Distinct pathways involving the FK506-binding proteins 12 and 12.6 underlie IL-2-versus IL-15-mediated proliferation of T cells

IL15RA-STAT3-GPX4/ACSL3 signaling leads to ferroptosis resistance in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant disease with a poor prognosis, and the lack of effective treatment methods accounts for its high mortality. Pancreatic stellate cells (PSCs) in the tumor microenvironment play an important role in the development of PDAC. Previous studies have reported that patients with PDAC are more vulnerable to ferroptosis inducers. To investigate the relationship between PSCs and pancreatic cancer cells, a coculture system is used to further reveal the influence of PSCs on ferroptosis resistance in PDAC using many in vitro and in vivo experiments. Our results show that PSCs promote ferroptosis resistance in pancreatic cancer cells. We further demonstrate that IL15 secretion by PSCs activates the IL15RA-STAT3-GPX4/ACSL3 axis. The simultaneous upregulation of GPX4 and ACSL3 prevents lipid peroxidation and ultimately protects pancreatic cancer cells from ferroptosis both in vitro and in vivo. This study demonstrates that PSCs protect pancreatic cancer cells in a paracrine manner and may indicate a novel strategy for the treatment of PDAC.

Personalized neoantigen vaccines as early intervention in untreated patients with lymphoplasmacytic lymphoma: a non-randomized phase 1 trial

Lymphoplasmacytic lymphoma (LPL) is an incurable low-grade lymphoma with no standard therapy. Nine asymptomatic patients treated with a first-in-human, neoantigen DNA vaccine experienced no dose limiting toxicities (primary endpoint, NCT01209871). All patients achieve stable disease or better, with one minor response, and median time to progression of 72+ months. Post-vaccine single-cell transcriptomics reveal dichotomous antitumor responses, with reduced tumor B-cells (tracked by unique B cell receptor) and their survival pathways, but no change in clonal plasma cells. Downregulation of human leukocyte antigen (HLA) class II molecules and paradoxical upregulation of insulin-like growth factor (IGF) by the latter suggest resistance mechanisms. Vaccine therapy activates and expands bone marrow T-cell clonotypes, and functional neoantigen-specific responses (secondary endpoint), but not co-inhibitory pathways or Treg, and reduces protumoral signaling by myeloid cells, suggesting favorable perturbation of the tumor immune microenvironment. Future strategies may require combinations of vaccines with agents targeting plasma cell subpopulations, or blockade of IGF-1 signaling or myeloid cell checkpoints.

Signalling mechanisms driving homeostatic and inflammatory effects of interleukin-15 on tissue lymphocytes

There is an intriguing dichotomy in the function of cytokine interleukin-15-at low levels, it is required for the homeostasis of the immune system, yet when it is upregulated in response to pathogenic infections or in autoimmunity, IL-15 drives inflammation. IL-15 associates with the IL-15Rα within both myeloid and non-haematopoietic cells, where IL-15Rα trans-presents IL-15 in a membrane-bound form to neighboring cells. Alongside homeostatic maintenance of select lymphocyte populations such as NK cells and tissue-resident T cells, when upregulated, IL-15 also promotes inflammatory outcomes by driving effector function and cytotoxicity in NK cells and T cells. As chronic over-expression of IL-15 can lead to autoimmunity, IL-15 expression is tightly regulated. Thus, blocking dysregulated IL-15 and its downstream signalling pathways are avenues for immunotherapy. In this review we discuss the molecular pathways involved in IL-15 signalling and how these pathways contribute to both homeostatic and inflammatory functions in IL-15-dependent mature lymphoid populations, focusing on innate, and innate-like lymphocytes in tissues.

New insights into the stemness of adoptively transferred T cells by γc family cytokines

T cell-based adoptive cell therapy (ACT) has exhibited excellent antitumoral efficacy exemplified by the clinical breakthrough of chimeric antigen receptor therapy (CAR-T) in hematologic malignancies. It relies on the pool of functional T cells to retain the developmental potential to serially kill targeted cells. However, failure in the continuous supply and persistence of functional T cells has been recognized as a critical barrier to sustainable responses. Conferring stemness on infused T cells, yielding stem cell-like memory T cells (TSCM) characterized by constant self-renewal and multilineage differentiation similar to pluripotent stem cells, is indeed necessary and promising for enhancing T cell function and sustaining antitumor immunity. Therefore, it is crucial to identify TSCM cell induction regulators and acquire more TSCM cells as resource cells during production and after infusion to improve antitumoral efficacy. Recently, four common cytokine receptor γ chain (γc) family cytokines, encompassing interleukin-2 (IL-2), IL-7, IL-15, and IL-21, have been widely used in the development of long-lived adoptively transferred TSCM in vitro. However, challenges, including their non-specific toxicities and off-target effects, have led to substantial efforts for the development of engineered versions to unleash their full potential in the induction and maintenance of T cell stemness in ACT. In this review, we summarize the roles of the four γc family cytokines in the orchestration of adoptively transferred T cell stemness, introduce their engineered versions that modulate TSCM cell formation and demonstrate the potential of their various combinations. Video Abstract.

First-in-human clinical trial of personalized neoantigen vaccines as early intervention in untreated patients with lymphoplasmacytic lymphoma

Lymphoplasmacytic lymphoma (LPL) is an incurable low-grade B-cell lymphoma of the bone marrow. Despite a cumulative risk of progression, there is no approved therapy for patients in the asymptomatic phase. We conducted a first-in-human clinical trial of a novel therapeutic DNA idiotype neoantigen vaccine in nine patients with asymptomatic LPL. Treatment was well tolerated with no dose limiting toxicities. One patient achieved a minor response, and all remaining patients experienced stable disease, with median time to disease progression of 61+ months. Direct interrogation of the tumor microenvironment by single-cell transcriptome analysis revealed an unexpected dichotomous antitumor response, with significantly reduced numbers of clonal tumor mature B-cells, tracked by their unique BCR, and downregulation of genes involved in signaling pathways critical for B-cell survival post-vaccine, but no change in clonal plasma cell subpopulations. Downregulation of HLA class II molecule expression suggested intrinsic resistance by tumor plasma cell subpopulations and cell-cell interaction analyses predicted paradoxical upregulation of IGF signaling post vaccine by plasma cell, but not mature B-cell subpopulations, suggesting a potential mechanism of acquired resistance. Vaccine therapy induced dynamic changes in bone marrow T-cells, including upregulation of signaling pathways involved in T-cell activation, expansion of T-cell clonotypes, increased T-cell clonal diversity, and functional tumor antigen-specific cytokine production, with little change in co-inhibitory pathways or Treg. Vaccine therapy also globally altered cell-cell communication networks across various bone marrow cell types and was associated with reduction of protumoral signaling by myeloid cells, principally non-classical monocytes. These results suggest that this prototype neoantigen vaccine favorably perturbed the tumor immune microenvironment, resulting in reduction of clonal tumor mature B-cell, but not plasma cell subpopulations. Future strategies to improve clinical efficacy may require combinations of neoantigen vaccines with agents which specifically target LPL plasma cell subpopulations, or enable blockade of IGF-1 signaling or myeloid cell checkpoints.

Neutrophil functions can be regulated by IL-35, which is mainly expressed in IL-15Rα+ cells in grass carp (Ctenopharyngodon idella)

IL-35 plays a key role in regulatory T (Treg) and regulatory B (Breg) cell functions in mammals. CD25 has been demonstrated as one of the markers of Treg cells, and CD19⁺CD25^hiCD71^hi cells have been verified as a type of Breg cells in humans. These results indicate that there is a close relationship between IL-35 and CD25⁺ cells. In mammals, CD25 (alias IL-2Rα) has been identified as having high affinity and specificity for IL-2 binding, and is closely linked and structurally related to IL-15Rα, which having high affinity for IL-15 binding. In teleost, IL-15Rα can bind to both IL-2 and IL-15, with higher affinity to IL-15 than IL-2, and has been termed a CD25-like molecule in some research studies. To date, no studies of IL-35 and IL-15Rα have been documented in fish. In this work, five isoforms of IL-15Rα were cloned from grass carp, and a monoclonal antibody to the protein was developed. The results of flow cytometry and quantitative real-time PCR analyses demonstrated that grass carp IL-35 subunit genes EBI3a and IL-12p35 were mainly expressed in IL-15Rα⁺ cells, while the expression levels of IL-10 and TGF-β in IL-15Rα⁺ and IL-15Rα^- cells were insignificant. Recombinant grass carp IL-35 (rgcIL-35) could increase the proportion of IL-15Rα⁺ cells in leukocytes, and a certain proportion of IL-15Rα⁺ cells also appeared in myeloid cell subset II after stimulation with rgcIL-35. Meanwhile, the migration, phagocytic ability, and bactericidal ability of grass carp neutrophils were significantly decreased after stimulation with certain concentrations of rgcIL-35. Moreover, neutrophil apoptosis could be significantly inhibited by rgcIL-35.

Immunomodulatory Effects of IL-2 and IL-15; Implications for Cancer Immunotherapy

The type I cytokine family members interleukin-2 (IL-2) and IL-15 play important roles in the homeostasis of innate and adaptive immunity. Although IL-2 and IL-15 receptor complexes activate similar signal transduction cascades, triggering of these receptors results in different functional activities in lymphocytes. While IL-2 expands regulatory T cells and CD4+ helper T cells, IL-15 supports the development of central memory T cells and NK cells. Recent data have provided evidence that IL-2 and IL-15 differ in their ability to activate T and NK cells to resist various forms of immune suppression. The diverse roles of these two cytokines have on immune cells lead to critical therapeutic implications for cancer treatment. In this review, we discuss the distinct roles of IL-2 and IL-15 in activating various functions in T and NK cells with a particular focus on the signals that participate in the resistance of tumor-derived immune suppressive factors. Furthermore, we summarize current clinical applications of IL-2 and IL-15 in metastatic malignancies, either as monotherapy or in combination with other agents, and highlight the future trends for research on these cytokine-based immunotherapies.

Tumor cell-expressed IL-15Rα drives antagonistic effects on the progression and immune control of gastric cancer and is epigenetically regulated in EBV-positive gastric cancer

PURPOSE

Epstein-Barr virus associated gastric cancer (EBVaGC) often exhibits a favorable prognosis that correlates with highly methylated viral and host genes and significant immune cell infiltration compared to EBV-negative gastric cancers (GCs). Previously, it has been reported that expression of the IL-15 receptor α (IL-15Rα) is down-regulated in EBVaGC via promoter hypermethylation. In the present study, we offer a novel explanation for this puzzle by associating IL-15Rα expression with infiltration of lymphocytes in GC lesions.

METHODS

We investigated the expression of IL-15Rα by RT-PCR, Western-blotting and immunohistochemistry in GC cell lines and primary tissues, respectively. IL-15Rα promoter methylation was analyzed using genomic methylation sequencing. The growth behavior of GC cells was analyzed using MTT, flow cytometry, colony formation, transwell invasion and scratch wound healing assays. Demethylation of IL-15Rα was carried out using 5-Aza-CdR, and rIL-15 was added to evaluate growth promoting effects of the IL-15/IL-15Rα complex. Human peripheral blood mononuclear cells (PBMCs) were co-cultured with GC cells with/without the addition of rIL-15, after which the phosphorylation of STAT5 in PBMCs was evaluated using flow cytometry to estimate the activation of these immune cells through IL-15 binding to IL-2Rβ/γ receptors by in trans presentation.

RESULTS

We found that EBV-positive GC cells (AE) expressed IL-15Rα at a significantly lower level than EBV-negative GC cells (AGS) due to promoter hypermethylation. In the absence of immune cells, IL-15Rα on the cancer cell surface induced a malignant phenotype, including augmented cell growth, migration and invasion, and decreased apoptosis. 5-Aza-CdR reverted AE cells to a more malignant phenotype similar to AGS cells, which may be attributed to activation of the STAT1, STAT3 and ERK1/2 pathways. However, when PBMCs were added to the GC cell cultures, these immune cells were activated as detected by increased pSTAT5 levels. Also, more GC cells underwent apoptosis. These effects were enhanced by the addition of rIL-15 and, subsequently, confirmed in EBVaGC patient samples exhibiting increased expression of T cell surface markers and activation of immune co-stimulating pathways.

CONCLUSIONS

Our findings suggest a mechanistic explanation for the clinical association of EBVaGC with a lower IL-15Rα expression, a better prognosis and an increased lymphocyte infiltration. We propose that in highly infiltrated GCs the IL-15/IL-15Rα complex on the GC cell surface may present IL-15 in trans to IL-2Rβ/γ-expressing immune cells to activate these cells in the tumor microenvironment.

IL-2 and IL-15 blockade by BNZ-1, an inhibitor of selective γ-chain cytokines, decreases leukemic T-cell viability

Interleukin-15 (IL-15) and IL-2 drive T-cell malignancies including T-cell large granular lymphocyte leukemia (T-LGLL) and HTLV-1 driven adult T-cell leukemia (ATL). Both cytokines share common γ-chain receptors and downstream signaling pathways. T-LGLL is characterized by clonal expansion of cytotoxic T cells and is associated with abnormal JAK/STAT signaling. ATL is an aggressive CD4+ T-cell neoplasm associated with HTLV-1. T-LGLL and ATL share dependence on IL-2 and IL-15 for survival and both diseases lack effective therapies. BNZ-1 is a pegylated peptide designed to specifically bind the γc receptor to selectively block IL-2, IL-15, and IL-9 signaling. We hypothesized that treatment with BNZ-1 would reduce cytokine-mediated proliferation and viability. Our results demonstrated that in vitro treatment of a T-LGLL cell line and ex vivo treatment of T-LGLL patient cells with BNZ-1 inhibited cytokine-mediated viability. Furthermore, BNZ-1 blocked downstream signaling and increased apoptosis. These results were mirrored in an ATL cell line and in ex vivo ATL patient cells. Lastly, BNZ-1 drastically reduced leukemic burden in an IL-15-driven human ATL mouse xenograft model. Thus, BNZ-1 shows great promise as a novel therapy for T-LGLL, ATL, and other IL-2 or IL-15 driven hematopoietic malignancies.

Specific and Novel microRNAs Are Regulated as Response to Fungal Infection in Human Dendritic Cells

Within the last two decades, the incidence of invasive fungal infections has been significantly increased. They are characterized by high mortality rates and are often caused by Candida albicans and Aspergillus fumigatus. The increasing number of infections underlines the necessity for additional anti-fungal therapies, which require extended knowledge of gene regulations during fungal infection. MicroRNAs are regulators of important cellular processes, including the immune response. By analyzing their regulation and impact on target genes, novel therapeutic and diagnostic approaches may be developed. Here, we examine the role of microRNAs in human dendritic cells during fungal infection. Dendritic cells represent the bridge between the innate and the adaptive immune systems. Therefore, analysis of gene regulation of dendritic cells is of particular significance. By applying next-generation sequencing of small RNAs, we quantify microRNA expression in monocyte-derived dendritic cells after 6 and 12 h of infection with C. albicans and A. fumigatus as well as treatment with lipopolysaccharides (LPS). We identified 26 microRNAs that are differentially regulated after infection by the fungi or LPS. Three and five of them are specific for fungal infections after 6 and 12 h, respectively. We further validated interactions of miR-132-5p and miR-212-5p with immunological relevant target genes, such as FKBP1B, KLF4, and SPN, on both RNA and protein level. Our results indicate that these microRNAs fine-tune the expression of immune-related target genes during fungal infection. Beyond that, we identified previously undiscovered microRNAs. We validated three novel microRNAs via qRT-PCR. A comparison with known microRNAs revealed possible relations with the miR-378 family and miR-1260a/b for two of them, while the third one features a unique sequence with no resemblance to known microRNAs. In summary, this study analyzes the effect of known microRNAs in dendritic cells during fungal infections and proposes novel microRNAs that could be experimentally verified.

The shared and contrasting roles of IL2 and IL15 in the life and death of normal and neoplastic lymphocytes: implications for cancer therapy

IL2 and IL15, members of the 4α-helix bundle family of cytokines, play pivotal roles in the control of the life and death of lymphocytes. Although their heterotrimeric receptors have two receptor subunits in common, these two cytokines have contrasting roles in adaptive immune responses. The unique role of IL2 through maintenance of fitness of regulatory T cells and activation-induced cell death is the elimination of self-reactive T cells to prevent autoimmunity. In contrast with IL2, IL15 is dedicated to the prolonged maintenance of memory T-cell responses to invading pathogens. Blockade of IL2 and IL15 using monoclonal antibodies has been reported to be of value in the treatment of patients with leukemia, autoimmune disorders, and in the prevention of allograft rejection. IL2 has been approved by the FDA for the treatment of patients with malignant renal cell cancer and metastatic malignant melanoma. Clinical trials involving recombinant human IL15 given by bolus infusions have been completed, and studies assessing subcutaneous and continuous intravenous infusions are under way in patients with metastatic malignancy. Furthermore, clinical trials are being initiated that employ the combination of IL15 with IL15Rα(+/-) IgFc.

IL-15: a central regulator of celiac disease immunopathology

Interleukin-15 (IL-15) exerts many biological functions essential for the maintenance and function of multiple cell types. Although its expression is tightly regulated, IL-15 upregulation has been reported in many organ-specific autoimmune disorders. In celiac disease, an intestinal inflammatory disorder driven by gluten exposure, the upregulation of IL-15 expression in the intestinal mucosa has become a hallmark of the disease. Interestingly, because it is overexpressed both in the gut epithelium and in the lamina propria, IL-15 acts on distinct cell types and impacts distinct immune components and pathways to disrupt intestinal immune homeostasis. In this article, we review our current knowledge of the multifaceted roles of IL-15 with regard to the main immunological processes involved in the pathogenesis of celiac disease.

Systemic infection generates a local-like immune response of the bacteriome organ in insect symbiosis

Endosymbiosis is common in insects thriving in nutritionally unbalanced habitats. The cereal weevil, Sitophilus oryzae, houses Sodalis pierantonius, a Gram-negative intracellular symbiotic bacterium (endosymbiont), within a dedicated organ called a bacteriome. Recent data have shown that the bacteriome expresses certain immune genes that result in local symbiont tolerance and control. Here, we address the question of whether and how the bacteriome responds to insect infections involving exogenous bacteria. We have established an infection model by challenging weevil larvae with the Gram-negative bacterium Dickeya dadantii. We showed that D. dadantii infects host tissues and triggers a systemic immune response. Gene transcript analysis indicated that the bacteriome is also immune responsive, but it expresses immune effector genes to a lesser extent than the systemic and intestinal responses. Most genes putatively involved in immune pathways remain weakly expressed in the bacteriome following D. dadantii infection. Moreover, quantitative PCR experiments showed that the endosymbiont load is not affected by insect infection or the resulting bacteriome immune activation. Thus, the contained immune effector gene expression in the bacteriome may prevent potentially harmful effects of the immune response on endosymbionts, whilst efficiently protecting them from bacterial intruders.

How longevity research can lead to therapies for Alzheimer's disease: The rapamycin story

The discovery that rapamycin increases lifespan in mice and restores/delays many aging phenotypes has led to the speculation that rapamycin has 'anti-aging' properties. The major question discussed in this review is whether a manipulation that has anti-aging properties can alter the onset and/or progression of Alzheimer's disease, a disease in which age is the major risk factor. Rapamycin has been shown to prevent (and possibly restore in some cases) the deficit in memory observed in the mouse model of Alzheimer's disease (AD-Tg) as well as reduce Aβ and tau aggregation, restore cerebral blood flow and vascularization, and reduce microglia activation. All of these parameters are widely recognized as symptoms central to the development of AD. Furthermore, rapamycin has also been shown to improve memory and reduce anxiety and depression in several other mouse models that show cognitive deficits as well as in 'normal' mice. The current research shows the feasibility of using pharmacological agents that increase lifespan, such as those identified by the National Institute on Aging Intervention Testing Program, to treat Alzheimer's disease.

The IL-2 cytokine family in cancer immunotherapy

The use of cytokines from the IL-2 family (also called the common γ chain cytokine family) such as interleukin (IL)-2, IL-7, IL-15, and IL-21 to activate the immune system of cancer patients is one of the most important areas of current cancer immunotherapy research. The infusion of IL-2 at low or high doses for multiple cycles in patients with metastatic melanoma and renal cell carcinoma was the first successful immunotherapy for cancer proving that the immune system could completely eradicate tumor cells under certain conditions. The initial clinical success observed in some IL-2-treated patients encouraged further efforts focused on developing and improving the application of other IL-2 family cytokines (IL-4, IL-7, IL-9, IL-15, and IL-21) that have unique biological effects playing important roles in the development, proliferation, and function of specific subsets of lymphocytes at different stages of differentiation with some overlapping effects with IL-2. IL-7, IL-15, and IL-21, as well as mutant forms or variants of IL-2, are now also being actively pursued in the clinic with some measured early successes. In this review, we summarize the current knowledge on the biology of the IL-2 cytokine family focusing on IL-2, IL-15 and IL-21. We discuss the similarities and differences between the signaling pathways mediated by these cytokines and their immunomodulatory effects on different subsets of immune cells. Current clinical application of IL-2, IL-15 and IL-21 either as single agents or in combination with other biological agents and the limitation and potential drawbacks of these cytokines for cancer immunotherapy are also described. Lastly, we discuss the future direction of research on these cytokines, such as the development of new cytokine mutants and variants for improving cytokine-based immunotherapy through differential binding to specific receptor subunits.

IL-15: a central regulator of celiac disease immunopathology

Interleukin-15 (IL-15) exerts many biological functions essential for the maintenance and function of multiple cell types. Although its expression is tightly regulated, IL-15 upregulation has been reported in many organ-specific autoimmune disorders. In celiac disease, an intestinal inflammatory disorder driven by gluten exposure, the upregulation of IL-15 expression in the intestinal mucosa has become a hallmark of the disease. Interestingly, because it is overexpressed both in the gut epithelium and in the lamina propria, IL-15 acts on distinct cell types and impacts distinct immune components and pathways to disrupt intestinal immune homeostasis. In this article, we review our current knowledge of the multifaceted roles of IL-15 with regard to the main immunological processes involved in the pathogenesis of celiac disease.

Interleukin 15 and CD4⁺ T cells cooperate to promote small intestinal enteropathy in response to dietary antigen

BACKGROUND & AIMS

CD4(+) T cells specific for dietary gluten and interleukin 15 (IL15) contribute to the pathogenesis of celiac disease. We investigated whether and how they interact to damage the intestine using mice that overexpress human IL15 in the intestinal epithelium and have CD4(+) T cells specific for ovalbumin, a dietary antigen.

METHODS

We crossed mice with CD4(+) T cells specific for ovalbumin (OTII) with mice that overexpress human IL15 under an intestine-specific promoter (B6 × IL15Tge). The offspring (OTII × IL15Tge mice) received control or ovalbumin-containing diets until 3 months of age. Enteropathy was monitored by weight, ratio of villous:crypt length, and the number of intestinal lymphocytes. Phenotype, cytokine production, and degranulation of mucosal and spleen lymphocytes were analyzed by multicolor flow cytometry or enzyme-linked immunosorbent assay. Regulatory T-cell function and CD8(+) T-cell activation were analyzed in co-culture assays.

RESULTS

Exposure to ovalbumin reduced growth and led to enteropathy in OTII × IL15Tge mice but not in control OTII × B6 littermates. Enteropathy was associated with expansion of mucosal granzyme B(+) CD8(+) T cells, and developed despite increased frequency of functional ovalbumin-specific regulatory T cells. Ovalbumin-activated CD4(+) T cells secreted IL2, which along with IL15 stimulated expansion of noncognate intestinal cytotoxic CD8(+) T cells, which did not respond to regulatory T cells and induced epithelial damage.

CONCLUSIONS

We observed that in mice given food antigen, cooperation between IL15 and CD4(+) T cells is necessary and sufficient to activate CD8(+) T cells and damage the small intestine. We propose that this process is involved in the development of celiac disease.

The impact of KLF2 modulation on the transcriptional program and function of CD8 T cells

Krüppel-like factor 2 (KLF2) is a transcription factor that is highly expressed in quiescent T lymphocytes and downregulated in effector T cells. We now show that antigen receptor engagement downregulates KLF2 expression in a graded response determined by the affinity of T cell antigen receptor (TCR) ligand and the integrated activation of protein kinase B and the MAP kinases ERK1/2. The present study explores the importance of KLF2 downregulation and reveals that the loss of KLF2 controls a select portion of the CD8 effector T cell transcriptional program. In particular, KLF2 loss is required for CD8 T cells to express the inflammatory chemokine receptor CXCR3 and for maximum clonal expansion of T cells. KLF2 thus negatively controls the ability of CD8 T cells to respond to the CXCR3 ligand CXCL10. Strikingly, the KLF2 threshold for restraining expression of CXCR3 is very low and quite distinct to the KLF2 threshold for restraining T cell proliferation. KLF2 is thus an analogue (tunable) not a digital (on/off) cellular switch where the magnitude of KLF2 expression differentially modifies the T cell responses.

Molecular cloning and characterization of two 12 kDa FK506-binding protein genes in the Chinese oak silkworm, Antheraea pernyi

Two 12 kDa FK506-binding protein (FKBP12) genes were isolated and characterized from Chinese oak silkworm Antheraea pernyi , an important agricultural and edible insect, designated ApFKBP12 A and B, respectively. Both ApFKBP12 A and B contained 108 amino acids with 82% sequence identity. Phylogenetic analysis showed that FKBP12 B sequences of A. pernyi, Bombyx mori , and Danaus plexippus were clearly separated from FKBP12 A sequences of these three species, suggesting that insect FKBP12 A and B may have been evolving independently. RT-PCR analyses revealed that two ApFKBP12 genes were expressed during the four developmental stages and in all tested tissues, and that the mRNA expression level of the ApFKBP12 A gene was significantly higher than that of the ApFKBP12 B gene. After heat shock treatment, expressions of the two FKBP12 genes were up-regulated, but at different time points. The results suggested that each paralogue of the FKBP12 genes may play a distinct functional role in the development of A. pernyi.

Large FK506-binding proteins shape the pharmacology of rapamycin

The immunosuppressant and anticancer drug rapamycin works by inducing inhibitory protein complexes with the kinase mTOR, an important regulator of growth and proliferation. The obligatory accessory partner of rapamycin is believed to be FK506-binding protein 12 (FKBP12). Here we show that rapamycin complexes of larger FKBP family members can tightly bind to mTOR and potently inhibit its kinase activity. Cocrystal structures with FKBP51 and FKBP52 reveal the modified molecular binding mode of these alternative ternary complexes in detail. In cellular model systems, FKBP12 can be functionally replaced by larger FKBPs. When the rapamycin dosage is limiting, mTOR inhibition of S6K phosphorylation can be enhanced by FKBP51 overexpression in mammalian cells, whereas FKBP12 is dispensable. FKBP51 could also enable the rapamycin-induced hyperphosphorylation of Akt, which depended on higher FKBP levels than rapamycin-induced inhibition of S6K phosphorylation. These insights provide a mechanistic rationale for preferential mTOR inhibition in specific cell or tissue types by engaging specific FKBP homologs.

Evolution of the 12 kDa FK506-binding protein gene

BACKGROUND INFORMATION

The FKBPs (FK506-binding proteins) belong to a ubiquitous family of proteins that are found in a wide range of taxonomic groups. These proteins participate in a variety of pathways, including protein folding, down-regulation of T-cell activation and inhibition of cell-cycle progression.

RESULTS

A cDNA encoding the 12 kDa FKBP gene orthologue (FKBP12) in Bombyx mori was been isolated from both Bm-5 cultured cells and silk-gland tissue. Using the FKBP12 cDNA in combination with the B. mori 6x whole-genome shotgun database, we were able to identify the FKBP12 gene, as well as the positions of its intron-exon junctions.

CONCLUSIONS

FKBP12 exon sizes and intronic positions are highly conserved among FKBP12 orthologues in 24 diverse genomes. Comparison of 41 FKBP12 genes revealed several intronic insertion and deletion events throughout evolution. In addition, paralogous FKBP12 isoforms were identified in all 12 vertebrate genomes. Both structural and phylogenetics analyses suggest that the isoforms may be evolving independently, possibly due to the distinct functional roles played by each paralogue.

Distinctive in vitro effects of T-cell growth cytokines on cytomegalovirus-stimulated T-cell responses of HIV-infected HAART recipients

Functional immune reconstitution is limited after HAART, maintaining the interest in adjunctive immune-modulators. We compared in vitro the effects of the gamma-chain T-cell growth cytokines IL-2, IL-4, IL-7 and IL-15 on cytomegalovirus-stimulated cell-mediated immunity. IL-2 and IL-15 increased cytomegalovirus-specific lymphocyte proliferation in HAART recipients, whereas IL-4 and IL-7 did not. The boosting effect of IL-2 and IL-15 on proliferation correlated with their ability to prevent late apoptosis. However, IL-2 increased the frequency of cells in early apoptosis, whereas IL-15 increased the frequency of fully viable cells. Both IL-2 and IL-15 increased cytomegalovirus-induced CD4+ and CD8+ T-cell proliferation and the synthesis of Th1 and pro-inflammatory cytokines and chemokines. However, only IL-2 increased the frequency of regulatory T cells and Th2 cytokine production, both of which have the potential to attenuate antiviral immune responses. Overall, compared to other gamma-chain cytokines, IL-15 had the most favorable profile for boosting antiviral cell-mediated immunity.

Interleukin 2: from immunostimulation to immunoregulation and back again

Interleukin 2 (IL-2) was one of the first cytokines to be discovered. However, the complex role of IL-2 and its receptor in the regulation of immune responses is only now emerging. This review explores the various signals triggered by IL-2 and discusses their translation into biological function. A model is outlined that accommodates the seemingly contradictory functions of IL-2, and explains how one cytokine can be an essential T-cell growth and differentiation factor and yet also be indispensable to maintain peripheral tolerance.

NK cell survival mediated through the regulatory synapse with human DCs requires IL-15Ralpha

DCs activate NK cells during innate immune responses to viral infections. However, the composition and kinetics of the immunological synapse mediating this interaction are largely unknown. Here, we report the rapid formation of an immunological synapse between human resting NK cells and mature DCs. Although inhibitory NK cell receptors were polarized to this synapse, where they are known to protect mature DCs from NK cell lysis, the NK cell also received activation signals that induced mobilization of intracellular calcium and CD69 upregulation. The high-affinity component of the receptor for IL-15, IL-15Ralpha, accumulated at the synapse center on NK cells, and blocking of IL-15Ralpha increased NK cell apoptosis and diminished NK cell survival during their interaction with DCs. Furthermore, IL-15Ralpha-deficient NK cells, obtained from donors with a history of infectious mononucleosis, showed diminished survival in culture with DCs. Synapse formation was required for IL-15Ralpha-mediated NK cell survival, because synapse disruption by adhesion molecule blocking decreased DC-induced NK cell survival. These results identify what we believe to be a novel regulatory NK cell synapse with hallmarks of spatially separated inhibitory and activating interactions at its center. We suggest that this synapse formation enables optimal NK cell activation by DCs during innate immune responses.

TGF-beta inhibits IL-2 production and promotes cell cycle arrest in TCR-activated effector/memory T cells in the presence of sustained TCR signal transduction

TGF-beta signaling is critical for controlling naive T cell homeostasis and differentiation; however, the biological and biochemical changes induced by TGF-beta in effector/memory T cells are poorly defined. We show that although TGF-beta inhibits effector/memory peripheral blood T lymphoblast proliferation and IL-2 production, the intensity and kinetics for TCR-induced global tyrosine phosphorylation are markedly increased compared with that in untreated cells or naive T cells. After TCR ligation, tyrosine phosphorylation of proximal tyrosine kinases and docking proteins like linker for activation of T cells is maintained for >30 min in TGF-beta-primed cells compared with untreated cells where phosphorylation of these targets returned to basal levels by 10 min. Extended phosphorylation of linker for activation of T cells in treated peripheral blood T selectively prolongs ERK 1/2 signaling and phospholipase C-gamma1 activation leading to increased Ca(2+) flux. A kinase/phosphatase imbalance could not account for extended phosphorylation as CD45R, SHP-1, and SHP-2 expression remains unaltered. The contradiction between prolonged signal transduction and inhibition of proliferation is partially explained by the observation that TGF-beta priming results in ERK 1/2-independent p21 induction and decreased cyclin D1 expression leading to accumulation of T cells in G(0)/G(1) phases of the cell cycle and cell cycle arrest. Despite inhibition of T cell function by TGF-beta priming, TCR and cytokine signaling pathways are intact and selectively extended, suggesting that suppression in the effector/memory T cell is mediated by reprogramming signal transduction, rather than its inhibition as in the naive T cell.

Common gamma chain cytokines: dissidence in the details

Cytokines of the common cytokine-receptor gamma-chain (gamma(c)) family are essential for the development and maintenance of lymphocytes. Herein, we will focus on the roles of interleukin-2 (IL-2), IL-7, IL-15 and IL-21, in the orchestration of CD8 T cell responses. Among these cytokines, IL-7 has emerged as a master regulator of survival of immature and mature T lymphocytes, while IL-2, IL-15 and IL-21 appear to have specific functions in T cell homeostasis and differentiation. Hence, the gamma(c) has evolved as an elegant anchor through which related cytokines regulate distinct biological responses in T cells.

The biology of interleukin-2 and interleukin-15: implications for cancer therapy and vaccine design

Interleukin-2 and interleukin-15 have pivotal roles in the control of the life and death of lymphocytes. Although their heterotrimeric receptors have two receptor subunits in common, these two cytokines have contrasting roles in adaptive immune responses. The unique role of interleukin-2 is in the elimination of self-reactive T cells to prevent autoimmunity. By contrast, interleukin-15 is dedicated to the prolonged maintenance of memory T-cell responses to invading pathogens. As discussed in this Review, the biology of these cytokines will affect the development of novel therapies for malignancy and autoimmune diseases, as well as the design of vaccines against infectious diseases.

Differential regulation of T-cell growth by IL-2 and IL-15

Although interleukin 2 (IL-2) and IL-15 signal through the common gamma chain (γc) and through IL-2 receptor β–chain (CD122) subunits, they direct distinct physiologic and immunotherapeutic responses in T cells. The present study provides some insight into why IL-2 and IL-15 differentially regulate T-cell function by revealing that these cytokines are strikingly distinct in their ability to control protein synthesis and T-cell mass. IL-2 and IL-15 are shown to be equivalent mitogens for antigen-stimulated CD8+ T cells but not for equivalent growth factors. Antigen-primed T cells cannot autonomously maintain amino acid incorporation or de novo protein synthesis without exogenous cytokine stimulation. Both IL-2 and IL-15 induce amino acid uptake and protein synthesis in antigen-activated T cells; however, the IL-2 response is strikingly more potent than the IL-15 response. The differential action of IL-2 and IL-15 on amino acid uptake and protein synthesis is explained by temporal differences in signaling induced by these 2 cytokines. Hence, the present results show that cytokines that are equivalent mitogens can have different potency in terms of regulating protein synthesis and cell growth.

Profiling humoral autoimmune repertoire of dilated cardiomyopathy (DCM) patients and development of a disease-associated protein chip

Dilated cardiomyopathy (DCM) is a myocardial disease characterized by progressive depression of myocardial contractile function and ventricular dilatation. Thirty percent of DCM patients belong to the inherited genetic form; the rest may be idiopathic, viral, autoimmune, or immune-mediated associated with a viral infection. Disturbances in humoral and cellular immunity have been described in cases of myocarditis and DCM. A number of autoantibodies against cardiac cell proteins have been identified in DCM. In this study, we have profiled the autoantibody repertoire of plasma from DCM patients against a human protein array consisting of 37,200 redundant, recombinant human proteins and performed qualitative and quantitative validation of these putative autoantigens on protein microarrays to identify novel putative DCM specific autoantigens. In addition to analyzing the whole IgG autoantibody repertoire, we have also analyzed the IgG3 antibody repertoire in the plasma samples to study the characteristics of IgG3 subclass antibodies. By combining screening of a protein expression library with protein microarray technology, we have detected 26 proteins identified by the IgG antibody repertoire and 6 proteins bound by the IgG3 subclass. Several of these autoantibodies found in plasma of DCM patients, such as the autoantibody against the Kv channel-interacting protein, are associated with heart failure.

High-affinity CD25-binding IL-2 mutants potently stimulate persistent T cell growth

We have used directed evolution to construct IL-2 mutants that bind the IL-2 alpha receptor subunit (IL-2Ralpha, CD25) with affinities comparable to that of the IL-15-IL-15 alpha receptor subunit (IL-15Ralpha) interaction. T cells proliferate for up to 6 days following a 30 minute incubation with these IL-2 mutants, which may lead to potential applications for cancer and viral immunotherapy. Several alternative mechanisms have been proposed to explain the contrasting effects of IL-2 and IL-15 on T cell proliferation and death. These IL-2 mutants exhibit T cell growth response-receptor occupancy curves indistinguishable from that for IL-15, suggesting that much of the difference between wild-type IL-2 and IL-15 effects arises simply from their 1000-fold differing affinities for their private alpha receptor subunits.

Inducing P-selectin ligand formation in CD8 T cells: IL-2 and IL-12 are active in vitro but not required in vivo

In vitro studies have demonstrated that IL-2 and IL-12 can support formation of P-selectin ligands (P-SelL) in activated T cells, ligands that are variably required for efficient lymphocyte recruitment to sites of inflammation. To ascertain whether these cytokines were required for P-SelL formation in vivo, TCR transgenic CD8 T cells specific for male Ag (HY) were transferred into male mice under conditions in which either IL-2 and/or IL-15 or IL-12Rp40 were absent. P-SelL formation at day 2 was unperturbed in HY-TCR IL-2(null) CD8 T cells responding in doubly deficient IL-2(null)IL-12(null) or IL-2(null)IL-15(null) male recipients. HY-specific CD8 T cell proliferative responses detected in both spleen and peritoneum occurred vigorously, but only splenic CD8 T cells up-regulated P-SelL, demonstrating that in vivo induction of P-SelL is an active, nonprogrammed event following T cell activation and that despite the efficacy of IL-2 and IL-12 in supporting P-SelL formation in vitro, these cytokines appear to be dispensable for this purpose in vivo.

Rapamycin ameliorates proteinuria-associated tubulointerstitial inflammation and fibrosis in experimental membranous nephropathy

Proteinuria is a risk factor for progression of chronic renal failure. A model of proteinuria-associated tubulointerstitial injury was developed and was used to examine the therapeutic effect of rapamycin. Two studies were performed. In study A, proteinuric rats were given sheep anti-Fx1A to induce experimental membranous nephropathy; control rats received normal sheep serum. Four weeks later, groups were subdivided and underwent laparotomy alone (two kidneys), nephrectomy alone (one kidney), or nephrectomy with polectomy (0.6 kidney). Renal function and morphology were evaluated 4 wk later. Whereas control rats never developed proteinuria, anti-Fx1A induced severe proteinuria. Proteinuria was unaffected by renal mass reduction. Proteinuric rats developed tubulointerstitial disease that was most severe in rats with 0.6 kidneys. Renal function (GFR) was reduced by loss of renal mass and was reduced further in proteinuric rats with 0.6 kidneys. In study B, the effect of rapamycin on the expression of candidate proinflammatory and profibrotic genes and the progression of proteinuria-associated renal disease were examined. All rats received an injection of anti-Fx1A and were nephrectomized and then divided into groups to receive rapamycin or vehicle. Gene expression, renal morphology, and GFR were evaluated after 4, 8, and 12 wk. Rapamycin reduced expression of the proinflammatory and profibrotic genes (monocyte chemotactic protein-1, vascular endothelial growth factor, PDGF, TGF-beta(1), and type 1 collagen). Tubulointerstitial inflammation and progression of interstitial fibrosis that were present in vehicle-treated rats were ameliorated by rapamycin. Rapamycin also completely inhibited compensatory renal hypertrophy. In summary, rapamycin ameliorates the tubulointerstitial disease associated with chronic proteinuria and loss of renal mass.

IL-2 and IL-15 receptor alpha-subunits are coexpressed in a supramolecular receptor cluster in lipid rafts of T cells

The private alpha-chains of IL-2 and IL-15 receptors (IL-2R and IL-15R) share the signaling beta- and gamma(c)-subunits, resulting in both common and contrasting roles of IL-2 and IL-15 in T cell function. Knowledge of the cytokine-dependent subunit assembly is indispensable for understanding the paradox of distinct signaling capacities. By using fluorescence resonance energy transfer and confocal microscopy, we have shown that IL-2R alpha, IL-15R alpha, IL-2/15R beta and gamma(c)-subunits, as well as MHC class I and II glycoproteins formed supramolecular receptor clusters in lipid rafts of the T lymphoma line Kit 225 FT7.10. Fluorescence crosscorrelation microscopy demonstrated the comobility of IL-15R alpha with IL-2R alpha and MHC class I. A model was generated for subunit switching between IL-2R alpha and IL-15R alpha upon the binding of the appropriate cytokine resulting in the formation of high-affinity heterotrimeric receptors. This model suggests a direct role for the alpha-subunits, to which no definite function has been assigned so far, in tuning cellular responses to IL-2 or IL-15. In addition, both alpha-chains were at least partially homodimerized/oligomerized, which could be the basis of distinct signaling pathways by the two cytokines.