γδ T cells are potent anticancer effectors with the potential to target tumours broadly, independent of patient-specific neoantigens or human leukocyte antigen background
. γδ T cells can sense ...conserved cell stress signals prevalent in transformed cells
, although the mechanisms behind the targeting of stressed target cells remain poorly characterized. Vγ9Vδ2 T cells-the most abundant subset of human γδ T cells
-recognize a protein complex containing butyrophilin 2A1 (BTN2A1) and BTN3A1 (refs.
), a widely expressed cell surface protein that is activated by phosphoantigens abundantly produced by tumour cells. Here we combined genome-wide CRISPR screens in target cancer cells to identify pathways that regulate γδ T cell killing and BTN3A cell surface expression. The screens showed previously unappreciated multilayered regulation of BTN3A abundance on the cell surface and triggering of γδ T cells through transcription, post-translational modifications and membrane trafficking. In addition, diverse genetic perturbations and inhibitors disrupting metabolic pathways in the cancer cells, particularly ATP-producing processes, were found to alter BTN3A levels. This induction of both BTN3A and BTN2A1 during metabolic crises is dependent on AMP-activated protein kinase (AMPK). Finally, small-molecule activation of AMPK in a cell line model and in patient-derived tumour organoids led to increased expression of the BTN2A1-BTN3A complex and increased Vγ9Vδ2 T cell receptor-mediated killing. This AMPK-dependent mechanism of metabolic stress-induced ligand upregulation deepens our understanding of γδ T cell stress surveillance and suggests new avenues available to enhance γδ T cell anticancer activity.
CD1c is a member of the group 1 CD1 family of proteins that are specialized for lipid antigen presentation. Despite high cell surface expression of CD1c on key antigen-presenting cells and the ...discovery of its mycobacterial lipid antigen presentation capability, the molecular basis of CD1c recognition by T cells is unknown. Here we present a comprehensive functional and molecular analysis of αβ T-cell receptor (TCR) recognition of CD1c presenting mycobacterial phosphomycoketide antigens. Our structure of CD1c with the mycobacterial phosphomycoketide (PM) shows similarities to that of CD1c-mannosyl-β1-phosphomycoketide in that the A' pocket accommodates the mycoketide alkyl chain; however, the phosphate head-group of PM is shifted ∼6 Å in relation to that of mannosyl-β1-PM. We also demonstrate a bona fide interaction between six human TCRs and CD1c-mycoketide complexes, measuring high to moderate affinities. The crystal structure of the DN6 TCR and mutagenic studies reveal a requirement of five complementarity determining region (CDR) loops for CD1c recognition. Furthermore, mutagenesis of CD1c reveals residues in both the α1 and α2 helices involved in TCR recognition, yet not entirely overlapping among the examined TCRs. Unlike patterns for MHC I, no archetypical binding footprint is predicted to be shared by CD1c-reactive TCRs, even when recognizing the same or similar antigens.
Significance Mycobacterium tuberculosis infects more than one-third of humans yet no effective vaccine exists. This study shows how a subset of αβ T cells targets M. tuberculosis lipid antigens that are presented by the MHC molecule CD1c. In contrast to many T cells that recognize CD1d, these αβ T cells express diverse T-cell receptors and have differing footprints on CD1c during lipid recognition. This study also shows that some CD1c-specific αβ T cells are exquisitely specific for the lipid presented, whereas others have a more promiscuous reactivity, demonstrating that the αβ T-cell response to CD1c lipid presentation is diverse and adaptable. These data may provide additional resources for development of MHC-independent vaccines against M. tuberculosis .
To become specialized binders, antibodies undergo a process called affinity maturation to maximize their binding affinity. Despite this process, some antibodies retain low-affinity binding to diverse ...epitopes in a phenomenon called polyreactivity. Here we seek to understand the molecular basis of this polyreactivity in antibodies. Our results highlight that polyreactive antigen-binding fragments (Fabs) bind their targets with low affinities, comparable to T cell receptor recognition of autologous classical major histocompatibility complex. Extensive mutagenic studies find no singular amino acid residue or biochemical property responsible for polyreactive interaction, suggesting that polyreactive antibodies use multiple strategies for engagement. Finally, our crystal structures and all-atom molecular dynamics simulations of polyreactive Fabs show increased rigidity compared to their monoreactive relatives, forming a neutral and accessible platform for diverse antigens to bind. Together, these data support a cooperative strategy of rigid neutrality in establishing the polyreactive status of an antibody molecule.
Display omitted
•Polyreactive antibodies show increased rigidity and neutrality in their binding surfaces•Polyreactive antibodies engage with low affinities akin to autologous TCR-MHC interactions
Binding promiscuity is an inherent property of immune recognition, manifested in antibodies as polyreactivity. Borowska et al. dissect this phenomenon at the molecular level and show that the binding surfaces of polyreactive antibodies use increased rigidity and neutrality in ligand engagement. This provides a key mechanism for understanding polyreactivity in antibodies.
MR1-restricted T cells (MR1Ts) are a T cell subset that recognize and mediate host defense to a broad array of microbial pathogens, including respiratory pathogens (e.g.,
,
,
) and enteric pathogens ...(e.g.,
and
species). Mucosal-associated invariant T (MAIT) cells, a subset of MR1Ts, were historically defined by the use of a semi-invariant T cell receptor (TCR) and recognition of small molecules derived from the riboflavin biosynthesis pathway presented on MR1. We used mass spectrometry to identify the repertoire of ligands presented by MR1 from the microbes
and
We found that the MR1 ligandome is unexpectedly broad, revealing functionally distinct ligands derived from
and
The identification, synthesis, and functional analysis of mycobacterial ligands reveal that MR1T ligands can be distinguished by MR1Ts with diverse TCR usage. These data demonstrate that MR1 can serve as an immune sensor of the microbial ligandome.
γδ T cell receptors (TCRs), αβ TCRs, and antibodies are the three lineages of somatically recombined antigen receptors. The structural basis for ligand recognition is well defined for αβ TCR and ...antibodies but is lacking for γδ TCRs. We present the 3.4 Å structure of the murine γδ TCR G8 bound to its major histocompatibility complex (MHC) class Ib ligand, T22. G8 predominantly uses germline-encoded residues of its δ chain complementarity-determining region 3 (CDR3) loop to bind T22 in an orientation substantially different from that seen in αβ TCR/peptide-MHC. That junctionally encoded G8 residues play an ancillary role in binding suggests a fusion of innate and adaptive recognition strategies.
Recognition of phosphatidylserine (PS) lipids exposed on the extracellular leaflet of plasma membranes is implicated in both apoptotic cell removal and immune regulation. The PS receptor T cell ...immunoglobulin and mucin-domain-containing molecule 4 (Tim4) regulates T-cell immunity via phagocytosis of both apoptotic (high PS exposure) and nonapoptotic (intermediate PS exposure) activated T cells. The latter population must be removed at lower efficiency to sensitively control immune tolerance and memory cell population size, but the molecular basis for how Tim4 achieves this sensitivity is unknown. Using a combination of interfacial X-ray scattering, molecular dynamics simulations, and membrane binding assays, we demonstrate how Tim4 recognizes PS in the context of a lipid bilayer. Our data reveal that in addition to the known Ca ²⁺-coordinated, single-PS binding pocket, Tim4 has four weaker sites of potential ionic interactions with PS lipids. This organization makes Tim4 sensitive to PS surface concentration in a manner capable of supporting differential recognition on the basis of PS exposure level. The structurally homologous, but functionally distinct, Tim1 and Tim3 are significantly less sensitive to PS surface density, likely reflecting the differences in immunological function between the Tim proteins. These results establish the potential for lipid membrane parameters, such as PS surface density, to play a critical role in facilitating selective recognition of PS-exposing cells. Furthermore, our multidisciplinary approach overcomes the difficulties associated with characterizing dynamic protein/membrane systems to reveal the molecular mechanisms underlying Tim4’s recognition properties, and thereby provides an approach capable of providing atomic-level detail to uncover the nuances of protein/membrane interactions.
CD1c is abundantly expressed on human dendritic cells (DC) and B cells, where it binds and displays lipid Ags to T cells. In this study, we report that CD1c tetramers carrying Mycobacterium ...tuberculosis phosphomycoketide bind γδ TCRs. An unbiased method of ligand-based TCR selection detects interactions only with Vδ1(+) TCRs, and mutational analyses demonstrate a role of the Vδ1 domain during recognition. These results strengthen evidence for a role of CD1c in the γδ T cell response, providing biophysical evidence for CD1c-γδ TCR interactions and a named foreign Ag. Surprisingly, TCRs also bind CD1c complexes formed with diverse lipids such as lysophosphatidylcholine, sulfatide, or mannosyl-phosophomycoketide, but not lipopeptide ligands. Dissection of TCR interactions with CD1c carrying foreign Ags, permissive ligands, and nonpermissive lipid ligands clarifies the molecular basis of the frequently observed but poorly understood phenomenon of mixed self- and foreign Ag reactivity in the CD1 system.
γδ T cell surveillance via CD1 molecules Luoma, Adrienne M; Castro, Caitlin D; Adams, Erin J
Trends in immunology,
12/2014, Letnik:
35, Številka:
12
Journal Article, Book Review
Recenzirano
Odprti dostop
Highlights • Vδ1+ γδ T cells engage CD1 molecules using a diverse structural footprint. • The recognition of CD1d–lipid is dominated by the Vδ1 domain. • The CDR3 loops make important contacts in ...lipid–antigen discrimination. • Autoreactivity of Vδ1+ γδ T cells may be modulated by co-stimulatory signals.
Regulatory T (Treg) cells expressing the transcription factor Foxp3 are critical for the prevention of autoimmunity and the suppression of anti-tumor immunity. The major self-antigens recognized by ...Treg cells remain undefined, representing a substantial barrier to the understanding of immune regulation. Here, we have identified natural Treg cell ligands in mice. We found that two recurrent Treg cell clones, one prevalent in prostate tumors and the other associated with prostatic autoimmune lesions, recognized distinct non-overlapping MHC-class-II-restricted peptides derived from the same prostate-specific protein. Notably, this protein is frequently targeted by autoantibodies in experimental models of prostatic autoimmunity. On the basis of these findings, we propose a model in which Treg cell responses at peripheral sites converge on those self-proteins that are most susceptible to autoimmune attack, and we suggest that this link could be exploited as a generalizable strategy for identifying the Treg cell antigens relevant to human autoimmunity.
Display omitted
•Two Treg cell clones recognize distinct peptides from the prostatic protein Tcaf3•Tcaf3 is recurrently targeted by autoantibodies in settings of immune dysregulation•Thymic development of the MJ23 Treg cell clone is dependent on a single Tcaf3 peptide•Peptide-MHC tetramers identify endogenous Tcaf3-specific Treg cells in prostate tumors
The endogenous antigens recognized by thymus-derived Treg cells have remained largely undefined. Leonard et al. identify natural Treg cell ligands in mice, demonstrating that two recurrent Treg cell clones recognize distinct non-overlapping peptides derived from a single prostate-specific protein.
PDF
