Interleukin‐21 (IL‐21) synergizes with IL‐2 to enhance T‐cell receptor‐induced human T‐cell proliferation and counteracts IL‐2/transforming growth factor‐β‐induced regulatory T‐cell development

Interleukin‐2 (IL‐2) is a mainstay for current immunotherapeutic protocols but its usefulness in patients is reduced by severe toxicities and because IL‐2 facilitates regulatory T (Treg) cell development. IL‐21 is a type I cytokine acting as a potent T‐cell co‐mitogen but less efficient than IL‐2 in sustaining T‐cell proliferation. Using various in vitro models for T‐cell receptor (TCR)‐dependent human T‐cell proliferation, we found that IL‐21 synergized with IL‐2 to make CD4⁺ and CD8⁺ T cells attain a level of expansion that was impossible to obtain with IL‐2 alone. Synergy was mostly evident in naive CD4⁺ cells. IL‐2 and tumour‐released transforming growth factor‐β (TGF‐β) are the main environmental cues that cooperate in Treg cell induction in tumour patients. Interleukin‐21 hampered Treg cell expansion induced by IL‐2/TGF‐β combination in naive CD4⁺ cells by facilitating non‐Treg over Treg cell proliferation from the early phases of cell activation. Conversely, IL‐21 did not modulate the conversion of naive activated CD4⁺ cells into Treg cells in the absence of cell division. Treg cell reduction was related to persistent activation of Stat3, a negative regulator of Treg cells associated with down‐modulation of IL‐2/TGF‐β‐induced phosphorylation of Smad2/3, a positive regulator of Treg cells. In contrast to previous studies, IL‐21 was completely ineffective in counteracting the suppressive activity of Treg cells on naive and memory, CD4⁺ and CD8⁺ T cells. Present data provide proof‐of‐concept for evaluating a combinatorial approach that would reduce the IL‐2 needed to sustain T‐cell proliferation efficiently, thereby reducing toxicity and controlling a tolerizing mechanism responsible for the contraction of the T‐cell response.     

Expansion of regulatory T cells via IL‐2/anti‐IL‐2 mAb complexes suppresses experimental myasthenia

Human autoimmune diseases are often characterized by a relative deficiency in CD4⁺CD25⁺ regulatory T cells (Treg). We therefore hypothesized that expansion of Treg can ameliorate autoimmune pathology. We tested this hypothesis in an experimental model for autoimmune myasthenia gravis (MG), a B‐cell‐mediated disease characterized by auto‐Ab directed against the acetylcholine receptor within neuromuscular junctions. We showed that injection of immune complexes composed of the cytokine IL‐2 and anti‐IL‐2 mAb (JES6‐1A12) induced an effective and sustained expansion of Treg, via peripheral proliferation of CD4⁺CD25⁺Foxp3⁺ cells and peripheral conversion of CD4⁺CD25^?Foxp3^? cells. The expanded Treg potently suppressed autoreactive T‐ and B‐cell responses to acetylcholine receptor and attenuated the muscular weakness that is characteristic of MG. Thus, IL‐2/anti‐IL‐2 mAb complexes can expand functional Treg in vivo, providing a potential clinical application of this modality for treatment of MG and other autoimmune disorders.     

Anti‐CD25 monoclonal antibody Fc variants differentially impact regulatory T cells and immune homeostasis

Interleukin‐2 (IL‐2) is a critical regulator of immune homeostasis through its non‐redundant role in regulatory T (Treg) cell biology. There is major interest in therapeutic modulation of the IL‐2 pathway to promote immune activation in the context of tumour immunotherapy or to enhance immune suppression in the context of transplantation, autoimmunity and inflammatory diseases. Antibody‐mediated targeting of the high‐affinity IL‐2 receptor α chain (IL‐2Rα or CD25) offers a direct mechanism to target IL‐2 biology and is being actively explored in the clinic. In mouse models, the rat anti‐mouse CD25 clone PC61 has been used extensively to investigate the biology of IL‐2 and Treg cells; however, there has been controversy and conflicting data on the exact in vivo mechanistic function of PC61. Engineering antibodies to alter Fc/Fc receptor interactions can significantly alter their in vivo function. In this study, we re‐engineered the heavy chain constant region of an anti‐CD25 monoclonal antibody to generate variants with highly divergent Fc effector function. Using these anti‐CD25 Fc variants in multiple mouse models, we investigated the in vivo impact of CD25 blockade versus depletion of CD25⁺ Treg cells on immune homeostasis. We report that immune homeostasis can be maintained during CD25 blockade but aberrant T‐cell activation prevails when CD25⁺ Treg cells are actively depleted. These results clarify the impact of PC61 on Treg cell biology and reveal an important distinction between CD25 blockade and depletion of CD25⁺ Treg cells. These findings should inform therapeutic manipulation of the IL‐2 pathway by targeting the high‐affinity IL‐2R.     

Induced regulatory T cells are phenotypically unstable and do not protect mice from rapidly progressive glomerulonephritis

Regulatory T (Treg) cells are a suppressive CD4⁺ T‐cell subset. We generated induced Treg (iTreg) cells and explored their therapeutic potential in a murine model of rapidly progressive glomerulonephritis. Polyclonal naive CD4⁺ T cells were cultured in vitro with interleukin‐2 (IL‐2), transforming growth factor‐β1, all‐trans‐retinoic acid and monoclonal antibodies against interferon‐γ and IL‐4, generating Foxp3⁺ iTreg cells. To enhance their suppressive phenotype, iTreg cultures were modified with the addition of a monoclonal antibody against IL‐12p40 or by using RORγt^–/– CD4⁺ T cells. Induced Treg cells were transferred into models of delayed‐type hypersensitivity and experimental glomerulonephritis. The iTreg cells exhibited comparable surface receptor expression and in vitro suppressive ability to natural Treg cells, but did not regulate antigen‐specific delayed‐type hypersensitivity or systemic inflammatory immune responses, losing Foxp3 expression in vivo. In glomerulonephritis, transferred iTreg cells did not prevent renal injury or modulate systemic T helper type 1 immune responses. Induced Treg cells cultured with anti‐IL‐12p40 had an enhanced suppressive phenotype in vitro and regulated dermal delayed‐type hypersensitivity in vivo, but were not protective against renal injury, losing Foxp3 expression, especially in the transferred cells recruited to the kidney. Use of RORγt^–/– CD4⁺ T cells or iTreg cells generated from sensitized CD4⁺ Foxp3^– cells did not regulate renal or systemic inflammatory responses in vivo. In conclusion, iTreg cells suppress T‐cell proliferation in vitro, but do not regulate experimental glomerulonephritis, being unstable in this inflammatory milieu in vivo.     

Influenza matrix 1‐specific human CD4+FOXP3+ and FOXP3− regulatory T cells can be detected long after viral clearance

Control and termination of infection with Influenza A virus is associated with increased IL‐10 production in mouse models. Notably, IL‐10 can be produced by Treg. Therefore, we investigated whether the population of IL‐10‐producing influenza‐specific CD4⁺ T cells comprised Treg as they are potent suppressors of the adaptive immune response. Influenza‐specific IL‐10‐producing T cells were detected in all human donors displaying influenza‐specific immunity. Isolation of Matrix 1 protein‐specific IL‐10‐producing T‐cell clones revealed that a substantial proportion of these T‐cell clones displayed the capacity to suppress effector cells, functionally identifying them as Treg. Both FOXP3⁺ and FOXP3^? CD4⁺ Treg were isolated and all were able to exert their suppressive capacity when stimulated with cognate antigen, including influenza virus‐infected cells. In vitro suppression was not mediated by IL‐10 but involved interference with the IL‐2 axis. The isolated Treg suppressed amongst others the IL‐2 production of influenza‐specific T‐helper cells as well as partially prevented the upregulation of the high‐affinity IL‐2 receptor on CD8 effector cells. So far the induction of virus‐specific Treg has only been studied in the context of chronic viral infections. This study demonstrates that virus‐specific Treg can also be induced by viruses that are rapidly cleared in humans.     

P21‐activated kinase 2 is essential in maintenance of peripheral Foxp3+ regulatory T cells

The p21‐activated kinase 2 (Pak2), an effector molecule of the Rho family GTPases Rac and Cdc42, regulates diverse functions of T cells. Previously, we showed that Pak2 is required for development and maturation of T cells in the thymus, including thymus‐derived regulatory T (Treg) cells. However, whether Pak2 is required for the functions of various subsets of peripheral T cells, such as naive CD4 and helper T‐cell subsets including Foxp3⁺ Treg cells, is unknown. To determine the role of Pak2 in CD4 T cells in the periphery, we generated inducible Pak2 knockout (KO) mice, in which Pak2 was deleted in CD4 T cells acutely by administration of tamoxifen. Temporal deletion of Pak2 greatly reduced the number of Foxp3⁺ Treg cells, while minimally affecting the homeostasis of naive CD4 T cells. Pak2 was required for proliferation and Foxp3 expression of Foxp3⁺ Treg cells upon T‐cell receptor and interleukin‐2 stimulation, differentiation of in vitro induced Treg cells, and activation of naive CD4 T cells. Together, Pak2 is essential in maintaining the peripheral Treg cell pool by providing proliferation and maintenance signals to Foxp3⁺ Treg cells.     

Inhibition of murine γδ lymphocyte expansion and effector function by regulatory αβ T cells is cell‐contact‐dependent and sensitive to GITR modulation

γδ T cells are highly cytolytic lymphocytes that produce large amounts of pro‐inflammatory cytokines during immune responses to multiple pathogens. Furthermore, their ability to kill tumor cells has fueled the development of γδ‐T‐cell‐based cancer therapies. Thus, the regulation of γδ‐T‐cell activity is of great biological and clinical relevance. Here, we show that murine CD4⁺CD25⁺ αβ T cells, the vast majority of which express the Treg marker, Foxp3, abolish key effector functions of γδ T cells, namely the production of the pro‐inflammatory cytokines, IFN‐γ and IL‐17, cytotoxicity, and lymphocyte proliferation in vitro and in vivo. We further show that suppression is dependent on cellular contact between Treg and γδ T cells, results in the induction of an anergic state in γδ lymphocytes, and can be partially reversed by manipulating glucocorticoid‐induced TNF receptor‐related protein (GITR) signals. Our data collectively dissect a novel mechanism by which the expansion and pro‐inflammatory functions of γδ T cells are regulated.     

IL‐12 and IL‐4 activate a CD39‐dependent intrinsic peripheral tolerance mechanism in CD8+ T cells

Immune responses to protein antigens involve CD4⁺ and CD8⁺ T cells, which follow distinct programs of differentiation. Naïve CD8 T cells rapidly develop cytotoxic T‐cell (CTL) activity after T‐cell receptor stimulation, and we have previously shown that this is accompanied by suppressive activity in the presence of specific cytokines, i.e. IL‐12 and IL‐4. Cytokine‐induced CD8⁺ regulatory T (Treg) cells are one of several Treg‐cell phenotypes and are Foxp3^? IL‐10⁺ with contact‐dependent suppressive capacity. Here, we show they also express high level CD39, an ecto‐nucleotidase that degrades extracellular ATP, and this contributes to their suppressive activity. CD39 expression was found to be upregulated on CD8⁺ T cells during peripheral tolerance induction in vivo, accompanied by release of IL‐12 and IL‐10. CD39 was also upregulated during respiratory tolerance induction to inhaled allergen and on tumor‐infiltrating CD8⁺ T cells. Production of IL‐10 and expression of CD39 by CD8⁺ T cells was independently regulated, being respectively blocked by extracellular ATP and enhanced by an A2A adenosine receptor agonist. Our results suggest that any CTL can develop suppressive activity when exposed to specific cytokines in the absence of alarmins. Thus negative feedback controls CTL expansion under regulation from both nucleotide and cytokine environment within tissues.     

Proliferation of weakly suppressive regulatory CD4+ T cells is associated with over‐active CD4+ T‐cell responses in HIV‐positive patients with mycobacterial immune restoration disease

The role of Treg in patients with late‐stage HIV disease, who commence combination antiretroviral therapy (cART) and develop pathogen‐specific immunopathology manifesting as immune restoration disease (IRD) remains unclear. We hypothesised that Treg could be defective in either numbers and/or function and therefore unable to ensure the physiological equilibrium of the immune system in patients with IRD. Phenotypic and functional CD4⁺ T‐cell subsets of eight late‐stage HIV patients with nadir CD4 count <50 cells/μL, who developed mycobacterial IRD upon commencing cART were compared with six therapy naive HIV⁺ patients (nadir CD4 count <50 cells/μL), who did not develop an IRD after cART. Mycobacterium‐avium‐specific CD4⁺ T cells from IRD patients produced high levels of IFN‐γ and IL‐2 compared with controls (p<0.001). Surprisingly, we found a significant expansion of CD127^loFoxp3⁺CD25⁺ Treg in IRD patients and a higher ratio of Treg to effector/memory subsets (p<0.001). In vitro suppression assays demonstrated reduced functional capacity of suppressor cells and diminished IL‐10 secretion in IRD patients. Plasma levels of IL‐7 were increased in patients and, interestingly, exogenous IL‐7 and other cytokines strongly inhibited Treg suppression. These data suggest that despite substantial Treg expansion in IRD, their ability to induce suppression, and thereby downregulate aberrant immune responses, is compromised.     

c‐Rel is crucial for the induction of Foxp3+ regulatory CD4+ T cells but not TH17 cells

The NF‐κB/Rel family member c‐Rel was described to be required for the development of T_H1 responses. However, the role of c‐Rel in the differentiation of T_H17 and regulatory CD4⁺Foxp3⁺ T cells (Treg) remains obscure. Here, we show that in the absence of c‐Rel, in vitro differentiation of pro‐inflammatory T_H17 cells is normal. In contrast, generation of inducible Treg (iTreg) within c‐Rel‐deficient CD4⁺ T cells was severely hampered and correlated to reduced numbers of Foxp3⁺ T cells in vivo. Mechanistically, in vitro conversion of naive CD4⁺ T cells into iTreg was crucially dependent on c‐Rel‐mediated synthesis of endogenous IL‐2. The addition of exogenous IL‐2 was sufficient to rescue the development of c‐Rel‐deficient iTreg. Thus, c‐Rel is essential for the development of Foxp3⁺ Treg but not for T_H17 cells via regulating the production of IL‐2.     

KLRG1 impairs regulatory T‐cell competitive fitness in the gut

Immune homeostasis requires the tight, tissue‐specific control of the different CD4⁺ Foxp3⁺ regulatory T (Treg) cell populations. The cadherin‐binding inhibitory receptor killer cell lectin‐like receptor G1 (KLRG1) is expressed by a subpopulation of Treg cells with GATA3⁺ effector phenotype. Although such Treg cells are important for the immune balance, especially in the gut, the role of KLRG1 in Treg cells has not been assessed. Using KLRG1 knockout mice, we found that KLRG1 deficiency does not affect Treg cell frequencies in spleen, mesenteric lymph nodes or intestine, or frequencies of GATA3⁺ Treg cells in the gut. KLRG1‐deficient Treg cells were also protective in a T‐cell transfer model of colitis. Hence, KLRG1 is not essential for the development or activity of the general Treg cell population. We then checked the effects of KLRG1 on Treg cell activation. In line with KLRG1's reported inhibitory activity, in vitro KLRG1 cross‐linking dampened the Treg cell T‐cell receptor response. Consistently, lack of KLRG1 on Treg cells conferred on them a competitive advantage in the gut, but not in lymphoid organs. Hence, although absence of KLRG1 is not enough to increase intestinal Treg cells in KLRG1 knockout mice, KLRG1 ligation reduces T‐cell receptor signals and the competitive fitness of individual Treg cells in the intestine.     

Targeted therapy to the IL‐2R using diphtheria toxin and caspase‐3 fusion proteins modulates Treg and ameliorates inflammatory colitis

Pathogenic lymphocytes in the enteric wall of inflammatory bowel disease patients display various abnormalities, including reduced sensitivity to apoptosis. We evaluated a therapeutic approach to elimination of cytotoxic cells, using two IL‐2 fusion proteins, a diphtheria toxin (IL2‐DT) and a caspase‐3 (IL2‐cas) conjugate. In models of acute (dextran sodium sulfate and trinitrobenzene sulfonic acid) and chronic (dextran sodium sulfate) toxic colitis, therapeutic doses of the fusion proteins improved survival and prevented colon shortening. While both chimeric proteins eradicated CD4⁺CD25⁺Foxp3⁺ T cells in mesenteric LN, IL2‐DT caused severe lymphopenia. In contrast, IL2‐cas was equally protective and increased fractional expression of Foxp3. Similar effects of the fusion proteins were observed in healthy mice: IL2‐DT caused lymphopenia and IL2‐cas increased fractional expression of FoxP3. The fusion proteins induced apoptosis in CD25⁺ T cells in vitro, with lower toxicity of IL2‐cas to Foxp3⁺ T cells. These data infer that targeted depletion of cells expressing the IL‐2 receptor has therapeutic potential in models of inflammatory colitis, despite depletion of CD25⁺ Treg. The IL2‐cas fusion protein is particularly relevant to inflammatory bowel disease, as direct internalization of toxic moieties overcomes multiple pathways of resistance to apoptosis of colitogenic T cells.     

CTLA‐4 is required by CD4+CD25+ Treg to control CD4+ T‐cell lymphopenia‐induced proliferation

CTLA‐4 is constitutively expressed by CD4⁺CD25⁺Foxp3⁺ Treg but its precise role in Treg function is not clear. Although blockade of CTLA‐4 interferes with Treg function, studies using CTLA‐4‐deficient Treg have failed to reveal an essential requirement for CTLA‐4 in Treg suppression in vivo. Conditional deletion of CTLA‐4 in Foxp3⁺ T cells disrupts immune homeostasis in vivo but the immune processes disrupted by CTLA‐4 deletion have not been determined. We demonstrate that Treg expression of CTLA‐4 is essential for Treg control of lymphopenia‐induced CD4 T‐cell expansion. Despite IL‐10 expression, CTLA‐4‐deficient Treg were unable to control the expansion of CD4⁺ target cells in a lymphopenic environment. Moreover, unlike their WT counterparts, CTLA‐4‐deficient Treg failed to inhibit cytokine production associated with homeostatic expansion and were unable to prevent colitis. Thus, while Treg developing in the absence of CTLA‐4 appear to acquire some compensatory suppressive mechanisms in vitro, we identify a non‐redundant role for CTLA‐4 in Treg function in vivo.     

Mesenchymal Stem Cells Overexpressing Interleukin‐35 Propagate Immunosuppressive Effects in Mice

To explore generation of interleukin (IL)‐35‐expressing mouse adipocyte‐derived mesenchymal stem cells (Ad‐MSCs) using lentiviral vector and their potential immunosuppressive effects in mice. Ad‐MSCs were isolated and cultured in vitro and transfected with a lentivirus vector for overexpression of the therapeutic murine IL‐35 gene. IL‐35 expression in transfected MSCs (IL‐35‐MSCs) was quantified by enzyme‐linked immunosorbent assay (ELISA). The lymphocytes subsets after one‐way mixed lymphocyte culture and in vivo intravenous transplantation were analysed by flow cytometry to evaluate the immunosuppressive effects of IL‐35‐MSCs. ELISA was performed to examine IL‐10, IL‐17A and IL‐35 expression in lymphocyte culture. Mouse Ad‐MSCs were isolated and cultured. IL‐35 was expressed in the MSC supernatant and serum after IL‐35 transduction into Ad‐MSCs by lentiviral vector transfection in vitro and in vivo. The percentage of CD4⁺ CD25⁺ T regulatory (Treg) cells in mice treated with IL‐35‐MSCs significantly increased. IL‐35‐MSCs upregulated the CD4⁺ CD25⁺ Treg cells in the allogeneic mixed lymphocyte reaction system, and lowered the percentage of CD4⁺ T cells compared with the other two control groups (P < 0.01). IL‐17A expression significantly decreased and IL‐10 expression significantly increased in IL‐35‐MSCs and MSCs when compared by ELISA to the control groups (P < 0.01). IL‐35‐transduced Ad‐MSCs in vivo can enhance proliferation of CD4⁺ CD25⁺ Treg cells and suppress the function of effector T cells such as T helper (Th) 1, Th2 and Th17 cells and may reduce the development of allograft rejection. Our data suggest that transduced Ad‐MSCs overexpressing IL‐35 may provide a useful approach for basic research on cell‐based immunotolerance therapy for inducing transplantation tolerance.     

Control of Schistosoma mansoni egg‐induced inflammation by IL‐4‐responsive CD4+CD25−CD103+Foxp3− cells is IL‐10‐dependent

Host protection to helminth infection requires IL‐4 receptor α chain (IL‐4Rα) signalling and the establishment of finely regulated Th2 responses. In the current study, the role of IL‐4Rα‐responsive T cells in Schistosoma mansoni egg‐induced inflammation was investigated. Egg‐induced inflammation in IL‐4Rα‐responsive BALB/c mice was accompanied with Th2‐biased responses, whereas T‐cell‐specific IL‐4Rα‐deficient BALB/c mice (iLck^creIl4ra^?/lox) developed Th1‐biased responses with heightened inflammation. The proportion of Foxp3⁺ Treg in the draining LN of control mice did not correlate with the control of inflammation and was reduced in comparison to T‐cell‐specific IL‐4Rα‐deficient mice. This was due to IL‐4‐mediated inhibition of CD4⁺Foxp3⁺ Treg conversion, demonstrated in adoptively transferred Rag2^?/? mice. Interestingly, reduced footpad swelling in Il4ra^?/lox mice was associated with the induction of IL‐4 and IL‐10‐secreting CD4⁺CD25^?CD103⁺Foxp3^? cells, confirmed in S. mansoni infection studies. Transfer of IL‐4Rα‐responsive CD4⁺CD25^?CD103⁺ cells, but not CD4⁺CD25^high or CD4⁺CD25^?CD103^? cells, controlled inflammation in iLck^creIl4ra^?/lox mice. The control of inflammation depended on IL‐10, as transferred CD4⁺CD25^?CD103⁺ cells from IL‐10‐deficient mice were not able to effectively downregulate inflammation. Together, these results demonstrate that IL‐4 signalling in T cells inhibits Foxp3⁺ Treg in vivo and promotes CD4⁺CD25^?CD103⁺Foxp3^? cells that control S. mansoni egg‐induced inflammation via IL‐10.     

Curcumin induces the tolerogenic dendritic cell that promotes differentiation of intestine‐protective regulatory T cells

The gut is home to a large number of Treg, with both CD4⁺ CD25⁺ Treg and bacterial antigen‐specific Tr1 cells present in normal mouse intestinal lamina propria. It has been shown recently that intestinal mucosal DC are able to induce Foxp3⁺ Treg through production of TGF‐β plus retinoic acid (RA). However, the factors instructing DC toward this mucosal phenotype are currently unknown. Curcumin has been shown to possess a number of biologic activities including the inhibition of NF‐κB signaling. We asked whether curcumin could modulate DC to be tolerogenic whose function could mimic mucosal DC. We report here that curcumin modulated BM‐derived DC to express ALDH1a and IL‐10. These curcumin‐treated DC induced differentiation of naïve CD4⁺ T cells into Treg resembling Treg in the intestine, including both CD4⁺CD25⁺ Foxp3⁺ Treg and IL‐10‐producing Tr1 cells. Such Treg induction required IL‐10, TGF‐β and retinoic acid produced by curcumin‐modulated DC. Cell contact as well as IL‐10 and TGF‐β production were involved in the function of such induced Treg. More importantly, these Treg inhibited antigen‐specific T‐cell activation in vitro and inhibited colitis due to antigen‐specific pathogenic T cells in vivo.     

Membrane‐bound Dickkopf‐1 in Foxp3+ regulatory T cells suppresses T‐cell‐mediated autoimmune colitis

Induction of tolerance is a key mechanism to maintain or to restore immunological homeostasis. Here we show that Foxp3⁺ regulatory T (Treg) cells use Dickkopf‐1 (DKK‐1) to regulate T‐cell‐mediated tolerance in the T‐cell‐mediated autoimmune colitis model. Treg cells from DKK‐1 hypomorphic doubleridge mice failed to control CD4⁺ T‐cell proliferation, resulting in CD4 T‐cell‐mediated autoimmune colitis. Thymus‐derived Treg cells showed a robust expression of DKK‐1 but not in naive or effector CD4 T cells. DKK‐1 expression in Foxp3⁺ Treg cells was further increased upon T‐cell receptor stimulation in vitro and in vivo. Interestingly, Foxp3⁺ Treg cells expressed DKK‐1 in the cell membrane and the functional inhibition of DKK‐1 using DKK‐1 monoclonal antibody abrogated the suppressor function of Foxp3⁺ Treg cells. DKK‐1 expression was dependent on de novo protein synthesis and regulated by the mitogen‐activated protein kinase pathway but not by the canonical Wnt pathway. Taken together, our results highlight membrane‐bound DKK‐1 as a novel Treg‐derived mediator to maintain immunological tolerance in T‐cell‐mediated autoimmune colitis.     

IL‐7 is superior to IL‐2 for ex vivo expansion of tumour‐specific CD4+ T cells

It is well established that tumours hinder both natural and vaccine‐induced tumour‐specific CD4⁺ T‐cell responses. Adoptive T‐cell therapy has the potential to circumvent functional tolerance and enhance anti‐tumour protective responses. While protocols suitable for the expansion of cytotoxic CD8⁺ T cells are currently available, data on tumour‐specific CD4⁺ T cells remain scarce. We report here that CD4⁺ T cells sensitized to tumour‐associated Ag in vivo, proliferate in vitro in response to IL‐7 without the need for exogenous Ag stimulation and accumulate several folds while preserving a memory‐like phenotype. Both cell proliferation and survival accounts for the outgrowth of tumour‐sensitized T cells among other memory and naive lymphocytes following exposure to IL‐7. Also IL‐2, previously used to expand anti‐tumour CTL, promotes tumour‐specific CD4⁺ T‐cell accumulation. However, IL‐7 is superior to IL‐2 at preserving lymphocyte viability, in vitro and in vivo, maintaining those properties, that are required by helper CD4⁺ T cells to confer therapeutic efficacy upon transplantation in tumour‐bearing hosts. Together our data support a unique role for IL‐7 in retrieving memory‐like CD4⁺ T cells suitable for adoptive T‐cell therapy.