma interferon [IFN-gamma] and MIP-1beta) responses (by flow cytometry) and virus-specific cytotoxic T-cell (CTL) activity (by the chromium release assay). Virally infected IEL were detected through the entire course of SIV infection by in situ hybridization. Severe depletion of CD4(+) single-positive and CD4(+)CD8(+) double-positive T cells occurred early in primary SIV infection, which was coincident with an increased prevalence of CD8(+) T cells. This was in contrast to a gradual depletion of CD4(+) T cells in peripheral blood. The CD8(+) IEL were the primary producers of IFN-gamma and MIP-1beta and were found to retain their potential to produce both IFN-gamma and MIP-1beta through the entire course of SIV infection. SIV-specific CTL activity was detected in primary IEL at 1, 2, and 4 weeks post-SIV infection. These results demonstrated that IEL may be involved in generating antiviral immune responses early in SIV infection and in suppressing viral infection thereafter. Alterations in homeostasis in epithelia due to severe CD4(+) T-cell depletion accompanied by changes in the cytokine and chemokine production by IEL may play a role in the enteropathogenesis of SIV infection.

Intrahepatic hepatitis C virus-specific cytotoxic T lymphocyte activity and response to interferon alfa therapy in chronic hepatitis C

Hepatitis C virus (HCV)-specific cytotoxic T lymphocytes (CTL) have been shown to play a role in host defense and pathogenesis of chronic HCV infection. Our aim was to test the hypothesis that intrahepatic HCV-specific CTL activity may impact subsequent response to interferon alfa (IFN-alpha) therapy. Of the 37 patients that we have prospectively evaluated for HCV-specific CTL activity in liver, 21 received IFN therapy, and 19 completed a 6-month course and attended 6 to 18 months of follow-up. Intrahepatic CD8+ cells were isolated from liver biopsy tissue and tested against target cells expressing HCV antigens to determine intrahepatic CTL activity. The relationship between treatment response and HCV-specific CTL activity and other factors known to associate with response (genotype, viremia, histology) was analyzed. HCV-specific CTL activity was detected in 9 of 21 patients (and 9 of 19 who completed therapy). After 6 months of IFN therapy, 8 of 19 (42%) patients had normal serum alanine transaminase (ALT) (complete responders). After 18 months of follow-up, only 3 patients (16%) had a sustained biochemical response. Of the 9 patients with detectable HCV-specific CTL activity in their liver before treatment, 7 (78%) developed a complete response. In contrast, only 1 of the 10 patients with no detectable HCV-specific CTL activity developed a complete response to IFN (P < .01). In 6 of 8 patients with a complete response, including the 3 sustained responders, the CTL response appeared to be directed predominately to the HCV core region. These data suggest that the host immune response, particularly that mediated by CD8+ CTL, may be important in determining the outcome of IFN therapy for chronic HCV infection. Further understanding of the mechanism of action of IFN should impact the design of better therapeutic strategies against chronic HCV infection.