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IL-21: An Executor of Fate Danijela Konforte, Nathalie Simard and Christopher J. Paige J Immunol 2009; 182:1781-1787; ; This information is current as doi: 10.4049/jimmunol.0803009 of September 25, 2021. http://www.jimmunol.org/content/182/4/1781 Downloaded from References This article cites 71 articles, 35 of which you can access for free at: http://www.jimmunol.org/content/182/4/1781.full#ref-list-1

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The Journal of Immunology is published twice each month by The American Association of Immunologists, Inc., 1451 Rockville Pike, Suite 650, Rockville, MD 20852 Copyright © 2009 by The American Association of Immunologists, Inc. All rights reserved. Print ISSN: 0022-1767 Online ISSN: 1550-6606. IL-21: An Executor of B Cell Fate1 Danijela Konforte,*‡ Nathalie Simard,*‡ and Christopher J. Paige2*†‡

IL-21 is a type I that shares the common recep- press similarly low levels of IL-21R (10). As T1 B cells mature to tor ␥-chain with IL-2, IL-4, IL-7, IL-9, and IL-15. B the T2 stage, the expression of IL-21R increases to levels com- cells are one of the lymphoid cell types whose develop- parable to that found on follicular B cells (10). IL-21R is also ment and function are regulated by IL-21. Depending present on human naive and germinal center (GC) B cells, but on the interplay with costimulatory signals and on the not on memory B cells and plasma cells (PCs) (11). The surface developmental stage of a B cell, IL-21 can induce pro- levels of IL-21R increase on murine naive B cells when they get liferation, differentiation into Ig-producing plasma activated either through the TLR or CD40, and on human memory B cells after stimulation through CD40 (9, 11). De-

cells, or apoptosis in both mice and humans. Alone and Downloaded from in combination with Th cell-derived IL-21 velopment- and activation-dependent regulation of IL-21R ex- can regulate class switch recombination to IgG, IgA, or pression on the surface of B cells suggests that IL-21 has impor- IgE isotypes, indicating its important role in shaping the tant functions late in B cell development and in the immune effector function of B cells. This review highlights the response. role of IL-21 in B cell development, function, and dis- Like other ␥c-dependent cytokines, IL-21 activates the Janus ease and provides some perspectives on the future stud- family kinases, Jak1 and Jak3, which, in turn, activate http://www.jimmunol.org/ ies in this area. The Journal of Immunology, 2009, 182: STAT1 and STAT3 and to a lesser extent STAT5. In vitro re- 1781–1787. sults obtained from activated murine splenocytes, EBV-in- fected human B cell lines, human chronic lymphocytic leuke- mia (CLL) B cells, and multiple myeloma lines indicate that terleukin-21 is a member of the family of common recep- IL-21:IL-21R binding leads to strong STAT3 activation (12– ␥ ␥ 3 tor -chain ( c) -dependent cytokines. Its structure is re- 15). In EBV-infected B cells, activated STAT3 is observed as I lated to the four- type I cytokine and shows early as 5 min after binding and persists to up to 6 days (12). significant homology to IL-2, IL-4, and IL-15 (1). IL-21 was

Activation of STAT1 is weaker, whereas activation of STAT5 is by guest on September 25, 2021 originally identified in the culture supernatants of activated hu- ϩ transient (Ͻ60 min) and is observed only in some cells, such as man CD3 T cells (1). Further studies established that Th17, T CLL B cells and activated murine splenocytes (12–14). Work- follicular helper (Tfh), and NKT cells also secrete IL-21 (2–5). ing with EBV-infected human B cell lines we found that inhi- IL-21 exerts pleiotropic actions on the . Its bition of IL-21-induced JAK/STAT signaling did not interfere functional receptor, IL-21R, consisting of the IL-21R␣/␥c with the initial increase in proliferation of EBV-infected B cell complex, is expressed on various hematopoietic cells. The ef- lines. By contrast, intact JAK/STAT signaling was required for fects of IL-21 on T, NK, and dendritic cells (DCs) have been reviewed elsewhere and will not be discussed here (reviewed in the subsequent differentiation into late plasmablasts/early PCs (12). Biochemical studies of murine IL-21R␣ showed that si- Refs. 6–8). This review focuses on the influence of IL-21 in B ␣ cell biology. multaneous mutation of all six tyrosine residues in the IL-21R cytoplasmic domain greatly reduced IL-21-mediated prolifera- IL-21R expression and signaling tion of murine T cells, whereas retention of tyrosine 510 (Y510) In mice, the cell surface levels of IL-21R progressively increase only was sufficient for the full proliferative response. Y510 me- as B cells develop from progenitors in the to ma- diated IL-21-induced activation of STAT1 and STAT3, but ture B cells in the peripheral lymphoid tissues (9). Transitional not STAT5, in T cells (14). The precise role of Y510 and the 1 (T1) B cells, which represent the most immature B cell pop- other tyrosine residues in IL-21R signaling in B cells has not yet ulation in the periphery, and marginal zone (MZ) B cells ex- been determined. Similarly, it is of interest to determine

*Division of Stem Cell and Developmental Biology, Princess Margaret Hospital, Ontario 2 Address correspondence and reprint requests to Dr. Christopher J. Paige, Division of Cancer Institute, University Health Network, Toronto, Canada; and †Department of Stem Cell and Developmental Biology, Princess Margaret Hospital, Ontario Cancer In- Medical Biophysics and ‡Department of Immunology, University of Toronto, Toronto, stitute, No. 7-504, 610 University Avenue, Toronto, Ontario M5G 2M9. E-mail address: Canada [email protected] Received for publication November 17, 2008. Accepted for publication December 3 Abbreviations used in this paper: ␥c, common receptor ␥-chain; AID, activation-induced 24, 2008. cytidine deaminase; BAFF, B cell-activating factor (TNF family); CB, cord blood; CD40L, CD40 ligand; CSR, class switch recombination; CLL, chronic lymphocytic leukemia; DC, The costs of publication of this article were defrayed in part by the payment of page charges. dendritic cell; GC, germinal center; MZ, marginal zone; MZA, MZ analog; PB, peripheral This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. blood; PC, plasma cell; RA, rheumatoid arthritis; SHM, somatic hypermutation; SLE, Section 1734 solely to indicate this fact. systemic lupus erythematosus; Tfh, T follicular helper cell; WT, wild type. 1 This work was supported by the grants from the National Cancer Institute of Canada and by the Canadian Institutes of Health Research (CIHR) Grant 9862. N.S. is the recipient of Copyright © 2009 by The American Association of Immunologists, Inc. 0022-1767/09/$2.00 a graduate student scholarship from the CIHR. www.jimmunol.org/cgi/doi/10.4049/jimmunol.0803009 1782 BRIEF REVIEWS: IL-21 AND B CELLS whether certain IL-21R tyrosine residues can recruit phospha- and increase the cell death of murine follicular, MZ, and total tases or other that inhibit STAT activation and help splenic B cells (9). In human in vitro systems, IL-2, IL-4, IL-10, terminate IL-21 signaling. and IL-13, known for their key roles in B cell function, had notably It will also be important to investigate whether the balance lower effects on proliferation of anti-CD40-stimulated B cells between IL-21-induced STAT1 and STAT3 signals influ- compared with IL-21 (11, 27, 28). Similarly as for murine B cells, ences different B cell fates. Generally, STAT1 has been im- anti-CD40 stimulation protected anti-IgM-activated human B plicated in cell cycle arrest and apoptotic cell death (16). By cells from IL-21-mediated death (27). contrast, STAT3 mostly functions as an antiapoptotic or The ability of IL-21 to induce apoptosis sets it apart from , especially in numerous malignancies where it other members of the ␥c-dependent family of cytokines, most is constitutively active (17–19). The consequence of STAT of which activate prosurvival and proliferation signals. Com- activation depends on the expression of STAT target plete protection from IL-21-mediated apoptosis was observed that are regulated directly or indirectly. Granzyme A, Jak3, when murine B cells were pretreated for 6 h with anti-CD40 Ab and IL-17R are among the genes activated by IL-21 in a and then cultured with IL-21 for 24 h. In this case, it was found STAT3-dependent fashion (20). We showed that intact that anti-CD40 induced and expression of a pro- JAK/STAT signal is required for IL-21-induced c-myc re- survival factor, Bcl-xL (29). IL-21-mediated apoptosis was not pression and subsequent differentiation of EBV-infected B blocked in or TNFRI- or TNFRII-transgenic mice, cell lines into late plasmablasts/early PCs (12). but it was blocked in Bcl-2 transgenic mice (9). Functional

In addition to the JAK/STAT pathway, two other signaling studies demonstrated that IL-21 substantially inhibited prolif- Downloaded from regulators activated by ␥c-dependent cytokines are the PI3K/ eration and induced Bim-dependent apoptosis of LPS or CpG Akt and RAS/MAPK (21, 22). Three members of the MAPK DNA-activated murine B cells (9). Collectively, these results family, ERK1/2, p54 (JNK), and p38 participate in the control suggest that the mitochondrial death pathway plays a role in of cell proliferation and survival downstream of IL-2 and IL-4 IL-21-induced apoptosis of murine B cells. In contrast to mu- receptors (23–25). Because IL-21R␣ shows the highest homol- rine B cells, Bim did not seem to play a role in IL-21-induced ogy to IL-2R␤ and IL-4R␣ (22), it is likely that the MAPK cell death in human B cells, as its expression did not change http://www.jimmunol.org/ pathway could also contribute to IL-21-mediated proliferation when B cells were stimulated with anti-IgM and IL-21 (30). of B cells. IL-21-induced ERK1/2 was shown Genetic background also influences the response of murine B in multiple myeloma cell lines (15). In murine T cells it was cells to IL21. For example, in BALB/c mice, IL-21 stimulated shown that IL-21 slightly induced phosphorylation of Shc the proliferation of B cells activated with anti-CD40. This ef- (SRC homology 2 domain containing) and Akt, whose inhibi- fect was not observed in C57BL/6 mice treated in the same way. tion partially prevented IL-21-induced proliferation of T cells In addition, B cells from C57BL/6 mice were more susceptible (14). It remains to be determined how the MAPK and PI3K to IL-21-mediated cell death after stimulation with LPS, CpG

pathways contribute to IL-21-regulated proliferative, survival, DNA, or anti-CD40 than B cells from BALB/c mice (9). by guest on September 25, 2021 or differentiation signals in B cells. The capacity of IL-21 to regulate survival and proliferation of B cells demonstrates its importance in controlling the fate of IL-21 regulates proliferation and survival of B cells activated B cells. Taken together, current data suggest that Cytokines influence B cell development and homeostasis by IL-21 promotes survival and proliferation of appropriately ac- regulating their proliferation and survival. Critical insights into tivated B cells that respond to Ag and receive cognate the role of IL-21 in murine B cell proliferation and survival help. By contrast, IL-21 inhibits proliferation and/or initiates come from experiments in which IL-21 is overexpressed in vivo. apoptosis of B cells that receive a nonspecific signal via BCR This was achieved using either transgenic methods or by hydro- only or that receive a strong signal via TLR. dynamic transfection of IL-21 cDNA into wild-type (WT) mice. In both cases, increased numbers of immature transi- IL-21 induces activation-induced cytidine deaminase (AID) and tional B cells, isotype-switched memory B cells, and PCs were regulates class switch recombination (CSR) to IgG and IgA observed. In addition, total serum IgG and IgM were found to Ab diversity is critical to eliciting an efficient be increased in these animals (26). Of the tested splenic B cell against a plethora of different pathogens. Two mechanisms in- populations, the follicular B cell subset was significantly lower, volved in creating such diversity are somatic hypermutation whereas the percentage of splenic MZ B cells was normal, al- (SHM) and CSR. Both processes require the AID enzyme, though MZ B cells were found to be relocated outside the MZ which converts cytosines in switch and Ig V regions to uracils by area (26, 27). deamination (31, 32). IL-21 stimulation of mouse and human In vitro experiments show that IL-21 can have both positive naive B cells has been shown to induce the expression of AID and negative effects on B lineage cells depending on the pres- when used in combination with CD40- and IgM-specific Abs ence or absence of other signals. For example, the addition of (28, 33). Interestingly, although AID catalyzes both CSR and IL-21 increased the proliferation of murine splenic B cells that SHM, only CSR was induced in naive human B cells after treat- had been stimulated by a combination of anti-IgM, which ment with IL-21 and anti-CD40 (28). The discovery that the mimics a BCR-mediated signal, and anti-CD40, which mimics C-terminal 10 aa of AID were required for CSR but not for a signal provided by Th cells. By contrast, proliferation induced SHM could explain this observation (34, 35). It has been hy- by anti-IgM and IL-4 was inhibited by IL-21, although this ef- pothesized that IL-21 induces activity of AID, but only at the C fect could be reversed when anti-CD40 was added, resulting in terminus (28). increased proliferation (26). In the presence of strong innate Multiple studies have shown that IL-21 causes CSR of ϩ signals such as LPS or CpG DNA, the addition of IL-21 alone CD40-stimulated human naive splenic IgM B cells to IgG1 or in combination with IL-4 was shown to inhibit proliferation and IgG3 and that of CD40-stimulated cord blood (CB) B cells The Journal of Immunology 1783 to IgA (36, 37). The addition of IL-4 to these cultures prevents Ig-secreting PCs vary between the different subsets of human B class switching to IgA (37, 38). There is no evidence that IL-21 cells (28, 30, 37, 38). IL-21 induced PC differentiation and Ig alone activates CSR to the IgE isotype. In the absence of IL-4, production when used in combination with anti-CD40 or with IL-21 does not induce CSR of human CD40-activated naive B anti-IgM and anti-CD40 in human naive and memory B cells cells to IgE (39, 40). Furthermore, IL-21 does not affect anti- from PB, tonsil, and spleen, as well as in CB B cells (11, 28, 37, ϩ CD40 mAb- and IL-4-induced C␧ promoter activation or 38). However, IgM and isotype-switched memory B cells germline C␧ mRNA expression in purified human spleen or pe- were much more sensitive to CD40L/IL-21 than naive B cells, ripheral blood B cells (39, 40). Overall, the studies discussed which was reflected in a greater rate of differentiation to Ig-se- here show that IL-21 regulates CSR of naive B cells to IgG-and creting PCs (38). Also, Ͼ50% of PCs resulting from IgM mem- IgA- expressing B cells, thereby contributing to the diversity of ory B cells were secreting IgG and IgA, in addition to IgM. By Ig function. It remains to be determined how other cytokines contrast, most PCs produced from naive B cells secreted IgM, that regulate B cell differentiation, such as IL-2, IL-6, and with low frequencies of IgG and IgA (38). This result reflects a TGF-␤, can affect the outcome of IL-21-mediated CSR. greater ability of IgM memory B cells to undergo CSR com- pared with naive B cells. IL-21 regulates differentiation of B cells to Ig-secreting PCs Some B cell subsets do not require BCR- and CD40-medi- Studies of IL-21R knockout mice. PCs represent the end point of B ated stimulation to differentiate to PCs in response to IL-21. cell lineage differentiation and are essential for protective im- For instance, Ettinger et al. (30) isolated novel MZ analog Ϫ/Ϫ munity. IL-21R mice provide important insights into the (MZA) B cell populations from human spleen, which consisted Downloaded from ϩ ϩ role of IL-21 in the differentiation of B cells to the PC stage. of both IgG and IgM memory B cells that expressed a unique Ϫ Steady-state serum levels of IgG2a, IgG3, and IgM were normal set of markers (CD27highCD21highCD23 CD38int; where Ϫ/Ϫ in naive IL-21R mice, but the amounts of IgG1 and IgG2b “int” is “intermediate”). In this population, IL-21 and B cell- were lower compared with WT controls (41). By contrast, activating factor (BAFF; belonging to the TNF family) co- Ϫ/Ϫ steady-state serum levels of IgE were higher in IL-21R mice stimulation alone was sufficient to induce PC differentiation Ϫ/Ϫ (41). T cell-dependent Ag immunization of IL-21R mice and the production of large amounts of IgG (30). This suggests http://www.jimmunol.org/ with OVA or keyhole limpet hemocyanin resulted in a severe that IL-21 and BAFF could participate in the Ag-independent defect in the production of both total serum and Ag-specific replenishment of serologic memory by inducing differentiation IgG1. Moreover, Ag-specific IgG2b and IgG3 responses were of MZA B cell to PCs. Ϫ/Ϫ also impaired in immunized IL-21R mice, although the to- IL-21 and other Th-secreted cytokines in B cell differentiation. IL-21 is tal serum levels of IgG2b and IgG3 as well as IgM and IgA re- not only a potent inducer of PC differentiation by all types of mained normal. Serum concentrations of IgE, an isotype whose human B cells, but its effects also greatly exceed those of other production is usually associated with IL-4, were variable al- Ϫ Ϫ cytokines such as IL-2, IL-10, and IL-4. For example, IL-21 and though distinctly higher in IL-21R / mice (41, 42). Aug- Ϫ/Ϫ CD40 stimulation of human PB naive B cells caused secretion by guest on September 25, 2021 mented IgE response was also observed in IL-21R mice in- of IgG that was up to 10-fold higher than that induced by IL-4 fected with Toxoplasma gondii, a parasite that is not normally or IL-2 in combination with CD40 stimulation (11, 27, 28). associated with the induction of an IgE response (43). Alto- IL-21 increased the frequency of Ig-secreting cells generated in gether, these results clearly show that IL-21 plays an essential cultures of human CB, GC, naive, and memory B cells by 5- to role in the generation of Ig-secreting B cells, both at steady state 20-fold compared with that induced by CD40L alone or the and during the immune response. combination of CD40L and IL-10 (38). In vitro studies of T cell-B cell interactions. Most PCs develop from B The outcome of IL-21-mediated Ig secretion depends on the cells that have passed through the GC reaction (44). In GC, Tfh presence of other cytokines. For example, IL-10 has been shown cells provide help to GC B cells in the form of CD40 ligand to synergize with IL-21 to induce the secretion of IgA by (CD40L) and cytokines, thereby promoting the differentiation CD40L-stimulated human B cells, whereas IL-4 diminished it of Ag-selected, high-affinity B cells into PCs or memory B cells (37). Most studies have focused on the interplay between IL-21 (45). Both murine and human Tfh cells were shown to produce and IL-4 in differentiation of B cells to IgE-secreting PCs. As IL-21 (5, 38, 46). Coculture experiments of human B cells and mentioned above, the inhibitory effect of IL-21 on IgE produc- Ϫ Ϫ T cells have addressed the contribution of T cell-secreted IL-21 tion was first reported in IL-21R / mice, which produced in the differentiation of B cells. These experiments showed that ϩ larger quantities of IgE than WT mice. In agreement with this anti-CD3-activated CD4 peripheral blood (PB) and tonsillar observation, the administration of IL-21 in WT mice or the T cells, and activated tonsillar Tfh cells can induce proliferation addition of IL-21 to cultures of murine splenic B cells stimu- and differentiation of autologous naive B cells in an IL-21-de- lated with LPS and IL-4 prevented the production of Ag-spe- pendent manner (5, 38, 47). In this system, the production of cific IgE (48). Generation of mice deficient for both IL-4 and IgM, IgG, and IgA by naive B cells was almost exclusively de- IL-21R revealed that IL-4 was needed for the production of IgE Ϫ Ϫ Ϫ Ϫ Ϫ Ϫ pendent on IL-21 (47). In comparison, the ability of memory B in IL-21R / mice, as IL-4 / IL-21R / mice, similarly as Ϫ Ϫ cells to secrete IgM in response to activated T cells was only IL-4 / mice, did not make IgE. IL-21 has also been shown to marginally affected by blocking IL-21, whereas IgG production inhibit the IL-4-driven production of IgE in cultured human from memory B cells required IL-21 (47). It will be of interest PBMC or total splenocytes. This inhibition was not the result to determine whether IL-21 produced by other cells, such as of a direct effect of IL-21 on B cells but was dependent on the Th17 and NKT cells, plays a similar role in B cell differentia- presence of IFN-␥ (39, 40). By contrast, when purified naive tion to PCs. and memory B cells from PB or spleen were used, IL-21 en- Effects of IL-21 on differentiation of human B cell subsets. In vitro stud- hanced the production of IgE (39, 40). The reasons for the op- ies revealed that the effects of IL-21 on the differentiation to posite in vitro effects of IL-21 on IgE secretion observed in 1784 BRIEF REVIEWS: IL-21 AND B CELLS

Table I. Modulation of IL-21 for therapy In addition, based on results from experimental animal mod- els, there is a growing body of evidence that links IL-21 to the Potential Benefits of IL-21 Administration and Reduction/Neutralization regulation of B cell responses in autoimmune diseases such as (with references) systemic lupus erythematosus (SLE), rheumatoid arthritis Potential benefits of IL-21 administration: (RA), and inflammatory bowel disease. For example, it was Treatment of (4, 56–58) shown that IL-21 has a pathogenic role in the MRL-Fas(lpr) Treatment of cancer (direct cytotoxicity) Chronic lymphocytic leukemia (15) murine model of SLE by impacting B cell function and regu- Diffuse large B cell lymphoma (67) lating the production of pathogenic autoantibodies (57). In this Cancer (69–71) model, extrafollicular Th cells governed the high-affinity, iso- Treatment of immunodeficiency (39) Vaccine development (29, 32) type-switched autoantibody production via IL-21 and CD40 (58). Higher serum levels of IL-21 were also detected in the Potential benefits of IL-21 reduction/neutralization: BSXB-Yaa SLE mouse model, and neutralization of IL-21 in Treatment of late disease improved animal survival, presumably by dampen- SLE (59–61) RA (62) ing the humoral components of lupus (59). In the collagen-in- Treatment of cancer duced and adjuvant murine model of arthritis, blockade of Multiple myeloma (17) IL-21 with the IL-21R-Fc fusion protein reversed clinical dis- Burkitt’s lymphoma (67) Hodgkin’s lymphoma (68) ease severity (60). In humans, a higher percentage of IL-21R positive cells was detected in the blood and synovial fluid of Downloaded from patients with RA (61). It remains to be determined whether mouse vs human purified B cells are not clear. It was suggested IL-21 affects the generation or function of autoreactive B cells that the impact of IL-21 and IL-4 on IgE secretion depends on in RA. Multiple studies have demonstrated that Th17 cells are B cell density. When IL-4- and CD40-stimulated murine implicated in the pathogenesis of SLE and RA (62, 63). As splenic B cells as well as human tonsillar B cells were cultured at Th17 cells also represent a rich source of IL-21 (64), it will be of low cell density, the secretion of IgE was increased by the addi- interest to determine whether Th17-produced IL-21 contrib- http://www.jimmunol.org/ tion of IL-21. By contrast, the production of IgE was dimin- utes to aberrant B cell responses in these diseases. ished when the murine B cells were plated at high density (49). Apart from its involvement in autoimmunity, there is evi- At low cell density IL-21 increased the rate of cell division, dence that IL-21 can be an important factor in the regulation of which was suggested to be a mechanism to enhance IL-4-me- growth and survival of various B cell malignancies. Exposure to diated switching to IgE (49). This hypothesis is supported by IL-21 induces apoptosis of CLL B cells and diffuse large B cell the demonstration that B cell division is required for isotype lymphoma cells (13, 65). Targeted delivery of IL-21 may be switching. For example, in mouse cells, isotype switching to beneficial for the therapy of these types of cancers. By contrast,

IgG and IgE required a minimum of three or five divisions, re- IL-21 increases the proliferation of Burkitt’s lymphoma and by guest on September 25, 2021 spectively (50, 51). multiple myeloma cells in vitro (13, 15, 65). Hodgkin Reed- IL-21 regulates expression of PC fate-determining transcription factors. Sternberg cells from Hodgkin’s lymphoma were shown to both IL-21-mediated induction of PCs is driven by the expression of secrete and respond to IL-21. IL-21 protects Hodgkin Reed- multiple transcription factors. Induction of Blimp1, Irf4, Sternberg cells, which are thought to be crippled B cells, from Xbp1s, and Bcl6 with a parallel decrease in Pax5 could explain CD95 death receptor-induced apoptosis (66). Therefore, lim- how IL-21 regulates the maturation of both murine and human iting IL-21 may be beneficial for treatment of Burkitt’s lym- B cells into both PCs and isotype-switched memory B cells (26, phoma, multiple myeloma, and Hodgkin’s lymphoma. 38, 47, 52). It is hypothesized that an IL-21-mediated increase IL-21 has been used in primarily to in Blimp1 leads to differentiation to PC, whereas induction of elicit protective T cell responses. However, there exists some Bcl6 may be important for the differentiation of GC B cells into evidence that the function of IL-21 in the differentiation of B isotype-switched memory B cells (53). The IL-21-mediated de- cells to Ab-producing PCs is critical for mounting antitumor crease of Pax5 may bias responses toward PC differentiation, as humoral responses. Administration of IL-21-transduced gli- Pax5 is known to inhibit this process (38, 52). oma cells resulted in Ab responses to glioma Ags, predomi- nantly IgG2a and IgG2b isotypes, which mediated comple- IL-21 in disease ment- or cell-dependent glioma cell lysis in immunocompetent The discovery that IL-21 controls B cell maturation and func- mice. This protocol failed in syngeneic ␮MT B cell-deficient tion prompted multiple studies into its involvement in those mice (67). In a different model, IL-21 gene transfer promoted diseases that have a major B cell component. (Table I). Some the production of tumor-specific IgG in mice bearing s.c. head insight into the role of IL-21 in allergic responses came from and neck squamous cell carcinomas (68). Injection of IL-21 and studies showing that exposure to IL-21 resulted in decreased IL-2 as adjuvants to a T cell transfer caused an effective regres- IgE production in an OVA-induced mouse model of allergic sion of established pulmonary metastatic tumors and s.c. tu- rhinitis and in a mouse food allergy model (54, 55). In humans, mors in mice. Tumor-specific IgG2b from the sera of treated diminution of IgE production has been reported following vac- animals mediated tumor cell lysis in the presence of comple- cination with Mycobacterium bovis bacillus Calmette Guerin, ment. Use of B cell-deficient ␮MT mice provided direct evi- BCG (56). This effect has been attributed to the apoptosis of dence that humoral responses contributed to antitumor immu- IgE-producing B cells caused by the IL-21 secreted by NKT nity (69). Importantly, IL-21 is being tested in clinical trials for cells (4). Collectively, these studies suggest that IL-21 modula- advanced , , as well as in clinical ϩ tion of IgE production may have potential therapeutic applica- trials for CD20 B cell non-Hodgkin’s lymphoma in combi- tions in the treatment of IgE-mediated diseases such as allergy. nation with (70, 71). The Journal of Immunology 1785 Downloaded from http://www.jimmunol.org/ by guest on September 25, 2021

FIGURE 1. Functional outcomes of IL-21 signaling in B cells. a, In GCs, B cells that have undergone somatic hypermutation pass through checkpoints where they get tested for their ability to bind Ag presented in the form of immune complexes on the surface of follicular DCs. If B cells recognize an Ag via BCR, they can process and present it to Tfh cells and elicit their help via CD40L-mediated and IL-21-mediated signals. This results in survival, proliferation, CSR, and differen- tiation of B cells to IgM-, IgG-, or IgA-secreting PCs. Other cytokines, such as IL-4 and IL-10, can modulate IL-21 effects on CSRs to certain Ig isotypes. In vivo results suggest an inhibitory role for IL-21 in differentiation to IgE-secreting PCs, but in vitro results are conflicting. b, IL-21 costimulation causes Bim-mediated apoptosis in murine naive B cells that receive strong signals via TLR or via BCR in the absence of adequate T cell help. c, In human spleen, MZA IgGϩ memory B cells respond to T cell- produced IL-21 and DC-produced BAFF by differentiating to IgG-secreting PCs. BCMA, B cell maturation Ag; TACI, transmembrane activator and calcium modulator and ligand interactor.

Conclusions IL-21 (Fig. 1c). Balance between proliferation/survival and apo- The effects of IL-21 on normal and malignant B cells vary (Fig. ptosis signals is necessary to maintain B cell homeostasis, mount 1). In B cells that recognize Ag and receive T cell help, IL-21 effective immune responses, and prevent the development of induces survival, proliferation, isotype switching, and differen- autoimmunity or cancer. Future studies should focus on under- tiation to Ig-secreting PCs (Fig. 1a). In those B cells receiving a standing the complete signaling cascades and downstream strong signal via BCR alone, as can be the case for some autoan- changes in the patterns of gene and protein expression in B cells tigens, or via TLR, IL-21 costimulation causes death (Fig. 1b). in response to IL-21 alone or in combination with other Th- Signals via CD40L or BAFF, provided by bystander T cell help produced cytokines such as IL-2, IL-4, IL-10, IL-6, and IL-12. or DCs, respectively, can promote differentiation of human B This knowledge may help us predict the functional outcomes of cells in an Ag-independent manner when costimulated with IL-21 signaling in different B cell backgrounds, which will be 1786 BRIEF REVIEWS: IL-21 AND B CELLS crucial for the manipulation of humoral responses for purposes 27. Ettinger, R., S. Kuchen, and P. E. Lipsky. 2008. The role of IL-21 in regulating B-cell function in health and disease. Immunol. Rev. 223: 60–86. of vaccine development and for therapy of immunodeficiency, 28. Ettinger, R., G. P. Sims, A. M. Fairhurst, R. Robbins, Y. S. da Silva, R. Spolski, cancer, allergy, and autoimmunity. W. J. Leonard, and P. E. Lipsky. 2005. IL-21 induces differentiation of human naive and memory B cells into antibody-secreting plasma cells. J. Immunol. 175: 7867–7879. Disclosures 29. Mehta, D. S., A. L. Wurster, M. J. Whitters, D. A. Young, M. Collins, and The authors have no financial conflict of interest. M. J. Grusby. 2003. IL-21 induces the apoptosis of resting and activated primary B cells. J. Immunol. 170: 4111–4118. 30. Ettinger, R., G. P. Sims, R. Robbins, D. Withers, R. T. Fischer, A. C. Grammer, References S. Kuchen, and P. E. Lipsky. 2007. IL-21 and BAFF/BLyS synergize in stimulating plasma cell differentiation from a unique population of human splenic memory B 1. Parrish-Novak, J., S. R. Dillon, A. Nelson, A. Hammond, C. Sprecher, J. A. Gross, cells. J. Immunol. 178: 2872–2882. J. Johnston, K. Madden, W. Xu, J. West, et al. 2000. 21 and its receptor 31. Peled, J. U., F. L. Kuang, M. D. Iglesias-Ussel, S. Roa, S. L. Kalis, M. F. Goodman, are involved in NK cell expansion and regulation of function. Nature 408: and M. D. Scharff. 2008. The biochemistry of somatic hypermutation. Annu. Rev. 57–63. Immunol. 26: 481–511. 2. Nurieva, R., X. O. Yang, G. Martinez, Y. Zhang, A. D. Panopoulos, L. Ma, K. Schluns, Q. Tian, S. S. Watowich, A. M. Jetten, and C. Dong. 2007. Essential 32. Stavnezer, J., J. E. Guikema, and C. E. Schrader. 2008. Mechanism and regulation of autocrine regulation by IL-21 in the generation of inflammatory T cells. Nature 448: class switch recombination. Annu. Rev. Immunol. 26: 261–292. 480–483. 33. Saito, T., D. Kitayama, A. Sakamoto, N. Tsuruoka, M. Arima, M. Hatano, 3. Coquet, J. M., K. Kyparissoudis, D. G. Pellicci, G. Besra, S. P. Berzins, M. J. Smyth, M. Miyazaki, and T. Tokuhisa. 2008. Effective collaboration between IL-4 and IL-21 and D. I. Godfrey. 2007. IL-21 is produced by NKT cells and modulates NKT cell on B cell activation. Immunobiology 213: 545–555. activation and cytokine production. J. Immunol. 178: 2827–2834. 34. Wu, X., P. Geraldes, J. L. Platt, and M. Cascalho. 2005. The double-edged sword of 4. Harada, M., K. Magara-Koyanagi, H. Watarai, Y. Nagata, Y. Ishii, S. Kojo, activation-induced cytidine deaminase. J. Immunol. 174: 934–941. S. Horiguchi, Y. Okamoto, T. Nakayama, N. Suzuki, et al. 2006. IL-21-induced Bep- 35. Shinkura, R., S. Ito, N. A. Begum, H. Nagaoka, M. Muramatsu, K. Kinoshita,

silon cell apoptosis mediated by natural killer T cells suppresses IgE responses. J. Exp. Y. Sakakibara, H. Hijikata, and T. Honjo. 2004. Separate domains of AID are re- Downloaded from Med. 203: 2929–2937. quired for somatic hypermutation and class-switch recombination. Nat. Immunol. 5: 5. Chtanova, T., S. G. Tangye, R. Newton, N. Frank, M. R. Hodge, M. S. Rolph, and 707–712. C. R. Mackay. 2004. T follicular helper cells express a distinctive transcriptional pro- 36. Pene, J., J. F. Gauchat, S. Lecart, E. Drouet, P. Guglielmi, V. Boulay, A. Delwail, file, reflecting their role as non-Th1/Th2 effector cells that provide help for B cells. D. Foster, J. C. Lecron, and H. Yssel. 2004. Cutting edge: IL-21 is a switch factor for J. Immunol. 173: 68–78. the production of IgG1 and IgG3 by human B cells. J. Immunol. 172: 5154–5157. 6. Leonard, W. J., and R. Spolski. 2005. Interleukin-21: a modulator of lymphoid pro- 37. Avery, D. T., V. L. Bryant, C. S. Ma, R. de Waal Malefyt, and S. G. Tangye. 2008. liferation, apoptosis and differentiation. Nat. Rev. Immunol. 5: 688–698. IL-21-induced isotype switching to IgG and IgA by human naive B cells is differen- 7. Spolski, R., and W. J. Leonard. 2008. Interleukin-21: basic biology and implications tially regulated by IL-4. J. Immunol. 181: 1767–1779. http://www.jimmunol.org/ for cancer and autoimmunity. Annu. Rev. Immunol. 26: 57–79. 38. Bryant, V. L., C. S. Ma, D. T. Avery, Y. Li, K. L. Good, L. M. Corcoran, 8. Brandt, K., P. B. Singh, S. Bulfone-Paus, and R. Ruckert. 2007. Interleukin-21: a new R. de Waal Malefyt, and S. G. Tangye. 2007. Cytokine-mediated regulation of human modulator of , , and cancer. Cytokine Growth Factor Rev. 18: B cell differentiation into Ig-secreting cells: predominant role of IL-21 produced by 223–232. CXCR5ϩ T follicular helper cells. J. Immunol. 179: 8180–8190. 9. Jin, H., R. Carrio, A. Yu, and T. R. Malek. 2004. Distinct activation signals determine 39. Pene, J., L. Guglielmi, J. F. Gauchat, N. Harrer, M. Woisetschlager, V. Boulay, whether IL-21 induces B cell costimulation, growth arrest, or Bim-dependent apopto- J. M. Fabre, P. Demoly, and H. Yssel. 2006. IFN-␥-mediated inhibition of human sis. J. Immunol. 173: 657–665. IgE synthesis by IL-21 is associated with a polymorphism in the IL-21R gene. J. Im- 10. Jin, H., and T. R. Malek. 2006. Redundant and unique regulation of activated mouse munol. 177: 5006–5013. B by IL-4 and IL-21. J. Leukocyte Biol. 80: 1416–1423. 40. Wood, N., K. Bourque, D. D. Donaldson, M. Collins, D. Vercelli, S. J. Goldman, and 11. Good, K. L., V. L. Bryant, and S. G. Tangye. 2006. Kinetics of human B cell behavior M. T. Kasaian. 2004. IL-21 effects on human IgE production in response to IL-4 or and amplification of proliferative responses following stimulation with IL-21. J. Im- IL-13. Cellular immunology 231: 133–145.

munol. 177: 5236–5247. 41. Ozaki, K., R. Spolski, C. G. Feng, C. F. Qi, J. Cheng, A. Sher, H. C. Morse, III, by guest on September 25, 2021 12. Konforte, D., and C. J. Paige. 2006. Identification of cellular intermediates and mo- C. Liu, P. L. Schwartzberg, and W. J. Leonard. 2002. A critical role for IL-21 in reg- lecular pathways induced by IL-21 in human B cells. J. Immunol. 177: 8381–8392. ulating immunoglobulin production. Science 298: 1630–1634. 13. de Totero, D., R. Meazza, S. Zupo, G. Cutrona, S. Matis, M. Colombo, E. Balleari, 42. Shang, X. Z., K. Y. Ma, J. Radewonuk, J. Li, X. Y. Song, D. E. Griswold, E. Emmell, I. Pierri, M. Fabbi, M. Capaia, et al. 2006. Interleukin-21 receptor (IL-21R) is up- and L. Li. 2006. IgE isotype switch and IgE production are enhanced in IL-21-defi- regulated by CD40 triggering and mediates proapoptotic signals in chronic lympho- cient but not IFN-␥-deficient mice in a Th2-biased response. Cell Immunol. 241: cytic leukemia B cells. Blood 107: 3708–3715. 66–74. 14. Zeng, R., R. Spolski, E. Casas, W. Zhu, D. E. Levy, and W. J. Leonard. 2007. The 43. Suzuki, Y., Q. Yang, S. Yang, N. Nguyen, S. Lim, O. Liesenfeld, T. Kojima, and molecular basis of IL-21-mediated proliferation. Blood 109: 4135–4142. J. S. Remington. 1996. IL-4 is protective against development of toxoplasmic enceph- 15. Brenne, A. T., T. Baade Ro, A. Waage, A. Sundan, M. Borset, and H. Hjorth-Hansen. alitis. J. Immunol. 157: 2564–2569. 2002. Interleukin-21 is a growth and survival factor for human myeloma cells. Blood 44. MacLennan, I. C. 1994. Germinal centers. Annu. Rev. Immunol. 12: 117–139. 99: 3756–3762. 45. Allen, C. D., T. Okada, H. L. Tang, and J. G. Cyster. 2007. Imaging of germinal 16. Durbin, J. E., R. Hackenmiller, M. C. Simon, and D. E. Levy. 1996. Targeted dis- center selection events during affinity maturation. Science 315: 528–531. ruption of the mouse Stat1 gene results in compromised innate immunity to viral 46. Vogelzang, A., H. M. McGuire, D. Yu, J. Sprent, C. R. Mackay, and C. King. 2008. disease. Cell 84: 443–450. A fundamental role for interleukin-21 in the generation of T follicular helper cells. 17. Stephanou, A., and D. S. Latchman. 2005. Opposing actions of STAT-1 and Immunity 29: 127–137. STAT-3. Growth Factors 23: 177–182. 47. Kuchen, S., R. Robbins, G. P. Sims, C. Sheng, T. M. Phillips, P. E. Lipsky, and 18. Bowman, T., R. Garcia, J. Turkson, and R. Jove. 2000. STATs in oncogenesis. On- R. Ettinger. 2007. Essential role of IL-21 in B cell activation, expansion, and plasma cogene 19: 2474–2488. ϩ cell generation during CD4 T cell-B cell collaboration. J. Immunol. 179: 19. Garcia, R., T. L. Bowman, G. Niu, H. Yu, S. Minton, C. A. Muro-Cacho, C. E. Cox, 5886–5896. R. Falcone, R. Fairclough, S. Parsons, et al. 2001. Constitutive activation of Stat3 by the Src and JAK tyrosine kinases participates in growth regulation of human breast 48. Suto, A., H. Nakajima, K. Hirose, K. Suzuki, S. Kagami, Y. Seto, A. Hoshimoto, Y. Saito, D. C. Foster, and I. Iwamoto. 2002. prevents -induced carcinoma cells. Oncogene 20: 2499–2513. ⑀ 20. Zeng, R., R. Spolski, S. E. Finkelstein, S. Oh, P. E. Kovanen, C. S. Hinrichs, IgE production by inhibiting germ line C transcription of IL-4-stimulated B cells. C. A. Pise-Masison, M. F. Radonovich, J. N. Brady, N. P. Restifo, et al. 2005. Synergy Blood 100: 4565–4573. of IL-21 and IL-15 in regulating CD8ϩ T cell expansion and function. J. Exp. Med. 49. Caven, T. H., A. Shelburne, J. Sato, Y. Chan-Li, S. Becker, and D. H. Conrad. 2005. 201: 139–148. IL-21 dependent IgE production in human and mouse in vitro culture systems is cell 21. Nutt, S. L., J. Brady, Y. Hayakawa, and M. J. Smyth. 2004. Interleukin 21: a key density and cell division dependent and is augmented by IL-10. Cell. Immunol. 238: player in lymphocyte maturation. Crit. Rev. Immunol. 24: 239–250. 123–134. 22. Mehta, D. S., A. L. Wurster, and M. J. Grusby. 2004. Biology of IL-21 and the IL-21 50. Hasbold, J., A. B. Lyons, M. R. Kehry, and P. D. Hodgkin. 1998. Cell division num- receptor. Immunol. Rev. 202: 84–95. ber regulates IgG1 and IgE switching of B cells following stimulation by CD40 ligand 23. Williamson, P., I. Merida, and G. Gaulton. 1993. Protein and lipid kinase activation and IL-4. Eur. J. Immunol. 28: 1040–1051. cascades in interleukin-2 receptor signalling. Semin. Immunol. 5: 337–344. 51. Hodgkin, P. D., J. H. Lee, and A. B. Lyons. 1996. B cell differentiation and isotype 24. Benczik, M., and S. L. Gaffen. 2004. The interleukin (IL)-2 family cytokines: survival switching is related to division cycle number. J. Exp. Med. 184: 277–281. and proliferation signaling pathways in T lymphocytes. Immunol. Invest. 33: 52. Johnson, K., M. Shapiro-Shelef, C. Tunyaplin, and K. Calame. 2005. Regulatory 109–142. events in early and late B-cell differentiation. Mol. Immunol. 42: 749–761. 25. Nelms, K., A. D. Keegan, J. Zamorano, J. J. Ryan, and W. E. Paul. 1999. The IL-4 53. Scheeren, F. A., M. Naspetti, S. Diehl, R. Schotte, M. Nagasawa, E. Wijnands, receptor: signaling mechanisms and biologic functions. Annu. Rev. Immunol. 17: R. Gimeno, F. A. Vyth-Dreese, B. Blom, and H. Spits. 2005. STAT5 regulates the 701–738. self-renewal capacity and differentiation of human memory B cells and controls Bcl-6 26. Ozaki, K., R. Spolski, R. Ettinger, H. P. Kim, G. Wang, C. F. Qi, P. Hwu, expression. Nat. Immunol. 6: 303–313. D. J. Shaffer, S. Akilesh, D. C. Roopenian, et al. 2004. Regulation of B cell differen- 54. Hiromura, Y., T. Kishida, H. Nakano, T. Hama, J. Imanishi, Y. Hisa, and O. Mazda. tiation and plasma cell generation by IL-21, a novel inducer of Blimp-1 and Bcl-6. 2007. IL-21 administration into the nostril alleviates murine allergic rhinitis. J. Im- J. Immunol. 173: 5361–5371. munol. 179: 7157–7165. The Journal of Immunology 1787

55. Kishida, T., Y. Hiromura, M. Shin-Ya, H. Asada, H. Kuriyama, M. Sugai, A. Shimizu, reveals a novel immunoregulatory pathway for Th1 and Th17 cells. J. Exp. Med. 205: Y. Yokota, T. Hama, J. Imanishi, Y. Hisa, and O. Mazda. 2007. IL-21 induces inhib- 2491–2497. itor of differentiation 2 and leads to complete abrogation of anaphylaxis in mice. J. Im- 64. Wei, L., A. Laurence, K. M. Elias, and J. J. O’Shea. 2007. IL-21 is produced by Th17 munol. 179: 8554–8561. cells and drives IL-17 production in a STAT3-dependent manner. J. Biol. Chem. 282: 56. Cavallo, G. P., M. Elia, D. Giordano, C. Baldi, and R. Cammarota. 2002. Decrease of 34605–34610. specific and total IgE levels in allergic patients after BCG vaccination: preliminary 65. Akamatsu, N., Y. Yamada, H. Hasegawa, K. Makabe, R. Asano, I. Kumagai, report. Arch. Otolaryngol. Head Neck Surg. 128: 1058–1060. K. Murata, Y. Imaizumi, K. Tsukasaki, K. Tsuruda, et al. 2007. High IL-21 receptor 57. Herber, D., T. P. Brown, S. Liang, D. A. Young, M. Collins, and expression and apoptosis induction by IL-21 in follicular lymphoma. Cancer Lett. 256: K. Dunussi-Joannopoulos. 2007. IL-21 has a pathogenic role in a lupus-prone mouse 196–206. model and its blockade with IL-21R.Fc reduces disease progression. J. Immunol. 178: 66. Lamprecht, B., S. Kreher, I. Anagnostopoulos, K. Johrens, G. Monteleone, F. Jundt, 3822–3830. H. Stein, M. Janz, B. Dorken, and S. Mathas. 2008. Aberrant expression of the Th2 58. Odegard, J. M., B. R. Marks, L. D. DiPlacido, A. C. Poholek, D. H. Kono, C. Dong, cytokine IL-21 in cells regulates STAT3 signaling and attracts R. A. Flavell, and J. Craft. 2008. ICOS-dependent extrafollicular helper T cells elicit Treg cells via regulation of MIP-3␣. Blood 112: 3339–3347. IgG production via IL-21 in systemic autoimmunity. J. Exp. Med. 205: 2873–2886. 67. Daga, A., A. M. Orengo, R. M. Gangemi, D. Marubbi, M. Perera, A. Comes, 59. Bubier, J. A., S. M. Bennett, T. J. Sproule, B. L. Lyons, S. Olland, D. A. Young, and S. Ferrini, and G. Corte. 2007. Glioma immunotherapy by IL-21 gene-modified cells D. C. Roopenian. 2007. Treatment of BXSB-Yaa mice with IL-21R-Fc fusion protein or by recombinant IL-21 involves antibody responses. Int. J. Cancer 121: 1756–1763. minimally attenuates systemic lupus erythematosus. Ann. NY Acad. Sci. 1110: 68. Nakano, H., T. Kishida, H. Asada, M. Shin-Ya, T. Shinomiya, J. Imanishi, 590–601. T. Shimada, S. Nakai, M. Takeuchi, Y. Hisa, and O. Mazda. 2006. Interleukin-21 60. Young, D. A., M. Hegen, H. L. Ma, M. J. Whitters, L. M. Albert, L. Lowe, M. Senices, triggers both cellular and humoral immune responses leading to therapeutic antitumor P. W. Wu, B. Sibley, Y. Leathurby, et al. 2007. Blockade of the interleukin-21/inter- effects against head and neck squamous cell carcinoma. J. Gene Med. 8: 90–99. leukin-21 receptor pathway ameliorates disease in animal models of rheumatoid ar- 69. Iuchi, T., S. Teitz-Tennenbaum, J. Huang, B. G. Redman, S. D. Hughes, M. Li, thritis. Arthritis Rheum. 56: 1152–1163. G. Jiang, A. E. Chang, and Q. Li. 2008. Interleukin-21 augments the efficacy of T-cell 61. Li, J., W. Shen, K. Kong, and Z. Liu. 2006. Interleukin-21 induces T-cell activation therapy by eliciting concurrent cellular and humoral responses. Cancer Res. 68: and proinflammatory cytokine secretion in rheumatoid arthritis. Scand. J. Immunol. 4431–4441. 64: 515–522. 70. Davis, I. D., K. Skak, M. J. Smyth, P. E. Kristjansen, D. M. Miller, and 62. Wong, C. K., L. C. Lit, L. S. Tam, E. K. Li, P. T. Wong, and C. W. Lam. 2008. P. V. Sivakumar. 2007. Interleukin-21 signaling: functions in cancer and autoimmu- Downloaded from Hyperproduction of IL-23 and IL-17 in patients with systemic lupus erythematosus: nity. Clin. Cancer Res. 13: 6926–6932. implications for Th17-mediated inflammation in auto-immunity. Clin. Immunol. 71. Davis, I. D., B. K. Skrumsager, J. Cebon, T. Nicholaou, J. W. Barlow, N. P. Moller, 127: 385–393. K. Skak, D. Lundsgaard, K. S. Frederiksen, P. Thygesen, and G. A. McArthur. 2007. 63. Notley, C. A., J. J. Inglis, S. Alzabin, F. E. McCann, K. E. McNamee, and An open-label, two-arm, phase I trial of recombinant human interleukin-21 in pa- R. O. Williams. 2008. Blockade of in collagen-induced arthritis tients with metastatic melanoma. Clin. Cancer Res. 13: 3630–3636. http://www.jimmunol.org/ by guest on September 25, 2021