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CD11c+CD8+ T cells: Two-faced adaptive immune regulators
Cellular Immunology 264 (2010) 18–22
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Review
CD11c+CD8+ T cells: Two-faced adaptive immune regulators Dass S. Vinay a, Byoung S. Kwon a,b,* a b
Section of Clinical Immunology, Allergy, and Rheumatology, Department of Medicine, Tulane University Health Sciences Center, New Orleans, LA, USA Cell and Immunobiology, and R and D Center for Cancer Therapeutics, National Cancer Center, Ilsan, Gyeonggi-Do, Republic of Korea
a r t i c l e
i n f o
Article history: Received 17 February 2010 Accepted 23 May 2010 Available online 27 May 2010 Keywords: CD11c+CD8+ T cells 4-1BB IFN-c IDO GCN2
a b s t r a c t Regulatory cells, important controllers of immune homeostasis, carry out a multi-pronged attack by deleting overactive pathogenic immune cells, by supporting anergy, and by blocking effector functions, thereby contributing to the amelioration of disease. CD8+ T cells co-expressing CD11c are a new addition to the growing list of regulatory cells. Naïve mice harbor CD11c-expressing CD8+ T cells (<3%) that expand further in an antigen-dependent manner. Although activated CD11c+CD8+ T cells express suppressive cytokines such as IL-10 and TGF-b, their production of IFN-c is central to their immune suppressive potential. The CD11c+CD8+ T cells target pathogenic CD4+ T cells in a cell–cell contact dependent manner via IDO- and GCN2-dependent mechanisms. Adoptive transfer of activated CD11c+CD8+ T cells halts the progression of autoimmune rheumatoid arthritis and colitis. However, in certain virus and cancer models the CD11c+CD8+ T cells assume the role of immune effectors, boosting immune potential. This seemingly dual nature of these cells – exerting regulatory vs. effector activities – makes them an attractive therapeutic target. In this review, we discuss the discovery, origins and developmental requirements of CD11c+CD8+cells, and the basis of their immuno-suppressive and effector potentials. Published by Elsevier Inc.
1. Introduction Soon after the discovery of T cells 40 years ago [1], the existence of suppressor T cells was reported [2,3]. In the decades that followed, great advances were made towards understanding the nature and identity of regulatory T cells and the basis of their immune regulatory activities [4]. This period also witnessed the recognition of several new classes of regulatory/suppressor cells including subpopulations of CD4 cells [5], NK cells [6], DCs [7,8], CD8+ T cells [9], and B cells [10]. Each of these regulatory cells is known to possess distinct but sometimes overlapping phenotypes [5–10]. That CD8+ T cells have regulatory activity was discovered long before the discovery of CD4+Foxp3+ Tregs (T regulatory cells) [11], but follow-up studies did not keep pace with knowledge about the latter. This was mainly due to lack of techniques for identifying and studying these populations in isolation. However, significant advances have been made, mainly in the last decade, in understanding the nature of CD8+ Tregs [9,12,13]. Functionally, there are overlaps in the manner in which the individual Tregs exert their respective suppressive functions [9,12–14]. The Abbreviations: 1-MT, 1-methyl D,L-tryptophan; GCN2, general control nonderepressible-2; IDO, indoleamine 2,3-dioxygenase. * Corresponding author at: Section of Clinical Immunology, Allergy, and Rheumatology, Department of Medicine, Tulane University Health Sciences Center, New Orleans, LA, USA. E-mail address: [email protected] (B.S. Kwon). 0008-8749/$ - see front matter Published by Elsevier Inc. doi:10.1016/j.cellimm.2010.05.010
recently reported CD8+ T cell subpopulation co-expressing CD11c represents an important category of adaptive immune regulator with the ability to perform suppressive as well as effector functions both in vitro and in vivo [14–16,17,18]. The purpose of this review is to discuss the nature of CD11c+CD8+ T cells; their developmental requirements, and the basis of their effector and suppressor functions, as well as to contrast their phenotype with other classes of CD8+ Tregs. 2. Discovery and history of CD11c+CD8+ T cells The first report that CD8+ T cells express CD11c dates back more than two decades when it was observed that some cytotoxic T cells (CTLs) express p50,95 (CD11c/CD18; CR4) [18]. Moreover antip50,90 Abs were found to inhibit CTL-mediated killing, suggesting that such expression was crucial for conjugate formation with target cells [18] (Fig. 1). Nearly a decade later Huleatt and Lefrancois [19] identified a minor CD8+ T cell fraction in the intestinal epithelium of naïve mice that expressed CD11c. Activation via induction of GVHD in mice resulted in upregulation of CD11c expression on donor-derived CD8+ T cells in the intestinal epithelium, as well as in the spleen and lymph nodes, suggesting that CD11c expression on CD8+ T cells is inducible and occurs in response to antigenic stimulation via the T cell receptor (TCR), and is not driven by bystander mechanisms [19]. Working with a virus model, Kim et al. [20] noted increased CD11c expression on mucosal CD8+ T cells.
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Fig. 1. Development and phenotype of CD11c+CD8+ T cells. Less that 5% of CD8+ T cells in naïve mice co-express CD11c and can be detected in various lymphoid tissues and are characterized by their increased co-expression of various integrins than conventional CD8+ (CD11c CD8+) T cells. The naïve CD11c+CD8+ T cells show moderate in vitro cell division than CD11c+CD8+ T cells and possess no regulatory activity. Inflammation due to virus infection or anti-4-1BB therapy increases their effector functions. That activated CD11c+CD8+ T cells are efficient immune effectors is revealed by adoptive transfer experiments.
Similarly, Ward et al. [21] observed increased CD11c+CD8+ T cells in the bronchoalveolar lavage fluid of lung transplant recipients, a finding that underscored the role of these cells in pathological situations. In addition, work with mice infected with lymphocytic choriomeningitis virus (LCMV), vesicular stomatitis virus (VSV), and vaccinia virus (VV) demonstrated that virus-specific CTLs coexpressed CD11c and CD8b [22]. Similarly, increased CD11c+CD8+ T cells were noted in the lungs of mice infected with respiratory syncytial virus (RSV) [23,24]. Taken together these findings indicate that the CD11c+CD8+ T cells, whose numbers increase during inflammation, represent an important class of adaptive immune regulator. 3. How do CD11c+CD8+ T cells develop? Until recently CD11c+CD8+ T cells had only been identified in animals exposed to inflammatory conditions. Although there were reports of naturally existing CD11c+CD8+ T cells in naïve mice [19,20], information on their phenotype and function was lacking. Vinay et al. [14] demonstrated that CD11c+CD8+ T cells exist in naïve mice (<3%) but they concluded that these did not contribute substantially to the increase in number of mature CD11c+CD8+ T cells [14]. Instead, CD11csurface-CD8+ T cells when stimulated with Ag and anti-4-1BB developed into CD11c+CD8+ T cells in an Ag-specific manner [14]. They also demonstrated that signals other than 4-1BB such as anti-CD3, CD28 or cytokines, were less effective in supporting CD11c+CD8+ T cell expansion [14]. Similarly Lin et al. [22] showed that addition of various interleukins and other factors did not stimulate the expression of CD11c on CD8+ T cells. These findings indicate that expansion of CD11c+CD8+ T cells is a tightly governed process and underscore the importance of Ag and 4-1BB signaling for these responses [14]. 4. Phenotype of naïve CD11c+CD8+ T cells In depth characterization of naïve CD11c+CD8+ T cells is not available, as opposed to the body of data generated from in vivo
disease models, perhaps due to the low abundance of these cells in naïve mice. A few isolated studies revealed that CD11c+CD8+ T cells could be detected in the secondary lymphoid organs, bone marrow, and thymus of naïve mice and that they displayed the characteristics of naïve T cells, as judged by their CD25, CD44, and CD62L expression pattern [14]. Naïve CD11c+CD8+ T have a reduced ability to undergo in vitro cell division compared to naïve CD11c CD8+ T cells, when stimulated with anti-CD3/anti-4-1BB Abs [14]. Although no cell surface molecules other than CD11c were able to distinguish CD11c+CD8+ T from CD11 CD8+ T cells, CD11b, CD18, CD28, CD36, and CD103 were co-expressed at several-fold higher levels in the former than in the latter [14]. Co-culture assays of naïve CD11c+CD8+ T and CD4+CD25 T cells, however, failed to reveal any immunosuppressive activity on the part of the former, as the CD4+ T cells underwent normal cell division [14]; this implied that activation of the CD11c+CD8+ T cells was mandatory for the acquisition of suppressive ability.
5. Phenotype of activated CD11c+CD8+ T cells 5.1. CD11c+CD8+ T cells as regulatory cells Much of our current understanding of CD11c+CD8+ T cells was obtained from in vivo disease models. Compelling evidence for regulatory activity of CD11c+CD8+ T cells first emerged in the study of Seo et al. [16]. These authors observed that CD11c+CD8+ T cells were inducible in vivo by the T cell costimulatory molecule 4-1BB (CD137). The anti-4-1BB-expanded CD11c+CD8+ T cells were characterized by strong expression of IFN-c, which in turn primed dendritic cells (DCs)/macrophages to generate immunosuppressive IDO [15,16]. Interaction of the IDO+ cells with autoreactive CD4+ T cells then led to elimination of the latter [14–16]. A recent report described CD11c+CD8+ T cell expansion in the peripheral blood of humans suffering from autoimmune rheumatoid arthritis, where the proportion of these cells increased with disease progression [25]. The latter study, however, found no correlation between expanded CD11c+CD8+ T cells and amelioration of
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arthritis-associated clinical signs, in contrast to the observations of Seo et al. [16]. Both studies imply that CD11c+CD8+ T cells are not naturally immunoregulatory and need a stimulatory signal such as 4-1BB in addition to Ag to become fully functional [14]. That the anti-4-1BB signal is mandatory for CD11c+CD8+ T cell expansion and function was confirmed by Choi et al. [15] who found that treatment of mice with interphotoreceptor retinoid binding protein (IRBP) peptide and anti-4-1BB mAb led to expansion of CD11c+CD8+ T cells, upregulation of IFN-c and IDO, and elimination of Ag–CD4+ T cells, with concomitant protection against experimental autoimmune uveitis. Studies showing reversal of the clinical symptoms associated with colitis [14] and arthritis [16] in mice receiving CD11c+CD8+ T cell therapy showed that CD11c+CD8+ T cells directly mediate immune suppressive functions and play a central role in the reversal of disease. Although several candidate providers of CD11c+CD8+ T cellmediated suppressive functions have been identified [14–16,26], the increased expression of IFN-c by these cells stands out as the chief promoter of their suppressive effects [14–16,26] since the latter were largely reversed by neutralization of IFN-c [27]. The first evidence that IDO was required for elimination of autoreactive CD4+ T cells came from the studies of Seo et al. [16] in which reversal of the suppressive function of CD11c+CD8+ T cells was prevented by treatment with 1-MT (a pharmacological inhibitor of IDO activity). These findings have been confirmed more recently by work with IDO / and GCN2 / mice [14]. Further, adoptive transfer of OT-I CD11c+CD8+ T cells into syngeneic 4-1BB / recipients and additional treatment with SIINFEKL (a CD8+ T cell-spe-
cific activating peptide) and anti-4-1BB, led to an increase in CHOP (GADD 153; an indicator of GCN2 kinase activity; [28,29]) in CD4+ T cells, and resulted in deletion of the latter cells. Levels of CHOP rise due to nutritional deficiency, as may occur when tryptophan levels are affected by increased IDO activity [28,29]. Although increased IDO activity is linked to CD4+ T cell depletion by CD11c+CD8+ T cells, it is surprising that the latter are themselves impervious to the effect of the IDO. Insight into this puzzle was recently provided by Vinay et al. [14] who suggested that although CD11c+CD8+ T cells are refractory to the effects of IDO they constrict in the presence of the IDO inhibitor, 1-MT [14], which would explain why 1-MT treatment reverses their suppressive effect (Fig. 2). 5.2. CD11c+CD8+ T cells as effectors cells A fascinating aspect of CD11c+CD8+ T cells is their ability to function as immune effectors, an attribute that somewhat conflicts with their proposed immune regulatory role [14–16]. Lin et al. [22] have demonstrated that CD11c+CD8+ T cells display higher levels of LCMV-specific killing activity than CD8+ T cells without CD11c, suggesting that the former possess important anti-viral properties. It was not clear from the above study whether these cells directly mediate virus clearance or act in a bystander fashion. This issue was addressed recently by the study of Kim et al. [30] who demonstrated that when HSV-1-infected mice are treated with anti-4-1BB numbers of IFN-c-producing CD11c+CD8+ T cells increase. The increased IFN-c in turn enhances the anti-viral properties of
Fig. 2. Basis of CD11c+CD8+ T cell-mediated immune responses. The activated CD11c+CD8+ T cells exert both effector (left panel) as well as regulatory (right panel) functions. Virus-induced inflammation enhances both CD11c+CD8+ T cell numbers and their cytolytic potential presumably through their expression of CD11c which helps form the critical conjugation with virus-infected cells. Blockade of conjugation between CD11c+CD8+ T and virus-infected cells by anti-CD11c Abs reduces the cytolytic activity of the former. When virus infected mice are treated with anti-4-1BB mAbs expand IFN-c+CD11c+CD8+ T cell numbers. The increased IFN-c in turn primes the CTLs to accelerate viral clearance. Interestingly, treatment of tumor-bearing mice with anti-4-1BB mAb alone had no effect on tumor growth despite expansion of moderate CD11c+CD8+ T cell numbers. However, when tumor-bearing mice were depleted of their CD4+ T cells and additionally treated with anti-4-1BB mAb significantly suppressed tumor growth via massive expansion of IFN-c+CD11c+CD8+ T cells and via production of immune suppressive IDO enzyme. In autoimmunity disease and colitis models, the anti-4-1BB mAb therapy expands IL-10-, IFN-c-, TGF-b, and TNF-a-expressing CD11c+CD8+ T cells. The IFN-c secreted by the CD11c+CD8+ T cells then primes the DCs and macrophages to upregulate IDO enzyme. Such IDO+ APCs when collaborate with autoreactive CD4+ T cells cause their deletion. These observations were authenticated with studies utilizing blockade experiments with 1-MT (a pharmacological inhibitor of IDO activity), IDO / , and GCN2 / mice.
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conventional CTLs [30], suggesting that the CD11c+CD8+ T cells act as supporters of CTLs in this model. In human cytotoxic T cell clones, CD11c seems to be important for conjugate formation and target cell lysis [18]. Similarly, increased CD11c+CD8+ T cells in branchioalveolar lavage fluid after lung transplant correlated with lung pathology [21]. Beyer et al. [24] have demonstrated that RSV infection expands the number of IFN-c+ secreting CD11c+CD8+ T cells. Moreover when these cells were isolated and their effector functions analyzed, they were found to have higher in vitro cytolytic activity on RSV M2 peptide-labeled P815 target cells than CD11c CD8+ T cells. These authors also reported that pre-incubation of target cells with anti-CD11c mAb had no effect on the cytolytic activity of CD11c+CD8+ T cells [24]. Thus, it appears that IFN-c is central to CD11c+CD8+ T cell-mediated effector function. Similarly, treatment of tumor-bearing mice with anti-4-1BB mAb was paralleled by expansion of CD11c+CD8+ T cells in both the tumordraining lymph nodes and the tumor itself [17]. This expansion, however, had no effect on tumor growth or on CD4+ T cells [17]. On the other hand, anti-4-1BB therapy combined with depletion of CD4+ T cells with depleting Ab did increase levels of CD11c+CD8+ T cells many-fold and was accompanied by tumor suppression [31]. In contrast, in another model we obtained evidence that treatment with anti-4-1BB mAb neither supported the generation of CD11c+CD8+ T cells nor reduced CD4+ T cell numbers [31]. Instead, anti-4-1BB mAb (which is known to support CD11c+CD8+ T cell expansion) was found to increase numbers of CD4+ T cells [31]. Collectively, these studies suggest that the outcome of CD1c+CD8+ T cell function i.e. ‘‘regulatory” or ‘‘effector” is dictated by the microenvironment of the disease-induced inflammation.
6. Relation of CD11c+CD8+ T cells to other known CD8+ Tregs Each of the various CD8+ Tregs described so far exhibit distinct, sometimes overlapping, functions that to a large extent are dictated by changes in the inflammation-induced microenvironment. It is not possible to evaluate the functions of all the reported CD8+ Tregs here; therefore in the ensuing account we will briefly highlight a few randomly selected and well investigated CD8+ Treg subsets. The CD28 CD8+ Tregs, first identified in EAE mice by Najafian et al. [32], inhibit clonal expansion of encephalitogenic CD4+ Th1 cells via cell–cell contact [32]. Additional studies revealed that the CD28 CD8+ Tregs in graft recipients have a reduced ability to express IFN-c [33,34] and that CD28 CD8+ T–DC interaction results in increased expression of inhibitory immunoglobulin-like transcripts (ILT3) and of surface ILT4 [35]. Such expression in DCs is associated with inhibition of nuclear factor kappa B (NF-jB) activation causing obstruction of ongoing immune responses. About 4% of circulating CD8+ T cells express CD103 [36] and are present in lung, gut, mucosal tissues, and allograft-infiltrating T cells [37–41]. TGF-b is critical for inducing and maintaining CD103 on CD8+ Tregs [42]. Although the CD103+CD8+ Tregs express high IL-10 and reduced IFN-c, these cytokines do not contribute to the overall suppressive function that these cells mediate, which occurs in a cell–cell contact-dependent fashion [36]. Similarly, the CD8+Foxp3+ Tregs, whose induction is mediated largely by IL-2, TGF-b, and IL-15, exert their suppressive function in a cell–cell contact dependent and IL-10-independent manner [43–46]. The CD8+ T cells co-expressing CD122 are an important class of Tregs. Evidence suggests that CD122+CD8+ Treg-mediated immune suppression is also cell–cell contact dependent and is mediated by IL-10 and not by the TGF-b they produce [47]. Thus, a majority of the CD8 Tregs described above has overlapping functions such as production of IL-10 and TGF-b and mediates suppression in a cell–cell contact dependent manner. The CD11c+CD8+ Tregs are strikingly different in this regard, in that
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their suppressive function is elicited via induction of IFN-c, and in an IDO- and GCN-2-dependent manner [14]. Although activated CD11c+CD8+ T cells, among others, co-express CD103, CD122, IL10, and TGF-b [14] and have similarities to the other classes of CD8+ Tregs discussed above, these cells represent a distinct cell population in that their development, expansion, and, more importantly, acquisition of suppressive properties, are dependent on anti-4-1BB signals [14]. Thus, the CD11c+CD8+ T cells are a unique population with distinctive suppressive functions. 7. Conclusions Taken collectively, current findings indicate that CD11c+CD8+ T cells, which are the main agents of anti-4-1BB mAb therapy, function sometimes as immune regulators by suppressing CD4+ T cell numbers/function, and sometimes as immune effectors. Interestingly, in both cases their activities are beneficial to the host. Why the CD11c+CD8+ T cells adopt these alternative ways of exerting their beneficial effects is not clear. Nevertheless, they represent an important therapeutic option for targeting autoimmune diseases, tumors and viral infections. In order to obtain a better understanding of the dual effects of CD11c+CD8+ T cells, future studies should address the mechanism that switches between ‘‘effector functions” and ‘‘regulatory functions”. Conflict of interest None. Acknowledgement We acknowledge grants from the National Cancer Center, Korea (NCC-0810720), National Research Foundation (KRF-2005-084E00001 and M10641000040). References [1] J.F.A.P. Miller, G.F. Mitchell, Cell to cell interaction in the immune response: I. Hemolysin forming cells in neonatally thymectomized mice reconstituted with thymus or thoracic duct lymphocytes, J. Exp. Med. 128 (1968) 801–820. [2] Y. Nishizuka, T. Sakakura, Thymus and reproduction: sex-linked dysgenesia of the gonad after neonatal thymectomy in mice, Science 166 (1969) 753–755. [3] R.K. Gershon, K. Kondo, Cell interactions in the induction of tolerance: the role of thymic lymphocytes, Immunology 18 (1970) 723–735. [4] R.N. Germain, Special regulatory T-cell review: a rose by any other name: from suppressor T cells to Tregs, approbation to unbridled enthusiasm, Immunology 123 (2008) 20–27. [5] S. Sakaguchi, N. Sakaguchi, M. Asano, M. Itoh, M. Toda, Immunologic selftolerance maintained by activated T cells expressing IL-2 receptor a-chains (CD25). Breakdown of a single mechanism of self-tolerance causes various autoimmune diseases, J. Immunol. 155 (1995) 1151–1164. [6] S. Roy, P.F. Barnes, A. Garg, S. Wum, D. Cosmanm, R. Vankayalapatim, NK cells lyse regulatory cells that expand in response to an intracellular pathogen, J. Immunol. 180 (2008) 1729–1736. [7] C.W. Chan, E. Crafton, H.N. Fan, J. Flook, K. Yoshimura, M. Skarcia, D. Brockstedt, T.W. Dubensky, M.F. Stins, L.L. Lanier, D.M. Pardoll, F. Housseau, Interferon-producing killer dendritic cells provide a link between innate and adaptive immunity, Nat. Med. 12 (2006) 207–213. [8] J. Taieb, N. Chaput, C. Menard, L. Apetoh, E. Ulrich, M. Bonmort, M. Pequignot, et al., A novel dendritic cell subset involved in tumor immunosurveillance, Nat. Med. 12 (2006) 214–219. [9] D.S. Vinay, B.S. Kwon, Regulatory CD8+ T cells, in: J. Jim Xiang (Ed.), Recent Development in Immunology, Transworld Research Network, India, 2008, pp. 57–71. [10] A. Mizoguchi, A.K. Bhan, A case for regulatory B cells, J. Immunol. 176 (2006) 705–710. [11] R.K. Gershon, K. Kondo, Infectious tolerance, Immunology 21 (1971) 903–914. [12] T.R.F. Smith, V. Kumar, Revival of CD8+ Treg-mediated suppression, Trends Immunol. 29 (2008) 337–342. [13] Y.M. Wang, S.I. Alexander, CD8 regulatory T cells: what’s old is now new, Immunol. Cell Biol. 87 (2009) 192–193. [14] D.S. Vinay, C.H. Kim, B.K. Choi, B.S. Kwon, Origins and functional basis of regulatory CD11c+CD8+ T cells, Eur. J. Immunol. 39 (2009) 1552–1563.
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[15] B.K. Choi, T. Asai, D.S. Vinay, Y.H. Kim, B.S. Kwon, 4-1BB-mediated amelioration of experimental autoimmune uveoretinitis is caused by indoleamine 2, 3dioxygenase-dependent mechanisms, Cytokine 34 (2006) 233–242. [16] S.K. Seo, J.H. Choi, Y.H. Kim, W.J. Kang, Y.H. Park, J.H. Suh, B.K. Choi, D.S. Vinay, B.S. Kwon, 4-1BB-mediated immunotherapy of rheumatoid arthritis, Nat. Med. 10 (2004) 1088–1094. [17] B.K. Choi, Y.H. Kim, W.J. Kang, S.K. Lee, S.H. Kim, S.M. Shin, W.M. Yokoyama, T.Y. Kim, B.S. Kwon, Mechanisms involved in synergistic anti-cancer immunity of anti-4-1BB and anti-CD4 therapy, Cancer Res. 67 (2007) 8891–8899. [18] G.D. Keizer, J. Borst, W. Visser, R. Schwarting, J.E. de Vries, C.G. Figdor, Membrane glycoprotein p150, 95 of human cytotoxic T cell clone is involved in conjugate formation with target cells, J. Immunol. 138 (1987) 3130–3136. [19] J.W. Huleatt, L. Lefranqcois, Antigen-driven induction of CD11c on intestinal intraepithelial lymphocytes and CD8+ T cells in vivo, J. Immunol. 154 (1995) 5684–5693. [20] S.W. Kim, K.S. Schluns, L. Lefrancois, Induction and visualization of mucosal CD8 T cells following systemic virus infection, J. Immunol. 163 (1999) 4125–4132. [21] C. Ward, H. Whitford, G. Snell, H. Bao, L. Zheng, D. Reid, T.J. Williams, E.H. Walters, Bronchoalveolar lavage macrophage and lymphocyte phenotypes in lung transplant recipients, J. Heart Lung Transplant. 20 (2001) 1064–1074. [22] Y. Lin, T.J. Roberts, S. Venkataraman, C. Sungyoo, R.R. Brutkiewicz, Myeloid marker expression on antiviral CD8+ T cells following an acute virus infection, Eur. J. Immunol. 33 (2003) 2736–2743. [23] M. Beyer, H. Bartz, K. Hörner, S. Doths, C. Koerner-Rettberg, J. Schwarze, Sustained increases in numbers of pulmonary dendritic cells following respiratory syncytial virus infection, J. Allergy Clin. Immunol. 113 (2004) 127–133. [24] M. Beyer, H. Wang, N. Peters, S. Doths, C. Koerner-Rettberg, P.J.M. Openshaw, J. Schwarze, The beta2 integrin CD11c distinguishes a subset of cytotoxic pulmonary T cells with potent antiviral effects in vitro and in vivo, Respir. Res. 6 (2005) 70–81. [25] J.K. Kao, Y.T. Hsue, C.Y. Lin, Role of new population of peripheral CD11c(+)CD8(+) T cells and CD4(+)CD25(+) regulatory T cells during acute and remission stages in rheumatoid arthritis patients, J. Microbiol. Immunol. Infect. 40 (2007) 419–427. [26] D.S. Vinay, K. Cha, B.S. Kwon, Dual immunoregulatory pathways of 4-1BB signaling, J. Mol. Med. 84 (2006) 726–736. [27] Y.H. Kim, B.K. Choi, W.J. Kang, K.H. Kim, S.W. Kang, A.L. Mellor, D.H. Munn, B.S. Kwon, IFN-gamma-indoleamine-2,3-dioxygenase acts as a major suppressive factor in 4-1BB-mediated immune suppression in vivo, J. Leukobiol. 85 (2009) 817–825. [28] M.D. Sharma, B. Baban, P. Chandler, D.Y. Hou, N. Singh, H. Yagita, M. Azuma, B.R. Blazar, A.L. Mellor, D.H. Munn, Plasmacytoid dendritic cells from mouse tumor-draining lymph nodes directly activate mature Tregs via indoleamine 2,3-dioxygenase, J. Clin. Invest. 117 (2007) 570–2582. [29] D.H. Munn, M.D. Sharma, B. Baban, H.P. Harding, Y. Zhang, D. Ron, A.L. Mellor, GCN2 kinase in T cell mediates proliferative arrest and anergy induction in response to indoleamine 2,3-dioxygenase, Immunity 22 (2005) 633–642. [30] Y.H. Kim, S.K. Seo, B.K. Choi, W.J. Kang, C.H. Kim, S.K. Lee, B.S. Kwon, 4-1BB costimulation enhances HSV-1-specific CD8+ T cell responses by the induction of CD11c+CD8+ T cells, Cell. Immunol. 238 (2005) 76–86.
[31] D.S. Vinay, J.D. Kim, B.S. Kwon, Amelioration of mercury-induced autoimmunity by 4-1BB, J. Immunol. 177 (2006) 5708–5717. [32] N. Najafian, T. Chitnis, A.D. Salama, B. Zhu, C. Benou, X. Yuan, M.R. Clarkson, M.H. Sayegh, S.J. Khoury, Regulatory functions of CD8+CD28 T cells in an autoimmune disease model, J. Clin. Invest. 112 (2003) 1037–1048. [33] G.P. Westall, A.G. Brooks, T. Kotsimbos, CD8+ T-cell maturation following lung transplantation: the differential impact of CMV and acute rejection, Transpl. Immunol. 18 (2007) 186–192. [34] S. Jiang, R.I. Lechler, X.S. He, J.F. Huang, Regulatory T cells and transplantation tolerance, Hum. Immunol. 67 (2006) 765–776. [35] C.C. Chang, R. Ciubotariu, J.S. Manavalan, J. Yuan, A.I. Colovai, F. Piazza, S. Lederman, et al., Tolerization of dendritic cells by TS cells: the critical role of inhibitory receptors ILT3 and ILT4, Nat. Immunol. 3 (2002) 237–243. [36] E. Uss, A.T. Rowshani, B. Hooibrink, N.M. Lardy, R.A. van Lier, I.J. ten Berge, CD103 is a marker for alloantigen-induced regulatory CD8+ T cells, J. Immunol. 177 (2006) 2775–2783. [37] S. Rihs, C. Walker, J.C. Virchow, C. Boer, C. Kroegel, S.N. Giri, R.K. Braun, Differential expression of alpha E beta 7 integrins on bronchoalveolar lavage T lymphocyte subsets: regulatory by alpha 4 beta 1-integrin crosslinking and TGF-beta, Am. J. Respir. Cell Mol. Biol. 15 (1996) 600–610. [38] S. Sarnacki, B. Bègue, H. Buc, F. Le Deist, N. Cerf-Bensussan, Enhancement of CD3-induced activation of human intestinal intraepithelial lymphocytes by stimulation of the beta 7-containing integrin defined by HML-1 monoclonal antibody, Eur. J. Immunol. 22 (1992) 2887–2892. [39] K. Pauls, M. Schön, R.C. Kubitza, B. Homey, A. Wiesenborn, P. Lehmann, T. Ruzicka, C.M. Parker, M.P. Schon, Role of integrin alpha E (CD103) beta 7 for tissue-specific epidermal localization of CD8+ T lymphocytes, J. Invest. Dermatol. 117 (2001) 569–575. [40] P.J. Kilshaw, K.C. Baker, A unique surface antigen on intraepithelial lymphocytes in the mouse, Immunol. Lett. 18 (1988) 149–154. [41] N. Cerf-Bensussan, A. Jarry, N. Brousse, B. Lisowska-Grospierre, D. Guy-Grand, C. Griscelli, A monoclonal antibody (HML-1) defining a novel membrane molecule present on human intestinal lymphocytes, Eur. J. Immunol. 17 (1987) 1279–1285. [42] A. Hamann, D.P. Andrew, D. Jablonski-Westrich, B. Holzmann, E.C. Butcher, Role of alpha 4-integrins in lymphocyte homing to mucosal tissues in vivo, J. Immunol. 152 (1994) 3282–3293. [43] M. Ahmadzadeh, P.A. Antony, S.A. Rosenberg, IL-2 and IL-15 each mediate de novo induction of FOXP3 expression in human tumor antigen-specific CD8 T cells, J. Immunother. 30 (2007) 294–302. [44] Y. Peng, H. Shao, Y. Ke, P. Zhang, G. Han, H.J. Kaplan, D. Sun, Minimally activated CD8 autoreactive T cells specific for IRBP express a high level of Foxp3 and are functionally suppressive, Invest. Opthalmol. Vis. Sci. 48 (2007) 2178–2184. [45] L.B. Jarvis, M.K. Matyszak, R.C. Duggleby, J.C. Goodall, F.C. Hall, J.S. Gaston, Autoreactive human peripheral blood CD8+ T cells with a regulatory phenotype and function, Eur. J. Immunol. 35 (2005) 2896–2908. [46] E. Billerbeck, H.E. Blum, R. Thimme, Parallel expansion of human virus-specific Foxp3-effector memory and de novo-generated Foxp3+ regulatory CD8+ T cells upon antigen recognition in vitro, J. Immunol. 179 (2007) 1039–1048. [47] A.T. Endharti, M. Rifa’I, Z. Shi, Y. Fukuoka, Y. Nakahara, Y. Kawamoto, K. Takeda, K. Isobe, H. Suzuki, CD8+CD122+ regulatory T cells produce IL-10 to suppress IFN-gamma production and proliferation of CD8+ T cells, J. Immunol. 175 (2005) 7093–7097.
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Cellular Immunology journal homepage: www.elsevier.com/locate/ycimm
Review
CD11c+CD8+ T cells: Two-faced adaptive immune regulators Dass S. Vinay a, Byoung S. Kwon a,b,* a b
Section of Clinical Immunology, Allergy, and Rheumatology, Department of Medicine, Tulane University Health Sciences Center, New Orleans, LA, USA Cell and Immunobiology, and R and D Center for Cancer Therapeutics, National Cancer Center, Ilsan, Gyeonggi-Do, Republic of Korea
a r t i c l e
i n f o
Article history: Received 17 February 2010 Accepted 23 May 2010 Available online 27 May 2010 Keywords: CD11c+CD8+ T cells 4-1BB IFN-c IDO GCN2
a b s t r a c t Regulatory cells, important controllers of immune homeostasis, carry out a multi-pronged attack by deleting overactive pathogenic immune cells, by supporting anergy, and by blocking effector functions, thereby contributing to the amelioration of disease. CD8+ T cells co-expressing CD11c are a new addition to the growing list of regulatory cells. Naïve mice harbor CD11c-expressing CD8+ T cells (<3%) that expand further in an antigen-dependent manner. Although activated CD11c+CD8+ T cells express suppressive cytokines such as IL-10 and TGF-b, their production of IFN-c is central to their immune suppressive potential. The CD11c+CD8+ T cells target pathogenic CD4+ T cells in a cell–cell contact dependent manner via IDO- and GCN2-dependent mechanisms. Adoptive transfer of activated CD11c+CD8+ T cells halts the progression of autoimmune rheumatoid arthritis and colitis. However, in certain virus and cancer models the CD11c+CD8+ T cells assume the role of immune effectors, boosting immune potential. This seemingly dual nature of these cells – exerting regulatory vs. effector activities – makes them an attractive therapeutic target. In this review, we discuss the discovery, origins and developmental requirements of CD11c+CD8+cells, and the basis of their immuno-suppressive and effector potentials. Published by Elsevier Inc.
1. Introduction Soon after the discovery of T cells 40 years ago [1], the existence of suppressor T cells was reported [2,3]. In the decades that followed, great advances were made towards understanding the nature and identity of regulatory T cells and the basis of their immune regulatory activities [4]. This period also witnessed the recognition of several new classes of regulatory/suppressor cells including subpopulations of CD4 cells [5], NK cells [6], DCs [7,8], CD8+ T cells [9], and B cells [10]. Each of these regulatory cells is known to possess distinct but sometimes overlapping phenotypes [5–10]. That CD8+ T cells have regulatory activity was discovered long before the discovery of CD4+Foxp3+ Tregs (T regulatory cells) [11], but follow-up studies did not keep pace with knowledge about the latter. This was mainly due to lack of techniques for identifying and studying these populations in isolation. However, significant advances have been made, mainly in the last decade, in understanding the nature of CD8+ Tregs [9,12,13]. Functionally, there are overlaps in the manner in which the individual Tregs exert their respective suppressive functions [9,12–14]. The Abbreviations: 1-MT, 1-methyl D,L-tryptophan; GCN2, general control nonderepressible-2; IDO, indoleamine 2,3-dioxygenase. * Corresponding author at: Section of Clinical Immunology, Allergy, and Rheumatology, Department of Medicine, Tulane University Health Sciences Center, New Orleans, LA, USA. E-mail address: [email protected] (B.S. Kwon). 0008-8749/$ - see front matter Published by Elsevier Inc. doi:10.1016/j.cellimm.2010.05.010
recently reported CD8+ T cell subpopulation co-expressing CD11c represents an important category of adaptive immune regulator with the ability to perform suppressive as well as effector functions both in vitro and in vivo [14–16,17,18]. The purpose of this review is to discuss the nature of CD11c+CD8+ T cells; their developmental requirements, and the basis of their effector and suppressor functions, as well as to contrast their phenotype with other classes of CD8+ Tregs. 2. Discovery and history of CD11c+CD8+ T cells The first report that CD8+ T cells express CD11c dates back more than two decades when it was observed that some cytotoxic T cells (CTLs) express p50,95 (CD11c/CD18; CR4) [18]. Moreover antip50,90 Abs were found to inhibit CTL-mediated killing, suggesting that such expression was crucial for conjugate formation with target cells [18] (Fig. 1). Nearly a decade later Huleatt and Lefrancois [19] identified a minor CD8+ T cell fraction in the intestinal epithelium of naïve mice that expressed CD11c. Activation via induction of GVHD in mice resulted in upregulation of CD11c expression on donor-derived CD8+ T cells in the intestinal epithelium, as well as in the spleen and lymph nodes, suggesting that CD11c expression on CD8+ T cells is inducible and occurs in response to antigenic stimulation via the T cell receptor (TCR), and is not driven by bystander mechanisms [19]. Working with a virus model, Kim et al. [20] noted increased CD11c expression on mucosal CD8+ T cells.
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Fig. 1. Development and phenotype of CD11c+CD8+ T cells. Less that 5% of CD8+ T cells in naïve mice co-express CD11c and can be detected in various lymphoid tissues and are characterized by their increased co-expression of various integrins than conventional CD8+ (CD11c CD8+) T cells. The naïve CD11c+CD8+ T cells show moderate in vitro cell division than CD11c+CD8+ T cells and possess no regulatory activity. Inflammation due to virus infection or anti-4-1BB therapy increases their effector functions. That activated CD11c+CD8+ T cells are efficient immune effectors is revealed by adoptive transfer experiments.
Similarly, Ward et al. [21] observed increased CD11c+CD8+ T cells in the bronchoalveolar lavage fluid of lung transplant recipients, a finding that underscored the role of these cells in pathological situations. In addition, work with mice infected with lymphocytic choriomeningitis virus (LCMV), vesicular stomatitis virus (VSV), and vaccinia virus (VV) demonstrated that virus-specific CTLs coexpressed CD11c and CD8b [22]. Similarly, increased CD11c+CD8+ T cells were noted in the lungs of mice infected with respiratory syncytial virus (RSV) [23,24]. Taken together these findings indicate that the CD11c+CD8+ T cells, whose numbers increase during inflammation, represent an important class of adaptive immune regulator. 3. How do CD11c+CD8+ T cells develop? Until recently CD11c+CD8+ T cells had only been identified in animals exposed to inflammatory conditions. Although there were reports of naturally existing CD11c+CD8+ T cells in naïve mice [19,20], information on their phenotype and function was lacking. Vinay et al. [14] demonstrated that CD11c+CD8+ T cells exist in naïve mice (<3%) but they concluded that these did not contribute substantially to the increase in number of mature CD11c+CD8+ T cells [14]. Instead, CD11csurface-CD8+ T cells when stimulated with Ag and anti-4-1BB developed into CD11c+CD8+ T cells in an Ag-specific manner [14]. They also demonstrated that signals other than 4-1BB such as anti-CD3, CD28 or cytokines, were less effective in supporting CD11c+CD8+ T cell expansion [14]. Similarly Lin et al. [22] showed that addition of various interleukins and other factors did not stimulate the expression of CD11c on CD8+ T cells. These findings indicate that expansion of CD11c+CD8+ T cells is a tightly governed process and underscore the importance of Ag and 4-1BB signaling for these responses [14]. 4. Phenotype of naïve CD11c+CD8+ T cells In depth characterization of naïve CD11c+CD8+ T cells is not available, as opposed to the body of data generated from in vivo
disease models, perhaps due to the low abundance of these cells in naïve mice. A few isolated studies revealed that CD11c+CD8+ T cells could be detected in the secondary lymphoid organs, bone marrow, and thymus of naïve mice and that they displayed the characteristics of naïve T cells, as judged by their CD25, CD44, and CD62L expression pattern [14]. Naïve CD11c+CD8+ T have a reduced ability to undergo in vitro cell division compared to naïve CD11c CD8+ T cells, when stimulated with anti-CD3/anti-4-1BB Abs [14]. Although no cell surface molecules other than CD11c were able to distinguish CD11c+CD8+ T from CD11 CD8+ T cells, CD11b, CD18, CD28, CD36, and CD103 were co-expressed at several-fold higher levels in the former than in the latter [14]. Co-culture assays of naïve CD11c+CD8+ T and CD4+CD25 T cells, however, failed to reveal any immunosuppressive activity on the part of the former, as the CD4+ T cells underwent normal cell division [14]; this implied that activation of the CD11c+CD8+ T cells was mandatory for the acquisition of suppressive ability.
5. Phenotype of activated CD11c+CD8+ T cells 5.1. CD11c+CD8+ T cells as regulatory cells Much of our current understanding of CD11c+CD8+ T cells was obtained from in vivo disease models. Compelling evidence for regulatory activity of CD11c+CD8+ T cells first emerged in the study of Seo et al. [16]. These authors observed that CD11c+CD8+ T cells were inducible in vivo by the T cell costimulatory molecule 4-1BB (CD137). The anti-4-1BB-expanded CD11c+CD8+ T cells were characterized by strong expression of IFN-c, which in turn primed dendritic cells (DCs)/macrophages to generate immunosuppressive IDO [15,16]. Interaction of the IDO+ cells with autoreactive CD4+ T cells then led to elimination of the latter [14–16]. A recent report described CD11c+CD8+ T cell expansion in the peripheral blood of humans suffering from autoimmune rheumatoid arthritis, where the proportion of these cells increased with disease progression [25]. The latter study, however, found no correlation between expanded CD11c+CD8+ T cells and amelioration of
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arthritis-associated clinical signs, in contrast to the observations of Seo et al. [16]. Both studies imply that CD11c+CD8+ T cells are not naturally immunoregulatory and need a stimulatory signal such as 4-1BB in addition to Ag to become fully functional [14]. That the anti-4-1BB signal is mandatory for CD11c+CD8+ T cell expansion and function was confirmed by Choi et al. [15] who found that treatment of mice with interphotoreceptor retinoid binding protein (IRBP) peptide and anti-4-1BB mAb led to expansion of CD11c+CD8+ T cells, upregulation of IFN-c and IDO, and elimination of Ag–CD4+ T cells, with concomitant protection against experimental autoimmune uveitis. Studies showing reversal of the clinical symptoms associated with colitis [14] and arthritis [16] in mice receiving CD11c+CD8+ T cell therapy showed that CD11c+CD8+ T cells directly mediate immune suppressive functions and play a central role in the reversal of disease. Although several candidate providers of CD11c+CD8+ T cellmediated suppressive functions have been identified [14–16,26], the increased expression of IFN-c by these cells stands out as the chief promoter of their suppressive effects [14–16,26] since the latter were largely reversed by neutralization of IFN-c [27]. The first evidence that IDO was required for elimination of autoreactive CD4+ T cells came from the studies of Seo et al. [16] in which reversal of the suppressive function of CD11c+CD8+ T cells was prevented by treatment with 1-MT (a pharmacological inhibitor of IDO activity). These findings have been confirmed more recently by work with IDO / and GCN2 / mice [14]. Further, adoptive transfer of OT-I CD11c+CD8+ T cells into syngeneic 4-1BB / recipients and additional treatment with SIINFEKL (a CD8+ T cell-spe-
cific activating peptide) and anti-4-1BB, led to an increase in CHOP (GADD 153; an indicator of GCN2 kinase activity; [28,29]) in CD4+ T cells, and resulted in deletion of the latter cells. Levels of CHOP rise due to nutritional deficiency, as may occur when tryptophan levels are affected by increased IDO activity [28,29]. Although increased IDO activity is linked to CD4+ T cell depletion by CD11c+CD8+ T cells, it is surprising that the latter are themselves impervious to the effect of the IDO. Insight into this puzzle was recently provided by Vinay et al. [14] who suggested that although CD11c+CD8+ T cells are refractory to the effects of IDO they constrict in the presence of the IDO inhibitor, 1-MT [14], which would explain why 1-MT treatment reverses their suppressive effect (Fig. 2). 5.2. CD11c+CD8+ T cells as effectors cells A fascinating aspect of CD11c+CD8+ T cells is their ability to function as immune effectors, an attribute that somewhat conflicts with their proposed immune regulatory role [14–16]. Lin et al. [22] have demonstrated that CD11c+CD8+ T cells display higher levels of LCMV-specific killing activity than CD8+ T cells without CD11c, suggesting that the former possess important anti-viral properties. It was not clear from the above study whether these cells directly mediate virus clearance or act in a bystander fashion. This issue was addressed recently by the study of Kim et al. [30] who demonstrated that when HSV-1-infected mice are treated with anti-4-1BB numbers of IFN-c-producing CD11c+CD8+ T cells increase. The increased IFN-c in turn enhances the anti-viral properties of
Fig. 2. Basis of CD11c+CD8+ T cell-mediated immune responses. The activated CD11c+CD8+ T cells exert both effector (left panel) as well as regulatory (right panel) functions. Virus-induced inflammation enhances both CD11c+CD8+ T cell numbers and their cytolytic potential presumably through their expression of CD11c which helps form the critical conjugation with virus-infected cells. Blockade of conjugation between CD11c+CD8+ T and virus-infected cells by anti-CD11c Abs reduces the cytolytic activity of the former. When virus infected mice are treated with anti-4-1BB mAbs expand IFN-c+CD11c+CD8+ T cell numbers. The increased IFN-c in turn primes the CTLs to accelerate viral clearance. Interestingly, treatment of tumor-bearing mice with anti-4-1BB mAb alone had no effect on tumor growth despite expansion of moderate CD11c+CD8+ T cell numbers. However, when tumor-bearing mice were depleted of their CD4+ T cells and additionally treated with anti-4-1BB mAb significantly suppressed tumor growth via massive expansion of IFN-c+CD11c+CD8+ T cells and via production of immune suppressive IDO enzyme. In autoimmunity disease and colitis models, the anti-4-1BB mAb therapy expands IL-10-, IFN-c-, TGF-b, and TNF-a-expressing CD11c+CD8+ T cells. The IFN-c secreted by the CD11c+CD8+ T cells then primes the DCs and macrophages to upregulate IDO enzyme. Such IDO+ APCs when collaborate with autoreactive CD4+ T cells cause their deletion. These observations were authenticated with studies utilizing blockade experiments with 1-MT (a pharmacological inhibitor of IDO activity), IDO / , and GCN2 / mice.
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conventional CTLs [30], suggesting that the CD11c+CD8+ T cells act as supporters of CTLs in this model. In human cytotoxic T cell clones, CD11c seems to be important for conjugate formation and target cell lysis [18]. Similarly, increased CD11c+CD8+ T cells in branchioalveolar lavage fluid after lung transplant correlated with lung pathology [21]. Beyer et al. [24] have demonstrated that RSV infection expands the number of IFN-c+ secreting CD11c+CD8+ T cells. Moreover when these cells were isolated and their effector functions analyzed, they were found to have higher in vitro cytolytic activity on RSV M2 peptide-labeled P815 target cells than CD11c CD8+ T cells. These authors also reported that pre-incubation of target cells with anti-CD11c mAb had no effect on the cytolytic activity of CD11c+CD8+ T cells [24]. Thus, it appears that IFN-c is central to CD11c+CD8+ T cell-mediated effector function. Similarly, treatment of tumor-bearing mice with anti-4-1BB mAb was paralleled by expansion of CD11c+CD8+ T cells in both the tumordraining lymph nodes and the tumor itself [17]. This expansion, however, had no effect on tumor growth or on CD4+ T cells [17]. On the other hand, anti-4-1BB therapy combined with depletion of CD4+ T cells with depleting Ab did increase levels of CD11c+CD8+ T cells many-fold and was accompanied by tumor suppression [31]. In contrast, in another model we obtained evidence that treatment with anti-4-1BB mAb neither supported the generation of CD11c+CD8+ T cells nor reduced CD4+ T cell numbers [31]. Instead, anti-4-1BB mAb (which is known to support CD11c+CD8+ T cell expansion) was found to increase numbers of CD4+ T cells [31]. Collectively, these studies suggest that the outcome of CD1c+CD8+ T cell function i.e. ‘‘regulatory” or ‘‘effector” is dictated by the microenvironment of the disease-induced inflammation.
6. Relation of CD11c+CD8+ T cells to other known CD8+ Tregs Each of the various CD8+ Tregs described so far exhibit distinct, sometimes overlapping, functions that to a large extent are dictated by changes in the inflammation-induced microenvironment. It is not possible to evaluate the functions of all the reported CD8+ Tregs here; therefore in the ensuing account we will briefly highlight a few randomly selected and well investigated CD8+ Treg subsets. The CD28 CD8+ Tregs, first identified in EAE mice by Najafian et al. [32], inhibit clonal expansion of encephalitogenic CD4+ Th1 cells via cell–cell contact [32]. Additional studies revealed that the CD28 CD8+ Tregs in graft recipients have a reduced ability to express IFN-c [33,34] and that CD28 CD8+ T–DC interaction results in increased expression of inhibitory immunoglobulin-like transcripts (ILT3) and of surface ILT4 [35]. Such expression in DCs is associated with inhibition of nuclear factor kappa B (NF-jB) activation causing obstruction of ongoing immune responses. About 4% of circulating CD8+ T cells express CD103 [36] and are present in lung, gut, mucosal tissues, and allograft-infiltrating T cells [37–41]. TGF-b is critical for inducing and maintaining CD103 on CD8+ Tregs [42]. Although the CD103+CD8+ Tregs express high IL-10 and reduced IFN-c, these cytokines do not contribute to the overall suppressive function that these cells mediate, which occurs in a cell–cell contact-dependent fashion [36]. Similarly, the CD8+Foxp3+ Tregs, whose induction is mediated largely by IL-2, TGF-b, and IL-15, exert their suppressive function in a cell–cell contact dependent and IL-10-independent manner [43–46]. The CD8+ T cells co-expressing CD122 are an important class of Tregs. Evidence suggests that CD122+CD8+ Treg-mediated immune suppression is also cell–cell contact dependent and is mediated by IL-10 and not by the TGF-b they produce [47]. Thus, a majority of the CD8 Tregs described above has overlapping functions such as production of IL-10 and TGF-b and mediates suppression in a cell–cell contact dependent manner. The CD11c+CD8+ Tregs are strikingly different in this regard, in that
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their suppressive function is elicited via induction of IFN-c, and in an IDO- and GCN-2-dependent manner [14]. Although activated CD11c+CD8+ T cells, among others, co-express CD103, CD122, IL10, and TGF-b [14] and have similarities to the other classes of CD8+ Tregs discussed above, these cells represent a distinct cell population in that their development, expansion, and, more importantly, acquisition of suppressive properties, are dependent on anti-4-1BB signals [14]. Thus, the CD11c+CD8+ T cells are a unique population with distinctive suppressive functions. 7. Conclusions Taken collectively, current findings indicate that CD11c+CD8+ T cells, which are the main agents of anti-4-1BB mAb therapy, function sometimes as immune regulators by suppressing CD4+ T cell numbers/function, and sometimes as immune effectors. Interestingly, in both cases their activities are beneficial to the host. Why the CD11c+CD8+ T cells adopt these alternative ways of exerting their beneficial effects is not clear. Nevertheless, they represent an important therapeutic option for targeting autoimmune diseases, tumors and viral infections. In order to obtain a better understanding of the dual effects of CD11c+CD8+ T cells, future studies should address the mechanism that switches between ‘‘effector functions” and ‘‘regulatory functions”. Conflict of interest None. Acknowledgement We acknowledge grants from the National Cancer Center, Korea (NCC-0810720), National Research Foundation (KRF-2005-084E00001 and M10641000040). References [1] J.F.A.P. Miller, G.F. Mitchell, Cell to cell interaction in the immune response: I. Hemolysin forming cells in neonatally thymectomized mice reconstituted with thymus or thoracic duct lymphocytes, J. Exp. Med. 128 (1968) 801–820. [2] Y. Nishizuka, T. Sakakura, Thymus and reproduction: sex-linked dysgenesia of the gonad after neonatal thymectomy in mice, Science 166 (1969) 753–755. [3] R.K. Gershon, K. Kondo, Cell interactions in the induction of tolerance: the role of thymic lymphocytes, Immunology 18 (1970) 723–735. [4] R.N. Germain, Special regulatory T-cell review: a rose by any other name: from suppressor T cells to Tregs, approbation to unbridled enthusiasm, Immunology 123 (2008) 20–27. [5] S. Sakaguchi, N. Sakaguchi, M. Asano, M. Itoh, M. Toda, Immunologic selftolerance maintained by activated T cells expressing IL-2 receptor a-chains (CD25). Breakdown of a single mechanism of self-tolerance causes various autoimmune diseases, J. Immunol. 155 (1995) 1151–1164. [6] S. Roy, P.F. Barnes, A. Garg, S. Wum, D. Cosmanm, R. Vankayalapatim, NK cells lyse regulatory cells that expand in response to an intracellular pathogen, J. Immunol. 180 (2008) 1729–1736. [7] C.W. Chan, E. Crafton, H.N. Fan, J. Flook, K. Yoshimura, M. Skarcia, D. Brockstedt, T.W. Dubensky, M.F. Stins, L.L. Lanier, D.M. Pardoll, F. Housseau, Interferon-producing killer dendritic cells provide a link between innate and adaptive immunity, Nat. Med. 12 (2006) 207–213. [8] J. Taieb, N. Chaput, C. Menard, L. Apetoh, E. Ulrich, M. Bonmort, M. Pequignot, et al., A novel dendritic cell subset involved in tumor immunosurveillance, Nat. Med. 12 (2006) 214–219. [9] D.S. Vinay, B.S. Kwon, Regulatory CD8+ T cells, in: J. Jim Xiang (Ed.), Recent Development in Immunology, Transworld Research Network, India, 2008, pp. 57–71. [10] A. Mizoguchi, A.K. Bhan, A case for regulatory B cells, J. Immunol. 176 (2006) 705–710. [11] R.K. Gershon, K. Kondo, Infectious tolerance, Immunology 21 (1971) 903–914. [12] T.R.F. Smith, V. Kumar, Revival of CD8+ Treg-mediated suppression, Trends Immunol. 29 (2008) 337–342. [13] Y.M. Wang, S.I. Alexander, CD8 regulatory T cells: what’s old is now new, Immunol. Cell Biol. 87 (2009) 192–193. [14] D.S. Vinay, C.H. Kim, B.K. Choi, B.S. Kwon, Origins and functional basis of regulatory CD11c+CD8+ T cells, Eur. J. Immunol. 39 (2009) 1552–1563.
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[15] B.K. Choi, T. Asai, D.S. Vinay, Y.H. Kim, B.S. Kwon, 4-1BB-mediated amelioration of experimental autoimmune uveoretinitis is caused by indoleamine 2, 3dioxygenase-dependent mechanisms, Cytokine 34 (2006) 233–242. [16] S.K. Seo, J.H. Choi, Y.H. Kim, W.J. Kang, Y.H. Park, J.H. Suh, B.K. Choi, D.S. Vinay, B.S. Kwon, 4-1BB-mediated immunotherapy of rheumatoid arthritis, Nat. Med. 10 (2004) 1088–1094. [17] B.K. Choi, Y.H. Kim, W.J. Kang, S.K. Lee, S.H. Kim, S.M. Shin, W.M. Yokoyama, T.Y. Kim, B.S. Kwon, Mechanisms involved in synergistic anti-cancer immunity of anti-4-1BB and anti-CD4 therapy, Cancer Res. 67 (2007) 8891–8899. [18] G.D. Keizer, J. Borst, W. Visser, R. Schwarting, J.E. de Vries, C.G. Figdor, Membrane glycoprotein p150, 95 of human cytotoxic T cell clone is involved in conjugate formation with target cells, J. Immunol. 138 (1987) 3130–3136. [19] J.W. Huleatt, L. Lefranqcois, Antigen-driven induction of CD11c on intestinal intraepithelial lymphocytes and CD8+ T cells in vivo, J. Immunol. 154 (1995) 5684–5693. [20] S.W. Kim, K.S. Schluns, L. Lefrancois, Induction and visualization of mucosal CD8 T cells following systemic virus infection, J. Immunol. 163 (1999) 4125–4132. [21] C. Ward, H. Whitford, G. Snell, H. Bao, L. Zheng, D. Reid, T.J. Williams, E.H. Walters, Bronchoalveolar lavage macrophage and lymphocyte phenotypes in lung transplant recipients, J. Heart Lung Transplant. 20 (2001) 1064–1074. [22] Y. Lin, T.J. Roberts, S. Venkataraman, C. Sungyoo, R.R. Brutkiewicz, Myeloid marker expression on antiviral CD8+ T cells following an acute virus infection, Eur. J. Immunol. 33 (2003) 2736–2743. [23] M. Beyer, H. Bartz, K. Hörner, S. Doths, C. Koerner-Rettberg, J. Schwarze, Sustained increases in numbers of pulmonary dendritic cells following respiratory syncytial virus infection, J. Allergy Clin. Immunol. 113 (2004) 127–133. [24] M. Beyer, H. Wang, N. Peters, S. Doths, C. Koerner-Rettberg, P.J.M. Openshaw, J. Schwarze, The beta2 integrin CD11c distinguishes a subset of cytotoxic pulmonary T cells with potent antiviral effects in vitro and in vivo, Respir. Res. 6 (2005) 70–81. [25] J.K. Kao, Y.T. Hsue, C.Y. Lin, Role of new population of peripheral CD11c(+)CD8(+) T cells and CD4(+)CD25(+) regulatory T cells during acute and remission stages in rheumatoid arthritis patients, J. Microbiol. Immunol. Infect. 40 (2007) 419–427. [26] D.S. Vinay, K. Cha, B.S. Kwon, Dual immunoregulatory pathways of 4-1BB signaling, J. Mol. Med. 84 (2006) 726–736. [27] Y.H. Kim, B.K. Choi, W.J. Kang, K.H. Kim, S.W. Kang, A.L. Mellor, D.H. Munn, B.S. Kwon, IFN-gamma-indoleamine-2,3-dioxygenase acts as a major suppressive factor in 4-1BB-mediated immune suppression in vivo, J. Leukobiol. 85 (2009) 817–825. [28] M.D. Sharma, B. Baban, P. Chandler, D.Y. Hou, N. Singh, H. Yagita, M. Azuma, B.R. Blazar, A.L. Mellor, D.H. Munn, Plasmacytoid dendritic cells from mouse tumor-draining lymph nodes directly activate mature Tregs via indoleamine 2,3-dioxygenase, J. Clin. Invest. 117 (2007) 570–2582. [29] D.H. Munn, M.D. Sharma, B. Baban, H.P. Harding, Y. Zhang, D. Ron, A.L. Mellor, GCN2 kinase in T cell mediates proliferative arrest and anergy induction in response to indoleamine 2,3-dioxygenase, Immunity 22 (2005) 633–642. [30] Y.H. Kim, S.K. Seo, B.K. Choi, W.J. Kang, C.H. Kim, S.K. Lee, B.S. Kwon, 4-1BB costimulation enhances HSV-1-specific CD8+ T cell responses by the induction of CD11c+CD8+ T cells, Cell. Immunol. 238 (2005) 76–86.
[31] D.S. Vinay, J.D. Kim, B.S. Kwon, Amelioration of mercury-induced autoimmunity by 4-1BB, J. Immunol. 177 (2006) 5708–5717. [32] N. Najafian, T. Chitnis, A.D. Salama, B. Zhu, C. Benou, X. Yuan, M.R. Clarkson, M.H. Sayegh, S.J. Khoury, Regulatory functions of CD8+CD28 T cells in an autoimmune disease model, J. Clin. Invest. 112 (2003) 1037–1048. [33] G.P. Westall, A.G. Brooks, T. Kotsimbos, CD8+ T-cell maturation following lung transplantation: the differential impact of CMV and acute rejection, Transpl. Immunol. 18 (2007) 186–192. [34] S. Jiang, R.I. Lechler, X.S. He, J.F. Huang, Regulatory T cells and transplantation tolerance, Hum. Immunol. 67 (2006) 765–776. [35] C.C. Chang, R. Ciubotariu, J.S. Manavalan, J. Yuan, A.I. Colovai, F. Piazza, S. Lederman, et al., Tolerization of dendritic cells by TS cells: the critical role of inhibitory receptors ILT3 and ILT4, Nat. Immunol. 3 (2002) 237–243. [36] E. Uss, A.T. Rowshani, B. Hooibrink, N.M. Lardy, R.A. van Lier, I.J. ten Berge, CD103 is a marker for alloantigen-induced regulatory CD8+ T cells, J. Immunol. 177 (2006) 2775–2783. [37] S. Rihs, C. Walker, J.C. Virchow, C. Boer, C. Kroegel, S.N. Giri, R.K. Braun, Differential expression of alpha E beta 7 integrins on bronchoalveolar lavage T lymphocyte subsets: regulatory by alpha 4 beta 1-integrin crosslinking and TGF-beta, Am. J. Respir. Cell Mol. Biol. 15 (1996) 600–610. [38] S. Sarnacki, B. Bègue, H. Buc, F. Le Deist, N. Cerf-Bensussan, Enhancement of CD3-induced activation of human intestinal intraepithelial lymphocytes by stimulation of the beta 7-containing integrin defined by HML-1 monoclonal antibody, Eur. J. Immunol. 22 (1992) 2887–2892. [39] K. Pauls, M. Schön, R.C. Kubitza, B. Homey, A. Wiesenborn, P. Lehmann, T. Ruzicka, C.M. Parker, M.P. Schon, Role of integrin alpha E (CD103) beta 7 for tissue-specific epidermal localization of CD8+ T lymphocytes, J. Invest. Dermatol. 117 (2001) 569–575. [40] P.J. Kilshaw, K.C. Baker, A unique surface antigen on intraepithelial lymphocytes in the mouse, Immunol. Lett. 18 (1988) 149–154. [41] N. Cerf-Bensussan, A. Jarry, N. Brousse, B. Lisowska-Grospierre, D. Guy-Grand, C. Griscelli, A monoclonal antibody (HML-1) defining a novel membrane molecule present on human intestinal lymphocytes, Eur. J. Immunol. 17 (1987) 1279–1285. [42] A. Hamann, D.P. Andrew, D. Jablonski-Westrich, B. Holzmann, E.C. Butcher, Role of alpha 4-integrins in lymphocyte homing to mucosal tissues in vivo, J. Immunol. 152 (1994) 3282–3293. [43] M. Ahmadzadeh, P.A. Antony, S.A. Rosenberg, IL-2 and IL-15 each mediate de novo induction of FOXP3 expression in human tumor antigen-specific CD8 T cells, J. Immunother. 30 (2007) 294–302. [44] Y. Peng, H. Shao, Y. Ke, P. Zhang, G. Han, H.J. Kaplan, D. Sun, Minimally activated CD8 autoreactive T cells specific for IRBP express a high level of Foxp3 and are functionally suppressive, Invest. Opthalmol. Vis. Sci. 48 (2007) 2178–2184. [45] L.B. Jarvis, M.K. Matyszak, R.C. Duggleby, J.C. Goodall, F.C. Hall, J.S. Gaston, Autoreactive human peripheral blood CD8+ T cells with a regulatory phenotype and function, Eur. J. Immunol. 35 (2005) 2896–2908. [46] E. Billerbeck, H.E. Blum, R. Thimme, Parallel expansion of human virus-specific Foxp3-effector memory and de novo-generated Foxp3+ regulatory CD8+ T cells upon antigen recognition in vitro, J. Immunol. 179 (2007) 1039–1048. [47] A.T. Endharti, M. Rifa’I, Z. Shi, Y. Fukuoka, Y. Nakahara, Y. Kawamoto, K. Takeda, K. Isobe, H. Suzuki, CD8+CD122+ regulatory T cells produce IL-10 to suppress IFN-gamma production and proliferation of CD8+ T cells, J. Immunol. 175 (2005) 7093–7097.