Phenotypic switch of CD8⁺ T cells reactivated under hypoxia toward IL‐10 secreting, poorly proliferative effector cells

Abstract

CD8+ T cells controlling pathogens or tumors must function at sites where oxygen tension is frequently low, and never as high as under atmospheric culture conditions. However, T-cell function in vivo is generally analyzed indirectly, or is extrapolated from in vitro studies under nonphysiologic oxygen tensions. In this study, we delineate the role of physiologic and pathologic oxygen tension in vitro during reactivation and differentiation of tumor-specific CD8 + T cells. Using CD8 + T cells from pmel-1 mice, we observed that the generation of CTLs under 5% O 2 , which corresponds to physioxia in lymph nodes, gave rise to a higher effector signature than those generated under atmospheric oxygen fractions (21% O 2 ). Hypoxia (1% O 2 ) did not modify cytotoxicity, but decreasing O 2 tensions during CTL and CD8 + tumor-infiltrating lymphocyte reactivation dose-dependently decreased proliferation, induced secretion of the immunosuppressive cytokine IL-10, and upregulated the expression of CD137 (4-1BB) and CD25. Overall, our data indicate that oxygen tension is a key regulator of CD8 + T-cell function and fate and suggest that IL-10 release may be an unanticipated component of CD8 + T cell-mediated immune responses in most in vivo microenvironments. Keywords: CD8+ T cell r Oxygen r Hypoxia r IL-10 r T-cell reactivation Additional supporting information may be found in the online version of this article at the publisher's web-site IntroductionIn a healthy physiologic context, oxygen tensions in mammalian tissues are tightly regulated, but still show significant variation both between tissues and within the same tissue (Supporting Information Fig. 1A) [1][2][3]. However, oxygen tensions are far below physiologic values in different pathologic conditions, mostly involving inflammation [4], solid tumors [5,6], and infections [7]. In contrast to sufficient oxygen supply (i.e. normoxia), oxygen deprivation (i.e. hypoxia) leads to cellular responses involving Correspondence: Dr. Paul R. Walker e-mail: Paul.Walker@hcuge.ch stabilization of HIFs (hypoxia-inducible factors), transcription factors that are composed of an inducible α-subunit (i.e. HIF-1α, HIF-2α, or HIF-3α) together with a constitutive β-subunit (i.e. HIF-1β, HIF-2β, or HIF-3β) [8]. Upon stabilization, HIFs transcribe various genes with HIF-responsive elements in their promoter; these include those that increase angiogenesis (e.g. VEGF) and glucose metabolism (e.g. glucose transporters) [9]. Interestingly, HIF-1α and HIF-2α can have unique, redundant, or opposing roles [9,10]. Furthermore, while HIF-1α is described to be stabilized and active below 2% O 2 in an acute manner, HIF-2α has been shown to be stable below 5% O 2 in a chronic manner [11,12]. However, although HIFs are central to many hypoxia responses, certain effects have been shown to be HIF-independent [13][14][15]. Intriguingly, HIF-1α can also be involved in immune cell activation Eur. J. Immunol. 2015Immunol. . 45: 2263Immunol. -2275 under atmospheric oxygen fractions (AtO 2 ; i.e. 21%), as rep...

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“…Specifically, granzyme A and B were upregulated when CTLs were generated under physiological normoxia, as were FasL and Blimp-1, with capacity to secrete higher amounts of IFNγ 21,49 . The metabolic profile of the cells was also described to switch from an oxidative phosphorylation metabolism toward a more glycolytic one when O 2 availability was lowered 38 .…”