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Intracellular Domain of CD3 zeta chain

Sequence and Features

Usage and Biology

T-cell surface glycoprotein CD3 zeta chain is part of the TCR-CD3 complex present on T-lymphocyte cell surface that plays an essential role in adaptive immune response. When antigen presenting cells (APCs) activate T-cell receptor (TCR), TCR-mediated signals are transmitted across the cell membrane by the CD3 chains CD3D, CD3E, CD3G and CD3Z. All CD3 chains contain immunoreceptor tyrosine-based activation motifs (ITAMs) in their cytoplasmic domain. Upon TCR engagement, these motifs become phosphorylated by Src family protein tyrosine kinases LCK and FYN, resulting in the activation of downstream signaling pathways [1,2].

CD3Z ITAMs phosphorylation creates multiple docking sites for the protein kinase ZAP70 leading to ZAP70 phosphorylation and its conversion into a catalytically active enzyme [2].

It plays an important role in intrathymic T-cell differentiation. Additionally, participates in the activity-dependent synapse formation of retinal ganglion cells (RGCs) in both the retina and dorsal lateral geniculate nucleus (dLGN) (By similarity).

Figure 1. Structure of CD3 zeta chain.

Background and detail description

Used in our project

The synthetic receptors were constructed to contain an scFv derived from an antibody recognizing the virus spike protein, CR3022, which has been reported to bind with the receptor-binding domain of the SARS-CoV-2 S glycoprotein with high affinity, and the CD8 transmembrane domain present in the aCD19 CAR for T cells (12). For the cytoplasmic domains, we used the common g subunit of Fc receptors (CARg), MEGF10 (CARMEGF10), MERTK (CARMERTK) and CD3z (CARz) in our study. These cytoplasmic domains are capable of promoting phagocytosis by macrophages[3]. More details and experimental results can be found in CAR-CD3 zeta(BBa_K4040017)

Used in the construction of CAR-T cells

Used in the construction of CAR-Macrophages cells

In T cells, phosphorylated ITAMs in CD3z bind to tandem SH2 domains (tSH2) in the kinase ZAP70. Zap70 is not expressed in macrophages, but Syk, a phagocytic signaling effector and tSH2 domain containing protein, is expressed at high levels (Andreu et al., 2017). Previous work suggested that Syk kinase can also bind to the CD3z ITAMs (Bu et al., 1995), indicating that the CAR-T may promote engulfment through a similar mechanism as CAR-PFcRV. To quantitatively compare the interaction between SyktSH2and CD3z or FcRV in a membrane proximal system recapitulating physiological geometry, a study used a liposome-based assay (Figure 2 [Hui and Vale, 2014]). In this system, His10CD3z and His10-Lck (the kinase that phosphorylates CD3z) are bound to a liposome via NiNTA-lipids and the binding of labeled tandem SH2 domains to phosphorylated CD3z was measured using fluorescence quenching. Their results show that Syk-tSH2 binds the CD3z and FcRV with comparable affinity (~15 nM and ~30 nM respectively, Figure 2).

Collectively, these results demonstrate that the TCR CD3z chain can promote phagocytosis in a CAR-P, likely through the recruitment of Syk kinase[4].

Figure 2. Model of the liposome-based fluorescence quenching assay used to determine affinity between the Syk tSH2 domains and the receptor tails of CD3z and FcRV, two intracellular signaling domains that promote engulfment. Binding between the Syk tSH2 reporter (Syk tSH2), green, and a receptor tail, purple, was detected by rhodamine quenching of BG505 dye on the reporter (see Materials and methods). Kd was determined by assessing mean fluorescence quenching for the last 20 timepoints collected ~45 min after ATP addition over a receptor titration from 0 to 500 nM. Each point represents the mean ± SD from three independent experiments. Kd ± SE was calculated by nonlinear fit assuming one site specific binding.

Previous study has generated CAR-Ms targeting the solid tumor antigens mesothelin or HER2 and demonstrated phagocytosis of antigen-positive target cells (Fig.3a,b)[5]. Together, these data demonstrated that CD3ζ based CARs can direct anti-tumor phagocytic activity and provided support for subsequent efforts to translate this platform to primary human macrophages.

Figure 3. a,b, In vitro phagocytosis by UTD or CAR-meso-ζ THP-1 macrophages of mesothelin+ve K562 cells (a) or by CAR-HER2-ζ macrophages of HER2+ K562 cells (b).

References

[1]Barber EK, Dasgupta JD, Schlossman SF, Trevillyan JM, Rudd CE. The CD4 and CD8 antigens are coupled to a protein-tyrosine kinase (p56lck) that phosphorylates the CD3 complex. Proc Natl Acad Sci U S A. 1989 May;86(9):3277-81. doi: 10.1073/pnas.86.9.3277. PMID: 2470098; PMCID: PMC287114.

[2]Iwashima M, Irving BA, van Oers NS, Chan AC, Weiss A. Sequential interactions of the TCR with two distinct cytoplasmic tyrosine kinases. Science. 1994 Feb 25;263(5150):1136-9. doi: 10.1126/science.7509083. PMID: 7509083.

[3]Fu W, Lei C, Ma Z, Qian K, Li T, Zhao J, Hu S. CAR Macrophages for SARS-CoV-2 Immunotherapy. Front Immunol. 2021 Jul 23;12:669103. doi: 10.3389/fimmu.2021.669103. PMID: 34367135; PMCID: PMC8343226.

[4]Morrissey MA, Williamson AP, Steinbach AM, Roberts EW, Kern N, Headley MB, Vale RD. Chimeric antigen receptors that trigger phagocytosis. Elife. 2018 Jun 4;7:e36688. doi: 10.7554/eLife.36688. PMID: 29862966; PMCID: PMC6008046.