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A Role for Mammalian Target of Rapamycin in Regulating T Cell Activation versus Anergy¹

The Sidney Kimmel Comprehensive Cancer Center, Johns Hopkins University Medical Institutions, Baltimore, MD 21231

Whether TCR engagement leads to activation or tolerance is determined by the concomitant delivery of multiple accessory signals, cytokines, and environmental cues. In this study, we demonstrate that the mammalian target of rapamycin (mTOR) integrates these signals and determines the outcome of TCR engagement with regard to activation or anergy. In vitro, Ag recognition in the setting of mTOR activation leads to full immune responses, whereas recognition in the setting of mTOR inhibition results in anergy. Full T cell activation is associated with an increase in the phosphorylation of the downstream mTOR target S6 kinase 1 at Thr⁴²¹/Ser⁴²⁴ and an increase in the mTOR-dependent cell surface expression of transferrin receptor (CD71). Alternatively, the induction of anergy results in markedly less S6 kinase 1 Thr⁴²¹/Ser⁴²⁴ phosphorylation and CD71 surface expression. Likewise, the reversal of anergy is associated not with proliferation, but rather the specific activation of mTOR. Importantly, T cells engineered to express a rapamycin-resistant mTOR construct are resistant to anergy induction caused by rapamycin. In vivo, mTOR inhibition promotes T cell anergy under conditions that would normally induce priming. Furthermore, by examining CD71 surface expression, we are able to distinguish and differentially isolate anergic and activated T cells in vivo. Overall, our data suggest that by integrating environmental cues, mTOR plays a central role in determining the outcome of Ag recognition.

The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ This work was supported by National Institutes of Health Grants; National Institute of Allergy and Infection Diseases Grant 5K22AI1773 and National Cancer Institute Grant RO1CA98109.

² Address correspondence and reprint requests to Dr. Jonathan D. Powell, Department of Oncology-Immunology/Hematopoiesis, Johns Hopkins School of Medicine, 1650 Orleans Street, CRB 443, Baltimore, MD 21231. E-mail address: Poweljo{at}jhmi.edu

³ Abbreviations used in this paper: mTOR, mammalian target of rapamycin; CSA, cyclosporin A; PCC, pigeon cytochrome c; RR-mTOR, rapamycin-resistant mTOR; S6K-1, S6 kinase-1; SFA, sanglifehrin A; WT-mTOR, wild-type mTOR.