Cellular immune responses against hepatitis C virus: the evidence base 2002

Hepatitis C virus (HCV) is an RNA virus which is estimated to persistently infect about 170 million people worldwide. After acute infection, there is an initial period during which long-term outcome is decided. There is strong evidence that the cellular immune responses, involving both CD4+ and CD8+ T lymphocytes, are involved at this stage and it is their effectiveness which determines outcome. What is not understood is what determines their effectiveness. The most important component of this is likely to be some aspect of epitope selection, itself dictated by host MHC. Thus, to understand host immunity to HCV, we need to have a detailed understanding of the peptides involved in T lymphocyte responses. In this review, we discuss the peptide epitopes that have been identified so far, and their potential significance. We relate this to a scheme of host defence which may be useful for understanding natural and vaccine-induced immunity.     

Antigen presentation and the regulation of CD4 memory generation to influenza

Influenza virus epidemics are responsible for approximately 1 million human deaths annually, and a pandemic caused by H5N1 avian influenza viruses could result in over 50 million deaths. Current vaccine strategies cannot prevent the first wave of an influenza pandemic because their formulation is virus-strain specific and requires advance knowledge of the specific virus strain circulating in any given year. We must develop innovative vaccine strategies in order to vaccinate effectively against newly emerging and highly virulent influenza virus strains. Since CD4 T-cell responses are required for long-lived and protective B-cell and CD8 T-cell immunity, new vaccines must be designed to elicit both T- and B-cell immunity against a broader range of influenza virus strains.     

Lower cellular immune responses to influenza A (H3N2) in the elderly

Influenza epidemic is an important cause of severe illness in the elderly. Age‐dependent morbidity of influenza in the elderly is associated with weakened immunity. The baseline age‐related memory T cell activity in Chinese persons who are exposed to influenza virus through natural infection, are associated with the protective response to the virus after vaccination, thus providing important pre‐vaccination information. A cohort from the general population was established at the end of an influenza season in an area where influenza occurs regularly, and followed for 24 weeks. The subjects had no vaccination history for 5 years. Memory T cell responses were evaluated using a set of peptides spanning the influenza A (H3N2) entire proteome in a gamma interferon (IFN‐γ)‐enzyme‐linked immunospot (ELISPOT) assay, prior to the next influenza season. Changes of hemagglutination inhibition (HI) antibody titers were also evaluated. IFN‐γ⁺ T cell responses against influenza peptides were significantly lower in subjects of 60 years and older. Although the age‐related decline of cellular immune response was clear, no significant association of antibody titers with age was found. The pre‐vaccination baseline of memory IFN‐γ⁺ T cell immunity state in elderly Chinese was significantly lower than in people younger than 60 years. Measurement of the ex vivo cellular immune responses to influenza should be incorporated into the evaluation of protective immunity in elderly persons. J. Med. Virol. 81:1471–1476, 2009. © 2009 Wiley‐Liss, Inc.     

Cellular and humoral immune responses to measles in immune adults re-immunized with measles vaccine

The objective of this study was to characterize the kinetics of the cellular and humoral immune responses elicited by measles vaccine given to previously immune adults. The cellular and humoral immune responses to measles were measured in seven healthy adults, before vaccination and at 1, 2, 3, and 4 weeks and 3 months after vaccination, using measles-specific T-cell proliferation and plaque reduction neutralization assays. All study subjects had detectable measles antibodies, but only six (85%) showed protective titers, defined as >1:120, before immunization. However measles-specific T-cell proliferation was not detectable before vaccination in any of the subjects. The six subjects with protective titers showed a positive stimulation index (SI) of >3.0 within the first 4 weeks after vaccination, an SI of 5 at the 4th week, and an SI of 3 at 3 months after vaccination. The subject with a low antibody titer (1:99) before vaccination developed a high SI at 3 months after vaccination. This subject was the only participant whose neutralizing antibody titers increased more than 4-fold by 3 months after vaccination. No significant increases in geometric mean titers were detected in the other six subjects during the follow-up period. These data suggest that high measles antibody titers interfere with the humoral response in subjects who receive a booster immunization, whereas the cellular response is boosted at least transiently, after revaccination.     

Interrupting CD28 costimulation before antigen rechallenge affects CD8+ T‐cell expansion and effector functions during secondary response in mice

The role of CD28‐mediated costimulation in secondary CD8⁺ T‐cell responses remains controversial. Here, we have used two tools — blocking mouse anti‐mouse CD28‐specific antibodies and inducible CD28‐deleting mice — to obtain definitive answers in mice infected with ovalbumin‐secreting Listeria monocytogenes. We report that both blockade and global deletion of CD28 reveal its requirement for full clonal expansion and effector functions such as degranulation and IFN‐γ production during the secondary immune response. In contrast, cell‐intrinsic deletion of CD28 in transferred TCR‐transgenic CD8⁺ T cells before primary infection leads to impaired clonal expansion but an increase in cells able to express effector functions in both primary and secondary responses. We suggest that the proliferation‐impaired CD8⁺ T cells respond to CD28‐dependent help from their environment by enhanced functional differentiation. Finally, we report that cell‐intrinsic deletion of CD28 after the peak of the primary response does not affect the establishment, maintenance, or recall of long‐term memory. Thus, if given sufficient time, the progeny of primed CD8⁺ T cells adapt to the absence of this costimulator.     

CD8 T cell responses to influenza virus infection in aged mice

Influenza is one of the most common infectious diseases afflicting humans, particularly the elderly. The murine model has been widely employed for investigation of immunity to influenza virus infection. In this paper, we review the recent advances in understanding the diminished CD8 T cell immune response to influenza virus infection in aged mice. Possible mechanisms of impaired CD8 T cell responses with aging are addressed, including: (1) the role of dendritic cells (DCs); (2) the effect of age-associated changes in the T cell repertoire; and (3) the interactions with CD4 T cells, including T regulatory (Treg) cells and CD4 T helper cells. The aged murine model of the CD8 T cell response to influenza virus is helping to elucidate the mechanisms of immunosenescence which can lead to therapeutic improvements in the primary CD8 T cell response to new infections, as well as the development of new strategies for immunization to prevent influenza in the elderly.     

Evaluation of CD62L expression as a marker for vaccine-elicited memory cytotoxic T lymphocytes

The development of successful vaccination strategies for eliciting cytotoxic T lymphocytes (CTLs) will be facilitated by the definition of strategies for subdividing CTLs into functionally distinct subpopulations. We assessed whether surface expression of a number of cell‐surface proteins could be used to define functionally distinct subpopulations of memory CTLs in mice immunized with a recombinant vaccinia virus expressing human immunodeficiency virus (HIV)‐1 envelope (Env). We found changes in cell‐surface expression of CD11a, CD44, CD45RB, CD49d, CD54 and CD62L on Env‐specific CD8⁺ T cells that appeared to differentiate them from other CD8⁺ T cells within 1 week to 1 month following immunization. Further, we saw an up‐regulation of CD62L surface expression on Env‐specific CD8⁺ memory T cells several months after immunization. However, CD62L expression did not correlate with differences in the abilities of CTLs to proliferate or produce interferon gamma (IFN‐γ) and tumour necrosis factor alpha (TNF‐α) in vitro in response to Env peptide stimulation. Moreover, the expression of CD62L did not allow differentiation of CTLs into subpopulations with distinct expansion kinetics in vivo after adoptive transfer into naïve mice and subsequent boosting of these mice with a recombinant adenovirus expressing HIV‐1 Env. Therefore, the definition of memory CD8⁺ T‐cell subpopulations on the basis of CD62L expression in mice does not allow the delineation of functionally distinct CTL subpopulations.     

Immunoregulation of fetal and anti-paternal immune responses

Immunological tolerance to the fetus is essential for fetal survival during pregnancy. The semi-allogeneic fetus expresses genes foreign to the mother that can be recognized by maternal T cells. Under times of stress or infection, deleterious immune responses can result in fetal destruction and/or maternal death. Exposure to non-maternal antigens begins as early as insemination and some of the mechanisms required to prevent maternal priming against these antigens are in place before sexual encounter. Continuous and overlapping regulatory mechanisms must cooperate to allow the best chances for fertilization, implantation, and healthy gestation, simultaneously protecting the fetus from maternal immune attack yet making minimal compromises in resistance to infection. Several types of immune cell from both the innate and adaptive arms of the immune system help protect both the mother and fetus during pregnancy. It’s the intricate communication and interplay between the immune system and the endocrine system that will ultimately decide the success or fate of the developing fetus.     

Strategies and challenges in eliciting immunity to melanoma

Summary: The ability of CD8⁺ T cells to recognize melanoma tumors has led to the development of immunotherapeutic approaches that use the antigens CD8⁺ T cells recognize. However, clinical response rates have been disappointing. Here we summarize our work to understand the mechanisms of self-tolerance that limit responses to currently utilized antigens and our approach to identify new antigens directly tied to malignancy. We also explore several aspects of the anti-tumor immune response induced by peptide-pulsed dendritic cells (DCs). DCs differentially augment the avidity of recall T cells specific for self-antigens and overcome a process of aberrant CD8⁺ T-cell differentiation that occurs in tumor-draining lymph nodes. DC migration is constrained by injection route, resulting in immune responses in localized lymphoid tissue, and differential control of tumors depending on their location in the body. We demonstrate that CD8⁺ T-cell differentiation in different lymphoid compartments alters the expression of homing receptor molecules and leads to the presence of systemic central memory cells. Our studies highlight several issues that must be addressed to improve the efficacy of tumor immunotherapy.     

B7-1-dependent co-stimulation results in qualitatively and quantitatively different responses by CD4+ and CD8+ T cells

To characterize better the co-stimulatory activity of native B7-1 in the absence of other receptor/ligand interactions that might contribute to the response, B7-1 was purified by monoclonal antibody (mAb) affinity chromatography. Immobilization of purified B7-1 with anti-T cell receptor (TCR) mAb on cell-sized latex microspheres provided an effective stimulus for activation of both CD4⁺ and CD8⁺ T cells as measured by proliferation, development of effector function, and changes in motility and adhesion. The CD4⁺ T cell response was prolonged and resulted in efficient interleukin-2 production and clonal expansion. In contrast, CD8⁺ responses were transient. Proliferation and clonal expansion peaked on days 3 and 4, coincident with maximal expression of lytic effector function, and the cells then died. These results demonstrate that B7-1 mediated co-stimulation is sufficient for the induction of effector function in both helper and cytotoxic T cell precursors, but suggest that B7-1 co-stimulation is not sufficient to sustain helper-independent CD8⁺ CTL responses. When the dose responses of CD4⁺ and CD8⁺ T cells to B7-1 were compared, CD8⁺ T cells were found to require higher densities of B7-1 to attain an equivalent level of activation, suggesting that the level of expression of B7-1 by APC may influence the development of helper or CTL responses. Finally, in contrast to results obtained by others with B7-1 transfectants, purified B7-1 did not provide co-stimulation when presented on a surface separate from the TCR stimulus.     

Relationship of Th1/Th2 cell balance with the immune response to influenza vaccine during pregnancy

To determine the optimal timing for influenza vaccination in pregnant women, we measured alterations in the types 1 and 2 T helper cell (Th1/Th2) balance during pregnancy, monitored specific immunity to inoculated antigens after vaccination with inactivated influenza vaccine, evaluated the relevance of the Th1/Th2 ratio and immune responses to the vaccination, monitored the maintenance of high antibody titers until delivery and measured the transplacental antibody transfer rate. No significant alterations of the Th1/Th2 balance were noted in the 65% of pregnant women among whom the Th1/Th2 ratio was lower than 9.9% in the first trimester. In those groups with a ratio higher than 10% in the first trimester, there was a tendency for the ratio to decrease as gestation advanced. The efficiency of immunization was not influenced by the Th1/Th2 status or by the stage of gestation. The antibody titer decreased steadily with time from 1 month after vaccination to the time of delivery. Conversely, the transfer rate of antibodies from maternal to fetal blood at the time of delivery increased with the duration of gestation after vaccination. Nevertheless, the antibody titers in both maternal and fetal blood were sufficient to afford protection against infection. Thus, efficient influenza vaccination can be undertaken at any stage of pregnancy. J. Med. Virol. 81:1923–1928, 2009. © 2009 Wiley‐Liss, Inc.     

A correlation between function and selected measures of T cell avidity in influenza virus-specific CD8+ T cell responses

Activation of mature CD8+ T cells requires recognition, via the T cell receptor (TCR), of peptide + MHC (pMHC) complexes with an avidity that exceeds a designated threshold. Multiple indicators of T cell avidity have been described that provide unique information on the characteristics of T cell interactions. However, these indicators are routinely used in isolation, and, consequently, little is known about correlations between these measures or which measure, if any, correlates with the quality of the T cell response. Following influenza virus infection of C57BL/6J mice, we analyzed the relative avidities of five epitope-specific CD8+ T cell populations using five different measures. We demonstrated that the quality of CD8+ T cell responses, in terms of cytokine profiles, correlates with TCR dissociation rate and CD8 dependence, but not with the sensitivity to tetramer binding or peptide stimulation. Thus, we propose that, despite significant differences in TCR dissociation rate, the stimulation threshold of influenza-specific CD8+ T cell populations may be equivalent due to compensatory mechanisms largely provided by the CD8 coreceptor. Furthermore, this study shows that different indicators of avidity do not necessarily provide similar information and should be used in combination to obtain an overall picture of the characteristics of TCR binding.     

Lapatinib and doxorubicin enhance the Stat1‐dependent antitumor immune response

The dual erbB1/2 tyrosine kinase inhibitor lapatinib as well as the anthracycline doxorubicin are both used in the therapy of HER2‐positive breast cancer. Using MMTV‐neu mice as an animal model for HER2‐positive breast cancer, we observed enhanced tumor infiltration by IFN‐γ‐secreting T cells after treatment with doxorubicin and/or lapatinib. Antibody depletion experiments revealed a contribution of CD8⁺ but not CD4⁺ T cells to the antitumor effect of these drugs. Doxorubicin treatment additionally decreased the content of immunosuppressive tumor‐associated macrophages (TAMs) in the tumor bed. In contrast, Stat1‐deficient mice were resistant to tumor growth inhibition by lapatinib and/or doxorubicin and exhibited impaired T‐cell activation and reduced T‐cell infiltration of the tumor in response to drug treatment. Furthermore, Stat1‐deficiency resulted in reduced expression of the T‐cell chemotactic factors CXCL9, CXCL10, and CXCL11 in the tumor epithelium. The inhibition of TAM infiltration of the tumor by doxorubicin and the immunosuppressive function of TAMs were found to be Stat1 independent. Taken together, the results point to an important contribution toward enhancing T‐cell and IFN‐γ‐based immunity by lapatinib as well as doxorubicin and emphasize the role of Stat1 in building an effective antitumor immune response.     

Modulating numbers and phenotype of CD8+ T cells in secondary immune responses

Prime‐boost regimens are frequently used to increase the number of memory CD8⁺ T cells and thus the protective capacity of experimental vaccinations; however, it is currently unknown how the frequency and phenotype of primary (1°) memory CD8⁺ T cells impact the quantity and phenotype of secondary (2°) memory CD8⁺ T‐cell populations. Here, we show that 2° infections of mice that received different 1° infections and/or immunizations generated similar numbers of 2° effector and memory CD8⁺ T cells. Remarkably, this result was independent of the numbers and phenotype of 1° memory CD8⁺ T cells present at the time of rechallenge. However, after adoptive transfer of low numbers of 1° memory CD8⁺ T cells, a linear correlation between 1° memory CD8⁺ T‐cell input and 2° memory CD8⁺ T‐cell numbers was observed. These data suggest that, above a very low threshold, boosting of 1° memory CD8⁺ T‐cell populations elicits 2° immune responses of similar magnitude. Therefore, our study has important implications for the design of prime‐boost regimens that aim to generate protective CD8⁺ T‐cell‐mediated immunity.     

Critical role for IL-21 in both primary and memory anti-viral CD8+ T-cell responses

While it is well established that CD8(+) T cells generated in the absence of CD4(+) T cells mediate defective recall responses, the mechanism by which CD4(+) T cells confer help in the generation of CD8(+) T-cell responses remains poorly understood. To determine whether CD4(+) T-cell-derived IL-21 is an important regulator of CD8(+) T-cell responses in help-dependent and -independent viral infections, we examined these responses in the IL-21Rα(-/-) mouse model. We show that IL-21 has a role in primary CD8(+) T-cell responses and in recall CD8(+) T-cell responses in help-dependent viral infections. This effect is due to a direct action of IL-21 in enhancing the proliferation of virus-specific CD8(+) T cells and reducing their TRAIL expression. These findings indicate that IL-21 is an important mediator of CD4(+) T-cell help to CD8(+) T cells.     

SARS-CoV-2 breakthrough infection induces rapid memory and de novo T cell responses

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Human CD8+ T cells specific for influenza A virus M1 display broad expression of maturation-associated phenotypic markers and chemokine receptors

To define the role of memory T cells in a non-persistent viral infection, we have delineated the phenotype of memory CD8+ T cells specific for influenza A virus (FluA; matrix protein M158-66) based on the expression of several memory/effector lineage markers and relevant chemokine receptors. We found a majority of FluA-specific CD8+ T cells expressed CD27 and CD28, and variably expressed CD45RA, CD62L, CD94 and granzyme A. A majority of FluA-specific CD8+ T cells expressed high levels of CXCR3, and moderate levels of CCR5 and CXCR4, whereas a limited proportion expressed CCR7, CCR6 and CXCR5. A phenotypic profile based on these observations showed that there are both immature and mature memory CD8+ T cells specific for FluA.     

CD8类McAb—SM4的研制与鉴定

本文报导一株抗人T细胞亚群单克隆抗体SM_4的研制与鉴定。SM_4仅与T细胞中的一个亚群反应,在淋巴组织冰冻切片上,SM_4只与胸腺依赖区的部分细胞反应,其组织分布特征与CD_8单抗相类似。叠加试验结果表明SM_4与CD_8类单抗识别同一细胞亚群——Ts/Tc亚群。竞争抑制试验进一步证明SM_4识别CD_8分子上某一特定表位。本文还就CD_8亚群异质性问题及SM_4的应用潜力进行了讨论。     

Vaccine molecules targeting Xcr1 on cross‐presenting DCs induce protective CD8+ T‐cell responses against influenza virus

Targeting antigens to cross‐presenting dendritic cells (DCs) is a promising method for enhancing CD8⁺ T‐cell responses. However, expression patterns of surface receptors often vary between species, making it difficult to relate observations in mice to other animals. Recent studies have indicated that the chemokine receptor Xcr1 is selectively expressed on cross‐presenting murine CD8α⁺ DCs, and that the expression is conserved on homologous DC subsets in humans (CD141⁺ DCs), sheep (CD26⁺ DCs), and macaques (CADM1⁺ DCs). We therefore tested if targeting antigens to Xcr1 on cross‐presenting DCs using antigen fused to Xcl1, the only known ligand for Xcr1, could enhance immune responses. Bivalent Xcl1 fused to model antigens specifically bound CD8α⁺ DCs and increased proliferation of antigen‐specific T cells. DNA vaccines encoding dimeric Xcl1‐hemagglutinin (HA) fusion proteins induced cytotoxic CD8⁺ T‐cell responses, and mediated full protection against a lethal challenge with influenza A virus. In addition to enhanced CD8⁺ T‐cell responses, targeting of antigen to Xcr1 induced CD4⁺ Th1 responses and highly selective production of IgG2a antibodies. In conclusion, targeting of dimeric fusion vaccine molecules to CD8α⁺ DCs using Xcl1 represents a novel and promising method for induction of protective CD8⁺ T‐cell responses.