Cholesteryl esters stabilize human CD1c conformations for recognition by self-reactive T cells

Abstract

Cluster of differentiation 1c (CD1c)-dependent self-reactive T cells are abundant in human blood, but self-antigens presented by CD1c to the T-cell receptors of these cells are poorly understood. Here we present a crystal structure of CD1c determined at 2.4 Å revealing an extended ligand binding potential of the antigen groove and a substantially different conformation compared with known CD1c structures. Computational simulations exploring different occupancy states of the groove reenacted these different CD1c conformations and suggested cholesteryl esters (CE) and acylated steryl glycosides (ASG) as new ligand classes for CD1c. Confirming this, we show that binding of CE and ASG to CD1c enables the binding of human CD1c self-reactive T-cell receptors. Hence, human CD1c adopts different conformations dependent on ligand occupancy of its groove, with CE and ASG stabilizing CD1c conformations that provide a footprint for binding of CD1c self-reactive T-cell receptors.CD1 | lipid antigen | antigen presentation | T cell | cholesteryl ester C luster of differentiation 1 (CD1) proteins are a family of MHC class I-like glycoproteins that present lipid antigens to T cells. CD1 restricted T cells are abundant in humans and play important roles in host defense and immune regulation. Human CD1 proteins comprise five CD1 isoforms, CD1a, CD1b, CD1c, CD1d, and CD1e, which exhibit different intracellular trafficking behaviors and ligand binding preferences (1). Structurally, the main differences between these CD1 isoforms lie in the architecture of their lipophilic ligand binding grooves. Whereas all CD1 isoforms share a highly conserved A′ channel (or pocket) for binding C18-C26 acyl chains, specialization is provided by further connecting channels (2-7). In CD1a, the A′ channel is "fused" to a wide and shallow F′ channel, enabling binding of lipopeptides such as mycobacterial didehydroxymycobactin (DDM) (8). CD1b features a unique T′ tunnel that connects A′ and F′, thereby forming a "superchannel" for accommodating very long acyl chains (e.g., mycobacterial mycolates) (2, 4). CD1d, the only isoform also conserved in rodents, exhibits a twobranched ligand binding groove with two linear channels A′ and F′ connected near the main portal into the groove, known as the F′ portal. A similar two-branched arrangement of A′ and F′ is seen in CD1e, the only CD1 isoform not expressed on the cell surface. Compared with CD1d, CD1a, and CD1b, the portal into the groove in CD1e is widely exposed, consistent with its known role in lipid transfer processes inside lysosomes (6).CD1c presents foreign-(9, 10) as well as self-lipid antigens to T cells (11). Two recent crystal structures of human CD1c revealed a two-branched design similar to that of CD1d and CD1e, with two channels A′ and F′ connecting near the groove portal. In these structures, a mycobacterial phosphomycoketide (PM) or mannosyl-β1-phosphomycoketide (MPM) occupied the A′ channel, whereas an undefined short ligand was present in the F′ channel (7, 12). The spatial arrangement of...

CD1b-restricted GEM T cell responses are modulated byMycobacterium tuberculosismycolic acid meromycolate chains

“…Site-directed mutagenesis was subsequently performed on the TCRα-chain to yield a complete GEM1 TCRα sequence (TRAV1-2, accession JQ778263.1), using the following primers: forward 5'-GCCGTGC-GGGTCACCGGCGGCT-3', reverse 5'-AGCCGCCGGTGACCCGCACGGC-3'. LDN5-TCRα and TCRβ (TRAV17/TRBV4-1) was cloned as previously described (47).…”

“…Soluble TCR and TCR dextramers: Generation of TCR heterodimers were performed as previously described (47). Briefly, the extracellular domains of TCRα and TCRβ chains were produced in E.coli Rosetta as inclusion bodies after cloning into the bacterial expression vector pGMT7.…”

“…To produce stably refolded disulphide-linked heterodimers, cysteines were incorporated into the TCRα-and β-chain constant domains, by replacing Thr48 and Ser57, respectively. The disulphide-linked GEM18-TCR αβ heterodimers were expressed, refolded, and purified as previously described (47). Refolded and purified TCR was assessed by a reducing and non-reducing SDS/PAGE gel analysis.…”

CD1b-autoreactive T cells contribute to hyperlipidemia-induced skin inflammation in mice

“…CD1b-autoreactive T cells can recognize phospholipids (17,19), and a higher frequency of sulfatide and monosialotetrahexosylganglioside-specific (GM1-specific) T cells was detected in multiple sclerosis patients compared with normal controls (26). Moreover, CD1c-restricted T cells specific for cholesteryl esters have recently been identified (31). Finally, most CD1d-restricted NKT cells also exhibit autoreactivity and A large proportion of human T cells are autoreactive to group 1 CD1 proteins, which include CD1a, CD1b, and CD1c.…”

CD1b-autoreactive T cells recognize phospholipid antigens and contribute to antitumor immunity against a CD1b+T cell lymphoma

“…29 In addition, recent studies have shown that CD1a-restricted human T cell clones recognize skin-derived apolar oils and phospholipids; autoreactive CD1b-restricted human T cell clones recognize a range of phospholipids, whereas CD1c-reactive clones can bind cholesterol and its esters. [31][32][33] Considering that these lipids accumulate in most tumors, it is imperative to explore the role of autoreactive group 1 CD1-restricted T cells in tumor immunity. This would shed light on the potential use of these T cells in cancer immunotherapy.…”