Potent induction of long-term CD8+ T cell memory by short-term IL-4 exposure during T cell receptor stimulation

A translational approach to improve therapeutics in atopic dermatitis and beyond

Atopic dermatitis (AD) and alopecia areata are highly prevalent inflammatory skin/hair conditions. While previously not fully understood and limited in treatment options, AD is currently undergoing a therapeutic revolution. Our increased understanding of the underlying immunologic and barrier dysregulations and disease heterogeneity across its spectrum is facilitating hypothesis-driven therapeutic development. Early transcriptomic analyses in AD skin and blood have identified disease-specific biomarkers and uncovered immune and barrier abnormalities that may contribute to disease pathogenesis. From these findings, various therapeutic targets were then proposed and investigated in clinical trials, leading to the Food and Drug Administration approval of several biologics and small molecule drugs that are now widely used in the clinical setting. Molecular phenotyping of patient samples before and after treatment has further elucidated the specific immunomodulatory effect of each therapeutic, as well as the relative contributions of various immune pathways to disease pathogenesis. This bench-to-bedside cyclical approach has rapidly broadened our understanding of AD and enabled the rapid expansion of the AD therapeutic pipeline. In this brief review, we detail how molecular and blood profiling studies in AD laid the foundation for a therapeutic revolution, discuss currently approved and potential therapeutics for AD resulting from this bench-to-bedside approach, and highlight how this translational approach is being applied to advancing the therapeutic pipeline of alopecia areata.

Resident memory T cells in nonlesional skin and healed lesions of patients with chronic inflammatory diseases: Appearances can be deceptive

Tissue-resident memory T (TRM) cells serve as a first line of defense in peripheral tissues to protect the organism against foreign pathogens. However, autoreactive TRM cells are increasingly implicated in autoimmunity, as evidenced in chronic autoimmune and inflammatory skin conditions. This highlights the need to characterize their phenotype and understand their role for the purpose of targeting them specifically without affecting local immunity. To date, the investigation of TRM cells in human skin diseases has focused mainly on lesional tissues of patients. Accumulating evidence suggests that self-reactive TRM cells are still present in clinically healed lesions of patients and play a role in disease flares, but TRM cells also populate skin that is apparently normal. This review discusses the ontogeny of TRM cells in the skin as well as recent insights regarding the presence of self-reactive TRM cells in both clinically healed skin and nonlesional skin of patients with autoimmune and inflammatory skin conditions, with a particular focus on psoriasis, atopic dermatitis, and vitiligo.

CD8+ T cell memory is sustained in mice by hepatic stellate cells

BACKGROUND AND AIMS

Long-lasting immunological memory is the ultimate goal of vaccination. Homeostatic maintenance of memory CD8⁺ cytotoxic T cells (MemCD8TCs) is thought to be mediated by IL-15/IL-15R heterodimer (15HD)-expressing myeloid cells. Nonmyeloid hepatic stellate cells (HSCs) also express 15HD, but their role in maintaining MemCD8TC homeostasis is unknown.

APPROACH AND RESULTS

We engineered a genetically engineered mouse in which IL-15R complementary DNA (cDNA) had been inserted in-frame with lecithin-retinol acyltransferase gene and bred onto an IL-15R-KO (15R-KO) genetic background (L15R) that expressed IL-15R in HSCs at normal levels, but not in other liver cells. Outside of the liver of L15R mice, IL-15R expression was found in a number of organs, but not in dendritic cells and macrophages. The low IL-15R expression in the bone marrow (BM) of L15R mice was eliminated by the reconstitution of lethally-irradiated L15R mice with 15R-KO BM to generate L15RC mice. Because MemCD8TC maintenance is mediated by 15HD, not empty IL-15R, 15HD content in L15R mice was determined and found for liver, lung, kidney, and heart. L15R and L15RC mice developed and maintained long-lasting, systemic antigen-specific MemCD8TCs that were efficacious against tumor growth and Listeria monocytogenes infection in an antigen-specific manner. Among the four organs with 15HD content, liver-associated MemCD8TCs were different from those found in the lung, kidney, and heart in two ways: (1) they were quantitatively the most numerous, and (2) they appeared uniquely in the form of clusters in a specialized structure, sinusoidal niches of the liver.

CONCLUSIONS

The liver, the largest organ of the body, is endowed with the capability of effectuating long-lasting functional cytotoxic T cell memory.

Chronic Porphyromonas gingivalis lipopolysaccharide induces adverse myocardial infarction wound healing through activation of CD8+ T cells

Oral and gum health have long been associated with incidence and outcomes of cardiovascular disease. Periodontal disease increases myocardial infarction (MI) mortality by sevenfold through mechanisms that are not fully understood. The goal of this study was to evaluate whether lipopolysaccharide (LPS) from a periodontal pathogen accelerates inflammation after MI through memory T-cell activation. We compared four groups [no MI, chronic LPS, day 1 after MI, and day 1 after MI with chronic LPS (LPS + MI); n = 68 mice] using the mouse heart attack research tool 1.0 database and tissue bank coupled with new analyses and experiments. LPS + MI increased total CD8+ T cells in the left ventricle versus the other groups (P < 0.05 vs. all). Memory CD8+ T cells (CD44 + CD27+) were 10-fold greater in LPS + MI than in MI alone (P = 0.02). Interleukin (IL)-4 stimulated splenic CD8+ T cells away from an effector phenotype and toward a memory phenotype, inducing secretion of factors associated with the Wnt/β-catenin signaling that promoted monocyte migration and decreased viability. To dissect the effect of CD8+ T cells after MI, we administered a major histocompatibility complex-I-blocking antibody starting 7 days before MI, which prevented effector CD8+ T-cell activation without affecting the memory response. The reduction in effector cells diminished infarct wall thinning but had no effect on macrophage numbers or MertK expression. LPS + MI + IgG attenuated macrophages within the infarct without effecting CD8+ T cells, suggesting these two processes were independent. Overall, our data indicate that effector and memory CD8+ T cells at post-MI day 1 are amplified by chronic LPS to potentially promote infarct wall thinning.NEW & NOTEWORTHY Although there is a well-documented link between periodontal disease and heart health, the mechanisms are unclear. Our study indicates that in response to circulating periodontal endotoxins, memory CD8+ T cells are activated, resulting in an acceleration of macrophage-mediated inflammation after MI. Blocking activation of effector CD8+ T cells had no effect on the macrophage numbers or wall thinning at post-MI day 1, indicating that this response was likely due in part to memory CD8+ T cells.

A Correlation Between Differentiation Phenotypes of Infused T Cells and Anti-Cancer Immunotherapy

T-cell therapy, usually with ex-vivo expansion, is very promising to treat cancer. Differentiation status of infused T cells is a crucial parameter for their persistence and antitumor immunity. Key phenotypic molecules are effective and efficient to analyze differentiation status. Differentiation status is crucial for T cell exhaustion, in-vivo lifespan, antitumor immunity, and even antitumor pharmacological interventions. Strategies including cytokines, Akt, Wnt and Notch signaling, epigenetics, and metabolites have been developed to produce less differentiated T cells. Clinical trials have shown better clinical outcomes from infusion of T cells with less differentiated phenotypes. CD27+, CCR7+ and CD62L+ have been the most clinically relevant phenotypic molecules, while Tscm and Tcm the most clinically relevant subtypes. Currently, CD27+, CD62L+ and CCR7+ are recommended in the differentiation phenotype to evaluate strategies of enhancing stemness. Future studies may discover highly clinically relevant differentiation phenotypes for specific T-cell production methods or specific subtypes of cancer patients, with the advantages of precision medicine.

Targeting IL-4 for the Treatment of Atopic Dermatitis

Atopic dermatitis (AD) is an immune-mediated inflammatory skin disease characterized by a predominant type 2 immune response. Type 2 immunity is driven by multiple cytokines, including interleukin (IL)‑4 and IL-13 that are considered central to AD pathogenesis and key therapeutic targets. The dual inhibition of these two cytokines or the selective inhibition of IL-13 proved elevated efficacy in treating AD, whereas the selective inhibition of IL-4 has been poorly investigated as IL-4 inhibiting agents did not show any advance in clinical development programs. This review describes the pathogenic role of IL-4 in AD and briefly resumes the main features of compounds selectively blocking IL-4.

MERTK Acts as a Costimulatory Receptor on Human CD8+ T Cells

The TAM family of receptor tyrosine kinases (TYRO3, AXL, and MERTK) is known to be expressed on antigen-presenting cells and function as oncogenic drivers and as inhibitors of inflammatory responses. Both human and mouse CD8⁺ T cells are thought to be negative for TAM receptor expression. In this study, we show that T-cell receptor (TCR)-activated human primary CD8⁺ T cells expressed MERTK and the ligand PROS1 from day 2 postactivation. PROS1-mediated MERTK signaling served as a late costimulatory signal, increasing proliferation and secretion of effector and memory-associated cytokines. Knockdown and inhibition studies confirmed that this costimulatory effect was mediated through MERTK. Transcriptomic and metabolic analyses of PROS1-blocked CD8⁺ T cells demonstrated a role of the PROS1-MERTK axis in differentiation of memory CD8⁺ T cells. Finally, using tumor-infiltrating lymphocytes (TIL) from melanoma patients, we show that MERTK signaling on T cells improved TIL expansion and TIL-mediated autologous cancer cell killing. We conclude that MERTK serves as a late costimulatory signal for CD8⁺ T cells. Identification of this costimulatory function of MERTK on human CD8⁺ T cells suggests caution in the development of MERTK inhibitors for hematologic or solid cancer treatment.

Donor lymphocyte infusion leads to diversity of specific T cell responses and reduces regulatory T cell frequency in clinical responders

T cell responses against malignant cells play a major role in maintaining remission and prolonging overall survival in patients after allogeneic stem cell transplantation and donor lymphocyte infusion (DLI) due to graft-versus-leukemia effect. For better characterization of the T cell responses, we assessed frequency and diversity of leukemia-associated antigen (LAA)-specific cytotoxic T cells using ELISpot and pMHC multimer assays and analyzed the frequency of regulatory T cells (Treg) as well as cytokine profiles before/after DLI. The data were correlated to the clinical course of patients. Significantly more LAA-derived T cell epitopes (p = 0.02) were recognized in clinical responders (R) when compared to nonresponders (NR). In addition, pMHC multimer-based flow cytometry showed a significantly higher frequency of LAA-specific T cells in R versus NR. The frequency of Treg in R decreased significantly (p = 0.008) while keeping stable in NR. No differences in T cell subset analysis before/after DLI were revealed. Clinical responders were correlated to specific immune responses and all clinical responders showed an increase of specific immune responses after DLI. Cytokine assays using enzyme-linked immunosorbent assay showed a significant increase of IL-4 after DLI. Taken together, an increase of specific CTL responses against several LAA after DLI was detected. Moreover, this study suggests that enhanced LAA diversity in T cell responses as well as decreasing numbers of Treg contribute to clinical outcome of patients treated with DLI.

Therapeutic vaccines for allergic disease

Allergic diseases are highly prevalent worldwide and affect all age groups, contributing to a high personal and socioeconomic burden. Treatment with an “allergy vaccine” or allergen immunotherapy aims to provide long-lasting benefits by inducing unresponsiveness to the relevant antigen. The consequences of the therapy are considered disease modifying and range from dampening of the immediate immune responses to the reduction of secondary tissue remodeling. Furthermore, allergen immunotherapy interventions have a potential to slow or cease the development of additional allergic manifestations with a long-term overall effect on morbidity and quality of life. Here, we review proposed mechanisms underlying the therapeutic effects of immunotherapy for allergic diseases. Further, we discuss both standard and novel approaches and possible future directions in the development of allergen immunotherapy.

Identification of BALB/c Immune Markers Correlated with a Partial Protection to Leishmania infantum after Vaccination with a Rationally Designed Multi-epitope Cysteine Protease A Peptide-Based Nanovaccine

BACKGROUND

Through their increased potential to be engaged and processed by dendritic cells (DCs), nanovaccines consisting of Poly(D,L-lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) loaded with both antigenic moieties and adjuvants are attractive candidates for triggering specific defense mechanisms against intracellular pathogens. The aim of the present study was to evaluate the immunogenicity and prophylactic potential of a rationally designed multi-epitope peptide of Leishmania Cysteine Protease A (CPA160-189) co-encapsulated with Monophosphoryl lipid A (MPLA) in PLGA NPs against L. infantum in BALB/c mice and identify immune markers correlated with protective responses.

METHODOLOGY/PRINCIPAL FINDINGS

The DCs phenotypic and functional features exposed to soluble (CPA160-189, CPA160-189+MPLA) or encapsulated in PLGA NPs forms of peptide and adjuvant (PLGA-MPLA, PLGA-CPA160-189, PLGA-CPA160-189+MPLA) was firstly determined using BALB/c bone marrow-derived DCs. The most potent signatures of DCs maturation were obtained with the PLGA-CPA160-189+MPLA NPs. Subcutaneous administration of PLGA-CPA160-189+MPLA NPs in BALB/c mice induced specific anti-CPA160-189 cellular and humoral immune responses characterized by T cells producing high amounts of IL-2, IFN-γ and TNFα and IgG1/IgG2a antibodies. When these mice were challenged with 2x107 stationary phase L. infantum promastigotes, they displayed significant reduced hepatic (48%) and splenic (90%) parasite load at 1 month post-challenge. This protective phenotype was accompanied by a strong spleen lymphoproliferative response and high levels of IL-2, IFN-γ and TNFα versus low IL-4 and IL-10 secretion. Although, at 4 months post-challenge, the reduced parasite load was preserved in the liver (61%), an increase was detected in the spleen (30%), indicating a partial vaccine-induced protection.

CONCLUSIONS/SIGNIFICANCE

This study provide a basis for the development of peptide-based nanovaccines against leishmaniasis, since it reveals that vaccination with well-defined Leishmania MHC-restricted epitopes extracted from various immunogenic proteins co-encapsulated with the proper adjuvant or/and phlebotomine fly saliva multi-epitope peptides into clinically compatible PLGA NPs could be a promising approach for the induction of a strong and sustainable protective immunity.

Association Between IL-4 and IL-6 Expression Variants and Gastric Cancer Among Portuguese Population

Introduction

Multiple studies have reported strong associations between Helicobacter pylori (Hp) inflammation and gastric cancer (GC) development. Altered expressions of pro/anti-inflammatory cytokines have a crucial role in Hp and GC proliferation. Although there are many studies related to cytokines polymorphisms involvement in GC risk, the role of Interleukin-4 (IL-4) and Interleukin-6 (IL-6) in gastric inflammation process is not yet clarified.

Aim

This study aimed to investigate the impact of common IL-4 and IL-6 polymorphisms in GC development risk among Portuguese population.

Methods

A total of 100 GC biopsies (50 with intestinal type, IGC, 50 with diffuse type, DGC) and 50 chronic gastritis cases, used as control group, were included in this case-control study. IL-4 and IL-6 common polymorphisms were genotyped by PCR-SSP, using commercially available kits.

Results

IL-4 low producer genotypes, IL-4-590TT (OR = 6.7; 95% CI 1.4–32.4) and IL-4-1098GG (OR = 4.4; 95% CI 1.7–16.9) were found associated with IGC and DGC, respectively. We also verified that IL-4 TTT haplotype was linked with both IGC (OR = 5.8; 95% CI 2.3–14.4) and DGC (OR = 2.3; 95% CI 1.0–5.5) groups. Concerning IL-6 results, IL-6-174CG genotype showed a higher prevalence among IGC cases (OR = 7.3; 95% CI 2.7–20.3), and IL-6-174CC (OR = 3.8; 95% CI 1.7–8.7) showed upper prevalence within DGC subjects. Finally, IL-6-174/nt565CG haplotype showed a significant association with both IGC (OR = 7.3; 95% CI 2.7–20.3) and DGC (OR = 7.9; 95% CI 4.2–14.9).

Conclusion

IL-6 and IL-4 expression variants seem to have an important role in GC risk mechanisms. This study provides preliminary evidence that IL-4 and IL-6 polymorphisms, although not directly linked to the disease, may be useful tools in the study of this multifactorial disease.

Interleukin-4 regulates eomesodermin in CD8+ T cell development and differentiation

Interleukin (IL)-4 is a cytokine classically associated with CD4(+) T helper type 2 differentiation, but has been recently shown to also be required for the development of CD8(+) innate-like lymphocytes. CD8(+) innate-like lymphocytes are non-conventional lymphocytes that exhibit characteristics typically associated with memory CD8(+) T cells, including expression of the T-box transcription factor Eomesodermin (Eomes). Here we investigate the signaling pathways required for IL-4 induction of Eomes and CD8(+) innate-like lymphocyte markers in murine CD8SP thymocytes and peripheral CD8(+) T cells. We demonstrate that IL-4 is sufficient to drive Eomes expression and the CD8(+) innate-like lymphocyte phenotype through cooperation between STAT6- and Akt-dependent pathways. Furthermore, we show that while IL-4 has little effect on the induction of Eomes in the setting of robust T cell receptor (TCR) activation, this cytokine promotes Eomes in the setting of attenuated TCR stimulation in mature CD8(+) T cells suggesting that cytokine signaling pathways may direct cell fate when TCR signals are limiting.

Epigenetic plasticity of Cd8a locus during CD8(+) T-cell development and effector differentiation and reprogramming

Modulation of CD8 coreceptor levels can profoundly affect T-cell sensitivity to antigen. Here we show that the heritable downregulation of CD8 during type 2 polarization of murine CD8⁺ effector T cells in vitro and in vivo is associated with CpG methylation of several regions of the Cd8a locus. These epigenetic modifications are maintained long-term in vivo following adoptive transfer. Even after extended type 2 polarization, however, some CD8^low effector cells respond to interferon-γ by re-expressing CD8 and a type 1 cytokine profile in association with partial Cd8a demethylation. Cd8a methylation signatures in naive, polarized and repolarized cells are distinct from those observed during the initiation, maintenance and silencing of CD8 expression by developing T cells in the thymus. This persistent capacity for epigenetic reprogramming of coreceptor levels on effector CD8⁺ T cells enables the heritable tuning of antigen sensitivity in parallel with changes in type 1/type 2 cytokine balance.

CD8 expression levels on peripheral CD8+ T cells are regulated during development and effector differentiation. Here, the authors show that methylation patterns at the Cd8a locus, whose product is essential for surface CD8 expression, can change during T-cell development, activation, cytokine polarization and reprogramming.

Induction of protection against leishmaniasis in susceptible BALB/c mice using simple DOTAP cationic nanoliposomes containing soluble Leishmania antigen (SLA)

A suitable adjuvant and delivery system are needed to develop an effective vaccine against leishmaniasis. To induce a Th1 type of response and protection in BALB/c mice against Leishmania major infection, 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) nanoliposomes bearing an intrinsic adjuvanticity, were used as an antigen delivery system and immunoadjuvant for soluble Leishmania antigens (SLA). DOTAP liposomes containing different concentrations of SLA were prepared by using lipid film method followed by sonication. The prepared vesicles showed a diameter of about 100nm, a positive zeta potential and approximately 70% encapsulation efficiency of SLA. BALB/c mice were immunized subcutaneously (SC), three times in a 3-week interval with different concentrations of liposomal SLA (12.5, 25, and 50μg of SLA/50μl/mice), free SLA and as well as free liposome. The group of mice received 50μg of SLA in DOTAP-nanoliposomes showed a significantly (p<0.001) smaller footpad swelling and the lowest spleen and footpad parasite burden after the challenge. This group also showed the highest IFN-γ production compared to the other groups, lower IL-4 level and higher IgG2a antibody titer. Taken together, the results indicated that simple DOTAP nanoliposome containing 1μg/μl SLA are appropriate delivery systems to induce a Th1 type of immune response and protection against L. major infection in BALB/c mice.

Vaccination with Leishmania histone H1-pulsed dendritic cells confers protection in murine visceral leishmaniasis

Visceral leishmaniasis is the most severe form of leishmaniases affecting millions of people worldwide often resulting in death despite optimal therapy. Thus, there is an urgent need for the development of effective anti-infective vaccine(s). In the present study, we evaluated the prophylactic value of bone marrow-derived dendritic cells (BM-DCs) pulsed with the Leishmania (L.) infantum histone H1. We developed fully mature BM-DCs characterized by enhanced capacity of IL-12 production after ex vivo pulsing with GST-LeishH1. Intravenous administration of these BM-DCs in naive BALB/c mice resulted in antigen-specific spleenocyte proliferation and IgG1 isotype antibody production and conferred protection against experimental challenge with L. infantum independently of CpG oligonucleotides (ODNs) co-administration. Protection was associated with a pronounced enhancement of parasite-specific IFNγ-producing cells and reduction of cells producing IL-10, whereas IL-4 production was comparable in protected and non-protected mice. The polarization of immune responses to Th1 type was further confirmed by the elevation of parasite-specific IgG2a/IgG1 ratio in protected mice. The above data indicate the immunostimulatory capacity of Leishmania histone H1 and further support its exploitation as a candidate protein for vaccine development against leishmaniasis.

Indoleamine 2,3-dioxygenase and metabolites protect murine lung allografts and impair the calcium mobilization of T cells

The enzyme indoleamine 2,3-dioxygenase (IDO) converts tryptophan into kynurenine metabolites that suppress effector T-cell function. In this study, we investigated IDO and its metabolite, 3-hydroxyanthranilic acid (3HAA), in regulating lung allograft rejection, using a murine orthotopic lung transplant model with a major mismatch (BALB/c donor and C57BL6 recipient). IDO was overexpressed in murine donor lungs, using an established nonviral (polyethylenimine carrier)-based gene transfer approach, whereas 3HAA was delivered daily via intraperitoneal injection. Increased IDO expression or its metabolite, 3HAA, resulted in a remarkable therapeutic effect with near normal lung function and little acute rejection, approximately A1, compared with A3 in untreated allografts (grading based on International Society for Heart and Lung Transplantation guidelines). We found that a high IDO environment for 7 days in lung allografts resulted in impaired T-cell activation, the production of multiple effector cytokines (IL-2, IL-4, IL-5, IL-6, IFN-γ, TNF-α, IL-12, and IL-13), and the generation of effector memory T cells (CD62L(lo)CD44(hi) phenotype). In isolated murine splenocytes, we observed that IDO/3HAA impaired T-cell receptor (TCR)-mediated T-cell activation, and more importantly, a decrease of intracellular calcium, phospholipase C-γ1 phosphorylation, and mitochondrial mass was evident. This work further illustrates the potential role of a high IDO environment in lung transplantation, and that the high IDO environment directly impairs TCR activation via the disruption of calcium signaling.

Liposomal SLA co-incorporated with PO CpG ODNs or PS CpG ODNs induce the same protection against the murine model of leishmaniasis

First generation Leishmania vaccines consisting of whole killed parasites with or without adjuvants have reached phase 3 trial and failed to show enough efficacy mainly due to the lack of an appropriate adjuvant. In this study, the nuclease-resistant phosphorothioate CpG oligodeoxynucleotides (PS CpG) or nuclease-sensitive phosphodiester CpG ODNs (PO CpG) were used as adjuvants to enhance immunogenicity and rate of protection against leishmaniasis. Due to the susceptibility of PO CpG to nuclease degradation, an efficient liposomal delivery system was developed to protect them from degradation. 1, 2-dioleoyl-3-trimethylammonium-propane (DOTAP) as a cationic lipid was used because of its unique adjuvanticity and electrostatic interaction with negatively charged CpG ODNs. To evaluate the role of liposomal formulation in protection rate and enhanced immune response, BALB/c mice were immunized subcutaneously with liposomal soluble Leishmania antigens (SLA) co-incorporated with PO CpG (Lip-SLA-PO CpG), Lip-SLA-PS CpG, SLA+PO CpG, SLA+PS CpG, SLA or buffer. As criteria for protection, footpad swelling at the site of challenge, parasite loads, the levels of IFN-γ and IL-4, and the IgG subtypes were evaluated. The groups of mice receiving Lip-SLA-PO CpG or Lip-SLA-PS CpG showed a high protection rate compared with the control groups. In addition, there was no significant difference in immune response generation between mice immunized with PS CpG and the group receiving PO CpG when incorporated into the liposomes. The results suggested that liposomal form of PO CpG might be used instead of PS CpG in future vaccine formulations as an efficient adjuvant.

IL-4 acts as a potent stimulator of IFN-γ expression in CD8+ T cells through STAT6-dependent and independent induction of Eomesodermin and T-bet

CD8+ T cell synthesis of IFN-γ is an important component of the CD8+ T cell immune response. In short-term cultures of murine pan-T cells, we found that IL-4 was the principal cytokine responsible for driving IFN-γ synthesis by CD3/CD28-activated CD8+ T cells. IL-4 was able to induce low levels of IFN-γ mRNA in CD8+ T cells even in the absence of CD3/CD28 engagement, although concomitant CD3/CD28 stimulation was necessary for IFN-γ secretion. IL-4 induction of IFN-γ was explained by its ability to induce Eomesodermin and T-bet transcription factors whose expression was further increased by CD3/CD28. Expression of Eomesodermin, T-bet and IFN-γ induced by IL-4 was partially dependent upon activation of MAPK and PI3K but independent of the canonical IL-4-activated transcription factor, STAT6. In contrast, expression of IFN-γ induced by IL-4/CD3/CD28 stimulation showed additional dependency upon STAT6 which functions to increase expression of Eomesodermin specifically. These novel findings point to a function for IL-4 as a direct regulator of IFN-γ expression in CD8+ T cells and reveal the molecular mechanisms involved.

Tumor Therapy Applying Membrane-bound Form of Cytokines

Tumor therapy using cytokines has been developed for last two decades. Several recombinant cytokines and tumor cell vaccines produced by cytokine gene transfer have been in clinical trials, but several side effects hamper routine clinical applications. Many cytokines are originally expressed as membrane-bound form and then processed to secretory form exerting paracrine effects. Though functional differences of these two types of cytokines are elusive yet, the membrane-bound form of cytokine may exert its effects on restricted target cells as a juxtacrine, which are in physical contacts. With the efforts to improve antitumor activities of cytokines in cancer patients, developing new strategies to alleviate life-threatening side effects became an inevitable goal of tumor immunologists. Among these, tumor cell vaccines expressing cytokines as membrane-bound form on tumor cell surface have been developed by genetic engineering techniques with the hope of selective stimulation of the target cells that are in cell-to-cell contacts. In this review, recent progress of tumor cell vaccines expressing membrane-bound form of cytokines will be discussed.

Endogenously produced IL-4 nonredundantly stimulates CD8+ T cell proliferation

T cell proliferation and survival are regulated by the cytokine receptor common gamma-chain-associated cytokines IL-2, IL-7, and IL-15, while IL-4, another gamma-chain-associated cytokine, is thought to primarily affect T cell quality rather than quantity. In contrast, our experiments reveal that endogenously produced IL-4 is a direct, nonredundant, and potent stimulator of CD8(+) T cell proliferation in Ag- and pathogen-induced CD8(+) T cell responses. These stimulatory effects of IL-4 are observed in both BALB/c and C57BL/6 mice and activate both naive and memory/activated phenotype CD8(+) T cells, although the former are stimulated less than are the latter. IL-4 effects are IL-7- and IL-15-independent, but MHC class I-dependent stimulation appears to be required for the mitogenic effect of IL-4 on naive phenotype CD8(+) T cells. Thus, endogenously produced IL-4 is an important regulator of quantitative as well as qualitative aspects of T cell immunity.

gp63 in stable cationic liposomes confers sustained vaccine immunity to susceptible BALB/c mice infected with Leishmania donovani

Visceral leishmaniasis is deadly if not treated, and development of a vaccine with long-term immunity remains a challenge. In this study, we showed that cationic distearoyl phosphatidylcholine (DSPC) liposomes, when used as vaccine adjuvant with the immunodominant 63-kDa glycoprotein (gp63) of Leishmania donovani promastigotes, induced significant protection against progressive visceral leishmaniasis in susceptible BALB/c mice. gp63 used without adjuvant elicited partial protection but in association with liposomes exhibited marked resistance in both the livers and spleens of the mice challenged 10 days after the last vaccination. The protective efficacy of liposomal gp63 vaccination was dose dependent, with 2.5 mug of protein showing optimal protection. The immunity conferred by this vaccine formulation was durable, as mice challenged 12 weeks after immunization were still protected, and the infection was controlled for at least 3 months postchallenge. Production of gamma interferon (IFN-gamma) and interleukin-4 (IL-4) by splenic T cells, and of serum immunoglobulin G1 (IgG1) and IgG2a following immunization, suggested that a mixed Th1/Th2 response had been induced following immunization. However, control of disease progression and parasitic burden in mice vaccinated with gp63 in cationic DSPC liposomes was associated with enhancement of antigen-specific IFN-gamma and downregulation of IL-4, demonstrating a Th1 bias. Long-term immunity elicited by this vaccine corresponded to, in addition to the presence of antigen-specific Th1, CD8+ T-cell responses. Our results demonstrated that stable cationic liposomes containing gp63 acted as a potent adjuvant for protein antigen to induce long-term protection against L. donovani that represents an alternative to DNA vaccination.

Temporal cross-talk between TCR and STAT signals for CD8 T cell effector differentiation

The strength and duration of signaling through surface receptors is a primary means of controlling cell fate decisions. In adaptive immunity, Ag-initiated T cell stimulation is secondarily regulated by cytokines. We here summarize evidence for temporal control of a gene expression program in naive CD8 T cells. It is initiated in response to TCR engagement but relies on secondary signaling from cytokine receptors to be sustained and to allow development of full effector capacity. This mechanism permits cytokine receptor signaling to rescue abortive TCR signaling, such as that induced in response to weak or partial TCR agonists. Indeed, limiting TCR-initiated signaling on the Ras/ERK pathway may be complemented by STAT activation. Thus, TCR- and cytokine-driven activation of transcription factors and epigenetic modifications may act in concert in a temporally staggered process to establish the functional program of effector CD8 T cells. Based on gene expression profiling, molecular targets whose activation or inactivation may boost or dampen CD8 T cell effectors are also identified. Manipulation of these targets may, respectively, increase anti-tumor responses or prevent graft-versus-host reactions.

IL-4 induces a wide-spectrum intracellular signaling cascade in CD8+T cells

IL-4 has distinct effects on the differentiation and functional properties of CD8+ T cells. In vivo studies have shown that it is critical for the development of protective memory responses against tumors and infections by Leishmania and Plasmodium parasites. The intracellular signaling events mediated by IL-4/IL-4 receptor (IL-4R) interactions on CD4+ T cells have been studied extensively; however, the nature of IL-4-induced signaling on CD8+ T cells has not been characterized. Using naïve, activated, as well as differentiated CD8+ T cells, we show that IL-4 has a strong in vivo and in vitro antiapoptotic effect on activated and resting CD8+ T cells. We demonstrate that IL-4 induces the phosphorylation of the IL-4R, which is followed by the activation of at least two distinct intracellular signaling cascades: the Jak1/STAT6 and the insulin receptor substrate/PI-3K/protein kinase B pathways. We also found that IL-4 induces the Jak3-mediated phosphorylation and nuclear migration of STAT1, STAT3, and STAT5 in naïve, activated, as well as differentiated, IFN-gamma-producing CD8+ T cells. The induction of this broad signaling activity in CD8+ T cells coincides with a transcriptional activity of suppressors of cytokine signaling genes, which are decreased significantly in comparison with CD4+ T cells. To our knowledge, this report constitutes the first comprehensive analysis of the signaling events that shape CD8+ T cell responses to IL-4.

Dysregulation of IL-15-mediated T-cell homeostasis in TGF-beta dominant-negative receptor transgenic mice

T-cell subpopulations, defined by their expression of CD4, CD8, naive, and memory cell-surface markers, occupy distinct homeostatic compartments that are regulated primarily by cytokines. CD8+ memory T cells, as defined by CD44(hi) surface expression, are dependent on IL-15 as a positive regulator of their homeostatic maintenance. Manipulation of IL-15 signaling through gene aberration, overexpression, or receptor alterations has been shown to dramatically affect T-cell homeostasis, with overexpression leading to fatal leukemia. Here we show that TGF-beta is the critical negative regulator of murine CD8+ memory T-cell homeostasis with direct opposition to the positive effects of IL-15. This negative regulation is mediated, at least in part, by the ability of TGF-beta to modulate expression of the beta-chain of the IL-15 receptor, thus establishing a central axis between these 2 cytokines for homeostatic control of CD8+ memory T-cell populations. These data establish TGF-beta as a critical and dominant tumor-suppressor pathway opposing IL-15-mediated CD8+ T-cell expansion and potential malignant transformation.

IL-4 influences the differentiation and the susceptibility to activation-induced cell death of human naive CD8+ T cells

It is now well established that the cytokine environment influences the activation, differentiation, proliferation and death of T lymphocytes during the primary response to antigen. Using an in vitro model, we investigated the influence of IL-4, added at the onset of TCR stimulation, on phenotypic and functional markers of naive CD8+ T cell activation including the up-regulation of activation markers, proliferation as well as the susceptibility to activation-induced cell death (AICD). We report that IL-4, unlike IL-2 added at the onset of repeated TCR stimulation of naive CD8+ T cells prevents AICD, in part due to its ability to maintain the level of the survival-related protein Bcl-2. Moreover, TCR-triggered activation of naive CD8+ T cells in the presence of IL-4 leads to the development of a CD8+ T cell subset that proliferates normally, but which fails to exhibit characteristic activation parameters such as the up-regulation of CD25 and Granzyme B. Taken together, these results demonstrate that exposure to IL-4 during primary activation influences CD8+ T cell differentiation by inducing the development of a sub-population of AICD-resistant, proliferation-competent cells that do not show some of the typical features of CD8+ T cell activation.

Clonal restriction of the expansion of antigen-specific CD8+ memory T cells by transforming growth factor-{beta}

Recent evidence showed that transforming growth factor-beta (TGF-beta) regulates the global expansion of CD8+ T cells, which are CD44hi, a marker for memory cells. However, it is not clear whether this regulatory mechanism also applies to the antigen-specific CD8+ memory cells. By using a murine mixed lymphocyte culture (MLC) model, we examined the effect of TGF-beta on antigen-specific CD8+ memory cells [cytotoxic T lymphocyte (CTL)]. We found that the secondary CTL response in CD8+ memory cells from untreated MLC was not affected by TGF-beta but augmented by interleukin (IL)-2, whereas the CD8+ memory cells from TGF-beta-pretreated MLC (MLC-TGF-beta) failed to mount a significant, secondary CTL response, even when IL-2 was added. In exploring this dichotomy, in combination with flow cytometry analysis, we found that prolonged exposure to TGF-beta reduces the CTL activity in CD8+ memory cells. The increase by IL-2 and the reduction by TGF-beta of the CTL responses were clonal-specific. TGF-beta did not affect the CTL response to a third-party antigen or polyclonal T cell activation. Experiments performed with transgenic 2C cells gave similar results. Cell-cycle study performed with adoptive transfer of the cell tracker-labeled MLC cells revealed that the in vivo expansion of CD8+ memory cells from MLC-TGF-beta was restricted severely, and the restriction was clonal-specific, thus offering direct evidence to show that TGF-beta induces clonal restriction of CD8+ memory cell expansion.

Recombinant bovine interleukin 2 enhances immunity and protection induced by Brucella abortus vaccines in cattle

Augmentation of immunization of cattle Brucella abortus S19 or a B. abortus soluble protein extract (SPEBA) vaccine through administration of recombinant bovine IL 2 (rBoIL 2) was evaluated. Seventy-five heifers were divided among 6 groups that were treated with the following: Group 1, no treatment; Group 2, rBoIL 2 (1microg/kg) on day 0; Group 3, SPEBA (2 mg) on day 0 and week 9; Group 4, SPEBA + rBoIL 2 on day 0, SPEBA on week 9; Group 5, S19 (10(7) CFU) on day 0 and week 9; Group 6, S19 + rBoIL 2 on day 0, S19 only on week 9. Approximately, 6 months after vaccination, cattle were bred by natural service, and at mid-gestation pregnant cattle were challenged intraconjunctivally with 9.1 x 10(5) CFU of virulent B. abortus S2308. Pre- and post-challenge antibody responses were measured by an enzyme-linked immunosorbent assay, a particle concentration fluorescence assay, and the card test. Lymphoproliferation (LP) responses to gamma-irradiated B. abortus and SPEBA antigens were measured in peripheral blood mononuclear cells. After vaccination, antibody responses to B. abortus elevated rapidly in SPEBA- and S19-vaccinates with and without rBoIL 2, however, these responses were significantly (P < 0.05) higher in vaccinates which also received rBoIL 2. Antibody levels for all vaccinated groups had returned to those of negative control groups by the challenge date with the exception of the SPEBA/rBoIL 2 group. In general, LP responses were higher in vaccinated or rBoIL 2-treated cattle than for unvaccinated controls. Challenge of 48 pregnant heifers resulted in abortions in 4/9 of Group 1, 0/9 of Group 2, 4/8 of Group 3, 2/9 of Group 4, 1/7 of Group 5, and 0/6 of Group 6 cattle. Treatment with rBoIL 2 alone (Group 2) provided significant (P < 0.05) protection from infection, abortions and induction of sero-positive status compared to untreated (Group 1) cattle. Co-administration of rBoIL 2 with S19 resulted in significant (P < 0.05) augmentation in onset, duration and magnitude of LP responses to B. abortus antigens following challenge. Characterization of the cytokine response of bovine monocyte-derived macrophages by real-time polymerase chain reaction indicated that in vitro stimulation of these cells with rBoIL 2 resulted in a profound up-regulation of genes encoding tumor necrosis factor-alpha, IL 12p40, and interferon-gamma reflecting activation of the cells. Overall, rBoIL 2-treatment was associated with fewer infections, sero-conversions and a significant (P = 0.02) level of protection against abortion as compared to vaccination alone or no treatment.

IL-4 receptor expression on CD8+ T cells is required for the development of protective memory responses against liver stages of malaria parasites

IL-4 receptor (IL-4R)-deficient CD8+ T cells specific for the circumsporozoite protein of Plasmodium yoelii develop a severely impaired memory response after priming with parasites. Memory CD8+ T cells lacking the IL-4R are unable to establish a stable population residing in nonlymphoid organs, although they develop normally in lymphoid organs. Because memory cells from nonlymphoid organs disappear shortly after immunization, the protective antiparasitic activity of this T cell response also is lost. These results demonstrate that IL-4/IL-4R interactions on CD8+ T cells play a critical role in modulating the development and tissue distribution of memory cells induced by parasite immunization. They also indicate that memory cells residing in nonlymphoid tissues are critical for protective immunity against malaria parasites.

Invariant Valpha14 chain NKT cells promote Plasmodium berghei circumsporozoite protein-specific gamma interferon- and tumor necrosis factor alpha-producing CD8+ T cells in the liver after poxvirus vaccination of mice

Understanding the protective mechanism in the liver induced by recombinant vaccines against the pre-erythrocytic stages of malaria is important for vaccine development. Most studies in mice have focused on splenic and peripheral blood T cells and identified gamma interferon (IFN-gamma)-producing CD8+ T cells as correlates of protection, which can be induced by prime-boost vaccination with recombinant poxviruses. Invariant natural killer T (Valpha14iNKT) cells can also protect against liver stage malaria, when activated, and are abundant in the liver. Since poxviruses have nonspecific immunomodulating effects, which are incompletely understood, we investigated whether recombinant poxviruses affect the protective properties of hepatic Valpha14iNKT cells and thus vaccine efficacy. We show that intradermal vaccination with recombinant poxviruses activated Valpha14iNKT cells and NK cells in the livers of BALB/c mice while inducing IFN-gamma- and tumor necrosis factor alpha (TNF-alpha)-producing pre-erythrocytic stage antigen-specific CD8+ T cells. Greater numbers of hepatic Valpha14iNKT cells secreted interleukin-4 than IFN-gamma. Vaccinated Valpha14iNKT-cell-deficient mice had lower, but still protective levels of hepatic and splenic IFN-gamma+ and TNF-alpha+ CD8+ T cells and better protection rates later after challenge with Plasmodium berghei sporozoites. Therefore, vaccine-activated hepatic Valpha14iNKT cells help in generating specific T cells but are not required for protection induced by recombinant poxviruses. Furthermore, double-positive INF-gamma+/TNF-alpha+ CD8+ T cells were enriched in protected livers, suggesting that cells expressing both of these cytokines may be most relevant for protection.

Interferon gamma enhances both in vitro and in vivo priming of CD4+ T cells for IL-4 production

Classical studies have demonstrated that in vitro priming of naive CD4 T cells to become T helper (Th)2 cells is strikingly dependent on interleukin (IL)-4, whereas priming for interferon (IFN)γ production is IL-12/IFNγ-dependent. Therefore, it was quite surprising when we noted that priming of naive C57BL/6 CD4⁺ cells to become IL-4 producers was substantially inhibited by the addition of anti-IFNγ antibodies. This was true using immobilized anti-CD3 and anti-CD28 antibodies or soluble anti-CD3/anti-CD28 and antigen-presenting cells in the presence or absence of added IL-4. Priming of CD4 T cells from IFNγ^−/− C57BL/6 mice with immobilized anti-CD3 and anti-CD28 resulted in limited production of IL-4, even with the addition of 1,000 U/ml of IL-4. Titrating IFNγ into such cultures showed a striking increase in the proportion of T cells that secreted IL-4 upon challenge; this effect was completely IL-4–dependent in that it was blocked with anti–IL-4 antibody. Thus, IFNγ plays an unanticipated but substantial role in Th2 priming, although it is an important Th1 cytokine, and under certain circumstances a Th1 inducer.

Complete tumor prevention by engineered tumor cell vaccines employing nonviral vectors

We report that 100% mice survival after tumor challenge is achieved with cytokine-engineered cells employing nonviral lipoplexes and without using viral vectors. We describe this effect with cytokine-secreting tumor cell vaccines, based on cell clones or fresh transfected cells. Tumor cells were transfected with murine granulocyte-macrophage colony-stimulating factor (GM-CSF) or IL-4 plasmids employing the cationic lipid DOTAP, were irradiated (150 Gy) and kept frozen until use. The transfection efficacy was analyzed by qRT-PCR and flow cytometry. Vaccination induced potent antitumor rejection, resulting in 100% mice survival. Furthermore, the antitumor immunity was long lasting, since a two-fold survival delay was observed in mice after tumor rechallenge (6 months later). While cell clones secreting GM-CSF were the most effective in wild-type tumor cell rejection, little or no effect was observed with clones secreting IL-4. We found similar antitumor efficacy employing fresh transfected cells by nonviral procedures, demonstrating that cells genetically modified by nonviral vectors (both clones and fresh transfected cells) are a safe and efficient tool for antitumor vaccines. These vaccines allow us to achieve the highest antitumor efficacy based on nonviral gene therapy techniques. In addition, the vaccination success with fresh transfected cells simplifies the procedure and provides new insights into the clinical application of nonviral gene therapy procedures.

Proliferation and differentiation potential of human CD8+ memory T-cell subsets in response to antigen or homeostatic cytokines

Four human CD8+ T-cell subsets, naive (CCR7+CD45RA+), central memory (TCM, CCR7+CD45RA-), effector memory (TEM, CCR7-CD45RA-), and CD45RA+ effector memory cells (TEMRA, CCR7-CD45RA+) were compared for their capacity to proliferate and differentiate in response to antigen or homeostatic cytokines. Cytokine responsiveness and interleukin-15 receptor expression were low in naive T cells and progressively increased from TCM to TEM and TEMRA. In contrast, the capacity to accumulate in response to T-cell receptor (TCR) or cytokine stimulation showed a reciprocal pattern and was associated with resistance to cell death and Bcl-2 expression. Whereas all TCR-stimulated cells acquired a CD45RA-CCR7- phenotype, cytokine-stimulated cells maintained their phenotype with the exception of TCM cells, which expressed CCR7, CD45RA, and perforin in various combinations. Single CD8+ TCM cells, but not TEM cells, could be expanded with cytokines, and the obtained clones displayed several distinct phenotypes, suggesting that TCM cells are heterogeneous. Consistently, CCR4 expression in the CD8+ TCM pool discriminated CCR4+ type 2 polarized cells (Tc2) and CCR4-CTL precursors. Finally, ex vivo bromodeoxyuridine (BrdU) incorporation experiments revealed that memory subsets have different in vivo proliferation rates, with CCR4-TCM having the highest turnover and TEMRA the lowest. These results show that human CD8+ memory T-cell subsets have different proliferation and differentiation potentials in vitro and in vivo. Furthermore, they suggest that TEMRA cells are generated from a TCM subset upon homeostatic proliferation in the absence of antigen.

IL-15 is a growth factor and an activator of CD8 memory T cells

Memory lymphocytes, arising from naïve lymphocytes after antigenic stimulation and being long-lived, are the cellular basis for immunological memory. Recent studies of CD8 T cells suggest that generation of CD8 memory T cells requires the engagement of T cell antigen receptors (TCR) with antigen, yet the maintenance of CD8 memory T cells appears to be dependent on cytokines, such as IL-15, independent of TCR. Although considerable progress has been made in understanding the molecular and cellular events of TCR-induced differentiation and proliferation in the past decade, less is known about the mechanisms of IL-15 action. From a kinetic and comparative analysis of the responses of memory phenotype CD8 T cells to IL-15 and TCR stimulation in vitro, we found that IL-15 and anti-CD3 induce highly similar responses in memory phenotype CD8 T cells as measured by general gene expression profiles, synthesis of effector molecules (IFNgamma, TNFbeta, granzyme B and perforin), induction of cytotoxicity, and cellular proliferation. These findings indicate that IL-15 is not only a growth factor but also an antigen-independent activator for CD8 memory T cells.

Interleukin 15 controls both proliferation and survival of a subset of memory-phenotype CD8(+) T cells

Previous work has shown that memory-phenotype CD44(hi) CD8(+) cells are controlled by a cytokine, interleukin (IL)-15. However, the dependency of CD44(hi) CD8(+) cells on IL-15 is partial rather than complete. Here, evidence is presented that CD44(hi) CD8(+) cells comprise a mixed population of IL-15-dependent and IL-15-independent cells. The major subset of CD122(hi) CD44(hi) CD8(+) cells is heavily dependent on IL-15 by three different parameters, namely (1) "bystander" proliferation induced via IFN-induced stimulation of the innate immune system, (2) normal "background" proliferation, and (3) T cell survival; IL-15 dependency is most extreme for the Ly49(+) subset of CD122(hi) CD44(hi) CD8(+) cells. In contrast to CD122(hi) cells, the CD122(lo) subset of CD44(hi) CD8(+) cells is IL-15 independent; likewise, being CD122(lo), CD44(hi) CD4(+) cells are IL-15 independent. Thus, subsets of memory-phenotype T cells differ radically in their sensitivity to IL-15.

Enhanced immunogenicity of pneumococcal surface adhesin A by genetic fusion to cytokines and evaluation of protective immunity in mice

Immunization of mice with pneumococcal surface adhesin A (PsaA) emulsified in complete Freund's adjuvant (CFA) provides protection against systemic infection with Streptococcus pneumoniae. Because the use of CFA is not acceptable in humans, we sought to develop alternative means of enhancing the immunogenicity of protein antigens of potential use in pneumococcal vaccines. We designed a series of genetic constructs in which coding sequences for PsaA were linked to sequences encoding either murine interleukin-2 (mIL-2), mIL-4, or two copies of an immunostimulatory nonapeptide derived from mIL-1beta. The PsaA-cytokine constructs were cloned and expressed in Escherichia coli. Mice immunized twice with PsaA-IL-2, or PsaA-IL-4 responded with PsaA-specific antibody production comparable in magnitude to that of mice primed with PsaA in CFA and boosted with PsaA in incomplete Freund's adjuvant (PsaA-Adj). Antibodies elicited by PsaA-Adj were predominantly of the immunoglobulin G1 (IgG1) subclass, while PsaA-IL-2 and PsaA-IL-4 elicited substantial amounts of IgG2a in addition to IgG1. Mice immunized with PsaA-Adj or PsaA-IL-4 were partially protected against intraperitoneal challenge with virulent S. pneumoniae (30% overall survival beyond 15 days postchallenge). Mice immunized with PsaA and no adjuvant or PsaA-IL-2 exhibited 0 or 5% survival rates, respectively, following challenge. In contrast, mice immunized twice with capsular polysaccharide were 100% protected. The modest levels of protection seen in mice immunized with PsaA and its more immunogenic derivatives may be explained in part by the relative inaccessibility of antibody to PsaA on the surface of encapsulated S. pneumoniae.

T cell memory

Typical immune responses lead to prominent clonal expansion of antigen-specific T and B cells followed by differentiation into effector cells. Most effector cells die at the end of the immune response but some of these cells survive and form long-lived memory cells. The factors controlling the formation and survival of memory T cells are reviewed.

IL-15 mimics T cell receptor crosslinking in the induction of cellular proliferation, gene expression, and cytotoxicity in CD8+ memory T cells

Generation of CD8(+) memory T cells requires antigenic stimulation through T cell receptor (TCR); however, maintenance of CD8(+) memory T cells seems to be mediated by cytokines, such as IL-15, in a TCR-independent manner. Compared with the TCR-induced activation, less is known about the mechanisms of IL-15 action. We report here a comparative and kinetic analysis of the responses of memory phenotype CD8(+) T cells to IL-15 or TCR (anti-CD3) stimulation in vitro. These two stimuli induce highly similar responses in memory phenotype CD8(+) T cells as measured by cellular proliferation, gene expression changes, synthesis of effector molecules (IFNgamma, tumor necrosis factor beta, granzyme B, and perforin), and induction of cytotoxicity. From 189 genes/expressed sequence tags (ESTs) whose expression changed in CD8(+) memory T cells after IL-15 and anti-CD3 stimulation identified by cDNA microarray analysis, 77% of the genes/ESTs exhibit a highly similar pattern of expression between IL-15 and anti-CD3-treated cells, and only 16% and 7% of the genes/ESTs are differentially expressed in response to IL-15 and anti-CD3 treatments, respectively. These results show that IL-15 and anti-CD3 stimulation induced remarkably similar gene expression and effector function. Thus, IL-15 acts not only as a crucial growth factor but also as an antigen-independent activator of effector functions for CD8(+) memory T cells.

Exhaustion of cytotoxic T cells during adoptive immunotherapy of virus carrier mice can be prevented by B cells or CD4+ T cells

Rapid disappearance of antiviral CTL after transfusion into persistently infected individuals is a serious limitation of adoptive immunotherapy protocols. In the mouse model of persistent infection with lymphocytic choriomeningitis virus (LCMV) naive or immune virus-specific donor CD8+ T cells are exhausted after transfusion into carrier recipients with similar kinetics. Here we show that cotransfusion of immune CD4+ T cells prevents exhaustion of immune CD8+ T cells. Interestingly, cotransfer of primed B cells also prevented CD8+ T cell exhaustion in carriers even in the absence of T helper cells. This effect required the presence of immune B cells as repetitive treatment with hyperimmune serum led to the generation of antibody escape mutants. A combination of primed CD4+ T cells and primed B cells enhanced antiviral effects and prevented exhaustion also of naive CD8+ T cells. One key factor for prevention of CD8+ T cell exhaustion was the antiviral effect of the cotransfused cells thus reducing the time that CD8+ T cells are confronted with a high systemic viral load. These findings have implications for improving adoptive immunotherapy for persistent human viral infections.

IL-4-secreting CD4+ T cells are crucial to the development of CD8+ T-cell responses against malaria liver stages

CD4+ T cells are crucial to the development of CD8+ T cell responses against hepatocytes infected with malaria parasites. In the absence of CD4+ T cells, CD8+ T cells initiate a seemingly normal differentiation and proliferation during the first few days after immunization. However, this response fails to develop further and is reduced by more than 90%, compared to that observed in the presence of CD4+ T cells. We report here that interleukin-4 (IL-4) secreted by CD4+ T cells is essential to the full development of this CD8+ T cell response. This is the first demonstration that IL-4 is a mediator of CD4/CD8 cross-talk leading to the development of immunity against an infectious pathogen.

T cell death and memory

In typical immune responses, contact with antigen causes naive T cells to proliferate and differentiate into effector cells. After the pathogen is destroyed, most effector T cells are eliminated-thereby preserving the primary T cell repertoire-but some cells survive and form long-lived memory cells. During each stage of this process, the life or death fate of T cells is strictly regulated.

Burnet oration. T-cell survival and the role of cytokines

Typical T cells are long-lived resting cells. Despite their quiescent appearance, there is increasing evidence that T cells are subjected to continuous stimulation through contact with various stimuli, notably by self peptide/MHC complexes and cytokines. These stimuli keep T cells alive and also cause intermittent entry into cell cycle.