TIGIT A Rising Star in Immunotherapy

What is TIGIT?

TIGIT, short for T cell immunoreceptor with Ig and ITIM domains, stands as a pivotal immune regulatory protein nestled within the immunoglobulin (Ig) superfamily. Carving its place as both a co-stimulatory and co-inhibitory receptor, TIGIT assumes a substantial role in orchestrating immune responses. Its predominant expression resides within T cells, NK cells, and select plasma cells situated within the intricate framework of the immune system.

Structure of TIGIT: Insights and Complexities

TIGIT (also known as WUCAM[1] and VSTM3[2]) emerged onto the immunological scene in 2009[3] as a notable co-inhibitory molecule. Much like LAG3 and TIM3, TIGIT finds its place within the expansive immunoglobulin superfamily[4]. Its composition comprises an extracellular immunoglobulin variable (IgV) domain, a transmembrane domain of the type 1, and an intracellular tail harboring both an immunoreceptor tyrosine-based inhibitory motif (ITIM) and an Ig tail-tyrosine (ITT)-like motif[3-6]. Uniquely, TIGIT finds its expression confined to lymphocytes, encompassing CD8+ T cells, memory and regulatory CD4+ T cells, follicular CD4+ T cells, and the ever-versatile NK cells.

TIGIT stands as a binding partner to a minimum of two nectin family members: CD155 (PVR, Necl-5) and CD112 (PVRL2, Nectin-2). It is important to note that TIGIT exhibits markedly higher affinity towards CD155 (Kd=1-3 nM) in comparison to CD112 (Kd unmeasurable). Intriguingly, these ligands are shared with two other receptors - CD226 (DNAM-1) and CD96 (TACTILE) - that furnish co-stimulatory and co-inhibitory signals, respectively. TIGIT engages in a competitive binding dance with the costimulatory receptor CD226, both vying for CD155's attention. Remarkably, TIGIT's allure for CD155 (Kd=1-3 nM) surpasses that of CD226 (Kd=119 nM). Recent research introduced a novel element: TIGIT's interaction with nectin-4. Notably, nectin-4 exclusively interacts with TIGIT, remaining unengaged with CD226 and CD96[7]. However, the functional implications of the TIGIT-nectin-4 interaction within the context of anti-tumor immunity are yet to be fully unraveled.

Unraveling TIGIT Expression Patterns

TIGIT predominantly finds its expression niche among activated T cells and NK cells, but intriguingly, it remains absent on initial CD45RA+CD4+ T cells. In parallel, when gauged against the TIGIT levels found on activated memory CD45RO+CD4+ T cells, sparked by CD3 and CD28 antibodies, TIGIT's presence on quiescent memory CD45RO+CD4+ T cells stands comparatively lower. Worth noting, this elevated TIGIT expression gradually wanes within six days. The regulatory T cells (Tregs) also play host to TIGIT, particularly gracing CD4+CD25hi Tregs, with its expression witnessing an uptick upon activation. An intriguing discovery points towards cells co-expressing TIGIT, Foxp3, and GITR[8-9]. A prior investigation unveiled that TIGIT stamps its presence across all human NK cell categories, exerting its inhibitory effect on NK cytotoxicity by linking with PVR and PVRL via its ITIM region[10]. Notably, within the PVR family, TIGIT shares its space with companions like CD155, CD96, CD112, CD112R, and CD226.

The tapestry of TIGIT expression unfolds under the influence of specific transcription factors and epigenetic regulations. One such conductor is Eomesodermin (Eomes), found within CD8+ T cells of acute myeloid leukemia patients. Eomes binds to the promoter region of TIGIT, bolstering its expression[11]. Beyond this, TIGIT paints its mark on follicular B helper T cells (Tfh) and graces certain CD3+CD8int T cells in tonsils. Tfh cells, characterized by diminished Bach2 transcription factor levels, encounter gene repression, most notably affecting TIGIT, upon Bach2 overexpression[12]. Long non-coding RNA, maternally expressed gene 3 (MEG3), weaves into the narrative by elevating TIGIT expression in CD4+ T cells through miRNA-23a absorption. TIGIT+ Tregs harness this to quell Th1 and Th17 cell expansion, alleviating autoimmune-mediated aplastic anemia[13]. Moreover, TIGIT's expression intricacies intertwine with methylation mechanisms. Notably, the hypomethylation and Foxp3 binding at the TIGIT locus join forces to elevate TIGIT's presence in Tregs[14].

Mechanism of Action of TIGIT: Orchestrating Immune Responses

TIGIT, expressed on both NK cells and T cells, forges a dynamic interaction with CD155, the counterpart on dendritic cells (DCs), creating a two-way signaling avenue. This intricate exchange orchestrates a double-barreled suppression, reining in DC function alongside quelling NK cell and T cell activation. Compelling research highlights that TIGIT's rendezvous with CD155 on human DCs or other antigen-presenting cells (APCs) wielding PVR insignias orchestrates a symphony: inhibiting IL-12p40 production while amplifying IL-10 secretion through orchestrated phosphorylation of p38 and Erk. In the realm of reality, administering TIGIT-Fc spurs the reduction of inflammatory cytokine levels, catalyzing the emergence of tolerogenic DCs[15].

Within NK cells, TIGIT's liaison with CD155 prompts phosphorylation of tyrosine residues in the ITIM and ITT-like motifs through the agency of Src family kinases Fyn and Lck. A duo of cytoplasmic collaborators, namely growth factor receptor binding protein 2 (Grb2) and β-arrestin2, beckons SH2-containing inositol phosphatase-1 (SHIP1) to TIGIT's tail[16]. SHIP1, marshaled by Grb2, stifles phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) signaling routes, enfolding NK cell inhibition within its embrace[17]. β-arrestin2 escorts SHIP1 to the scene, joining hands with ITT-like motifs to impede TRAF6 self-ubiquitination, culminating in NF-κB activation restraint and IFN-γ production reduction within NK cells.

Much akin to T cells, NK cells boast the presence of both CD226, a co-stimulatory entity, and TIGIT, the co-suppressor. The delicate equilibrium is often tipped toward TIGIT's co-suppressive harmony due to its greater affinity for CD155 over CD226 in normal circumstances.

TIGIT's engagement appears to interrupt T cell priming, possibly through the TCR complex, while nurturing T cell survival through anti-apoptotic agents[18]. TIGIT signaling takes center stage in bolstering the inhibitory prowess of regulatory T cells (Tregs). TIGIT-endowed Tregs, sporting elevated CXCR3 levels, become adept at taming Th1 and Th17 responses. The act of ligation by Fc-CD155 propels Tregs into the role of proliferation suppressors under specific conditions. This intricate ballet curtails IFN-γ expression and rectifies the suppression anomaly seen in Tregs from multiple sclerosis patients[19]. In a novel exploration, the TIGIT signaling journey within Tregs uncovers its sway on the PI3K pathway. Triggered TIGIT dials down PI3K activity while boosting Akt suppression, accompanied by the diminished phosphorylation of FoxO1 and its nuclear presence. Previous revelations pinpoint PI3K activation and FoxO1 phosphorylation as prerequisites for Th1 reprogramming within Tregs. This mechanistic insight fuels the conjecture that TIGIT might tamper with the induction of Th1 programs. TIGIT's hold over PI3K is further evident through its inhibition of mTOR[20], reinforcing the linkage between TIGIT signaling and PI3K's dynamic realm.

In a remarkable twist, the Fap2 protein of F. nucleatum wields the power to mute NK cells' cytotoxic potential while stifling tumor-infiltrating T lymphocyte activity. Fap2's prowess stems from its interaction with TIGIT, propelling tumor survival. Multi-faceted indeed, TIGIT orchestrates an array of mechanisms to wield supremacy over T cell functions, sculpting immune responses and nurturing peripheral tolerance. This intricate web makes TIGIT an enticing candidate for therapeutic interventions aimed at ameliorating autoimmune diseases.

TIGIT Signaling Pathway

The intricate TIGIT signaling pathway revolves around its intricate dance with the ligands CD155 (also referred to as PVR) and CD112 (also known as PVRL2 or Nectin-2).

TIGIT's interaction with CD155 and CD112 unfolds through its Ig-like ectodomain, a step that resonates as a catalyst. This initial binding triggers a symphony of events, culminating in the phosphorylation of TIGIT's intracellular ITIM (immunoreceptor tyrosine-based phosphorylated kinase) domain. The parade of phosphorylated ITIM domains heralds the arrival of phosphotyrosinases (SHP-1 and SHP-2), silent regulators that usher in the inhibition of T cell activation signals.

In a fascinating twist, TIGIT's affinity for CD155 and CD112 initiates a strategic battle. TIGIT squares off against fellow ligands DNAM-1 and CD96, engaging in a competition for these shared trophies. DNAM-1 and CD96, champions of activating immune receptors, rally T cell troops through their dance with CD155 and CD112. Herein, TIGIT's triumphant binding sabotages this union, adeptly blocking the access of DNAM-1 and CD96 to their beloved ligands, thus stifling the activation of T cells.

The TIGIT signaling pathway unfurls its playbook with the primary aim of reigning in the fervor of T cell activation signals. This goal is realized through several avenues. First and foremost, TIGIT's binding operation suppresses the signaling prowess of CD28, the eminent costimulatory entity within the T cell receptor complex. Consequently, the fervor of T cell activation is noticeably tamed. Furthermore, TIGIT's masterstroke involves the recruitment of phosphotyrosinases SHP-1 and SHP-2, orchestrating a symphony of inhibition against the phosphorylation of key signaling entities within the T cell receptor complex.

This orchestration by the TIGIT signaling pathway echoes profound repercussions in the realm of immune regulation. Meticulous studies highlight how TIGIT's activation throttles the vigor and cytotoxicity of T cells, thereby wielding a director's wand over the immune cells' lethal dance with tumor cells. Yet, a note of caution lingers. Overexuberance in TIGIT's role is entwined with delicate imbalances in immune regulation, where immune tolerance and the art of tumor evasion are conjured.

In summation, TIGIT's role as an immune regulator finds its zenith in its interaction with CD155 and CD112, orchestrating a dance of balance. The strategic recruitment of phosphotyrosinases SHP-1 and SHP-2 is the crescendo, dousing the flames of T cell activation signaling. This exploration of the signaling pathway not only paints a vivid picture of immune symphony but also unfurls a canvas for the future. The realm of immunotherapy stands to harness the potential embedded within the TIGIT signaling pathway.

TIGIT Protein

Recombinant Human TIGIT Protein

Click here for more TIGIT

Synonym : VSIG9, VSTM3, WUCAM, V-set and immunoglobulin domain-containing protein 9, V-set and transmembrane domain-containing protein 3.

References:

 

[1] Boles KS, Vermi W, Facchetti F, Fuchs A, Wilson TJ, Diacovo TG, Cella M, Colonna M. A novel molecular interaction for the adhesion of follicular CD4 T cells to follicular DC. Eur J Immunol. 2009 Mar;39(3):695-703. doi: 10.1002/eji.200839116. PMID: 19197944; PMCID: PMC3544471.
[2] Levin SD, Taft DW, Brandt CS, Bucher C, Howard ED, Chadwick EM, Johnston J, Hammond A, Bontadelli K, Ardourel D, Hebb L, Wolf A, Bukowski TR, Rixon MW, Kuijper JL, Ostrander CD, West JW, Bilsborough J, Fox B, Gao Z, Xu W, Ramsdell F, Blazar BR, Lewis KE. Vstm3 is a member of the CD28 family and an important modulator of T-cell function. Eur J Immunol. 2011 Apr;41(4):902-15. doi: 10.1002/eji.201041136. Epub 2011 Mar 18. PMID: 21416464; PMCID: PMC3733993.
[3] Yu X, Harden K, Gonzalez LC, Francesco M, Chiang E, Irving B, Tom I, Ivelja S, Refino CJ, Clark H, Eaton D, Grogan JL. The surface protein TIGIT suppresses T cell activation by promoting the generation of mature immunoregulatory dendritic cells. Nat Immunol. 2009 Jan;10(1):48-57. doi: 10.1038/ni.1674. Epub 2008 Nov 16. PMID: 19011627.
[4] Stanietsky N, Simic H, Arapovic J, Toporik A, Levy O, Novik A, Levine Z, Beiman M, Dassa L, Achdout H, Stern-Ginossar N, Tsukerman P, Jonjic S, Mandelboim O. The interaction of TIGIT with PVR and PVRL2 inhibits human NK cell cytotoxicity. Proc Natl Acad Sci U S A. 2009 Oct 20;106(42):17858-63. doi: 10.1073/pnas.0903474106. Epub 2009 Oct 7. PMID: 19815499; PMCID: PMC2764881.
[5] Liu S, Zhang H, Li M, Hu D, Li C, Ge B, Jin B, Fan Z. Recruitment of Grb2 and SHIP1 by the ITT-like motif of TIGIT suppresses granule polarization and cytotoxicity of NK cells. Cell Death Differ. 2013 Mar;20(3):456-64. doi: 10.1038/cdd.2012.141. Epub 2012 Nov 16. PMID: 23154388; PMCID: PMC3569986.
[6] Li M, Xia P, Du Y, Liu S, Huang G, Chen J, Zhang H, Hou N, Cheng X, Zhou L, Li P, Yang X, Fan Z. T-cell immunoglobulin and ITIM domain (TIGIT) receptor/poliovirus receptor (PVR) ligand engagement suppresses interferon-γ production of natural killer cells via β-arrestin 2-mediated negative signaling. J Biol Chem. 2014 Jun 20;289(25):17647-57. doi: 10.1074/jbc.M114.572420. Epub 2014 May 9. PMID: 24817116; PMCID: PMC4067199.
[7] Reches A, Ophir Y, Stein N, Kol I, Isaacson B, Charpak Amikam Y, Elnekave A, Tsukerman P, Kucan Brlic P, Lenac T, Seliger B, Jonjic S, Mandelboim O. Nectin4 is a novel TIGIT ligand which combines checkpoint inhibition and tumor specificity. J Immunother Cancer. 2020 Jun;8(1):e000266. doi: 10.1136/jitc-2019-000266. PMID: 32503945; PMCID: PMC7279670.
[8] Boles KS, Vermi W, Facchetti F, Fuchs A, Wilson TJ, Diacovo TG, Cella M, Colonna M. A novel molecular interaction for the adhesion of follicular CD4 T cells to follicular DC. Eur J Immunol. 2009 Mar;39(3):695-703. doi: 10.1002/eji.200839116. PMID: 19197944; PMCID: PMC3544471.
[9] Fontenot JD, Rasmussen JP, Williams LM, Dooley JL, Farr AG, Rudensky AY. Regulatory T cell lineage specification by the forkhead transcription factor foxp3. Immunity. 2005 Mar;22(3):329-41. doi: 10.1016/j.immuni.2005.01.016. PMID: 15780990.
[10] Stanietsky N, Simic H, Arapovic J, Toporik A, Levy O, Novik A, Levine Z, Beiman M, Dassa L, Achdout H, Stern-Ginossar N, Tsukerman P, Jonjic S, Mandelboim O. The interaction of TIGIT with PVR and PVRL2 inhibits human NK cell cytotoxicity. Proc Natl Acad Sci U S A. 2009 Oct 20;106(42):17858-63. doi: 10.1073/pnas.0903474106. Epub 2009 Oct 7. PMID: 19815499; PMCID: PMC2764881.
[11] Jia B, Zhao C, Rakszawski KL, Claxton DF, Ehmann WC, Rybka WB, Mineishi S, Wang M, Shike H, Bayerl MG, Sivik JM, Schell TD, Drabick JJ, Hohl RJ, Zheng H. Eomes+T-betlow CD8+ T Cells Are Functionally Impaired and Are Associated with Poor Clinical Outcome in Patients with Acute Myeloid Leukemia. Cancer Res. 2019 Apr 1;79(7):1635-1645. doi: 10.1158/0008-5472.CAN-18-3107. Epub 2019 Feb 1. PMID: 30709927.
[12] Lahmann A, Kuhrau J, Fuhrmann F, Heinrich F, Bauer L, Durek P, et al. Bach2 Controls T Follicular Helper Cells by Direct Repression of Bcl-6. J Immunol (Baltimore Md 1950) (2019) 202(8):2229–39. doi: 10.4049/jimmunol.1801400
[13] Yang M, Liu Y, Mo B, Xue Y, Ye C, Jiang Y, et al. Helios But Not CD226, TIGIT and Foxp3 is a Potential Marker for CD4 Treg Cells in Patients With Rheumatoid Arthritis. Cell Physiol Biochem Int J Exp Cell physiology biochem. Pharmacol (2019) 52(5):1178–92. doi: 10.33594/000000080
[14] Zhang Y, Maksimovic J, Naselli G, Qian J, Chopin M, Blewitt ME, Oshlack A, Harrison LC. Genome-wide DNA methylation analysis identifies hypomethylated genes regulated by FOXP3 in human regulatory T cells. Blood. 2013 Oct 17;122(16):2823-36. doi: 10.1182/blood-2013-02-481788. Epub 2013 Aug 23. PMID: 23974203; PMCID: PMC3798997.
[15] Yu X, Harden K, Gonzalez LC, Francesco M, Chiang E, Irving B, Tom I, Ivelja S, Refino CJ, Clark H, Eaton D, Grogan JL. The surface protein TIGIT suppresses T cell activation by promoting the generation of mature immunoregulatory dendritic cells. Nat Immunol. 2009 Jan;10(1):48-57. doi: 10.1038/ni.1674. Epub 2008 Nov 16. PMID: 19011627.
[16] Liu S, Zhang H, Li M, Hu D, Li C, Ge B, et al. Recruitment of Grb2 and SHIP1 by the ITT-Like Motif of TIGIT Suppresses Granule Polarization and Cytotoxicity of NK Cells. Cell Death Diff (2013) 20(3):456–64. doi: 10.1038/cdd.2012.141
[17] Li M, Xia P, Du Y, Liu S, Huang G, Chen J, Zhang H, Hou N, Cheng X, Zhou L, Li P, Yang X, Fan Z. T-cell immunoglobulin and ITIM domain (TIGIT) receptor/poliovirus receptor (PVR) ligand engagement suppresses interferon-γ production of natural killer cells via β-arrestin 2-mediated negative signaling. J Biol Chem. 2014 Jun 20;289(25):17647-57. doi: 10.1074/jbc.M114.572420. Epub 2014 May 9. PMID: 24817116; PMCID: PMC4067199.
[18] Joller N, Hafler J, Brynedal B, Kassam N, Spoerl S, Levin S, et al. Cutting Edge: TIGIT has T Cell-Intrinsic Inhibitory Functions. J Immunol (Baltimore Md 1950) (2011) 186(3):1338–42. doi: 10.4049/jimmunol.1003081
[19] Lucca L, Axisa P, Singer E, Nolan N, Dominguez-Villar M, Hafler D. TIGIT Signaling Restores Suppressor Function of Th1 Tregs. JCI Insight (2019) 4(3):e124427. doi: 10.1172/jci.insight.124427
[20] Urbanellis P, Shyu W, Khattar R, Wang J, Zakharova A, He W, Sadozai H, Amir AZ, Shalev I, Phillips MJ, Adeyi O, Ross H, Grant D, Levy GA, Chruscinski A. The regulatory T cell effector molecule fibrinogen-like protein 2 is necessary for the development of rapamycin-induced tolerance to fully MHC-mismatched murine cardiac allografts. Immunology. 2015 Jan;144(1):91-106. doi: 10.1111/imm.12354. PMID: 24990517; PMCID: PMC4264913.
[21] Yue C, Gao S, Li S, Xing Z, Qian H, Hu Y, Wang W, Hua C. TIGIT as a Promising Therapeutic Target in Autoimmune Diseases. Front Immunol. 2022 Jun 3;13:911919. doi: 10.3389/fimmu.2022.911919. PMID: 35720417; PMCID: PMC9203892.
[22] Chiang EY, Mellman I. TIGIT-CD226-PVR axis: advancing immune checkpoint blockade for cancer immunotherapy. J Immunother Cancer. 2022 Apr;10(4):e004711. doi: 10.1136/jitc-2022-004711. PMID: 35379739; PMCID: PMC8981293.