IL-7R alpha versus CCR7 and CD45 as markers of virus-specific CD8+ T cell differentiation: contrasting pictures in blood and tonsillar lymphoid tissue

Memory inflation: Beyond the acute phase of viral infection

Memory inflation is confirmed as the most commonly dysregulation of host immunity with antigen-independent manner in mammals after viral infection. By generating large numbers of effector/memory and terminal differentiated effector memory CD8+ T cells with diminished naïve subsets, memory inflation is believed to play critical roles in connecting the viral infection and the onset of multiple diseases. Here, we reviewed the current understanding of memory inflated CD8+ T cells in their distinct phenotypic features that different from exhausted subsets; the intrinsic and extrinsic roles in regulating the formation of memory inflation; and the key proteins in maintaining the expansion and proliferation of inflationary populations. More importantly, based on the evidences from both clinic and animal models, we summarized the potential mechanisms of memory inflation to trigger autoimmune neuropathies, such as Guillain-Barré syndrome and multiple sclerosis; the correlations of memory inflation between tumorigenesis and resistance of tumour immunotherapies; as well as the effects of memory inflation to facilitate vascular disease progression. To sum up, better understanding of memory inflation could provide us an opportunity to beyond the acute phase of viral infection, and shed a light on the long-term influences of CD8+ T cell heterogeneity in dampen host immune homeostasis.

Cytotoxic CD8+ Temra cells show loss of chromatin accessibility at genes associated with T cell activation

As humans age, their memory T cell compartment expands due to the lifelong exposure to antigens. This expansion is characterized by terminally differentiated CD8+ T cells (Temra), which possess NK cell-like phenotype and are associated with chronic inflammatory conditions. Temra cells are predominantly driven by the sporadic reactivation of cytomegalovirus (CMV), yet their epigenomic patterns and cellular heterogeneity remain understudied. To address this gap, we correlated their gene expression profiles with chromatin openness and conducted single-cell transcriptome analysis, comparing them to other CD8+ subsets and CMV-responses. We confirmed that Temra cells exhibit high expression of genes associated with cytotoxicity and lower expression of costimulatory and chemokine genes. The data revealed that CMV-responsive CD8+ T cells (Tcmv) were predominantly derived from a mixed population of Temra and memory cells (Tcm/em) and shared their transcriptomic profiles. Using ATAC-seq analysis, we identified 1449 differentially accessible chromatin regions between CD8+ Temra and Tcm/em cells, of which only 127 sites gained chromatin accessibility in Temra cells. We further identified 51 gene loci, including costimulatory CD27, CD28, and ICOS genes, whose chromatin accessibility correlated with their gene expression. The differential chromatin regions Tcm/em cells were enriched in motifs that bind multiple transcriptional activators, such as Jun/Fos, NFkappaB, and STAT, whereas the open regions in Temra cells mainly contained binding sites of T-box transcription factors. Our single-cell analysis of CD8+CCR7loCD45RAhi sorted Temra population showed several subsets of Temra and NKT-like cells and CMC1+ Temra populations in older individuals that were shifted towards decreased cytotoxicity. Among CD8+CCR7loCD45RAhi sorted cells, we found a decreased proportion of IL7R+ Tcm/em-like and MAIT cells in individuals with high levels of CMV antibodies (CMVhi). These results shed new light on the molecular and cellular heterogeneity of CD8+ Temra cells and their relationship to aging and CMV infection.

The hallmarks of CMV-specific CD8 T-cell differentiation

Upon cytomegalovirus (CMV) infection, large T-cell responses are elicited that remain high or even increase over time, a phenomenon named memory T-cell inflation. Besides, the maintained robust T-cell response, CMV-specific T cells seem to have a distinctive phenotype, characterized by an advanced differentiation state. Here, we will review this "special" differentiation status by discussing the cellular phenotype based on the expression of CD45 isoforms, costimulatory, inhibitory and natural killer receptors, adhesion and lymphocyte homing molecules, transcription factors, cytokines and cytotoxic molecules. In addition, we focus on whether the differentiation state of CMV-specific CD8 T cells is unique in comparison with other chronic viruses and we will discuss the possible impact of factors such as antigen exposure and aging on the advanced differentiation status of CMV-specific CD8 T cells.

Tissue reservoirs of antiviral T cell immunity in persistent human CMV infection

T cell responses to viruses are initiated and maintained in tissue sites; however, knowledge of human antiviral T cells is largely derived from blood. Cytomegalovirus (CMV) persists in most humans, requires T cell immunity to control, yet tissue immune responses remain undefined. Here, we investigated human CMV-specific T cells, virus persistence and CMV-associated T cell homeostasis in blood, lymphoid, mucosal and secretory tissues of 44 CMV seropositive and 28 seronegative donors. CMV-specific T cells were maintained in distinct distribution patterns, highest in blood, bone marrow (BM), or lymph nodes (LN), with the frequency and function in blood distinct from tissues. CMV genomes were detected predominantly in lung and also in spleen, BM, blood and LN. High frequencies of activated CMV-specific T cells were found in blood and BM samples with low virus detection, whereas in lung, CMV-specific T cells were present along with detectable virus. In LNs, CMV-specific T cells exhibited quiescent phenotypes independent of virus. Overall, T cell differentiation was enhanced in sites of viral persistence with age. Together, our results suggest tissue T cell reservoirs for CMV control shaped by both viral and tissue-intrinsic factors, with global effects on homeostasis of tissue T cells over the lifespan.

Efforts of the human immune system to maintain the peripheral CD8+ T cell compartment after childhood thymectomy

Background

Homeostatic mechanisms to maintain the T cell compartment diversity indicate an ongoing process of thymic activity and peripheral T cell renewal during human life. These processes are expected to be accelerated after childhood thymectomy and by the influence of cytomegalovirus (CMV) inducing a prematurely aged immune system.

The study aimed to investigate proportional changes and replicative history of CD8+ T cells, of recent thymic emigrants (RTEs) and CD103+ T cells (mostly gut-experienced) and the role of Interleukin-(IL)-7 and IL-7 receptor (CD127)-expressing T cells in thymectomized patients compared to young and old healthy controls.

Results

Decreased proportions of naive and CD31 + CD8+ T cells were demonstrated after thymectomy, with higher proliferative activity of CD127-expressing T cells and significantly shorter relative telomere lengths (RTLs) and lower T cell receptor excision circles (TRECs). Increased circulating CD103+ T cells and a skewed T cell receptor (TCR) repertoire were found after thymectomy similar to elderly persons. Naive T cells were influenced by age at thymectomy and further decreased by CMV.

Conclusions

After childhood thymectomy, the immune system demonstrated constant efforts of the peripheral CD8+ T cell compartment to maintain homeostasis. Supposedly it tries to fill the void of RTEs by peripheral T cell proliferation, by at least partly IL-7-mediated mechanisms and by proportional increase of circulating CD103+ T cells, reminiscent of immune aging in elderly. Although other findings were less significant compared to healthy elderly, early thymectomy demonstrated immunological alterations of CD8+ T cells which mimic features of premature immunosenescence in humans.

A Gene Expression Signature That Correlates with CD8+ T Cell Expansion in Acute EBV Infection

Virus-specific CD8(+) T cells expand dramatically during acute EBV infection, and their persistence is important for lifelong control of EBV-related disease. To better define the generation and maintenance of these effective CD8(+) T cell responses, we used microarrays to characterize gene expression in total and EBV-specific CD8(+) T cells isolated from the peripheral blood of 10 individuals followed from acute infectious mononucleosis (AIM) into convalescence (CONV). In total CD8(+) T cells, differential expression of genes in AIM and CONV was most pronounced among those encoding proteins important in T cell activation/differentiation, cell division/metabolism, chemokines/cytokines and receptors, signaling and transcription factors (TF), immune effector functions, and negative regulators. Within these categories, we identified 28 genes that correlated with CD8(+) T cell expansion in response to an acute EBV infection. In EBV-specific CD8(+) T cells, we identified 33 genes that were differentially expressed in AIM and CONV. Two important TF, T-bet and eomesodermin, were upregulated and maintained at similar levels in both AIM and CONV; in contrast, protein expression declined from AIM to CONV. Expression of these TF varied among cells with different epitope specificities. Collectively, gene and protein expression patterns suggest that a large proportion, if not a majority of CD8(+) T cells in AIM are virus specific, activated, dividing, and primed to exert effector activities. High expression of T-bet and eomesodermin may help to maintain effector mechanisms in activated cells and to enable proliferation and transition to earlier differentiation states in CONV.

Decreases in activated CD8+ T cells in patients with severe hepatitis B are related to outcomes

BACKGROUND

Many studies on T helper (Th)1, Th2, T regulatory and Th17 cells have been carried out in acute-on-chronic liver failure (ACLF). However, CD8(+) T cell, as a main participant in immune-mediated injuries and defense against microorganisms, has seldom been studied in ACLF.

AIMS

The purpose of this study was to investigate the CD8(+) T cell function, and the outcomes of patients with severe hepatitis [SH; serum bilirubin (SB) ≥ 10 mg/dl and prothrombin activity (PTA) < 60 %].

METHODS

Thirty-six patients with chronic HBV-associated SH were included. Twenty normal chronic hepatitis B (CHB) patients (2 < SB < 10 (mg/dl) and PTA ≥ 60 %) and 28 healthy volunteers were enrolled as control groups.

RESULTS

Twenty-six patients with SH were diagnosed with ACLF (SB ≥ 10 mg/dl and PTA ≤ 40 %). The non-recovered ACLFs (NR-ACLF) had higher HBV DNA loads than recovered ACLFs (R-ACLF) (6.03 ± 1.79 vs. 4.36 ± 1.61 (log10, IU/L)). The NR-ACLFs had the highest neutrophil:lymphocyte ratios (5.10 ± 2.37) (all P < 0.001; a = 0.05). The CHBs had higher perforin(+) and TCM (CD45RA(-)CD62L(hi)CCR7(+)) proportions [31.28 ± 19.51, 5.32 ± 3.57 (%)] compared to R-ACLFs (11.75 ± 15.35, 0.78 ± 0.76 (%); P = 0.004, 0.001, respectively), or NR-ACLFs (11.61 ± 5.79, 1.14 ± 0.67 (%); P = 0.006, 0.003). The non-ACLF SHs had higher CD38(+) proportions than R-ACLFs or NR-ACLFs (25.46 ± 8.02 vs. 16.24 ± 7.77 or 16.81 ± 6.30 (%), P = 0.039, 0.023).

CONCLUSIONS

High neutrophil:lymphocyte ratios and a decrease in activated CD8(+) T cells may be related to poor outcomes in patients with SH.

Diverse specificities, phenotypes, and antiviral activities of cytomegalovirus-specific CD8+ T cells

CD8(+) T cells specific for pp65, IE1, and IE2 are present at high frequencies in human cytomegalovirus (HCMV)-seropositive individuals, and these have been shown to have phenotypes associated with terminal differentiation, as well as both cytokine and proliferative dysfunctions, especially in the elderly. However, more recently, T cell responses to many other HCMV proteins have been described, but little is known about their phenotypes and functions. Consequently, in this study, we chose to determine the diversity of HCMV-specific CD8(+) T cell responses to the products of 11 HCMV open reading frames (ORFs) in a cohort of donors aged 20 to 80 years old as well as the ability of the T cells to secrete gamma interferon (IFN-γ). Finally, we also tested their functional antiviral capacity using a novel viral dissemination assay. We identified substantial CD8(+) T cell responses by IFN-γ enzyme-linked immunospot (ELISPOT) assays to all 11 of these HCMV proteins, and across the cohort, individuals displayed a range of responses, from tightly focused to highly diverse, which were stable over time. CD8(+) T cell responses to the HCMV ORFs were highly differentiated and predominantly CD45RA(+), CD57(+), and CD28(-), across the cohort. These highly differentiated cells had the ability to inhibit viral spread even following direct ex vivo isolation. Taken together, our data argue that HCMV-specific CD8(+) T cells have effective antiviral activity irrespective of the viral protein recognized across the whole cohort and despite viral immune evasion.

IMPORTANCE

Human cytomegalovirus (HCMV) is normally carried without clinical symptoms and is widely prevalent in the population; however, it often causes severe clinical disease in individuals with compromised immune responses. HCMV is never cleared after primary infection but persists in the host for life. In HCMV carriers, the immune response to HCMV includes large numbers of virus-specific immune cells, and the virus has evolved many mechanisms to evade the immune response. While this immune response seems to protect healthy people from subsequent disease, the virus is never eliminated. It has been suggested that this continuous surveillance by the immune system may have deleterious effects in later life. The study presented in this paper examined immune responses from a cohort of donors and shows that these immune cells are effective at controlling the virus and can overcome the virus' lytic cycle immune evasion mechanisms.

Varicella zoster-specific CD4+Foxp3+ T cells accumulate after cutaneous antigen challenge in humans

We investigated the relationship between varicella zoster virus (VZV)-specific memory CD4(+) T cells and CD4(+)Foxp3(+) regulatory T cells (Tregs) that accumulate after intradermal challenge with a VZV skin test Ag. VZV-specific CD4(+) T cells were identified with a MHC class II tetramer or by intracellular staining for either IFN-γ or IL-2 after Ag rechallenge in vitro. VZV-specific T cells, mainly of a central memory (CD45RA(-)CD27(+)) phenotype, accumulate at the site of skin challenge compared with the blood of the same individuals. This resulted in part from local proliferation because >50% of tetramer defined Ag-specific CD4(+) T cells in the skin expressed the cell cycle marker Ki67. CD4(+)Foxp3(+) T cells had the characteristic phenotype of Tregs, namely CD25(hi)CD127(lo)CD39(hi) in both unchallenged and VZV challenged skin and did not secrete IFN-γ or IL-2 after antigenic restimulation. The CD4(+)Foxp3(+) T cells from unchallenged skin had suppressive activity, because their removal led to an increase in cytokine secretion after activation. After VZV Ag injection, Foxp3(+)CD25(hi)CD127(lo)CD39(hi) T cells were also found within the VZV tetramer population. Their suppressive activity could not be directly assessed by CD25 depletion because activated T cells in the skin were also CD25(+). Nevertheless, there was an inverse correlation between decreased VZV skin responses and proportion of CD4(+)Foxp3(+) T cells present, indicating indirectly their inhibitory activity in vivo. These results suggest a linkage between the expansion of Ag-specific CD4(+) T cells and CD4(+) Tregs that may provide controlled responsiveness during Ag-specific stimulation in tissues.

IL-7 downregulates IL-7Rα expression in human CD8 T cells by two independent mechanisms

Interleukin (IL)-7 is an essential nonredundant cytokine, and throughout the lifespan of a T-cell signaling via the IL-7 receptor influences cell survival, proliferation and differentiation. It is therefore no surprise that expression of the IL-7 receptor alpha-chain (CD127) is tightly regulated. We have previously shown that IL-7 downregulates expression of CD127 at the cell surface and now elucidate the kinetics of that suppression and demonstrate that IL-7 downregulates CD127 transcripts and surface protein in primary human CD8 T cells by two separate pathways. We show that IL-7 induces the initial reduction in cell-surface CD127 protein independent of transcriptional suppression, which is delayed by 40-60 min. Although IL-7-mediated downregulation of CD127 transcripts is dependent on Janus kinase (JAK)/STAT5, the early downregulation of surface CD127 protein is independent of JAK activity. The data further illustrate that low levels of IL-7 induce smaller and transient decreases in CD127 transcripts and surface protein, whereas higher concentrations induce more profound and sustained suppression. Such flexibility in receptor expression likely allows for fine-tuned immune responses in human CD8 T cells in different microenvironments and in response to different immunological challenges.

A spatial view of the CD8+ T-cell response: the case of HCV

In viral infections, a memory T-cell population comprises multiple subtypes of cells, distributed in diverse anatomic compartments and possibly re-circulating among them. Accordingly, memory T cells display distinct phenotypes and functions, depending on the nature of the infecting virus, the anatomic location of the infection, and the differences between the sites of active infection and T-cell collection. This paper explores the body compartments where virus-specific CD8(+) T cells have been found during chronic hepatitis C virus infection, describes the cells' memory qualities, and discusses how they are spatially regulated, in comparison with other human viral infections. Understanding the role of compartmentalization and diversity of HCV-specific memory T-cell subsets may be the key to developing effective immunotherapies.

Human cytomegalovirus immunity and immune evasion

Human cytomegalovirus (HCMV) infection induces both innate immune responses including Natural Killer cells as well as adaptive humoral and cell mediated (CD4+ helper, CD8+ cytotoxic and γδ T cell) responses which lead to the resolution of acute primary infection. Despite such a robust primary immune response, HCMV is still able to establish latency. Long term memory T cell responses are maintained at high frequency and are thought to prevent clinical disease following periodic reactivation of the virus. As such, a balance is established between the immune response and viral reactivation. Loss of this balance in the immunocompromised host can lead to unchecked viral replication following reactivation of latent virus, with consequent disease and mortality. HCMV encodes multiple immune evasion mechanisms that target both the innate and acquired immune system. This article describes the current understanding of Natural killer cell, antibody and T cell mediated immune responses and the mechanisms that the virus utilizes to subvert these responses.

Programmed Death-1 expression on Epstein Barr virus specific CD8+ T cells varies by stage of infection, epitope specificity, and T-cell receptor usage

BACKGROUND

Programmed Death-1 (PD-1) is an inhibitory member of the CD28 family of molecules expressed on CD8+ T cells in response to antigenic stimulation. To better understand the role of PD-1 in antiviral immunity we examined the expression of PD-1 on Epstein-Barr virus (EBV) epitope-specific CD8+ T cells during acute infectious mononucleosis (AIM) and convalescence.

METHODOLOGY/PRINCIPAL FINDINGS

Using flow cytometry, we observed higher frequencies of EBV-specific CD8+ T cells and higher intensity of PD-1 expression on EBV-specific CD8+ T cells during AIM than during convalescence. PD-1 expression during AIM directly correlated with viral load and with the subsequent degree of CD8+ T cell contraction in convalescence. Consistent differences in PD-1 expression were observed between CD8+ T cells with specificity for two different EBV lytic antigen epitopes. Similar differences were observed in the degree to which PD-1 was upregulated on these epitope-specific CD8+ T cells following peptide stimulation in vitro. EBV epitope-specific CD8+ T cell proliferative responses to peptide stimulation were diminished during AIM regardless of PD-1 expression and were unaffected by blocking PD-1 interactions with PD-L1. Significant variability in PD-1 expression was observed on EBV epitope-specific CD8+ T cell subsets defined by V-beta usage.

CONCLUSIONS/SIGNIFICANCE

These observations suggest that PD-1 expression is not only dependent on the degree of antigen presentation, but also on undefined characteristics of the responding cell that segregate with epitope specificity and V-beta usage.

Long-term outcome of EBV-specific T-cell infusions to prevent or treat EBV-related lymphoproliferative disease in transplant recipients

T-cell immunotherapy that takes advantage of Epstein-Barr virus (EBV)-stimulated immunity has the potential to fill an important niche in targeted therapy for EBV-related cancers. To address questions of long-term efficacy, safety, and practicality, we studied 114 patients who had received infusions of EBV-specific cytotoxic T lymphocytes (CTLs) at 3 different centers to prevent or treat EBV(+) lymphoproliferative disease (LPD) arising after hematopoietic stem cell transplantation. Toxicity was minimal, consisting mainly of localized swelling at sites of responsive disease. None of the 101 patients who received CTL prophylaxis developed EBV(+) LPD, whereas 11 of 13 patients treated with CTLs for biopsy-proven or probable LPD achieved sustained complete remissions. The gene-marking component of this study enabled us to demonstrate the persistence of functional CTLs for up to 9 years. A preliminary analysis indicated that a patient-specific CTL line can be manufactured, tested, and infused for $6095, a cost that compares favorably with other modalities used in the treatment of LPD. We conclude that the CTL lines described here provide safe and effective prophylaxis or treatment for lymphoproliferative disease in transplantation recipients, and the manufacturing methodology is robust and can be transferred readily from one institution to another without loss of reproducibility.

Upregulation of interleukin 7 receptor alpha and programmed death 1 marks an epitope-specific CD8+ T-cell response that disappears following primary Epstein-Barr virus infection

In immunocompetent individuals, the stability of the herpesvirus-host balance limits opportunities to study the disappearance of a virus-specific CD8(+) T-cell response. However, we noticed that in HLA-A 0201-positive infectious mononucleosis (IM) patients undergoing primary Epstein-Barr virus (EBV) infection, the initial CD8 response targets three EBV lytic antigen-derived epitopes, YVLDHLIVV (YVL), GLCTLVAML (GLC), and TLDYKPLSV (TLD), but only the YVL and GLC reactivities persist long-term; the TLD response disappears within 10 to 27 months. While present, TLD-specific cells remained largely indistinguishable from YVL and GLC reactivities in many phenotypic and functional respects but showed unique temporal changes in two markers of T-cell fate, interleukin 7 receptor alpha (IL-7Ralpha; CD127) and programmed death 1 (PD-1). Thus, following the antigen-driven downregulation of IL-7Ralpha seen on all populations in acute IM, in every case, the TLD-specific population recovered expression unusually quickly post-IM. As well, in four of six patients studied, TLD-specific cells showed very strong PD-1 upregulation in the last blood sample obtained before the cells' disappearance. Our data suggest that the disappearance of this individual epitope reactivity from an otherwise stable EBV-specific response (i) reflects a selective loss of cognate antigen restimulation (rather than of IL-7-dependent signals) and (ii) is immediately preceded, and perhaps mediated, by PD-1 upregulation to unprecedented levels.

T lymphocyte maturation is impaired in healthy young individuals carrying trisomy 21 (Down syndrome)

Cytokine production, immune activation, T lymphocytes maturation, and serum IL-7 concentration were examined in 24 youngsters with Down syndrome and no acquired diseases (healthy Down syndrome [12 prepubertal, 13 pubertal]) and 42 age- and gender-matched controls (20 prepubertal, 22 pubertal). Results showed that a complex immune and impairment is present in healthy individuals with Down syndrome in whom interferon gamma, interleukin (IL) IL-10 production, as well as serum IL-7 concentrations and activation markers-bearing T lymphocytes were significantly augmented. Additionally, a complex skewing of post-thymic lymphocyte maturation pathways was observed in patients: significant reduction of CD4+ and CD8+ naive (RA+CCR7+) lymphocytes, significant increase of CD4+ and CD8+ central memory (RA-CCR7+), and terminally differentiated (TD) (RA+CCR7-) lymphocytes.

CD40 regulates human dendritic cell-derived IL-7 production that, in turn, contributes to CD8(+) T-cell antigen-specific expansion

CD40L (CD154) expressed on activated CD4(+) T cells has been shown to provide CD40(+) dendritic cells (DCs), a critical signal for establishing CD8(+) T-cell immunity. CD40L-CD40 interaction leads to DC maturation with IL-12 production and upregulation of various costimulatory molecules. In this study, we show that CD40 engagement provides a unique maturation signal for human monocyte-derived DCs to upregulate IL-7 production. Other inducers of DC maturation, such as TLR 4 and TLR 7/8 agonist, fail to induce IL-7 upregulation. Neutralization of IL-7 activity in human CD8(+) T-cell cultures stimulated with CMV pp65-NLV peptide-pulsed mature DCs (mDCs) leads to a reduction in antigen-specific CD8(+) T-cell yields suggesting a role for mDC-derived IL-7 during T-cell receptor (TCR) activation. Furthermore, IL-7 signaling requires a temporal coordination with TCR activation for maximal antigen-specific T-cell yields. These results show that CD40 signals regulate DC-derived IL-7 production that, in turn, may instruct CD8(+) T cells at the time of TCR engagement for survival leading to an increased expansion of antigen-specific T cells.

Alloreactivity of ex vivo-expanded T cells is correlated with expansion and CD4/CD8 ratio

Background We have demonstrated previously that retroviral-mediated transfer of a suicide gene into bone marrow (BM) donor T cells allows an efficient control of graft-versus-host disease (GvHD) after allogeneic BM transplantation. However, the 12 days of ex vivo culture required for the production of gene-modified cells (GMC), including soluble CD3 monoclonal antibody (MAb)-mediated activation and expansion with interleukin (IL)-2, induced a decrease of GMC alloreactivity and a reversal of their CD4/CD8 ratio. Improving the culture protocol in order to maintain the highest alloreactivity is of critical importance in obtaining an optimal graft-versus-leukemia (GvL) effect. Methods Peripheral blood mononuclear cells were activated with soluble CD3 MAb or CD3 and CD28 MAb co-immobilized on beads and expanded for 12 days in the presence of IL-2, IL-7 or IL-15 before analysis of alloreactivity and phenotype. Results Replacing the CD3 MAb by CD3/CD28 beads led to similar in vitro alloreactivity but improved the expansion and in vivo alloreactivity of GMC. Replacing the IL-2 with IL-7, but not IL-15, or decreasing IL-2 or IL-7 concentrations, improved the in vitro alloreactivity of expanded cells but was associated with lower expansion. Indeed, the alloreactivity of expanded cells was negatively correlated with cell expansion and positively correlated with CD4/CD8 ratio and CD8 expression level. Discussion Quantitative (i.e. low CD4/CD8 ratio) and qualitative (e.g. low CD8 expression) defects may account for the decreased alloreactivity of GMC. Using CD3/CD28 beads and/or IL-7 is more beneficial than CD3 MAb and IL-2 for preventing perturbations of the alloreactivity and phenotype of GMC.

Memory CD8+ T cell differentiation in viral infection: A cell for all seasons

Chronic viral infections such as hepatitis B virus (HBV), hepatitis C virus (HCV) and human immunodeficiency virus (HIV) are major global health problems affecting more than 500 million people worldwide. Virus-specific CD8+ T cells play an important role in the course and outcome of these viral infections and it is hypothesized that altered or impaired differentiation of virus-specific CD8+ T cells contributes to the development of persistence and/or disease progression. A deeper understanding of the mechanisms responsible for functional differentiation of CD8+ T cells is essential for the generation of successful therapies aiming to strengthen the adaptive component of the immune system.

An in vitro model of T cell receptor revision in mature human CD8+ T cells

V(D)J recombination is a mechanism peculiar to the somatic rearrangement of antigen receptor genes. It requires both expression of the RAG-1 and RAG-2 recombinases and accessibility of the substrate to its recombinase and post-cleavage/DNA repair stage. TCR revision is a genetic correction mechanism that changes T cell specificity by re-activating V(D)J recombination in peripheral T cells. This process is now well described in both normal or pathological murine and human settings. Many of its features, such as the question of whether it occurs in truly mature T cells, remain to be elucidated. Its occurrence in human CD8+ T cells is also an open question. We have therefore established an in vitro model of TCR revision in mature human CD8+ T cells to determine whether down-regulation of the TCR/CD3 complex from the cell surface in the presence of IL7 as a factor favouring chromatin remodelling initiates a TCR revision pathway. Only mature CD8+ T cells carrying already-formed antigen receptors were used. CD8+ T cells treated with anti-CD3 and IL7 showed rearrangement intermediates and expressed new Vbeta-chains on their surface. Investigation of the molecular pathway thus induced disclosed up-regulation of the RAG-2 transcript, but absence of the 'canonical' RAG-1 mRNA. A surprising finding was the demonstration of alternative splice forms of this mRNA, already expressed in untreated CD8+ T cells, encoding for the full-length RAG-1 protein, which was increased three-fold in the treated cells. All the V(D)J requirements were thus fulfilled when mature human CD8+ T cells were stimulated with anti-CD3 and IL7. Induction of TCR revision in vitro in mature T cells is an easily controllable system that could be employed in further studies to elucidate the molecular pathways involved in secondary V(D)J rearrangements in peripheral cells.

Cellular responses to viral infection in humans: lessons from Epstein-Barr virus

Epstein-Barr virus (EBV) provides a useful model to study cellular immunity to a genetically stable, persistent human virus. Different sets of proteins expressed during EBV's lytic and cell transforming infections induce qualitatively different cellular immune responses. The factors governing immunodominance hierarchies and the biological effectiveness of these different responses are now being revealed. Analysis of infectious mononucleosis (IM), a clinical syndrome that can arise during primary EBV infection, has allowed the evolution of the responses to be tracked over time, giving an understanding of the immune response kinetics and of those determinants affecting selection into memory. Furthermore, following IM, expression of the receptor for the homeostatic cytokine IL-15 on NK and T cells is lost within these individuals. This experiment of nature provides a system to advance understanding of immunological homeostasis in humans, illustrating how data obtained from the study of EBV have wider significance to the immunological community.

Adenoviral vectors persist in vivo and maintain activated CD8+ T cells: implications for their use as vaccines

CD8(+) T cell-numbers rapidly expand and then contract after exposure to their cognate antigen. Here we show that the sustained frequencies of transgene product-specific CD8(+) T cells elicited by replication-defective adenovirus vectors are linked to persistence of low levels of transcriptionally active adenovirus vector genomes at the site of inoculation, in liver, and lymphatic tissues. Continuously produced small amounts of antigen maintain fully active effector CD8(+) T cells, while also allowing for their differentiation into central memory cells. The long-term persistence of adenoviral vectors may be highly advantageous for their use as vaccines against pathogens for which T-cell-mediated protection requires both fully activated T cells for immediate control of virus-infected cells and central memory CD8(+) T cells that, because of their higher proliferative capacity, may be suited best to eliminate cells infected by pathogens that escaped the initial wave of effector T cells.

Epstein-Barr Virus and Hodgkin Lymphoma

Epstein-Barr virus (EBV) is detected in some Hodgkin lymphoma (HL) tumor cells. Primary infection is associated with infectious mononucleosis and EBV+ HL. Vaccines and antiviral drugs show promise in modulating the clinical course of infectious mononucleosis. Their impact on HL is entirely unknown. T-cell function may be important in the pathogenesis of HL. In HIV patients, higher CD4 counts are associated with an increased incidence of EBV+ HL. One of the roles of the virus in the pathogenesis of HL may be to mimic signals associated with surface immunoglobulin molecules. New approaches to imaging EBV-associated tumors may be on the horizon. Adoptive immunotherapy and virus-specific pharmacologic therapies offer promise for future treatment.