Interleukin-21 Induces Short-Lived Effector CD8+ T Cells but Does Not Inhibit Their Exhaustion after Mycobacterium bovis BCG Infection in Mice.

Interleukin 21 (IL-21) is a pleiotropic common cytokine receptor γ chain cytokine that promotes the effector functions of NK cells and CD8+ T cells and inhibits CD8+ T cell exhaustion during chronic infection. We found that the absolute number of short-lived effector CD8+ T cells (SLECs) (KLRG1high CD127low) decreased significantly in IL-21 receptor-deficient (IL-21R-/-) mice during Mycobacterium bovis bacillus Calmette-Guérin (BCG) infection. Early effector CD8+ T cells (EECs) (KLRG1low CD127low) were normally generated in IL-21R-/- mice after infection. Exhausted CD8+ T cells (PD-1high KLRG1low) were also normally generated in IL-21R-/- mice after infection. Mixed bone marrow (BM) chimera and transfer experiments showed that IL-21R on CD8+ T cells was essential for the proliferation of EECs, allowing them to differentiate into SLECs after BCG infection. On the other hand, the number of SLECs increased significantly after infection with recombinant BCG (rBCG) that secreted an antigen 85B (Ag85B)-IL-21 fusion protein (rBCG-Ag85B-IL-21), but the number of exhausted CD8+ T cells did not change after rBCG-Ag85B-IL-21 infection. These results suggest that IL-21 signaling drives the differentiation of SLECs from EECs but does not inhibit the exhaustion of CD8+ T cells following BCG infection in mice.

Autocrine IL-21 stimulation is involved in the maintenance of constitutive STAT3 activation in Sézary syndrome.

Sézary syndrome (SS) is a cutaneous T-cell lymphoma (CTCL) with malignant CD4+ T cells (SS cells) in skin, lymph nodes, and blood. Signal transducer and activator of transcription 3 (STAT3) is constitutively activated in SS cells, whereas this activation is lost upon in vitro culturing, indicating that STAT3 activation observed in vivo is the result of activating factors in the micromilieu of the malignant cells. We investigated which factors are involved in STAT3 activation in SS, focusing on cytokines of the common γ-chain family because of their crucial role in T-cell activation. Furthermore, downstream effects of STAT3 signaling in SS cells were assayed. In SS cells, STAT3 was strongly activated by IL-21, and increased expression of IL-21 and its receptor chains was observed in peripheral blood SS cells. IL-21 and IL-21R protein expression was detectable on neoplastic cells in SS skin biopsies. Using short-term culturing experiments, we demonstrate that IL-21 itself and the α-chain of the IL-2 receptor are STAT3 target genes in SS cells, thereby rendering cells more sensitive to stimulation with the T-cell proliferation and activating cytokine IL-2. Combined, our data point toward a pivotal role for an autocrine positive feedback loop involving IL-21 and consequent persistent STAT3 activation in the pathogenesis of SS, thereby indicating IL-21 and IL-21R as new therapeutical targets.

Interleukin-21 can efficiently restore impaired antibody-dependent cell-mediated cytotoxicity in patients with oesophageal squamous cell carcinoma.

BACKGROUND: We previously reported that Trastuzumab- and Cetuximab-mediated antibody-dependent cell-mediated cytotoxicity (ADCC) in cancer patients was impaired in comparison with that in healthy donors because of NK-cell dysfunction. In this study, we evaluated whether IL-21 could improve the impairment of ADCC in patients with oesophageal squamous cell carcinoma (ESCC), as IL-21 was reported to have the ability to activate NK cells. METHODS: We examined Trastuzumab- and Cetuximab-mediated ADCC of peripheral blood mononuclear cells (PBMCs) or of enriched NK cells derived from ESCC patients (n=20) and healthy donors (n=16) in the presence of IL-21. We further analysed ADCC-related molecules (perforin, granzyme-B, and CD247) on NK cells in response to IL-21. RESULTS: Trastuzumab- and Cetuximab-mediated ADCC of PBMCs or of enriched NK cells was enhanced by the addition of IL-21 in a dose-dependent manner and the levels of ADCC enhanced by IL-21 in patients were high enough in comparison with those in healthy donors, paralleling the upregulation of CD247 on NK cells. CONCLUSION: IL-21 could efficiently restore impaired ADCC in ESCC patients with the upregulation of CD247 molecules.

IL-21 is expressed in Hodgkin lymphoma and activates STAT5: evidence that activated STAT5 is required for Hodgkin lymphomagenesis.

Classical Hodgkin lymphoma (HL) is a malignant disorder characterized by the presence of neoplastic mononucleated Hodgkin and multinucleated Reed-Sternberg cells. Here, we show that both the interleukin (IL)-21 receptor as well as IL-21 are expressed by HL cells. IL-21 activates signal transducer of activation and transcription 3 (STAT3) and STAT5 in HL cell lines and activated human B cells. Ectopic expression of constitutively active STAT5 in primary human B cells resulted in immortalized B cells that have lost the B-cell phenotype and strongly resembled HL cells, which could partially be rescued by ectopic expression of the B cell-determining transcription factor E47. Data from experiments using reporter assays and overexpression of constitutively active IKK2 support the hypothesis that the STAT5 and nuclear factor-kappaB (NF-kappaB) pathways collaborate in HL genesis.

Kinetics of human B cell behavior and amplification of proliferative responses following stimulation with IL-21.

Although recent studies indicated that IL-21 is an important regulator of human B cell activation, detailed comparison of the effects of IL-21 on distinct B cell subsets have not been performed. Our studies revealed that IL-21R is expressed by naive and germinal center B cells, but not memory or plasma cells. IL-21R was increased on naive and memory B cells following in vitro activation. Investigation into the kinetics and magnitude of responses of human B cells to IL-21 revealed that IL-21 potently augmented proliferation of CD40L-stimulated neonatal, splenic naive, and memory and tonsil germinal center B cells. This response exceeded that induced by IL-4, IL-10, and IL-13, cytokines that also induce B cell proliferation. Remarkably, CD40L/IL-21-stimulated naive B cells underwent the same number of divisions as memory cells and exhibited a greater enhancement in their response compared with CD40L alone than memory B cells. Therefore, IL-21 is a powerful growth factor for naive B cells. This may result from the higher expression of IL-21R on naive, compared with memory, B cells. Stimulation of human B cells with CD40L/IL-21 also induced IL-10 production and activation of STAT3. We propose that IL-21 may have therapeutic application in conditions of immunodeficiency where it could expand naive B cells, the predominant B cell subset in such patients. Conversely, because IL-21 is increased in murine models of lupus, dysregulated IL-21 production may contribute to perturbed B cell homeostasis observed in systemic lupus erythematosus. Thus, antagonizing IL-21 may be a novel strategy for treating Ab-mediated autoimmune diseases.

Control of matrix metalloproteinase production in human intestinal fibroblasts by interleukin 21.

BACKGROUND: T cell-mediated immunity plays a central part in the pathogenesis of tissue damage in inflammatory bowel disease (IBD). The mechanism by which T cells mediate tissue damage during IBD remains unclear, but evidence indicates that T cell-derived cytokines stimulate fibroblasts to synthesise matrix metalloproteinases (MMPs), which then mediate mucosal degradation. We have previously shown that, in IBD, there is high production of interleukin (IL) 21, a T cell-derived cytokine, which enhances Th1 activity. AIM: To investigate whether IL21 controls MMP production by intestinal fibroblasts. METHODS: IL21 receptor (IL21R) was evaluated in intestinal fibroblasts by reverse transcriptase-polymerase chain reaction (RT-PCR) and western blotting. Fibroblasts were stimulated with IL21 and MMPs were evaluated by RT-PCR and western blotting. The effect of a neutralising IL21R fusion protein (IL21R/Fc) on the induction of MMPs in fibroblasts stimulated with IBD lamina propria mononuclear cell (LPMC) supernatants was also evaluated. RESULTS: Intestinal fibroblasts constitutively express both IL21R and the common gamma chain receptor, which are necessary for IL21-driven signalling. IL21 enhances fibroblast production of MMP-1, MMP-2, MMP-3 and MMP-9, but not tissue inhibitors of MMP-1 and MMP-2. Moreover, IL21 synergises with tumour necrosis factor alpha to increase synthesis of MMP synthesis. IL21 enhances MMP secretion without affecting gene transcription and protein synthesis. IBD LPMC supernatants stimulate MMP secretion by intestinal fibroblasts, and this effect is partly inhibited by IL21R/Fc. CONCLUSIONS: These results suggest that fibroblasts are a potential target of IL21 in the gut and that IL21 controls MMP secretion by fibroblasts.