Gamma(c) deficiency precludes CD8+ T cell memory despite formation of potent T cell effectors

Optimising IL-2 for Cancer Immunotherapy

The key role of T cells in cancer immunotherapy is well established and is highlighted by the remarkable capacity of Ab-mediated checkpoint blockade to overcome T-cell exhaustion and amplify anti-tumor responses. However, total or partial tumor remission following checkpoint blockade is still limited to only a few types of tumors. Hence, concerted attempts are being made to devise new methods for improving tumor immunity. Currently, much attention is being focused on therapy with IL-2. This cytokine is a powerful growth factor for T cells and optimises their effector functions. When used at therapeutic doses for cancer treatment, however, IL-2 is highly toxic. Nevertheless, recent work has shown that modifying the structure or presentation of IL-2 can reduce toxicity and lead to effective anti-tumor responses in synergy with checkpoint blockade. Here, we review the complex interaction of IL-2 with T cells: first during normal homeostasis, then during responses to pathogens, and finally in anti-tumor responses.

Crosstalk of Transcriptional Regulators of Adaptive Immune System and microRNAs: An Insight into Differentiation and Development

MicroRNAs (miRNAs), as small regulatory RNA molecules, are involved in gene expression at the post-transcriptional level. Hence, miRNAs contribute to gene regulation of various steps of different cell subsets' differentiation, maturation, and activation. The adaptive immune system arm, which exhibits the most specific immune responses, is also modulated by miRNAs. The generation and maturation of various T-cell subsets concomitant with B-cells is under precise regulation of miRNAs which function directly on the hallmark genes of each cell subset or indirectly through regulation of signaling pathway mediators and/or transcription factors involved in this maturation journey. In this review, we first discussed the origination process of common lymphocyte progenitors from hematopoietic stem cells, which further differentiate into various T-cell subsets under strict regulation of miRNAs and transcription factors. Subsequently, the differentiation of B-cells from common lymphocyte progenitors in bone marrow and periphery were discussed in association with a network of miRNAs and transcription factors.

Exhaustion‑like dysfunction of T and NKT cells in an X‑linked severe combined immunodeficiency patient with maternal engraftment by single‑cell analysis

Maternal engraftment is frequently present in X‑linked severe combined immunodeficiency (X‑SCID) patients caused by pathogenic mutations in IL2GR. However, the functional status of the engrafted cells remains unclear because of the difficulty in separately evaluating the function of the maternal and autologous cells. The present study reported an X‑SCID patient with a de novo c.677C>T (p.R226H) variant in exon 5 of IL2RG, exhibiting recurrent and persistent infections from 3‑months‑old. After the male patient suffering recurrent pneumonia and acute hematogenous disseminated tuberculosis when 13‑months‑old, single‑cell RNA sequencing was applied to characterize the transcriptome landscape of his bone marrow mononuclear cells (BMMNCs). A novel bioinformatic analysis strategy was designed to discriminate maternal and autologous cells at single‑cell resolution. The maternal engrafted cells consisted primarily of T, NKT and NK cells and the patient presented with the coexistence of autologous cells of these cell types. When compared respectively with normal counterparts, both maternal and autologous T and NKT cells increased the transcription of some important cytokines (GZMB, PRF1 and NKG7) against infections, but decreased the expression of a number of key transcription factors (FOS, JUN, TCF7 and LEF1) related to lymphocyte activation, proliferation and differentiation. Notably, the expression of multiple inhibitory factors (LAG3, CTLA4 and HAVCR2) were substantially enhanced in the T and NKT cells of both origins. In conclusion, both maternal and autologous T and NKT cells exhibited exhaustion‑like dysfunction in this X‑SCID patient suffering recurrent and persistent infections.

Combined IFN-γ and JAK inhibition to treat hemophagocytic lymphohistiocytosis in mice

BACKGROUND

Familial hemophagocytic lymphohistiocytosis is a life-threatening hyperinflammatory disease caused by genetic defects in the granule-mediated cytotoxic pathway. Success of hematopoietic cell transplantation, the only cure, is correlated with the extent of disease control before transplantation. Unfortunately, disease refractoriness and toxicities to standard chemotherapy-based regimens are fatal in a fraction of patients. Novel targeted immunotherapies, such as IFN-γ blocking antibodies or ruxolitinib, a Janus kinase (JAK) 1/2 inhibitor, are promising but only partially effective at controlling disease.

OBJECTIVE

We asked whether combinations of cytokine-targeted therapies, using antibodies or JAK inhibitor, work synergistically to counteract HLH.

METHODS

Genetically predisposed mice were infected and treated with distinct combinations of immunotherapies. Disease outcome was monitored and compared to monotherapies.

RESULTS

We showed that inhibiting IL-6 or IL-18 signaling in combination with IFN-γ blockade or ruxolitinib did not increase disease control compared to anti-IFN-γ antibodies or ruxolitinib monotherapies. In contrast, clinically relevant doses of ruxolitinib combined with low doses of anti-IFN-γ blocking antibodies corrected cytopenias, prevented overt neutrophilia, limited cytokinemia, and resolved HLH immunopathology and symptomatology.

CONCLUSIONS

Our findings demonstrate that IFN-γ blockade and ruxolitinib act synergistically to suppress HLH progression. This supports the use of combined cytokine-targeted therapies as a bridge to hematopoietic cell transplantation in severe familial hemophagocytic lymphohistiocytosis.

An Updated Model for the Epigenetic Regulation of Effector and Memory CD8+ T Cell Differentiation

Naive CD8⁺ T cells, upon encountering their cognate Ag in vivo, clonally expand and differentiate into distinct cell fates, regulated by transcription factors and epigenetic modulators. Several models have been proposed to explain the differentiation of CTLs, although none fully recapitulate the experimental evidence. In this review article, we will summarize the latest research on the epigenetic regulation of CTL differentiation as well as provide a combined model that contemplates them.

Allospecific Memory B Cell Responses Are Dependent on Autophagy

Long-lived, donor-reactive memory B cells (Bmems) can produce alloantibodies that mediate transplant injury. Autophagy, an intrinsic mechanism of cell organelle/component recycling, is required for Bmem survival in infectious and model antigen systems, but whether autophagy affects alloreactive Bmem is unknown. We studied mice with an inducible yellow fluorescent protein (YFP) reporter expressed under the activation-induced cytidine deaminase (AID) promoter active in B cells undergoing germinal center reactions. Up to 12 months after allogeneic sensitization, splenic YFP⁺ B cells were predominantly IgD^- IgM^- IgG⁺ and expressed CD73, CD80, and PD-L2, consistent with Bmems. Labeled cells contained significantly more cells with autophagosomes and more autophagosomes per cell than unlabeled, naïve B cells. To test for a functional link, we quantified alloantibody formation in mice with B cells conditionally deficient in the requisite autophagy gene ATG7. These experiments revealed absent B cell ATG7 (1) prevented B cell autophagy, (2) inhibited secondary alloantibody responses without altering primary alloantibody formation, and (3) diminished frequencies of alloreactive Bmems. Pharmacological autophagy inhibition with 3-methyladenine had similar effects on wild-type mice. Together with new documentation of increased autophagosomes within human Bmems, our data indicate that targeting autophagy has potential for eliminating donor-reactive Bmems in transplant recipients.

Identification of lineage-specifying cytokines that signal all CD8+-cytotoxic-lineage-fate 'decisions' in the thymus

T cell antigen receptor (TCR) signaling in the thymus initiates positive selection but CD8 lineage fate is thought to be induced by cytokines after TCR signaling has ceased, although this remains controversial and unproven. We now identify four non-common gamma chain (γc) receptor-signaling cytokines (IL-6, IFN-γ, TSLP, TGF-β) that, like IL-7 and IL-15, induce expression of the lineage-specifying transcription factor Runx3d and signal the generation of CD8 T cells. Remarkably, elimination of in vivo signaling by all ‘lineage-specifying cytokines’ during positive selection eliminated Runx3d expression and completely abrogated CD8 single-positive thymocyte generation. Thus, this study proves that signaling during positive selection by lineage-specifying cytokines is responsible for all CD8 lineage fate decisions in the thymus.

The MicroRNA miR-191 Supports T Cell Survival Following Common γ Chain Signaling

To ensure lifelong immunocompetency, naïve and memory T cells must be adequately maintained in the peripheral lymphoid tissues. Homeostatic maintenance of T cells is controlled by tonic signaling through T cell antigen receptors and common γ chain cytokine receptors. In this study, we identify the highly expressed microRNA miR-191 as a key regulator of naïve, memory, and regulatory T cell homeostasis. Conditional deletion of miR-191 using LckCre resulted in preferential loss of peripheral CD4⁺ regulatory T cells as well as naïve and memory CD8⁺ T cells. This preferential loss stemmed from reduced survival following deficient cytokine signaling and STAT5 activation. Mechanistically, insulin receptor substrate 1 (Irs1) is a direct target of miR-191, and dysregulated IRS1 expression antagonizes STAT5 activation. Our study identifies a novel role for microRNAs in fine-tuning immune homeostasis and thereby maintaining the lymphocyte reservoir necessary to mount productive immune responses.

IL2Rβ-dependent signals drive terminal exhaustion and suppress memory development during chronic viral infection

Exhaustion of CD8(+) T cells severely impedes the adaptive immune response to chronic viral infections. Despite major advances in our understanding of the molecular regulation of exhaustion, the cytokines that directly control this process during chronicity remain unknown. We demonstrate a direct impact of IL-2 and IL-15, two common gamma-chain-dependent cytokines, on CD8(+) T-cell exhaustion. Common to both cytokine receptors, the IL-2 receptor β (IL2Rβ) chain is selectively maintained on CD8(+) T cells during chronic lymphocytic choriomeningitis virus and hepatitis C virus infections. Its expression correlates with exhaustion severity and identifies terminally exhausted CD8(+) T cells both in mice and humans. Genetic ablation of the IL2Rβ chain on CD8(+) T cells restrains inhibitory receptor induction, in particular 2B4 and Tim-3; precludes terminal differentiation of highly defective PD-1(hi) effectors; and rescues memory T-cell development and responsiveness to IL-7-dependent signals. Together, we ascribe a previously unexpected role to IL-2 and IL-15 as instigators of CD8(+) T-cell exhaustion during chronic viral infection.

IL-2 and IL-15 regulate CD8+ memory T-cell differentiation but are dispensable for protective recall responses

The ability to mount effective secondary responses is a cardinal feature of memory CD8(+) T cells. An understanding of the factors that regulate the generation and recall capacities of memory T cells remains to be ascertained. Several cues indicate that two highly related cytokines, IL-2 and IL-15, share redundant functions in this process. To establish their combined roles in memory CD8(+) T-cell development, maintenance, and secondary responses, we compared the outcome of adoptively transferred IL2Rβ(+/-) or IL2Rβ(-/-) CD8(+) T cells after an acute viral infection in mice. Our results demonstrate that both IL-2 and IL-15 signals condition the differentiation of primary and secondary short-lived effector cells by altering the transcriptional network governing lineage choices. These two cytokines also regulate the homeostasis of the memory T-cell pool, with effector memory CD8(+) T cells being the most sensitive to these two interleukins. Noticeably, the inability to respond to both cytokines limits the proliferation and survival of primary and secondary effectors cells, whereas it does not preclude potent cytotoxic functions and viral control either initially or upon rechallenge. Globally, these results indicate that lack of IL-2 and IL-15 signaling modulates the CD8(+) T-cell differentiation program but does not impede adequate effector functions.

microRNAs function in CD8+T cell biology

During an immune response, CD8(+)T cells can differentiate into multiple types of effector and memory cells that are important components of immune surveillance. However, their dysregulation has been implicated in infection with viruses or intracellular bacteria and tumorigenesis. miRNAs have been identified as crucial regulators of gene expression, and they perform this function by repressing specific target genes at the post-transcriptional level. Most miRNAs expressed in a given cell type serve the function to impede broadly cell-type-inappropriate gene expression and potently deepen a pre-existing differentiation program. It is increasingly recognized that miRNAs directly modulate the concentration of many regulatory proteins that are required for the development of immune cells in the thymus and their responses in the periphery. This review outlines our current understanding of the function of miRNAs in CD8(+)T cell biology as it impacts expression of protein-coding genes in the context of proper development, infection, as well as oncogenesis. In addition, we conclude with a perspective on future challenges and the clinical relevance of miRNA biology.

A cytokine cocktail directly modulates the phenotype of DC-enriched anti-tumor T cells to convey potent anti-tumor activities in a murine model

Adoptive cell transfer (ACT) using ex vivo-expanded anti-tumor T cells such as tumor-infiltrated lymphocytes or genetically engineered T cells potently eradicates established tumors. However, these two approaches possess obvious limitations. Therefore, we established a novel methodology using total tumor RNA (ttRNA) to prime dendritic cells (DC) as a platform for the ex vivo generation of anti-tumor T cells. We evaluated the antigen-specific expansion and recognition of T cells generated by the ttRNA-DC-T platform, and directly modulated the differentiation status of these ex vivo-expanded T cells with a cytokine cocktail. Furthermore, we evaluated the persistence and in vivo anti-tumor efficacy of these T cells through murine xenograft and syngeneic tumor models. During ex vivo culture, IL-2 preferentially expanded CD4 subset, while IL-7 enabled homeostatic proliferation from the original precursors. T cells tended to lose CD62L during ex vivo culture using IL-2; however, IL-12 could maintain high levels of CD62L by increasing expression on effector T cells (Tem). In addition, we validated that OVA RNA-DC only selectively expanded T cells in an antigen-specific manner. A cytokine cocktail excluding the use of IL-2 greatly increased CD62Lhigh T cells which specifically recognized tumor cells, engrafted better in a xenograft model and exhibited superior anti-tumor activities in a syngeneic intracranial model. ACT using the ex vivo ttRNA-DC-T platform in conjunction with a cytokine cocktail generated potent CD62Lhigh anti-tumor T cells and imposes a novel T cell-based therapeutic with the potential to treat brain tumors and other cancers.

MicroRNA-155 is required for effector CD8+ T cell responses to virus infection and cancer

MicroRNAs (miRNAs) regulate the function of several immune cells, but their role in promoting CD8(+) T cell immunity remains unknown. Here we report that miRNA-155 is required for CD8(+) T cell responses to both virus and cancer. In the absence of miRNA-155, accumulation of effector CD8(+) T cells was severely reduced during acute and chronic viral infections and control of virus replication was impaired. Similarly, Mir155(-/-) CD8(+) T cells were ineffective at controlling tumor growth, whereas miRNA-155 overexpression enhanced the antitumor response. miRNA-155 deficiency resulted in accumulation of suppressor of cytokine signaling-1 (SOCS-1) causing defective cytokine signaling through STAT5. Consistently, enforced expression of SOCS-1 in CD8(+) T cells phenocopied the miRNA-155 deficiency, whereas SOCS-1 silencing augmented tumor destruction. These findings identify miRNA-155 and its target SOCS-1 as key regulators of effector CD8(+) T cells that can be modulated to potentiate immunotherapies for infectious diseases and cancer.

The survival of memory CD8 T cells that is mediated by IL-15 correlates with sustained protection against malaria

Ag-specific memory T cell responses elicited by infections or vaccinations are inextricably linked to long-lasting protective immunity. Studies of protective immunity among residents of malaria endemic areas indicate that memory responses to Plasmodium Ags are not adequately developed or maintained, as people who survive episodes of childhood malaria are still vulnerable to either persistent or intermittent malaria infections. In contrast, multiple exposures to radiation-attenuated Plasmodium berghei sporozoites (Pb γ-spz) induce long-lasting protective immunity to experimental sporozoite challenge. We previously demonstrated that sterile protection induced by Pb γ-spz is MHC class I-dependent and CD8 T cells are the key effectors. IFN-γ(+) CD8 T cells that arise in Pb γ-spz-immunized B6 mice are found predominantly in the liver and are sensitive to levels of liver-stage Ag depot and they express CD44(hi)CD62L(lo) markers indicative of effector/effector memory phenotype. The developmentally related central memory CD8 T (TCM) cells express elevated levels of CD122 (IL-15Rβ), which suggests that CD8 TCM cells depend on IL-15 for maintenance. Using IL-15-deficient mice, we demonstrate in this study that although protective immunity is inducible in these mice, protection is short-lived, mainly owing to the inability of CD8 TCM cells to survive in the IL-15-deficient milieu. We present a hypothesis consistent with a model whereby intrahepatic CD8 TCM cells, being maintained by IL-15-mediated survival and basal proliferation, are conscripted into the CD8 effector/effector memory T cell pool during subsequent infections.

Memory CD8 T cells specific for plasmodia liver-stage antigens maintain protracted protection against malaria

Immunologic memory induced by pathogenic agents or vaccinations is inextricably linked to long-lasting protection. Adequately maintained memory T and B cell pools assure a fast, effective, and specific response against re-infections. Studies of immune responses amongst residents of malaria endemic areas suggest that memory responses to Plasmodia antigens appear to be neither adequately developed nor maintained, because persons who survive episodes of childhood malaria remain vulnerable to persistent or intermittent malaria infections. By contrast, multiple exposures of humans and laboratory rodents to radiation-attenuated Plasmodia sporozoites (γ-spz) induces sterile and long-lasting protection against experimental sporozoite challenge. Protection is associated with MHC-class I-dependent CD8 T cells, the key effectors against pre-erythrocytic stage infection. We have adopted the P. berghei γ-spz mouse model to study memory CD8 T cells that are specific for antigens expressed by Pb liver-stage (LS) parasites and are found predominantly in the liver. On the basis of phenotypic and functional characteristics, we have demonstrated that liver CD8 T cells form two subsets: CD44^hiCD62L^loKLRG-1⁺CD107⁺CD127⁻CD122^loCD8 T effector/effector memory (T_E/EM) cells that are the dominant IFN-γ producers and CD44^hiCD62L^hiKLRG-1⁻CD107⁻CD127⁺CD122^hiCD8 T central memory (T_CM) cells. In this review, we discuss our observations concerning the role of CD8 T_E/EM and CD8 T_CM cells in the maintenance of protracted protective immunity against experimental malaria infection. Finally, we present a hypothesis consistent with a model whereby intrahepatic CD8 T_CM cells, that are maintained in part by LS-Ag depot and by IL-15-mediated survival and homeostatic proliferation, form a reservoir of cells ready for conscription to CD8 T_E/EM cells needed to prevent re-infections.

Modulating the differentiation status of ex vivo-cultured anti-tumor T cells using cytokine cocktails

The genetic modification of CD8+ T cells using anti-tumor T-cell receptors (TCR) or chimeric antigen receptors is a promising approach for the adoptive cell therapy of patients with cancer. We previously developed a simplified method for the clinical-scale generation of central memory-like (Tcm) CD8+ T cells following transduction with lentivirus encoding anti-tumor TCR and culture in the presence of IL-2. In this study, we compared different cytokines or combinations of IL-2, IL-7, IL-12, IL-15, and IL-21 to expand genetically engineered CD8+ T cells. We demonstrated that specific cytokine combinations IL-12 plus IL-7 or IL-21 for 3 days followed by withdrawal of IL-12 yielded the phenotype of CD62L(high)CD28(high) CD127(high)CD27(high)CCR7(high), which is associated with less-differentiated T cells. Genes associated with stem cells (SOX2, NANOG, OCT4, and LIN28A), were also up-regulated by this cytokine cocktail. Moreover, the use of IL-12 plus IL-7 or IL-21 yielded CD8 T cells showing enhanced persistence in the NOD/SCID/γc-/- mouse model. This defined cytokine combination could also alter highly differentiated TIL from melanoma patients into cells with a less-differentiated phenotype. The methodology that we developed for generating a less-differentiated anti-tumor CD8+ T cells ex vivo may be ideal for the adoptive immunotherapy of cancer.

Fragmentation of SIV-gag vaccine induces broader T cell responses

Background

High mutation rates of human immunodeficiency virus (HIV) allows escape from T cell recognition preventing development of effective T cell vaccines. Vaccines that induce diverse T cell immune responses would help overcome this problem. Using SIV gag as a model vaccine, we investigated two approaches to increase the breadth of the CD8 T cell response. Namely, fusion of vaccine genes to ubiquitin to target the proteasome and increase levels of MHC class I peptide complexes and gene fragmentation to overcome competition between epitopes for presentation and recognition.

Methodology/Principal Findings

Three vaccines were compared: full-length unmodified SIV-mac239 gag, full-length gag fused at the N-terminus to ubiquitin and 7 gag fragments of equal size spanning the whole of gag with ubiquitin-fused to the N-terminus of each fragment. Genes were cloned into a replication defective adenovirus vector and immunogenicity assessed in an in vitro human priming system. The breadth of the CD8 T cell response, defined by the number of distinct epitopes, was assessed by IFN-γ-ELISPOT and memory phenotype and cytokine production evaluated by flow cytometry. We observed an increase of two- to six-fold in the number of epitopes recognised in the ubiquitin-fused fragments compared to the ubiquitin-fused full-length gag. In contrast, although proteasomal targeting was achieved, there was a marked reduction in the number of epitopes recognised in the ubiquitin-fused full-length gag compared to the full-length unmodified gene, but there were no differences in the number of epitope responses induced by non-ubiquitinated full-length gag and the ubiquitin-fused mini genes. Fragmentation and ubiquitination did not affect T cell memory differentiation and polyfunctionality, though most responses were directed against the Ad5 vector.

Conclusion/Significance

Fragmentation but not fusion with ubiquitin increases the breadth of the CD8 T vaccine response against SIV-mac239 gag. Thus gene fragmentation of HIV vaccines may maximise responses.

Conditional deletion of cytokine receptor chains reveals that IL-7 and IL-15 specify CD8 cytotoxic lineage fate in the thymus

The thymus generates T cells with diverse specificities and functions. To assess the contribution of cytokine receptors to the differentiation of T cell subsets in the thymus, we constructed conditional knockout mice in which IL-7Rα or common cytokine receptor γ chain (γ(c)) genes were deleted in thymocytes just before positive selection. We found that γ(c) expression was required to signal the differentiation of MHC class I (MHC-I)-specific thymocytes into CD8(+) cytotoxic lineage T cells and into invariant natural killer T cells but did not signal the differentiation of MHC class II (MHC-II)-specific thymocytes into CD4(+) T cells, even into regulatory Foxp3(+)CD4(+) T cells which require γ(c) signals for survival. Importantly, IL-7 and IL-15 were identified as the cytokines responsible for CD8(+) cytotoxic T cell lineage specification in vivo. Additionally, we found that small numbers of aberrant CD8(+) T cells expressing Runx3d could arise without γ(c) signaling, but these cells were developmentally arrested before expressing cytotoxic lineage genes. Thus, γ(c)-transduced cytokine signals are required for cytotoxic lineage specification in the thymus and for inducing the differentiation of MHC-I-selected thymocytes into functionally mature T cells.

Homeostatic maintenance of T cells and natural killer cells

Homeostasis in the immune system encompasses the mechanisms governing maintenance of a functional and diverse pool of lymphocytes, thus guaranteeing immunity to pathogens while remaining self-tolerant. Antigen-naïve T cells rely on survival signals through contact with self-peptide-loaded major histocompatibility complex (MHC) molecules plus interleukin (IL)-7. Conversely, antigen-experienced (memory) T cells are typically MHC-independent and they survive and undergo periodic homeostatic proliferation through contact with both IL-7 and IL-15. Also, non-conventional γδ T cells rely on a mix of IL-7 and IL-15 for their homeostasis, whereas natural killer cells are mainly dependent on contact with IL-15. Homeostasis of CD4(+) T regulatory cells is different in being chiefly regulated by contact with IL-2. Notably, increased levels of these cytokines cause expansion of responsive lymphocytes, such as found in lymphopenic hosts or following cytokine injection, whereas reduced cytokine levels cause a decline in cell numbers.

CD8(+) T cells: foot soldiers of the immune system

Resting naive CD8(+) T cells have an astounding capacity to react to pathogens by massive expansion and differentiation into cytotoxic effector cells that migrate to all corners of the body to clear the infection. The initial interaction with antigen-presenting cells in the central lymphoid organs drives an orchestrated program of differentiation aimed at producing sufficient numbers of effectors to get the job done without resulting in clonal exhaustion. Interactions with antigen-presenting cells and other immune cells continue at the site of infection to regulate further on-site expansion and differentiation, all with the goal of protecting the host with minimal bystander tissue damage. Here we review recent advances in CD8(+) T cell recognition of antigen in lymphoid as well as in nonlymphoid tissues in the periphery, and how CD8(+) T cell expansion and differentiation are controlled in these contexts.

The gamma-chain cytokine/receptor system in fish: more ligands and receptors

The mammalian gamma-chain (γC) cytokine family consists of interleukin (IL)-2, IL-4, IL-7, IL-9, IL-15 and IL-21. They signal through a receptor complex containing the common γC and a private alpha chain, and in the case of IL-2 and IL-15 an additional common IL-2/15Rβ chain. Deficiency of γC signalling in mammals prevents CD4+ T cells from developing effector functions and CD8+ T cells from developing immunological memory. Thus γC cytokines are critical for the generation and peripheral homeostasis of naïve and memory T cells. This review will give an update on the γC ligands and receptor subunits in fish, and also present some new data on the cloning and expression of a second γC and two IL-2Rβ chains in rainbow trout Oncorhynchus mykiss. In recent years, aided by the availability of sequenced fish genomes and expressed sequence tag databases, five of the six mammalian γC cytokines and their cognate receptors have been discovered in fish, with only the IL-9/IL-9R homologues apparently absent. Paralogues have been discovered in diploid fish and all the receptors described in the tetraploid rainbow trout, including γC itself, IL-2Rβ, IL-4Rα, IL-13Rα1, IL-13Rα2 and IL-2/15Rα, have duplicates. As a consequence of the teleost and salmonid whole genome duplications, even more paralogues may yet be discovered. Some of the paralogues have changes in domain structures and show differential expression and modulation, suggesting the potential for a change in function. Functional characterisation of fish γC cytokines is beginning but made more difficult by the co-existence of so many paralogues of the ligands and their receptors. Initial functional studies have shown that fish γC cytokines can modulate the expression of key cytokines (e.g. interferon-γ, IL-10 and IL-22) of the adaptive immune response, and may thus have promise as adjuvants to improve vaccination efficiency in fish.

Interleukin-2 rescues helpless effector CD8+ T cells by diminishing the susceptibility to TRAIL mediated death

CD8(+) T cells primed in the absence of CD4(+) T cell help are programmed to produce TRAIL, which results in Death receptor (DR5) mediated apoptosis upon restimulation. Here, we studied whether these 'helpless' effector CD8(+) T cells are consigned to an apoptotic fate or whether their helpless program can be altered by inflammatory or growth cytokines. We found that helpless CD8(+) T cells regained their full proliferative and functional capacity only when IL-2 was added to cell cultures, while IL-7 and IL-15, two common gamma chain cytokines associated with CD8(+) T cell homeostasis and memory, could only partly restore secondary expansion in helpless CD8(+) T cells. Recovery of functional CD8(+) T cell immunity by IL-2 was concomitant with induction of IL2Rα (CD25) expression, downregulation of TRAIL, and the upregulation of anti-apoptotic molecules Bcl-2 and FLIP. The addition of IL-2 to helpless CD8(+) T cells also interfered with DR5-mediated apoptosis induction, indicating that IL-2 affects several components of the TRAIL-DR5 pathway. Collectively, these data demonstrate that the helpless phenotype is not fixed, and that IL-2R signaling at the time of reactivation can play an important role in restoring CD8(+) T cell function.

Cytokines and the inception of CD8 T cell responses

The activation and differentiation of CD8 T cells is a necessary first step that endows these cells with the phenotypic and functional properties required for the control of intracellular pathogens. The induction of the CD8 T cell responses typically results in the development of a massive overall population of effector cells, comprising both highly functional but short-lived terminally differentiated cells, as well as a smaller subset of precursors that are predisposed to survive and transition into the memory T cell pool. In this review, we discuss how inflammatory cytokines and IL-2 bias the initial response towards short-lived effector generation, and also highlight the potential counterbalancing role of IL-21.

Analytical capabilities of the ImageStream cytometer

Imaging cytometry has recently become an important achievement in development of flow cytometric technologies. The ImageStream cytometer combines the vast features of classical flow cytometry including an impartial analysis of great number of cells in short period of time which results in strong statistical data output, with essential features of fluorescence microscopy such us collecting of real multiparameter images of analyzed objects. In this chapter, we would like to introduce an overview of imaging cytometry platform and emphasize the potential advantages of using this system for several experimental purposes. Moreover, both well established as well as potential applications of imaging cytometry will be described. Eventually, we would like to illustrate the unique use of ImageStream cytometer for identification and characterization of subpopulations of stem/ progenitor cells present in different biological specimens.

Interleukin-2 receptor signaling: at the interface between tolerance and immunity

Interleukin-2 receptor (IL-2R) signaling regulates tolerance and immunity. Here, we review recent work concerning the structure, signaling, and function of the IL-2R, emphasizing the contribution of IL-2 for T cell-dependent activity in vivo. IL-2R signaling influences two discrete aspects of immune responses by CD8(+) T cells, terminal differentiation of effector cells in primary responses, and aspects of memory recall responses. IL-2 also delivers essential signals for thymic development of regulatory T (Treg) cells and later to promote their homeostasis and function. Each of these outcomes on T effector and Treg cells requires distinct amounts of IL-2R signaling, with low IL-2R signaling sufficient for many key aspects of Treg cells. Thus, tolerance is readily maintained and favored with limited IL-2.