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.     

Ex Vivo Expansion and Th1/Tc1 Maturation of Umbilical Cord Blood T Cells by CD3/CD28 Costimulation

One major limitation of UCBT is the lack of donor cells available for posttransplantation donor leukocyte infusions (DLI) to boost immunity or induce graft-versus-leukemia (GVL) activity. Starting from a ∼5% fraction of a UCB graft, we report the feasibility and biological characteristics of ex vivo expansion of frozen/thawed CB T cells by anti-CD3 and anti-CD28 antibody–coated Dynal beads in the presence of interleukin (IL)-2. We postulated that while undergoing expansion, UCB T cells may mature toward a Th1/Tc1 phenotype and acquire the potential for cytotoxicity. Whereas an almost 2-log expansion also led to the acquisition of IL-12Rα and an increase in Th1 characteristics, postexpansion lymphocytes produced less interferon-γ, tumor necrosis factor-α, and granzyme B; stored almost no perforin; and lacked cytotoxicity against allogeneic targets. Collectively, these suggest relative safety from acute/hyperacute graft-versus-host disease. CD8⁺ T cells expanded preferentially, whereas a higher rate of apoptosis in CD4⁺ T cells also promoted an inverted CD4/CD8 ratio. Most expanded T cells retained expression of CD27, CD28, and L-selectin but down-regulated CCR-7. In summary, UCB T cell proliferation sustained by CD3/CD28 co-stimulatory beads and IL-2 can lead to clinically relevant doses of DLI from a very small fraction of the UCB graft, although future strategies to reduce apoptosis may enhance their clinical potential.     

CD147 modulates the differentiation of T‐helper 17 cells in patients with rheumatoid arthritis

The role of CD147 in regulation of rheumatoid arthritis (RA) is not fully elucidated. The aim of this study was to investigate the effect of cell‐to‐cell contact of activated CD14⁺ monocytes with CD4⁺ T cells, and the modulatory role of CD147 on T‐helper 17 (Th17) cells differentiation in patients with RA. Twenty confirmed active RA patients and twenty normal controls were enrolled. CD4⁺ T cells and CD14⁺ monocytes were purified by magnetic beads cell sorting. Cells were cultured under different conditions in CD4⁺ T cells alone, direct cell‐to‐cell contact co‐culture of CD4⁺ and CD14⁺ cells, or indirect transwell co‐culture of CD4⁺/CD14⁺ cells in response to LPS and anti‐CD3 stimulation with or without anti‐CD147 antibody pretreatments. The proportion of IL‐17‐producing CD4⁺ T cells (defined as Th17 cells) was determined by flow cytometry. The levels of interleukin (IL)‐17, IL‐6, and IL‐1β in the supernatants of cultured cells were measured by ELISA. The optimal condition for in vitro induction of Th17 cells differentiation was co‐stimulation with 0.1 μg/mL of LPS and 100 ng/mL of anti‐CD3 for 3 days under direct cell‐to‐cell contact co‐culture of CD4⁺ and CD14⁺ cells. Anti‐CD147 antibody reduced the proportion of Th17 cells, and also inhibited the productions of IL‐17, IL‐6, and IL‐1β in PBMC culture from RA patients. The current results revealed that Th17 differentiation required cell‐to‐cell contact with activated monocytes. CD147 promoted the differentiation of Th17 cells by regulation of cytokine production, which provided the evidence for pathogenesis and potential therapeutic targets for RA.     

The Ex Vivo Induction of Human CD103+ CD25hi Foxp3+ CD4+ and CD8+ Tregs is IL‐2 and TGF‐β1 Dependent

The expression of the integrin αE (CD103), may enhance the retention of regulatory T cells to peripheral inflammatory sites and possibly contribute to their suppressive potential. The aim of this study was to define the regulatory role of IL‐2 and TGF‐β1 on the CD103 expression and the optimal in vitro conditions for the induction/expansion of human CD4⁺ and CD8⁺ Tregs. Cord blood mononuclear cells (CBMC) were stimulated under various culture conditions, including anti‐CD3, anti‐CD28, IL‐2 and TGF‐β1. TGF‐β1 and IL‐2 were both required for optimal expression of CD103. In addition, TGF‐β1 and IL‐2 synergistically induced CD103 expression on CD8⁺ T cells, whereas, only additive induced expression was noted on CD4⁺ T cells. Surprisingly, CD103 expression was not dependent upon CD28 costimulation. IL‐2 also played a central role in CD103 expression by CD25^hi Foxp3+ Tregs. IL‐2, TGF‐β1 and anti‐CD3 defined the optimal stimulatory conditions favouring the induction/expansion of both CD4⁺ and CD8⁺ human Tregs from naive CBMC. Thus, this study provides new insights into the regulatory role of IL‐2 upon CD103 expression by human cord blood CD4⁺ and CD8⁺ T cells. Furthermore, it identifies the in vitro culture conditions driving the differentiation of the novel phenotype CD4⁺ and CD8⁺ CD103⁺ CD25^hi Foxp3+ Tregs from human CBMC.     

Interleukin (IL)-21-independent pathogen-specific CD8+ T-cell expansion, and IL-21-dependent suppression of CD4+ T-cell IL-17 production

Although interleukin‐21 (IL‐21) potently activates and controls the differentiation of immune cells after stimulation in vitro, the role for this pleiotropic cytokine during in vivo infection remains poorly defined. Herein, the requirement for IL‐21 in innate and adaptive host defence after Listeria monocytogenes infection was examined. In the innate phase, IL‐21 deficiency did not cause significant defects in infection susceptibility, or in the early activation of natural killer and T cells. In the adaptive phase, L. monocytogenes‐specific CD8⁺ T cells expand to a similar magnitude in IL‐21‐deficient mice compared with control mice. Interestingly, the IL‐21‐independent expansion of L. monocytogenes‐specific CD8⁺ T cells was maintained even in the combined absence of IL‐12 and type I interferon (IFN) receptor. Similarly, L. monocytogenes‐specific CD4⁺ T cells expanded and produced similar levels of IFN‐γ regardless of IL‐21 deficiency. Unexpectedly however, IL‐21 deficiency caused significantly increased CD4⁺ T‐cell IL‐17 production, and this effect became even more pronounced after L. monocytogenes infection in mice with combined defects in both IL‐12 and type I IFN receptor that develop a T helper type 17‐dominated CD4⁺ T‐cell response. Despite increased CD4⁺ T‐cell IL‐17 production, L. monocytogenes‐specific T cells re‐expanded and conferred protection against secondary challenge with virulent L. monocytogenes regardless of IL‐21 deficiency, or combined defects in IL‐21, IL‐12, and type I IFN receptor. Together, these results demonstrate non‐essential individual and combined roles for IL‐21, IL‐12 and type I IFNs in priming pathogen‐specific CD8⁺ T cells, and reveal IL‐21‐dependent suppression of IL‐17 production by CD4⁺ T cells during in vivo infection.     

TRAF2 regulates peripheral CD8+ T‐cell and NKT‐cell homeostasis by modulating sensitivity to IL‐15

In this study, a critical and novel role for TNF receptor (TNFR) associated factor 2 (TRAF2) is elucidated for peripheral CD8⁺ T‐cell and NKT‐cell homeostasis. Mice deficient in TRAF2 only in their T cells (TRAF2TKO) show ∼40% reduction in effector memory and ∼50% reduction in naïve CD8⁺ T‐cell subsets. IL‐15‐dependent populations were reduced further, as TRAF2TKO mice displayed a marked ∼70% reduction in central memory CD8⁺CD44^hiCD122⁺ T cells and ∼80% decrease in NKT cells. TRAF2TKO CD8⁺CD44^hi T cells exhibited impaired dose‐dependent proliferation to exogenous IL‐15. In contrast, TRAF2TKO CD8⁺ T cells proliferated normally to anti‐CD3 and TRAF2TKO CD8⁺CD44^hi T cells exhibited normal proliferation to exogenous IL‐2. TRAF2TKO CD8⁺ T cells expressed normal levels of IL‐15‐associated receptors and possessed functional IL‐15‐mediated STAT5 phosphorylation, however TRAF2 deletion caused increased AKT activation. Loss of CD8⁺CD44^hiCD122⁺ and NKT cells was mechanistically linked to an inability to respond to IL‐15. The reduced CD8⁺CD44^hiCD122⁺ T‐cell and NKT‐cell populations in TRAF2TKO mice were rescued in the presence of high dose IL‐15 by IL‐15/IL‐15Rα complex administration. These studies demonstrate a critical role for TRAF2 in the maintenance of peripheral CD8⁺ CD44^hiCD122⁺ T‐cell and NKT‐cell homeostasis by modulating sensitivity to T‐cell intrinsic growth factors such as IL‐15.     

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.     

Interleukin‐4 downregulates CD127 expression and activity on human thymocytes and mature CD8+ T cells

Signaling via the IL‐7 receptor complex (IL‐7Rα/CD127 and IL‐2Rγ/CD132) is required for T‐cell development and survival. Decreased CD127 expression has been associated with persistent viral infections (e.g. HIV, HCV) and cancer. Many IL‐2Rγ‐sharing (γ_C) cytokines decrease CD127 expression on CD4⁺ and CD8⁺ T cells in mice (IL‐2, IL‐4, IL‐7, IL‐15) and in humans (IL‐2, IL‐7), suggesting a common function. IL‐4 is of particular interest as it is upregulated in HIV infection and in thyroid and colon cancers. The role of IL‐4 in regulating CD127 expression and IL‐7 activity in human thymocytes and mature CD8⁺ T cells is unknown and was therefore investigated. IL‐4 decreased CD127 expression on all thymocyte subsets tested and only on naïve (CD45RA⁺) CD8⁺ T cells, without altering membrane‐bound CD127 mRNA expression. Pre‐treatment of thymocytes or CD8⁺ T cells with IL‐4 inhibited IL‐7‐mediated phosphorylation of STAT5 and decreased proliferation of CD8⁺ T cells. By downregulating CD127 expression and signaling on developing thymocytes and CD8⁺ T cells, IL‐4 is a potential contributor to impaired CD8⁺ T‐cell function in some anti‐viral and anti‐tumor responses. These findings are of particular consequence to diseases such as HIV, HCV, RSV, measles and cancer, in which CD127 expression is decreased, IL‐7 activity is impaired and IL‐4 concentrations are elevated.     

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.     

Foxp3+ regulatory T cells are activated in spite of B7‐CD28 and CD40‐CD40L blockade

Costimulatory signals are required for priming and activation of naive T cells, while it is less clear how they contribute to induction of regulatory T (Treg)‐cell activity. We previously reported that the blockade of the B7‐CD28 and CD40L‐CD40 interaction efficiently suppresses allogeneic T‐cell activation in vivo. This was characterized by an initial rise in Foxp3⁺ cells, followed by depletion of host‐reactive T cells. To further investigate effects of costimulatory blockade on Treg cells, we used an in vitro model of allogeneic CD4⁺ cell activation. When CTLA‐4Ig and anti‐CD40L mAb (MR1) were added to the cultures, T‐cell proliferation and IL‐2 production were strongly reduced. However, Foxp3⁺ cells proliferated and acquired suppressive activity. They suppressed activation of syngeneic CD4⁺ cells much more efficiently than did freshly isolated Treg cells. CD4⁺ cells activated by allogeneic cells in the presence of MR1 and CTLA‐4Ig were hyporesponsive on restimulation, but their response was restored to that of naive CD4⁺ cells when Foxp3⁺ Treg cells were removed. We conclude that natural Treg cells are less dependent on B7‐CD28 or CD40‐CD40L costimulation compared with Foxp3^? T cells. Reduced costimulation therefore alters the balance between Teff and Treg‐cell activation in favor of Treg‐cell activity.     

Functional exhaustion of CD4+ T cells induced by co‐stimulatory signals from myeloid leukaemia cells

To cope with immune responses, tumour cells implement elaborate strategies such as adaptive resistance and induction of T‐cell exhaustion. T‐cell exhaustion has been identified as a state of hyporesponsiveness that arises under continuous antigenic stimulus. Nevertheless, contribution of co‐stimulatory molecules to T‐cell exhaustion in cancer remains to be better defined. This study explores the role of myeloid leukaemia‐derived co‐stimulatory signals on CD4⁺ T helper (Th) cell exhaustion, which may limit anti‐tumour immunity. Here, CD86 and inducible T‐cell co‐stimulator ligand (ICOS‐LG) co‐stimulatory molecules that are found on myeloid leukaemia cells supported Th cell activation and proliferation. However, under continuous stimulation, T cells co‐cultured with leukaemia cells, but not with peripheral blood monocytes, became functionally exhausted. These in vitro‐generated exhausted Th cells were defined by up‐regulation of programmed cell death 1 (PD‐1), cytotoxic T‐lymphocyte antigen 4 (CTLA‐4), lymphocyte activation gene 3 (LAG3) and T‐cell immunoglobulin and mucin domain‐containing protein 3 (TIM‐3) inhibitory receptors. They were reluctant to proliferate upon re‐stimulation and produced reduced amounts of interleukin‐2 (IL‐2), tumour necrosis factor‐α (TNF‐α) and interferon‐γ (IFN‐γ). Nonetheless, IL‐2 supplementation restored the proliferation capacity of the exhausted Th cells. When the co‐stimulation supplied by the myeloid leukaemia cells were blocked, the amount of exhausted Th cells was significantly decreased. Moreover, in the bone marrow aspirates from patients with acute myeloid leukaemia (AML) or myelodysplastic syndrome (MDS), a subpopulation of Th cells expressing PD‐1, TIM‐3 and/or LAG3 was identified together with CD86⁺ and/or ICOS‐LG⁺ myeloid blasts. Collectively, co‐stimulatory signals derived from myeloid leukaemia cells possess the capacity to facilitate functional exhaustion in Th cells.     

Selective depletion of CD11c+CD11b+ dendritic cells partially abrogates tolerogenic effects of intravenous MOG in murine EAE

Intravenous (i.v.) injection of a soluble myelin antigen can induce tolerance, which effectively ameliorates experimental autoimmune encephalomyelitis (EAE). We have previously shown that i.v. myelin oligodendrocyte glycoprotein (MOG) induces tolerance in EAE and expands a subpopulation of tolerogenic CD11c⁺CD11b⁺ dendritic cells (DCs) with an immature phenotype having low expression of IA and co‐stimulatory molecules CD40, CD86, and CD80. Here, we further investigate the role of tolerogenic DCs in i.v. tolerance by injecting clodronate‐loaded liposomes, which selectively deplete CD11c⁺CD11b⁺ and immature DCs, but not CD11c⁺CD8⁺ DCs and mature DCs. I.v. MOG‐induced suppression of EAE was partially, yet significantly, blocked by CD11c⁺CD11b⁺ DC depletion. While i.v. MOG inhibited IA, CD40, CD80, CD86 expression and induced TGF‐β, IL‐27, IL‐10 production in CD11c⁺CD11b⁺ DCs, these effects were abrogated after injection of clodronate‐loaded liposomes. Depletion of CD11c⁺CD11b⁺ DCs also precluded i.v. autoantigen‐induced T‐cell tolerance, such as decreased production of IL‐2, IFN‐γ, IL‐17 and numbers of IL‐2⁺, IFN‐γ⁺, and IL‐17⁺ CD4⁺ T cells, as well as an increased proportion of CD4⁺CD25⁺Foxp3⁺ regulatory T cells and CD4⁺IL‐10⁺Foxp3^? Tr1 cells. CD11c⁺CD11b⁺ DCs, through low expression of IA and costimulatory molecules as well as high expression of TGF‐β, IL‐27, and IL‐10, play an important role in i.v. tolerance‐induced EAE suppression.     

DX5+CD4+ T cells modulate CD4+ T‐cell response via inhibition of IL‐12 production by DCs

DX5⁺CD4⁺ T cells have been shown to dampen collagen‐induced arthritis and delayed‐type hypersensitivity reactions in mice. These cells are also potent modulators of T‐helper cell responses through direct effects on CD4⁺ T cells in an IL‐4 dependent manner. To further characterize this T‐cell population, we studied their effect on DCs and the potential consequences on T‐cell activation. Here, we show that mouse DX5⁺CD4⁺ T cells modulate DCs by robustly inhibiting IL‐12 production. This modulation is IL‐10 dependent and does not require cell contact. Furthermore, DX5⁺CD4⁺ T cells modulate the surface phenotype of LPS‐matured DCs. DCs modulated by DX5⁺CD4⁺ T‐cell supernatant express high levels of the co‐inhibitor molecules PDL‐1 and PDL‐2. OVA‐specific CD4⁺ T cells primed with DCs exposed to DX5⁺CD4⁺ T‐cell supernatant produce less IFN‐γ than CD4⁺ T cells primed by DCs exposed to either medium or DX5^?CD4⁺ T‐cell supernatant. The addition of IL‐12 to the co‐culture with DX5⁺ DCs restores IFN‐γ production. When IL‐10 present in the DX5⁺CD4⁺ T‐cell supernatant is blocked, DCs re‐establish their ability to produce IL‐12 and to efficiently prime CD4⁺ T cells. These data show that DX5⁺CD4⁺ T cells can indirectly affect the outcome of the T‐cell response by inducing DCs that have poor Th1 stimulatory function.     

Multifunctional CD4+ T cells correlate with active Mycobacterium tuberculosis infection

Th1 CD4⁺ T cells and their derived cytokines are crucial for protection against Mycobacterium tuberculosis. Using multiparametric flow cytometry, we have evaluated the distribution of seven distinct functional states (IFN‐γ/IL‐2/TNF‐α triple expressors, IFN‐γ/IL‐2, IFN‐γ/TNF‐α or TNF‐α/IL‐2 double expressors or IFN‐γ, IL‐2 or TNF‐α single expressors) of CD4⁺ T cells in individuals with latent M. tuberculosis infection (LTBI) and active tuberculosis (TB). We found that triple expressors, while detectable in 85–90%TB patients, were only present in 10–15% of LTBI subjects. On the contrary, LTBI subjects had significantly higher (12‐ to 15‐fold) proportions of IL‐2/IFN‐γ double and IFN‐γ single expressors as compared with the other CD4⁺ T‐cell subsets. Proportions of the other double or single CD4⁺ T‐cell expressors did not differ between TB and LTBI subjects. These distinct IFN‐γ, IL‐2 and TNF‐α profiles of M. tuberculosis‐specific CD4⁺ T cells seem to be associated with live bacterial loads, as indicated by the decrease in frequency of multifunctional T cells in TB‐infected patients after completion of anti‐mycobacterial therapy. Our results suggest that phenotypic and functional signatures of CD4⁺ T cells may serve as immunological correlates of protection and curative host responses, and be a useful tool to monitor the efficacy of anti‐mycobacterial therapy.     

In CD28‐costimulated human naïve CD4+ T cells,I‐κB kinase controls the expression of cell cycle regulatory proteins via interleukin‐2‐independent mechanisms

Stimulation of naïve CD4⁺ T cells through engagement of the T‐cell receptor (TCR) and the CD28 co‐receptor initiates cell proliferation which critically depends on interleukin (IL)‐2 secretion and subsequent autocrine signalling via the IL‐2 receptor. However, several studies indicate that in CD28‐costimulated T cells additional IL‐2‐independent signals are also required for cell proliferation. In this study, using a neutralizing anti‐human IL‐2 antibody and two selective, structurally unrelated, cell‐permeable I‐κB kinase (IKK) inhibitors, BMS‐345541 and PS‐1145, we show that in human naïve CD4⁺ T cells stimulated through a short engagement of the TCR and the CD28 co‐receptor, IKK controls the expression of the cell cycle regulatory proteins cyclin D3, cyclin E and cyclin‐dependent kinase 2 (CDK2) and the stability of the F‐box protein S‐phase kinase‐associated protein 2 (SKP2) and its co‐factor CDC28 protein kinase regulatory subunit 1B (CKS1B), through IL‐2‐independent mechanisms.     

IL‐17‐producing CD4+ T cells contribute to the loss of B‐cell tolerance in experimental autoimmune myasthenia gravis

The role of Th17 cells in the pathogenesis of autoantibody‐mediated diseases is unclear. Here, we assessed the contribution of Th17 cells to the pathogenesis of experimental autoimmune myasthenia gravis (EAMG), which is induced by repetitive immunizations with Torpedo californica acetylcholine receptor (tAChR). We show that a significant fraction of tAChR‐specific CD4⁺ T cells is producing IL‐17. IL‐17^ko mice developed fewer or no EAMG symptoms, although the frequencies of tAChR‐specific CD4⁺ T cells secreting IL‐2, IFN‐γ, or IL‐21, and the percentage of FoxP3⁺ T_reg cells were similar to WT mice. Even though the total anti‐tAChR antibody levels were equal, the complement fixating IgG2b subtype was reduced in IL‐17^ko as compared to WT mice. Most importantly, pathogenic anti‐murine AChR antibodies were significantly lower in IL‐17^ko mice. Furthermore, we confirmed the role of Th17 cells in EAMG pathogenesis by the reconstitution of TCR β/δ^ko mice with WT or IL‐17^ko CD4⁺ T cells. In conclusion, we show that the level of IgG2b and the loss of B‐cell tolerance, which results in pathogenic anti‐murine AChR‐specific antibodies, are dependent on IL‐17 production by CD4⁺ T cells. Thus, we describe here for the first time how Th17 cells are involved in the induction of classical antibody‐mediated autoimmunity.