Differential costimulation through CD137 (4-1BB) restores proliferation of human virus-specific "effector memory" (CD28(-) CD45RA(HI)) CD8(+) T cells

CD28/PD1 co-expression: dual impact on CD8+ T cells in peripheral blood and tumor tissue, and its significance in NSCLC patients' survival and ICB response

BACKGROUND

Immune checkpoint blockade (ICB) has significantly prolonged survival of non-small cell lung cancer (NSCLC) patients, although most patients develop mechanisms of resistance. Recently single-cell RNA-sequencing (scRNA-Seq) revealed a huge T-cell phenotypic and (dys)functional state variability. Accordingly, T-cell exhaustion is recognized as a functional adaptation, with a dynamic progression from a long-lived "pre-exhausted stem-like progenitor" to a "terminally exhausted" state. In this scenario it is crucial to understand the complex interplay between co-stimulatory and inhibitory molecules in CD8+ T-cell functionality.

METHODS

To gain a baseline landscape of the composition, functional states, and transcriptomic signatures predictive of prognosis, we analyzed CD8+ T-cell subsets characterized by the presence/absence of PD1 and CD28 from periphery, adjacent non-tumor tissue and tumor site of a cohort of treatment-naïve NSCLC patients, by integrated multiparametric flow cytometry, targeted multi-omic scRNA-seq analyses, and computational pipelines.

RESULTS

Despite the increased PD1 levels, an improved PD1+CD28+ T-cell polyfunctionality was observed with the transition from periphery to tumor site, associated with lack of TIGIT, TIM-3 and LAG-3, but not with Ag-experienced-marker CD11a. Differently from CD28+ T cells, the increased PD1 levels in the tumor were associated with reduced functionality in PD1+CD28- T cells. CD11ahigh, although expressed only in a small fraction of this subset, still sustained its functionality. Absence of TIGIT, TIM-3 and CTLA-4, alone or combined, was beneficial to CD28- T cells. Notably, we observed distinct TRM phenotypes in the different districts, with CD28+ T cells more capable of producing TGFβ in the periphery, potentially contributing to elevated CD103 levels. In contrast CD28- TRM mainly produced CXCL13 within the tumor. ScRNA-seq revealed 5 different clusters for each of the two subsets, with distinctive transcriptional profiles in the three districts. By interrogating the TCGA dataset of patients with lung adenocarcinoma (LUAD) and metastatic NSCLC treated with atezolizumab, we found signatures of heterogeneous TRM and "pre-exhausted" long-lived effector memory CD8+ T cells associated with improved response to ICB only in the presence of CD28.

CONCLUSIONS

Our findings identify signatures able to stratify survival of LUAD patients and predict ICB response in advanced NSCLC. CD28 is advocated as a key determinant in the signatures identified, in both periphery and tumor site, thus likely providing feasible biomarkers of ICB response.

Agonism of 4-1BB for immune therapy: a perspective on possibilities and complications

Costimulatory receptors on immune cells represent attractive targets for immunotherapy given that these molecules can increase the frequency of individual protective immune cell populations and their longevity, as well as enhance various effector functions. 4-1BB, a member of the TNF receptor superfamily, also known as CD137 and TNFRSF9, is one such molecule that is inducible on several cell types, including T cells and NK cells. Preclinical studies in animal models have validated the notion that stimulating 4-1BB with agonist reagents or its natural ligand could be useful to augment conventional T cell and NK cell immunity to protect against tumor growth and against viral infection. Additionally, stimulating 4-1BB can enhance regulatory T cell function and might be useful in the right context for suppressing autoimmunity. Two human agonist antibodies to 4-1BB have been produced and tested in clinical trials for cancer, with variable results, leading to the production of a wealth of second-generation antibody constructs, including bi- and multi-specifics, with the hope of optimizing activity and selectivity. Here, we review the progress to date in agonism of 4-1BB, discuss the complications in targeting the immune system appropriately to elicit the desired activity, together with challenges in engineering agonists, and highlight the untapped potential of manipulating this molecule in infectious disease and autoimmunity.

T-lymphocyte subtyping: an early warning and a potential prognostic indicator of active cytomegalovirus infection in patients with sepsis

Cytomegalovirus (CMV) infection is very common in patients suffering from sepsis and may cause poor prognosis. To explore the relationship between immune status of patients with sepsis and CMV infection, we assessed T lymphocyte subtyping and other commonly used clinical parameters in patients with sepsis upon admission to the intensive care unit (ICU) and evaluated their potential impact on diagnosis and outcomes of active CMV infection. In our study, 82 of 599 patients with sepsis were diagnosed with active CMV infection. The 28-day mortality was higher in active CMV-infected than nonactive CMV-infected patients (20.7% versus 9.9%); 51of 82 active CMV-infected patients with sepsis were assessed to have CMV-DNA-negative conversion, while 31 were persistently positive for CMV DNA. Higher CD8⁺ CD28⁺ T-cell counts at presentation were associated with CMV-DNA-negative conversion and lower 28-day mortality. The CMV-DNA-negative conversion and 28-day mortality of active CMV-infected patients with sepsis could be predicted using cutoff values of 151 (74.5% sensitivity and 87.1% specificity) and 64.5 (52.9% sensitivity and 92.3% specificity) CD8⁺ CD28⁺ T cells mL^-1 at ICU admission, respectively. Higher CD8⁺ CD28⁺ T-cell count was significantly associated with active CMV infection, higher CMV-DNA-negative conversion and lower 28-day mortality, which may be a potential marker for early warning of active CMV infection and outcome prediction.

Grant M. The Immune Response Against Human Cytomegalovirus Links Cellular to Systemic Senescence

Aging reflects long-term decline in physiological function and integrity. Changes arise at a variable pace governed by time-dependent and -independent mechanisms that are themselves complex, interdependent and variable. Molecular decay produces inferior cells that eventually dominate over healthy counterparts in tissues they comprise. In a form of biological entropy, progression from molecular through cellular to tissue level degeneration culminates in organ disease or dysfunction, affecting systemic health. To better understand time-independent contributors and their potential modulation, common biophysical bases for key molecular and cellular changes underlying age-related physiological deterioration must be delineated. This review addresses the potential contribution of cytomegalovirus (CMV)-driven T cell proliferation to cellular senescence and immunosenescence. We first describe molecular processes imposing cell cycle arrest, the foundation of cellular senescence, then focus on the unique distribution, phenotype and function of CMV-specific CD8⁺ T cells in the context of cellular senescence and "inflammaging". Their features position CMV infection as a pathogenic accelerant of immune cell proliferation underlying immune senescence. In human immunodeficiency virus (HIV) infection, where increased inflammation and exaggerated anti-CMV immune responses accelerate immune senescence, CMV infection has emerged as a major factor in unhealthy aging. Thus, we speculate on mechanistic links between CMV-specific CD8⁺ T-cell expansion, immune senescence and prevalence of age-related disorders in HIV infection.

Vaccine Vectors Harnessing the Power of Cytomegaloviruses

Cytomegalovirus (CMV) species have been gaining attention as experimental vaccine vectors inducing cellular immune responses of unparalleled strength and protection. This review outline the strengths and the restrictions of CMV-based vectors, in light of the known aspects of CMV infection, pathogenicity and immunity. We discuss aspects to be considered when optimizing CMV based vaccines, including the innate immune response, the adaptive humoral immunity and the T-cell responses. We also discuss the antigenic epitopes presented by unconventional major histocompatibility complex (MHC) molecules in some CMV delivery systems and considerations about routes for delivery for the induction of systemic or mucosal immune responses. With the first clinical trials initiating, CMV-based vaccine vectors are entering a mature phase of development. This impetus needs to be maintained by scientific advances that feed the progress of this technological platform.

Cytomegalovirus: Shape-Shifting the Immune System

Systems-based based approaches have begun to shed light on extrinsic factors that contribute to immune system variation. Among these, CMV (HHV-5, a β-herpesvirus) imposes a surprisingly profound impact. Most of the world's population is CMV⁺, and the virus goes through three distinct infection phases en route to establishing lifelong détente with its host. Immune control of CMV in each phase recruits unique arms of host defense, and in turn the virus employs multiple immune-modulatory strategies that help facilitate the establishment of lifelong persistence. In this review, we explain how CMV shapes immunity and discuss the impact it may have on overall health.

Robust Identification of Suitable T-Cell Subsets for Personalized CMV-Specific T-Cell Immunotherapy Using CD45RA and CD62L Microbeads

Viral infections and reactivations remain a serious obstacle to successful hematopoietic stem cell transplantation (HSCT). When antiviral drug treatment fails, adoptive virus-specific T-cell transfer provides an effective alternative. Assuming that naive T cells (T_N) are mainly responsible for GvHD, methods were developed to generate naive T-cell-depleted products while preserving immune memory against viral infections. We compared two major strategies to deplete potentially alloreactive T cells: CD45RA and CD62L depletion and analyzed phenotype and functionality of the resulting CD45RA^-/CD62L^- naive T-cell-depleted as well as CD45RA⁺/CD62L⁺ naive T-cell-enriched fractions in the CMV pp65 and IE1 antigen model. CD45RA depletion resulted in loss of terminally differentiated effector memory T cells re-expressing CD45RA (T_EMRA), and CD62L depletion in loss of central memory T cells (T_CM). Based on these differences in target cell-dependent and target cell-independent assays, antigen-specific T-cell responses in CD62L-depleted fraction were consistently 3⁻5 fold higher than those in CD45RA-depleted fraction. Interestingly, we also observed high donor variability in the CD45RA-depleted fraction, resulting in a substantial loss of immune memory. Accordingly, we identified donors with expected response (DER) and unexpected response (DUR). Taken together, our results showed that a naive T-cell depletion method should be chosen individually, based on the immunophenotypic composition of the T-cell populations present.

The impact of inflationary cytomegalovirus-specific memory T cells on anti-tumour immune responses in patients with cancer

Human cytomegalovirus (CMV) is a ubiquitous, persistent beta herpesvirus. CMV infection contributes to the accumulation of functional antigen-specific CD8⁺ T-cell pools with an effector-memory phenotype and enrichment of these immune cells in peripheral organs. We review here this 'memory T-cell inflation' phenomenon and associated factors including age and sex. 'Collateral damage' due to CMV-directed immune reactivity may occur in later stages of life - arising from CMV-specific immune responses that were beneficial in earlier life. CMV may be considered an age-dependent immunomodulator and a double-edged sword in editing anti-tumour immune responses. Emerging evidence suggests that CMV is highly prevalent in patients with a variety of cancers, particularly glioblastoma. A better understanding of CMV-associated immune responses and its implications for immune senescence, especially in patients with cancer, may aid in the design of more clinically relevant and tailored, personalized treatment regimens. 'Memory T-cell inflation' could be applied in vaccine development strategies to enrich for immune reactivity where long-term immunological memory is needed, e.g. in long-term immune memory formation directed against transformed cells.

Suppression of costimulation by human cytomegalovirus promotes evasion of cellular immune defenses

CD58 is an adhesion molecule that is known to play a critical role in costimulation of effector cells and is intrinsic to immune synapse structure. Herein, we describe a virally encoded gene that inhibits CD58 surface expression. Human cytomegalovirus (HCMV) UL148 was necessary and sufficient to promote intracellular retention of CD58 during HCMV infection. Blocking studies with antagonistic anti-CD58 mAb and an HCMV UL148 deletion mutant (HCMV∆UL148) with restored CD58 expression demonstrated that the CD2/CD58 axis was essential for the recognition of HCMV-infected targets by CD8⁺ HCMV-specific cytotoxic T lymphocytes (CTLs). Further, challenge of peripheral blood mononuclear cells ex vivo with HCMV∆UL148 increased both CTL and natural killer (NK) cell degranulation against HCMV-infected cells, including NK-driven antibody-dependent cellular cytotoxicity, showing that UL148 is a modulator of the function of multiple effector cell subsets. Our data stress the effect of HCMV immune evasion functions on shaping the immune response, highlighting the capacity for their potential use in modulating immunity during the development of anti-HCMV vaccines and HCMV-based vaccine vectors.

The (gradual) rise of memory inflation

Memory inflation, as a term, has been used for 15 years now to describe the longitudinal development of stable, expanded CD8+ T memory pools with a distinct phenotype and functional profile which emerge in specific infection and vaccine settings. These settings have in common the persistence of antigen, especially cytomegalovirus infection but also more recently adenoviral vector vaccination. However, in contrast to chronic infections which lead to "exhaustion" the repeated antigen encounters experienced by CD8+ T cells lead to development of a robust T-cell population structure which maintains functionality and size. In this review, I will discuss how the ideas around this form of memory have evolved over time and some new models which can help explain how these populations are induced and sustained. These models are relevant to immunity against persistent viruses, to novel vaccine strategies and to concepts about aging.

The function and dysfunction of memory CD8+ T cells in tumor immunity

The generation and maintenance of CD8+ T cell memory is crucial to long-term host survival, yet the basic tenets of CD8+ T cell immunity are still being established. Recent work has led to the discovery of tissue-resident memory cells and refined our understanding of the transcriptional and epigenetic basis of CD8+ T cell differentiation and dysregulation. In parallel, the unprecedented clinical success of immunotherapy has galvanized an intense, global research effort to decipher and de-repress the anti-tumor response. However, the progress of immunotherapy is at a critical juncture, since the efficacy of immuno-oncology agents remains confined to a fraction of patients and often fails to provide durable benefit. Unlocking the potential of immunotherapy requires the design of strategies that both induce a potent effector response and reliably forge stable, functional memory T cell pools capable of protecting from recurrence or relapse. It is therefore essential that basic and emerging concepts of memory T cell biology are rapidly and faithfully transposed to advance therapeutic development in cancer immunotherapy. This review highlights seminal and recent reports in CD8+ T cell memory and tumor immunology, and evaluates recent data from solid cancer specimens in the context of the key paradigms from preclinical models. We elucidate the potential significance of circulating effector cells poised downstream of neoantigen recognition and upstream of T cell dysfunction and propose that cells in this immunological 'sweet spot' may be key anti-tumor effectors.

Tumor immunotherapy: drug-induced neoantigens (xenogenization) and immune checkpoint inhibitors

More than 40 years ago, we discovered that novel transplantation antigens can be induced in vivo or in vitro by treating murine leukemia with dacarbazine. Years later, this phenomenon that we called “Chemical Xenogenization” (CX) and more recently, “Drug-Induced Xenogenization” (DIX), was reproduced by Thierry Boon with a mutagenic/carcinogenic compound (i.e. N-methyl-N’-nitro-N-nitrosoguanidine). In both cases, the molecular bases of DIX rely on mutagenesis induced by methyl adducts to oxygen-6 of DNA guanine. In the present review we illustrate the main DIX-related immune-pharmacodynamic properties of triazene compounds of clinical use (i.e. dacarbazine and temozolomide).

In recent years, tumor immunotherapy has come back to the stage with the discovery of immune checkpoint inhibitors (ICpI) that show an extraordinary immune-enhancing activity. Here we illustrate the salient biochemical features of some of the most interesting ICpI and the up-to-day status of their clinical use. Moreover, we illustrate the literature showing the direct relationship between somatic mutation burden and susceptibility of cancer cells to host’s immune responses.

When DIX was discovered, we were not able to satisfactorily exploit the possible presence of triazene-induced neoantigens in malignant cells since no device was available to adequately enhance host’s immune responses in clinical settings. Today, ICpI show unprecedented efficacy in terms of survival times, especially when elevated mutation load is associated with cancer cells. Therefore, in the future, mutation-dependent neoantigens obtained by appropriate pharmacological intervention appear to disclose a novel approach for enhancing the therapeutic efficacy of ICpI in cancer patients.

Features of Effective T Cell-Inducing Vaccines against Chronic Viral Infections

For many years, the focus of prophylactic vaccines was to elicit neutralizing antibodies, but it has become increasingly evident that T cell-mediated immunity plays a central role in controlling persistent viral infections such as with human immunodeficiency virus, cytomegalovirus, and hepatitis C virus. Currently, various promising prophylactic vaccines, capable of inducing substantial vaccine-specific T cell responses, are investigated in preclinical and clinical studies. There is compelling evidence that protection by T cells is related to the magnitude and breadth of the T cell response, the type and homing properties of the memory T cell subsets, and their cytokine polyfunctionality and metabolic fitness. In this review, we evaluated these key factors that determine the qualitative and quantitative properties of CD4+ and CD8+ T cell responses in the context of chronic viral disease and prophylactic vaccine development. Elucidation of the mechanisms underlying T cell-mediated protection against chronic viral pathogens will facilitate the development of more potent, durable and safe prophylactic T cell-based vaccines.

CD45 in human physiology and clinical medicine

CD45 is an evolutionary highly conserved receptor protein tyrosine phosphatase exclusively expressed on all nucleated cells of the hematopoietic system. It is characterized by the expression of several isoforms, specific to a certain cell type and the developmental or activation status of the cell. CD45 is one of the key players in the initiation of T cell receptor signaling by controlling the activation of the Src family protein-tyrosine kinases Lck and Fyn. CD45 deficiency results in T- and B-lymphocyte dysfunction in the form of severe combined immune deficiency. It also plays a significant role in autoimmune diseases and cancer as well as in infectious diseases including fungal infections. The knowledge collected on CD45 biology is rather vast, but it remains unclear whether all findings in rodent immune cells also apply to human CD45. This review focuses on human CD45 expression and function and provides an overview on its ligands and role in human pathology.

Latent Cytomegalovirus (CMV) Infection Does Not Detrimentally Alter T Cell Responses in the Healthy Old, But Increased Latent CMV Carriage Is Related to Expanded CMV-Specific T Cells

Human cytomegalovirus (HCMV) primary infection and periodic reactivation of latent virus is generally well controlled by T-cell responses in healthy people. In older donors, overt HCMV disease is not generally seen despite the association of HCMV infection with increased risk of mortality. However, increases in HCMV DNA in urine of older people suggest that, although the immune response retains functionality, immunomodulation of the immune response due to lifelong viral carriage may alter its efficacy. Viral transcription is limited during latency to a handful of viral genes and there is both an IFNγ and cellular IL-10 CD4⁺ T-cell response to HCMV latency-associated proteins. Production of cIL-10 by HCMV-specific CD4⁺ T-cells is a candidate for aging-related immunomodulation. To address whether long-term carriage of HCMV changes the balance of cIL-10 and IFNγ-secreting T-cell populations, we recruited a large donor cohort aged 23–78 years and correlated T-cell responses to 11 HCMV proteins with age, HCMV IgG levels, latent HCMV load in CD14⁺ monocytes, and T-cell numbers in the blood. IFNγ responses by CD4⁺ and CD8⁺ T-cells to all HCMV proteins were detected, with no age-related increase in this cohort. IL-10-secreting CD4⁺ T cell responses were predominant to latency-associated proteins but did not increase with age. Quantification of HCMV genomes in CD14⁺ monocytes, a known site of latent HCMV carriage, did not reveal any increase in viral genome copies in older donors. Importantly, there was a significant positive correlation between the latent viral genome copy number and the breadth and magnitude of the IFNγ T-cell response to HCMV proteins. This study suggests in healthy aged donors that HCMV-specific changes in the T cell compartment were not affected by age and were effective, as viremia was a very rare event. Evidence from studies of unwell aged has shown HCMV to be an important comorbidity factor, surveillance of latent HCMV load and low-level viremia in blood and body fluids, alongside typical immunological measures and assessment of the antiviral capacity of the HCMV-specific immune cell function would be informative in determining if antiviral treatment of HCMV replication in the old maybe beneficial.

CMV-Specific CD8 T Cell Differentiation and Localization: Implications for Adoptive Therapies

Human cytomegalovirus (HCMV) is a ubiquitous virus that causes chronic infection and, thus, is one of the most common infectious complications of immune suppression. Adoptive transfer of HCMV-specific T cells has emerged as an effective method to reduce the risk for HCMV infection and/or reactivation by restoring immunity in transplant recipients. However, the CMV-specific CD8⁺ T cell response is comprised of a heterogenous mixture of subsets with distinct functions and localization, and it is not clear if current adoptive immunotherapy protocols can reconstitute the full spectrum of CD8⁺ T cell immunity. The aim of this review is to briefly summarize the role of these T cell subsets in CMV immunity and to describe how current adoptive immunotherapy practices might affect their reconstitution in patients. The bulk of the CMV-specific CD8⁺ T cell population is made up of terminally differentiated effector T cells with immediate effector function and a short life span. Self-renewing memory T cells within the CMV-specific population retain the capacity to expand and differentiate upon challenge and are important for the long-term persistence of the CD8⁺ T cell response. Finally, mucosal organs, which are frequent sites of CMV reactivation, are primarily inhabited by tissue-resident memory T cells, which do not recirculate. Future work on adoptive transfer strategies may need to focus on striking a balance between the formation of these subsets to ensure the development of long lasting and protective immune responses that can access the organs affected by CMV disease.

T cell responses to cytomegalovirus

Human cytomegalovirus (HCMV) establishes a latent infection that generally remains asymptomatic in immune-competent hosts for decades but can cause serious illness in immune-compromised individuals. The long-term control of CMV requires considerable effort from the host immune system and has a lasting impact on the profile of the immune system. One hallmark of CMV infection is the maintenance of large populations of CMV-specific memory CD8(+) T cells - a phenomenon termed memory inflation - and emerging data suggest that memory inflation is associated with impaired immunity in the elderly. In this Review, we discuss the molecular triggers that promote memory inflation, the idea that memory inflation could be considered a natural pathway of T cell maturation that could be harnessed in vaccination, and the broader implications of CMV infection and the T cell responses it elicits.

CD58/CD2 Is the Primary Costimulatory Pathway in Human CD28-CD8+ T Cells

A substantial proportion of CD8(+) T cells in adults lack the expression of the CD28 molecule, and the aging of the immune system is associated with a steady expansion of this T cell subset. CD28(-)CD8(+) T cells are characterized by potent effector functions but impaired responses to antigenic challenge. CD28 acts as the primary T cell costimulatory receptor, but there are numerous additional receptors that can costimulate the activation of T cells. In this study, we have examined such alternative costimulatory pathways regarding their functional role in CD28(-)CD8(+) T cells. Our study showed that most costimulatory molecules have a low capacity to activate CD28-deficient T cells, whereas the engagement of the CD2 molecule by its ligand CD58 clearly costimulated proliferation, cytokine production, and effector function in this T cell subset. CD58 is broadly expressed on APCs including dendritic cells. Blocking CD58 mAb greatly reduced the response of human CD28(-)CD8(+) T cells to allogeneic dendritic cells, as well as to viral Ags. Our results clearly identify the CD58/CD2 axis as the primary costimulatory pathway for CD8 T cells that lack CD28. Moreover, we show that engagement of CD2 amplifies TCR signals in CD28(-)CD8(+) T cells, demonstrating that the CD2-CD58 interaction has a genuine costimulatory effect on this T cell subset. CD2 signals might promote the control of viral infection by CD28(-)CD8(+) T cells, but they might also contribute to the continuous expansion of CD28(-)CD8(+) T cells during chronic stimulation by persistent Ag.

Committing Cytomegalovirus-Specific CD8 T Cells to Eliminate Tumor Cells by Bifunctional Major Histocompatibility Class I Antibody Fusion Molecules

Tumor cells escape immune eradication through multiple mechanisms, including loss of antigenicity and local suppression of effector lymphocytes. To counteract these obstacles, we aimed to direct the unique cytomegalovirus (CMV)-specific immune surveillance against tumor cells. We developed a novel generation of fusion proteins composed of a tumor antigen-specific full immunoglobulin connected to a single major histocompatibility class I complex bearing a covalently linked virus-derived peptide (pMHCI-IgG). Here, we show that tumor antigen-expressing cancer cells, which are decorated with pMHCI-IgGs containing a HLA-A*0201 molecule associated with a CMV-derived peptide, are specifically eliminated through engagement of antigen-specific CD8(+) T cells isolated from peripheral blood mononuclear cell preparations of CMV-infected humans. These CD8(+) T cells act without additional expansion, preactivation, or provision of costimulatory signals. Elimination of tumor cells is induced at similar concentrations and with similar time kinetics as those seen with bispecific T-cell engagers (BiTE). However, while BiTE-like reagents indiscriminately activate T cells through binding to the T-cell receptor complex, pMHCI-IgGs selectively engage antigen-specific, constantly renewable, differentiated effector cytotoxic T lymphocytes to tumor cells, thereby representing a novel class of anticancer immunotherapeutics with potentially improved safety and efficacy profiles.

Memory T cells specific for murine cytomegalovirus re-emerge after multiple challenges and recapitulate immunity in various adoptive transfer scenarios

Reconstitution of CMV-specific immunity after transplant remains a primary clinical objective to prevent CMV disease, and adoptive immunotherapy of CMV-specific T cells can be an effective therapeutic approach. Because of viral persistence, most CMV-specific CD8(+) T cells become terminally differentiated effector phenotype CD8(+) T cells (TEFF). A minor subset retains a memory-like phenotype (memory phenotype CD8(+) T cells [TM]), but it is unknown whether these cells retain memory function or persist over time. Interestingly, recent studies suggest that CMV-specific CD8(+) T cells with different phenotypes have different abilities to reconstitute sustained immunity after transfer. The immunology of human CMV infections is reflected in the murine CMV (MCMV) model. We found that human CMV- and MCMV-specific T cells displayed shared genetic programs, validating the MCMV model for studies of CMV-specific T cells in vivo. The MCMV-specific TM population was stable over time and retained a proliferative capacity that was vastly superior to TEFF. Strikingly, after transfer, TM established sustained and diverse T cell populations even after multiple challenges. Although both TEFF and TM could protect Rag(-/-) mice, only TM persisted after transfer into immune replete, latently infected recipients and responded if recipient immunity was lost. Interestingly, transferred TM did not expand until recipient immunity was lost, supporting that competition limits the Ag stimulation of TM. Ultimately, these data show that CMV-specific TM retain memory function during MCMV infection and can re-establish CMV immunity when necessary. Thus, TM may be a critical component for consistent, long-term adoptive immunotherapy success.

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.

Intrinsic TGF-β signaling promotes age-dependent CD8+ T cell polyfunctionality attrition

Advanced age is associated with immune system deficits that result in an increased susceptibility to infectious diseases; however, specific mediators of age-dependent immune dysfunction have not been fully elucidated. Here we demonstrated that aged mice exhibit poor effector CD8+ T cell polyfunctionality, primarily due to CD8+ T cell-extrinsic deficits, and that reduced CD8+ T cell polyfunctionality correlates with increased susceptibility to pathogenic diseases. In aged animals challenged with the parasite Encephalitozoon cuniculi, effector CD8+ T cell survival and polyfunctionality were suppressed by highly elevated TGF-β1. Furthermore, TGF-β depletion reduced effector CD8+ T cell apoptosis in both young and aged mice and enhanced effector CD8+ T cell polyfunctionality in aged mice. Surprisingly, intrinsic blockade of TGF-β signaling in CD8+ T cells was sufficient to rescue polyfunctionality in aged animals. Together, these data demonstrate that low levels of TGF-β1 promote apoptosis of CD8+ effector T cells and high TGF-β1 levels associated with age result in both CD8+ T cell apoptosis and an altered transcriptional profile, which correlates with loss of polyfunctionality. Furthermore, elevated TGF-β levels are observed in the elderly human population and in aged Drosophila, suggesting that TGF-β represents an evolutionarily conserved negative regulator of the immune response in aging organisms.

Skewed distribution of IL-7 receptor-α-expressing effector memory CD8+ T cells with distinct functional characteristics in oral squamous cell carcinoma

CD8⁺ T cells play important roles in anti-tumor immunity but distribution profile or functional characteristics of effector memory subsets during tumor progression are unclear. We found that, in oral squamous carcinoma patients, circulating CD8⁺ T cell pools skewed toward effector memory subsets with the distribution frequency of CCR7⁻CD45RA⁻CD8⁺ T cells and CCR7⁻ CD45RA⁺CD8⁺ T cells negatively correlated with each other. A significantly higher frequency of CD127^lo CCR7⁻CD45RA⁻CD8⁺ T cells or CCR7⁻CD45RA⁺CD8⁺ T cells among total CD8⁺ T cells was found in peripheral blood or tumor infiltrating lymphocytes, but not in regional lymph nodes. The CD127^hi CCR7⁻CD45RA⁻CD8⁺ T cells or CCR7⁻CD45RA⁺CD8⁺ T cells maintained significantly higher IFN-γ, IL-2 productivity and ex vivo proliferative capacity, while the CD127^lo CCR7⁻CD45RA⁻CD8⁺ T cells or CCR7⁻CD45RA⁺CD8⁺ T cells exhibited higher granzyme B productivity and susceptibility to activation induced cell death. A higher ratio of CCR7⁻CD45RA⁺CD8⁺ T cells to CCR7⁻CD45RA⁻CD8⁺ T cells was associated with advanced cancer staging and poor differentiation of tumor cells. Therefore, the CD127^lo CCR7⁻CD45RA⁻CD8⁺ T cells and CCR7⁻CD45RA⁺CD8⁺ T cells are functionally similar CD8⁺ T cell subsets which exhibit late differentiated effector phenotypes and the shift of peripheral CD8⁺ effector memory balance toward CCR7⁻CD45RA⁺CD8⁺ T cells is associated with OSCC progression.

Turning T cells on: epigenetically enhanced expression of effector T-cell costimulatory molecules on irradiated human tumor cells

BACKGROUND

Sub-lethal doses of radiation can alter the phenotype of target tissue by modulating gene expression and making tumor cells more susceptible to T-cell-mediated immune attack. We have previously shown that sub-lethal tumor cell irradiation enhances killing of colorectal carcinoma cells by tumor-specific cytotoxic T cells by unknown mechanisms. Recent data from our lab indicates that irradiation of tumor cells results in the upregulation of OX40L and 41BBL, and that T cells incubated with irradiated tumor cells displayed improved CTL survival, activation and effector activity. The objective of this current study was to determine the mechanism of enhanced OX40L and 41BBL expression in human colorectal tumor cells.

METHODS

Two colorectal carcinoma cell lines, HCT116 and SW620, were examined for changes in the expression of 41BBL and OX40L in response to inhibition of histone deacetylases (using TSA) and DNA methyltransferases (using 5-Aza-2'-deoxycytidine) to evaluate if epigenetic mechanisms of gene expression can modulate these genes. Tumor cells were treated with radiation, TSA, or 5-Aza-dC, and subsequently evaluated for changes in gene expression using RT-qPCR and flow cytometry. Moreover, we assessed levels of histone acetylation at the 41BBL promoter using chromatin immunoprecipitation assays in irradiated HCT116 cells.

RESULTS

Our data indicate that expression of 41BBL and OX40L can indeed be epigenetically regulated, as inhibition of histone deacetylases and of DNA methyltransferases results in increased OX40L and 41BBL mRNA and protein expression. Treatment of tumor cells with TSA enhanced the expression of these genes more than treatment with 5-Aza-dC, and co-incubation of T cells with TSA-treated tumor cells enhanced T-cell survival and activation, similar to radiation. Furthermore, chromatin immunoprecipitation experiments revealed significantly increased histone H3 acetylation of 41BBL promoters specifically following irradiation.

CONCLUSIONS

Full understanding of specific mechanisms of immunogenic modulation (altered expression of immune relevant genes) of irradiated tumor cells will be required to determine how to best utilize radiation as a tool to enhance cancer immunotherapy approaches. Overall, our results suggest that radiation can be used to make human tumors more immunogenic through epigenetic modulation of genes stimulatory to effector T-cells.

Human T cell aging and the impact of persistent viral infections

Aging is associated with a dysregulation of the immune response, loosely termed “immunosenescence.” Each part of the immune system is influenced to some extent by the aging process. However, adaptive immunity seems more extensively affected and among all participating cells it is the T cells that are most altered. There is a large body of experimental work devoted to the investigation of age-associated differences in T cell phenotypes and functions in young and old individuals, but few longitudinal studies in humans actually delineating changes at the level of the individual. In most studies, the number and proportion of late-differentiated T cells, especially CD8+ T cells, is reported to be higher in the elderly than in the young. Limited longitudinal studies suggest that accumulation of these cells is a dynamic process and does indeed represent an age-associated change. Accumulations of such late-stage cells may contribute to the enhanced systemic pro-inflammatory milieu commonly seen in older people. We do not know exactly what causes these observed changes, but an understanding of the possible causes is now beginning to emerge. A favored hypothesis is that these events are at least partly due to the effects of the maintenance of essential immune surveillance against persistent viral infections, notably Cytomegalovirus (CMV), which may exhaust the immune system over time. It is still a matter of debate as to whether these changes are compensatory and beneficial or pathological and detrimental to the proper functioning of the immune system and whether they impact longevity. Here, we will review present knowledge of T cell changes with aging and their relation to chronic viral and possibly other persistent infections.

The distinct role of T cell costimulation in antiviral immunity

Defining the critical molecular interactions for inducing antiviral T cell responses is important for improvement of vaccines. Recent progress in understanding the role of T cell costimulatory molecules provides the insight that these molecules not only enhance CD4 and CD8 T cell responses in acute infections but also have an impact in latent and chronic viral infections. Intriguingly, the requirements for T cell costimulation seem to be distinct for each virus but nonetheless at least one or more costimulatory pathways are instrumental for development of protective immunity. Remarkably, certain viruses have evolved mechanisms to evade host costimulatory pathways to their advantage. These new insights have important implications for rational vaccine design.

Cancer therapy and vaccination

Cancer remains one of the leading causes of death worldwide, both in developed and in developing nations. It may affect people at all ages, even fetuses, but the risk for most varieties increases with age. Current therapeutic approaches which include surgery, chemotherapy and radiotherapy are associated with adverse side effects arising from lack of specificity for tumors. The goal of any therapeutic strategy is to impact on the target tumor cells with limited detrimental effect to normal cell function. Immunotherapy is cancer specific and can target the disease with minimal impact on normal tissues. Cancer vaccines are capable of generating an active tumor-specific immune response and serve as an ideal treatment due to their specificity for tumor cells and long lasting immunological memory that may safeguard against recurrences. Cancer vaccines are designed to either prevent (prophylactic) or treat established cancer (therapeutic). Identification of tumor-associated antigens (TAAs) and tumor-specific antigens (TSAs) has led to increased efforts to develop vaccination strategies. Vaccines may be composed of whole cells or cell extracts, genetically modified tumor cells to express costimulatory molecules, dendritic cells (DCs) loaded with TAAs, immunization with soluble proteins or synthetic peptides, recombinant viruses or bacteria encoding tumor-associated antigens, and plasmid DNA encoding TSAs or TAAs in conjunction with appropriate immunomodulators. All of these antitumor vaccination approaches aim to induce specific immunological responses and localized to TAAs, destroying tumor cells alone and leaving the vast majority of other healthy cells of the body untouched.

Properties of end-stage human T cells defined by CD45RA re-expression

Persistent viral infections, inflammatory syndromes and ageing all induce the accumulation of highly differentiated CD45RA re-expressing memory T cells. These cells increase during ageing, especially in individuals who are infected with cytomegalovirus (CMV). These cells have decreased proliferative capacity, increased activation of senescence signalling pathways and greater susceptibility to apoptosis in vitro. However these cells are capable of multiple effector functions and thus bear all the hallmarks of short-lived effector T cells. This indicates that senescence signalling may govern the unique characteristics of effector T cells. In this article, we address the functional and migratory properties of these T cells and mechanisms that are involved in their generation. Finally we assess the potential for manipulation of their activity and whether this may improve immune function during ageing.

Reversal of functional defects in highly differentiated young and old CD8 T cells by PDL blockade

Highly differentiated CD8(+) CD28(-) CD27(-) T cells have short telomeres, defective telomerase activity and reduced capacity for proliferation. In addition, these cells express increased levels of inhibitory receptors and display defective Akt(ser(473)) phosphorylation following activation. It is not known whether signalling via programmed death 1 (PD-1) contributes to any of the attenuated differentiation-related functional changes in CD8(+) T cells. To address this we blocked PD-1 signalling during T-cell receptor (TCR) activation using antibodies against PD-1 ligand 1 (PDL1) and PDL2. This resulted in a significant enhancement of Akt(ser(473)) phosphorylation and TCR-induced proliferative activity of highly differentiated CD8(+) CD28(-) CD27(-) T cells. In contrast, the reduced telomerase activity in these cells was not altered by blockade of PDL1/2. We also demonstrate that PD-1 signalling can inhibit the proliferative response in primary human CD8(+) T cells from both young and older humans. These data collectively highlight that some, but not all, functional changes that arise during progressive T-cell differentiation and during ageing are maintained actively by inhibitory receptor signalling.

Possible involvement of CD14+ CD16+ monocyte lineage cells in the epidermal damage of Stevens-Johnson syndrome and toxic epidermal necrolysis

BACKGROUND

Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) are characterized by keratinocyte apoptosis and necrosis, resulting in epidermal detachment. Although monocytes abundantly infiltrate the epidermis in SJS/TEN skin lesions, the properties and functions of these cells have not been fully examined.

OBJECTIVES

To determine the properties of monocytes infiltrating into the epidermis in SJS/TEN.

METHODS

Immunostaining of skin sections was performed to examine the membrane markers of monocytes infiltrating into skin lesions.

RESULTS

Immunostaining of cryosections from 11 SJS/TEN skin lesions revealed numerous CD14+ monocytes located along the dermoepidermal junction and throughout the epidermis. The cells coexpressed CD16, CD11c and HLA-DR. CD14+ CD16+ cells were identified in very early lesions without epidermal damage, suggesting that their infiltration is a cause, rather than a result, of epidermal damage. Moreover, these cells expressed CD80, CD86 and CD137 ligand, indicative of their ability to facilitate the proliferation and cytotoxicity of CD8+ T cells. CD16+ cells infiltrating the epidermis and detected at the dermoepidermal junction were immunostained and counted in paraffin-embedded skin sections obtained from 47 patients with drug rash manifested as TEN, SJS, maculopapular-type rash or erythema multiform-type rash. The number of CD16+ monocytes infiltrating the epidermis increased significantly, depending on the grade of epidermal damage.

CONCLUSIONS

These findings suggest that the appearance of CD14+ CD16+ cells of monocyte lineage plays an important role in the epidermal damage associated with SJS/TEN, most probably by enhancing the cytotoxicity of CD8+ T cells.

B cell immunosenescence: different features of naive and memory B cells in elderly

Elderly people show a reduced protection against new infections and a decreased response to vaccines as a consequence of impairment of both cellular and humoral immunity. In this paper we have studied memory/naïve B cells in the elderly, evaluating surface immunoglobulin expression, production of the pro- and anti-inflammatory cytokines, tumor necrosis factor (TNF)-α and interleukin (IL)-10, and presence of somatic hypermutation, focusing on the IgG(+)IgD(-)CD27(-) double negative (DN) B cells that are expanded in the elderly. Our results show that naïve B cells from young donors need a sufficiently strong stimulus to be activated "in vitro", while naïve B cells from old subjects are able to produce IL-10 and TNF-α when stimulated "physiologically" (α-CD40/IL-4), suggesting that these cells might play a role in the control of the immuno-inflammatory environment in the elderly. In addition, in the elderly there is an accumulation of DN B cells with a reduced rate of somatic hypermutation. Thus, DN B lymphocytes may be exhausted cells that are expanded and accumulate as a by-product of persistent stimulation or impaired germinal center formation.

4-1BB signaling synergizes with programmed death ligand 1 blockade to augment CD8 T cell responses during chronic viral infection

Previous studies have identified the inhibitory role that the programmed death 1 (PD-1) pathway plays during chronic infection. Blockade of this pathway results in rescue of viral-specific CD8 T cells, as well as reduction of viral loads in mice chronically infected with lymphocytic choriomeningitis virus (LCMV). We tested the effect of combining PD ligand 1 (PD-L1) blockade with an agonistic regimen that induces 4-1BB costimulation during chronic LCMV infection. There is a boosting effect in the rescue of LCMV-specific CD8 T cell responses after dual treatment with PD-L1 blockade and 4-1BB agonistic Abs when the amount and timing of 4-1BB costimulation are carefully controlled. When PD-L1-blocking Abs are given together with a single low dose of anti-4-1BB agonistic Abs, there is an enhanced and stable expansion of viral-specific CD8 T cells. Conversely, when blocking Abs to PD-L1 are given with a repetitive high dose of anti-4-1BB, there is an initial synergistic expansion of viral-specific CD8 T cells by day 7, followed by dramatic apoptosis by day 14. Viral control paralleled CD8 T cell kinetics after dual treatment. By day 7 posttreatment, viral titers were lower in both of the combined regimens (compared with PD-L1 blockade alone). However, whereas the high dose of anti-4-1BB plus PD-L1 blockade resulted in rebound of viral titers to original levels, the low dose of anti-4-1BB plus PD-L1 blockade resulted in a stable reduction of viral loads. These findings demonstrate the importance of carefully manipulating the balance between activating and inhibitory signals to enhance T cell responses during chronic infection.

Successful generation of primary virus-specific and anti-tumor T-cell responses from the naive donor T-cell repertoire is determined by the balance between antigen-specific precursor T cells and regulatory T cells

BACKGROUND

One of the major challenges in allogeneic stem cell transplantation is to find a balance between the harmful induction of graft-versus-host disease and the beneficial graft-versus-leukemia and pathogen-specific immune responses. Adoptive transfer of in-vitro generated donor T cells with specific anti-leukemic or pathogen-specific activity may be effective. However, in many cases this requires the in-vitro priming and expansion of antigen-specific precursor T cells from the naïve donor T-cell repertoire.

DESIGN AND METHODS

Antigen-specific CD8 T cells were generated by co-culture of CD45RO-depleted, regulatory T cell-depleted donor peripheral blood mononuclear cells with autologous peptide-loaded dendritic cells, followed by two re-stimulations with peptide-loaded autologous monocytes. Responding T cells were isolated based on CD137 expression and further purified using peptide/major histocompatibility complex tetramers.

RESULTS

Using this method we were able to reproducibly generate functionally high avidity T cells directed against multiple viral antigens and minor histocompatibility antigens from the naïve T-cell repertoire of seronegative, minor histocompatibility antigen-negative donors. Furthermore, we demonstrated that reduction of the regulatory T-cell frequency by depletion of CD45RO(+) responder cells resulted in improved priming and expansion of antigen-specific precursor T cells.

CONCLUSIONS

In conclusion, we present a robust method for the in-vitro induction and isolation of antigen-specific T cells from the naïve repertoire. We demonstrate that the likelihood of successful generation of primary immune responses is determined by a delicate balance between the numbers of antigen-specific precursor T cells and the numbers and activation state of regulatory T cells locally at the site of priming of the immune response.

Differential B7-CD28 costimulatory requirements for stable and inflationary mouse cytomegalovirus-specific memory CD8 T cell populations

CMV establishes a lifelong persistent infection, and viral immune-modulating strategies are important in facilitating this. A particularly diverse CD8 T cell response develops as a result of this host-virus détente, with the CMV-specific memory T cell pool displaying unique functions and phenotypes. To gain insight into the factors that regulate CMV-specific CD8 T cell responses, we examined the influence of the B7-CD28 costimulatory pathway on magnitude, kinetics, and phenotype. Initial expansion of mouse CMV-specific CD8 T cells that establish stable memory pools was severely lower in mice lacking B7-CD28 signaling, and the resulting memory levels also remained reduced during persistent/latent infection. In contrast, expansion of CD8 T cells that undergo memory inflation during chronic infection was less affected in the absence of B7-CD28 costimulatory signals, eventually reaching the levels seen in wild-type mice at later times. Regardless of their differential requirements for B7-CD28 signals, both stable and inflationary memory T cell populations showed normal cytotoxic capacity. These results reveal that B7-CD28 costimulation differentially regulates the magnitude and kinetics of the multifaceted CD8 T cell response that develops during CMV infection.

Cytomegalovirus infection induces the accumulation of short-lived, multifunctional CD4+CD45RA+CD27+ T cells: the potential involvement of interleukin-7 in this process

The relative roles that ageing and lifelong cytomegalovirus (CMV) infection have in shaping naive and memory CD4+ T-cell repertoires in healthy older people is unclear. Using multiple linear regression analysis we found that age itself is a stronger predictor than CMV seropositivity for the decrease in CD45RA+ CD27+ CD4+ T cells over time. In contrast, the increase in CD45RA⁻ CD27⁻ and CD45RA+ CD27⁻ CD4+ T cells is almost exclusively the result of CMV seropositivity, with age alone having no significant effect. Furthermore, the majority of the CD45RA⁻ CD27⁻ and CD45RA+ CD27⁻ CD4+ T cells in CMV-seropositive donors are specific for this virus. CD45RA+ CD27⁻ CD4+ T cells have significantly reduced CD28, interleukin-7 receptor α (IL-7Rα) and Bcl-2 expression, Akt (ser473) phosphorylation and reduced ability to survive after T-cell receptor activation compared with the other T-cell subsets in the same donors. Despite this, the CD45RA+ CD27⁻ subset is as multifunctional as the CD45RA⁻ D27+ and CD45RA⁻ CD27⁻ CD4+ T-cell subsets, indicating that they are not an exhausted population. In addition, CD45RA+ CD27⁻ CD4+ T cells have cytotoxic potential as they express high levels of granzyme B and perforin. CD4+ memory T cells re-expressing CD45RA can be generated from the CD45RA⁻ CD27+ population by the addition of IL-7 and during this process these cells down-regulated expression of IL-7R and Bcl-2 and so resemble their counterparts in vivo. Finally we showed that the proportion of CD45RA+ CD27⁻ CD4+ T cells of multiple specificities was significantly higher in the bone marrow than the blood of the same individuals, suggesting that this may be a site where these cells are generated.

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.

Biphasic role of 4-1BB in the regulation of mouse cytomegalovirus-specific CD8(+) T cells

The initial requirement for the emergence of CMV-specific CD8(+) T cells is poorly understood. Mice deficient in the cosignaling TNF superfamily member, 4-1BB, surprisingly developed exaggerated early CD8(+) T-cell responses to mouse CMV (MCMV). CD8(+) T cells directed against acute MCMV epitopes were enhanced, demonstrating that 4-1BB naturally antagonizes these primary populations. Paradoxically, 4-1BB-deficient mice displayed reduced accumulation of memory CD8(+) T cells that expand during chronic/latent infection. Importantly, the canonical TNF-related ligand, 4-1BBL, promoted the accumulation of these memory CD8(+) T cells, whereas suppression of acute CD8(+) T cells was independent of 4-1BBL. These data highlight the dual nature of the 4-1BB/4-1BBL system in mediating both stimulatory and inhibitory cosignaling activities during the generation of anti-MCMV immunity.

Tumor necrosis factor receptor/tumor necrosis factor family members in antiviral CD8 T-cell immunity

CD8 memory T cells can play a critical role in protection against repeated exposure to infectious agents such as viruses, yet can also contribute to the immunopathology associated with these pathogens. Understanding the mechanisms that control effective memory responses has important ramifications for vaccine design and in the management of adverse immune reactions. Recent studies have implicated several members of the tumor necrosis factor receptor (TNFR) family as key stimulatory and inhibitory molecules involved in the regulation of CD8 T cells. In this review, we discuss their control of the generation, persistence, and reactivation of CD8 T cells during virus infection.

Human cytomegalovirus-specific CD8(+) T-cell expansions contain long-lived cells that retain functional capacity in both young and elderly subjects

The immune response to human cytomegalovirus (HCMV) infection is characterized by the accumulation of HCMV-specific CD8(+) T cells, particularly in the elderly; such expansions may impair immune responses to other pathogens. We investigated mechanisms underlying HCMV-specific expansions in 12 young and 21 old healthy subjects (although not all analyses were performed on all subjects). Phenotypically, HCMV-pentamer(+) CD8(+) T cells were characterized by marked Vβ restriction, advanced differentiation (being predominantly CD27(-) CD28(-) ), and variable CD45RO/RA expression. Although more common and larger in older subjects, expansions had similar phenotypic characteristics in the young. In one old subject, repeated studies demonstrated stability in size and Vβ distribution of pentamer(+) populations over 6 years. We tested whether HCMV-specific CD8(+) T-cell expansions arose from accelerated proliferation or extended lifespan by in vivo labelling with deuterated glucose and ex vivo Ki-67 expression. Uptake of deuterated glucose was lower in pentamer(+) cells than in pentamer(-) CD8(+) CD45RO(+) or CD8(+) CD45RA(+) cells in three old subjects, consistent with reduced proliferation and extended lifespan. Similarly Ki-67 labelling showed no evidence for increased proliferation in HCMV-specific CD8(+) expansions in older subjects, although pentamer(-) CD45RA(+) cells from young donors expressed very little Ki-67. We investigated Bcl-2 and CD95 as possible anti-apoptotic mediators, but neither was associated with pentamer-positivity. To investigate whether expansion represents a compensatory response to impaired functionality, we performed two tests of functionality, peptide-stimulated proliferation and CD107 expression; both were intact in pentamer(+) cells. Our data suggest that HCMV-specific CD8(+) expansions in older subjects accumulate by extended lifespan, rather than accelerated proliferation.

SA-4-1BBL as the immunomodulatory component of a HPV-16 E7 protein based vaccine shows robust therapeutic efficacy in a mouse cervical cancer model

Cervical cancer is the leading cause of cancer-related deaths among women worldwide. Current prophylactic vaccines based on HPV (Human papillomavirus) late gene protein L1 are ineffective in therapeutic settings. Therefore, there is an acute need for the development of therapeutic vaccines for HPV associated cancers. The HPV E7 oncoprotein is expressed in cervical cancer and has been associated with the cellular transformation and maintenance of the transformed phenotype. As such, E7 protein represents an ideal target for the development of therapeutic subunit vaccines against cervical cancer. However, the low antigenicity of this protein may require potent adjuvants for therapeutic efficacy. We recently generated a novel chimeric form of the 4-1BBL costimulatory molecule engineered with core streptavidin (SA-4-1BBL) and demonstrated its safe and pleiotropic effects on various cells of the immune system. We herein tested the utility of SA-4-1BBL as the immunomodulatory component of HPV-16 E7 recombinant protein based therapeutic vaccine in the E7 expressing TC-1 tumor as a model of cervical cancer in mice. A single subcutaneous vaccination was effective in eradicating established tumors in approximately 70% of mice. The therapeutic efficacy of the vaccine was associated with robust primary and memory CD4(+) and CD8(+) T cell responses, Th1 cytokine response, infiltration of CD4(+) and CD8(+) T cells into the tumor, and enhanced NK cell killing. Importantly, NK cells played an important role in vaccine mediated therapy since their physical depletion compromised vaccine efficacy. Collectively, these data demonstrate the utility of SA-4-1BBL as a new class of multifunctional immunomodulator for the development of therapeutic vaccines against cancer and chronic infections.

KLRG1--more than a marker for T cell senescence

The co-inhibitory receptor killer-cell lectin like receptor G1 (KLRG1) is expressed on NK cells and antigen-experienced T cells and has been postulated to be a marker of senescence. Whilst KLRG1 has frequently been used as a marker of cellular differentiation, data are emerging indicating that KLRG1 plays an inhibitory role. In this review we examine evidence highlighting this view of KLRG1 with emphasis on the functional defects that arise during T cell differentiation with age that may, in part, be actively maintained by inhibitory receptor signalling.

2B4 (CD244) signaling via chimeric receptors costimulates tumor-antigen specific proliferation and in vitro expansion of human T cells

Regulatory NK cell receptors can contribute to antigen-specific adaptive immune responses by modulating T cell receptor (TCR)-induced T cell activation. We investigated the potential of the NK cell receptor 2B4 (CD244) to enhance tumor antigen-induced activation of human T cells. 2B4 is a member of the CD2 receptor subfamily with both activating and inhibitory functions in NK cells. In T cells, its expression is positively associated with the acquisition of a cytolytic effector memory phenotype. Recombinant chimeric receptors that link extracellular single-chain Fv fragments specific for the tumor-associated surface antigens CD19 and G(D2) to the signaling domains of human 2B4 and/or TCRzeta were expressed in non-specifically activated peripheral blood T cells by retroviral gene transfer. While 2B4 signaling alone failed to induce T cell effector functions or proliferation, it significantly augmented the antigen-specific activation responses induced by TCRzeta. 2B4 costimulation did not affect the predominant effector memory phenotype of expanding T cells, nor did it increase the proportion of T cells with regulatory phenotype (CD4+CD25(hi)FoxP3+). These data support a costimulatory role for 2B4 in human T cell subpopulations. As an amplifier of TCR-mediated signals, 2B4 may provide a powerful new tool for immunotherapy of cancer, promoting sustained activation and proliferation of gene-modified antitumor T cells.