Homeostasis of memory T cells

Origins of CD4(+) effector and central memory T cells

Lineage-committed effector CD4(+) T cells are generated at the peak of the primary response and are followed by heterogeneous populations of central and effector memory cells. Here we review the evidence that T helper type 1 (T(H)1) effector cells survive the contraction phase of the primary response and become effector memory cells. We discuss the applicability of this idea to the T(H)2 cell, T(H)17 helper T cell, follicular helper T cell (T(FH) cell) and induced regulatory T cell lineages. We also discuss how central memory cells are formed, with an emphasis on the role of B cells in this process.

Normal T cell homeostasis: the conversion of naive cells into memory-phenotype cells

Weak T cell antigen receptor (TCR) signals from contact with self ligands act in synergy with antiapoptotic signals induced by interleukin 7 (IL-7) to promote the survival of naive T cells in a resting state. The amount of background TCR signaling in naive T cells is set by post-thymic TCR tuning and operates at an intensity just below that required to induce entry into the cell cycle. Costimulation from higher concentrations of IL-7 and other common γ-chain cytokines can induce T cells to undergo homeostatic proliferation and conversion into cells with a memory phenotype; many of these memory phenotype cells may be the progeny of cells responding to self antigens. The molecular mechanisms that control the conversion of naive resting T cells into memory-phenotype cells TCR-dependent in normal animals are beginning to be understood.

IL-18 is required for self-reactive T cell expansion in NOD mice

IL-18 has a well-established role in pro-inflammatory responses in the islets in type 1 diabetes. Here, we identify a distinctive role for IL-18 in expanding pathogenic T cells in the periphery of NOD mice. Well in advance of disease onset, the periphery of IL-18-deficient mice exhibits reduced T cell turnover, an increased prevalence of naïve and quiescent T cells, emergence of fewer effector T cells, and disease protection. Islet-reactive T cells fail to become activated in the lymphoid organs of mice lacking IL-18 and their rapid expansion is inhibited. IL-18 secretion by antigen presenting cells increases with advancing disease and is required for expression of its receptor on T cells. Our results demonstrate that induction of the IL-18 receptor reflects a critical stage of autoreactive T cell activation and expansion on the pathway toward effector T cell differentiation. This study therefore assigns a novel role to IL-18 for expanding the pool of islet-destructive T cells during pre-diabetes. This report highlights a new basic mechanism in type 1 diabetes pathogenesis and suggests that targeting the IL-18 pathway should be explored as a potential treatment strategy.

Biomarkers in immune reconstitution inflammatory syndrome: signals from pathogenesis

PURPOSE OF REVIEW

Immune reconstitution inflammatory syndrome (IRIS) is the paradoxical worsening or unmasking of an infection or neoplasm in HIV-1-infected patients shortly after antiretroviral therapy (ART) initiation. New insights into the pathogenesis of IRIS may help identify biomarkers that could be useful in predicting or diagnosing IRIS.

RECENT FINDINGS

Studies of immunopathogenesis have shown a signification activation of both innate and adaptive immune responses with elevation of plasma or serum chemokines and cytokines. Markers of inflammation such as C-reactive protein, interferon-inducible protein 10 or interferon γ may be helpful as predictors of IRIS events. In addition, tuberculosis (TB)-associated IRIS is associated with a prominent Th1 response that can be heightened even prior to ART initiation in cases of unmasking TB, and may assist in early diagnosis. Large prospective studies are needed to elucidate the predictive and diagnostic value of IRIS biomarkers and advance them to the clinic.

SUMMARY

Reversal of immunosuppression by ART leads to exaggerated pathogen-specific immune responses (known as IRIS) that appear to be primed prior to therapy. Inflammatory markers, chemokines and cytokines that signify innate and adaptive immune activation are biomarkers that could prove of clinical value after appropriate validation.

Development of an IL-15-autocrine CD8 T-cell leukemia in IL-15-transgenic mice requires the cis expression of IL-15Rα

IL-15 has growth-promoting effects on select lymphoid subsets, including natural killer (NK) cells, NK T cells, intraepithelial lymphocytes (IELs), CD8 T cells, and γδ-T cells. Constitutive expression of murine IL-15 in IL-15-transgenic mice was reported to cause T-NK leukemia. We investigated whether IL-15 expression is sufficient for leukemic transformation using a human IL-15-transgenic (IL-15Tg) mouse model. We noted that 100% of the mice observed over a 2-year period (n > 150) developed fatal expansions of CD8 T cells with NK markers, and determined that these cells expressed IL-15 receptor alpha (IL-15Rα). The expression of IL-15Rα on CD8 T cells appears to be required for uncontrolled aggressive lymphoproliferation, because none of the IL-15Rα(-/-)-IL-15Tg mice that we followed for more than 2 years developed the fatal disease despite controlled expansion of CD8 T cells. In addition, in contrast to IL-15Tg mice, in which leukemia-like CD8 T cells expressed IL-15Rα persistently, acutely activated normal CD8 T cells only transiently expressed IL-15Rα. Inhibition of DNA methylation enabled sustained IL-15Rα expression induced by activation. We present a scenario for IL-15Tg mice in which CD8 T cells that acquire constitutive persistent IL-15Rα expression are at a selective advantage and become founder cells, outgrow other lymphocytes, and lead to the establishment of a leukemia-like condition.

Type 1 Diabetes: Etiology, Immunology, and Therapeutic Strategies

Type 1 diabetes (T1D) is a chronic autoimmune disease in which destruction or damaging of the beta-cells in the islets of Langerhans results in insulin deficiency and hyperglycemia. We only know for sure that autoimmunity is the predominant effector mechanism of T1D, but may not be its primary cause. T1D precipitates in genetically susceptible individuals, very likely as a result of an environmental trigger. Current genetic data point towards the following genes as susceptibility genes: HLA, insulin, PTPN22, IL2Ra, and CTLA4. Epidemiological and other studies suggest a triggering role for enteroviruses, while other microorganisms might provide protection. Efficacious prevention of T1D will require detection of the earliest events in the process. So far, autoantibodies are most widely used as serum biomarker, but T-cell readouts and metabolome studies might strengthen and bring forward diagnosis. Current preventive clinical trials mostly focus on environmental triggers. Therapeutic trials test the efficacy of antigen-specific and antigen-nonspecific immune interventions, but also include restoration of the affected beta-cell mass by islet transplantation, neogenesis and regeneration, and combinations thereof. In this comprehensive review, we explain the genetic, environmental, and immunological data underlying the prevention and intervention strategies to constrain T1D.

The immunobiology of cord blood transplantation

Despite significant recent advances in the applicability and outcome following unrelated cord blood transplantation (UCBT), infections remain a major cause of mortality associated with poor immune recovery in the first 6 months after UCBT. Enhanced immune reconstitution not only could improve survival by reduced transplant related mortality, but may also favorably impact on relapse incidence by improved graft-versus-leukemia effects. This review will summarize our current understanding of the biology of immune recovery post-UCBT with an emphasis on adaptive T cell dependent immunity. New efforts to boost immunity will be also highlighted including our own laboratory, where ex vivo T cell expansion is pursued towards adoptive immunotherapy.

Antigen-bearing dendritic cells regulate the diverse pattern of memory CD8 T-cell development in different tissues

Memory T cells of the effector type (T(EM)) account for the characteristic rapidity of memory T-cell responses, whereas memory T cells of the central type (T(CM)) account for long-lasting, vigorously proliferating memory T-cell responses. How antigen-stimulated (primed) T cells develop into different memory T-cell subsets with diverse tissue distributions is largely unknown. Here we show that after respiratory tract infection of mice with influenza virus, viral antigen associated with dendritic cells (DCs) was abundant in lung-draining lymph nodes (DLN) and the spleen for more than a week but was scant and transient in nondraining lymph nodes (NDLN). Correspondingly, activated CD8 T cells proliferated extensively in DLN and the spleen but minimally in NDLN. Strikingly, however, although most persisting CD8 T cells in DLN and spleen exhibited the T(EM) phenotype, those persisting in NDLN exhibited the T(CM) phenotype. Reducing antigen exposure by depleting DCs at the peak of primary T-cell responses enhanced the development of T(CM), whereas subjecting primed CD8 T cells from NDLN to additional antigen stimulation inhibited T(CM) development. These findings demonstrate that differences in persistence of antigen-bearing DCs in various tissues regulate the tissue-specific pattern of memory CD8 T-cell development. The findings have significant implications for design of vaccines and immunization strategies.

The burden of obesity on infectious disease

The world is now experiencing an epidemic of obesity. Although the effects of obesity on the development of metabolic and cardiovascular problems are well studied, much less is known about the impact of obesity on immune function and infectious disease. Studies in obese humans and with obese animal models have repeatedly demonstrated impaired immune function, including decreased cytokine production, decreased response to antigen/mitogen stimulation, reduced macrophage and dendritic cell function, and natural killer cell impairment. Recent studies have demonstrated that the impaired immune response in the obese host leads to increased susceptibility to infection with a number of different pathogens such as community-acquired tuberculosis, influenza, Mycobacterium tuberculosis, coxsackievirus, Helicobacter pylori and encephalomyocarditis virus. While no specific mechanism has been defined for the decreased immune response to infectious disease in the obese host, several obesity-associated changes such as excessive inflammation, altered adipokine signaling, metabolic changes and even epigenetic regulation could affect the immune response. This review will discuss what is currently known about the relationship between obesity and infectious disease.

Elevated frequencies of highly activated CD4+ T cells in HIV+ patients developing immune reconstitution inflammatory syndrome

Immune reconstitution inflammatory syndrome (IRIS) is a considerable problem in the treatment of HIV-infected patients. To identify immunologic correlates of IRIS, we characterized T-cell phenotypic markers and serum cytokine levels in HIV patients with a range of different AIDS-defining illnesses, before and at regular time points after initiation of antiretroviral therapy. Patients developing IRIS episodes displayed higher frequencies of effector memory, PD-1(+), HLA-DR(+), and Ki67(+) CD4(+) T cells than patients without IRIS. Moreover, PD-1(+) CD4(+) T cells in IRIS patients expressed increased levels of LAG-3, CTLA-4, and ICOS and had a Th1/Th17 skewed cytokine profile upon polyclonal stimulation. Elevated PD-1 and Ki67 expression was also seen in regulatory T cells of IRIS patients. Furthermore, IRIS patients displayed higher serum interferon-γ, compared with non-IRIS patients, near the time of their IRIS events and higher serum interleukin-7 levels, suggesting that the T-cell populations are also exposed to augmented homeostatic signals. In conclusion, our findings indicate that IRIS appears to be a predominantly CD4-mediated phenomenon with reconstituting effector and regulatory T cells showing evidence of increased activation from antigenic exposure. These studies are registered online at http://clinicaltrials.gov as NCT00557570 and NCT00286767.

Hepatitis C virus infection: a "liaison a trois" amongst the virus, the host, and chronic low-level inflammation for human survival

This review covers the various aspects of the immune system that allows the relationship between the hepatitis-C virus, the host and chronic low-level inflammation, to be highly flexible and able to defend the host from persistent infections. This ambiguity mainly stems from the property of the immune system that can be both protective and harmful. Immunity cannot be fully protective without producing a certain degree of damage (acute hepatitis resulting in resolving HCV infection). In addition, the balance between protection and tissue damage is critical for the development of chronic HCV infection. The establishment of a state of chronic low-level inflammation is instrumental to limit liver immunopathology, to limit viral spread, and ultimately to ensure a long-lasting survival of the host. It is dictated by a fine equilibrium maintained by multiple immunologic mechanisms, including: sensory perception of innate immunity, virus-specific T and B cell functions, control of immune responses, and finally the balance between immunity and immunopathology that has principally evolved to favor the survival of the species.

Loss of tonic T-cell receptor signals alters the generation but not the persistence of CD8+ memory T cells

The requirements for tonic T-cell receptor (TCR) signaling in CD8(+) memory T-cell generation and homeostasis are poorly defined. The SRC homology 2 (SH2)-domain-containing leukocyte protein of 76 kDa (SLP-76) is critical for proximal TCR-generated signaling. We used temporally mediated deletion of SLP-76 to interrupt tonic and activating TCR signals after clearance of the lymphocytic choriomeningitis virus (LCMV). SLP-76-dependent signals are required during the contraction phase of the immune response for the normal generation of CD8 memory precursor cells. Conversely, LCMV-specific memory CD8 T cells generated in the presence of SLP-76 and then acutely deprived of TCR-mediated signals persist in vivo in normal numbers for more than 40 weeks. Tonic TCR signals are not required for the transition of the memory pool toward a central memory phenotype, but the absence of SLP-76 during memory homeostasis substantially alters the kinetics. Our data are consistent with a model in which tonic TCR signals are required at multiple stages of differentiation, but are dispensable for memory CD8 T-cell persistence.

Cdc25A-driven proliferation regulates CD62L levels and lymphocyte movement in response to interleukin-7

OBJECTIVE

Interleukin-7 (IL-7) is a multifunctional cytokine and a promising immunotherapeutic agent. However, because transient T-cell depletion is an immediate outcome of IL-7 administration at supraphysiological doses, we investigated the mechanism by which the IL-7 proliferative signal transduced through Cdc25A, a key activator of cyclin-dependent kinases, could modulate lymphocyte movement.

MATERIALS AND METHODS

Employing novel methods of manipulating Cdc25A gene expression, combined with in vitro and in vivo evaluation of IL-7 application, we assessed the expression of activation and homing markers and identified the mechanism by which IL-7 could induce T-cell expansion and alter lymphocyte motility.

RESULTS

Constitutively active Cdc25A drove T-cell proliferation independently of IL-7 and resulted in an activated phenotype (CD69(hi), CD44(hi)). Conversely, inhibition of Cdc25A resulted in decreased proliferation, reduced expression of activation markers, and upregulation of the lymph node homing molecule, CD62L, which promoted cell adhesion when engaged by ligand. We found that IL-7 prevented the nuclear translocation of the transcription factor, Foxo1, in a manner dependent on the activity of Cdc25A, resulting in decreased levels of CD62L. In vivo administration of IL-7 decreased lymph node cellularity, while treatment with IL-7, premixed with a neutralizing IL-7 antibody (M25), increased total lymph node cells--with more nuclear Foxo1 detected in cells from mice receiving IL-7 + M25.

CONCLUSIONS

These results are consistent with the model that IL-7 drives Cdc25A-mediated T-cell proliferation, which prevents the nuclear translocation of Foxo1, leading to reduced expression of CD62L and the migration of T cells into circulation.

Diet-induced obesity in mice reduces the maintenance of influenza-specific CD8+ memory T cells

Obesity has been associated with increasing the risk for type 2 diabetes and heart disease, but its influence on the immune response to viral infection is understudied. Memory T cells generated during a primary influenza infection are important for protection against subsequent influenza exposures. Previously, we have demonstrated that diet-induced obese (DIO) mice have increased morbidity and mortality following secondary influenza infection compared with lean mice. To determine whether the problem resided in a failure to maintain functional, influenza-specific CD8(+) memory T cells, male DIO and lean mice were infected with influenza X-31. At 84 d postinfection, DIO mice had a 10% reduction in memory T cell numbers. This reduction may have resulted from significantly reduced memory T cell expression of interleukin 2 receptor beta (IL-2R beta, CD122), but not IL-7 receptor alpha (CD127), which are both required for memory cell maintenance. Peripheral leptin resistance in the DIO mice may be a contributing factor to the impairment. Indeed, leptin receptor mRNA expression was significantly reduced in the lungs of obese mice, whereas suppressor of cytokine signaling (Socs)1 and Socs3 mRNA expression were increased. It is imperative to understand how the obese state alters memory T cells, because impairment in maintenance of functional memory responses has important implications for vaccine efficacy in an obese population.

Regulation of memory CD8 T-cell differentiation by cyclin-dependent kinase inhibitor p27Kip1

Induction of potent T-cell memory is the goal of vaccinations, but the molecular mechanisms that regulate the formation of memory CD8 T cells are not well understood. Despite the recognition that controls of cellular proliferation and apoptosis govern the number of memory T cells, the cell cycle regulatory mechanisms that control these key cellular processes in CD8 T cells during an immune response are poorly defined. Here, we have identified the cyclin-dependent kinase inhibitor p27(Kip1) as a critical regulator of the CD8 T-cell homeostasis at all phases of the T-cell response to an acute viral infection in mice. By acting as a timer for cell cycle exit, p27(Kip1) curtailed the programmed expansion of interleukin-2-producing memory precursors and markedly limited the magnitude and quality of CD8 T-cell memory. In the absence of p27(Kip1), CD8 T cells showed superior recall responses shortly after vaccination with recombinant Listeria monocytogenes. Additionally, we show that p27(Kip1) constrains proliferative renewal of memory CD8 T cells, especially of the effector memory subset. These findings provide critical insights into the cell cycle regulation of CD8 T-cell homeostasis and suggest that modulation of p27(Kip1) could bolster vaccine-induced T-cell memory and protective immunity.

Serum IL-7 and G-CSF in major depressive disorder

Major depressive disorder (MDD) has been associated with dysregulated immune systems and impaired T cell function, but data on depression-related alterations in the levels of immunomodulatory growth factors are scarce. In order to further clarify the mechanisms underlying immune system dysregulation in depressed subjects, we examined the associations between MDD and serum levels of two immunomodulatory growth factors, interleukin (IL)-7 and granulocyte-colony stimulating factor (G-CSF), in 122 subjects (MDD with long-term symptomatology, n=61; controls, n=61). The MDD subjects had lowered levels of IL-7. In a model adjusted for age, gender and body mass index, subjects in the lowest tertile of IL-7 had a 3.4-fold increased likelihood for MDD (p=0.010). Further adjustments for sleep disturbances, alcohol use, smoking, and metabolic syndrome did not alter these findings. Moreover, the exclusion of subjects with rheumatoid arthritis, coronary heart disease, or the use of non-steroidal anti-inflammatory medications or oral corticosteroids only slightly attenuated the findings. The G-CSF levels did not differ between the two groups. The lowering of the serum levels of IL-7, a regulator of T cell homeostasis, in MDD subjects may underlie the depression-related impaired T cell function.

An update on regulatory T cells in transplant tolerance and rejection

Several types of T cells with immunosuppressive properties have been identified, but FOXP3(+) regulatory T (T(REG)) cells have emerged as a dominant cell type; they are critically involved in the induction and maintenance of immune tolerance. Manipulation of this cell type for the induction of transplant tolerance including renal transplant tolerance has attracted considerable attention. Studies in this area have demonstrated unexpected complexities, and attempts to translate T(REG) cells towards clinical utility have met with unanticipated difficulties. In this Review, a broad overview is provided on recent progress in the study of T(REG) cells, focusing on challenges, opportunities, and emerging approaches in exploiting T(REG) cells for the induction of transplant tolerance.

Generation of effector CD8+ T cells and their conversion to memory T cells

Immunological memory is a cardinal feature of adaptive immunity. We are now beginning to elucidate the mechanisms that govern the formation of memory T cells and their ability to acquire longevity, survive the effector-to-memory transition, and mature into multipotent, functional memory T cells that self-renew. Here, we discuss the recent findings in this area and highlight extrinsic and intrinsic factors that regulate the cellular fate of activated CD8+ T cells.

Interleukin-7 permits Th1/Tc1 maturation and promotes ex vivo expansion of cord blood T cells: a critical step toward adoptive immunotherapy after cord blood transplantation

Donor leukocyte infusions (DLI) in the allogeneic hematopoietic transplant setting can provide a clinically relevant boost of immunity to reduce opportunistic infections and to increase graft-versus-leukemia activity. Despite significant advances in applicability, DLI has not been available for single-unit recipients of unrelated cord blood transplant. Ex vivo expansion of cord blood T cells can be achieved with interleukin (IL)-2 and CD3/CD28 costimulatory beads. However, significant apoptosis occurs in proliferating T cells, diminishing the yield and skewing the CD4/CD8 ratio in the T-cell population, jeopardizing the potential efficacy of DLI. In this study, we show that interleukin (IL)-7 not only reduces apoptosis of activated T lymphocytes and enhances their proliferation but also promotes functional maturation, leading to secretion of IFN-gamma and other key cytokines. Recognizing that infused T lymphocytes will need to meet microbial antigens in secondary lymphoid organs to generate effectors, we also show that expansion with IL-7 promotes the preservation of a polyclonal broad T-cell receptor repertoire and a surface phenotype that favors lymph node homing. Expanded lymphocytes lack alloreactivity against recipient and other allogeneic cells, indicating a favorable safety profile from graft-versus-host disease. Nevertheless, expanded T cells can be primed subsequently against lymphoid and myeloid leukemia cells to generate tumor-specific cytotoxic T cells. Taken together, our findings offer a major step in fulfilling critical numerical and biological requirements to quickly generate a DLI product ex vivo using a negligible fraction of a cord blood graft that provides a flexible adoptive immunotherapy platform for both children and adults.

LFA-1 defect-induced effector/memory CD8+ T cell apoptosis is mediated via Bcl-2/Caspase pathways and associated with downregulation of CD27 and IL-15R

LFA-1 signaling is required for the generation of central memory CD8(+) T cells in priming phase. However, its role for effector and memory CD8(+) T cell survival in transition and maintenance phases is elusive. We transferred effector and memory CD8(+) T cells into C57BL/6 and CD54(-/-) mice, which were generated by cultivation of ovalbumin (OVA)-pulsed dendritic cells (DC(OVA)) with naïve CD8(+) T cells derived from transgenic OT I mice and purified from effector CD8(+) T cell-transferred C57BL/6 mice, respectively. We then assessed kinetics of T cell survival using PE-H2-K(b)/OVAI tetramer and FITC-CD8 staining by flow cytometry. We found that survival of transferred effector and memory CD8(+) T cells in CD54(-/-) mice significantly decreased (p<0.05) compared to that in C57BL/6 mice due to an increased T cell apoptosis, which is mediated via downregulation of proapoptotic Bid, anti-apoptotic Bcl-2, Bcl-X(L) and pro-Caspase-8, and up-regulation of apoptotic Bax and cleaved Caspase-3 and -7 by RNA array and Western blotting analyses. Decreased expression of CD27 and IL-15R on transferred CD8(+) T cells with less survival was found to be associated with increased T cell apoptosis, which was confirmed by silencing CD27 with siRNA transfection or using CD8(+) (IL-15R(-/-))T cells for adoptive transfer into C57BL/6 mice. These data indicate that LFA-1 signal defect-induced CD8(+) T cell apoptosis is associated with reduced CD27 costimulation and IL-15R survival signal. Therefore, our study provides important evidence on and elucidates the molecular mechanism associated with the role LFA-1 signaling plays in effector and memory CD8(+) T cell survival.

Regulation of CD8+ T cell responses to infection with parasitic protozoa

There are over 10,000 species of parasitic protozoa, a subset of which can cause considerable disease in humans. Here we examine in detail the complex immune response generated during infection with a subset of these parasites: Trypanosoma cruzi, Leishmania sp., Toxoplasma gondii, and Plasmodium sp. While these particular species perhaps represent the most studied parasites in terms of understanding how T cells function during infection, it is clear that the lessons learned from this body of work are also relevant to the other protozoa known to induce a CD8(+) T cell response. This review will highlight some of the key studies that established that CD8(+) T cells play a major role in protective immunity to protozoa, the factors that promote the generation as well as maintenance of the CD8(+) T cell response during these infections, and draw attention to some of the gaps in our knowledge. Moreover, the development of new tools, including MHC-Class I tetramer reagents and the use of TCR transgenic mice or genetically modified parasites, has provided a better appreciation of how parasite specific CD8(+) T cell responses are initiated and new insights into their phenotypic plasticity.

Intrinsic and extrinsic control of effector T cell survival and memory T cell development

Following infection or vaccination T cells expand exponentially and differentiate into effector T cells in order to control infection and coordinate the multiple effector arms of the immune system. Soon after this expansion, the majority of antigen-specific T cells die to reattain homeostasis and a small pool of memory T cells forms to provide long-term immunity to subsequent re-infection. Our understanding of how this process is controlled has improved considerably over the recent years, but many questions remain outstanding. This review focuses on the recent advancements in this area with an emphasis on how the contraction of activated T cells is coordinately regulated by a combination of factors extrinsic and intrinsic to the activated T cells.

Influenza-induced production of interferon-alpha is defective in geriatric individuals

BACKGROUND

The majority of deaths (90%) attributed to influenza are in person's age 65 or older. Little is known about whether defects in innate immune responses in geriatric individuals contribute to their susceptibility to influenza.

OBJECTIVE

Our aim was to analyze interferon-alpha (IFN-alpha) production in peripheral blood mononuclear cells (PBMCs) isolated from young and geriatric adult donors, stimulated with influenza A or Toll-like receptor (TLR) ligands. IFN-alpha is a signature anti-viral cytokine that also shapes humoral and cell-mediated immune responses.

RESULTS

Geriatric PBMCs produced significantly less IFN-alpha in response to live or inactivated influenza (a TLR7 ligand) but responded normally to CpG ODN (TLR9 ligand) and Guardiquimod (TLR7 ligand). All three ligands activate plasmacytoid dendritic cells (pDCs). While there was a modest decline in pDC frequency in older individuals, there was no defect in uptake of influenza by geriatric pDCs.

DISCUSSION AND CONCLUSION

Influenza-induced production of IFN-alpha was defective in geriatric PBMCs by a mechanism that was independent of reduced pDC frequency or viability, defects in uptake of influenza, inability to secrete IFN-alpha, or defects in TLR7 signaling.

Comparison of AAV/IL-7 autocrine (T cell) versus paracrine (DC) gene delivery for enhancing CTL stimulation and function

Adoptive transfer of antigen-specific cytotoxic T lymphocyte (CTL) into patients holds promise in treating cancer. Such anti-cancer CTL are stimulated by professional antigen-presenting dendritic cells (DC). We hypothesize the gene delivery of various Th1-response cytokines, such as interleukin 7 (IL-7), should further enhance CTL stimulation and activity. However, the issue as to which cell type, DC (paracrine) or the T cell (autocrine), should express a particular Th1 cytokine gene for optimal CTL stimulation has never been addressed. We used adeno-associated virus-2 (AAV) to compare delivery of IL-7 and IL-2 genes into DC or T cells and to exogenous commercial cytokines for generating robust carcinoembryonic antigen (CEA)-specific CTL. AAV/IL-7 transduction of T cells (autocrine delivery) generated CTL with the highest killing capability. Consistent with this, AAV/IL-7 delivery generated T cell populations with the highest proliferation, highest interferon gamma expression, highest CD8(+):CD4(+) ratio, highest CD8(+), CD69(+) levels, and lowest CD4(+), CD25(+) (Treg) levels. These data are consistent with higher killing by the AAV/IL-7-altered CTL. These data strongly suggest that IL-7 autocrine gene delivery is optimal for CTL generation. These data also suggest Th1 cytokine autocrine versus paracrine delivery is an important issue for immuno-gene therapy and uncovers new questions into cytokine mechanism of action.

Pulmonary dendritic cells: thinking globally, acting locally

The phrase “think globally, act locally” was coined in the early 1970s and directed individuals to clean up their local environment with the ultimate goal of improving the health of the entire planet. Several recent studies indicate that similar considerations apply to the immune system, in which small numbers of leukocytes, such as pulmonary dendritic cells, can modify the local immune environment in the lung and promote a positive outcome for the organism.

Immune impairment in patients with terminal cancers: influence of cancer treatments and cytomegalovirus infection

Although immunodeficiency is usually considered a prerequisite of oncogenesis, a detailed immune pro- file in cancer has not yet been described. Without such profiling, it is not surprising that there is a vast discrepancy in the responses of cancer patients to immunotherapy. Our results show that the integrity of the immune system deteriorates with cancer progression by displaying a trend toward decreasing levels of functional T cells, including CD4, naïve, and central memory T cells, and an expansion of hyporesponsive populations such as CD28⁻ and CMV-specific T cells. One hundred and one patients constitute the study group for the observational study reported in this paper. Forty-eight patients with newly diagnosed stages III and IV and 53 patients with extensively treated stage IV disease. The costimulatory molecules CD27 and CD28 were downregulated in all patients. Among the proinflammatory cytokines (IL-6, TNF-α, IFN-γ), only IL-6 differed significantly among the groups, increasing as the cancer stage progressed. Plasma IL-7 did not diVer among the participants. The relative deficits of naïve T cells in cancer patients may be associated with the downregulation of IL-7Rα expression rather than changes in the circulating levels of IL-7. The downregulation of IL-7Rα expression was shown to be associated with increased levels of intracellular CMV. The present study suggests that the immune impairment in patients with cancer is associated with multiple factors, such as the stage of cancer, consequence of CMV infection and impact of treatment.

Phenotypic definition of effector and memory T-lymphocyte subsets in mice chronically infected with Mycobacterium tuberculosis

The bacterium Mycobacterium tuberculosis remains one of the world's most successful pathogens, a situation that is aggravated by the fact that the existing vaccine, Mycobacterium bovis BCG, is not effective in adults. As with any vaccine, the purpose of giving BCG vaccination is to establish a long-lived state of memory immunity, but whether this is successfully completely established is still unclear. It is generally accepted that memory T cells can be divided into central and effector memory populations by function and by phenotype; however, the majority of data supporting this division have been generated using transgenic mouse models or mice that have recovered from acute viral infections. Tuberculosis, on the other hand, represents a persistent, chronic state of immunity in which the presence of memory T cells is far less well defined. We show here that mice vaccinated with BCG or chronically infected with M. tuberculosis establish antigen-specific populations of cells within the lungs that predominantly express a cellular phenotype consistent with their being effector or effector memory cells. In contrast, cells with a central memory phenotype exist in much lower numbers in the lungs but can be found in significantly larger numbers in the spleen, where they may represent a potential reservoir. These data suggest that the effector-to-central-memory T-cell transition may well be minimal in these persisting mycobacterial infections, and they support a novel hypothesis that this may explain the fundamental basis of the failure of the BCG vaccine in humans.

Increased intensity lymphodepletion enhances tumor treatment efficacy of adoptively transferred tumor-specific T cells

Lymphodepletion before adoptive cell transfer (ACT)-based immunotherapies can enhance anti-tumor responses by augmenting innate immunity, by increasing access to homeostatic cytokines, and by depressing the numbers of regulatory T cells and myeloid-derived suppressor cells. Although it is clear that high-dose total body irradiation given together with hematopoietic stem cell (HSC) transplantation effectively enhances ACT, the relationship between the intensity of lymphodepletion and tumor treatment efficacy has not been systematically studied. Using the pmel-1 mouse model of self/tumor-reactive CD8 T cells, we observed a strong correlation between the intensity of the conditioning regimen and the efficacy of ACT-based treatments using linear regression analysis. This was the case for preparative total body irradiation administered either as a single dose (R=0.97, P<0.001) or in fractionated doses (R=0.94, P<0.001). Increased amounts of preparative total body irradiation were directly correlated with progressively more favorable ratios of transferred tumor-reactive CD8 T cells toward endogenous cells with the potential for inhibitory activity including: CD4 cells (potentially T regulatory cells); Gr1 cells (which are capable of functioning as myeloid-derived suppressor cells); and endogenous CD8 and natural killer 1.1 cells (that can act as "sinks" for homeostatic cytokines in the postablative setting). With increasing ablation, we also observed elevated lipopolysaccharide levels in the sera and heightened levels of systemic inflammatory cytokines. Thus, increased intensity lymphodepletion triggers enhanced tumor treatment efficacy and the benefits of high-dose total body irradiation must be titrated against its risks.

Treatment of lymphoma with adoptively transferred T cells

BACKGROUND

Chemotherapy-resistant lymphomas can be cured with allogeneic hematopoietic cell transplantation, demonstrating the susceptibility of these tumors to T cell mediated immune responses. However, high rates of transplant-related morbidity and mortality limit this approach. Efforts have, therefore, been made to develop alternative T cell based therapies, and there is growing evidence that adoptive therapy with T cells targeted to lymphoma-associated antigens may be a safe and effective new method for treating this group of diseases.

OBJECTIVE/METHODS

We review publications on adoptive therapy with ex vivo expanded T cells targeting viral antigens, as well as genetically modified autologous T cells, as strategies for the treatment of lymphoma, with the goal of providing an overview of these approaches.

RESULTS/CONCLUSIONS

Epstein-Barr virus specific T cell therapy is an effective and safe method of treating Epstein-Barr virus associated lymphomas; however, most lymphoma subtypes do not express EBV antigens. For these diseases, adoptive immunotherapy with genetically modified T cells expressing chimeric T cell receptors targeting lymphoma-associated antigens such as CD19 and CD20 appears to be a promising alternative. Recent innovations including enhanced co-stimulation, exogenous cytokine administration and use of memory T cells promise to overcome many of the limitations and pitfalls initially encountered with this approach.

Immunological memory transferred with CD4 T cells specific for tuberculosis antigens Ag85B-TB10.4: persisting antigen enhances protection

Background

High levels of death and morbidity worldwide caused by tuberculosis has stimulated efforts to develop a new vaccine to replace BCG. A number of Mycobacterium tuberculosis (Mtb)-specific antigens have been synthesised as recombinant subunit vaccines for clinical evaluation. Recently a fusion protein of TB antigen Ag85B combined with a second immunodominant TB antigen TB10.4 was emulsified with a novel non-phospholipid-based liposomal adjuvant to produce a new subunit vaccine, investigated here. Currently, there is no consensus as to whether or not long-term T cell memory depends on a source of persisting antigen. To explore this and questions regarding lifespan, phenotype and cytokine patterns of CD4 memory T cells, we developed an animal model in which vaccine-induced CD4 memory T cells could transfer immunity to irradiated recipients.

Methodology/Principal Findings

The transfer of protective immunity using Ag85B-TB10.4-specific, CD45RB^low CD62L^low CD4 T cells was assessed in sub-lethally irradiated recipients following challenge with live BCG, used here as a surrogate for virulent Mtb. Donor T cells also carried an allotype marker allowing us to monitor numbers of antigen-specific, cytokine-producing CD4 T cells in recipients. The results showed that both Ag85B-TB10.4 and BCG vaccination induced immunity that could be transferred with a single injection of 3×10⁶ CD4 T cells. Ten times fewer numbers of CD4 T cells (0.3×10⁶) from donors immunised with Ag85B-TB10.4 vaccine alone, transferred equivalent protection. CD4 T cells from donors primed by BCG and boosted with the vaccine similarly transferred protective immunity. When BCG challenge was delayed for 1 or 2 months after transfer (a test of memory T cell survival) recipients remained protected. Importantly, recipients that contained persisting antigen, either live BCG or inert vaccine, showed significantly higher levels of protection (p<0.01). Overall the numbers of IFN-γ-producing CD4 T cells were poorly correlated with levels of protection.

Conclusions/Significance

The Ag85B-TB10.4 vaccine, with or without BCG-priming, generated TB-specific CD4 T cells that transferred protective immunity in mice challenged with BCG. The level of protection was enhanced in recipients containing a residual source of specific antigen that could be either viable or inert.

IL-15 regulates both quantitative and qualitative features of the memory CD8 T cell pool

Memory T cells are critical for immunity to various intracellular pathogens. Recent studies have indicated that CD8 secondary memory cells, induced by prime-boost approaches, show enhanced protective function compared with primary memory cells and exhibit phenotypic and functional characteristics that distinguish them from primary memory cells. However, little is known about the cytokine requirements for generation and maintenance of boosted memory CD8 T cells. We studied the role of IL-15 in determining the size and composition of the secondary (2 degrees) memory CD8 T cell pool induced by Listeria monocytogenes infection in mice. Following boosting, IL-15-deficient animals failed to generate a subset of CD8 effector memory cells, including a population of IL-7Ralpha(low) cells, which were prominent among secondary memory cells in normal mice. IL-15 deficiency also resulted in changes within the IL-7Ralpha(high)CD62L(low) subset of 2 degrees memory CD8 T cells, which expressed high levels of CD27 but minimal granzyme B. In addition to these qualitative changes, IL-15 deficiency resulted in reduced cell cycle and impaired Bcl-2 expression by 2 degrees memory CD8 T cells, suggesting a role for IL-15 in supporting both basal proliferation and survival of the pool. Analogous qualitative differences in memory CD8 T cell populations were observed following a primary response to Sendai virus in IL-15(-/-) animals. Collectively, these findings demonstrate that IL-15 plays an important role in dictating the composition rather than simply the maintenance of the CD8 memory pool.

Dynamic bookmarking of primary response genes by p300 and RNA polymerase II complexes

Profiling the dynamic interaction of p300 with proximal promoters of human T cells identified a class of genes that rapidly coassemble p300 and RNA polymerase II (pol II) following mitogen stimulation. Several of these p300 targets are immediate early genes, including FOS, implicating a prominent role for p300 in the control of primary genetic responses. The recruitment of p300 and pol II rapidly transitions to the assembly of several elongation factors, including the positive transcriptional elongation factor (P-TEFb), the bromodomain-containing protein (BRD4), and the elongin-like eleven nineteen lysine-rich leukemia protein (ELL). However, transcription at many of these rapidly induced genes is transient, wherein swift departure of P-TEFb, BRD4, and ELL coincides with termination of transcriptional elongation. Unexpectedly, both p300 and pol II remain accumulated or "bookmarked" at the proximal promoter long after transcription has terminated, demarking a clear mechanistic separation between the recruitment and elongation phases of transcription in vivo. The bookmarked pol II is depleted of both serine-2 and serine-5 phosphorylation of its C-terminal domain and remains proximally positioned at the promoter for hours. Surprisingly, these p300/pol II bookmarked genes can be readily reactivated, and elongation factors can be reassembled by subsequent addition of nonmitogenic agents that, alone, have minimal effects on transcription in the absence of prior preconditioning by mitogen stimulation. These findings suggest that p300 is likely to play an important role in biological processes in which transcriptional bookmarking or preconditioning influences cellular growth and development through the dynamic priming of genes for response to rechallenge by secondary stimuli.

IL-21 preferentially enhances IL-15-mediated homeostatic proliferation of human CD28+ CD8 memory T cells throughout the adult age span

An age-related decline in human immune response is marked by the accumulation of CD28(-) CD8 T cells, which is attributed to repeated antigenic stimulation and to homeostatic proliferation mediated by cytokines such as IL-15. However, the identity of the cytokines that are responsible for the maintenance of CD28 expression is less known. Here, we report the role of IL-21 in the regulation of IL-15-mediated growth and CD28 expression of CD8 memory T cells of young and old donors. We showed that IL-21 drives more IL-15-stimulated cells to enter cell division and to undergo apoptosis. Furthermore, IL-21 preferentially enhanced IL-15-induced proliferation of CD28(+) CD8 memory T cells over their CD28(-) counterparts, as CD28(+) cells expressed higher levels of IL-15R and IL-21R and greater pSTAT5 upon IL-15 and IL-21 stimulation. In addition, IL-21 reduced IL-15-induced CD28 down-regulation in CD8 memory T cells. Finally, the ability of proliferation and survival in response to homeostatic cytokines IL-15 and IL-21 of CD28(+) CD8 memory T cells was well-maintained with age. Together, these findings suggest that IL-21 enhances IL-15-mediated proliferation of CD8 memory T cells, particularly CD28(+) memory T cells, and also serves as an antagonist to the IL-15-induced increase of CD28(-) CD8 T cells.

De novo recruitment of antigen-experienced and naive T cells contributes to the long-term maintenance of antiviral T cell populations in the persistently infected central nervous system

Mice infected with attenuated strains of mouse hepatitis virus, strain JHM, develop a chronic infection in the brain and spinal cord characterized by low levels of viral Ag persistence and retention of virus-specific CD4 and CD8 T cells at the site of infection. It is not known whether these cells are maintained by proliferation of T cells that entered the CNS during acute infection or are newly recruited from Ag-experienced or naive T cell pools. In this study, using adoptive transfer experiments and bone marrow chimeras, we show that at least some of these cells are recruited from the periphery, predominantly from the viral Ag-experienced T cell pool. Both virus-specific CD4 and CD8 T cells are functional, as assessed by cytokine expression and degranulation after peptide exposure. In addition, populations of virus-specific CD4 T cells undergo dynamic changes in the infected CNS, as previously shown for CD8 T cells, because ratios of cells responding to two CD4 T cell epitopes change by a factor of five during the course of persistence. Collectively, these results show that maintenance of T cell responses in the virus-infected CNS is a dynamic process. Further, virus-specific T cell numbers at this site of infection are maintained by recruitment from peripheral Ag-experienced and naive T cell pools.

CD8+ cell depletion of SHIV89.6P-infected macaques induces CD4+ T cell proliferation that contributes to increased viral loads

Previous studies have shown that depletion of CD8(+) cells during acute and chronic simian immunodeficiency virus (SIV) infection leads to increased viral replication, morbidity, and mortality, which have been attributed to loss of CD8(+) T cell-mediated control of SIV. However, these studies did not exclude that CD8(+) cell depletion increased homeostatic proliferation of CD4(+) T cells, resulting in increased viral targets and, therefore, viral rebound. Chronically SHIV89.6P-infected cynomolgus macaques were CD8(+) cell-depleted, and the frequency, cell number, and phenotype of CD4(+) T cells and viral infection were examined using flow cytometry and quantitative real-time PCR. The frequency and number of Ki-67-expressing CD4(+) T cells were increased with CD8(+) cell depletion. This proliferation of CD4(+) T cells occurred even in animals with no rebound of viral loads. Most of the proliferating cells were effector memory CD4(+) T cells. Plasma simian HIV (SHIV) RNA copies positively correlated with proliferating CD4(+) T cells and SHIV DNA copies in Ki-67(+) CD4(+) T cells. Although this study does not exclude an important role for virus-specific CD8(+) T cells in SIV and SHIV infection, our data suggest that homeostatic proliferation is an important contributor to increases in plasma viremia that follow CD8(+) cell depletion.

TSLP and IL-7 use two different mechanisms to regulate human CD4+ T cell homeostasis

Whether thymic stromal lymphopoietin (TSLP) directly induces potent human CD4⁺ T cell proliferation and Th2 differentiation is unknown. We report that resting and activated CD4⁺ T cells expressed high levels of IL-7 receptor a chain but very low levels of TSLP receptor (TSLPR) when compared with levels expressed in myeloid dendritic cells (mDCs). This was confirmed by immunohistology and flow cytometry analyses showing that only a subset of mDCs, with more activated phenotypes, expressed TSLPR in human tonsils in vivo. IL-7 induced strong STAT1, -3, and -5 activation and promoted the proliferation of naive CD4⁺ T cells in the presence of anti-CD3 and anti-CD28 monoclonal antibodies, whereas TSLP induced weak STAT5 activation, associated with marginally improved cell survival and proliferation, but failed to induce cell expansion and Th2 differentiation. The effect of TSLP on enhancing strong human T cell proliferation was observed only when sorted naive CD4⁺ T cells were cultured with mDCs at levels as low as 0.5%. TSLP could only induce naive CD4⁺ T cells to differentiate into Th2 cells in the presence of allogeneic mDCs. These results demonstrate that IL-7 and TSLP use different mechanisms to regulate human CD4⁺ T cell homeostasis.

PD-1+ memory phenotype CD4+ T cells expressing C/EBPalpha underlie T cell immunodepression in senescence and leukemia

Although altered T cell function plays a part in immunosenescence, the mechanisms remain uncertain. Here we identify a bona fide age-dependent PD-1(+) memory phenotype (MP) CD4(+) T cell subpopulation that hardly proliferates in response to T cell receptor (TCR) stimulation and produces abundant osteopontin at the cost of typical T cell lymphokines. These T cells demonstrate impaired repopulation in Rag2(-/-) mice, but a homeostatic proliferation in gamma-ray-irradiated mice. These T cells also reveal a unique molecular signature, including a strong expression of C/EBPalpha normally expressed in myeloid-lineage cells, with diminished c-Myc and cyclin D1. Transduction of Cebpa in regular CD4(+) T cells inhibited the TCR-mediated proliferation with c-Myc and cyclin D1 repression and caused a striking activation of Spp1 encoding osteopontin along with concomitant repression of T cell lymphokine genes. Although these T cells gradually increase in number with age and become predominant at the senescent stage in normal mice, the generation is robustly accelerated during leukemia. In both conditions, their predominance is associated with the diminution of specific CD4(+) T cell response. The results suggest that global T cell immunodepression in senescence and leukemia is attributable to the increase in PD-1(+) MP CD4(+) T cells expressing C/EBPalpha.

Epitope specificity and relative clonal abundance do not affect CD8 differentiation patterns during lymphocytic choriomeningitis virus infection

To evaluate the impact of immunodominance on CD8 T-cell properties, we compared the functional properties of dominant and subdominant populations in the response to lymphocytic choriomeningitis virus (LCMV). To improve functional discrimination, in addition to the usual tests of phenotype and function, we used a sensitive technique that allows the screening of all CD8 effector genes simultaneously in single cells. Surprisingly, these methods failed to reveal a major impact of clonal dominance in CD8 properties throughout the response. Aiming to increase clonal dominance, we examined high-frequency transferred P14 T-cell receptor transgenic (TCR Tg) cells. Under these conditions LCMV is cleared faster, and accordingly we found an accelerated response. However, when Tg and endogenous cells were studied in the same mice, where they should be subjected to the same antigen load, they showed overlapping properties, and the presence of P14 cells did not modify endogenous responses to other LCMV epitopes or a perturbed immunodominance hierarchy in the memory phase. Using allotype-labeled Tg cells, we found that during acute infection up to 80% downregulated their TCR and were undetectable by tetramer binding, and that tetramer-negative and tetramer-positive cells had very different features. Since Tg cells are not available to evaluate immune responses in humans and, in many cases, are not available from the mouse, the tetramer-based evaluation of early immune responses in most situations of high viremia may be incomplete and biased.

Fixed drug eruption: a prototypic disorder mediated by effector memory T cells

Effector memory T cells are uniquely specialized to mediate protective immunity. However, their excessive activation may result in the development of organ-specific inflammatory diseases, which have not been extensively studied. Fixed drug eruption (FDE), a localized variant of drug-induced dermatoses characterized by relapse in the same location, is a prototypic disorder mediated by excessive activation of effector memory T cells, which are resident in the lesional epidermis. A variety of clinical and pathologic features uniquely observed in FDE lesions can be explained by the presence of CD8(+) intraepidermal T cells with the effector memory phenotype in the FDE lesion. This review focuses on how these T cells are generated, retained in the epidermis, and activated to cause epidermal damage.

The magnitude of CD4+ T cell recall responses is controlled by the duration of the secondary stimulus

The parameters controlling the generation of robust CD4(+) T cell recall responses remain poorly defined. In this study, we compare recall responses by CD4(+) and CD8(+) memory T cells following rechallenge. Homologous rechallenge of mice immune to either lymphocytic choriomeningitis virus or Listeria monocytogenes results in robust CD8(+) T cell recall responses but poor boosting of CD4(+) T cell recall responses in the same host. In contrast, heterologous rechallenge with a pathogen sharing only a CD4(+) T cell epitope results in robust boosting of CD4(+) T cell recall responses. The disparity in CD4(+) and CD8(+) T cell recall responses cannot be attributed to competition for growth factors or APCs, as robust CD4(+) and CD8(+) T cell recall responses can be simultaneously induced following rechallenge with peptide-pulsed dendritic cells. Instead, CD4(+) T cell recall responses are dependent on the duration of the secondary challenge. Increasing the rechallenge dose results in more potent boosting of CD4(+) T cell recall responses and artificially limiting the duration of secondary infection following heterologous rechallenge adversely impacts the magnitude of CD4(+) T cell, but not CD8(+) T cell, recall responses. These findings suggest that rapid pathogen clearance by secondary CTL following homologous rechallenge prevents optimal boosting of CD4(+) T cell responses and therefore have important practical implications in the design of vaccination and boosting strategies aimed at promoting CD4(+) T cell-mediated protection.

Differential association of programmed death-1 and CD57 with ex vivo survival of CD8+ T cells in HIV infection

Recent studies have revealed the critical role of programmed death-1 (PD-1) in exhaustion of HIV- and SIV-specific CD8(+) T cells. In this study, we show that high expression of PD-1 correlates with increased ex vivo spontaneous and CD95/Fas-induced apoptosis, particularly in the "effector-memory" CD8(+) T cell population from HIV(+) donors. High expression of PD-1 was linked to a proapoptotic phenotype characterized by low expression of Bcl-2 and IL7-R alpha, high expression of CD95/Fas and high mitochondrial mass. Expression of PD-1 and CD57 was differentially associated with the maturation status of CD8(+) T cells in HIV infection. CD57 was linked to higher apoptosis resistance, with cells expressing a PD-1(L)CD57(H) phenotype exhibiting lower levels of cell death. The majority of HIV-specific CD8(+) T cells were found to express a PD-1(H)CD57(L) or PD-1(H)CD57(H) phenotype. No correlation was found between PD-1 expression and ex vivo polyfunctionality of either HIV- or CMV-specific CD8(+) T cells. Contrary to CD57, high expression of PD-1 was characterized by translocation of PD-1 into the area of CD95/Fas-capping, an early necessary step of CD95/Fas-induced apoptosis. Thus, our data further support the role of PD-1 as a preapoptotic factor for CD8(+) T cells in HIV infection.

Tuberculosis subunit vaccination provides long-term protective immunity characterized by multifunctional CD4 memory T cells

Improved vaccines capable of promoting long-term cellular immunity are urgently required for a number of diseases that remain global health problems. In the present study, we demonstrate that a tuberculosis subunit vaccine, Ag85B-ESAT-6/CAF01 (where ESAT-6 is early secreted antigenic target of 6 kDa and CAF01 is cationic adjuvant formulation 01), induces very robust memory CD4 T cell responses that are maintained at high levels for >1 year postvaccination. This long-term, vaccine-induced memory response protects against a challenge with Mycobacterium tuberculosis at levels that are comparable to or better than those of bacillus Calmette-Guérin. Characterization of the CD4 memory T cells by multicolor flow cytometry demonstrated that the long-lived memory population consisted almost exclusively of TNF-alpha(+)IL-2(+) and IFN-gamma(+)TNF-alpha(+)IL-2(+) multifunctional T cells. In addition, memory cells isolated >1 year postvaccination maintained a strong, vaccine-specific proliferative potential. Long-term memory induced by the BCG vaccine contained fewer multifunctional T cells and was biased toward effector cells mainly of the TNF-alpha(+)IFN-gamma(+)-coexpressing subset. Ag85B-ESAT-6/CAF01 vaccination very efficiently sustained multifunctional CD4 T cells that accumulated at the site of infection after M. tuberculosis challenge, whereas the response in unvaccinated animals was characterized by CD4 effector T cells. Our data demonstrate that adjuvanted subunit vaccines can promote long-term protective immune responses characterized by high levels of persisting multifunctional T cells and that the quality and profile of this response is sustained postinfection.

IFN-alpha enhances peptide vaccine-induced CD8+ T cell numbers, effector function, and antitumor activity

Type I IFNs, including IFN-alpha, enhance Ag presentation and promote the expansion, survival, and effector function of CD8(+) CTL during viral infection. Because these are ideal characteristics for a vaccine adjuvant, we examined the efficacy and mechanism of exogenous IFN-alpha as an adjuvant for antimelanoma peptide vaccination. We studied the expansion of pmel-1 transgenic CD8(+) T cells specific for the gp100 melanocyte differentiation Ag after vaccination of mice with gp100(25-33) peptide in IFA. IFN-alpha synergized with peptide vaccination in a dose-dependent manner by boosting relative and absolute numbers of gp100-specific T cells that suppressed B16 melanoma growth. IFN-alpha dramatically increased the accumulation of gp100-specific, IFN-gamma-secreting, CD8(+) T cells in the tumor through reduced apoptosis and enhanced proliferation of Ag-specific CD8(+) T cells. IFN-alpha treatment also greatly increased the long-term maintenance of pmel-1 CD8(+) T cells with an effector memory phenotype, a process that required expression of IFN-alpha receptor on the T cells and IL-15 in the host. These results demonstrate the efficacy of IFN-alpha as an adjuvant for peptide vaccination, give insight into its mechanism of action, and provide a rationale for clinical trials in which vaccination is combined with standard-of-care IFN-alpha therapy for melanoma.

Impaired STAT phosphorylation in T cells from melanoma patients in response to IL-2: association with clinical stage

PURPOSE

To assess the extent of signal transducer and activator of transcription (STAT) activation in response to interleukin 2 (IL-2) in melanoma patients' T cells, along with clinical stage of tumor progression.

EXPERIMENTAL DESIGN

T lymphocytes from peripheral blood of healthy donors and of American Joint Committee on Cancer stage I to IV melanoma patients, as well as from metastatic lymph nodes of patients, were evaluated for responsiveness to IL-2. CFSE assays and single-cell phospho-STAT-specific flow cytometry screening were used. Results. T cells from advanced melanoma patients, in comparison with healthy donors, showed reduced proliferation to IL-2 and IL-15, but not to anti-CD3 monoclonal antibody. Impaired response occurred in CCR7(+) and CCR7(-) T-cell subsets, but not in CD3(-) CD8(+) natural killer (NK) cells, and was not explained by induction of apoptosis, increased cytokine consumption, or altered IL-2R subunit expression in patients' T lymphocytes. By phospho-specific flow cytometry, defective STAT1 and STAT5 activation in response to IL-2 was found mainly in T lymphocytes from peripheral blood and/or tumor site of American Joint Committee on Cancer stage III and IV patients, compared with stage I and II patients and to donors, and in melanoma antigen-specific T cells isolated from metastatic lymph nodes. At tumor site, impaired STAT activation in T cells did not correlate with frequency of CD4(+) CD25(+) Foxp3(+) T cells. Serum from advanced melanoma patients inhibited IL-2-dependent STAT activation in donors' T cells and a neutralizing monoclonal antibody to transforming growth factor beta1 counteracted such inhibition.

CONCLUSIONS

These results provide evidence for development of impaired STAT signaling in response to IL-2, along with clinical evolution of the disease, in melanoma patients' T cells.

Vaccination with vif-deleted feline immunodeficiency virus provirus, GM-CSF, and TNF-alpha plasmids preserves global CD4 T lymphocyte function after challenge with FIV

Feline immunodeficiency virus (FIV) DNA vaccine approaches that included a vif-deleted FIV provirus (FIV-pPPRDeltavif) and feline cytokine expression plasmids were tested for immunogenicity and efficacy by immunization of specific pathogen free cats. Vaccine protocols included FIV-pPPRDeltavif plasmid alone; a combination of FIV-pPPRDeltavif DNA and feline granulocyte macrophage-colony stimulating factor (GM-CSF) and tumor necrosis factor (TNF)-alpha expression plasmids; or a combination of FIV-pPPRDeltavif and feline interleukin (IL)-15 plasmids. Cats immunized with FIV-pPPRDeltavif, GM-CSF and TNF-alpha plasmids demonstrated an increased frequency of FIV-specific T cell proliferation responses compared to other vaccine groups. Immunization with FIV-pPPRDeltavif and IL-15 plasmids was distinguished from other vaccine protocols by the induction of antiviral antibodies. Suppression of virus loads was not observed for any of the FIV-pPPRDeltavif DNA vaccine protocols after challenge with the FIV-PPR isolate. However, prior immunization with FIV-pPPRDeltavif, GM-CSF, and TNF-alpha plasmids resulted in preservation of CD4 T cell functions, including mitogen-induced cytokine expression and antigen-specific proliferation upon infection with FIV. These findings justify further examination of cytokine combinations as adjuvants for lentiviral DNA vaccines.

Enhancing CD8 T-cell memory by modulating fatty acid metabolism

CD8 T cells, which have a crucial role in immunity to infection and cancer, are maintained in constant numbers, but on antigen stimulation undergo a developmental program characterized by distinct phases encompassing the expansion and then contraction of antigen-specific effector (T(E)) populations, followed by the persistence of long-lived memory (T(M)) cells. Although this predictable pattern of CD8 T-cell responses is well established, the underlying cellular mechanisms regulating the transition to T(M) cells remain undefined. Here we show that tumour necrosis factor (TNF) receptor-associated factor 6 (TRAF6), an adaptor protein in the TNF-receptor and interleukin-1R/Toll-like receptor superfamily, regulates CD8 T(M)-cell development after infection by modulating fatty acid metabolism. We show that mice with a T-cell-specific deletion of TRAF6 mount robust CD8 T(E)-cell responses, but have a profound defect in their ability to generate T(M) cells that is characterized by the disappearance of antigen-specific cells in the weeks after primary immunization. Microarray analyses revealed that TRAF6-deficient CD8 T cells exhibit altered expression of genes that regulate fatty acid metabolism. Consistent with this, activated CD8 T cells lacking TRAF6 display defective AMP-activated kinase activation and mitochondrial fatty acid oxidation (FAO) in response to growth factor withdrawal. Administration of the anti-diabetic drug metformin restored FAO and CD8 T(M)-cell generation in the absence of TRAF6. This treatment also increased CD8 T(M) cells in wild-type mice, and consequently was able to considerably improve the efficacy of an experimental anti-cancer vaccine.